Diagnostic Ultrasound - Abdomen and Pelvis
Complex Renal Cyst TERMINOLOGY Definitions • Benign, fluid-filled nonneoplastic renal lesion not meeting criteria of simple renal cyst ○ Bosniak classes II, IIF, and III IMAGING General Features • Best diagnostic clue ○ Well-defined fluid-filled renal lesion with internal features: Calcifications, septations, turbid content; wall thickening, absent or equivocal enhancement • Size ○ Usually 2-5 cm in diameter (up to 10 cm) • Morphology ○ Depends on histology Ultrasonographic Findings • Grayscale ultrasound ○ Round, oval, or irregular-shaped anechoic lesion ○ Hemorrhagic cyst: Appearance varies with age of blood – Acute: Hyperechoic, hypoechoic, or isoechoic, containing fluid-debris level or solid avascular clot, later septated lesion – Chronic: Thick calcified wall ± multiloculated ○ Proteinaceous cyst: May contain low-level echoes, with bright reflectors or even layers of echoes ○ Infected cyst: Thick wall with scattered internal echoes ± debris-fluid level ○ Calcified cyst: Wall or septal calcification ± shadowing – Milk of calcium cyst: "Comet tail" artifact + line of calcium intracystic debris – Wall nodularity may be obscured by wall or diffuse calcification of cystic mass ○ Neoplastic features: Solid mural or septal nodules, irregular wall, or irregular septal thickening • Color Doppler ○ Lack of intracystic color signal ○ Low sensitivity for detecting vascularity • Contrast-enhanced US (CEUS) ○ Provides information analogous to Bosniak classification ○ Increased sensitivity for detecting color flow (and malignancy) compared with unenhanced US and CECT ○ Contrast uptake within cystic lesion is suspicious for malignancy (other than a few bubbles in thin smooth septa or wall) CT Findings • Denser than simple fluid on NECT (> 20 HU) • Lack of enhancement on CECT: Change of < 10 HU from pre- to postcontrast images • Hemorrhagic cyst ○ NECT: Hyperdense; CECT: Hypodense relative to enhancing parenchyma ○ Homogeneous density 60-90 HU (acute) ○ Heterogeneous (clot or debris), ↑ wall thickness and ↓ attenuation ± calcification (chronic) • Infected cyst: Thick wall, septated, heterogeneous fluid, debris- or gas-fluid level; ± calcification (chronic) • Ruptured cyst: Retroperitoneal or perinephric fluid collection, blood (varied density) • Septations: 1 or more thin partial or complete septa • Milk of calcium cyst: Dependent, fluid-calcium layer • Neoplastic wall: Focal thickening or enhancing nodule MR Findings • Contrast-enhanced MR is useful to detect intracystic enhancement • MR superior to CECT for detection of internal septa within cyst • Hemorrhagic cyst:Variable signal intensity dependent on age of hemorrhage ○ T1WI: Highest intensity in subacute (< 72 hr) ○ T2WI: Hyperintense but less than simple cyst; fluid-debris level; ± heterogeneous mass and lobulation of contour • Proteinaceous cyst: ↑ protein simulates hemorrhage: T1 hyperintense • Infected cyst: T1WI: ↑ intensity, less homogeneous than simple cyst; ↓ intensity than subacute hemorrhage (similar to chronic); ± thickened wall • Calcified cyst: MR is insensitive to detect calcification but is superior to CT to detect enhancement within calcified cyst • Neoplastic wall: Focal thickening or enhancing nodule mass or wall thickening Imaging Recommendations • Best imaging tool ○ US, as initial investigation for characterizing simple or minimally complex renal cysts + monitoring of complex renal cysts (Bosniak class IIF) ○ CEUS or MR best to evaluate for internal cyst enhancement, further characterize Bosniak II and III lesions • Protocol advice ○ Complex cysts should be evaluated with CEUS, CECT, or CEMR for decision of surgical intervention ○ CT evaluation must include NECT and CECT on same scanner, same time, same technique DIFFERENTIAL DIAGNOSIS Renal Cell Carcinoma (RCC) • Cystic RCC: Thick septa, septal or peripheral calcification, enhancing wall, or septal nodularity • Papillary RCCs are homogeneous with minimal enhancement, can mimic complex cysts on CT/MR Localized Cystic Disease • Conglomerate of simple cysts simulating a multilocular cystic mass, usually unilateral • Lacks well-defined pseudocapsule around aggregate of cysts • Renal parenchyma is present between cysts • Can simulate multilocular cystic nephroma, cystic neoplasm, or autosomal dominant polycystic kidney disease Multilocular Cystic Nephroma • Multilocular cystic lesion with thick and thin septa • Propensity to herniate into renal pelvis Renal Abscess • May extend into calyces and perinephric space Diagnoses: Urinary Tract 467
