Benign peripheral nerve tumors: Analysis of 89 FNA cases emphasizing diagnostic accuracy and their morphologic spectrum

Abstract

Introduction Benign peripheral nerve tumors (BPNTs) are a heterogenous group of soft tissue tumors that include a variety of nerve sheath tumors, granular cell tumor (GCT), and ganglioneuroma. Only a few large studies exist on cytopathology and diagnostic accuracy using fine‐needle aspiration (FNA) biopsy for this set of neoplasms. Materials and methods Both surgical and cytopathology files were searched for cases of BPNT. FNA biopsy was performed using standard techniques. Results Eighty‐nine cases from 88 patients (male:female = 1:1; age range: 16–85 years, mean age, 51 years) met inclusion criteria. FNA sites included extremities (58, 65%), head/neck (14, 16%), deep (9, 10%), and trunk (8, 10%). Aspirates were from primary neoplasms in all but one instance. There were 65 schwannomas, seven neurofibromas, seven perineuriomas, seven GCTs, and three ganglioneuromas/neuromas. Aspirates of schwannoma, GCT, neurofibroma (NF), and perineurioma (PN) were correctly diagnosed in 86%, 100%, 29%, and 0% of cases, respectively. Five tumors (6%) were interpreted as either a specific sarcoma or suspicious for sarcoma. Remaining aspirates were classified as spindle cell neoplasm, salivary gland neoplasm, and nondiagnostic. Cytologic features for schwannoma, NF, PN, and ganglioneuroma showed spindle cell–dominant smears arranged mainly in syncytial clusters. GCT aspirates contained a population of epithelioid cells harboring coarsely granular cytoplasm and bare nuclei. Immunohistochemical (IHC) staining in 55 (62%) cases showed S‐100 expression in 95%. Conclusion FNA biopsy coupled with IHC is reliable in correctly classifying schwannoma and GCT, but less so for NF. Perineurioma can be mistaken for sarcoma.

Pitfalls in soft tissue cytopathology

“…43 CKIT/CD117 and DOG1 are negative and rule out a gastrointestinal stromal tumour (GIST), especially in abdominopelvic locations, where these two tumours are close differential diagnoses. In a recent study describing the wide cytomorphological spectrum of 89 benign peripheral nerve sheath tumours, Wakely 44 reported that FNAB in combination with immunostains is reliable for correctly diagnosing schwannoma and granular cell tumours but is less reliable for diagnosing neurofibroma. He observed that none of the seven perineuriomas in his study were accurately diagnosed on cytology.…”

Cytological features of cranial and paraspinal nerve Tumours

“…• Architecture and cellularity ○ Smears are moderately to highly cellular, demonstrating cohesive, three-dimensional fragments showing fascicular to the patternless arrangement, with rare single cells in the background. 2,3 ○ Verocay bodies are seen in a minority of cases. 2,3 • Stroma and cytoplasm ○ Metachromatic stroma may be seen on air-dried stains.…”

“…2,3 ○ Verocay bodies are seen in a minority of cases. 2,3 • Stroma and cytoplasm ○ Metachromatic stroma may be seen on air-dried stains. 2,3 ○ Cytoplasm is usually fibrillary, with indistinct borders, and may display feathery edges.…”

“…2,3 • Stroma and cytoplasm ○ Metachromatic stroma may be seen on air-dried stains. 2,3 ○ Cytoplasm is usually fibrillary, with indistinct borders, and may display feathery edges. 2,4 • Nuclei ○ Nuclei are generally ovoid with fine chromatin, absent or indistinct nucleoli and smooth, regular membranes.…”

“…2,4 ○ Intranuclear pseudoinclusions may be present. 2,3 ○ Marked nuclear pleomorphism and anisonucleosis may also be seen in a subset of cases. 2,4 ○ Occasionally, ancient change is appreciable with hyperchromatic, smudged nuclei showing loss of chromatin detail.…”