S5039 Fungal Impostor: Gastrointestinal Basidiobolomycosis Mimicking an Obstructive Colon Mass

Introduction: Gastrointestinal basidiobolomycosis (GIB) is a rare fungal infection in immunocompetent host, characterized by submucosal growth that mimics malignancy and complicates endoscopic diagnosis. Early surgical intervention with surgery and antifungals are critical. Case Description/Methods: A 45-year-old man with uncontrolled type 2 diabetes presented with melena, right lower quadrant pain, and weight loss. Examination revealed a tender abdominal mass. Labs showed anemia (Hb 67 g/L), leukocytosis (16 × 10⁹/L), and eosinophilia. Computed tomography (CT) revealed a locally invasive 10 cm cecal mass with right sided hydronephrosis. Colonoscopy demonstrated an ulcerated obstructive, circumferential mass in the ascending colon. Biopsies were inconclusive for malignancy. After multidisciplinary tumor board review, open right colectomy with ileotransverse anastomosis and diverting loop ileostomy was performed. Histology revealed granulomatous inflammation, eosinophilic microabscesses, and pauci-septate hyphae (PAS/GMS+) confirming basidiobolomycosis. He was started on amphotericin B followed by oral posaconazole for long-term antifungal therapy. Discussion: GIB caused by Basidiobolus ranarum often mimics malignancy or inflammatory conditions, with hallmark features including abdominal mass, GI bleeding, eosinophilia, and neoplastic-like imaging. Histologic clues (granulomatous inflammation, Splendore-Hoeppli phenomenon). with culture stains confirm diagnosis. This case underscores the diagnostic challenge of GIB despite classic presentation. Multidisciplinary collaboration and histopathologic analysis prevented delayed treatment. Combined surgical resection and prolonged antifungals remain essential for favorable outcomes.