Primary Nonneoplastic Cysts Overview

General Considerations

Overview : Cysts are common findings on MR and CT brain scans. There are many types of intracranial cysts, some significant, some incidental. In this section, we exclude cystic neoplasms (such as pilocytic astrocytoma and hemangioblastoma), solid neoplasms that commonly have intratumoral cysts (such as ependymoma), and tumors that often display central necrosis (e.g., glioblastoma).

We also exclude parasitic cysts (neurocysticercosis, hydatid disease) and cystic brain malformations (Dandy-Walker spectrum) from the discussion. Thus, the focus of this particular section is primary nonneoplastic cysts.

Because the etiology, pathology, and clinical importance of nonneoplastic cysts is so varied, classifying them presents a real challenge. Some neuropathologists typically classify cysts according to the histology of the cyst wall. Others group them according to putative origin or pathogenesis.

In a schema based on pathogenesis, cysts may occur as normal anatomic variants [e.g., enlarged perivascular (Virchow-Robin) spaces] (PVSs), congenital inclusion cysts [e.g., dermoid and epidermoid cysts (ECs)], or lesions derived from embryonic ecto-/endoderm [colloid cysts (CCs) and neurenteric cysts (NCs)]. Of course, there is a group of miscellaneous cysts [such as choroid plexus cysts (CPCs) and nonneoplastic tumor-associated cysts (TACs)] that does not fit nicely into any category.

Neurologists and their neuroradiology colleagues face a very real dilemma: A cystic-appearing lesion is identified on MR or CT. What is it? What else could it be? Histopathology of the cyst wall isn't a practical consideration. What is readily apparent is (1) the anatomic location of the cyst, (2) its imaging characteristics (density/signal intensity, presence or absence of calcification, enhancement, etc.), and (3) the patient's age. The recommended initial approach to analyzing brain cysts is anatomy based.