Pseudomyxoma Peritonei: A Case Report

Pseudomyxoma peritonei (PMP) is a rare clinicopathologic syndrome characterized by progressive accumulation of mucinous ascites within the peritoneal cavity, most commonly arising from an appendiceal mucinous neoplasm. Diagnosis is frequently delayed because of nonspecific symptoms and variable radiographic findings. We present a case of high-grade PMP in a 41-year-old man whose initial presentation was notable for atypical endocrine and genitourinary symptoms, including progressive gynecomastia, ejaculatory dysfunction, pelvic pain, and hydrocele formation. Initial abdominal magnetic resonance imaging (MRI) was unremarkable; however, subsequent computed tomography demonstrated loculated ascites and a large abdominal mass. Exploratory laparotomy revealed extensive peritoneal disease with mucinous adenocarcinoma and large-volume malignant ascites. The patient subsequently developed radiographic findings concerning for thoracic involvement, including bilateral loculated pleural effusions and mediastinal abnormalities, with respiratory failure requiring prolonged mechanical ventilation. The diagnosis of PMP had previously been established during exploratory laparotomy at an outside institution, where malignant ascitic-fluid cytology and an intraoperative biopsy demonstrated mucinous adenocarcinoma. Because the complete outside pathology report was unavailable following transfer, additional tissue sampling was pursued. Thoracentesis, abdominal fluid drainage, and endobronchial ultrasound-guided sampling were nondiagnostic, whereas diagnostic laparoscopy subsequently provided confirmatory tissue demonstrating high-grade mucinous adenocarcinoma with positive CK7, CK20, CDX2, and SATB2 immunostaining, supporting lower gastrointestinal differentiation. However, a definitive primary tumor site could not be established based on the available clinical, operative, and pathologic information. Owing to unresectable peritoneal disease, ventilator-dependent respiratory failure, severe chronic illness-related malnutrition, declining functional status, and radiographic findings concerning for extra-abdominal involvement, the patient was not a candidate for cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy. Following multidisciplinary discussion, he received one cycle of palliative FOLFOXIRI (5-fluorouracil, leucovorin, oxaliplatin, and irinotecan). No further chemotherapy was administered because of persistent ventilator dependence, Enterobacterales and Serratia bacteremia requiring vasopressor support, and continued clinical deterioration, and the patient died shortly thereafter. This case highlights several uncommon features of PMP, including atypical initial manifestations, initially negative imaging, radiographic findings concerning for thoracic involvement, and repeated false-negative cytologic studies. It underscores the importance of obtaining adequate tissue for histopathologic confirmation when prior pathology is unavailable or minimally invasive studies are nondiagnostic, as well as early referral to specialized centers before disease progression precludes potentially curative treatment.