Melanoma develops in the melanocytes, which are dendritic cells present in the skin, the eye, and the epithelium of the nasal cavity, oropharynx, anus, vagina, and urinary tract. In addition to these sites, it was proven by immunoperoxidase studies that melanocytes are present in Meckel’s diverticulum [
7,
8]. Normally, the small intestine and the colon do not contain melanocytes. Embryologically, they arise from neural crest melanoblasts which migrate to the distal ileum through the umbilical-mesenteric canal [
7,
9]. They differentiate by amine precursor uptake and decarboxylation (APUD), and can undergo neoplastic transformation in noncutaneous sites [
10]. According to this theory, the ileum is the most common site for the development of primary melanoma of the small intestine, although some authors still deny the existence of primary melanoma in the gastrointestinal tract. They argue that primary cutaneous tumors can regress before metastatic manifestations or they are too small to be identified by clinical and laboratory examinations [
2]. Primary or secondary gastrointestinal melanoma is difficult to establish resulting in many controversies [
11].The gastrointestinal tract is the most common site of cutaneous melanoma metastasis [
4,
10]. Usually asymptomatic, metastases are diagnosed at autopsy in 58% of patients with cutaneous melanoma [
9], they may be clinically detected only after treatment of primary melanoma, or spontaneous regression [
5], affecting primarily the small intestine, stomach, and colon [
4,
12]. However, some gastrointestinal melanomas remain undocumented and without evidence of a primary lesion, cutaneous or elsewhere, even after a thorough examination [
13].The incidence of metastatic gastrointestinal melanoma of unknown primary origin is from 4 to 9% in case series [
14]. In order to distinguish between primary and metastatic intestinal melanoma, Bender et al. were able to identify four different types of metastatic melanoma of the small intestine based solely on histopathological features: cavitary, infiltrating, eccentric, and polypoid [
15]. Lymphocytic infiltrate with melanophages, restorative fibrosis, and a vascular proliferation present in the dermis are commonly seen in intestinal metastatic melanoma developed after spontaneous regression of the primary cutaneous lesion [
6]. To make the diagnosis of primary malignant melanoma of the small intestine, other authors recommend excluding any history of melanoma in the other major sites. Sacks et al. established three diagnostic criteria: (1) single lesion, (2) no metastatic location other than in the regional lymph nodes, (3) relapse-free survival of more than 1 year after diagnosis [
16].
In our case, histological study confirmed the diagnosis of intestinal melanoma with concordant immunohistochemical profile; our patient had no history of cutaneous melanoma, and etiological examination found no other melanoma lesion. At 1-year follow-up, clinical examination and abdominal CT scan control showed no intraperitoneal signs of recurrence. The diagnosis of a primary malignant melanoma of the small bowel has been established.