Evaluation of the Solitary Pulmonary Nodule

Evaluation of the Solitary Pulmonary Nodule


  • This is defined as a solitary circumscribed pulmonary opacity with no associated pulmonary, pleural, or mediastinal abnormality ▸ it measures < 3 cm in diameter

  • Many are discovered incidentally (but up to 40% may be malignant)

  • <10% are due to a solitary pulmonary metastasis

  • Benign intrapulmonary lymph nodes: nodules <15 mm from the pleural surface ▸ ellipsoid in shape, usually connected to the pleural surface by a fine linear opacity

  • Ground-glass nodules :

    • Ground-glass density: focal area of increased lung attenuation (well or poorly defined) through which normal structures can be seen

    • Pure ground-glass nodule: no soft tissue component

    • Part solid ground-glass nodule: a solid component obscuring lung architecture

Differentiation Between Benign and Malignant Masses

  • The two primary criteria are the rate of growth (or stability over time) and the attenuation of the nodule ▸ the patient's age is also a significant distinguishing feature (a carcinoma is only seen in < 1% of patients < 35 years old)

    • Rate of growth/stability over time: benign lesions invariably have a doubling time of < 1 month or > 18 months (bronchoalveolar carcinomas are an exception in that they may have very slow growth rates) ▸ bronchial carcinomas usually have a doubling time of between 1 and 18 months

    • Attenuation/enhancement: a dense central nidus or lamellated calcification indicates a granulomatous process (e.g. tuberculosis, histoplasmosis) ▸ irregular ‘popcorn’ calcification suggests a hamartoma ▸ fat is virtually diagnostic of a hamartoma ▸ a lack of enhancement (<15HU) following IV contrast medium is indicative of benignity

      • Granular calcification is seen on CT in up to 7% of carcinomas (and can represent either tumour calcification or a granuloma engulfed by tumour) ▸ eccentric or stippled calcification within soft tissue may indicate malignancy

      • A mixture of soft tissue and ground-glass attenuation nodules is more likely to be malignant than soft tissue nodules alone

    • Size: this is of little diagnostic value ▸ most benign nodules are <2 cm ▸ round, flat or tubular nodules tend to be benign

    • Margins: a well-defined mass with a smooth pencil sharp margin is likely to be benign ▸ carcinomas typically have ill-defined margins which are irregular, spiculated, or lobulated and may exhibit umbilication or a notch – unfortunately all these features can be seen with benign disease


This is useful for nodules >1 cm ▸ a positive result is 97% sensitive and 82% specific for malignancy

  • False-positive result: this can be secondary to an infectious or inflammatory processes (e.g. TB, sarcoid or rheumatoid nodules)

  • False-negative result: this can occur if a nodule is <1 cm ▸ it can also occur if the nodule is due to a carcinoid tumour or a slow-growing adenocarcinoma subtype

The Fleischner Society guidelines: a strategy for follow-up and management of pulmonary nodules in patients over 35 years of age with no known malignancy. ©1

Axial image from a contrast enhanced CT and CT image, FDG PET image and fused image from a CT PET study, demonstrating a PET positive right lung nodule. (A) Lung nodule close to the right hilum with (B) increased uptake on PET/CT corresponding to lung cancer. **

Recommendations for the management of subsolid pulmonary nodules detected at CT: a statement from the Fleischner Society
Nodule type Management recommendations Additional remarks
Solitary pure GGNs
≤5 mm No CT follow-up required Obtain contiguous 1-mm-thick sections to confirm that nodule is truly a pure GGN
>5 mm Initial follow-up CT at 3 months to confirm persistence then annual surveillance CT for a minimum of 3 years FDG PET is of limited value, potentially misleading, and therefore not recommended
Solitary part-solid nodules Initial follow-up CT at 3 months to confirm persistence. If persistent and solid component <5 mm, then yearly surveillance CT for a minimum of 3 years. If persistent and solid component ≥5 mm, then biopsy or surgical resection Consider PET/CT for part-solid nodules >10 mm
Multiple subsolid nodules
Pure GGNs ≤5 mm Obtain follow-up CT at 2 and 4 years Consider alternate causes for multiple GGNs ≤5 mm
Pure GGNs >5 mm without a dominant lesion(s) Initial follow-up CT at 3 months to confirm persistence and then annual surveillance CT for a minimum of 3 years FDG PET is of limited value, potentially misleading, and therefore not recommended
Dominant nodule(s) with part-solid or solid component Initial follow-up CT at 3 months to confirm persistence. If persistent, biopsy or surgical resection is recommended, especially for lesions with >5 mm solid component Consider lung-sparing surgery for patients with dominant lesion(s) suspicious for lung cancer
Note—These guidelines assume meticulous evaluation, optimally with contiguous thin sections (1 mm) reconstructed with narrow and/or mediastinal windows to evaluate the solid component and wide and/or lung windows to evaluate the nonsolid component of nodules, if indicated. When electronic calipers are used, bidimensional measurements of both the solid and ground-glass components of lesions should be obtained as necessary. The use of a consistent low-dose technique is recommended, especially in cases for which prolonged follow-up is recommended, particularly in younger patients. With serial scans, always compare with the original baseline study to detect subtle indolent growth.

