Introduction: Small bowel neuroendocrine tumors (NETs) are the most common malignancy of the small intestine but often face diagnostic delays due to their subtle presentation. While they originate from the submucosa, advanced lesions can develop specific mucosal alterations. We present a case that illustrates the classic "yellowish and ulcerated" morphology, a key endoscopic sign that should trigger immediate suspicion of a NET during ileoscopy.

Case Description: A 72-year-old male was referred for evaluation of chronic intermittent diarrhea, right lower quadrant pain, and significant weight loss (10 kg). Biochemical workup revealed elevated serum chromogranin A and urinary catecholamines, raising suspicion for a neuroendocrine etiology.

High-definition ileocolonoscopy was performed. The colon was endoscopically normal. However, deep intubation of the terminal ileum (5 cm proximal to the valve) revealed a solitary, 3-cm exophytic lesion. Morphologically, the mass was striking: it presented a distinct yellowish submucosal hue that differentiated it from typical adenomas. Furthermore, the lesion exhibited a central surface ulceration with irregular edges and friability upon contact.

Biopsies taken from the ulcerated margin confirmed a well-differentiated, low-grade neuroendocrine tumor. The patient underwent oncological resection, confirming the diagnosis.

Conclusion: This case underscores the importance of recognizing specific visual patterns during ileoscopy. The combination of a yellowish coloration (reflecting the lipid-rich neuroendocrine tissue) and spontaneous surface ulceration constitutes a highly suggestive phenotype for ileal NETs. Endoscopists observing a "yellowish ulcerated nodule" in the distal ileum should prioritize this diagnosis over Crohn’s disease or simple inflammatory polyps to expedite appropriate surgical management.