Non-neoplastic Cystic Lesions of the Central Nervous System: Part 1: Developmental Cysts

Magnetic resonance imaging (MRI) is the preferred modality to confirm giant PVS, but they can also be diagnosed with computed tomography (CT.) On both modalities these structures behave similarly to CSF and show no contrast enhancement in the wall.1,3 Epidermoid Cysts Epidermoid cysts account for approximately 1-2% of all intracranial tumors.4 Men and women are affected equally, with peak incidence in the third and fourth decades. Findings on MRI depend on maturation of the cysts but generally epidermoids are hypointense on T1 images and hyperintense on T2 images.6 Distinguishing epidermoid from arachnoid cysts can be challenging with CT; MRI is more useful, as epidermoids are brighter than CSF on fluid attenuation inversion recovery (FLAIR) and, unlike arachnoid cysts, which demonstrate facilitated diffusion owing to their cystic nature, epidermoids typically have reduced diffusion on diffusion weighted imaging (DWI) with low apparent diffusion coefficient (ADC) values (Figure 2). Hormonal disturbances may occur as a result of pituitary and hypothalamic compression.18 Hormonal abnormalities may include hyperprolactinemia, cortisol deficiency, diabetes insipidus, syndrome of inappropriate antidiuretic hormone secretion, and hypogonadism.17 On CT, the density of Rathke cleft cysts varies according to their contents. Cysts may appear hyperdense, isodense, or hypodense.19 These noncalcified lesions have well-defined margins and typically do not show contrast enhancement.20 Their typical appearance on MRI reflects high proteinaceous content with T1 hyperintensity and T2 hypointensity (Figure 7).18 However, the signal intensity varies with the nature of the fluid contents.19,20 Intracystic hemorrhage may result in hyperintense signal on both T1 and T2 imaging.