To report a case and highlight the diagnostic challenges of Primary Skull Base Lymphoma.

Primary skull base lymphoma is an exceedingly rare manifestation of extranodal lymphoma. Vague presentation with B-symptoms, headaches and sequential involvement of different cranial nerve as well as the non-specific imaging findings makes it a diagnostic challenge.

We report a case of a 56-year-old male who presented with a 3-week history of progressive left facial pain followed by facial weakness, he had no double vision and no systemic symptoms like fevers, chills or weight loss. On exam, he had hyperesthesia over the V1/V2/V3 distribution of left trigeminal nerve and left lower motor neuron facial palsy.

CT Head was reported as normal, and the patient was started on Prednisone and Valaciclovir for presumed Bell’s palsy. MRI Brain was obtained due to worsening symptoms and revealed a homogenously enhancing mass involving the left trigeminal nerve which extends through the foramen ovale (In retrospect was visible on CT Head) and a 3mm enhancing nodule at the fundus of the left internal auditory canal. CSF analysis, cytology and flow cytometry were unremarkable. Pathologic analysis of a trans-sphenoidal biopsy revealed diffuse large B-cell Lymphoma. Whole-body PET scan and bone marrow biopsy confirmed isolated skull base involvement.

Primary Skull Base Lymphoma is a rare etiology of Multiple Cranial Neuropathies. Diagnostic challenges include: 1-Nonspecific symptomatology with diplopia(52%) being the most common manifestation and trigeminal nerve hyperesthesia, facial weakness, headaches, B-symptoms and hearing loss as less common findings. 2-CSF is diagnostic in only 25% of the cases. 3-MRI findings of diffusion restriction, homogenous post-contrast enhancement and dural infiltration are suggestive but inconsistent findings. 4-The diagnostic yield of pathology could be affected by steroids. Recognition of this diagnosis is crucial as these tumors tend to be chemo-sensitive and potentially treatable although long-term outcomes are not known.