A Collision Tumour Phenomenon: Dual Metastatic Deposits From Melanoma and Adrenal Carcinoma Causing Small Bowel Intussusception.

Adult intussusception is rare and is usually associated with an underlying pathological lead point, often malignancy. While melanoma commonly metastasises to the gastrointestinal tract, melanoma-related intussusception remains uncommon, and small bowel metastasis from adrenal cortical carcinoma is exceptionally rare. This case describes synchronous metastatic melanoma and adrenal carcinoma causing jejunal intussusception. A 43-year-old male with stage 3B melanoma and an oligometastatic right adrenal lesion presented with two days of bilious vomiting and reduced oral intake, with minimal abdominal symptoms and no significant examination findings. CT imaging, prompted by his oncological history, revealed high-grade small bowel obstruction secondary to jejunal intussusception. He underwent laparoscopic-assisted reduction and small bowel resection, with a 5 cm melanoma deposit identified as the lead point. Histopathology demonstrated a rare collision tumour comprising metastatic melanoma and metastatic adrenal cortical carcinoma. The patient recovered well postoperatively and was discharged home. This case highlights the diagnostic challenge of malignant adult intussusception, particularly in patients with complex oncological histories and subtle clinical presentations. The coexistence of metastatic melanoma and adrenal cortical carcinoma as dual pathological lead points represents an exceptionally rare finding. It emphasises the importance of maintaining clinical suspicion, early cross-sectional imaging and multidisciplinary management in oncology patients presenting with gastrointestinal symptoms. Synchronous metastatic melanoma and adrenal cortical carcinoma causing small bowel intussusception is an exceptionally rare presentation. A low threshold for imaging and timely intervention is essential to avoid diagnostic delay and optimise outcomes in patients with metastatic malignancy.