S3947 Villous Volcano: An Atypical Presentation of the Volcano Sign

Introduction: The “volcano sign” is a well-established radiologic and endoscopic feature classically associated with appendiceal mucoceles and mucinous neoplasms. Characterized by a dome-like protrusion from the appendiceal orifice resembling a volcanic eruption, it typically suggests a mucus-filled lesion. We present a unique case in which a villous lesion was observed endoscopically at the appendiceal orifice and initially diagnosed by pathology as a villous adenoma. Given its endoscopic appearance, a computed tomography (CT) was obtained, which prompted surgical referral for resection. Final pathology revealed a low-grade appendiceal mucinous neoplasm (LAMN). This “villous volcano” variant expands the spectrum of LAMN presentations and suggests that a villous appearance should raise suspicion for the volcano sign and underlying appendiceal mucinous neoplasm. Case Description/Methods: A 72-year-old asymptomatic man underwent routine surveillance colonoscopy. Endoscopy revealed a polypoid, villous-appearing lesion at the appendiceal orifice. Initial biopsy pathology demonstrated a villous adenoma. However, due to the endoscopic appearance of an appendiceal lesion, a contrast-enhanced CT scan was obtained. Imaging showed a dome-shaped protrusion at the base of the cecum consistent with the volcano sign. The patient underwent appendectomy. Gross pathology revealed a dilated appendix, and final histology confirmed a LAMN with negative margins. Notably, the lesion exhibited prominent villous mucosal architecture corresponding to the endoscopic appearance - distinct from the mucin-filled morphology typically associated with the volcano sign. Discussion: This case illustrates a rare and distinctive endoscopic presentation of the volcano sign, characterized by a villous lesion at the appendiceal orifice rather than the classic mucin-filled dome. The unusual villous appearance was initially diagnosed as a villous adenoma. Further imaging and surgical pathology identified a LAMN - a typically slow-growing lesion with low malignant potential -emphasizing the need for early recognition to guide management and prevent complications like mucin spread. This case suggests that villous morphology at the appendiceal orifice should raise suspicion for the volcano sign and underlying mucinous neoplasm, even in asymptomatic patients. Awareness of this unique feature may improve early diagnosis and expand understanding of LAMN presentations.