A case of a pineal parenchymal tumor of intermediate differentiation with bifocal lesions differentiated by negative placental alkaline phosphatase in the spinal fluid

Placental alkaline phosphatase (PLAP) in the spinal fluid is helpful for the diagnosis of intracranial germinomas. Bifocal lesions involving the pineal and pituitary regions have also been reported as characteristic findings of intracranial germinomas. We present a rare case of a 15-year-old boy with a pineal parenchymal tumor of intermediate differentiation (PPTID) with bifocal lesions negative for PLAP. Magnetic resonance imaging of the brain revealed bifocal mass lesions in the pineal and suprasellar regions and non-communicating hydrocephalus. We initially suspected a germinoma based on imaging findings, but all tumor markers, including PLAP, in the spinal fluid were negative. Based on these results, germinoma was considered less likely, and an endoscopic third ventriculostomy and endoscopic tumor biopsy were performed for diagnosis. The histopathological diagnosis was PPTID, corresponding to World Health Organization grade 3, in both pineal and suprasellar specimens. A craniotomy for tumor removal was performed, resulting in total resection. PLAP is known to have high sensitivity and extremely high negative predictive value for germinomas. Although bifocal lesions highly suggest germ cell tumors, there are exceptions, as in the present case. This case suggests that PLAP measurements are useful for differentiation, leading to appropriate treatment strategies.