Collision tumors at the skull base: unveiling a somatotroph pituitary adenoma coexisting with a petroclival meningioma. Illustrative case.

backgroundCollision tumors, defined as the coexistence of two distinct neoplasms with independent origins in the same anatomical location, are rare entities that pose diagnostic and therapeutic challenges. While pituitary adenomas and meningiomas are individually common intracranial tumors, their coexistence as collision tumors is exceptionally uncommon, with only a handful of cases reported in the literature. Even fewer involve growth hormone-secreting pituitary adenomas, and none have involved sphenoid wing meningiomas to date. OBSERVATIONS: The authors present the case of a 54-year-old female who presented with progressive expressive aphasia, right-sided weakness, gait imbalance, and memory decline. Initial MRI demonstrated a large dural-based mass involving the left sphenoid wing and sellar region; the tumor was resected in staged procedures and diagnosed as a meningothelial meningioma. Fourteen months later, follow-up imaging revealed a distinct sellar lesion. Endoscopic endonasal resection demonstrated a pituitary adenoma extensively involved by the meningioma, establishing the diagnosis of a collision tumor. LESSONS: The authors highlight the importance of recognizing the potential for dual pathology in complex intracranial tumors. This case describes the limitations of preoperative imaging in diagnosing collision tumors. Careful long-term surveillance and multidisciplinary management are essential for accurate diagnosis and optimal treatment of collision tumors. https://thejns.org/doi/10.3171/CASE25709.