Angiomyolipoma is a mesenchymal benign tumor involving the smooth muscle tissue, mature adipocytes, as well as large and small blood vessels, the majority of which are present in the kidney . Although angiomyolipoma that develops outside the kidney is rare, it has been reported to occur in various parts, such as liver, uterus, adrenal gland and retroperitoneum, among others [1,2,3]. However, we came across only one case report on angiomyolipoma originating from the spleen when searching in PubMed with the keywords “spleen” and “angiomyolipoma” . This case concerned a 51-year-old man who had angiomyolipoma of the spleen and adenocarcinoma of the appendix, for which he underwent splenectomy and right hemicolectomy . Splenic tumors can be either primary or metastatic, and primary tumors can be divided into the nonlymphatic and lymphatic categories. The most common nonlymphatic tumors are vascular tumors, including benign and malignant tumors. Angiomyolipoma is a nonlymphatic tumor. Metastatic tumors include melanoma, breast cancer, and lung cancer . The average age of patients with retroperitoneal extrarenal angiomyolipomas is 45 years (range 22–80 years), with a male–female ratio of 1:5.3 . Among the patients with renal angiomyolipomas, 30–40% may also exhibit features of TS. Similarly, 40–80% of the patients with TS are likely to develop renal angiomyolipoma [6,7,8]. However, the present case involved a 27-year-old man with no TS. Furthermore, a rare case of angiomyolipoma malignant transformation with lymph node metastasis has been reported [6,7,8,9,10]. However, all of these cases were associated with renal angiomyolipoma and TS. This case was not associated with malignant tumor, but Tang et al. reported an angiomyolipoma case of appendix carcinoid and Mogi et al. reported a case of gastric cancer [4, 11]. Although the number of cases of primary angiomyolipoma of the spleen is extremely small, it is necessary to consider the malignant complications.
CT is the most commonly used imaging technique in investigating angiomyolipomas . As a typical imaging finding of angiomyolipoma, contrast-enhanced CT reveals a low-density part that reflects the fat component and a part that is strongly contrasted by enhancement. MRI shows a high signal in both T1- and T2-weighted images, and a decrease in the signal is observed in fat-suppressed images . In this case, MRI could not be performed as the patient was claustrophobic, but CT exposed a low-concentration part reflecting the fat component and a solid part with a strong contrast effect. CT findings included differential diagnosis of the splenic angiomyolipoma, angioma including fat, and hamartoma. Angiomyolipoma is immunohistochemically positive for the melanocytic marker HMB45 and the smooth muscle marker SMA in many cases . However, some cases are negative for HMB45. Tang et al. have reported a case that was positive for SMA but negative for HMB45 . This case also consisted of three components, that is, smooth muscle, adipose tissue, and blood vessels. The patient was negative for HMB45 and positive for SMA; thus, splenic angiomyolipoma was diagnosed. These markers are useful for arriving at a definitive diagnosis, and preoperative biopsy may also aid in establishing the diagnosis. The protocol developed by Oesterling et al. is widely used to determine the treatment strategy for angiomyolipoma . If the patient is asymptomatic, follow-up is sufficient. However, if the patient is symptomatic, treatment to alleviate the symptoms should be provided whenever the tumor size is ≥ 4 cm; if the tumor size is < 4 cm and the symptoms persist, treatment should be provided.
Treatment strategies for angiomyolipoma include surgery and arterial embolization, but the latter is less invasive and appears to be useful in preventing bleeding and achieving hemostasis . The primary treatments for extrarenal retroperitoneal angiomyolipomas commonly involve surgery (surgical excisions, and less often, embolization of the tumor) . Surgery should be considered when embolization is inadequate or when malignancy cannot be ruled out. The present case involved a giant tumor with a diameter of approximately 14 cm; there was a risk of rupture, and malignancy could not be ruled out.
Minja et al. have reported 16 cases of extrarenal MLs from 1982 to 2011 . Nine cases had follow-up evaluations for 2–60 months after the surgical resection. All nine cases remained disease-free and asymptomatic at the last follow-up, and recurrence has not been documented. In retroperitoneal angiomyolipoma abutting the kidney, the previously reported recurrence was a case of metastasis to the liver and bone, which occurred 12 months after radical nephrectomy . Metastatic masses were found on ultrasonography and CT. Extrarenal angiomyolipoma appears to have a good prognosis after surgical resection, but recurrence is possible in rare instances; hence, follow-up by imaging tests such as CT or ultrasonography may be necessary.