Computed tomography imaging features of hepatic perivascular epithelioid cell tumor: A case report and literature review.

RATIONALE: Perivascular epithelioid cell tumor (PEComa) is a rare tumor which is most frequently found in uterus. The tumor arising from liver is extremely uncommon. PATIENT CONCERNS: A 36-year-old female with abdominal distention, cramps, and low-grade fever for over 15 days. The patient had a history of gastric adenocarcinoma with ovarian, celiac lymph nodes, and retroperitoneal lymph nodes metastases. DIAGNOSES: Computed tomography (CT) imaging demonstrated an ill-defined heterogeneous hypo-dense mass in segment 8 (S8) of the liver. Contrast-enhanced CT imaging showed marked enhancement in arterial phase, mild-to-moderate enhancement in portal and equilibrium phases. Tumor-feeding artery was demonstrated from the right hepatic artery by the three-dimensional reconstruction images. Biopsy was performed, and a diagnosis of PEComa was rendered.
INTERVENTIONS: No intervention for this tumor before liver biopsy. LESSONS: We present a rare case of hepatic PEComa. The information we provided is useful for summarizing the CT features of this kind of tumors. It should be included in differential diagnoses from common hypervascular neoplasms of liver. The final diagnosis is established on histopathological and immunohistochemical studies that are the "gold standard."

Introduction

Perivascular epithelioid cell tumor (PEComa) is a rare tumor, comprising a group of mesenchymal neoplasms, including angiomyolipomas, lymphangioleiomyomatosis, clear cell “sugar” tumors, clear cell myomelanocytic tumors, sarcoma of perivascular cells, and pigmented melanotic tumors.[ In our case report, we follow the criterion proposed by Martignoni et al[ that hepatic PEComa is a true neoplasm without adipocytes and abnormal vessels. Computed tomography (CT) imaging typically demonstrates a heterogeneous hypo-dense mass with either well or ill-defined margin.[ Contrast-enhanced CT in almost all hepatic PEComas shows marked enhancement in arterial phase, while mild-to-moderate enhancement in equilibrium phase.[ The final diagnosis of PEComa is established on its histopathological characteristics, including epithelioid cells without adipocytes or abnormal blood vessels, and on immunohistochemical evidence, including positive human melanoma black 45(HMB-45), melanocytic, and smooth muscle markers.[

Case report

A 36-year-old female was admitted to the First Affiliated Hospital of Dalian Medical University with abdominal distention, cramps, and low-grade fever for over 15 days. She had previously experienced gastric adenocarcinoma with ovarian, celiac lymph nodes, and retroperitoneal lymph nodes metastases. Laboratory investigation revealed alpha-feto-protein (AFP) level of 10.44 IU/mL (normal ranges of AFP 0–5.8 IU/mL) and carbohydrate antigen125 (CA-125) of 202.90 U/mL (normal ranges of CA-125 0–35 U/mL).

The patient subsequently had a noncontrast CT scan of abdomen and demonstrated a 3.7 cm × 2.4 cm ill-defined hypodense lesion with an average CT value of 55 HU in S8 of the liver (Fig. 1). On the dynamic contrast-enhanced CT images, the CT values of this lesion were 118 HU, 110 HU, and 88 HU in arterial, portal, and equilibrium phases. It showed marked heterogeneous enhancement in arterial phase, with a tortuous vessel arising from right hepatic artery feeding the tumor (Fig. 2). The images in the portal phase showed slightly washout of partial areas inside the tumor. In the equilibrium phase, the contrast agent was persistent washout. Based on clinical history and CT features, a probability of liver metastasis was rendered.

Figure 1

CT image of hepatic PEComa. A, Noncontrast CT image reveales a slightly hypodense lesion in the right lobe of liver. B, Contrast-enhanced CT image demonstrates marked and heterogeneous enhancement during the arterial phase (arrow). C and D, The contrast agent is washout during the portal and equilibrium phase (arrows). CT = computed tomography, PEComa = perivascular epithelioid cell tumor.

Figure 2

Post procedure processing with (A) maximum intensity projection, (B) curved planar reconstruction, and (C) volume rendering technique algorithm. It shows the feeding vessel from the right hepatic artery (arrows).

The patient underwent biopsy for the lesion. Pathological finding revealed a neoplasm with sheets and nests of pleomorphic round epithelioid cells, infiltrating adjacent liver and there was no fatty component (Fig. 3A). Immunohistochemical results revealed the tumor cells were positive for HMB-45 (Fig. 3B), smooth muscle actin (SMA), and melan-A. The pathological and immunohistochemical findings confirmed hepatic PEComa.

Figure 3

A, Histology (×100). Sheets and nests of pleomorphic round epithelioid cells, infiltrating adjacent liver and there is no fatty component. B, Immunohistochemistry (×100). Tumor cells show strong expression of HMB-45. HMB-45 = human melanoma black 45.

