Primary Malignant Melanoma of the Small Intestine Presenting with Peritonitis: A Case Report.

Malignant melanoma of the small intestine is mostly a metastatic tumor of other primary lesions, especially of skin origin. Primary malignant melanoma of the small intestine is very uncommon. The clinical presentation is usually nonspecific, thus leading to late diagnosis. We report a 42-year-old man who presented to the emergency department of Imam-Reza Hospital with symptoms and signs of peritonitis and was a candidate for emergency laparotomy and enterectomy. The medical and family history were unremarkable. A bulky mass was seen 190 cm away from the Treitz band, and a diagnosis of malignant melanoma was confirmed by histologic and immunohistochemical study. Further clinical examination revealed no primary tumor elsewhere, so the diagnosis of primary small intestinal melanoma was concluded. Although metastatic malignant melanoma in the GI tract is common, the primary one is a very rare entity. The diagnosis could be challenging because a thorough investigation is needed to rule out the possible initial origin.