Soft tissue perineurioma (STP) is a benign peripheral nerve sheath tumor demonstrating uniform perineurial cell differentiation. To the authors' knowledge, the cytomorphologic features of STP remain incompletely characterized, and the distinction between STP and its benign (intramuscular/cellular myxoma) and malignant (low-grade fibromyxoid sarcoma [LGFMS]) mimics is challenging.
Fine-needle aspiration (FNA)/core needle biopsies of 25 low-grade myxoid spindle cell neoplasm cases including STP (5 cases), intramuscular/cellular myxoma (16 cases), and LGFMS (4 cases) were reviewed retrospectively for cytomorphologic and immunophenotypic comparison.
FNA smears of STP were hypocellular with scattered clusters of spindle cells with bland, slender nuclei; bipolar cytoplasmic processes; and scant myxoid to collagenous matrix. STP commonly lacked the abundant granular myxoid matrix material present in intramuscular/cellular myxoma (20% in STP vs 75% in intramuscular/cellular myxoma; P <.05), but these tumors were otherwise remarkably found to be similar on FNA smears. All STP and intramuscular/cellular myxoma cases lacked cytologic atypia, whereas 50% of LGFMS cases demonstrated mild nuclear atypia. EMA was positive in all STPs, but also was found to be at least focally positive in 60% of intramuscular/cellular myxoma cases (9 of 15 cases) and 75% of LGFMS cases (3 of 4 cases). MUC4 was found to be negative in all 15 intramuscular/cellular myxoma and 5 STP cases, but was positive in all 4 LGFMS cases.
STP, intramuscular/cellular myxoma, and LGFMS have significant cytomorphologic overlap. Immunohistochemical staining with EMA is not beneficial due to a lack of specificity. Negative MUC4 staining reliably excludes LGFMS. Therefore, a clinically meaningful approach to the FNA biopsy evaluation of a low-grade myxoid spindle cell neoplasm is to provide a differential diagnosis and to exclude a low-grade sarcoma. Cancer Cytopathol 2016;124:651-8. © 2016 American Cancer Society.