Discussion

PEComas are neoplasms of mesenchymal origin, and relatively rarer, malignant variants even more so.[ They have been documented in various anatomical sites, most frequently in the uterus whereas particularly uncommon in liver.[ Almost all the PEComas were identified to be strongly positive for HMB-45, SAM, and Melan-A, which are helpful for confirming the diagnosis.[

We summarize literature published in English after researching PubMed online database and inclusion terms are “hepatic” and “PEComa.” Twenty-nine cases (31 lesions) were found with primary hepatic PEComas, including our present patient, from 24 articles (Table 1).

Table 1

The authors, age, gender, location, size, enhanced CT imaging features, immunohistochemistry and preoperative diagnosis of 29 cases of hepatic perivascular epithelioid cell tumor.

The patients’ median age is 51 years (range 25–72 years). The maximum diameter of the tumors ranged from 0.8 to 19 cm (mean 5.96 cm). Male-to-female ratio is 6:23. Nine lesions are arising from the left lobe of the liver while rest lesions are from the right lobe (22/31). The vast majority of PEComas are solitary lesions (28/29), and only 1 case reported to have 3 lesions at initial diagnosis.[

The iso or hypodensity lesions with or without patchy lower density areas are described on noncontrast CT images. Only 3 cases (3/29) are reported as malignant PEComas.[ The malignant ones are heterogeneous lesions with obvious central necroses[ or with minute calcifications.[ Twenty-three lesions have detailed description of contrast-enhanced CT imaging characteristics. After contrast administration, 18 lesions show marked and heterogeneous enhancement in the arterial phase and slightly hypodense in the portal phase or equilibrium phase, including our case. The patchy lower density areas in the tumor are seen with no contrast uptake on contrast-enhanced CT images. There are 4 lesions with heterogeneous enhancement in the arterial phase and persistent enhancement in equilibrium phase. One lesion is unenhanced.[ In our case, maximum intensity projection (MIP), curved planar reconstruction (CPR), and volume rendering technique (VRT) algorithm are created for three-dimensional (3D) reconstruction and it is able to precisely show the supplying vessel for the tumor. This is the first paper that demonstrates the characteristic of tumor-feeding artery.

Immunohistochemical staining results show that all lesions are positive for human melanoma black 45 (HMB45) stain. Other positive immunostains are also reported including smooth muscle actin (SMA) (21/31) and melan-A (19/31).

The differential diagnoses of PEComas at imaging are wide; therefore, it is difficult to reach definite diagnosis preoperatively. Eighteen cases had mentioned imaging diagnosis was misleading to other diseases. Hence radiologists should promote cognition.

The differential diagnoses with imaging features similar to PEComas are as follows: hepatocellular carcinoma (HCC). To differentiate a HCC from a PEComa, we should consider the background of viral hepatitis or cirrhosis and the AFP level needs to be taken into account. Typical manifestation of HCC on contrast-enhanced CT is a hypodense tumor which is markedly enhanced in the arterial phase with the contrast reagent drain out in the portal and equilibrium phases. Pseudocapsule can also be seen in most cases. Metastasis. The patient with metastasis usually has a history of primary neoplasm. Necrosis, cystoid degeneration, and calcification were seen frequently. Ring enhancement is common on the contrast-enhanced CT image. Some metastases are surrounded by low-density edema. Our case represented a hepatic PEComa coexisting with a gastric adenocarcinoma. Combined with imaging features and the “monist” view, we make it a priority to metastasis. Hepatic cavernous hemangioma (HCH). The mass displays the nodosity enhancement in arterial phase, contrast medium fills gradually in portal phase, and prolonged enhancement during the equilibrium phase. Hepatocellular adenoma (HCA). It mainly occurs in young women who had an oral contraceptives history. Typical imaging findings suggest homogeneous enhancement in arterial phase and prolonged mild enhancement with well-defined margin. Moreover, rupture and bleeding may occur for a larger HCA. Some of HCA are surrounded by a low-density ring due to fatty infiltration. Focal nodular hyperplasia (FNH). CT imaging shows an ill-delineated, heterogeneously enhanced mass with a central star-like scar. The tumor has an early mild enhancement in arterial phase whereas marked enhancement in portal and equilibrium phases. The central scar appears hypodense in noncontrast CT and slightly delayed enhancement in equilibrium phase.

Conclusion

In summary, we can draw a conclusion that hepatic PEComa has a marked female predominance. The right lobe of the liver is the most common site and the lesion is usually solitary. It is most common that a heterogeneous hypodense lesion with marked enhancement in arterial phase and washout in portal or equilibrium phases. Persistent enhancement is observed in a few cases. When the CT features appear as explained above, PEComas should be taken into account as a rare differential diagnosis in addition to those common liver neoplasms. The lesions with obvious central necrosis or with minute calcification may be characteristics of the malignant ones. A wide immunohistochemical panel is necessary to approach this dilemma. If the lesion is positive for HMB-45, SAM, and melan-A additionally, there is a high likelihood of a PEComa. The diagnostic criteria of PEComa depend on histopathological findings.