Metastatic PEComa arising from renal angiomyolipoma: MRI findings

Authors

  • Amr K. El Jack MD, PhD,

    Corresponding author
    1. Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, USA
    • Body MRI Division, Department of Radiology, Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104
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  • John E. Tomaszewski MD,

    1. Department of Pathology and Laboratory Medicine, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, USA
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  • Daniel G. Haller MD,

    1. Department of Medicine, Hematology Oncology Division, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, USA
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  • Evan S. Siegelman MD

    1. Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, USA
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  • © Crown copyright 2007. Reproduced with the permission of the Controller of Her Majesty's Stationary Office.

Abstract

The perivascular epithelioid cell tumor (PEComa) is a neoplasm composed primarily of HMB-45-positive epithelioid cells with a perivascular distribution. Both benign and malignant PEComas have been reported in diverse anatomic locations. We report the MRI features of a metastatic PEComa to the liver that originated within a renal angiomyolipoma (AML). J. Magn. Reson. Imaging 2007;26:159–161. Published 2007 Wiley-Liss, Inc.

PERIVASCULAR EPITHELIOID CELL TUMORS (PEComas) are mesenchymal neoplasms composed predominately of perivascular epithelioid cell (PECs), which have been also described as a component of several types of tumors (1). PEComas are rare, and have been reported in many different locations (1–6).

We describe the MR appearance of a malignant metastatic PEComa in the right hepatic lobe of a 38-year-old man who had a nephrectomy 10 months earlier for an aggressive angiomyolipoma (AML). Although there have been prior reports of PEComa originating from a renal AML (2, 4), the MRI findings of malignant PEComa in the liver have not yet been described.

CASE REPORT

A 38-year-old male had MRI performed to further evaluate “hepatic and renal fossa masses.” The patient had undergone right nephrectomy 10 months earlier for an “atypical AML.” Preoperative computed tomography (CT) examination performed at an outside institution showed a necrotic 13-cm mass in the right kidney and multiple left renal AMLs (Fig. 1). While the CT did not show intratumoral fat, scattered adipocytes were present in the specimen.

Figure 1.

A 38-year-old man with right renal mass. Axial CT image obtained at the midlevel of the kidneys during the nephrographic phase of contrast enhancement demonstrates a 13-cm mass arising from the right kidney. There is extensive central necrosis with a thick, irregular, and enhancing soft tissue rim. No fat is revealed within the mass. Three <10-mm left renal AMLs are present.

The postnephrectomy MRI (Fig. 2) confirmed multiple left renal AMLs and showed a new multilobulated solid enhancing exophytic mass in the posterior segment of the right hepatic lobe. The mass exhibited heterogeneous signal intensity and areas of central necrosis. There was no intracellular lipid or macroscopic fat. There was an additional 1-cm lesion of the right lobe that had similar imaging features (not shown).

Figure 2.

A 38-year-old male with metastatic PEComa. Coronal T2-weighted single-shot fast spin-echo (a: TR = 1363 msec, TE 87 = msec), axial T2-weighted respiratory-triggered fat-saturated fast spin-echo (b: TR = 9600 msec, TE = 102 msec), axial in-phase (c: TR = 175 msec, TE = 4.5 msec), opposed-phase (d: TR = 175 msec, TE = 2.1 msec), and enhanced fat-saturated gradient-echo T1-weighted (e: TR = 190 msec, TE = 1.4 msec) images depict a right hepatic mass with heterogeneous T1 and T2 signal intensity between that of spleen and liver. There is no loss of signal with chemical shift imaging. There is heterogeneous nodular and linear enhancement with central foci of necrosis.

