Laparoscopic excision of infra-renal PEComa.

Perivascular epitheloid cell tumors (PEComas) are rare tumors of malignant potential. There is no normal cell variant to these cells. The family is large and includes angiomyolipoma, clear cell "sugar" tumor amongst others. Imaging modalities are not very diagnostic. The diagnosis hence is often postoperative. A 55-year old female presented to us with ultrasonographic diagnosis of solid mass in the right infrarenal region. Contrast-enhanced computerized sonography (CECT) suggested paraganglioma or a soft tissue retroperitoneal tumor. Laparoscopic excision was successful. The rarity of this pathology and laparoscopic modality of excision prompted us to publish this report.

INTRODUCTION

PEComas are rare soft tissue tumors of variable malignant potential. Available investigative modalities like CECT scan are often not diagnostic. The differential diagnosis usually depends upon the organ of origin. The final diagnosis is often obtained after histopathological examination. Laparosscopic excision has been sparsely reported. We report one such case of a patient having been diagnosed with an infra-renal mass that was excised laparoscopically and found to be PEComa.

CASE REPORT

A 55-year old postmenopausal woman presented with nonspecific abdominal pain. There were no obvious gastrointestinal or urinary complaints. She had visited a physician who had ordered an ultrasonography of the abdomen which revealed an 8 cm mass situated inferior and medial to the right kidney. The patient was referred to us for further treatment.

On investigations, biochemistry was normal with no hematuria. Contrast-enhanced computerized tomography (CECT) revealed a well-defined, heterogeneously enhancing soft tissue lesion, 7 × 5 × 4 cm anterior to the right psoas muscle and inferior to the right kidney. Possibilities of paraganglioma, soft tissue neoplasm, or a renal capsular tumor were raised. The fat planes with surrounding structures were maintained [Figure 1]. The patient was investigated with paraganglioma in mind. All the markers for functioning tumor were negative. The patient was scheduled for laparoscopic excision.

Figure 1

CECT showing the mass (marked in red arrow) around the lower pole of right kidney

The patient was placed in lateral position. One 10 mm (telescope) and two 5 mm ports were placed to get a triangulation with the mass. Laparoscopy revealed a solid mass possibly arising from the capsule of the right kidney. Clean and clear planes with the kidney and rest of the tissues with clipping of single major vascular pedicle arising from right renal artery allowed complete laparoscopic resection. The tumor was retrieved in a bag by extending the telescopic incision. Recovery was uneventful.

The histopathology revealed a vascular tumor without adipolytic component. Microscopy revealed polygonal and elongated cells with whorled appearance. Immunohistochemistry studies revealed dual myomelanocytic differentiation with expression of SMA, Desmin, Caldesmon and focal expression of HMB-45, and Melan-A. Screening with c-kit, DOG-1, Synaptophysin, Chromoganin A, Cytokeratin, CK-8/18, S-100 protein, and CD 34 yielded negative results.

Figure 2 shows intraoperative photograph, gross and microscopic nature of the tumor [Figure 2].

Figure 2

Intraoperative photograph, gross and microscopy of PEComa

DISCUSSION

Perivascular epitheloid cell tumor (PEComa) is a conglomerate of rare tumors comprising perivascular epitheloid cells. These can arise from various organs common being kidney and liver.[1234567] The diagnosis is established only after microscopy.

Bonetti (1992) first noted this cell type — epitheloid features, clear cytoplasm, perivascular distribution, and immunoreactive to melanocytic markers. There was no normal corresponding cell in this pathology.[8] World Health Organization (2002) recommended PEComas to be separate pathology.[9] Angiomyolipomas, clear cell “sugar” cell tumors have been included in this family. The family also includes lymphangioleiomyomatosis (LAM), primary extrapulmonary sugar cell tumor (PEST), and clear cell myomelanocytic tumor (CCMMT).[81011]

The tumors usually present as a mass symptomatic or otherwise as in our case. Due to heterogeneous composition of the mass, CECT imaging is usually inhomogeneous and hence exact pathological diagnosis is often not possible. In our case, fat component of angiomyolipoma being absent, PEComa was not suspected. The differential diagnosis includes a plethora of benign and malignant epithelial and mesenchymal tumors including retroperitoneal sarcomas. However, PEComas should come in the ambit of differential diagnosis if the tumor is well circumscribed as in our case.[12]

As there is no normal cell counterpart, it is proposed that tumors > 5 cm and showing infiltrative growth, necrosis, vascular invasion, hypercellularity, high nucleo-cytoplasmic ratio, and mitosis > 1 per 50 hpf (any two or more) should be considered at potentially malignant. Smaller tumors without mitosis are considered benign.[13] The group in between is considered as uncertain malignant potential. Our patient has a large tumor with positive focal HMB-45 but low atypia and hence considered as that with uncertain malignant potential.

Surgical excision is the treatment of choice. Laparoscopic resection of PEComas though reported at other sites;[1415] is not reported in this location.

Genetic abnormalities have found to be responsible for cell proliferation and sirolimus (and derivatives) have been shown to inhibit this activation especially in angiomyolipomas[16] which is not so in this case. These studies are unavailable in our place and hence were not done. The patient is 4 months postop, negative for tuberous sclerosis, and is under continued surveillance.

CONCLUSION

PEComas are a family of rare tumors comprising perivascular epitheloid cells. Since there is no normal cell to this tumor cell, all are considered malignant of different aggressive potential. Surgical excision offers best chance for cure. Laparoscopic excision provides the benefits of early recovery and less pain to these patients.