Mature teratoma with a germinoma component presenting with undetectable placental alkaline phosphatase in cerebrospinal fluid: illustrative case.

BACKGROUND

Diagnosing intracranial mixed germ cell tumors (GCTs) can be challenging due to intratumoral heterogeneity. Placental alkaline phosphatase (PLAP) in the cerebrospinal fluid (CSF) is a highly sensitive and specific marker for identifying pure germinomas and germinoma components within mixed GCTs.

OBSERVATIONS: The authors present the case of a 6-year-old boy presenting with a 5-day history of vomiting and headache. Magnetic resonance imaging revealed a heterogeneously enhanced mass with cystic areas in the pineal region. Preoperative serum levels of alpha-fetoprotein and human chorionic gonadotropin, as well as CSF PLAP levels, were not elevated, leading to a preliminary diagnosis of mature teratoma. The tumor was completely resected, and pathological examination of the resected tissue confirmed a mature teratoma with germinoma components. Given the diagnosis of mixed GCT with a germinoma component, the patient underwent postoperative radiation chemotherapy. There has been no recurrence after 8 years of follow-up.

LESSONS: In this case, the preoperative CSF PLAP level failed to predict the presence of a germinoma component. This report highlights a potential limitation of CSF PLAP as a diagnostic marker, noting that CSF PLAP may be undetectable if the germinoma is confined to a localized area. https://thejns.org/doi/10.3171/CASE24588.