Synchronous ordinary lipoma and spindle‐cell lipoma diagnosed by fine needle aspiration

Dear Dr. Bedrossian: Although histological examination is by-and-far considered the gold standard for most soft tissue diagnoses, fine needle aspiration (FNA) is an excellent modality to determine the initial characteristics of the lesion in question. To our knowledge, there have been only two reported cases of ordinary lipoma and spindle-cell lipoma occurring at the same time in the same patient; these were both diagnosed by excisional biopsy. We report a rare case in which synchronous ordinary lipoma and spindle-cell lipoma was first diagnosed by FNA. An 80-yr-old male presented for FNA of two neck masses in work up for basal-cell carcinoma of the scalp. Physical examination revealed the masses to be soft and painless to palpation. FNA of the right posterior neck mass demonstrated a few clusters of mature adipocytes (Fig. 1A) with small, round, and eccentric nuclei with no visible nucleoli, diagnostic of ordinary lipoma. FNA of the midline posterior neck mass demonstrated few cohesive fragments of uniform spindled cells in a myxoid matrix with scattered mast cells (Fig. 1B, C). The spindle-cell nuclei were generally smooth and fusiform; cytoplasm was scant and pale. Rare mature adipocytes are also present. No lipoblasts, mitotic figures, nor nuclear atypia were identified. The aspiration was interpreted as spindle-cell neoplasm, favor spindle-cell lipoma. Three months later, the patient had the excision of these masses along with his scalp basal-cell carcinoma. Grossly the right posterior neck mass was a well-circumscribed 2.0 cm yellow, lobular adipose tissue. Microscopically, there were mature, uniform fat cells with a delicate, almost inconspicuous vasculature (Fig. 1D), diagnostic of ordinary lipoma. The midline posterior neck mass was 2.5 cm, well circumscribed with variegated pink/tan/yellow cut surface. Microscopically, there were thick bands of collagen with scattered lobules of mature adipose tissue (Fig. 1E); spindle cells were positive for CD34 stain (Fig. 1F), diagnostic of spindle-cell lipoma. We report here what we believe is the first case of FNA diagnosing of coexisting ordinary lipoma and spindle cell lipoma. Histologically, spindle-cell lipoma is at one end of the spindle-cell lipoma/pleomorphic lipoma spectrum. The entity as a whole is composed of various amounts of mature adipose tissue, spindle cells, collagen, and often with myxoid change. Although any component may predominate, the relative amounts of each tend to be equal. The spindle cells are usually arranged in short fascicles but can also be randomly distributed. Mast cells are seen in approximately 50% of specimens. Almost all tumors are CD34 positive. Cytologically, spindle-cell lipomas show much overlap with other spindle-cell tumors, both benign and malignant. Having knowledge of the histological picture, one can predict the components that will be present in the FNA: adipocytes, spindle cells, collagen, and/or mast cells. Other spindle-cell tumors that should be considered in the differential diagnosis include neurogenic tumors, dermatofibrosarcoma protuberans (DFSP), and myxoid tumors. Absence of fat and immunohistochemical staining of the cell-block for CD34 (positive for spindle-cell lipomas and negative for neurogenic tumors) and S100 (negative for spindle-cell lipomas and positive for neurogenic tumors) are critical in making this distinction. Finally, depending on the myxoid nature of the lesion, one must consider various myxoid processes, such as post-traumatic/inflammatory, myxoid liposarcoma, and myxofibrosarcoma. The first of these is characterized by relatively high cellularity, adipocytes of various size and foamy histiocytes. The two latter malignant sarcomas might pose a diagnostic problem if they represent lowgrade varieties. Location and careful inspection for atypical features, such as lipoblasts, pleomorphism, and prominent vascular fragments, will prove to be beneficial in differenti*Correspondence to: Robert T. Pu, M.D., Ph.D., Department of Pathology, University of Michigan, 1500 E. Medical Center Drive, Room 2G332, Box 0054, Ann Arbor, Michigan, 48109. E-mail: robertpu@umich.edu Received 15 July 2005; Accepted 6 October 2005 DOI 10.1002/dc.20444 Published online in Wiley InterScience (www.interscience.wiley.com).