Exophytic Cerebral Hemispheric Low-Grade Glioma: Unusual Growth Pattern of Common Central Nervous System Tumor

Exophytic growth (EG), wherein the tumor mass grows beyond the neuraxial boundary formed by pia mater, remains a rare pattern of glioma growth. It has been described in gliomas at several locations like the brainstem, cerebellum, suprasellar area, spinal cord, and insula. However, EG in hemispheric grade 2 astrocytomas, particularly affecting the convexity subarachnoid space, as against the more spacious basal subarachnoid space, is exceedingly rare. To the best of our knowledge, there is only 1 such case reported in the English literature. Due to the extreme rarity, little is known about these tumors, particularly the mechanisms underlying the EG and their possible clinical implications.

A 32-year-old woman presented with partial motor seizures without any neurologic signs. On magnetic resonance imaging of the head, a nonenhancing, T2-hyperintense, right frontal lobe lesion was noted. The majority of the lesion was occupying the adjacent subdural space while still remaining in continuity with the intra-axial globular component. During surgery, the exophytic nature of the lesion was confirmed. We performed maximal resection of the exophytic portion with subtotal excision of the intra-axial component. She recovered uneventfully after surgery and subsequently received external beam radiotherapy for the residual tumor.

Although extremely rare, cerebral hemispheric grade 2 astrocytomas may have an EG pattern. The exact mechanisms underlying this are not clearly known. More such cases need to be reported so that we can decipher the true nature of these tumors.