Diffuse Infiltrating Perisellar Mass Mimicking Polyneuritis Cranialis.

[BACKGROUND] Subacute oculomotor dysfunction encompasses a broad differential diagnosis, including autoimmune, infectious, vascular, and neoplastic etiologies. Primary skull base diffuse large B-cell lymphoma (DLBCL) is a rare but treatable cause of cranial nerve dysfunction and may present subtly on conventional neuroimaging.

[METHODS] We report an 80-year-old man with subacute diplopia, dysfunction of multiple cranial nerves, left-sided ptosis, and headache. Diagnostic workup included cranial imaging, cerebrospinal fluid (CSF) analysis with cytology and flow cytometry, neurophysiological studies, serum diagnostics, and dedicated MRI of the skull base. Transsphenoidal biopsy was performed following identification of an infiltrative lesion.

[RESULTS] Initial investigations including cranial CT, CSF analysis, and serum diagnostics were unremarkable. Dedicated skull base MRI revealed a diffuse infiltrating mass involving the clivus, petrous bone, occipital condyles, and perisellar/posterior pituitary region, with anatomical correlation to multiple cranial nerves. Mildly elevated prolactin levels suggested a stalk effect. Histological analysis confirmed DLBCL (NOS, GCB type). Treatment with corticosteroids followed by dose-adjusted R-CHOP resulted in complete clinical remission and radiologically confirmed tumor regression.

[CONCLUSIONS] This case illustrates a rare presentation of primary bony skull base DLBCL with perisellar infiltration, highlighting the diagnostic challenges of complex oculomotor dysfunction. Dedicated skull base MRI is essential in the workup of unexplained cranial neuropathy. CSF-based molecular markers may complement the diagnostic approach in similar presentations.