Leptomeningeal fibrosis and the delayed diagnosis of a central nervous system neoplasm (primitive neuroectodermal tumor).

We report a unique case of histologically confirmed meningeal fibrosis in a child who had progressive ischemic neurologic symptoms before the delayed diagnosis of an intracranial primitive neuroectodermal tumor (PNET) was made > 1 year after initial presentation. This pathology has previously been described after neurosurgical procedures, subarachnoid hemorrhage, cranial irradiation, and with no known etiology, but has never been reported in association with a central nervous system neoplasm. In a 6-year-old boy with headaches of several months' duration MRI demonstrated hydrocephalus, a right cerebellopontine angle cyst, and dural enhancement. Biopsies of the thickened meninges taken when the cyst was surgically fenestrated demonstrated only fibrosis with no evidence of infection, hemorrhage, or neoplasm. In the next 6 months, the child had two acute stroke-like episodes with alternating hemiparesis that gradually improved. There were ischemic changes in the diencephalon on MRI. Repeat dural biopsies were unchanged. One year after the initial operation, a left hemiparesis recurred and MRI demonstrated multiple intracranial masses in the cerebral cortex, cerebellum, suprasellar area, and cauda equina. After surgical resection, the cortical mass was found to be a PNET. All the lesions regressed after treatment with radiation and chemotherapy. We hypothesize that the meningeal fibrosis represented a "desmoplastic" reaction to an occult PNET, similar to the fibrous proliferation with cerebellar desmoplastic medulloblastoma except for the extent of the meningeal involvement and the long undetected parenchymal tumor. The mechanism of the ischemic brain injury was most likely vascular involvement by the fibrotic process, either directly or by predisposition to vasoconstriction.