Imaging and Histopathologic Features of Incidentally Detected Hepatic Perivascular Epithelioid Cell Tumors: A Case Report

Abstract

Hepatic perivascular epithelioid cell tumor (PEComa) are rare mesenchymal neoplasms. The limited number of reported cases, along with nonspecific clinical symptoms and laboratory findings, often complicates accurate preoperative diagnosis. Here, we present a case of hepatic PEComa incidentally detected in a 64-year-old woman without underlying liver disease. We describe the clinical presentation, laboratory findings, CT and MRI features, and histopathological characteristics confirmed after surgical resection that may facilitate the diagnosis of hepatic PEComa.

INTRODUCTION

In 2020, the World Health Organization (WHO) defined perivascular epithelioid cell tumors (PEComas) as mesenchymal neoplasms composed of perivascular epithelioid cells (PECs), distinctive epithelioid cells often located adjacent to blood vessel walls, and expressing both melanocytic and smooth muscle markers (1). PEComas most commonly arise in the uterus but have also been reported in various other organs, including the kidneys, bladder, prostate, lungs, pancreas, and liver (2).

Hepatic PEComas are rare, and as their clinical manifestations are nonspecific, they are often discovered incidentally (3,4). In addition, liver function tests, including aspartate aminotransferase (AST) and alanine aminotransferase (ALT), as well as tumor markers such as alpha-fetoprotein (AFP), carcinoembryonic antigen, and CA 19-9, are often within normal limits, making the clinical diagnosis of PEComa particularly challenging (3,4). Here, we report a case of hepatic PEComa incidentally discovered in a 64-year-old woman without any underlying liver disease. We describe the CT and MRI findings, along with the histopathological features confirmed following surgical resection.

CASE REPORT

A 64-year-old woman with no significant medical history underwent a routine upper gastrointestinal endoscopy that revealed extrinsic compression of the stomach. The patient reported no associated symptoms, including abdominal pain or weight loss. Laboratory test results were within normal limits, including AST (17 IU/L), ALT (14 IU/L), and total bilirubin (0.49 mg/dL). Moreover, tumor marker levels were within normal ranges: AFP, 2.25 ng/mL (reference range <10 ng/mL); and protein induced by vitamin K absence-II (PIVKA-II), 20.9 mAU/mL (reference range <40 mAU/mL).

A four-phase contrast-enhanced abdominal CT scan was performed. Pre-contrast CT revealed a slightly hypodense, round mass with a well-defined border, measuring approximately 7.1 × 6.0 × 5.1 cm, located in segment 3 of the liver. The mass demonstrated marked rim enhancement during the arterial phase, whereas the internal portion of the mass exhibited relatively weaker enhancement compared with the surrounding liver parenchyma. As imaging progressed into the portal and delayed phases, the internal portion of the mass became progressively hypoattenuated, demonstrating a washout pattern (Fig. 1A). Despite its large size, the mass had well-defined margins relative to the surrounding normal liver parenchyma. No evidence of bile duct or portal vein invasion, dilatation, or thrombosis was observed. In addition, no evidence of distant metastasis to other abdominal organs, lymph node adenopathy, or ascites was noted.

Fig. 1. Contrast-enhanced CT, MRI, and pathological features of hepatic perivascular epithelioid cell tumors in a 64-year-old female.

A. On contrast-enhanced CT, a slightly hypodense mass in segment 3 of the liver displays a peripheral enhancement during the arterial phase, becoming progressively hypoattenuating compared to the surrounding liver parenchyma in the portal and delayed phases.

B. On MRI, the mass demonstrates low signal intensity on T1WIs and high signal intensity on T2WI, without signal drop on opposed-phase imaging. The mass exhibits definite diffusion restriction on DWI and the corresponding ADC map.

C. The mass demonstrates significant arterial phase enhancement followed by washout in the portal and delayed phases, similar to the findings on CT.

