Nodular fasciitis: A frequent diagnostic pitfall on fine-needle aspiration

BACKGROUND: Nodular fasciitis (NF) is a benign, self-limited, fibroblastic/myofibroblastic proliferation that is diagnostically challenging, often mimicking a malignant process due to its rapid growth clinically and its high cellularity, mitotic activity, and variable/nonspecific cytomorphologic findings. Herein, the authors report what to their knowledge is the largest and first multi-institutional study of the cytomorphologic characteristics of NF by fine-needle aspiration (FNA). METHODS: The pathology archives at The Johns Hopkins Hospital, The Ohio State University Wexner Medical Center, and Emory University Hospital were searched for soft tissue FNA cytology specimens of masses confirmed to be NF. The clinical history, actual FNA diagnosis, and cytomorphologic features were recorded by the authors. RESULTS: A total of 34 patients were identified, 33 of which had material available for review. The mean age of the patients was 40 years (range, 1-80 years); 18 patients (52.9%) were male. The mean duration of symptoms was 3.75 months. Four cases (11.8%) and 2 cases (5.9%) were signed out as NF and “malignant neoplasm, NOS [not otherwise specified],” respectively. On average, cases were hypercellular (mean, 3.27/4). Thirty cases (90.9%) contained spindled morphology, whereas 30 cases (90.9%) and 28 cases (84.4%) contained cells with unipolar and curved cytoplasmic tails, respectively. Eccentric, ovoid, and spindled/elongated nuclei were observed in 31 cases (93.9%), 30 cases (90.9%), and 29 cases (87.9%), respectively. Nineteen cases (57.6%) lacked atypia. CONCLUSIONS: In the current study, the diagnosis of NF was suggested in nearly 40% of cases. Combining the clinical presentation with the most commonly described cytomorphologic features will appropriately triage the majority of cases, although uncertainty will remain in a significant number of cases. Cancer Cytopathol 2017;125:20-29.