Rathke's cleft cysts are congenital non-neoplastic fluid filled cysts which arise from the embryonic remnants of Rathke's pouch (between anterior and intermediate lobes) and Rathke's pouch is a place where anterior and posterior glands meet which normally closes early in fetal development but a remnant often persists as a cleft. In some cases, this remnant gives rise to a large cyst called the Rathke's cleft cyst or pars intermedia cyst.
In cases where these lesions are large enough, they can compress adjacent structures causing symptoms such as headaches, vision problems or pituitary hormone deficits, but in general, they are asymptomatic.
Another important aspect of this case is not overinterpreting prolactin increase. A mild increase, as in this case, can merely be due to stalk effect (compression of the infundibulum, reducing anterior pituitary suppression by dopamine), or many medications.