Challenge of FNA diagnosis of angiomyolipoma: A study of 33 cases

BACKGROUND: Angiomyolipoma (AML), typically composed of smooth muscle, vessels, and fat, is generally a benign tumor in the kidneys. However, it occasionally occurs in extrarenal sites and behaves like a malignant tumor. AML is uncommonly encountered in fine-needle aspiration (FNA) samples and can cause diagnostic difficulty. METHODS: We searched our pathology database for FNA cases diagnosed between 2003 and 2015 that were subsequently confirmed to be AML in the same lesion by surgical pathologic evaluation. The diagnostic performance, challenges, and cytologic features were retrospectively reviewed. RESULTS: In total, 33 FNA cases from 31 patients were identified. The final surgical pathologic diagnoses included 30 primary AMLs (28 in kidneys and 2 in liver) and 3 were metastases (in liver, lung, and abdominal wall, respectively). Aspiration sites included kidney/retroperitoneum (n = 28), abdominal wall (n = 1), lung (n = 1), and liver (n = 3). The FNA diagnoses were consistent with/favor AML (n = 16), descriptive (n = 12), nondiagnostic (n = 2), and erroneous (n = 3). Of the 3 erroneous cases, 2 were diagnosed as renal cell carcinoma, and 1 was diagnosed as a pleomorphic malignant neoplasm. Cytologically, cases with predominantly spindle cells were the most commonly encountered (n = 19). Cases with predominantly epithelioid cells (n = 6) can pose a diagnostic difficulty and were observed in all 3 metastatic AMLs and in 2 of the 3 erroneous cases. Immunostains were performed on 11 FNAs and helped the diagnosis in 9 cases. CONCLUSIONS: FNA diagnosis of AML may be challenging, especially in cases with a predominantly epithelioid component and/or an extrarenal location. Immunostaining is important to improve diagnostic accuracy of this rare entity. Cancer Cytopathol 2017;125:257–266.