Genitourinary Imaging

Renal Pedicle ( Fig. 4.1 )

• Renal artery

• Renal vein

• Collecting system and ureter

• Lymphatics

Collecting System

• Minor calyces: most kidneys have 10–14 minor calyces.

• Major calyces

• Renal pelvis: may be completely within the renal sinus or partially “extrarenal.”

Orientation and Size of Kidneys

• Kidneys are 3 to 4 lumbar vertebral bodies in length, 12–14 cm long and 5–7 cm wide.

• Intravenous pyelograms (IVPs) overestimate the true renal length because of magnification and renal engorgement from osmotic diuresis. Ultrasound (US) often underestimates the true renal length because of technical difficulties in imaging the entire kidney.

• Left and right kidney size should not vary more than 1 cm.

• Right kidney is 1–2 cm lower than the left kidney and slightly more lateral.

• Renal axis parallels axis of psoas muscles.

Technique

• 1

  Kidney, ureter, bladder (KUB)

• 2

  Inject 100 mL of 30% contrast

• 3

  1-min and 5-min radiograph of both kidneys

• 4

  10-min KUB and both obliques

• 5

  Coned bladder view

• 6

  Postvoid KUB

Technique

• 1

  KUB and preliminary tomogram of kidneys (starting at 8 cm from back)

• 2

  Drip infusion of 300 mL of Urovist 14% (or Conray-30) or 150 mL of Isovue 300 (or Omnipaque 300)

• 3

  Obtain tomograms after 150 mL has been given. Usually 7 to 9 cuts are obtained.

• 4

  Postinfusion KUB and both oblique views

• 5

  Coned bladder view

• 6

  Postvoid KUB

Hematuria Protocol

Single bolus CT technique

• Phase 1: Noncontrast CT of the abdomen and pelvis, including KUB

• Single bolus (100–150 mL, 300–320 mg of iodine/mL) of IV contrast material at 2–4 mL/s

• Early images of kidney in nephrographic phase

• Excretory phase images (5 min following injection) through KUB

Split bolus CT technique:

• Phase 1: noncontrast CT of abdomen and pelvis. Immediately thereafter administer 30 mL of IV contrast and wait 5–10 min.

• Phase 2: place patient back on scanner and inject 100 mL of contrast at 2–3 mL/s, and scan patient prone from top of kidneys to pubic symphysis after 100 s.

• Phase 2: excretory phase (5 min) through the kidneys is obtained at the same time as the 100-s scan. The initial bolus of 30 mL should now be making its way through the collecting system.

Stone Protocol

• Noncontrast CT of the abdomen and pelvis using 5 mm slice thickness

• Coronal and sagittal reconstructions with 3 mm slice thickness

Renal Mass Protocol

• Phase 1: noncontrast CT images of abdomen

• Phase 2: corticomedullary phase, 25–30 s after contrast injection, through kidneys

• Phase 3: nephrographic phase, 60–80 s after injection

Indications

• Hydronephrosis (acute, subacute obstruction)

• Pyonephrosis

Technique ( Fig. 4.2 )

• 1

  Preprocedure workup:

  • Check coagulation status.

  • Cefazolin 2 g IV < 120 kg; 3 g IV > 120 kg and gentamicin 120 mg IV × 1

  • Penicillin-allergic patients: vancomycin as above and aztreonam 2 g IV

  • Review all radiographs and determine on plain film where kidneys are located, especially in relation to colon, spleen, and pleural reflections.

• 2

  Local lidocaine. Under US guidance, place a 20-gauge introducer system into a posterior, lower pole calyx.

• 3

  The inner needle stylet can be removed and free flow of urine checked. Aspirate a small amount for cultures and to mildly decompress the system when urine is obtained.

• 4

  Attach connector tubing and inject a small amount of contrast to confirm positioning at the tip of a calyx. Detach the connector tub­ing carefully to ensure that the needle stays in place.

• 5

  Use the microwire to gain access to the renal pelvis. Remove the introducer needle, and insert the plastic sheath that comes with the set.

• 6

  Place a 0.038 Amplatz wire through the sheath into the renal collecting system and down the ureter. Depending on the anatomy/obstruction, it may be necessary to use different wire combinations.

• 7

  Dilate skin up to 12 Fr.

• 8

  Pass 8–10-Fr percutaneous nephrostomy (PCN) catheter over guidewire. Remove stiffener and guidewire. Coil pigtail. Inject contrast to check position of catheter within the renal pelvis. Cut thread.

• 9

  In the setting of infection, complete evaluation of the ureter via an antegrade injection is best deferred to a second visit.

Bifid Renal Pelvis

One pelvis drains upper pole calyces; the other drains the middle and lower pole calyces. The two pelvises join proximally to the ureteropelvic junction (UPJ). Incidence: 10% of population. No complications.

Incomplete Ureteral Duplication

Duplications join distal to UPJ and proximal to bladder: Y-shaped ureters. No complications.

Complete Ureteral Duplication

See Chapter 11 .

Associations

• UPJ obstruction, 30%

• Ureteral duplication, 10%

• Genital anomalies

• Other anomalies: anorectal, cardiovascular, musculoskeletal anomalies

Complications

• Obstruction, infection, calculus formation in 30%

• Increased risk of renal malignancies, especially Wilms tumor

• Increased risk of traumatic injury

Imaging Features

• Abnormal axis of each kidney with lower calyx more medial than upper calyx

• Bilateral malrotation of renal pelvises in anterior position

• Isthmus lies anterior to aorta and inferior vena cava (IVC) but behind inferior mesenteric artery (IMA)

Imaging Features

• IVP

  • Lucent defect

  • Cortical bulge

  • Round indentations on collecting system

  • “Beak sign” can be seen with large cysts.

