An incidental rectal neuroendocrine microcarcinoma (‘micro-NEC’) coexistent with a high grade adenoma

A 72‐year‐old man came to the attention of the clinicians with a long history of diarrhea. The gastroenterologist performed a colonoscopy that revealed diverticular disease in colon and sigma and the presence of an exophytic lesion measuring 4 cm, located at 12 cm from the anals margin and that was biopsied. Histologically, it was a tubulo‐villous adenoma with low grade dysplasia. Computed tomography (CT) scan confirmed the diverticular disease but not the exophytic lesion of the rectum that was evident, instead, on magnetic resonance imaging of the abdomen. No lymph nodes adenomegalies were evident. The patient's medical history did not include any other pathology. A week later, the lesion was removed endoscopically with diathermic loop. Numerous fragments, measuring 5 × 4 cm, were examined. It was concluded that, in the context of a rectal tubulovillous adenoma with high grade dysplasia, a neuroendocrine ‘microcarcinoma’ was detected, that was confined to the mucosa. In the present case the diagnosis was made just by chance, because the adenomatous lesion was voluminous and it had caused diarrhea.