MRI of a cystic lactotroph adenoma

[A] Pretreatment, T1-weighted image, pre-gadolinium. [B] Pretreatment, T1-weighted image, post-gadolinium. [C] After cabergoline treatment for 2 months, T1-weighted image, post-gadolinium.
This sellar mass emitted a bright signal before administration of gadolinium (A) but did not enhance afterwards (B), suggesting a cyst. The radiologic diagnosis was a Rathke's cleft cyst. The prolactin concentration, however, was 190 ng/mL, and treatment with cabergoline for 2 months reduced the prolactin concentration to 2.9 ng/mL and greatly reduced the size (C), indicating that this was a cystic lactotroph adenoma.