• US

  • Anechoic

  • Enhanced through-transmission

  • Sharply marginated, smooth walls

  • Very thin septations may occasionally be seen.

• CT

  • Smooth cyst wall

  • Sharp demarcation from surrounding renal parenchyma

  • Water density (<10–15 HU) that is homogeneous throughout lesion

  • No significant enhancement after IV contrast administration (small increases of <5 HU, however, can be seen likely due to technical factors, not true enhancement)

  • Cyst wall too thin to be seen by CT (with small cysts, volume-averaging may create the false appearance of a thick wall)

• MRI

  • Indications (rather than CT): renal insufficiency, solitary kidney, contrast allergy, patients with complex cystic renal masses needing multiple follow-up examinations

  • End-expiration images are preferred because they are more reproducible in optimizing image coregistration and subtraction algorithms if the patient can hold his or her breath.

  • Simple renal cysts are uniformly hypointense on T1W and hyperintense on T2W images with no perceptible enhancement after gadolinium. MRI can characterize extremely small renal cysts.

  • Internal components of cystic masses and subtle enhancement are better appreciated by MRI than by CT.

Pearls

• True renal cysts should always be differentiated from hydronephrosis, calyceal diverticulum, and peripelvic cysts.

• Differentiate renal cyst from hypoechoic renal artery aneurysm using color Doppler US.

• Cysts that contain calcium, septations, and irregular margins (complicated cysts) need further workup.

Bosniak Classification

• Category 1: benign simple cyst

  • Simple cysts contain low-attenuation (0–20 HU) fluid and a hairline-thin smooth wall.

  • Cysts do not contain septations, calcifications, or enhancing nodular soft tissue.

• Category 2: minimally complicated cysts that are benign but have certain radiologic findings of concern.

  • Includes septated (paper-thin septations) cystic, minimally calcified cysts, high-density cysts.

  • Fine calcification or a short segment of slightly thickened calcification may be present in the wall or septa.

  • Hyperattenuating cysts contain more fluid than water attenuation (i.e., >20 HU). In general, cysts that measure between 20 and 40 HU are proteinaceous cysts and will show findings of a simple cyst using US; those with attenuations over 40–50 HU are likely to be hemorrhagic cysts and will be complex under US. When a hyperattenuating renal mass is encountered on an unenhanced CT scan, the probability of the mass being benign is more than 99% as long as the attenuation is 70 HU or more and the mass is homogeneous.

• Category 2F (the “F” means to follow) lesions cannot be considered benign without some period of observation.

  • Slightly more complicated (e.g., may contain multiple, hairline-thin septa that demonstrate perceived [not measurable] enhancement).

  • May have minimal smooth thickening of the wall or septa.

  • May contain thick irregular or nodular calcification.

  • No enhancing soft tissue components.

  • Hyperattenuating renal masses that exhibit all the features of hyperattenuating cysts but are larger than 3 cm and are completely intrarenal are also included in this category.

  • Recommended follow-up is to perform a CT or MR examination at 6 months, followed by yearly studies for a minimum of 5 years.

• Category 3: complicated cystic lesions that exhibit some radiologic features seen in malignancy

  • This category includes multiloculated cystic nephroma, multiloculated cysts, complex septated cysts, chronically infected cysts, heavily calcified cysts, and cystic renal cell carcinoma (RCC).

  • Because these entities are difficult to separate radiologically, surgery is usually performed.

• Category 4 lesion: clearly malignant lesions with large cystic component.

  • Irregular margins, solid vascular elements

Imaging Features

• Septations

  • Thin septa within cysts are usually benign.

  • Thick or irregular septa require workup.

• Calcifications

  • Thin calcifications in cyst walls are usually benign.

  • Milk of calcium: collection of small calcific granules in cyst fluid: usually benign

• Thick wall

  • Usually require surgical exploration

• Increased CT density (>15 HU) of cyst content

  • Vast majority are benign.

  • High density is usually due to hemorrhage, high protein content, and/or calcium.

  • 50% appear as simple cysts using US.

The remainder of patients require a further imaging workup (to exclude soft tissue mass) or occasionally cyst puncture (analyze fluid, inject contrast).

Indications for Cyst Aspiration

• Diagnosis

  • Complex, high-density cyst (type 2) ≥3 cm

  • Evaluate fluid for character, as well as cytology

  • After aspiration, inject contrast (“cystogram”) and obtain multiple projections so that all surfaces of the wall are smooth.

• Therapy

  • Most commonly performed for large cyst obstructing collecting system or causing dull, aching pain or, rarely, HTN (Page kidney)

  • If the cyst is simple and the fluid is clear, yellow, and free-flowing, laboratory analysis is not necessary. Bloody or brownish fluid should be sent for cytology.

Cyst Ablation

If a symptomatic cyst recurs after aspiration, percutaneous ablation may be considered to avoid surgery.

• 1

  Place a 20-gauge needle into cyst and measure total volume aspirated. Some interventional radiologists prefer a small pigtail catheter.

• 2

  Inject contrast to exclude communication with the collecting system, which would preclude alcohol ablation.

• 3

  Inject absolute ethanol, 25% of the volume of cyst fluid aspirated.

• 4

  Leave ethanol in place 15–20 min, turning the patient to different positions to maximize wall contact of alcohol with different surfaces.

