Retroperitoneal schwannoma mimicking hepatic tumor

Abstract

Retroperitoneal tumors are difficult to distinguish, especially because they share common radiological features with tumors of the liver.1 When we come across such tumors, the clinical diagnosis is often confusing. Here, we report a case of retroperitoneal schwannoma which mimicked a cystic right lobe hepatic tumor. CASE REPORT A 72-year-old man underwent CT at a medical check-up for a 7-day unidentified fever without any discomfort. A giant cystic tumor (18 cm in diameter) was detected in the right lobe of the liver (Figures 1 and 2). Blood analysis showed almost normal liver function. Carcinoembryonic antigen and alpha-fetoprotein were both negative. No evidence of tumor was found in the gastrointestinal tract, which ruled out the possibility of liver metastasis. The patient underwent laparotomy following preoperative diagnosis of primary hepatic tumor, possibly a cystic tumor. At operation, the tumor was found to be 18 cm in diameter. The tumor originated from the retroperitoneum and compressed the atrophic right lobe of the liver; it was therefore diagnosed as being of a retroperitoneal origin. Then, complete removal of the tumor and partial hepatectomy was performed.Figure 1.: CT showing a giant cystic mass in the right lobe of the liver (CT value 11 Hu).Figure 2. CT in the arterial phase showing enhancement of the tumor edge (CT value 50 Hu).Figure 3. Giant retroperitoneal mass with a well-formed envelope.Figure 4. Necrosis and liquefaction in the center of the tumor.The specimen demonstrated a well-circumscribed tumor, which was 18 cm × 20 cm × 22 cm in size, with a resected-tumor weight of 3200 g (Figure 3). It was well encapsulated and round, with a smooth surface and hard like a stone, and had necrosis and liquefaction in the center (Figure 4). It was yellowish with a heterogeneous consistency at the cut surface. The tumor lesions were separated by fibrous bands and surrounded by an envelope. Histological examination revealed that the tumor was composed of densely packed spindle cells with oval nuclei arranged in wide bands. The nuclei did not show palisading, and were not uniform in size, but there was no mitosis (Figure 5). The tumor stained positively for S-100 (Figure 6), vimentin (Figure 7), CD34 and CD99.Figure 5.: Image of HE staing (Original magnification ×40).Figure 6. Positive staining of S-100 (Immunohistochemical staining, original magnification ×40).Figure 7. Positive staining of vimentin (Immunohistochemical staining, original magnification ×10).DISCUSSION Schwannoma is a well-defined, usually benign, tumor arising from the nerve sheath (Schwann cells). It may present as a solitary mass in any part of the body, but is more commonly seen in the head and neck, the extremities, and on the trunk.2 It is rarely found in the abdomen, especially the retroperitoneum. It has a reported incidence of only 0.5%—1.2%,3 which makes accurate preoperative diagnosis difficult.4,5 During the normal check-up for an abdominal mass, ultrasonography is often the first-line imaging modality, and CT and MRI are both helpful for diagnosis.6 In particular, the tumor can be located by digital subtraction angiography, but unfortunately in our case, the examination was not performed preoperatively. The primary site of the tumor and its characteristics were difficult to determine. In the present case, dynamic CT revealed that the tumor was relatively hypovascular, which suggested a hypovascular primary liver tumor such as a scirrhous-type hepatocellular carcinoma or combined hepatocellular carcinoma and cholangiocellular carcinoma. Confirmation of the character of the tumor depends on the pathology and immunohistochemistry. The positive expression of S-100 protein is valuable for diagnosis.7 Different degrees of S-100 expression in tumor cells can be the means to differentiate schwannoma from fibrosarcoma, leiomyosarcoma and angiosarcoma. Surgical treatment is the only valid option for schwannoma, because it is not sensitive to radiotherapy and chemotherapy.8 Recurrence of schwannoma is very high if resection is not complete. The surgical technique is very important, such as gentle work, complete removal with envelope and cauterization to destroy the remaining tumor. The drawback of operation is mass bleeding, because of the abundant blood vessels in the core of the tumor and compression of adjacent blood vessels.9 Despite the giant size of the tumor in this case, we still removed it perfectly. The patient recovered uneventfully and was discharged, and is still in follow-up. We will take stock of the prognosis in the near future.