Infantile giant intracranial-extracranial communicating mixed germ cell tumor with ARID1B gene mutation: a case report.

Congenital intracranial-extracranial communicating mixed germ cell tumors (MGCTs) are extremely rare in infants, with no standardized treatment protocol. We report a 2-month-old female infant with giant congenital intracranial-extracranial communicating MGCT accompanied by typical "crater-like" skull defect. Preoperative serum alpha-fetoprotein (AFP) was significantly elevated, while β-human chorionic gonadotropin (β-HCG) was within normal range. Maximal safe resection was performed, and pathology confirmed mixed germ cell tumor (immature teratoma WHO grade 3 + yolk sac tumor). Next-generation sequencing identified a novel ARID1B c.1628C>G (p.A543G) somatic mutation, previously unreported in pediatric intracranial MGCTs. Postoperative imaging confirmed subtotal resection with continuous AFP decline. No tumor recurrence was observed during 3-month follow-up. This case expands the genomic mutation spectrum of pediatric intracranial MGCTs and supports maximal safe resection as first-line treatment for this rare infantile tumor.