• 5

  Aspirate residual ethanol.

Milk of Calcium Cyst

• Not a true cyst but a calyceal diverticulum, which may be communicating or closed off

• Contains layering calcific granules (calcium carbonate)

• No pathologic consequence

Parapelvic Cyst

• Originates from renal parenchyma but expands into the renal sinus

• May cause compression of the collecting system

Peripelvic Cyst

• Originates from sinus structures, most likely lymphatic in origin

• May be indistinguishable from hydronephrosis on US, requiring an IVP or CT for definitive diagnosis

• Attenuated, stretched infundibula

• IVP differential diagnosis (DDx): renal sinus lipomatosis

Perinephric Cyst

• Located beneath the renal capsule

• Not true cysts; represent extravasated urine trapped beneath renal capsule (pseudocysts, uriniferous cysts, urinoma)

Types

• Familial nephronophthisis, 70%, autosomal recessive (AR)

  • Juvenile type, onset at age 3–5 years (most common); adult type

• Adult MCD, 15%, autosomal dominant (AD)

• Renal-retinal dysplasia, 15%; recessive associated with retinitis pigmentosa

Imaging Features

• Small kidneys (as opposed to large kidneys in polycystic disease)

• Multiple small (<2 cm) cysts in medulla

• Cysts may be too small to resolve by imaging, but their multiplicity will result in increased medullary echogenicity and apparent widening of central sinus echoes.

• Cortex is thin and does not contain cysts.

• No calcifications

Associated Findings

• Hepatic cysts, 70%

• Intracranial berry aneurysm, 20%

• Cysts in pancreas and spleen, <5%

Imaging Features

• Kidneys are enlarged and contain innumerable cysts, creating a bosselated surface.

• Calcification of cyst walls is common.

• Pressure deformities of calyces and infundibula

• IVP: “Swiss-cheese” nephrogram

• Cysts have variable signal characteristics.

  • CT: hypodense, hyperdense (hemorrhage, protein, calcium)

  • T1-weighted (T1W): some cysts contain clear, watery fluid (hypointense); others contain blood and protein (hyperintense); layering in some cysts is caused by cellular debris.

• Hepatic cysts

Clinical Findings

• Hematuria, 50%

• Flank pain, 40%

• Palpable mass, 35%

• Weight loss, 25%

• Paraneoplastic syndrome: HTN (renin), erythrocytosis (erythropoietin), hypercalcemia (PTH), gynecomastia (gonadotropin), Cushing syndrome (ACTH)

Pathology

• Clear cell type (65% of RCC). Cell origin: proximal tubule. Cytogenetic abnormalities: chromosome 3p deletions, mutations of VHL gene (tumor suppressor gene)

• Papillary cell type (chromophil) (15%). Cell origin: proximal tubule. Cytogenetic abnormalities: trisomies of chromosomes 3q, 7, 12, 16, 17, 20; loss of Y chromosome

• Chromophobe cell type (10%). Cell origin: intercalated cell of cortical collecting duct. Cytogenetic abnormalities: monosomies of chromosomes 1, 2, 6, 10, 13, 17, and 21; –hypodiploidy

• Oncocytoma (5%). Cell origin: intercalated cell of cortical collecting duct. Cytogenetic abnormalities: loss of chromosomes 1 and Y

• Unclassified cell type (5% of RCC). Sarcomas, collecting duct tumors, others

Risk Factors

• Tobacco use

• Long-term phenacetin use

• VHL disease (bilateral tumors)

• Chronic dialysis (>3 years)

• Family history

Prognosis

• 5-year survival: stage I = 81%, stage II = 74%, stage III = 53%, stage IV = 8%

  • Tumors often have atypical behavior:

    • Late recurrence of metastases: 10% recur 10 years after nephrectomy.

    • Some patients survive for years with untreated tumor.

    • Spontaneous regression of tumor has been reported but is very rare.

Imaging Features

• Imaging findings

  • Mass lesion: renal contour abnormality, calyceal displacement

  • Large variability in signal characteristics on noncontrast CT and MRI depending on the degree of hemorrhage and necrosis

  • Contrast enhancement is usually heterogeneous; strong contrast enhancement (>15 HU)

  • Calcification, 10%

  • Cystic areas (2%–5% are predominantly cystic)

  • Filling defects (clots, tumor thrombus) in collecting system and renal veins.

  • US appearance

    • Hyperechoic: 70% of tumors >3 cm, 30% of tumors <3 cm

    • Hypoechoic

• Angiography

  • 95% of tumors are hypervascular.

    • Caliber irregularities of tumor vessels are typical (encasement).

    • Prominent AV shunting, venous lakes

  • Angiography may be useful for detection in complicated and equivocal cases:

    • Small tumors

    • Underlying abnormal renal parenchyma

    • VHL disease

  • Preoperative embolization

• MRI

  • Venous invasion of tumor is better diagnosed by MRI.

  • Using a 0.1-mmol/kg dose of gadolinium (Gd)-chelate, the percentage of enhancement suggestive of RCC is 15%, obtained after 2–4 min of contrast administration (1.5T).

  • DDx for enhancing renal lesions: RCC, oncocytoma, and AML. The likelihood of RCC increases with size and extension beyond kidney into Gerota fascia.

