Renal cysts are classified by malignant risk using the Bosniak classification system.
[7] The presence of measurable contrast enhancement of the lesion is the most important characteristic in distinguishing between high-risk cysts (classifications III and IV) from the typically benign, low-risk Bosniak I, II, and IIF cysts.
These alternatives are broadly to ignore the cyst, schedule follow-up or perform a surgical excision of it.
When a cyst shows discrepancy in severity across categories, it is the most worrisome feature that is used in deciding about management.
Peripelvic cysts are contained entirely within the renal sinus, possibly related to dilated lymphatic channels.
Simple renal cyst
A Bosniak category IIF cyst. This one is 3 cm wide, with calcifications within its wall, seen as very radiodense (white in this presentation) areas in its margins. There is also a septation which is calcified. Yet, the cyst does not show enhancement (uptake of contrast).
Histopathology of the lining of a simple cyst of the kidney, incidentally found on autopsy, with inconspicuous nuclei. They usually have a single layer of cuboidal, flattened or atrophic epithelium,
[
13
]
but this case has a somewhat thicker fibrous layer. H&E stain.
Non-contrast CT (at left) showing peripelvic fluid accumulations, which may be
hydronephrosis
.
CT urography
(at right) reveals non-dilated
calyces
and
pelvises
. The fluid accumulations are thus peripelvic cysts.
