A 15-year-old girl presented with a history of vague abdominal pain and loss of appetite. There was no significant past or family history of any diseases. On examination, the blood pressure was 140/60 mm Hg. Laboratory analysis revealed normal renal function tests. Urinary examination was normal. Blood investigations were unremarkable.
USG showed multiloculated, almost symmetrical, bilateral perirenal collections [Figure and ] with septae and internal echoes. The collections were also seen to insinuate into the renal sinuses. Both kidneys were normal in size and the corticomedullary differentiation was maintained.
Figure 1 (A,B)
Longitudinal (A) and transverse (B) USG images show perirenal collections (arrows) with septae
CT scan of the abdomen showed bilateral hypodense collections  with densities varying between 5 and 15 HU in the perirenal and peripelvic regions. Normal enhancement of the cortex  and normal corticomedullary differentiation were seen. The collections were seen indenting the cortices of both kidneys. The inferior venacava was displaced anteromedially.
Non-enhanced, axial CT scan shows symmetric, hypodense perirenal collections (arrows) with an average Hounsfield value of 8
Figure 3 (A,B)
Contrast-enhanced CT scans in the corticomedullary (A) and excretory (B) phases show normal cortical enhancement with nonenhancing perirenal collections. The excretory images show splaying of the non-dilated excreting collecting system (arrowhead)
Delayed scans obtained after 15 min  showed normal excretion, but splayed pelvi-calyceal systems  due to the intervening fluid within the sinuses. No invasion of the pelvi-calyceal systems was noted and no extravasation of contrast into the perirenal collections was seen.
CT urogram. A maximum intensity projection, coronal CT scan image shows splayed and non-dilated excreting collecting systems
These findings were considered suggestive of of perirenal lymphangiomatosis.
USG-guided aspiration of the perirenal fluid was performed as part of the treatment. The fluid was sent for biochemical analysis and it revealed a few lymphocytes with abundant proteins and renins specific to the kidneys. No organisms were isolated from the aspirated fluid.