Case Report & Case SeriesIDH1 mutant negative ganglioglioma progression to gliosarcoma

•Intracranial gangliogliomas are infrequent tumours that usually portend a benign clinical course.•Correspondingly, secondary gliosarcomas are uncommon, especially in the absence of previous radiation exposure.•At present, a definitive biological relationship between ganglioglioma and gliosarcoma is unknown.•The authors describe an IDH1-negative ganglioglioma that underwent malignant progression to become a secondary gliosarcoma.

Gangliogliomas comprise of less than 1% of all primary brain tumours. Malignant transformation is rare. Correspondingly, secondary gliosarcomas, especially in the absence of previous irradiation exposure is too, exceedingly rare. Recent evidence supports the use of mutant IDH1 testing in suspected adult gangliogliomas as a distinguishing feature between ganglioglioma and early diffuse astrocytoma. The authors report a case of a ganglioglioma (WHO I) in the cingulate gyrus that underwent malignant transformation and propagated into a multi-lesional gliosarcoma (WHO IV glioblastoma variant). A previously well 59-year-old lady presented with first-onset focal seizures secondary to a left cingulate gyrus lesion. Stereotactic biopsy of the lesion demonstrated an IDH1 (R132H) ganglioglioma. The patient remained well until a routine follow-up MRI performed 36 months later showed significant progression of the initial lesion and a new, separate lesion in the left temporoparietal lobe. Surgical excision was performed. The final histology reported a gliosarcoma. In view of the unusual findings, the case is reviewed corroboratively with current disease understanding.