Case Report
A 13-year-old female patient, who was previously healthy, applied with the complaints of fatigue and fever. On her physical examination, there was tenderness in the abdomen. The patient’s laboratory tests revealed elevations of the liver enzyme tests (Grade1-2, CTCAE v5). In the abdominal ultrasonography, omental thickening near the pelvic region, soft tissue appearance and dense fluid related to the parametrial areas were observed. Contrast-enhanced abdominal magnetic resonance imaging revealed soft tissue with diffusion restriction and contrast enhancement in the pelvic region, thickening of the peritoneal surface and omentum around the liver, and enlargement of the pelvic lymph nodes. The differential diagnosis included tuberculosis, peritoneal carcinomatosis, and lymphoma-like involvement. Laparoscopy was performed to investigate the etiology of fever of unknown origin and an abdominal mass. In the laparoscopy procedure, lymph node excision and biopsy, appendectomy (perforated appendicitis), omentectomy, peritoneal washing and debridement were performed. The pathology result was epithelioid type malignant mesothelioma. It was detected that the tumor infiltrated the appendix serosa and wall, peritoneal tissue, omental tissue and lymph nodes. Widespread positivity was detected with CK5, CK6, CK 7, mesothelin and calretinin in tumor cells. Mild to moderate positivity was observed with D2-40. Multifocal cytoplasmic positivity was detected with epithelial membrane antigen. Other markers were found negative. To determine the extent of the tumor, the first positron emission tomography (PET/CT) was obtained. Except for the normal physiological accumulation sites of the given radiopharmaceutical, diffuse pathological activity accumulation (maximum standard uptake value, SUVmax: 9.0) was observed on the peritoneal surface, prominently in the pelvis and in the pericapsular area of the liver periphery (Figure 1a).