Renal angiomyolipomas: Typical and atypical features on computed tomography and magnetic resonance imaging

Figure 1 Schematic representation of angiomyolipomas.

Figure 2 Classic angiomyolipoma containing macroscopic fat on computed tomography. A: Well-circumscribed, hypodense lesion in the right kidney containing macroscopic fat (yellow arrow) on non-enhanced computed tomography (CT); B and C: A heterogeneously enhanced lesion (red arrows) with central blood vessels on contrast-enhanced CT.

Figure 3 Exophytic angiomyolipoma on computed tomography. A and B: Non-enhanced computed tomography (CT) (A) and contrast-enhanced CT (B) in one patient; C and D: Contrast-enhanced CT in another patient, both with an exophytic mass in the right kidney with macroscopic fat and some vessels (blue arrows).

Figure 4 Exophytic angiomyolipomas on magnetic resonance imaging. Abdominal magnetic resonance imaging image showing a single lesion localized in the lower third of the left kidney (yellow arrows), with macroscopic fat. Presents heterogeneous signal intensity in T2WI, chemical shift artifacts in the T1 out phase and heterogeneous enhancement in T1WI with fat saturation and intravenous contrast (T1 C+ FS).

Figure 5 Hyperattenuating angiomyolipoma. A 9-year-old girl with a left renal mass suggesting Wilms’ tumor, and biopsy demonstrated angiomyolipoma. A: Axial, sagittal and coronal planes of a contrast-enhanced computed tomography image with a hyperattenuating renal mass without a recognizable fat component (white arrows); B: Macroscopic appearance of the tumor; C: Positive Human Melanoma Black 45 (HMB-45) staining in the cytoplasm of perivascular cells of large vessels was also observed (black arrows). The anti-HMB-45 antibody is a monoclonal antibody that reacts with an antigen present in melanocytic tumors and is nonreactive to most nonmelanoma human malignancies, with some notable exceptions, among which are perivascular epithelioid cell tumors; D: Hematoxylin-eosin staining showing mostly spindle-shaped perivascular cells (orange arrows).

Figure 6 Isoattenuating fat-poor angiomyolipoma. A: Non-enhanced computed tomography (CT) - no macroscopic fat is shown, and the lesion is isoattenuating to the renal parenchyma (yellow arrow). Contrast-enhanced CT: The renal mass shows some enhancement (white arrow); B: Magnetic resonance imaging - exophytic lesion without macroscopic fat (red arrow) and low signal intensity on T2WI.

Figure 7 Angiomyolipoma with epithelial cysts. T2WI hypointense exophytic lesion (red arrows) containing an epithelial cyst (yellow arrowhead) is shown. The lesion shows no significant signal drop on the fat-saturated T2 sequence (white arrow) and is homogeneously enhanced with contrast medium (blue arrow).

Figure 8 Epithelioid angiomyolipoma. A: Contrast-enhanced computed tomography image showing an aggressive epithelioid angiomyolipoma with a carcinoma-like growth pattern invading the right renal vein (red arrows); B: Macroscopic appearance of the tumor; C and D: Epithelioid smooth muscle cells around blood vessels shown by hematoxylin and eosin staining (C) and focal nuclear atypia CK-7 (+) by immunohistochemistry (D).

Figure 9 Angiomyolipoma associated with lymphangioleiomyomatosis and tuberous sclerosis. A and B: Giant angiomyolipoma with macroscopic fat in the left kidney; C: It is associated with a pulmonary cyst as an expression of lymphangioleiomyomatosis in a patient with tuberous sclerosis.

Figure 10  Angiomyolipoma complicated with hemorrhage. A: Contrast-enhanced computed tomography image showing a perirenal hematoma caused by bleeding from an angiomyolipoma; B: Percutaneous treatment with embolization using a Lipiodol-ethanol mixture.

Figure 11  Angiomyolipoma complicated with vein invasion. A: Aggressive angiomyolipoma invading the left renal vein on non-enhanced computed tomography (CT) and contrast-enhanced CT (red arrows); B: Histopathological correlation.