Rathke's cleft cyst and arachnoid cyst of the sella are rare lesions and are seen as incidental findings. The former is a remnant of the primitive stomodeum. The latter is formed due to maldevelopment of the meninges. They are usually hypointense on T1W, but can have a variable signal as in the following case, due to the difference in content.

Hyperintense on T1W & T2W involving the suprasellar cistern, pushing on the gland from above.
     Chordoma is a destructive tumor which, while being benign, is still locally invasive. It appears hyperintense on T2, isointense on T1 and enhances with Gadolinium.

Hyperintense on T2W, enhancing with contrast, involving clivus and sella.

     Craniopharyngioma arises from squamous cells along the Rathke's cleft. It is a circumscribed cyst with a mural nodule. The usual signal on MRI is hyperintensity on T1 and hyperintensity on T2W.