Computed tomographic distinction of perirenal liposarcoma from exophytic angiomyolipoma: a feature analysis study

Abstract

Purpose: To identify computed tomographic (CT) findings that distinguish perirenal liposarcomas from exophytic angiomyolipomas.

Materials and methods: We identified CT scans of 20 patients (13 women and 7 men; mean age, 63 years) with either perirenal liposarcoma (n = 11) proven at histopathology or large exophytic angiomyolipomas (n = 9) determined by 2-year stability (n = 6) or histopathology (n = 3). Two independent readers unaware of the final diagnoses recorded the presence of the following CT findings: (1) tumoral vessel extending into the renal cortex, (2) tumoral vessel extending into the renal hilum, (3) renal parenchymal defect at the site of tumor contact, (4) intratumoral hemorrhage, (5) nonfat attenuating intratumoral nodules, and (6) calcification.

Results: A tumoral vessel extending into the renal cortex was seen only in angiomyolipomas (7 and 6 of 9 patients versus 0 and 0 of 11 liposarcomas for readers 1 and 2, respectively; P < 0.005 for both). A parenchymal defect was more commonly seen in angiomyolipomas (7 and 6 of 9 angiomyolipomas versus 1 and 1 of 11 liposarcomas for readers 1 and 2, respectively; P < 0.05 for both). Calcifications were seen by both readers in 6 of 11 liposarcomas but not in any angiomyolipomas (P < 0.05). The other recorded findings were not useful in distinguishing CT features (P > 0.1 for both readers).

Conclusions: In the evaluation of a fatty perinephric mass at CT, the presence of a tumoral vessel extending into the renal cortex or a renal parenchymal defect at the site of tumor contact strongly favors the diagnosis of exophytic angiomyolipoma, whereas calcifications suggest liposarcoma.

FIGURE 1

A 54-year-old woman with angiomyolipoma misdiagnosed at biopsy immunohistochemistry as liposarcoma. Subsequent resection showed the mass was an angiomyolipoma. A, Oral and intravenous contrast-enhanced CT scan shows a fatty mass (arrowhead) arising from the kidney (small arrow) and a tumoral vessel (large arrow) extending from the mass through the renal parenchyma (images B and C) into the renal sinus.

FIGURE 2

Diagram of tumoral vessel insertions. A renal parenchymal vascular pedicle was considered to be present when a visible tumoral vessel extended from the perirenal fatty mass (M) into (A) or through (B) the renal parenchyma (K). In contrast, a renal hilar vascular pedicle (C) was considered to be present when a visible tumoral vessel extended from the perirenal fatty mass into a renal hilar vessel without traversing the renal parenchyma.

FIGURE 3

A 72-year-old man with angiomyolipoma. Computed tomographic scan with intravenous contrast shows a fat-attenuation mass (arrowhead) with a parenchymal vascular pedicle (large arrow), which is a visible intratumoral vessel extending into the renal parenchyma (small arrow).

FIGURE 4

A 65-year-old man with liposarcoma. A, Intravenous contrast-enhanced CT image above the level of the kidney shows a fat-attenuation mass (arrowhead) with a tumoral vessel (arrow) that extends caudally (B and C) into the renal hilum rather than into the renal parenchyma. This finding was termed a hilar pedicle.

FIGURE 5

A 72-year-old man with a retroperitoneal liposarcoma. A, Intravenous contrast-enhanced CT shows a large fat-attenuation mass (arrowheads) associated with a renal parenchymal defect (arrow). B, More inferiorly, this mass (arrowheads) engulfs the kidney and is associated with another renal parenchymal defect (arrow) which could possibly be an incidental renal cyst enveloped by the liposarcoma but which was not described on the pathology report.

FIGURE 6

An 82-year-old woman with a large perirenal retroperitoneal liposarcoma with a prominent intratumoral vein. This vein drained directly into the renal hilum (not shown).