Rathke cleft cyst - with a fluid-fluid level
Elevated prolactin. Headache with no visual disturbance, ? pituitary adenoma.
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Cystic mass in the pituitary with a fluid/fluid level on the axial scan (arrow). Peripheral enhancement is the normal gland being compressed by the cyst, not the cyst wall. On T2 coronal there is lower signal intensity sediment and in the higher signal supernatant there is a "dot sign" (arrow), seen commonly in Rathke cysts
Fluid/fluid levels in Rathke cysts are uncommon but well recognised. It might be due to recent haemorrhage but can also be a feature of proteinaceous debris within the cyst fluid.
Elevated prolactin is not due to the cyst excreting prolactin, rather a mass that compresses the pituitary stalk can lead to interruption of dopamine flow from the hypothalamus through the hypophyseal-portal circulation to the anterior pituitary. Unlike other hypothalamic control of the pituitary, control of prolactin secretion is primarily inhibitory.