Chest Imaging


Imaging Anatomy

Gross Lung Anatomy

Segmental Anatomy ( Figs. 1.1 1.2 )

FIG. 1.1

FIG. 1.2

Right Lung

Upper lobe Apical B1
Anterior B2
Posterior B3
Middle lobe Lateral B4
Medial B5
Lower lobe Superior B6
Medial basal B7
Anterior basal B8
Lateral basal B9
Posterior basal B10

Left Lung

Upper lobe
Upper Apicoposterior B1, B3
Anterior B2
Lingula Superior B4
Inferior B5
Lower lobe Superior B6
Medial basal B7
Anterior basal B8
Lateral basal B9
Posterior basal B10

Segmental Computed Tomography (CT) Anatomy ( Fig. 1.3 )

FIG. 1.3

Bronchial CT Anatomy ( Fig. 1.4 )

FIG. 1.4

Plain Radiograph Anatomic Landmarks ( Figs. 1.5–1.9 )

FIG. 1.5

FIG. 1.6

FIG. 1.7

FIG. 1.8

FIG. 1.9

Thoracic Inlet

The thoracic inlet represents the junction between structures at the base of the neck and those of the thorax. It parallels the first rib and is higher posteriorly than anteriorly.

Lines

  • Anterior junction line: 2-mm linear line that projects over the trachea. Represents the approximation of the visceral and parietal pleura of the right and left lungs anterior to the mediastinum (composed of four layers of pleura)

  • Posterior junction line (four layers of pleura): extends above clavicles and can often be seen on a frontal radiograph as a vertical line traversing the tracheal air column

  • Posterior tracheal stripe (normally measures <4 mm in diameter): thickening or presence of a focal opacity in the region of the posterior tracheal stripe should raise the possibility of esophageal carcinoma

  • Azygoesophageal line: interface between RLL air and mediastinum

  • Left paraspinal line: extends from aortic arch to diaphragm

  • Right paraspinal line

Paratracheal Stripe

  • Abnormal if >4 mm

  • Never extends below right bronchus

Fissures

The normal major fissures are seldom seen on a posteroanterior radiograph.

The top of the left lower lobe (LLL) is usually higher than the top of the right lower lobe (RLL).

  • Minor (horizontal) fissure

  • Major (oblique) fissure

  • Azygos fissure

  • Other fissures

    • Superior accessory fissure

    • Inferior accessory fissure

    • Left minor fissure

Pulmonary Ligament

  • Consists of a double layer of pleura that connects the medial aspect of the lower lobe (LL) to the adjacent mediastinum and diaphragm

  • Not seen on posteroanterior or lateral chest radiographs (CXRs)

  • Determines the shape of the collapsed LL in patients with atelectasis and the shape of the collapsed lung in patients with pneumothorax

Trachea

  • The trachea is a midline structure

  • The aorta commonly causes a smooth indentation on the left side

  • The trachea measures 10–12 cm in length

  • 16–20 U-shaped cartilage rings on its lateral and anterior aspects

  • Calcification of the cartilage rings is a common normal finding in patients older than 40 years, particularly women, but it is seldom evident on radiographs

  • Divides into the left and right main bronchi at the carina (approximately at the level of the fifth thoracic vertebra)

Upper Lobe (Ul) Bronchi ( Figs. 1.10 1.11 )

The right main bronchus divides into the RUL bronchus and the bronchus intermedius.

  • RUL bronchus is always higher than LUL bronchus on lateral view

  • Posterior wall of bronchus intermedius (right) is normally less than 2 mm thick and bifurcates into middle and LLs bronchi

  • Tracheal bronchus (bronchus suis): 0.1% of population, arises from right wall of trachea (left much less common), supplies apical segment or occasionally entire RUL

  • The left main bronchus is approximately 5 cm in length and divides into the LUL and LLL bronchi.

  • Accessory cardiac bronchus: 0.1% of population, extends inferomedially from medial wall of bronchus intermedius or RLL bronchus toward mediastinum; may be blind ending

FIG. 1.10

FIG. 1.11

Parenchymal Anatomy

Acinus

  • Includes all structures distal to one terminal bronchiole. The terminal bronchiole is the last purely air-conducting structure.

  • Acinus measures 7 mm

  • Acinus contains about 400 alveoli

Secondary Pulmonary Lobule

  • Smallest anatomic unit of the lung visible on high-resolution CT (HRCT)

  • Polygonal structure bounded by interlobular septa, 1.5–2 cm in diameter

  • Three to five acini per secondary lobule

  • Supplied by several terminal bronchioles

Epithelium

  • The alveolar epithelium is made up of two cell types:

    • Type 1 pneumocytes

    • Type 2 pneumocytes: produce surfactant, have phagocytic ability, and regenerate

High-Resolution Computed Tomography (HRCT) ( Fig. 1.12 )

FIG. 1.12

Technique

  • 1–1.5-mm thin collimation

  • High spatial frequency reconstruction

    • This helps to improve spatial resolution, thereby improving the ability to detect subtle abnormalities—thick interlobular septa, cyst walls, small nodules, ground glass opacities and bronchiectasis.

  • Optional

    • Increase in kVp or mA (140 kVp, 170 mA)

    • Targeted image reconstruction (one lung rather than both to increase spatial resolution)

HRCT Anatomy

The basic anatomic unit of pulmonary structure and function visible by HRCT is the secondary pulmonary lobule:

  • Polyhedral 1.5-cm structure surrounded by connective tissue (interlobular septa) and made up of 5–15 pulmonary acini, which contain the alveoli for gas exchange

  • Central artery and bronchiole

  • Peripheral pulmonary veins and lymphatics in septum

Dominant high-resolution pattern:

  • Reticular

  • Nodular

  • High attenuation (ground glass, consolidation)

  • Low attenuation (emphysema, cystic)

Questions:

  • Location within the secondary lobule

  • Upper versus lower zone or a central versus peripheral predominance

  • Presence of additional findings (pleural fluid, lymphadenopathy, traction bronchiectasis)

This protocol produces high-definition images of the lung alveoli, airways, interstitium, and pulmonary vasculature. Air trapping is identified on expiratory images.

Pulmonary Function ( Fig. 1.13 )

FIG. 1.13

Lung Volumes, Capacities, and Flow Rates

  • Tidal volume (TV): normal respiratory cycle

  • Vital capacity (VC): amount of air that can be expired with force after maximal inspiration

  • Functional residual capacity (FRC): volume remaining in lung after quiet expiration

  • Total lung capacity (TLC): volume contained in lung at maximum inspiration

  • Forced expiratory volume (FEV 1 ): amount of air expired in 1 second

Mediastinum ( Fig. 1.14 )

  • Superior mediastinum: plane above aortic arch; thoracic inlet structures

  • Anterior mediastinum: contains thymus, lymph nodes, mesenchymal tissue; some classifications include the heart and fat

  • Middle mediastinum: contains heart, major vessels, trachea and main bronchi, lymph nodes, phrenic nerve, and left recurrent laryngeal nerve

  • Posterior mediastinum: starts at anterior margin of vertebral bodies; contains descending thoracic aorta, esophagus, thoracic duct, azygos and hemiazygos veins, lymph nodes, autonomic nerves, paravertebral areas, and fat

FIG. 1.14

Imaging Protocols

Standard Chest CT Protocol

Supine position. Scan in suspended inspiration at total lung capacity. Scan setup:

  • 5 × 5-mm sections from apex of the lungs to the adrenals

  • Six 1.25-mm high-resolution cuts throughout lung at 2.5-cm intervals

  • 1-mm reconstructions through pulmonary nodules

  • Number of different combinations of pitch and section thickness

In interstitial lung disease the six cuts are repeated with the patient in the prone position. Reconstruction is done with a high-resolution bone algorithm.

Use of IV contrast medium:

  • Evaluation of vascular structures, arteriovenous malformation, aortic dissection

  • Evaluation of mediastinal tumors, enlarged lymph nodes

  • Hilar masses

  • Neck masses

Pulmonary Embolism (PE) CT Protocol

  • Patient in supine position

  • Scan range: adrenals to lung apex

  • Injection of 140 mL of nonionic iodinated contrast at 3 mL/second, with delay of 25–30 seconds. Scanning is performed with suspended respiration.

  • Scans are retrospectively reconstructed from the dome of the diaphragm as 2.5-mm-thick slices with 1-mm spacing.

