CSF seeding of primary brain tumors on CT scan

25 patients with CSF seeding of primary brain tumors were evaluated with computed tomography (CT). The primary tumors consisted of 8 gliomas (astrocytoma, glioblastoma), 6 medulloblastomas, 2 ependymomas, 8 pinealomas, and 1 lymphoma. The CT pattern, the location of CSF seeding, and the degree of hydrocephalus were examined. CSF seeding occurred in most cases of malignant tumors; that is, in 55% of those with medulloblastomas. A progressive ventricular enlargement was noted in 18 of the 21 patients with serial CT studies (86%); it was closely correlated with the degree of CSF seeding. In patients with gliomas, ventricular seeding was more common than subarachnoid seeding. Usually, the CT pattern of seeding was ''linear''. Most of the gliomas directly invaded the ventricular system, and metastases occurred relatively near the primary site. On the other hand, metastases of medulloblastomas in the basal cisterns were more common than in the ventricular system. Also they tended to form large nodules around the subarachnoid space. Metastases of pinealomas occurred in either the subarachnoid space or the ventricular system, and they showed slightly higher density before contrast administration. The seeding patterns of pinealomas were various on postcontrast CT.