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
], spermatic cord[7
], 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.
Only three cases of AML of the small intestine have been previously reported[2,3
]. All of the reported cases of small intestinal AMLs are summarized in Table . The mean age at diagnosis was 49 years. In renal AMLs, the ratio of male to female patients was 1:9[14
]. All of the reported cases of small intestinal AMLs occurred in females, whereas the case presented here occurred in a male. None of the cases were associated with tuberous sclerosis. Three patients with the ileal lesion presented with intussusception, while the patient with the duodenal lesion did not. The tumor sizes ranged from 2 to 4 cm. Also, all four lesions appeared grossly to have a single polypoid pattern.
Clinicopathological data and immunohistochemical staining results in small-intestinal AMLs
In conclusion, small intestinal AML is a very rare disease and preoperative diagnosis is difficult. When a patient has abdominal pain with associated ileal intussusception, AML should be considered in the differential diagnosis.