Diagnostic Radiology Report (American College of Radiology [ACR])

An authenticated written interpretation should be performed on all radiologic procedures. The report should include:

  • 1

    Name of patient and other identifier (e.g., birth date, Social Security number, or hospital or office identification number)

  • 2

    Name of the referring physician to provide more accurate routing of the report to one or more locations specified by the referring physician (e.g., hospital, office, clinic)

  • 3

    History

  • 4

    Name or type of examination

  • 5

    Dates of the examination and transcription

  • 6

    Time of the examination (for ICU/CCU patients) to identify multiple examinations (e.g., chest) that may be performed on a single day

  • 7

    Body of the report:

    • Procedures and materials

      • Include in the report a description of the procedures performed and any contrast media (agent, concentration, volume, and reaction, if any), medications, catheters, and devices.

    • Findings

      • Use precise anatomic and radiologic terminology to accurately describe findings.

    • Limitations

      • Where appropriate, identify factors that can limit the sensitivity and specificity of the examination. Such factors might include technical factors, patient anatomy, limitations of the technique, incomplete bowel preparation, and wrist examination for carpal scaphoid.

    • Clinical issues

      • The report should address or answer any pertinent clinical issues raised in the request for the imaging examination. For example, to rule out pneumothorax state: “There is no evidence of pneumothorax.” To rule out fracture state: “There is no evidence of fracture.” It is not advisable to use such universal disclaimers as “The mammography examination does not exclude the possibility of cancer.”

    • Comparative data

      • Comparisons with previous examinations and reports when possible are a part of the radiologic consultation and report and optionally may be part of the “impression” section.

  • 8

    Impression (conclusion or diagnosis):

    • Each examination should contain an “impression” section.

    • Give a precise diagnosis whenever possible.

    • Give a differential diagnosis when appropriate.

    • Recommend, only when appropriate, follow-up and additional diagnostic radiologic studies to clarify or confirm the impression.

      • In normal CXR section the only structures visible in normal lungs are the fissures and the pulmonary vessels.

      • Lung parenchymal abnormalities are divided into five basic patterns:

        • 1

          Mass

        • 2

          Consolidative

        • 3

          Interstitial

        • 4

          Vascular

        • 5

          Airway

Infection

General

Pathogens

  • Bacterial pneumonia

    • Streptococcus pneumoniae (pneumococcus)

    • Staphylococcus

    • Pseudomonas

    • Klebsiella

    • Nocardia

    • Chlamydia

    • Neisseria meningitides

    • Haemophilus influenzae

    • Anaerobes

    • Legionella

    • Mycoplasma pneumoniae

    • Actinomyces israelii

    • Mycobacterium tuberculosis

  • Viral pneumonia (25% of community-acquired pneumonias)

    • Influenza

    • Varicella, herpes zoster

    • Rubeola

    • Cytomegalovirus

    • Coxsackievirus, parainfluenza virus, adenovirus, respiratory syncytial virus (RSV)

  • Fungal pneumonia

    • Histoplasmosis

    • Coccidioidomycosis

    • Blastomycosis

    • Aspergillosis

    • Cryptococcosis

    • Candidiasis

    • Zygomycoses

  • Parasitic pneumonias

    • Pneumocystis jiroveci Frenkel 1999 (formerly Pneumocystis carinii )

    • Toxoplasma gondii

Acquisition of Pneumonia

  • Community-acquired pneumonia

    • S. pneumoniae , Haemophilus

    • Mycoplasma

  • Hospital-acquired pneumonia (incidence 1%, mortality 35%): nosocomial infection

    • Gram-negative bacteria: Pseudomonas , Proteus , Escherichia coli , Enterobacter , Klebsiella

    • Methicillin-resistant Staphylococcus aureus (MRSA)

    • Vancomycin-resistant enterococcus (VRE)

  • Pneumonia in immunosuppressed patients

    • Bacterial pneumonia (gram negative) still most common

    • Tuberculosis

    • Fungal

    • Pneumocystis pneumonia (PCP)

  • Endemic pneumonias

    • Fungal: histoplasmosis, coccidioidomycosis, blastomycosis

    • Viral

  • Aspiration-associated pneumonia (important)

Risk Factors

The radiographic appearance of pulmonary infections is variable depending on the pathogen, underlying lung disease, risk factors, and previous or partial treatment.

COMMUNITY-ACQUIRED INFECTIONS
Risk Factor Common Pathogens
Alcoholism Gram-negative bacteria, Streptococcus pneumoniae , Mycobacterium tuberculosis , aspiration (mouth flora)
Old age S. pneumoniae , Staphylococcus aureus , aspiration
Aspiration Mouth flora (anaerobes)
Cystic fibrosis Pseudomonas , S. aureus , Aspergillus
Chronic bronchitis S. pneumoniae , Haemophilus influenzae

  • Other risk factors for developing pneumonia:

    • Bronchiectasis

    • Coma, anesthesia, seizures (aspiration)

    • Tracheotomy

    • Antibiotic treatment

    • Immunosuppression (renal failure, diabetes, cancer, steroids, AIDS)

    • Chronic furunculosis ( Staphylococcus )

Radiographic Spectrum of Pulmonary Infections

SUMMARY
Type Pathogen Imaging
Lobar Pneumonia
  • Infection primarily involves alveoli

  • Spread through pores of Kohn and canals of Lambert throughout a segment and ultimately an entire lobe

  • Bronchi are not primarily affected and remain air filled; therefore:

    • Air bronchograms

    • No volume loss because airways are open

  • Streptococcus pneumoniae

  • Klebsiella pneumoniae

  • Others

    • Staphylococcus aureus

    • Haemophilus influenzae

    • Fungal

  • Nowadays uncommon because of early treatment

  • Round pneumonia (more common in children)

Bronchopneumonia
  • Primarily affects the bronchi and adjacent alveoli

  • Volume loss may be present as bronchi filled with exudates

  • Bronchial spread results in multifocal patchy opacities

  • S. aureus

  • Gram-negative bacteria

  • Others

    • H. influenzae

    • Mycoplasma

Nodules
  • Variable in size

  • Indistinct margins

  • Fungal

    • Histoplasma

    • Aspergillus

    • Cryptococcus

    • Coccidioides

  • Bacterial

    • Legionella

    • Nocardia

  • Septic emboli

    • S. aureus

Cavitary Lesions (Infectious)
  • Abscess: necrosis of lung parenchyma ± bronchial communication

  • Fungus ball (air crescent/monad sign)

  • Postprimary TB (favor apical and posterior segments of the upper lobes)

  • Pneumatoceles caused by air leak into pulmonary interstitium

  • Anaerobic bacteria

  • Aspergillus

  • M. tuberculosis

  • S. aureus

Diffuse Opacities
  • Reticulonodular pattern: interstitial peribronchial areas of inflammation (viral)

  • Alveolar location (PCP)

  • Miliary pattern: hematogenous spread (TB)

  • Viral

  • Mycoplasma

  • PCP

PCP , Pneumocystis pneumonia; TB , tuberculosis.

Complications of Pneumonia

  • Parapneumonic effusion

    • Stage 1: exudation: free flowing

    • Stage 2: fibropurulent: loculated

    • Stage 3: organization, erosion into lung or chest wall

  • Empyema

  • Bronchopleural fistula (BPF; fistula between bronchus and pleural space) with eroding pleural-based fluid collections

  • Bronchiectasis

  • Pulmonary fibrosis, especially after necrotizing pneumonia or acute respiratory distress syndrome (ARDS)

  • Adenopathy

Resolution of Pneumonia

  • 80%–90% of cases resolve within 4 weeks.

  • 5%–10% resolve within 4–8 weeks (usually in older or diabetic patients). Subsequent radiographs should always show interval improvement compared with the previous radiographs.

  • Nonclearance

    • Antibiotic resistance

    • Consider other pathogen (e.g., M. tuberculosis )

    • Recurrent infection

    • Obstruction pneumonitis due to tumor

Bacterial Infections

General

Common Pathogens

  • S. pneumoniae , 50% (40–60 years)

  • Mycoplasma , 30%

  • Anaerobes, 10%

  • Gram-negative bacteria, 5%

  • Staphylococcus , 5%

  • Haemophilus , 3% (especially in infants and patients with chronic obstructive pulmonary disease [COPD])

Clinical Findings

  • Pneumonic syndrome

    • Fever

    • Cough

    • Pleuritic pain

    • Sputum

  • Ancillary findings

    • Headache, arthralgia, myalgia

    • Diarrhea

    • Hemoptysis

Streptococcal Pneumonia

Radiographic Features

  • Lobar or segmental pneumonia pattern

  • Bronchopneumonia pattern

  • Round pneumonia (in children)

Staphylococcal Pneumonia ( Fig. 1.15 )

FIG. 1.15

Radiographic Features

  • Bronchopneumonia pattern

  • Bilateral, >60%

  • Abscess cavities, 25%–75%

  • Pleural effusion, empyema, 50%

  • Pneumatoceles, 50% (check valve obstruction), particularly in children

  • Central lines

  • Signs of endocarditis

Pseudomonas Pneumonia

Typical Clinical Setting

  • Hospital-acquired infection

  • Ventilated patient

  • Reduced host resistance

  • Patients with cystic fibrosis

Radiographic Features

Three presentations:

  • Extensive bilateral parenchymal consolidation (predilection for both LLs)

  • Abscess formation

  • Diffuse nodular disease (bacteremia with hematogenous spread; rare)

Legionnaires Disease

Severe pulmonary infection caused by Legionella pneumophila; 35% of patients require ventilation, 20% mortality. Most infections are community acquired. Patients have hyponatremia. Seroconversion for diagnosis takes 2 weeks.

