May Be Caused by

 Common

Carcinomatosis

Gliomatosis

Leptomeningeal neoplasm

Leukemia

Lymphoma

Melanoma

Meningitis

Subarachnoid hemorrhage

 Uncommon

Cryptococcosis

Polycythemia vera

Sarcoidosis

Seeding from primary neoplasm

Siderosis

Syphilis