Radiology Resident Case of the Week
Findings: Axial images through the abdomen were obtained following enteric and intravenous contrast. These show a heterogeneous mass in the right kidney. The mass demonstrates ill-defined regions of very low attenuation suggestive of fat.
Etiology/Pathophysiology
Pathology:
Angiomyolipoma, also called renal hamartomas or choristomas, contain
blood vessels, smooth muscle, and fatty tissues, although one or two of
these elements may predominate. It occurs as a solitary renal mass
usually in women older than 40. They also occur in more than 70% of
individuals with tuberous sclerosis, in whom they are frequently
multiple and bilateral. They're usually asymptomatic and are often
discovered incidentally during abdominal imaging. However, some
patients present with flank pain or hematuria due to intratumoral or
perinephric hemorrhage.
Miscellaneous
Imaging
Angiomyolipomas are seen on CT as well circumscribed renal masses. They
vary in size from tiny renal nodules to large tumors. The presence of
intratumoral fat is almost diagnostic of angiomyolipoma, although in
rare cases, fat has been described in Wilm's tumors. MRI may also
detect the presence of fat in renal angiomyolipomas. The fat has a
similar signal intensity to perinephric fat on spin echo and gradient
echo pulse sequences, and the fat signal is suppressed on images
obtained with fat-saturation techniques.
Angiomyolipomas are always benign in that no deaths from metastatic disease have been documented. However, the tumors may exhibit extrarenal extension. Coincident renal cell carcinoma and angiomyolipomas may occur in tuberous sclerosis. Surgery and biposy are rarely need in asymptomatic patients with typical imaging findings of angiomyolipoma. However, it may be needed in patients with extensive intratumoral or perinephric hemorrhage.
DDX
Key references
Haaga J.R., Computed Tomography and Magnetic Resonance Imaging of the
Whole Body. 3rd ed. Mosby. 1994.
ACR Code
Keywords:
kidney, renal, angiomyolipoma, CT, fat, choristoma,
hamartoma, tuberous sclerosis.