The patient subsequently underwent right hepatectomy, cholecystectomy, and appendectomy. Gross inspection of the liver specimen revealed a multiloculated infiltrating mass. Sectioning revealed a solid red-yellow tumor with foci of central necrosis. Microscopic evaluation revealed the tumor to be composed of large epithelioid appearing cells with abundant pink cytoplasm. The cells were arranged in cords and nests, and formed nodules with extensive necrosis. There was extensive vascular invasion. The tumor abutted the liver capsule without evidence of extrahepatic extension. No adipose tissue or thick vessels were identified; however, immunohistochemical analysis revealed an identical immunological profile to that of the original renal tumor. These findings included positive staining for melanogenesis markers HMB45 and MelanA, and lack of staining for epithelial markers CAM 5.2 and AE1/3, a pattern previously reported for PEComa (6). While areas of necrosis and lymphovascular invasion were present in the renal mass, the pleomorphism seen in the liver tumor was not present. These pathologic features indicated that the liver mass was a site of metastatic PEComa from a primary renal lesion. Six months following right hepatectomy, the patient developed new metastases in the left hepatic lobe and lungs.

DISCUSSION

PECs have recently been described as a component of several tumors, including lymphangiomyoma, clear cell “sugar” tumor of the lung (CCST), and AML (1). PECs are characterized as melanocyte antigen-expressing epithelioid cells with clear to eosinophilic granular cytoplasm and a propensity for a perivascular distribution (7). The proportion of PECs within a given tumor can vary, and indeed there have been reports of epithelioid cell-predominant variants of renal AML (4, 7). It has been suggested that tumors composed predominately of PECs be referred to as PEComa (5). PEComas are rare, and have been described in both pediatric and adult populations (3). They vary from benign to frankly malignant in behavior and have been reported in various locations, including the heart, soft tissues, gastrointestinal tract, and genitourinary tract (1–6). Effective treatment of malignant PEComa is not yet known (3).

AML is a mesenchymal neoplasm that is composed of tortuous, thick-walled blood vessels, smooth muscle, and adipocytes, the proportions of which vary widely (7). AML is the most common mesenchymal tumor of the kidney, and is also the most common lesion related to the tuberous sclerosis complex (TSC). To the best of our knowledge, our patient did not have a diagnosis of tuberous sclerosis, although the presence of bilateral AMLs suggests that he probably carries some genetic mutation at the TSC gene loci.

The liver mass that we present in this report was composed of large epithelioid cells with abundant pink cytoplasm growing in cords and nests, and forming nodules with extensive areas of necrosis. Although this mass did not contain adipose tissue or thick vessels, the epithelioid cells demonstrated cytological similarity to cells found in focal areas of the original renal tumor. Furthermore, immunohistochemical analysis yielded results that strongly suggest that the liver mass represents a more aggressive recurrence of the epithelioid component of the original renal tumor. This scenario is identical to that reported previously by Martignoni et al (4), except that the recurrence occurred seven years after surgical resection of the primary tumor in their case, as opposed to 10 months in our patient.

Interestingly, the authors of a recent report (2) of a 60-year-old woman with a large renal AML who, six years after resection, developed multiple malignant AMLs in the lungs, lymph nodes, mediastinum, and spine, conclude that there is no clear evidence to support that the occurrence of multiple AMLs can represent metastatic disease. Instead, they refer to this as “multicentric AML” and attribute the multicentricity to the congenital presence of cell precursors in multiple sites. Although multicentric AML may indeed represent a real entity, particularly in patients with a genetic predisposition, the matching immunological profile for both renal and hepatic tumors in our patient, and the temporal sequence of increasing pleomorphism strongly suggest malignant recurrence of the original tumor.

On MRI, the hepatic PEComa presented in this report demonstrated a heterogeneous appearance with T2 components that were isointense to spleen. There was no macroscopic adipose tissue, and chemical shift imaging did not reveal small amounts of fat that may be present in atypical AMLs. These findings may vary depending on the variable composition of these tumors as discussed above. Postgadolinium imaging demonstrated irregular nodular and linear enhancing regions intermixed with extensive areas of minimal or no enhancement.

In conclusion, the imaging characteristics described in this report are not specific for PEComa, and would not necessarily enable differentiation from other types of metastases. However, in a patient with an AML demonstrating atypical growth and/or the presence of solid metastases, PEComa should be considered in the differential diagnosis.

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