Unilateral progressive painless proptosis: a case report of isolated orbital perineurioma with myxoid changes

Perineuriomas are benign soft tissue neoplasms arising from the peripheral nerve sheath. They account for 1% of all peripheral nerve sheath tumors. To our knowledge, few reported cases of isolated orbital perineurioma are found in the English-written literature, including three cases of hybrid perineurioma/schwannoma or neurofibroma and one case of atypical perineurioma involving the bulbar conjunctiva.

We are reporting a case of orbital perineurioma presenting with right eye proptosis in a 45-year-old male with no other relevant systemic associations. Radiological studies of the right orbit showed an intraconal mass exhibiting benign features and suggestive of cavernous hemangioma. The histopathological diagnosis of perineurioma was unexpected; however, it was confirmed by immunohistochemical staining.

Perineurioma is a benign soft tissue tumor that arises in relation to the peripheral nerve sheath and accounts for 1% of all peripheral nerve sheath tumors. It is mainly composed of spindle-shaped perineurial cells and can be confused with other similar tumors, such as neurofibroma. Glucose transporter-1 (GLUT-1) is the most sensitive immunohistochemical stain used to differentiate perineurioma from other similarly appearing tumors. The accurate diagnosis in our patient was reached only after surgery and tissue diagnosis of the excised lesion.

Orbital surgeons should consider peripheral nerve sheath tumors in the differential diagnosis of intraconal orbital masses. The histopathological confirmation of orbital lesions' diagnoses, especially the ones arising from neural tissues, is the gold standard method, even in the presence of good clinical experience and radiological imaging.