Complex Renal Cyst Diagnoses: Urinary Tract Bosniak Classification of Renal Cysts (CT-Based) Class Definition Imaging Features Bosniak I Benign simple cyst Homogeneous, water density (< 20 HU), thin walls, no septations or calcifications, no enhancement Bosniak II MInimally complex benign cyst Hyperdense, thin septa, minimal thin septal or wall calcifications, no enhancement Bosniak IIF Bosniak III Bosniak IV Indeterminate complex cyst, requires follow-up Indeterminate complex cystic mass, surgery, or ablation recommended Malignant cystic lesion, surgery required Hyperdense, minimally thickened walls or septations, thickened calcifications, no enhancement or is questionable Smooth walls or septations with measurable enhancement Clearly malignant lesions with enhancing solid components • Appears as thick-walled, complex cystic mass with internal debris and septations • Clinical features point to diagnosis Renal Metastasis • Common in patients with advanced malignancy • Primary sites include lung, breast, melanoma, stomach, cervix, colon, pancreas, prostate, and contralateral kidney • May appear as isoechoic, hypoechoic, or hyperechoic masses Renal Lymphoma • Secondary renal lymphoma more common than primary • Diffuse renal enlargement, bilateral multiple hypoechoic renal masses, direct infiltration from retroperitoneum and perirenal space • Perinephric extension with vascular and ureteral encasement is common PATHOLOGY General Features • Hemorrhagic cyst (6%): Unknown, trauma, bleeding diathesis or varicosities in simple cyst • Calcified cyst (1-3%): Hemorrhage, infection, or ischemia • Infected cyst: Hematogenous spread, vesicoureteric reflux, surgery, or cyst puncture Gross Pathologic & Surgical Features • Hemorrhagic cyst: Rust-colored putty-like material surrounded by thick fibrosis and plates of calcification • Infected cyst: Markedly thickened wall ± calcification; varying pus, fluid, and calcified or noncalcified debris • Neoplastic wall: Discrete nodule at base of cyst Microscopic Features • Hemorrhagic cyst: Uni- or multilocular, thickened wall • Neoplastic wall: Well-differentiated clear/granular cell • Septated cyst: Compressed normal parenchyma or nonneoplastic connective tissue CLINICAL ISSUES Presentation • Most common signs/symptoms ○ Asymptomatic or palpable mass and flank pain ○ Infected cyst: Pain in flank, malaise, and fever ○ Hemorrhagic cyst: Abrupt and severe pain ○ Ruptured cyst: Severe abdominal pain, hematuria Demographics • Age ○ Present in 20-30% of middle-aged adults – > 50% of patients > 50 years of age – Rare in patients < 30 years of age • Gender ○ M > F Natural History & Prognosis • Complications: Hydronephrosis, hemorrhage, infection, cyst rupture, or carcinoma • Follow-up: Increase in size, change in configuration, and internal consistency suggest carcinoma • Prognosis: Very good Treatment • Bosniak class II: No treatment unless symptomatic • Bosniak class IIF: Follow-up by imaging • Bosniak class III and IV: Surgical excision (partial or radical nephrectomy) or ablation DIAGNOSTIC CHECKLIST Consider • CEUS when CECT or CEMR not feasible Image Interpretation Pearls • Correct imaging classification of cystic masses is key to management SELECTED REFERENCES 1. Nicolau C et al: Prospective evaluation of CT indeterminate renal masses using US and contrast-enhanced ultrasound. Abdom Imaging. 40(3):542-51, 2015 2. Wood CG 3rd et al: CT and MR imaging for evaluation of cystic renal lesions and diseases. Radiographics. 35(1):125-41, 2015 3. Barr RG et al: Evaluation of indeterminate renal masses with contrastenhanced US: a diagnostic performance study. Radiology. 271(1):133-42, 2014 4. Quaia E et al: Comparison of contrast-enhanced sonography with unenhanced sonography and contrast-enhanced CT in the diagnosis of malignancy in complex cystic renal masses. AJR Am J Roentgenol. 191(4):1239-49, 2008 468
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Complex Renal Cyst<br />
TERMINOLOGY<br />
Definitions<br />
• Benign, fluid-filled nonneoplastic renal lesion not meeting<br />
criteria of simple renal cyst<br />
○ Bosniak classes II, IIF, <strong>and</strong> III<br />
IMAGING<br />
General Features<br />
• Best diagnostic clue<br />
○ Well-defined fluid-filled renal lesion with internal<br />
features: Calcifications, septations, turbid content; wall<br />
thickening, absent or equivocal enhancement<br />
• Size<br />
○ Usually 2-5 cm in diameter (up to 10 cm)<br />
• Morphology<br />
○ Depends on histology<br />
Ultrasonographic Findings<br />
• Grayscale ultrasound<br />
○ Round, oval, or irregular-shaped anechoic lesion<br />
○ Hemorrhagic cyst: Appearance varies with age of blood<br />
