Diagnostic Ultrasound - Abdomen and Pelvis

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
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