Staging

• Stage I: tumor confined to kidney

• Stage II: extrarenal (may involve adrenal gland) but confined to Gerota fascia

• Stage III: A: venous invasion (renal vein); B: lymph node metastases; C: both

• Stage IV: A: direct extension into adjacent organs through Gerota fascia; B: metastases

  • Lungs, 55%

  • Liver, 25%

  • Bone, 20% (classic lesions are lytic, expansile)

  • Adrenal, 20%

  • Contralateral kidney, 10%

  • Other organs, <5%

Therapy

• Radical nephrectomy (entire contents of Gerota fascia are removed)

• Ablation (radiofrequency, microwave, cryo)

• Partial nephrectomy

• Chemotherapy

• Radiotherapy is used for palliation only.

Indications

• Comorbidities and contraindications to conventional or laparoscopic surgery

• Refusal of conventional surgery

• Compromised renal function; patients who have undergone a nephrectomy

• High risk of recurrence (e.g., VHL disease)

Technical Factors

• Tumors >3 cm can be difficult to treat with current ablation technology. Larger tumors often require multiple overlapping ablations, which increase the risk of complications.

• Tumors >5 cm have a higher incidence of recurrence.

• Complete ablation of central tumors is difficult owing to heat sink effect of large vessels within the renal hilum. Also, ablating central tumors poses the risk of injury to the collecting system or ureter.

• Anterior location of tumors can lead to colonic injury. This can be avoided with hydrodissection.

• Tumors are ablated under general anesthesia or deep conscious sedation.

• CT is the preferred modality for renal tumor ablation because of high spatial resolution and its ability to image structures that need to be avoided. US can also be used for superficial and peripheral exophytic lesions.

Complications

• Pain may last for several days to weeks.

• Postablation syndrome: fever, malaise, and body aches. Severity is related to volume of tissue ablated.

• Hemorrhage, often self-limited

• Injury to ureter, central collecting system, or adjacent organs

Established

• Renal mass presenting in a patient with other primary malignancy to rule out metastasis

• Rule out focal pyelonephritis

• Comorbid disease increases risk for surgery (e.g., solitary kidney)

• Unresectable mass, confirmation of diagnosis before systemic therapy

Emerging

• Confirmation of diagnosis before percutaneous ablation

• Hyperdense homogeneously enhancing mass, which may be a lipid-poor AML

• Bosniak category 3 lesion

• Multiple solid masses

Imaging Features

• Multiple lymphomatous masses (hypoechoic, hypodense), 50%

• Diffuse involvement of one or both kidneys

• Adenopathy

Associations

• Tuberous sclerosis: 80% of patients with tuberous sclerosis have AML, typically multiple, bilateral lesions. However, <40% of patients with AML have tuberous sclerosis. In the absence of tuberous sclerosis, 5% of all AML patients will have multiple, bilateral AML.

• Lymphangiomyomatosis

Imaging Features

• Fat appears hypodense (CT), hyperechoic (US), and hyperintense (T1W). The presence of fat in a renal lesion is virtually diagnostic of AML. There have been only a few case reports of fat in RCC or in oncocytomas. Five percent do not demonstrate fat on CT. Caveat: be certain that fat associated with a large mass is not trapped in renal sinus or peripheral fat.

• Predominance of blood vessels

  • Strong contrast enhancement

  • T2W hyperintensity

• Predominance of muscle: signal intensity (SI) similar to that of RCC

• AMLs do not contain calcifications; if a lesion does contain calcification, consider other diagnosis, such as RCC.

• Angiography: tortuous, irregular, aneurysmally dilated vessels are seen in 3%. Presence depends on the amount of angiomatous tissue. Predominantly myxomatous AMLs may be hypovascular.

Imaging Features

• Central stellate scar (CT) and spoke wheel appearance (angiography) are typical but not specific (also seen in adenocarcinoma).

• Well-defined, sharp borders

• Radiographically impossible to differentiate from RCC

Inverted Papilloma

• No malignant potential

• 20% are associated with uroepithelial malignancies elsewhere, most commonly in bladder.

Transitional Cell Carcinoma (TCC)

• Tumors are often multifocal: 40%–80% of patients have bladder TCC. However, only 3% of patients with bladder TCC later develop upper tract TCC.

• Radiographic finding: irregular filling defect

• Obliteration of renal sinus fat and infiltration of renal parenchyma (faceless kidney)

• 60% recurrence on ipsilateral side

• 50% have lung metastases.

• Staging

  • Stage I: mucosal lamina propria involved

  • Stage II: into, but not beyond, muscular layer

  • Stage III: invasion of adjacent fat/renal parenchyma

  • Stage IV: metastases

Squamous Cell Carcinoma (SCC)

• Represent 5% of renal pelvis tumors and <1% of all renal tumors

• Frequently associated with leukoplakia or chronic irritation (nephrolithiasis, schistosomiasis)

Collecting Duct Carcinoma

• Uncommon yet distinct epithelial neoplasm of the kidney.

• Aggressive malignancy derived from the renal medulla, possibly from the distal collecting ducts of Bellini.

• Propensity for showing infiltrative growth, which differs from the typical expansible pattern of growth exhibited by most renal malignancies.

Imaging Features

• By US, cortical RCC may be hypoechoic to normal renal parenchyma, isoechoic to renal parenchyma, hyperechoic to renal parenchyma, but hypoechoic to renal sinus fat, or isoechoic to renal sinus fat.

• By CT, the lesions are medullary in location and have an infiltrative appearance. The reniform contour of the kidney is maintained.

• By renal angiography, the tumors are usually hypovascular.

• By MR imaging, the tumors are hypointense on T2W images.