D. Grossly, the tumor is well-circumscribed and solid, with colors ranging from yellow to gray to brown. The tumor cells are large, epithelioid, and spindle-shaped with granular, eosinophilic cytoplasm. A significant infiltration of inflammatory cells is observed, including lymphocytes and plasma cells (hematoxylin and eosin stain, ×200). The tumor cells are positive for smooth muscle actin (immunostain, ×200) and for human melanoma black 45 (immunostain, ×200).

A = arterial phase, ADC = apparent diffusion coefficient, DWI = diffusion-weighted imaging, HBP = hepatobiliary phase, P = portal phase, T = transitional phase, T1WI = T1-weighted image, T2WI = T2-weighted image, V = venous (delayed) phase

Further evaluation with MRI demonstrated that the lesion exhibited mildly low signal intensity on T1-weighted images, without signal loss on opposed-phase imaging, suggesting the absence of intralesional fat. On T2-weighted images, the lesion demonstrated a high signal intensity. Diffusion-weighted imaging (b-values of 0 and 800 s/mm²) revealed a definite diffusion restriction (Fig. 1B). In contrast to CT findings, the lesion demonstrated significant and heterogeneous enhancement compared with the surrounding liver parenchyma during the arterial phase, followed by pronounced washout in the portal and transitional phases. The lesion appeared as a definite hypointense defect in the hepatobiliary phase on gadoxetic acid-enhanced MRI (Fig. 1C).

Although the lesion demonstrated marked arterial enhancement and washout on MRI, along with diffusion restriction—features initially suggestive of hepatocellular carcinoma (HCC)—the absence of underlying liver disease, normal liver function tests, and tumor markers, and the lack of portal vein invasion or thrombosis, despite the relatively large tumor size, made HCC less likely.

The patient underwent a laparoscopic lateral sectionectomy. Histopathological examination of the resected specimen confirmed the diagnosis of PEComa of the inflammatory subtype.

On histopathological examination, the tumor was >5 cm in the greatest dimension, with high nuclear grade and increased cellularity, features proposed as high-risk criteria associated with aggressive behavior in PEComas (Fig. 1D) (5).

Follow-up CT and MRI at 10 months postoperatively revealed no evidence of local recurrence or distant metastasis. The patient remained asymptomatic and continued to undergo regular surveillance.

This study was approved by our Institutional Review Board (IRB No. 2025-08-012). The need for informed consent was waived due to the retrospective nature of the study.

DISCUSSION

PEComas are rare mesenchymal neoplasms comprising distinctive PECs (1). These tumors typically exhibit a characteristic perivascular growth pattern, with tumor cells radially arranged around the blood vessels, often replacing the vessel wall and extending toward the endothelium (1). Furthermore, PEComas are immunohistochemically characterized by the co-expression of melanocytic markers, most notably human melanoma black-45 (the most sensitive marker), Melan-A, microphthalmia-associated transcription factor, as well as smooth muscle markers, such as smooth muscle actin, desmin, and caldesmon (1). PEComas exhibit a wide anatomical distribution, occurring predominantly in the uterus, while hepatic PEComas are particularly rare (6).

PEComas are classified into angiomyolipomas (AMLs) and non–AML tumors. Unlike AMLs, which exhibit a triphasic morphology with adipose tissue, non-AML PEComas lack intra-tumoral fat and are predominantly composed of epithelioid or spindle cells with perivascular accentuation. In the present case, the absence of intralesional fat on imaging and adipocytic components on histopathological examination supported the diagnosis of non-AML PEComa. Furthermore, a prominent infiltration of chronic inflammatory cells was observed, consistent with the inflammatory subtype of PEComa (5).

Although definitive criteria for malignancy in hepatic PEComa have not been established, several histopathological features have been proposed as indicators of malignant potential, including tumor size greater than 5 cm, high nuclear grade and cellularity, increased mitotic activity, necrosis, and an infiltrative growth pattern. Tumors with two or more of these features have been associated with a higher likelihood of malignant behavior. In our case, the tumor measured greater than 5 cm and demonstrated high nuclear grade with increased cellularity, thereby fulfilling the proposed criteria indicative of malignant potential (5). Nevertheless, follow-up imaging performed 10 months after the surgical resection revealed no evidence of local recurrence or distant metastasis.