Radiographic Features

  • Common features

    • Initial presentation of peripheral patchy consolidation

    • Bilateral severe disease

    • Rapidly progressive

    • Pleural effusions, <50%

    • LL predilection

  • Uncommon features

    • Abscess formation

    • Lymph node enlargement

Haemophilus Pneumonia

Caused by H. influenzae . Occurs most commonly in children, immunocompromised adults, or patients with COPD. Often there is concomitant meningitis, epiglottitis, and bronchitis.

Radiographic Features

  • Bronchopneumonia pattern

  • LL predilection, often diffuse

  • Empyema

Mycoplasma Pneumonia

Most common nonbacterial pneumonia (atypical pneumonia). Mild course. Age 5–20 years. Positive for cold agglutinins, 60%.

Radiographic Features

  • Reticular pattern

  • LL predominance, often diffuse

  • Consolidation, 50%

Complications

  • Autoimmune hemolytic anemia

  • Erythema nodosum, erythema multiforme

  • Stevens-Johnson syndrome

  • Meningoencephalitis

Klebsiella (Friedländer) Pneumonia

Gram-negative organism. Often in debilitated patients and/or alcoholics.

Radiographic Features

  • Consolidation appears similar to that of infection with S. pneumoniae

  • Lobar expansion

  • Cavitation, 30%–50%, typically multiple

  • Massive necrosis (pulmonary gangrene)

  • Pleural effusion uncommon

Tuberculosis (TB) ( Fig. 1.16 )

FIG. 1.16

Transmitted by inhalation of infected droplets of M. tuberculosis or M. bovis . TB acquisition usually requires constant or repeated contact with sputum-positive patients because the tubercle does not easily grow in the immunocompetent human host. Target population includes:

  • Patients of low socioeconomic status (homeless)

  • Alcoholics

  • Immigrants: from Mexico, Philippines, Indochina, Haiti

  • Elderly patients

  • AIDS patients

  • Prisoners

Primary Infection ( Fig. 1.17 )

Usually heals without complications. Sequence of events includes:

  • Pulmonary consolidation (1–7 cm); cavitation is rare; LL (60%) > UL

  • Caseous necrosis 2–10 weeks after infection

  • Lymphadenopathy (hilar and paratracheal), 95%

  • Pleural effusion, 10%

  • Spread of a primary focus occurs primarily in children or immunosuppressed patients.

FIG. 1.17

Secondary Infection ( Fig. 1.18 )

FIG. 1.18

Active disease in adults most commonly represents reactivation of a primary focus. However, primary disease is now also common in adults in developed countries because there is no exposure in childhood. Distribution is as follows:

  • Typically limited to apical and posterior segments of ULs or superior segments of LLs (because of high P o 2 ?)

  • Rarely in anterior segments of ULs (in contradistinction to histoplasmosis)

Radiographic Features

  • Exudative TB

    • Patchy or confluent air space disease

    • Adenopathy uncommon

  • Fibrocalcific TB

    • Sharply circumscribed linear densities radiating to hilum

  • Cavitation, 40%

Complications ( Fig. 1.19 )

  • Miliary TB may occur after primary or secondary hematogenous spread.

  • Bronchogenic spread occurs after communication of the necrotic area with a bronchus; it produces an acinar pattern (irregular nodules approximately 5 mm in diameter).

  • Tuberculoma (1–7 cm): nodule during primary or secondary TB; may contain calcification

  • Effusions are often loculated.

  • Bronchopleural fistula

  • Pneumothorax

COMPARISON
Primary TB Reinfection TB
Location Usually bases Upper lobes, superior segment
Lower lobes
Appearance Focal Patchy
Cavitation No Frequent
Adenopathy as only finding Common No
Effusion Common Uncommon
Miliary pattern Yes Yes
TB , Tuberculosis.

FIG. 1.19

Nontuberculous Mycobacterial (NTMB) Infections

The two most common NTMB pathogens are M. avium-intracellulare and M. kansasii (less common: M. xenopi , M. chelonei , M. gordonae, M. fortuitum , “fast grower”). Unlike TB, NTMB infections are not acquired by human-human transmission but are a direct infection from soil or water. There is also no pattern of primary disease or reactivation: the infection is primary, although some infections may become chronic. The infection often occurs in elderly patients with COPD, older women in good health, and AIDS patients.

Radiographic Features

  • NTMB infections may be indistinguishable from classic TB.

  • Atypical features such as bronchiectasis and bronchial wall thickening are common.

  • Nodules are common in older women.

    COMPUTED TOMOGRAPHY FINDINGS
    Findings TB (%) MAI Infection (%)
    Nodules <1 cm 80 95
    Nodules 1–3 cm 40 30
    Mass >3 cm 10 10
    Consolidation 50 50
    Cavity 30 30
    Bronchiectasis 30 95
    Bronchial wall thickening 40 95
    Septal thickening 50 15
    Emphysema 20 20
    Calcified granuloma 15 5
    MAI , Mycobacterium avium-intracellulare; TB , tuberculosis.

Nocardia Pneumonia

Caused by Nocardia asteroides , worldwide distribution. Common opportunistic invader in:

  • Lymphoma

  • Steroid therapy; especially transplant patients

  • Pulmonary alveolar proteinosis (common)

Radiographic Features

  • Focal consolidation (more common)

  • Cavitation

  • Irregular nodules

Actinomycosis

Actinomycosis is caused by Actinomyces israelii, a gram-positive normal saprophyte in the oral cavity. Pulmonary disease develops from aspiration of the organism (poor dentition) or from direct penetration into the thorax.

Radiographic Features

  • Focal consolidation > cavitating mass

  • Lymphadenopathy uncommon

  • Extension into the chest wall and pleural thickening is less common today but still occurs and is an important differential feature.

Pulmonary Abscess

The spectrum of anaerobic pulmonary infections includes:

  • Abscess: single or multiple cavities >2 cm, usually with AFL

  • Necrotizing pneumonia: analogous to abscess but more diffuse and cavities <2 cm

  • Empyema: suppurative infection of the pleural space, most commonly as a result of pneumonia

Predisposing Conditions

  • Aspiration (e.g., alcoholism, neurologic disease, coma)

  • Intubation

  • Bronchiectasis, bronchial obstruction

Treatment

  • Antibiotics, postural drainage

  • Percutaneous drainage of empyema

  • Drainage/resection of lung abscess only if medical therapy fails

Sickle Cell Anemia

  • Patients with sickle cell disease are at increased risk of pneumonia and infarction. These entities are difficult to differentiate, and hence are called acute chest syndrome .

  • Pneumonias were originally due to pneumococci but now are due to viruses or Mycoplasma. Differential diagnosis includes atelectasis and infarct.

  • Infarcts are more frequent in adults than in children. Rare in children younger than 12 years.

  • Consolidation is seen on CXRs; resolves more slowly than in the general population and tends to recur.

Viral Pneumonia

General

Classification

  • DNA viruses

    • Unenveloped

      • Parvoviruses

      • Papovaviruses

      • Adenoviruses

      • Hepatitis viruses (hepatitis B)

    • Enveloped

      • Herpesviruses (herpes simplex virus [HSV], Epstein-Barr virus [EBV], varicella-zoster virus [VZV], cytomegalovirus [CMV])

      • Poxviruses (variola virus, molluscum contagiosum virus)

  • RNA viruses

    • Unenveloped

      • Picornaviruses (hepatitis A virus, coxsackievirus)

      • Caliciviruses

      • Reoviruses

    • Enveloped

      • Retroviruses (HIV)

      • Arenaviruses

      • Coronaviruses

      • Togaviruses

      • Bunyaviruses

      • Orthomyxoviruses (influenza virus)

      • Paramyxoviruses (mumps virus, measles virus, RSV, parainfluenza virus)

Occurrence

  • Immunocompetent hosts

    • Influenza

    • Hantavirus

    • EBV

    • Adenovirus

  • Immunocompromised hosts

    • HSV

    • VZ

    • CMV

    • Measles virus

    • Adenovirus

Spectrum of Disease

  • Acute interstitial pneumonia (AIP): diffuse or patchy interstitial pattern, thickening of bronchi, thickened interlobar septa

  • Lobular inflammatory reaction: multiple nodular opacities 5–6 mm (varicella; late calcification)

  • Hemorrhagic pulmonary edema: mimics bacterial lobar pneumonia

  • Pleural effusion: usually absent or small

  • Chronic interstitial fibrosis (bronchiolitis obliterans)

Virus Centrilobular Nodules Lobar Ground Glass Diffuse Ground Glass Thickened Interlobular Septa Consolidation
Influenza virus +++ +++ + +
EBV + + + +
CMV ++ ++ ++ + +
VZ +++ + +
HSV + +++ + +++
Measles virus ++ + + +
Hantavirus +++ + ++
Adenovirus ++ + +++
CMV , Cytomegalovirus; EBV , Epstein-Barr virus; HSV , herpes simplex virus; VZ , varicella-zoster virus.