Risk Factors

• Urinary obstruction (e.g., benign prostatic hyperplasia, calculi)

• Vesicoureteral reflux

• Pregnancy (dilatation of ureters)

• Diabetes mellitus

• Immune deficiency

• Instrumentation

Complications

• Abscess formation

• Xanthogranulomatous pyelonephritis (XGP)

• Emphysematous pyelonephritis

• Scarring and renal failure

Common Underlying Conditions

• Diabetes mellitus (DM)

• Immunosuppression

• Obstruction

Types

• Focal type (lobar nephronia)

• Diffuse type: more severe and extensive

Imaging Features

Imaging studies (IVP, CT, US) are normal in 75%. In the remaining 25%, there are nonspecific findings:

• Renal enlargement (edema)

• Loss of the corticomedullary differentiation (edema)

• IVP findings:

  • Delay of contrast excretion

  • Narrowing of collecting system (edema)

  • Striated nephrogram

  • Ridging of uroepithelium

• Areas of decreased perfusion by contrast-enhanced CT

• Focal areas of hypodensity in lobar nephronia

• Complications: abscess, scarring

Imaging Features

• US

  • Best study to differentiate pyonephrosis from uninfected hydronephrosis

  • Echoes within collecting system

  • Urine/debris levels

  • Dense shadowing because of gas in collecting system

  • Poor through-transmission

• CT

  • Best study to show cause and level of obstruction, as well as complications

  • Dilated collecting system

  • Allows detection of perinephric or renal abscess

• Interventional procedures

  • Aspiration for culture and sensitivity (definitive diagnostic study)

  • Penicillin

  • Formal antegrade pyelography should be deferred to a second visit so as not to cause sepsis.

Imaging Features ( Fig. 4.6 )

• Well-delineated focal renal lesion

• Central necrosis (no enhancement with IV contrast)

• Thickened, hyperemic abscess wall with contrast enhancement

• Perinephric inflammatory involvement:

  • Thickening of Gerota fascia

  • Stranding of perirenal fat mass

Complications

• Retroperitoneal spread of abscess

• Renocolic fistula

Imaging Features

• Gas in collecting system and/or renal parenchyma

• Gas may extend to Gerota fascia (high mortality)

Treatment

• Nephrectomy

• In poor surgical candidates or in patients with focal disease, percutaneous drainage has been used as a temporizing or, occasionally, definitive therapy.

Imaging Features

• Large or staghorn calculus (thought to cause obstruction and inflammatory response), 75%; in the remaining 25% of patients, XGP is due to UPJ obstruction or ureteral tumors.

• Enlarged, nonexcreting kidney

• Multiple nonenhancing low-attenuation masses (–10 to 30 HU): xanthomatous masses. The masses may extend beyond the kidney into the perinephric space. There may be a thin peripheral ring of enhancement.

• Fine calcifications may be present in xanthomatous masses.

• Thickened Gerota fascia

• May be associated with psoas abscess

Replacement Lipomatosis

Also known as replacement fibrolipomatosis, replacement represents extreme form of renal sinus lipomatosis in which infection, long-term hydronephrosis, and calculi are associated with severe renal parenchymal atrophy. Calculi and inflammation are present in >70% of cases.

Imaging Features

• Enlarged renal outline, fatty lucent mass, and staghorn calculus

• IVP shows poorly functioning or nonfunctioning kidney.

• On US, kidney is enlarged but has a preserved shape. Residual hypoechoic renal parenchymal rim is surrounded by hyperechoic areas of fatty proliferation in both renal hilum and perinephric space.

• CT is the imaging modality of choice to best demonstrate fatty characteristics.

DDxs for this condition include XGP (on IVP only), fat-containing tumors such as AMLs, lipoma, and liposarcoma. CT can aid in differentiating XGP because CT shows attenuation values of –5 to +15 HU in XGP, in contrast to replacement lipomatosis where the fatty tissues measure –100 HU. Fat-containing tumors usually produce a mass effect and show renal function, unlike replacement lipomatosis.

Tuberculosis

The genitourinary (GU) tract is the second most common site of tuberculous involvement after the lung. GU disease is typically due to hematogenous spread. Clinical findings include history of pulmonary TB, pyuria, hematuria, and dysuria.

Sites of Involvement

• Renal

• Ureteral

• Bladder

• Seminal vesicles (SVs), epididymis

Imaging Features of Renal TB ( Fig. 4.7 )

• Distribution

  • Unilateral involvement is more common (70%) than bilateral (30%).

• Size

  • Early, kidneys are enlarged

  • Later, kidneys are small

  • Autonephrectomy (nonfunctioning kidney)

• Parenchyma

  • Parenchymal calcifications, 70%

  • Calcification may take on multiple forms: curvilinear, mottled, or amorphous; “putty kidney” results when calcification has homogeneous, ground-glass appearance.

  • Papillary necrosis; papillae may be irregular, necrotic, or sloughed

  • Tuberculoma

  • Parenchymal scarring, 20%

• Collecting system

  • Mucosal irregularity

  • Infundibular stenosis, hiked-up pelvis with narrowed pelvis pointing up

  • Amputated calyx

  • Corkscrew ureter: multiple infundibular and ureteral stenoses (hallmark finding)

  • “Purse-string” stenosis of renal pelvis

  • “Pipestem ureter” refers to a narrow, rigid, aperistaltic segment

  • Renal calculi, 10%

Imaging Features

• Multiple medullary and cortical abscesses

• Papillary necrosis because of diffuse fungal infiltration

• Fungus balls in collecting system (mycetoma) cause filling defects on IVP; nonshadowing echogenic foci on US

