Simple and Complex renal Cysts By: Nour-Eldin A Nour-Eldin

SIMPLE CYSTS Simple cysts (in > 50% of population > 50 years) probably arise from obstructed tubules or ducts. They do not, however, communicate with collecting system. Most commonly asymptomatic; rare: hematuria (from cyst rupture), HTN,cyst infection. Mass effect from large cysts may cause dull ache or discomfort.

Radiographic features , IVP: Lucent defect "Beak sign" can be seen with large cysts. Round indentations on collecting system Cortical bulge

Radiographic features , US: Anechoic Sharply marginated, smooth walls Enhanced through-transmission

Radiographic features , CT: No significant enhancement after IV contrast (<5HU) Smooth cyst wall Sharp demarcation Cyst wall too thin to be seen by CT Homogenous Water density (< 10-15 HU)

Be Careful: Cysts that contain calcium, septations, and irregular margins (complicated cysts) need further workup 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 and Angiography

Hydronephrosis:

Parapelvic Cyst Calyceal Diverticulum

Renal Artery Aneurysm

Complicated CYSTS Complicated cysts are cysts that do not meet the criteria of simple cysts and thus require further workup.

Bosniak Classification: Category (Bosniak) US Features Workup Type 1: Simple cyst Round, anechoic, thin wall enhanced through transmission None Type 2: Mildly complicated cyst Thin septation, calcium in wall CT or US follow-up Type 3: Indeterminate lesion Multiple septae, internal echos mural nodules Thick septae Partial nephrectomy, biopsy CT follow-up if surgery is high risk Type 4: Clearly malignant Solid mass component Nephrectomy

Radiographic Features of Complicated Cysts 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 Increased CT density (> 15 HU) of cyst content Vast majority of these lesions are benign. High density is usually due to hemorrhage, high protein content, and/or calcium. Thick wall These lesions usually require surgical exploration.

Simple renal cyst, Bosniak Category I.

Bosniak Category II cyst Curvilinear calcification within a thin septum

Bosniak Category II cyst Homogeneously hyperdense mass No increase in Density after IV contrast

Bosniak Category II cyst Cyst with several internal septations and a minimally thickened wall

Bosniak Category II cyst. Cyst with uniform, mild wall thickening and short, interrupted calcifications

Bosniak Category II hyperdense cyst.

Bosniak Category II cyst

Bosniak Category II cyst. Nearly completely calcified mass with no obvious enhancing elements

Bosniak Category II. subcentimeter rim calcified renal cyst

Bosniak Category III. cystic mass with irregular wall thickening and associated heterogeneous nonenhancing elements

Bosniak Category III complex cyst. multilocular, encapsulated mass

Bosniak Category III complex cyst. Thick-walled, encapsulated, multilocular cystic mass with enhancing septa

Bosniak Category IV cystic neoplasm.

Bosniak Category IV cystic neoplasm

A 42-year-old female with back pain, hematuria, and a renal mass discovered by lumbar spine MR. hyperdense (55 HU) 3 cm mass. enhance to 88 HU after IV contrast Renal cell carcinoma

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