Lung Cancer: Radiological Features

Lung Cancer: Radiological Features


  • SCLC: small (oat) cell carcinoma

    • This originates from submucosal neuroendocrine cells ▸ it rapidly spreads haematogenously and to the lymph nodes ▸ it behaves as a systemic disease and is usually disseminated at presentation

  • NSCLC: non-small cell lung cancer

    • Squamous cell carcinomas: arises from the proximal airway epithelium

    • Large cell carcinomas: atypical cells that appear ‘large’ under the microscope

    • Adenocarcinomas: arising from the bronchial glands

  • Risks: tobacco smoke (20- to 30-fold increased risk) – has the greatest association with squamous cell carcinomas and weakest association with bronchoalveolar carcinomas ▸ asbestos exposure, interstitial pulmonary fibrosis and radiotherapy are additional risks

Clinical presentation

  • Asymptomatic (25%): asymptomatic peripheral tumours are more likely to be incidental findings and surgically resectable

  • Symptomatic: recurrent pneumonia ▸ cough ▸ wheeze ▸ haemoptysis

  • Paraneoplastic syndromes: inappropriate ADH secretion ▸ Cushing's syndrome (ACTH) ▸ carcinoid syndrome ▸ hypercalcaemia (PTH)

  • Poor prognostic features: hoarseness ▸ chest pain ▸ brachial plexus neuropathy or Horner's syndrome (due to a Pancoast's tumour) ▸ SVC obstruction ▸ dysphagia

Radiological features

Peripheral tumours

  • The majority are spherical or oval in shape ▸ lobulated masses can occur due to uneven growth rates ▸ there may be a ‘corona radiata’ due to numerous fine strands radiating into the lung ▸ a bronchocele or mucoid impaction can be seen distal to an obstructing carcinoma ▸ collapse and consolidation is less commonly seen than with central tumours

    • Cavitation with irregular thick walls (≥8 mm) ± fluid levels (particularly squamous tumours)

    • Calcification is rare (6–10%) and may represent engulfed granulomatous disease ▸ amorphous or cloud-like calcification can be seen with dystrophic tumour calcification (10%)

    • Air bronchograms are rare but can be seen with adenocarcinoma

    • Ground-glass attenuation is associated with a higher risk of malignancy (and commonly seen with lepidic or invasive mucinous adenocarcinoma)

Central tumours

  • Collapse or consolidation can be seen peripheral to the tumour (due to bronchial narrowing ± hilar enlargement) ▸ any peripheral collapsed lung will enhance more than a central tumour ▸ collateral air drift may prevent some post-obstructive changes

    • Golden S’ sign : a fissure may show a central bulge due to collapse around a central tumour

Hilar enlargement (N1-N3)

  • This is a common presenting feature and may reflect a proximal central tumour, lymphadenopathy or consolidated lung ▸ extensive hilar and mediastinal lymphadenopathy is typical of small cell tumours ▸ simple pneumonias rarely cause hilar adenopathy

Chest wall invasion (T3)

  • This does not preclude surgical resection (although it adversely affects the prognosis)

  • CT: assessment is unreliable (with local chest wall pain remaining the most specific indicator) ▸ contact with or a thickened pleura does not necessarily indicate invasion ▸ a clear extrapleural fat plane is helpful but not definitive ▸ reliable signs include clear-cut bone destruction or a large soft tissue mass

  • MRI: this is better than CT in selected cases ▸ it is the optimal modality for demonstrating the extent of a superior sulcus tumour

  • Transthoracic ultrasound: this is an accurate technique

  • 99m Tc radionuclide skeletal scintigraphy: this is sensitive (and may detect bone invasion before plain radiography) ▸ PET-CT is now the technique of choice for distant spread

Mediastinal invasion (T4)

