Myxoid neurofibroma masquerading as lymphatic-venous malformation and poses a diagnostic challenge on fine needle aspiration biopsy.

Abstract

Myxoid neurofibromas (NF) are uncommon, benign spindle cell tumors that originate from peripheral nerve sheaths, often posing a diagnostic challenge due to their hypocellularity on cytology specimens. Distinguishing myxoid spindle cell lesions can be challenging, given the broad range of potential differential diagnoses. A 26-year-old female with a past medical history of embolized inguinal, flank, and retroperitoneal venolymphatic malformation presented with a left pelvic pain causing significant disability. CT scan showed an extensive 8.7 cm × 6.6 cm retroperitoneal mass. FNA was performed and alcohol-fixed papanicolaou-stained smears showed a hypocellular specimen with loosely arranged clusters of bland spindle cell proliferation in the background of a mucoid matrix. Spindle cells showed scant cytoplasm and elongated oval-shaped regular nuclei. Prominent nucleoli were not seen. An excisional biopsy revealed a bland spindle cell proliferation in a myxoid background associated with shredded collagen bundles. Immunohistochemical staining showed diffuse positivity for S100 and CD34. Based on the overall findings, a definitive diagnosis of myxoid neurofibroma was rendered. Cytological features of myxoid neurofibroma include the presence of hypocellular spindle-shaped cells arranged in small, loosely organized groups within a myxoid matrix background. Cells exhibit scant cytoplasm with regular oval and elongated nuclei. Nucleoli are typically not identified. The differential diagnosis includes myxoid neurofibroma, myxoma, myxoid liposarcoma, myxoid chondrosarcoma, myxoid dermatofibrosarcoma protuberans, low-grade fibromyxoid sarcoma, and low-grade myxo-fibrosarcoma. We aim to highlight the importance of considering myxoid neurofibroma in the differential diagnosis of hypocellular myxoid spindle cell lesions encountered on fine-needle aspiration cytology.