Basal ganglia glioblastoma with lung adenocarcinoma tumor-to-tumor metastasis and atypical early imaging presentation: illustrative case.

backgroundTumor-to-tumor metastasis is a rare oncological phenomenon in which one neoplasm serves as the recipient for metastatic seeding from another primary tumor. Glioblastoma is an exceptionally uncommon recipient, and no prior reports have described this process occurring in the setting of atypical early imaging presentation. OBSERVATIONS: The authors present an unusual case of a 75-year-old man with hemiplegia and hemianesthesia with initial brain imaging demonstrating a solitary right basal ganglia diffusion-restricting, nonenhancing lesion initially diagnosed as a subacute ischemic stroke. Follow-up imaging triggered by progression of patient's weakness revealed rapid lesion enlargement and new contrast enhancement. Stereotactic biopsy demonstrated features of both high-grade glioma and metastatic pulmonary adenocarcinoma. Subsequent molecular profiling confirmed glioblastoma, IDH-wildtype (CNS WHO grade 4) and concurrent metastatic pulmonary adenocarcinoma. Despite whole-brain radiation therapy, the patient's condition rapidly deteriorated. LESSONS: This case highlights the importance of maintaining diagnostic suspicion for dual pathology in atypical intracranial lesions with progressive, otherwise unexplained symptoms. Furthermore, this case highlights the challenges in recognizing early glioblastoma presenting with nonenhancing, diffusion-restricting imaging features that may closely mimic subacute ischemic stroke. The integration of histopathology, immunochemistry, and molecular profiling is critical in recognizing this entity and carries significant implications for accurate diagnosis and treatment. https://thejns.org/doi/10.3171/CASE25992.