Presentation
Patient with no significant past medical history and status post spontaneous vaginal delivery 4 weeks ago presents to OB-GYN clinic with persistent fevers. She had been seen recently at an urgency clinic and treated for mastitis. On physical exam, there appeared to be a mass in the left abdomen, which was presumably related to constipation. CT was performed for further evaluation.
Patient Data
Scout radiograph demonstrates suggestion of a mass in the left abdomen as evidenced by relative paucity of bowel gas in this region and displacement of bowel gas into the right abdomen.
CECT images demonstrate a large 20 cm heterogenous and hypervascular mass arising from the inferior pole of the left kidney. The mass contains large regions of fat attenuation, as well as internal vascularity and central regions of hyperattenuating tissue (>70 HU) suggestive of hemorrhage. Trace fluid was also noted surrounding the mass. There is mild left pelvicaliectasis as well as enlargement of the left renal vein, likely related to mass effect and shunting, respectively.
MRI images demonstrate a large hypervascular mass in the left abdomen which arises from the anterior inferior pole of the left kidney. The mass demonstrates multifocal regions of macroscopic and microscopic fat with central regions of increase T1 signal suggestive of internal hemorrhage. Post-contrast arterial phase images demonstrate that the mass is largely supplied by a single left main renal artery. Additionally, the mass appears to be drained by venous collaterals, which are incompletely included in the field of view.
(Three hepatic lesions were also noted, two of which demonstrate classic features of FNH. A third arterially enhancing lesion in the hepatic segment VII was indeterminate, though based on continued imaging FU, was presumed to represent atypical FNH).
DSA images showed single bilateral main renal arteries. Selective injection of the left renal artery demonstrated two large ectatic renal arteries supplying the vascular tumor, with possible small aneurysms.
Case Discussion
Patient underwent left renal angiogram with embolization, followed by left nephrectomy with pathology results proving the mass to represent a giant angiomyolipoma.
Key points:
most common benign tumor of the kidney
95% contain macroscopic fat, virtually diagnostic for AML (if calcifications are present, it could be an RCC)
associated with tuberous sclerosis, where they can be bilateral
if greater than 4 cm, portray a higher risk of bleeding and intervention may be necessary
5% are lipid poor (no macroscopic fat)
don't confuse microscopic with macroscopic fat. Drop of signal on out-of-phase imaging suggests intracellular or microscopic fat, a feature that can be seen not uncommonly with clear cell carcinoma
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