PEComas are characterized by profuse arterial vascularization, both within the tumor and along its periphery (4). Consequently, imaging studies employing intravenous contrast agents are particularly valuable for the evaluation of these lesions. The main imaging features included marked enhancement during the arterial phase, followed by contrast washout during the portal venous and delayed phases. These findings reflect the tumor’s rich vascular supply, primarily derived from branches of the hepatic artery (4).

According to a 2012 study by Tan & Xiao (7) which included seven histopathologically confirmed cases of hepatic PEComa, the tumors demonstrated a female predominance (6:1). Symptoms are mostly nonspecific and may include nausea, indigestion, intermittent colicky pain, and loss of appetite; in some cases, patients remain entirely asymptomatic. On diagnostic imaging, these tumors are most often detected incidentally as well-demarcated solitary hepatic masses. Tumor size varied, and most lesions demonstrated strong arterial enhancement, followed by hypoattenuation in the portal and delayed phases. These features often result in misdiagnosis as hypervascular hepatic tumors, such as HCC or hepatic adenoma. Some cases without contrast “wash-out” have also been reported, overlapping with features of benign, well vascularized tumors such as focal nodular hyperplasias and hemangioma (7).

In 2015, Maebayashi et al. (8) conducted a literature review of 25 publications encompassing 33 cases of primary hepatic PEComas. Consistent with the findings of an earlier study by Tan & Xiao (7), a female predilection was observed, and most patients presented with nonspecific clinical symptoms, such as abdominal pain or discomfort, or were asymptomatic. On diagnostic imaging, most cases demonstrate an enhancement pattern similar to that of HCC or at least some degree of enhancement, even when not typical of HCC (8). These findings suggest that hepatic PEComas display imaging features that may facilitate radiological diagnosis.

In our case, the hepatic PEComa arose in the lateral section of the liver and appeared as a well-demarcated, slightly hypodense mass on CT, with no evidence of portal vein or bile duct invasion, despite its relatively large size. The lesion demonstrated arterial-phase rim enhancement and washout during the portal and delayed phases. On MRI, the lesion exhibited more conspicuous intra-tumoral arterial enhancement than that observed on CT, followed by washout during the portal and transitional phases. The discrepancy in arterial phase enhancement between CT and MRI in our case was likely attributable to differences in arterial phase timing. At our institution, arterial phase images for gadoxetic acid–enhanced MRI are acquired approximately 30 seconds after contrast injection, whereas arterial phase CT images are obtained at approximately 40 seconds. This difference in acquisition timing may have led to an underestimation of early arterial enhancement on CT compared with MRI. Curved or dilated feeding arteries at the tumor periphery, previously described as characteristic imaging features of hepatic PEComas, were carefully evaluated but were not observed on dynamic CT or MRI in our case. These imaging findings can be easily confused with HCC. However, the absence of underlying liver disease and normal laboratory findings were inconsistent with the diagnosis of HCC. In several other case reports beyond the aforementioned studies (9,10), hepatic PEComas often exhibited imaging features similar to those of HCC. However, patients commonly had no history of hepatitis B or C infection, and laboratory findings, including tumor markers, were within normal limits.

In conclusion, hepatic PEComa is a rare mesenchymal neoplasm that displays imaging features mimicking those of other hypervascular hepatic tumors, particularly HCC. Accurate preoperative diagnosis is often challenging due to the nonspecific clinical and laboratory findings. When imaging findings are suggestive of HCC in the absence of underlying liver disease and with normal tumor marker levels, hepatic PEComa should be considered in the differential diagnosis. Histopathological confirmation is essential for a definitive diagnosis.