• Hydronephrosis secondary to mycetoma

• Scalloping of ureters (submucosal edema)

Imaging Features

• Increased cortical US echogenicity, 70%; (tubulointerstitial abnormalities)

• Renal enlargement without hydronephrosis, 40%

• Focal hypoechoic (US)/low-attenuation (CT) lesions (infection, tumor), 30%

Other Renal Abnormalities

• Acute tubular necrosis (ATN)

• Interstitial nephritis

• Focal nephrocalcinosis

• Infection: Cytomegalovirus (CMV), aspergillus, toxoplasmosis, Pneumocystis jiroveci Frenkel 1999, histoplasmosis, Mycobacterium avium-intracellulare (MAI)

• Tumors: increased incidence of RCC, lymphoma, Kaposi sarcoma (KS)

Prostate Abnormalities

• Prostatitis: bacterial, fungal, viral

• Prostate abscess

Testicular Abnormalities

• Testicular atrophy: common

• Infection: bacterial, fungal, viral

• Tumors: germ cell tumors, lymphoma

Imaging Features

• Calculus (determine size, number, location)

  • Radiopaque calculus, 90%

  • Radiolucent calculi are best detected by CT

  • Renal calculi can be detected by US: hyperechoic focus (calculus), posterior shadowing; calculi 3 mm or less may not be detected.

    CALCULUS VERSUS PHLEBOLITH

    	Calculus	Phlebolith
    Shape	Any shape	Round, smooth
    	90% homogeneously opaque	Central lucency
    Location	Along projected tract of ureter	In true pelvis (below distal ureter)

• IVP

  • Delayed and persistent nephrogram because of ureteral obstruction

  • Column of opacified urine extends in ureter from renal pelvis to lodged calculus (diminished or absent peristalsis).

  • Ureter distal to calculus is narrowed (edema, inflammation); may create false impression of stricture.

  • Ureter proximal to calculus is minimally dilated and straightened: columnization; degree of dilatation has no relation to stone size.

  • “Steinstrasse:” several calculi are bunched up along the ureter (common after lithotripsy).

  • Halo appearance (edema) around distal ureter may resemble appearance of ureterocele (pseudoureterocele) or bladder carcinoma. Thickness of radiolucent halo of pseudoureterocele is typically >2 mm as opposed to ureterocele.

• CT

  • CT detects most calculi regardless of calcium content. The exceptions are matrix stones.

  • Dedicated CT protocol for stone search is performed; rarely need to follow with contrast-enhanced CT (CECT) to differentiate stone in ureter from phlebolith. CECT may obscure a calcified ureteral calculus because it may blend in with high-density contrast material.

  • Dual energy CT: Acquisition of CT data from two different energy spectra. Most urinary calculi, regardless of composition, appear as opaque densities by conventional CT. In dual energy CT, the differences in x-ray attenuation properties at high and low kVp allow more accurate renal stone differentiation between uric acid- and calcium-containing stones. Stones that appear more dense on water decomposition images than iodine decomposition images have a significant uric acid component.

• Location: three narrow sites in the ureter at which calculi often lodge

  • UPJ: junction of renal pelvis and ureter proper

  • At crossing of ureter with iliac vessels

  • UVJ: insertion of ureters into bladder

Complications

• Forniceal rupture (pyelosinus backflow); inconsequential in isolation if urine is uninfected; chronic leak may result in periureteral/retroperitoneal fibrosis.

• Chronic calculous pyelonephritis

• XGP in the presence of staghorn calculus

• Squamous metaplasia (leukoplakia); more common in pyelocalyceal system and upper ureter than lower ureter or bladder. Cholesteatoma may result from desquamation of keratinized epithelium.

Treatment Options

• Small renal calculi (<2.5 cm): extracorporeal lithotripsy

• Large renal calculi (>2.5 cm): percutaneous removal

• Upper ureteral calculi: extracorporeal lithotripsy

• Lower ureteral calculi: ureteroscopy

Extracorporeal Shock Wave Lithotripsy (ESWL)

• Best results with calcium oxalate and uric acid stones and calculi <2.5 cm. Larger calculi are better treated by percutaneous removal.

• Contraindications for ESWL include:

  • Patient not eligible for anesthesia

  • Severe bleeding

  • Pregnancy

  • UTI

  • Nonfunctioning kidneys

  • Gross obesity

  • Small children

  • Tall patients (>200 cm)

  • Distal obstruction

  • Calyceal neck stenosis

  • UPJ obstruction

  • Prostatic enlargement

  • Renal artery aneurysm

• Complications of ESWL

  • Intrarenal; subscapular and perinephric hematoma

  • Decrease in effective renal plasma flow

Indications for Percutaneous Nephrostomy

• Large stones requiring initial debulking (e.g., staghorn calculus)

• Calculi not responding to ESWL (e.g., cysteine stones)

• Body habitus precludes ESWL

• Patients with certain types of pacemakers

• Renal artery aneurysms

• Calculi >5 cm

Causes

• Chronic glomerulonephritis

• Cortical necrosis (because of ischemia)

  • Pregnancy

  • Shock

  • Infection

  • Toxins: methoxyflurane, ethylene glycol

• AIDS-related nephropathy

  • Glomerular sclerosis

  • Punctate calcifications MAI

• Uncommon causes

  • Rejected renal transplants

  • Chronic hypercalcemia

  • Oxalosis

  • Alport syndrome

Imaging Features

• Peripheral calcifications (medullary pyramids are spared)

• Tramline calcifications are classic: interface of necrotic cortex and viable subcapsular cortex

• Columns of Bertin may be calcified.

