Imaging of Intracranial Cysts.

PURPOSE OF REVIEW: Intracranial cysts are common findings on both CT and MRI. The majority of intracranial cysts are benign and incidental and without clinical significance. However, a minority are due to infectious, neoplastic, or other pathologic processes.

RECENT FINDINGS: Neuroimaging, in particular brain MRI, can readily identify intracranial cysts. It can often be difficult to characterize the likely histopathology of intracranial cysts based solely on their signal intensity, even when using contrast. However, with the knowledge that most intracranial cysts occur within a fairly narrow anatomic distribution, a concise and specific differential diagnosis can often be developed based primarily on location. The first location-based question to consider regarding intracranial cysts is whether the lesion is intraaxial or extraaxial. Intraaxial cysts should be further characterized as intraparenchymal or intraventricular, and extraaxial cysts should be identified as either midline or nonmidline. Signal characteristics using CT, MRI, or both can help further characterize the cystic process.

SUMMARY: Neurologists should be familiar with the characteristic patterns of intracranial cysts to distinguish between benign and pathologic processes. A systematic approach to the assessment of intracranial cysts based on location and appearance should greatly narrow the differential diagnosis.