A Case of Pelvic Schwannoma Presenting Prominent Eggshell-Like Calcification

Pelvic schwannoma typically forms a large, well-circumscribed mass in the retroperitoneum or presacral area and frequently undergoes cystic degeneration. It appears as a well-demarcated round or oval mass, often showing prominent cystic degeneration and calcification. Characteristics of these calcifications are punctate, mottled, or curvilinear and are seen along the walls of the mass. Herein, we describe a case of schwannoma presenting a huge pelvic mass with unique eggshell-like calcification. 1. Introduction Schwannomas (neurilemmomas) are benign neurogenic tumors originating in Schwann cells of the nerve sheath. They generally occur in the head and neck and extremities but rarely in the pelvis or retroperitoneum [1]. Retroperitoneal and pelvic schwannomas typically form large, well-circumscribed masses in the retroperitoneum or presacral area and frequently undergo cystic degeneration [2]. We report a case of pelvic schwannoma presenting prominent calcification. 2. Case Presentation A 68-year-old man presented with anal pain for one month and underwent examination in a clinic. A giant pelvic mass was detected on imaging examinations, and he was admitted to our hospital for closer examination. He had no history of previous malignancy. On admission, he had only anal pain and no other symptoms. On rectal examination, a hard fixed mass was felt on the posterior wall of the rectum. No abnormal neurological signs were found. His blood test and tumor markers including CEA, CA19-9, and soluble IL-2 receptor were within normal limits. Contrast-enhanced computed tomography (CT) was performed using nonionic contrast material (Iopamiron 370; Bayer Health Care) and showed a well-defined hypoattenuation tumor in the pelvis measuring 87 × 65？mm in the transaxial diameter. The tumor was located close to the rectum, anterior to the sacrum. There were multiple, spotted, and oval eggshell-like calcifications within the tumor. Cystic change was not evident on CT. The tumor parenchyma revealed hypoattenuation in the early phase (40？s after administration of contrast agent) and was slightly enhanced in the delayed (240？s) phase (Figure 1). Magnetic resonance imaging (MRI) revealed a mass with heterogeneous low signal intensity on T1-weighted image and high signal intensity on T2-weighted image. There were high signal intensity areas indicating hemorrhage and signal voids corresponding to calcifications on the T1-weighted image and focal high signal intensity areas indicating myxoid or cystic degeneration on the T2-weighted image (Figure 2). A colonoscopy showed only