Influenza Pneumonia

Influenza is very contagious and thus occurs in epidemics. Pneumonia, however, is uncommon.

Involves the upper respiratory tract, including the trachea and major bronchi.

Radiographic Features

  • Acute phase: multiple acinar densities

  • Coalescence of acinar densities to diffuse patchy airspace disease (ASD; bronchopneumonia type)

Varicella-Zoster Pneumonia

Fifteen percent of infected patients have pneumonias; 90% are older than 20 years.

Radiographic Features

  • Acute phase: multiple acinar opacities

  • Coalescence of acinar opacities to diffuse patchy ASD

  • 1–2-mm calcifications throughout lungs after healing

  • HRCT usually shows 1–10-mm well-defined and ill-defined nodules diffusely throughout both lungs.

Measles Virus Pneumonia

  • Two forms:

    • Primary measles virus pneumonia and secondary bacterial pneumonia

    • Atypical measles virus pneumonia

Radiographic Features

  • Primary measles virus:

    • Mixed reticular opacities and air space consolidation.

    • Lymph node enlargement in the hilum.

    • CT findings include ground-glass attenuation, air space consolidation, and small centrilobular nodules.

  • Atypical measles virus:

    • Spherical or segmental consolidation, which clears rapidly

    • Hilar lymph node enlargement and pleural effusion are frequently present.

Cytomegalovirus (CMV) Pneumonia

Occurs most commonly in neonates or immunosuppressed patients.

Radiographic Features

  • Predominantly interstitial infection, multiple small nodules (common)

  • Adenopathy may be present

Swine-Origin Influenza a (H1N1) Virus Infection

Epidemiologic data to date suggest that the newly emerged H1N1 virus, although transmissible from person to person, is of relatively low virulence. CXRs are normal in more than half of patients. However, the disease can progress to bilateral extensive ASD in severely ill patients. These patients are also at high risk of PE, which should be sought carefully on contrast-enhanced CT scans.

Severe Acute Respiratory Syndrome

Emerging highly contagious infection caused by a coronavirus; first outbreak reported in southern China in 2002. The disease has two clinical stages: viral replicative stage and immunopathologic stage. The incubation period for the virus ranges from 2 to 12 days.

Radiographic Features

  • During viral replication stage, well-defined areas of ground-glass opacities seen in the LLs and periphery of the lungs. The LLs and peripheral areas of the lungs are most commonly involved.

  • During the immunopathologic phase, patients show the appearance of new lesions that are poorly defined and usually localized to the LLs and posterior or dependent regions of the lungs. Following the acute phase, there is a decrease in the extent of ground-glass opacity and consolidation. Some patients may develop spontaneous pneumomediastinum.

Fungal Infections

General

Two broad categories:

  • Endemic human mycoses (prevalent only in certain geographic areas):

    • Histoplasmosis (Ohio, Mississippi, St. Lawrence river valleys)

    • Coccidioidomycosis (San Joaquin Valley)

    • Blastomycosis

Opportunistic mycoses (worldwide in distribution) occur primarily in immunocompromised patients (aspergillosis and cryptococcosis may also occur in immunocompetent hosts):

  • Aspergillosis

  • Candidiasis

  • Cryptococcosis

  • Mucormycosis

Radiographic Features

  • Acute phase: pneumonic type of opacity (may be segmental, nonsegmental, or patchy); miliary (hematogenous) distribution in immunosuppressed patients

  • Reparative phase: nodular lesions with or without cavitations and crescent sign

  • Chronic phase: calcified lymph nodes or pulmonary focus with fungus (e.g., histoplasmosis)

  • Disseminated disease (spread to other organs) occurs primarily in immunocompromised patients

Histoplasmosis ( Fig. 1.20 ): Pulmonary and Mediastinal

FIG. 1.20

Histoplasma capsulatum is particularly prevalent in the Ohio, Mississippi, and St. Lawrence river valleys, although the agent has a worldwide distribution. The organism is most prevalent in soil that contains excrement of bats and birds (bat caves, chicken houses, old attics, or buildings).

Clinical Findings

Most patients are asymptomatic or have nonspecific respiratory symptoms, increased complement fixation titer, and H. capsulatum antigen positivity.

Radiographic Features

  • Consolidation (primary histoplasmosis)

    • Parenchymal consolidation

    • Adenopathy is very common and may calcify heavily later on.

  • Nodular form (chronic histoplasmosis, reinfection):

    • Histoplasmoma: usually solitary, sharply circumscribed nodule, most commonly in LLs

    • Fibrocavitary disease in ULs indistinguishable from postprimary TB

    • Cavitary nodules

  • Disseminated form (immunocompromised patients)

    • Miliary nodules

    • Calcifications in liver and spleen

Mediastinal Histoplasmosis

Mediastinal histoplasmosis may follow pulmonary histoplasmosis. There are two distinct entities (which may not always be separable from each other):

  • Mediastinal granuloma

    • Results from spread of H. capsulatum to lymph nodes

    • Granulomas usually calcified

    • Displacement of the superior vena cava or esophagus

  • Mediastinal fibrosis (fibrosing or sclerosing mediastinitis)

    • May cause superior vena cava syndrome, airway compression, PA occlusion, pericarditis

    • Diffuse infiltration of mediastinum

    • Multiple densely calcified nodes (CT is more useful than magnetic resonance imaging [MRI] in making this diagnosis)

Coccidioidomycosis ( Fig. 1.21 )

FIG. 1.21

Coccidioides immitis is endemic in the southwest United States (San Joaquin Valley, “valley fever”) and in Central America and South America. Infection occurs by inhalation of spores in soil. Human-to-human infection does not occur.

Clinical Findings

Cutaneous manifestations common; 70% are asymptomatic.

Radiographic Features

  • Consolidation (primary form)

    • “Fleeting” parenchymal consolidation, most commonly LLs

    • Adenopathy in 20%

  • Nodular form (chronic form, 5%)

    • 15% cavitate

      • 50% have a thin-walled cavity (suggestive of diagnosis)

      • 50% have a thick-walled cavity (i.e., nonspecific)

      • May present with pneumothorax

    • Nodules rarely calcify

    • Hilar or paratracheal adenopathy

  • Disseminated form (immunocompromised patients; rare: 0.5% of all forms)

    • Miliary nodules

    • Extrapulmonary spread

North American Blastomycosis ( Fig. 1.22 )

  • Caused by Blastomyces dermatitidis ; uncommon infection. Most infections are self-limited.

  • CXR is nonspecific: ASD > nodule (15% cavitate) or solitary mass > miliary spread.

  • Focal or diffuse air space consolidation is the most common radiologic finding.

  • Focal blastomycosis typically occurs in paramediastinal location and has an air bronchogram, findings that may suggest the diagnosis.

  • Satellite nodules around primary focus are common.

  • Chronic blastomycosis may mimic lung cancer because it can manifest itself as a focal mass. An air bronchogram or presence of satellite nodules is suggestive of correct diagnosis.

  • Adenopathy, pleural effusions, and calcifications are very uncommon.

  • Bone lesions, 25%

  • Skin lesions are common.

FIG. 1.22

Aspergillosis ( Fig. 1.23 )

FIG. 1.23

Aspergillus is a ubiquitous fungus that, when inhaled, leads to significant lung damage. The fungus grows in soil, water, decaying vegetation, and hospital air vents. Infection with A. fumigatus > A. flavus , A. niger , or A. glaucus. There are four unique forms of pulmonary aspergillosis, each associated with a specific immune status.

