A 28-year-old man presented to the emergency room complaining of progressive abdominal cramping pain, accompanied by nausea and vomiting for 6 h. He had no significant medical history except for having been admitted with pneumothorax 13 years previously. The pain was located over the right lower quadrant of the abdomen. He had no change in bowel habits, bloody stools, or tenesmus. Physical examination showed a palpable mass over the right lower quadrant with direct tenderness. Increased bowel sounds were noted during auscultation. Laboratory findings were normal; red blood cell count 5.02 × 10⁶/mm³, hemoglobin 15.7g/dL and hematocrit 44.1%, platelets 237 × 10³/mm³, and white blood cell count 7700/mm³. Serum analysis was as follows: total protein 8.6 g/dL, aspartate aminotransferase 19 U/L, alanine aminotransferase 13 U/L, blood urea nitrogen 13.5 mg/dL, and creatinine 0.7 mg/dL. An enhanced computed tomography (CT) scan of the abdomen showed ileocolic intussusception caused by an abnormal 3.0-cm soft tissue mass with increased thickness of the wall (Figure ​(Figure1A).1A). There was no evidence of any other soft tissue mass either in the liver or in the kidney. Colonoscopic examination could not be performed because of severe abdominal pain. The patient underwent surgery with the diagnosis of intussusception. During an exploratory laparotomy, the main polypoid mass was located approximately 60 cm from the ileocecal valve. An ileo-ileal intussusception, about 15 cm in length, was found. This mass protruded into the right colon, including the cecum. A right hemicolectomy was uneventfully performed.

AMLs are histologically benign tumors derived from mesenchymal tissue. The vast majority of AMLs arise in the kidney. In 45 to 80% of patients, they are associated with tuberous sclerosis, a multi-systemic disease with autosomal dominant inheritance, and the occasional association with the triad of epilepsy, mental retardation, and adenoma sebaceum[¹]. Extrarenal AMLs are very rare and have been reported in the liver[⁴], nasal cavity[⁵], vagina[⁶], spermatic cord[⁷], skin[⁸], mediastinum[⁹], and gastrointestinal (GI) tract, including the colon[^10,11–13] and small intestine[^2,3]. AMLs arising in the GI tract are extremely uncommon and usually present with melena, anemia, diarrhea, abdominal pain, and may even be clinically asymptomatic[^10–13]. Radiological diagnosis of extrarenal AMLs is difficult because of the rarity of the condition. CT is an effective means of imaging and identifying AMLs. Thin-section (3-5 mm) scanning is performed in an attempt to show fatty-tissue attenuation. Sonography can suggest the diagnosis, showing a well-defined hyperechoic lesion, but it is not diagnostic. On magnetic resonance imaging, lesions are bright on T1-weighted images and dark on fat-suppressed images[³]. Surgical excision is the treatment of choice, but inadequate resection may result in rapid local recurrence[^14,15]. Microscopically, most AMLs are composed of a variable mixture of mature fat, thick-walled poorly organized blood vessels, and smooth muscle (classic triphasic histology). Rarely, striking degrees of nuclear atypia may be seen in smooth muscle cells, raising the possibility of malignancy. Cells associated with thin-walled, branching vessels with a pattern similar to lymphangioleiomyoma is another variation of the smooth muscle component. The lipomatous component consists typically of mature adipose tissue but may contain vacuolated adipocytes, suggesting lipoblasts, thus mimicking a liposarcoma. The blood vessels are thick-walled and lack the normal elastic content of arteries. AMLs with a prominent vascular component may mimic a vascular malformation. Immunohistochemically, AMLs are characterized by coexpression of melanocytic markers (HMB45) and smooth muscle markers (SMA). However, previously reported cases of intestinal AML[^2,3,10–13] showed only focal or no immunoreactivity for HMB45, and the present case was also negative for HMB45. AMLs usually grow slowly. Malignant changes of AML are rare, and only sporadically reported cases have been documented in lesions arising in the kidney. However, to date, AMLs arising in the GI tract have never been reported to have malignant changes.