Extended endoscopic endonasal transplanum-transtuberculum surgery for optic pathway-hypothalamic glioma presenting with tonsillar herniation and syringomyelia: illustrative case.

backgroundOptic pathway-hypothalamic glioma (OPHG) typically presents as a suprasellar lesion, and posterior fossa involvement, such as tonsillar herniation or syringomyelia, is extremely rare. The underlying mechanism and optimal surgical strategy for such cases remain unclear. OBSERVATIONS: A teenage patient with a history of partial tumor resection and ventriculoperitoneal shunt placement presented with tumor regrowth extending into the basal cistern, resulting in marked narrowing of the prepontine cistern, secondary brainstem displacement, tonsillar herniation, and syringomyelia. Extended endoscopic endonasal transplanum-transtuberculum surgery was performed to decompress the suprasellar and basal cisterns of the brain. Postoperatively, adequate tumor debulking was achieved with preservation of the optic apparatus and pituitary structures. Brainstem compression was relieved, and syringomyelia showed marked improvement without new neurological deficits. LESSONS: OPHG can cause Chiari-like pathophysiology by obstructing CSF pathways at the suprasellar and basal cistern levels. Extended endoscopic endonasal surgery provides a safe, minimally invasive route for direct ventral decompression, restoration of CSF dynamics, and effective management of selected OPHG with posterior fossa manifestations. https://thejns.org/doi/10.3171/CASE2623.