TYPES OF ASPERGILLOSIS
Type Lung Structure Immune Status Pathology
Allergic (ABPA) Normal Hypersensitivity Hypersensitivity → bronchiectasis, mucus plugging
Aspergilloma Preexisting cavity Normal Saprophytic growth in preexisting cavity
Invasive Normal Severely impaired Vascular invasion, parenchymal necrosis
Semiinvasive Normal Normal or impaired Chronic local growth, local cavity formation
ABPA , Allergic bronchopulmonary aspergillosis.

Allergic Bronchopulmonary Aspergillosis (ABPA)

ABPA is a complex type I (IgE-mediated) and type III (IgG-mediated) hypersensitivity reaction to A. fumigatus, occurring primarily in individuals with asthma and occasionally in individuals with cystic fibrosis. The hypersensitivity initially causes bronchospasm, mucus production, and bronchial wall edema (IgE mediated); ultimately there is bronchial wall damage due to the type III IgG-mediated response, with resultant cystic bronchiectasis.

Clinical Findings

Elevated levels of specific serum IgE and IgG antibodies to A. fumigatus , asthma, peripheral eosinophilia, elevated serum IgE levels (≥1000 IU/mL), positive skin test for Aspergillus antigen. Treatment is with oral corticosteroids, antifungal agents, and omalizumab, which is a humanized monoclonal antibody targeted against IgE.

Radiographic Features

  • Fleeting pulmonary parenchymal opacities (common manifestation)

  • Central, UL saccular bronchiectasis (hallmark) ( Fig. 1.24A )

    FIG. 1.24

  • Mucus plugging (“finger-in-glove” appearance) ( Fig. 1.24B ) and bronchial wall thickening (common); 25% of patients will demonstrate high-attenuation mucus plugging.

  • Tree-in-bud nodularity

  • Cavitation, 10%

Aspergilloma (Mycetoma, Fungus Ball)

This is a saprophytic infection that occurs in the setting of structural lung disease (from TB, sarcoid, emphysema). Commonly in ULs, solitary lesions. The fungus grows into the preexisting cavity (e.g., cyst, bulla, bronchiectasis), creating a “fungus ball” consisting of fungus, mucus, and inflammatory cells. Individuals with mycetomas are often asymptomatic but may develop recurrent hemoptysis, which in rare cases can be massive. In these cases, bronchial artery embolization is indicated. The other treatment options include surgical resection, intracavity administration of amphotericin B, and systemic antifungal therapy.

Radiographic Features

  • Focal intracavitary mass (3–6 cm), typically in ULs.

  • Air may surround the aspergilloma (Monod sign), mimicking the appearance of cavitation seen with invasive aspergillosis.

  • Small area of consolidation around cavity is typical.

  • Adjacent pleural thickening is common.

  • Fungus ball moves with changing position.

Invasive Aspergillosis

Invasive aspergillosis has a high mortality rate (70%–90%) and occurs mainly in severely immunocompromised patients (bone marrow transplants, leukemia). The infection starts with endobronchial fungal proliferation and then leads to vascular invasion with thrombosis and infarction of the lung (“angioinvasive infection”). Additional sites of infection (in 30%) are the brain, liver, kidney, and GI tract. Treatment is with systemic and/or intracavitary administration of amphotericin.

Radiographic Features ( Fig. 1.25 )

  • Multiple pulmonary nodules, 40%

  • Nodules have a characteristic halo of ground-glass appearance (represents pulmonary hemorrhage)

  • Within 2 weeks, 50% of nodules undergo cavitation, which results in the air crescent sign. The appearance of the air crescent sign indicates the recovery phase (increased granulocytic response). The air crescent sign may also be seen in TB, actinomycosis, mucormycosis, septic emboli, and tumors. Do not confuse the air crescent sign with the Monod sign (clinical history helps to differentiate the two).

  • Other manifestations:

    • Peribronchial opacities

    • Focal areas of consolidation

FIG. 1.25

Semiinvasive Aspergillosis

This form of aspergillosis occurs in mildly immunocompromised patients and has a pathophysiology similar to that of invasive aspergillosis except that the disease progresses more chronically over months (mortality rate 30%). Risk factors include diabetes, alcoholism, pneumoconiosis, malnutrition, and COPD. Treatment is with systemic and/or intracavitary administration of amphotericin.

Radiographic Features

  • Appearance similar to that of invasive aspergillosis

  • Cavitation occurs at 6 months after infection

Cryptococcosis

Caused by Cryptococcus neoformans , which has a worldwide distribution and is ubiquitous in soil and pigeon excreta. Infection occurs through inhalation of contaminated dust.

Clinical Findings

Common in patients with lymphoma, diabetes, or AIDS and in patients receiving steroid therapy.

Radiographic Features

  • Most common findings in the lung are pulmonary mass, multiple nodules, or segmental or lobar consolidation.

  • Cavitation, adenopathy, and effusions are rare.

  • Disseminated form: CNS, other organs

Candidiasis

Caused by Candida albicans more frequently than other Candida species.

Clinical Findings

Typically in patients with lymphoreticular malignancy; suspect pulmonary disease if associated with oral disease. Often there is disseminated fungemia.

Radiographic Features

  • Plain radiograph is nonspecific: opacities (LL) > nodules.

  • Nodular disease in disseminated form

  • Pleural effusion, 25%

  • Cavitation and adenopathy are rare.

Zygomycoses

Group of severe opportunistic mycoses caused by fungi of the Zygomycetes class:

  • Mucormycosis ( Mucor )

  • Rhizopus

  • Absidia

Zygomycoses usually have two major clinical manifestations:

  • Pulmonary mucormycosis

  • Rhinocerebral mucormycosis

Zygomycoses are uncommon infections and occur primarily in immunocompromised patients (leukemia, AIDS, chronic steroid use, diabetes).

Radiographic Features

  • Radiographic features are similar to those of invasive aspergillosis because of angioinvasive behavior of fungi.

Acquired Immunodeficiency Syndrome

General

AIDS is caused by HTLV type III (human T-cell lymphotrophic virus = HIV [human immunodeficiency virus]). HIV-1 and HIV-2 are single-stranded RNA viruses that bind to CD4 present on T lymphocytes (other cells: glial cells, lung monocytes, dendritic cells in lymph nodes). The viral RNA genome is copied into DNA with the help of reverse transcriptase and integrated into the host cellular DNA.

Known routes of HIV transmission:

  • Blood and blood products

  • Sexual activity

  • In utero transmission

  • During delivery

Clinical Findings

  • Lymphadenopathy

  • Opportunistic infections

  • Tumors: lymphoma—usually B-cell non-Hodgkin's lymphoma (NHL), Kaposi sarcoma (KS)

  • Other manifestations:

    • Associated with lymphocytic interstitial pneumonia (LIP), usually in childhood

    • Spontaneous pneumothorax (development of cystic spaces, interstitial fibrosis related to PCP)

    • Septic emboli

  • Clinical findings supportive of AIDS diagnosis ( Fig. 1.26 ):

    • CD4 cell count <200/mm 3 ; the dysfunction of the immune system is inversely related to the CD4 cell count; PCP, CD4 cell count <200/mm 3 ; MAI infection, CD4 cell count <50/mm 3

    • Less than one case of bacterial pneumonia per year

    FIG. 1.26

Opportunistic Infections

  • P. jiroveci Frenkel 1999, 70%

  • Mycobacterial infection, 20%; CD4 cell counts often <50/mm 3

  • Bacterial infection, 10% ( S. pneumoniae , Haemophilus )

  • Fungal infection (<5% of AIDS patients)

  • Nocardia, <5%: cavitating pneumonia

  • CMV pneumonia (common at autopsy)

Chest

General

  • 50% of all AIDS patients have pulmonary manifestations of infection or tumor.

  • A normal CXR does not exclude the diagnosis of PCP.

  • CMV infection is common at autopsy but does not cause significant morbidity or death; CMV antibody titers are present in virtually all patients with AIDS.

  • Use of chest CT in AIDS patients:

    • Symptomatic patient with normal CXR; however, patients will commonly first undergo induced sputum or bronchoscopy or be given empirical therapy for PCP.

