Malignant lymphoma arising in the cerebral parenchyma adjacent to a parasagittal meningioma.

A 70-year-old woman with an asymptomatic parasagittal meningioma had been under observation with follow-up imaging for 2 years. She gradually developed motor weakness in the left hand. Magnetic resonance (MR) imaging disclosed a newly developed well-enhanced area in the cerebral parenchyma adjacent to the stable original meningioma. The new lesion was enhanced more intensely and less well demarcated. We suspected that the meningioma had enlarged into the brain parenchyma, although MR imaging suggested a border between the extra-axial and intra-axial portions. Craniotomy was performed. Two separate tumors were identified with quite different histological features. The extra-axial tumor was identified as benign transitional meningioma and the intra-axial tumor as diffuse large cell type malignant lymphoma. Immunostaining revealed the lymphoma had B cell origin. After surgical resection, stereotactic radiosurgery was performed for the residual lymphoma. The original site of the lymphoma remained free from relapse, but another lesion developed in the right frontal lobe 3 months later and chemotherapy was performed. The main concern for follow-up imaging of asymptomatic meningioma without surgical resection is growth of the meningioma. However, development of new different tumors is possible, although thought to be rare.