Unveiling the Uncommon: Gastrointestinal Basidiobolomycosis of the Colon and its Distinctive Splendore-Hoeppli Phenomenon

Background Basidiobolomycosis is a rare fungal infection caused by Basidiobolus ranarum. Case Presentation A 53-year-old man from Saudi Arabia with a known history of diverticulosis presented with severe abdominal pain and diarrhea. A CT scan revealed circumferential wall thickening of the descending and sigmoid colon with surrounding fat stranding, suggesting a diagnosis of complicated diverticulitis. Additional thick fluid was observed around the affected area. Surgical excision was pursued. A gross examination of two received large bowel segments disclosed marked ulcerated mucosa and wall thickening with exudate-covered serosal surfaces and adhesions. Microscopic examination unveiled significant infiltration by eosinophils, polymorphonuclear leukocytes, and granulomatous inflammation. Thin-walled, broad fungal hyphae of Basidiobolus, surrounded by eosinophilic material, were identified. Granulomas displayed abundant multinucleated giant cells and palisading histiocytes around central necrosis or abscess formation. Thin-walled, broad fungal hyphae of Basidiobolus, with sparse septations, are surrounded by a radiating, intensely eosinophilic cuff (Splendore-Hoeppli phenomenon). These hyphae, visible with hematoxylin and eosin staining, were further highlighted with periodic acid-Schiff and Gomori methenamine silver staining. Discussion Basidiobolomycosis may mimic neoplastic lesions. Histologically, the characteristic features include broad, thin-walled septate hyphae surrounded by eosinophilic material, a finding that is accentuated by the Splendore-Hoeppli phenomenon. Microscopic examination, along with special stains such as periodic acid-Schiff (PAS) and Gomori methenamine silver, is essential for accurate diagnosis. Conclusion Prompt recognition and appropriate antifungal therapy are vital for favorable patient outcomes. This report highlights the distinctive features of Basidiobolomycosis to raise awareness and understanding of this infrequent yet clinically significant fungal infection.