Diffuse glioneuronal tumor in Lynch syndrome: illustrative case.

backgroundLynch syndrome (LS) is an autosomal dominant disorder caused by impaired DNA mismatch repair during the DNA replication process. The condition increases the risk of gastrointestinal and gynecological cancers as well as oligodendrogliomas and astrocytoma. Herein, the authors report the case of a patient with LS with an unusual tumor with features of both glial and neuronal differentiation. OBSERVATIONS: The authors present the case of a 34-year-old female who presented with headaches and was found to have a large right anterior frontal lobe mass with patchy enhancement. The patient underwent a right-sided craniotomy for tumor resection, with final pathology revealing a low-grade-appearing glioneuronal tumor. Subsequent molecular testing showed an MSH2 mutation in the tumor, and germline testing confirmed a diagnosis of LS. The patient was monitored without adjuvant treatment and subsequently had tumor progression 12 months after her index surgery. A re-resection was performed. Since tumors arising in this setting typically have an aggressive course, Ki-67 was measured, showing an increase from 2%-5% to 15%-20%. The patient has since been started on concurrent temozolomide and radiation therapy. LESSONS: Although most glioneuronal tumors typically have an indolent course relative to their diffuse glial counterparts, this case suggests that those arising in the setting of LS can have a worse prognosis. https://thejns.org/doi/10.3171/CASE24811.