• US: hyperechoic cortex

Causes

• HPT (hypercalciuria, hypercalcemia), 40%

• Renal tubular acidosis (RTA), 20%

• Medullary sponge kidney, 20%

• Papillary necrosis

• Lasix in infancy

• Other causes

  • Nephrotoxic drugs (amphotericin B)

  • Chronic pyelonephritis

  • Oxalosis may produce both medullary and cortical nephrocalcinosis.

Imaging Features

• Bilateral, stippled calcification of medullary pyramids

• Calcifications may extend peripherally.

• US: hyperechoic medulla

Imaging Features

• Cystic lesion connects through channel with collecting system.

• If the neck is not obstructed, diverticula opacify retrograde from the collecting system on delayed CT.

• May contain calculi or milk of calcium, 50%

• Fragmented calculi after ESWL may fail to pass because of a narrow neck. Percutaneous stone retrieval may be indicated.

• Cortical divot may overlie diverticulum.

Causes

• Ischemic necrosis

  • DM

  • Chronic obstruction, calculus

  • Sickle cell disease

  • Analgesics

• Necrosis caused by infections

  • TB

  • Fungal

Imaging Features ( Fig. 4.10 )

• Papillae

  • Enlargement (early)

  • Small collection of contrast medium extends outside the interpapillary line in partial necrosis.

  • Contrast may extend into central portion of papilla in “medullary type” RPN.

  • Eventually contrast curves around papilla from both fornices, resulting in “lobster-claw” deformity.

  • Sequestered, sloughed papillae cause filling defects in collecting system: “ring sign.”

  • Tissue necrosis leads to blunted or clubbed calyces.

Multiple papillae affected in 85%. Rim like calcification of necrotic papilla occurs.

Associations (Rare)

• Hemihypertrophy

• Associated with Beckwith-Wiedemann syndrome

• Congenital pyloric stenosis

• Ehlers-Danlos syndrome

• Other renal abnormalities: cortical renal cysts, horseshoe kidney, renal ectopia, autosomal-dominant polycystic kidney disease (ADPKD), RTA

Imaging Features

• Striated nephrogram (contrast in dilated collecting ducts), “brush like” appearance

• Cystic tubular dilatation usually 1–3 mm; occasionally larger, usually too small for CT resolution

• Punctate calcifications in medullary distribution (located in dilated tubules), 50%

• Differentiate on IVP from “papillary blush,” a normal variant, representing amorphous enhancement without tubular dilation, streaks, or globules; nephrocalcinosis; or pyramidal enlargement. Papillary blush is also an inconstant finding on successive IVPs.

Causes

• Calculi

• Tumor

• Previous surgery (ligation, edema, clot)

Imaging Features

• IVP

  • Kidney

    • Delayed nephrogram (peak enhancement at >30 min after IV injection, slow fading)

    • Delayed renal (peak) density may be higher than in normal kidney.

    • Faint radial striations of nephrogram

    • Negative pyelogram: nephrogram with delayed pyelogram resulting in dilated unopacified calyces outlined by opacified parenchyma

    • Dunbar crescents (caliceal crescents): thin rings or crescents at interface with calyx and parenchyma resulting from contrast in dilated collecting ducts; disappear when collecting system is completely opacified

    • Atrophy of renal parenchyma in chronic obstruction: “rim nephrogram” or “shell nephrogram”

  • Collecting system

    • Blunting of forniceal angles

    • Dilatation of ureter and pelvis; decreased or absent peristalsis

    • Backflow

• US

  • Sensitivity for detection of chronic obstruction: 90%

  • Sensitivity for detection of acute obstruction: 60%

  • Common causes of false-positive examinations:

    • Extrarenal pelvis

    • Peripelvic cyst

    • Vessels: differentiate with color Doppler

    • Vesicoureteral reflux, full bladder

    • High urine flow (overhydration, furosemide)

    • Corrected long-standing obstruction with residual dilatation

    • Prune-belly syndrome

  • Common causes of false-negative examinations:

    • US performed early in disease before dilatation has occurred

    • Distal obstruction

Types ( Fig. 4.13 )

• Pyelosinus backflow (forniceal rupture): extravasation along infundibula, renal pelvis, ureter

• Pyelotubular backflow (no rupture): backflow into terminal collecting ducts; thin streaks with fanlike radiation from the papillae

• Pyelointerstitial backflow: extravasation into parenchyma and subcapsular structures; more amorphous than pyelotubular backflow

• Pyelolymphatic backflow: dilated lymphatic vessels (may occasionally rupture): thin irregular bands extending from hilum or calyces

• Pyelovenous backflow: contrast in interlobar or arcuate veins; rarely seen because venous flow clears contrast material rapidly: renal vein extends superiorly from renal hilum.

Mechanism

• Blunt trauma, 70%–80%

• Penetrating trauma, 20%–30%

Classification

• Minor injuries (conservative treatment), 85%

  • Hematomas

  • Contusion (any injury that results in hematuria)

  • Small lacerations

  • Subsegmental renal infarcts

• Moderate injuries, 10% (management controversial; 15%–50% will eventually require surgery)

  • Urine leak

  • Laceration communicating with collecting system

• Major injuries (surgical treatment), 15%

  • Multiple renal lacerations (rupture)

  • Pedicle injury avulsion, thrombosis

Imaging Features

The optimum type of imaging study depends on stability of patient and symptoms (hematuria, blood at meatus, multiple bony fractures):

• CT is the study of choice.