– Acute: Hyperechoic, hypoechoic, or isoechoic,<br />
containing fluid-debris level or solid avascular clot,<br />
later septated lesion<br />
– Chronic: Thick calcified wall ± multiloculated<br />
○ Proteinaceous cyst: May contain low-level echoes, with<br />
bright reflectors or even layers of echoes<br />
○ Infected cyst: Thick wall with scattered internal echoes ±<br />
debris-fluid level<br />
○ Calcified cyst: Wall or septal calcification ± shadowing<br />
– Milk of calcium cyst: "Comet tail" artifact + line of<br />
calcium intracystic debris<br />
– Wall nodularity may be obscured by wall or diffuse<br />
calcification of cystic mass<br />
○ Neoplastic features: Solid mural or septal nodules,<br />
irregular wall, or irregular septal thickening<br />
• Color Doppler<br />
○ Lack of intracystic color signal<br />
○ Low sensitivity for detecting vascularity<br />
• Contrast-enhanced US (CEUS)<br />
○ Provides information analogous to Bosniak classification<br />
○ Increased sensitivity for detecting color flow (<strong>and</strong><br />
malignancy) compared with unenhanced US <strong>and</strong> CECT<br />
○ Contrast uptake within cystic lesion is suspicious for<br />
malignancy (other than a few bubbles in thin smooth<br />
septa or wall)<br />
CT Findings<br />
• Denser than simple fluid on NECT (> 20 HU)<br />
• Lack of enhancement on CECT: Change of < 10 HU from<br />
pre- to postcontrast images<br />
• Hemorrhagic cyst<br />
○ NECT: Hyperdense; CECT: Hypodense relative to<br />
enhancing parenchyma<br />
○ Homogeneous density 60-90 HU (acute)<br />
○ Heterogeneous (clot or debris), ↑ wall thickness <strong>and</strong> ↓<br />
attenuation ± calcification (chronic)<br />
• Infected cyst: Thick wall, septated, heterogeneous fluid,<br />
debris- or gas-fluid level; ± calcification (chronic)<br />
• Ruptured cyst: Retroperitoneal or perinephric fluid<br />
collection, blood (varied density)<br />
• Septations: 1 or more thin partial or complete septa<br />
• Milk of calcium cyst: Dependent, fluid-calcium layer<br />
• Neoplastic wall: Focal thickening or enhancing nodule<br />
MR Findings<br />
• Contrast-enhanced MR is useful to detect intracystic<br />
enhancement<br />
• MR superior to CECT for detection of internal septa within<br />
cyst<br />
• Hemorrhagic cyst:Variable signal intensity dependent on<br />
age of hemorrhage<br />
○ T1WI: Highest intensity in subacute (< 72 hr)<br />
○ T2WI: Hyperintense but less than simple cyst; fluid-debris<br />
level; ± heterogeneous mass <strong>and</strong> lobulation of contour<br />
• Proteinaceous cyst: ↑ protein simulates hemorrhage: T1<br />
hyperintense<br />
• Infected cyst: T1WI: ↑ intensity, less homogeneous than<br />
simple cyst; ↓ intensity than subacute hemorrhage (similar<br />
to chronic); ± thickened wall<br />
• Calcified cyst: MR is insensitive to detect calcification but is<br />
superior to CT to detect enhancement within calcified cyst<br />
• Neoplastic wall: Focal thickening or enhancing nodule mass<br />
or wall thickening<br />
Imaging Recommendations<br />
• Best imaging tool<br />
○ US, as initial investigation for characterizing simple or<br />
minimally complex renal cysts + monitoring of complex<br />
renal cysts (Bosniak class IIF)<br />
○ CEUS or MR best to evaluate for internal cyst<br />
enhancement, further characterize Bosniak II <strong>and</strong> III<br />
lesions<br />
• Protocol advice<br />
○ Complex cysts should be evaluated with CEUS, CECT, or<br />
CEMR for decision of surgical intervention<br />
○ CT evaluation must include NECT <strong>and</strong> CECT on same<br />
scanner, same time, same technique<br />
DIFFERENTIAL DIAGNOSIS<br />
Renal Cell Carcinoma (RCC)<br />
• Cystic RCC: Thick septa, septal or peripheral calcification,<br />
enhancing wall, or septal nodularity<br />
• Papillary RCCs are homogeneous with minimal<br />
enhancement, can mimic complex cysts on CT/MR<br />
Localized Cystic Disease<br />
• Conglomerate of simple cysts simulating a multilocular<br />
cystic mass, usually unilateral<br />
• Lacks well-defined pseudocapsule around aggregate of<br />
cysts<br />
• Renal parenchyma is present between cysts<br />
• Can simulate multilocular cystic nephroma, cystic neoplasm,<br />
or autosomal dominant polycystic kidney disease<br />
Multilocular Cystic Nephroma<br />
• Multilocular cystic lesion with thick <strong>and</strong> thin septa<br />
• Propensity to herniate into renal pelvis<br />
Renal Abscess<br />
• May extend into calyces <strong>and</strong> perinephric space<br />
Diagnoses: Urinary Tract<br />
467
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