    • To clarify confusing CXR findings

    • Workup of focal opacities, adenopathy, nodules

Spectrum of Chest Manifestations ( Fig. 1.27 )

  • Nodules

    • KS (usually associated with skin lesions)

    • Septic infarcts (rapid size increase)

    • Fungal: Cryptococcus , Aspergillus

  • Large opacity: consolidation, mass

    • Hemorrhage

    • NHL

    • Pneumonia

    • Linear or interstitial opacities

    • PCP

    • Atypical mycobacteria

    • KS

  • Lymphadenopathy

    • Mycobacterial infections

    • KS

    • Lymphoma

    • Reactive hyperplasia, rare in thorax

  • Pleural effusion

    • KS

    • Mycobacterial, fungal infection

    • Pyogenic empyema

FIG. 1.27

Pneumocystis Jiroveci Pneumonia (PJP) ( Figs. 1.28–1.30 )

FIG. 1.28

FIG. 1.29

FIG. 1.30

General

P . jiroveci is an atypical fungus that can result in pneumonia in immunocompromised individuals. PJP affects individuals with AIDS, transplant recipients, and patients receiving long-term corticosteroid therapy. When PJP occurs in HIV-infected individuals, it is usually only after the CD4 count has decreased to less than 200/mm 3 . The diagnosis of PJP can be confirmed by bronchoalveolar lavage or presence of the organism in a sputum sample.

Radiographic Features

  • Interstitial pattern, 80%

    • CXR: bilateral perihilar ground-glass opacities or thickened interstitium

    • HRCT: ground-glass opacities, interlobular septal thickening, and in some cases multifocal areas of consolidation

  • Up to one-third of patients with PJP will have a normal CXR.

  • Multiple cysts of various sizes are seen in one-third of patients with PJP and may cause spontaneous pneumothorax.

  • UL P. jiroveci involvement is common, because aerosolized pentamidine may not get to ULs; UL disease may mimic TB, but the latter may have pleural effusions or lymphadenopathy, both of which are uncommon in PJP.

  • Atypical patterns, 5%

    • Unilateral disease

    • Granulomatous inflammation resulting in focal nodules or masses

  • PJP as a presenting manifestation of AIDS is decreasing in frequency because of trimethoprim-sulfamethoxazole prophylaxis.

Mycobacterial Infection

M. tuberculosis > M. avium-intracellulare (MAI) (this pathogen usually causes extrathoracic disease). CD4 cell count usually <50/mm 3 .

Radiographic Features

  • Hilar and mediastinal adenopathy common

    • Necrotic lymph nodes (TB) have a low attenuation center and only the rim is enhanced with contrast medium.

    • M. tuberculosis is more commonly associated with necrosis from MAI.

    • Adenopathy in KS or lymphoma is enhanced uniformly.

  • Pleural effusion

  • Other findings are similar to those of non-AIDS TB (UL consolidations, cavitations).

Fungal Infections

Fungal infections in AIDS are uncommon (<5% of patients):

  • Cryptococcosis (most common); 90% have CNS involvement.

  • Histoplasmosis: nodular or miliary pattern most common; 35% have a normal CXR.

  • Coccidioidomycosis: diffuse interstitial pattern, thin-walled cavities

Kaposi Sarcoma (KS) ( Fig. 1.31 )

The most common tumors in AIDS are:

  • KS (15% of patients); incidence declining; male-female ratio 50 : 1

  • Lymphoma (<5% of patients)

FIG. 1.31

Pulmonary manifestations of KS (almost always preceded by cutaneous/visceral involvement):

  • Nodules

    • 1–3 cm

    • Spiculated “flame-shaped” nodules with peribronchovascular distribution in advanced disease

  • Coarse reticular opacities emanating from hilum

  • Pleural effusions (serosanguineous), 40%

  • Adenopathy

  • Lymphangitic tumor spread

AIDS-Related Lymphoma

NHL (usually aggressive B-cell type) > Hodgkin lymphoma.

Poor prognosis. The spectrum includes:

  • Solitary or multiple pulmonary masses with or without air bronchogram, 25%

  • AIDS-related lymphoma is typically an extranodal disease (CNS, GI tract, liver, bone marrow): adenopathy not very prominent.

  • Pleural effusions are common.

Neoplasm

General

Location

Chest neoplasms are best categorized by their primary location:

  • Lung tumors

  • Pleural tumors

  • Mediastinal tumors

  • Tumors of the airway

  • Chest wall tumors

Classification of Pulmonary Neoplasm

  • Malignant tumors

    • Bronchogenic carcinoma

    • Lymphoma

    • Metastases

    • Sarcomas, rare

  • Low-grade malignancies (previously bronchial adenoma)

    • Carcinoid, 90%

    • Adenoid cystic carcinoma (previously cylindroma, resembles salivary gland tumor), 6%

    • Mucoepidermoid carcinoma, 3%

    • Pleomorphic carcinoma, 1%

  • Benign tumors, rare

    • Hamartoma

    • Papilloma

    • Leiomyoma

    • Hemangioma

    • Chemodectoma

    • Pulmonary blastoma

    • Chondroma

    • Multiple pulmonary fibroleiomyomas

    • Pseudolymphoma

Lung Cancer Screening

  • Low-dose chest CT

  • Uses the Lung-RADS assessment to categorize patients, which can be accessed at https://www.acr.org/Quality-Safety/Resources/LungRADS .

  • Lung-RADS stratifies patients on the basis of presence, size, and morphology of pulmonary nodules into different follow-up and management categories.

  • Patients qualify if they are between 55 and 74 years old with at least a 30-pack-year smoking history.

  • Yearly CT screening decreased lung cancer mortality in this subset of patients by 20% and all-cause mortality by 6.7% when compared with screening with radiography.

Percutaneous Biopsy

The true positive rate of percutaneous lung biopsy is 90%–95%. False-negative results are usually due to poor needle placement, necrotic tissue, and so on. Tumor seeding is extremely uncommon (1 in 20,000).

Contraindications to biopsy are usually relative and include:

  • Severe COPD

  • Pulmonary hypertension

  • Coagulopathy

  • Contralateral pneumonectomy

  • Suspected echinococcal cysts

Technique

  • 1

    Fluoroscopic or CT localization of nodule

  • 2

    Pass needle over superior border of rib to avoid intercostal vessels

  • 3

    Avoid traversing pulmonary veins and crossing fissure

  • 4

    Coaxial needle system:

    • 19-gauge introducer needle

    • 20-gauge core biopsy needle with 1–2-cm needle throw

  • 5

    Cytopathologist should be present to determine if sample is adequate and diagnostic.

  • 6

    CXR after procedure to determine presence of pneumothorax

Complications

  • Pneumothorax, 25%; 5%–10% of patients require a chest tube (i.e., pneumothorax >25% or if patient is symptomatic)

  • Hemoptysis

  • Systemic air embolism: extremely rare but most serious complication, approximately 0.02%–0.7%

Bronchogenic Carcinoma

Bronchogenic carcinoma refers broadly to any carcinoma of the bronchus.

Classification

  • Adenocarcinoma (most common), 40%:

  • 2011 International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society international multidisciplinary classification of lung adenocarcinoma:

    • Adenocarcinoma in situ: ≤3 cm, noninvasive lepidic growth pattern (along the alveolar walls), typically nonsolid on CT, usually nonmucinous

    • Minimally invasive adenocarcinoma: ≤3 cm, primarily lepidic growth with invasive component ≤5 mm, predominantly nonsolid appearance on CT but may contain central solid component (≤5 mm), typically nonmucinous

    • Lepidic predominant nonmucinous adenocarcinoma: invasive but with mainly lepidic growth, typically part solid on CT but may have nonsolid or cystic appearance

    • Invasive mucinous adenocarcinoma: predominantly lepidic growth pattern, formerly referred to as mucinous bronchioloalveolar carcinoma , may appear solid, primarily solid, part solid, or nonsolid on CT, can be multifocal

  • Atypical adenomatous hyperplasia is one of the preinvasive lesions for adenocarcinoma of the lung:

    • Typically a ground-glass nodule less than 5 mm in size

  • SCC, 30%:

    • Spindle cell carcinoma

  • Small cell carcinoma, 15%:

    • Oat cell

    • Intermediate cell type

    • Combined oat cell carcinoma

  • Large cell carcinoma, 1%:

    • Giant cell carcinoma

    • Clear cell carcinoma

  • Adenosquamous tumor

Risk Factors for Bronchogenic Carcinoma

  • Smoking: 98% of male patients and 87% of female patients with lung cancer smoke; 10% of heavy smokers will develop lung cancer. The strongest relationship between smoking and cancer has been established for SCC, followed by adenocarcinoma.

  • Radiation, uranium mining

  • Asbestos exposure

  • Genetic predisposition (HLA-Bw44 associated?)

Radiographic Spectrum

Primary Signs of Malignancy ( Fig. 1.32 )

  • Mass (>6 cm) or nodule (<6 cm) with spiculated, irregular borders

  • Unilateral enlargement of hilum: mediastinal widening, hilar prominence

  • Cavitation

    • Most common in ULs or superior segments of LLs

    • Wall thickness is indicative of malignancy

    • Less than 4 mm: 95% of cavitated lesions are benign

    • >15 mm: 85% of cavitated lesions are malignant

    • Cavitation is most common in SCC

  • Certain tumors may present as chronic ASD: adenocarcinoma, lymphoma

  • Some air bronchograms are commonly seen by HRCT in adenocarcinoma.