• One-shot IVP: visualization of both kidneys excludes pedicle avulsion

• Indications for angiography:

  • Nonvisualization of kidney on IVP in patient with abdominal trauma

  • Persistent hematuria in a patient with abdominal trauma

  • Hypotension or hypertension or persistent hematuria after an interventional urologic procedure

Imaging Features

• Renal vein

  • Absence of flow (US, CT, MRI)

  • Intraluminal thrombus

  • Renal vein dilatation proximal to occlusion

  • Renal venography: amputation of renal vein

  • Magnetic resonance venography (MRV) or conventional venography: studies of choice

• Kidneys

  • Renal enlargement

  • US: hypoechoic cortex (early edema); hyperechoic cortex after 10 days (fibrosis, cellular infiltrates) with preserved corticomedullary differentiationm (CMD); late phase (several weeks): decreased size, hyperechoic kidney with loss of CMD

  • IVP: little opacification, prolonged nephrogram, striated nephrogram (stasis in collecting tubules); intrarenal collecting system is stretched and compressed by edema

  • CT may show low-attenuation thrombus in renal vein or simple renal enlargement with collaterals; prolongation of CMD

  • Loss of CMD

  • Scintigraphy ( ^99m Tc DTPA): absent or delayed renal perfusion and excretion, alternatively may be delayed and reveal a large kidney

• Chronic thrombosis

  • Small kidneys

  • Collateral veins may cause pelvic and ureteral notches by extrinsic compression.

Causes

• Trauma to renal vessels

• Embolism

  • Cardiac causes (e.g., atrial fibrillation, endocarditis)

  • Catheter

• Thrombosis

  • Arterial

  • Venous

Imaging Features

• Smooth large kidneys

• Normal renal perfusion (MAG ₃ angiography)

• Diminished or absent opacification after IV contrast administration

• Persistent dense nephrogram at late time points, 75%

• Variable US features:

  • Increased cortical echogenicity with normal corticomedullary junction

  • Increased echogenicity of pyramids

Pearls

• ATN is the only renal process with normal renal flow but reduced excretion.

• Hyperacute rejection has decreased flow but excretion on delayed images (opposite to ATN).

• Cyclosporine toxicity has similar pattern as ATN but occurs later in the posttransplant period.

• ATN rarely occurs beyond 1 month after transplant.

• Cyclosporine toxicity is uncommon within first month after transplant.

• MAG ₃ results in better quality images in transplant patients with renal insufficiency compared with DTPA.

Causes

• Lymphocele: in 10%–20% of transplants at 1–4 months posttransplant. Usually inferomedial to kidney; linear septations are detectable in 80%. Most lymphoceles are inconsequential; if large and symptomatic or obstructing, percutaneous sclerosis with tetracycline or povidone-iodine may be tried.

• Abscess: develops within weeks; complex fluid collection; fever

• Urinoma: develops during first month; near UVJ; may be “cold” on nuclear medicine study if leak is not active at time of examination; may be associated with hydronephrosis

• Hematoma: immediate postoperative period; hyperechoic by US; pain, hematocrit drop

Clinical Findings

• UTI

• Obstruction

• Incontinence

Associations

• 80% have complete ureteral duplication.

• 30% have a ureterocele (“cobra head” appearance on IVP).

Insertion Sites

• Males: ureter inserts ectopically into the bladder > prostatic urethra > SVs, vas deferens, ejaculatory ducts

• Females: ectopic ureter commonly empties into postsphincteric urethra, vagina, tubes, perineum

Types

• Benign tumors

  • Epithelial: inverted papilloma, polyp, adenoma

  • Mesodermal: fibroma, hemangioma, myoma, lymphangioma

  • Fibroepithelial polyp: mobile long intraluminal mass, ureteral intussusception

• Malignant tumors

  • Epithelial: TCC, SCC, adenocarcinoma

  • Mesodermal: sarcoma, angiosarcoma, carcinosarcoma

Prognosis

• 50% of patients will develop bladder cancer.

• 75% of tumors are unilateral.

• 5% of patients with bladder cancer will develop ureteral cancer.

Imaging Features

• Intraluminal filling defect

• Goblet sign: retrograde pyelogram demonstrates dilated ureteral segment distal to obstruction with filling defect and meniscus.

• Bergman coiled catheter sign: on retrograde pyelogram, the catheter is typically coiled in dilated portion of ureter just distal to the lesion.

• Sites of metastatic spread of primary ureteral neoplasm (at autopsy):

  • Retroperitoneal lymph nodes, 75%

  • Liver, 60%

  • Lung, 60%

  • Bone, 40%

  • Gastrointestinal tract, 20%

  • Peritoneum, 20%

  • Other (<15%): adrenal glands, ovary, uterus

Ileal Loop ( Fig. 4.18 )

Ureter(s) drain into isolated ileal segment, which serves as an isoperistaltic conduit (not as a reservoir). May or may not have a surgical “intussusception” of conduit. Fifty percent of patients have hydronephrosis immediately postoperatively; the hydronephrosis should resolve by 3 months. Common locations of strictures are at the ureteroileal anastomosis and where the left ureter enters the peritoneum.

Colon Conduit

Ureter(s) drain into isolated colon segment. Ureters are tunneled submucosally for antireflux.

Ureterosigmoidostomy

Distal ureter(s) drain into sigmoid colon; ureters are tunneled for antiperistalsis. Procedure is largely surpassed by ileal conduit nowadays because of complications (e.g., pyelonephritis, reflux, hyperchloremic acidosis, high risk of colon cancer).