CNS lymphoma involving the trigeminal nerve is a rare condition which presents as a cavernous sinus lesion. It may mimic the radiological appearance of other lesions, and biopsy is essential before considering empirical radiotherapy for lesions in this region.

A 47-year-old man presented with aggravating left facial pain and hypesthesia within all three divisions of the trigeminal nerve. Magnetic resonance imaging (MRI) revealed a swollen left trigeminal nerve with gadolinium homogenous enhancement. An open biopsy had to be taken from two different locations of the tumor via the lateral suboccipital approach followed by subtemporal approach because adequate specimen volume was not obtained for definitive diagnosis at the first surgery. Histopathological examinations with flow cytometric analysis revealed diffuse large B cell lymphoma. Chemotherapy followed by whole-brain radiation therapy was effective. No recurrence was observed during a 15-month follow-up period.

This is a rare clinical presentation of malignant lymphoma of the trigeminal nerve. It is difficult to establish a correct diagnosis of trigeminal nerve lesions during the initial stages without biopsy. Therefore it is important that a sufficient specimen should be taken for biopsy without hesitation in order to diagnose and treat rapidly. The most suitable operative approach must be selected in trigeminal nerve lesions considering functional preservation, operative difficulty, preference of each surgeon, and quantity of specimen to be removed ¹⁾.