FIG. 1.32

Secondary Signs of Malignancy ( Fig. 1.33 )

  • Atelectasis (Golden inverted S sign in RUL, LUL collapse)

  • Obstructive pneumonia

  • Pleural effusion

  • Interstitial patterns: lymphangitic tumor spread

  • Hilar and mediastinal adenopathy

  • Metastases to ipsilateral, contralateral lung

LOCATIONS OF TUMORS
Tumor Frequency (%) Location Comments
Adenocarcinoma 40 Peripheral Scar carcinoma
Squamous cell carcinoma 30 Central, peripheral a Cavitation
Small cell carcinoma 15 Central, peripheral a Endocrine activity
Large cell carcinoma 1 Central, peripheral Large mass

a Rarely present as a resectable T1 lesion.

FIG. 1.33

Paraneoplastic Syndromes of Lung Cancer

  • Incidence: 2% of bronchogenic carcinoma

    • Metabolic

      • Cushing syndrome (ACTH)

      • Inappropriate antidiuresis (ADH)

      • Carcinoid syndrome (serotonin, other vasoactive substances)

      • Hypercalcemia (PTH, bone metastases)

      • Hypoglycemia (insulin-like factor)

    • Musculoskeletal

      • Neuromyopathies

      • Clubbing of fingers (HPO)

    • Other

      • Acanthosis nigricans

      • Thrombophlebitis

      • Anemia

Radiation Pneumonitis

Radiation pneumonitis is the acute phase of radiation damage and usually appears 3 weeks after treatment. The minimum radiation dose to induce pneumonitis is 30 Gy. The acute phase is typically asymptomatic but may be associated with fever and cough. Fibrosis usually occurs after 6–12 months.

Radiographic Features

  • Diffuse opacities in radiation port

  • HRCT allows better assessment of extent than plain radiograph

Tumor Staging ( Fig. 1.34 )

FIG. 1.34

American Joint Committee on Cancer Tumor-Node-Metastasis (TNM) Staging System, Seventh Edition (Nonsmall Cell Lung Cancer)

  • Primary tumor (T)

    • T0: No evidence of a primary tumor

    • T1: ≤3 cm, limited to lung, not more proximal than lobar bronchus

    • T1a: ≤2 cm

    • T1b: >2 and ≤3 cm

    • T2: >3 but ≤7 cm

      • Or invades parietal pleura

      • Or involves main bronchus ≥2 cm distal to carina

      • Or atelectasis/obstructive pneumonia extending to hilum but not involving entire lung

    • T2a: >3 but ≤5 cm

    • T2b: >5 but ≤7 cm

    • T3: >7 cm

      • Or directly invades chest wall, diaphragm, phrenic nerve, mediastinal pleura, parietal pericardium

      • Or mainstem bronchus <2 cm distal to carina

      • Or atelectasis/obstructive pneumonia involving entire lung

      • Or separate tumor nodules in a different ipsilateral lobe

    • T4: Any size

      • Heart, mediastinum, great vessels, trachea, recurrent laryngeal nerve, esophagus, vertebral body, or carina

      • Or separate tumor nodules in a different ipsilateral lobe

  • Nodes (N)

    • N0: No lymph node involvement

    • N1: Ipsilateral nodes in the hilar, interlobar, lobar, segmental, subsegmental regions

    • N2: Ipsilateral nodes in mediastinum. Affected regions include paratracheal, prevascular and retrotracheal, lower paratracheal, subcarinal, paraesophageal, and pulmonary ligament regions.

    • N3: Contralateral hilar or mediastinal nodes; all significantly large lymph nodes in the ipsilateral or contralateral supraclavicular or scalene regions

  • Metastases (M)

    • M0: No metastases

    • M1: Metastases

    • M1a: Intrathoracic metastases:

      • Tumor nodules in contralateral lung

      • Malignant pleural/pericardial effusion

      • Pleural dissemination

    • M1b: Distant (extrathoracic) metastases: liver, bone, brain, adrenal gland

Unresectable Stages

  • Tumors are unresectable if T4, N3, or M1 (stage 3b or 4)

  • Stage 3b: N3, M0, any T; T4, M0, any N ≥2

  • Stage 4: M1, any T, any N

Summary of Treatment

  • Tumors ≤5 cm without metastases can be treated surgically.

  • Tumors ≤7 cm with an ipsilateral hilar metastasis and tumors either >7 cm or invading the pleura, chest wall, or diaphragm without metastases are treated with surgery followed by chemotherapy.

  • Any tumor with ipsilateral mediastinal nodes, invasion of the mediastinum/mediastinal structures, and/or cancer in a different lobe is treated primarily with chemoradiation.

5-Year Survival

Overall 5-year survival rate is 15%.

  • Stage 1A: 50%

  • Stage 1B: 43%

  • Stage 2A (limited disease): 36%

  • Stage 2B (T4): 25%

  • Stage 3A (N3): 19%

  • Stage 3B: 7%

  • Stage 4: 2%

Small Cell Cancer Staging

Small cell lung cancer (SCLC) accounts for 15% of all lung cancers and is known for its rapid growth rate and its early dissemination to regional lymph nodes and distant sites.

Traditionally a two-stage system had been used for SCLC: “limited” and “extensive.” Limited disease is confined to one lung with ipsilateral lymph node metastasis (can be encompassed by a single radiation port) and has better prognosis. Extensive stage denotes metastases to the contralateral lung and nodes or distant organs (including the pleura). About two-thirds of patients with SCLC present at the extensive stage at the time of initial diagnosis. The International Committee for the Study of Lung Cancer now recommends that SCLC be staged with the eighth edition of the American Joint Committee on Cancer's TNM staging system.

Five-year survival rates in patients with SCLC:

  • Stage 1A: 56%

  • Stage 1B: 57%

  • Stage 2A: 38%

  • Stage 2B: 40%

  • Stage 3A: 12%

  • Stage 3B: 0%

Lymph Node Imaging

Anatomy ( Fig. 1.35 )

  • Anterior mediastinal nodes

    • Parietal node group

      • Internal mammary nodes

      • Superior diaphragmatic nodes

    • Prevascular node group (anterior to the great vessels)

  • Middle mediastinal nodes

    • Paratracheal *

      * Paratracheal and subcarinal nodes are best assessed by mediastinoscopy; the remainder of the nodes are best assessed by CT.

      ; the lowest node is the azygos node

    • Subcarinal * : below bifurcation; drainage to right paratracheal nodes

    • Subaortic; AP window node

    • Tracheobronchial (pulmonary root, hilar)

  • Posterior mediastinal nodes

    • Paraaortic

    • Prevertebral

    • Paraspinous: lateral to vertebral body

FIG. 1.35

American Thoracic Society Classification ( Fig. 1.36 )

This classification system assigns numbers to regional lymph nodes:

  • 2R, 2L: paratracheal

  • 4R, 4L: superior tracheobronchial

  • 5, 6: anterior mediastinal

  • 7: subcarinal

  • 8, 9: posterior mediastinal

  • 10R, 10L: bronchopulmonary

  • 11R, 11L: pulmonary

  • 14: diaphragmatic

FIG. 1.36

CT Criterion for Abnormal Nodes

Short-axis lymph node diameter >1 cm (60%–70% accuracy for differentiating between malignant and benign adenopathy)

Chest Wall Invasion

Accuracy for detection of chest wall invasion by CT is 40%–60%.

Radiographic Features ( Fig. 1.37 )

  • Reliable signs

    • Soft tissue mass in chest wall

    • Bone destruction

  • Unreliable signs

    • Obtuse angles at contact between tumor and pleura

    • >3 cm of contact between tumor and pleura

    • Pleural thickening

    • Increased density of extrapleural fat

FIG. 1.37

Mediastinal Invasion

Contiguous invasion of mediastinal organs, heart, great vessels, aerodigestive tract, and vertebra indicates nonresectability.

Radiographic Features

  • Diaphragmatic paralysis (phrenic nerve involvement)

  • Mediastinal mass with encasement of mediastinal structures

  • MRI may be useful to detect vascular invasion.

Malignant Pleural Effusion

Development of pleural effusions usually indicates a poor prognosis. Presence of a documented malignant pleural effusion makes a tumor unresectable (M1). Incidence of pleural effusion:

  • Bronchogenic carcinoma, 50%

  • Metastases, 50%

  • Lymphoma, 15%

Pericardial Metastasis

Pericardial effusion with enhanced nodules is highly suggestive of malignant involvement of the pericardium.

