Submucosal Necrotic Nodule of the Colon: An Enigmatic Entity Potentially Related to Anisakis Infection

Abstract

Context.— Discrete submucosal necrotic nodules may rarely manifest as colon polyps. Objective.— To characterize the clinical and pathologic features of this lesion, which has been under-studied in the literature. Design.— We conducted an international search to compile a series. For each potential case, photomicrographs were centrally reviewed to confirm the diagnosis. We gathered clinical and pathologic information on each confirmed case. Results.— The final cohort included 25 patients, with 23 having 1 lesion and 2 having several (31 lesions total). Mean patient age was 62 years; 13 (52%) were male. Symptoms were nonspecific, although 4 patients (16%) had blood in stool; 14 patients were asymptomatic. Patient history and medications appeared noncontributory. Most cases were located in the right colon (n = 18; 58%). Mean size was 0.4 cm (range, 0.1–1.7 cm). Histology typically showed a centrally necrotic nodule with peripheral fibrosis, chronic inflammation, and sometimes palisading granulomatous inflammation. Percent necrosis ranged from 5% to 95% (average, 70%), and percent fibrosis ranged from 3% to 70% (average, 25%). In 3 cases, degenerated parasitic structures consistent with Anisakis could be seen on hematoxylin-eosin and trichrome special stain. No patient experienced disease recurrence. Conclusions.— Submucosal necrotic nodules can present as colon polyps. Most cases are unifocal, and patients do well on follow-up. At least some examples appear to be caused by Anisakis, implicating patient diet. Patients are often asymptomatic, and many cases show no histologic evidence of the causative agent.