  • CT/MRI indicators: visible tumour deep within the mediastinal fat (mediastinal contact alone is not enough to diagnose invasion) ▸ encasement of the mediastinal vessels, oesophagus, or proximal mainstem bronchi ▸ SVC obstruction ▸ an elevated hemidiaphragm (indicating phrenic nerve involvement)

  • Criteria for resectability: < 3 cm of contact with the mediastinum ▸ < 90° of circumferential contact with the aorta ▸ a visible mediastinal fat plane between the mass and any vital mediastinal structure

  • Irresectability: tumours obliterating fat planes or showing greater contact than that described above (although less certain)

Bone involvement (M1)

  • Direct rib or spine invasion ▸ haematogenous osteolytic bone metastases ▸ hypertrophic osteoarthopathy

Cavitating squamous cell carcinoma. CT – the wall of the cavity is variable in thickness. *

Pancoast's tumour. Coronal CT demonstrating a large tumour in the left upper lobe invading the soft tissues, displacing and invading the left subclavian artery. *

CT demonstrating a second primary bronchogenic carcinoma in the right lung in a patient who had undergone a previous left pneumonectomy. The new tumour has spiculated edges infiltrating into the adjacent lung (corona radiata). *

Cavitating bronchogenic carcinoma. There is preservation of the extrapleural fat plane at the point of contact with the chest wall (arrow). Although the pleura may be involved, the chest wall is likely to be otherwise spared. *

MRI of a left lower lobe tumour that has directly invaded the aortic wall, which has altered the signal adjacent to the tumour (arrow). *

Tumour calcification. Large bronchial carcinoma within the left lower lobe showing extensive amorphous and cloud-like calcification. *

New classification for adenocarcinomas
Premalignant Malignant
Atypical adenomatous hyperplasia Minimally invasive adenocarcinoma
Adenocarcinoma in situ predominantly lepidic growth pattern
lepidic growth pattern (no solid components) ≤3 cm
pure ground-glass opacity on CT invasive component <5 mm
subsolid nodules on CT
Lepidic predominant adenocarcinoma
>5 mm invasion
previously known as non-mucinous bronchoalveolar carcinoma
Invasive mucinous adenocarcinoma
previously known as mucinous bronchoalveolar carcinoma

Lung Cancer: Pearls

Lung Cancer: Pearls

Pleural effusions (M1a)

  • They may occur due to direct spread, lymphatic involvement, or tumour emboli (an adenocarcinoma may cause lobular pleural thickening indistinguishable from a malignant mesothelioma)

  • A pleural effusion designates a tumour as M1a (unless clinically there is another cause and the pleural cytology is negative)

Lepidic predominant adenocarcinoma/invasive mucinous adenocarcinoma (formerly bronchoalveolar carcinoma)

  • This can appear as a solitary lobulated or spiculated pulmonary mass with air bronchograms and cavitation ▸ it may also appear as an ill-defined opacity resembling a pneumonia, homogeneous consolidation, multiple ill-defined nodules throughout the lung, or a focal ground-glass opacity

    • They are often PET negative

Pancoast's tumour (superior sulcus tumour)

  • A Pancoast's tumour is an apical lung tumour which can extend into the chest wall and may resemble apical pleural thickening (and is commonly a squamous carcinoma) ▸ it can invade the subclavian vessels, brachial plexus (with pain radiating into the arm) and cervical sympathetic chain (leading to Horner's syndrome)

  • MRI is the optimal modality for assessment but CT is used for assessing bony involvement

Lymph Node Staging

  • Lung cancers normally spread sequentially to the ipsilateral hilar nodes, ipsilateral mediastinal nodes and then the contralateral mediastinal and supraclavicular nodes

    • Skip metastases to the mediastinal nodes (in the absence of hilar nodes) can occur in of patients

  • Other causes of enlarged nodes: previous tuberculosis ▸ histoplasmosis ▸ pneumoconiosis ▸ sarcoidosis ▸ reactive hyperplasia to the tumour or an associated pneumonia


This is insensitive


Generally nodes with a short-axis diameter of > 10 mm are considered enlarged (normal subcarinal and lower mediastinal nodes can be up to 10 mm – upper paratracheal nodes rarely exceed 7 mm) ▸ increased signal on STIR imaging in abnormal nodes ▸ however microscopic tumour involvement can be present in normal-sized nodes


This can assess nodal size and morphology, and guide fine needle aspiration of the aortopulmonary, subcarinal and posterior mediastinal nodes ▸ it has greater sensitivity and specificity than CT or PET in some series

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