CT and MRI findings are inconclusive for determination of benign versus malignant pleural and pericardial disease. Fluorodeoxyglucose positron emission tomography (FDG PET) has been shown to have high sensitivity in detecting pleural malignancy.

Pathogenesis of Malignant Effusions

  • Pleural invasion increases capillary permeability.

  • Lymphatic or venous obstruction decreases clearance of pleural fluid.

  • Bronchial obstruction → atelectasis → decrease in intrapleural pressure.

Central Bronchial Involvement

Tumors that involve a central bronchus usually cause lung collapse or consolidation. These tumors are considered unresectable (T4 tumors) only if they involve the carina.

Metastases to Other Organs

  • Lung tumors most frequently metastasize to:

    • Liver (common)

    • Adrenal glands (common)

      • 30% of adrenal masses in patients with adenocarcinoma are adenomas.

      • Most adrenal masses in patients with small cell carcinomas are metastases.

      • Tumor may be present in a morphologically normal-appearing gland.

    • Other sites (especially small and large cell tumors)

      • Brain (common)

      • Bones

      • Kidney

Specific Lung Tumors

Adenocarcinoma

  • Now the most frequent primary lung cancer

  • Typically presents as a multilobulated, peripheral mass

  • May arise in scar tissue: scar carcinoma

  • KRAS mutation is the most frequent genetic mutation.

Bronchioloalveolar Carcinoma

  • Subtype of adenocarcinoma; slow growth. The characteristic radiographic presentations are:

    • Morphologic type

      • Small peripheral nodule (solitary form), 25% (most common)

      • Multiple nodules

      • Chronic ASD

    • Air bronchogram

    • Absent adenopathy

    • Cavitation may be seen by HRCT (Cheerio sign)

Squamous Cell Carcinoma (SCC)

SCC is most directly linked with smoking. SCC carries the most favorable prognosis. The most characteristic radiographic appearances are:

  • Cavitating lung mass, 30%

  • Peripheral nodule, 30%

  • Central obstructing lesion causing lobar collapse

  • Chest wall invasion

  • FGFR1 amplification is the most common mutation.

Large Cell Carcinoma

Usually presents as large (>70% are >4 cm at initial diagnosis) peripheral mass lesions. Overall uncommon tumor.

Pancoast Tumor (Superior Sulcus Tumor)

Tumor located in the lung apex that has extended into the adjacent chest wall. Histologically, Pancoast tumors are often SCCs.

Clinical Findings

  • Horner syndrome

  • Pain radiating into arm (invasion of pleura, bone, brachial plexus, or subclavian vessels)

Radiographic Features ( Fig. 1.38 )

  • Apical mass

  • Chest wall invasion

  • Involvement of subclavian vessels

  • Brachial plexus involvement

  • Bone involvement: rib, vertebral body

FIG. 1.38

Small Cell Carcinoma (SCC) (Neuroendocrine Tumor, Type 3)

Most aggressive lung tumor with poorest prognosis. At diagnosis, two-thirds of patients already have extrathoracic spread:

  • Typical initial presentation: massive bilateral lymphadenopathy

  • With or without lobar collapse

  • Brain metastases

Carcinoid (Neuroendocrine Tumor, Types 1 and 2)

Represent 90% of low-grade malignancy tumors of the lung. The 10-year survival rate with surgical treatment is 85%. Rarely results in carcinoid syndrome caused by the production of 5-hydroxytryptamine with flushing, diarrhea, nausea, and wheezing; carcinoid syndrome usually accompanied by liver metastases.

Types

  • Typical carcinoid: local tumor (type 1)

  • Atypical carcinoid (10%–20%): metastasizes to regional lymph nodes (type 2); liver metastases are very rare

Radiographic Features

  • PET negative

  • 80% centrally located within main, lobar, segmental bronchi

    • Segmental or lobar collapse (most common finding)

    • Periodic exacerbation of atelectasis

    • Endobronchial mass

    • Very rarely located within the trachea (1%)

  • Peripherally located carcinoid, 20%

    • Pulmonary nodule

    • May be enhanced with contrast medium

COMPARISON OF CLINICAL, PATHOLOGIC, AND IMAGING FINDINGS IN NEUROENDOCRINE TUMORS OF THE LUNG
Findings Typical Carcinoid Atypical Carcinoid LCNEC SCLC
Demographic Features
Mean patient age (years) 40–49 50–59 60–69 70–79
Association with smoking No Yes Yes Yes
Male-female ratio 1 : 1 2 : 1 >2.5 : 1 >2.5 : 1
Histopathologic Features
Mitoses per 10 HPFs <2 2–10 >10 >50
Necrosis No Yes Yes Yes
Imaging Findings
Central to peripheral ratio 3 : 1 3 : 1 1 : 4 10–20 : 1
Calcification or ossification 30% 30% 9% ≤23%
Extrathoracic metastases 15% 15% 35% 60%–70%
Enhancement High; central or rim High; central or rim High High with necrosis
FDG uptake on PET Low Low High High
FDG, Fluorodeoxyglucose; HPF, high-power field; LCNEC, large cell neuroendocrine carcinoma; PET , positron emission tomography; SCLC, small cell lung cancer.

Hamartoma ( Fig. 1.39 )

FIG. 1.39

Hamartomas are mesenchymal tumors and are the most common benign tumors of the lung composed of cartilage (predominantly), connective tissue, muscle, fat, and epithelial tissue. 85% are identified as solitary pulmonary nodules, 5%–15% are endobronchial. They typically occur in individuals older than 50 years and are more common in men.

Radiographic Features

  • Well-circumscribed, often lobulated pulmonary nodule

  • Calcification identified in only 10% of hamartomas <3 cm but seen in approximately 75% of hamartomas ≥5 cm in size

  • “Popcorn” calcification classically associated with hamartomas, but may also show stippled pattern

  • Slow growth: 0.5–5 mm/year

  • HRCT can show intralesional fat (65%)

Carney Triad

Predominant in Young Women (<30 Years Old)

  • Gastric smooth muscle tumors (epithelioid leiomyosarcoma)

  • Functioning extra-adrenal paraganglioma

  • Pulmonary chondromas

Tracheobronchial Papillomatosis

Radiographic Features

  • Multiple, well-demarcated nodules that can grow

  • Cavitate with 2–3-mm-thick walls

  • Air fluid levels may develop

  • Risk of SCC 15 years after diagnosis

Pulmonary Blastoma

  • Predominant in males, poor prognosis

Radiographic Features

  • Large peripheral mass that is well circumscribed

  • May show pleural invasion and may metastasize

Lung Metastases From Other Primary Lesions

General

Pathways of metastatic spread from a primary extrathoracic site to lungs (in order of frequency):

  • Spread via pulmonary arteries (PAs)

  • Lymphatic spread (celiac nodes → posterior mediastinal nodes + paraesophageal nodes) and in lung parenchyma

  • Direct extension

    • Endobronchial spread

    • Follow the invasion-metastasis cascade: invade locally, intravasate into blood, survive circulation, lodge in distant organ, merge into parenchyma, survive the foreign organ, and reinitiate growth.

Neoplasms with rich vascular supply draining into systemic venous system:

  • Renal cell carcinoma (RCC)

  • Sarcomas

  • Trophoblastic tumors

  • Testis

  • Thyroid

Neoplasms with lymphatic dissemination:

  • Breast (usually unilateral)

  • Stomach (usually bilateral)

  • Pancreas

  • Larynx

  • Cervix

Other neoplasms with high propensity to localize in lung:

  • Colon

  • Melanoma

  • Sarcoma

Radiographic Features

  • Multiple lesions, 95%; solitary lesions, 5%

  • Lung bases > apices (related to blood flow)

  • Peripheral, 90%; central, 10%

  • Metastases typically have sharp margins.

  • Fuzzy margins can result from peritumoral hemorrhage (choriocarcinoma, chemotherapy).

  • Cavitations are common in SCCs from head and neck primary lesions.

Calcified Metastases

  • Calcifications in lung metastases are observed in:

    • Bone tumor metastases

      • Osteosarcoma

      • Chondrosarcoma

    • Mucinous tumors

      • Ovarian

      • Thyroid

      • Pancreas

      • Colon

      • Stomach

    • Metastases after chemotherapy

Giant Metastases (“Cannon Ball” Metastases) in Asymptomatic Patients

  • Head and neck cancer

  • Testicular and ovarian cancer

  • Soft tissue cancer

  • Breast cancer

  • Renal cancer

  • Colon cancer

Sterile Metastases

Sterile metastases refers to pulmonary metastases under treatment that contain no viable tumor. Nodules typically consist of necrotic and/or fibrous tissue.

Chronic Lung Disease

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