No MRI evidence of a pituitary mass lesion.
The ventricles are enlarged consistent with obstructive hydrocephalus with marked lateral and third ventriculomegaly. The floor of the third ventricle is bowed into the suprasellar region. No evidence of transependymal edema, however, the cerebral cortical sulci appear mildly effaced. The sella appears "empty" with a prominent suprasellar cistern and pituitary tissue compressed along the floor of the sella. No pituitary mass lesion is identified.
The cerebellar tonsils extend 20 mm below the foramen magnum with marked crowding at the foramen magnum with mass effect on the upper cervical cord and brainstem. No evidence of syrinx within the upper cervical cord.
Impression:
Obstructive hydrocephalus. Chiari 1 malformation. It is unclear if the tonsillar descent is primary or secondary to hydrocephalus.