Sellar Cyst (MRI)	

Arachnoid cysts may arise in the suprasellar cistern, or adjacent parasellar regions. Remnants of Rathke's pouch may produce midline epithelial cysts termed Rathke's cleft cysts. These cysts may produce hydrocephalus or compress the optic chiasm, pituitary or infundibulum. These lesions may be difficult to identify because their signal intensities in MR imaging or density in CT is identical to CSF (Fig. 24.20). Rathke's cleft cysts, however, may be hyperintense to CSF on T1-weighted MR images. The diagnosis of arachnoid cysts is made radiologically by noting displacement of the pituitary stalk, chiasm or base of the brain.

Fig. 24.20 Sellar cyst: magnetic resonance imaging. T1-weighted coronal MR image showing a cystic sellar/suprasellar mass and displacement of the optic chiasm. Absence of an identifiable infundibulum differentiates this mass from an ‘empty sella’.