A case of a cellular schwannoma variant arisen in an intrapelvic space

Abstract

Cellular schwannoma is rare neoplasma and often situates in deep structures, so that its diagnosis is quite difficult. We herein report a case of a cellular schwannoma variant arisen in an intrapelvic space. A 62 year-old female had a magnetic resource imaging (MRI) examination of the lumber, which indicated a mass in the intrapelvic space behind the rectum. In T1-weighted image, the mass was slight low in intensity with cystic lesions being low. In T2-weighted image, the majority of the mass was low in intensity, whereas diffuse cystic lesions within it high. In computed tomography (CT), the tumor was well-demarcated round mass with heterogeneous low and intermediate attenuation area and punctual calcification. Because the mass was highly suspected as a pelvic mesenchymal neoplasm such as gastrointestinal stromal tumor or sarcoma, operation was performed. At laparotomy, the tumor had a thin capsule without invasion to the rectum or the mesorectum, and was arisen from the left hypogastric nerve. We cut off the left hypogastric nerve to extirpate the tumor. Macroscopically, it was a solid tumor and the color of the cutting surface was yellow-white with cysts. Pathologically, the tumor consisted of compact spindle cells arranged in short bundles or interlacing fascicles with high density. Nuclear palisading and Verocay body formation that is seen in the typical schwannomas were not spotted. Hyalinization, hemorrhage, xanthic change and lipofuscin precipitation were detected. Mitosis and necrosis were not present. Immunohistochemically, S-100β and glial fibrillary acidic protein (GFAP) was positive in tumor cells. Smooth muscle actin (SMA), CD34, CD117 and neurofilament were negative. MIB-1 index was less than 5%. Final diagnosis was obtained as a cellular schwannoma variant.