Myxoid Solitary Fibrous Tumor of the Nasal Vestibule: An Unusual Histological Subtype in the Head and Neck Region.

Abstract

Solitary fibrous tumors (SFTs) are mesenchymal neoplasms associated with the characteristic NAB2::STAT6 gene fusion. They frequently occur in extra-thoracic sites and are not uncommon in the head and neck (HN) region. Myxoid SFT is a rare morphological subtype of SFT, the features of which overlap with those of other myxoid-appearing tumors, making the diagnosis challenging. We describe the distinctive histopathological and immunohistochemical features of myxoid SFT that occurred in a 32-year-old man with a recurrent swelling in the nasal vestibule. Histological examination showed a nodular tumor composed of short spindle-shaped cells in an abundant myxoid stroma. Nuclei were ovoid, with minimal pleomorphism. Occasional intervening slender vascular channels were present; staghorn vasculature was absent. Tumor cells were diffusely immunopositive for STAT6, CD34, and BCL2, while S100, SOX10, EMA, ER, and CD10 were negative, confirming the diagnosis of myxoid SFT. Thus, myxoid SFTs are unusual in the HN, with potential for misdiagnosis. Due to their propensity for local recurrence if incompletely excised, a high index of suspicion is required to include them in differential diagnosis of myxoid mesenchymal neoplasms occurring at this location. STAT6 is a reliable immunohistochemical marker that aids in diagnosis, reducing the necessity for molecular testing.