MON-080 Cushing Disease Secondary To Rathke’s Cleft Cyst

Abstract Disclosure: S. Shrestha: None. K.H. Corpuz: None. J. Gopalakrishnan: None. H. Yeh: None. I. Shafiq: None. J. Hughes: None. Background: Rathke’s cleft cyst (RCC) is a rare benign sellar lesion originating from the remnants of Rathke’s pouch. Most RCCs are asymptomatic, and most symptoms are secondary to the mass effect of the lesion. Only 2 cases of Cushing disease secondary to RCC have been reported. We present a case of RCC presenting with biochemically confirmed Cushing disease. Case description:A 35-year-old female with a history of migraine presented to the clinic for evaluation of pituitary function. She was found to have an incidental pituitary lesion on MRI that was done for worsening headache with diplopia on lateral gaze. Pituitary lesion was cystic, sized 1.0 x 0.9 x 1.2 cm, with T1 hyperintensity and T2 hypointensity, which was initially suspected to be a possible pituitary hemorrhage. Initial blood tests for hypopituitarism were normal, with normal insulin-like growth factor-1 (IGF-1), Prolactin (PRL), follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), and free T4. Secondary adrenal insufficiency was ruled out after a normal cosyntropin stimulation test. She was being monitored with an annual brain MRI with stable findings. On follow-up, she reported unintentional 15-pound weight gain, increased hair loss, fatigue, memory loss, and acne. Repeat pituitary hormonal evaluation showed elevated adrenocorticotropic hormone (ACTH) (86 pg/ml, ref: 7.2-63) with normal baseline cortisol (14 ug/dl, ref: 6.7-22.6). The 24-hour urinary cortisol test (63 ug/24 hr, ref: 3.5-45), late-night salivary cortisol test (126 ng/dl, ref: <100), and a 1 mg dexamethasone suppression test (Serum cortisol level 8.8 ug/dl) were all elevated. She underwent transsphenoidal resection of the lesion, which showed an epithelial lining, representing RCC with negative ACTH immunostaining. The headache and ACTH improved after surgery. Discussion:Most cases of pituitary adenomas in association with RCCs that have been reported were nonfunctional, prolactinomas, or growth hormone-secreting adenomas. Only 2 other cases of Cushing disease secondary to RCC without an associated pituitary adenoma were reported in the past. The pathophysiology of RCC-caused overproduction of ACTH remains to be understood. RCCs typically present on MRI with a well-demarcated, homogeneous lesion with variable intensity depending on cyst content. In our case, the pituitary lesion was initially considered to be a pituitary hemorrhage, and only hypopituitarism blood tests were performed. In cases presenting with pituitary lesions not typical for pituitary adenoma, hormonal hypersecretion evaluation should be considered in addition to hypopituitarism workup, and repeated if there is clinical suspicion. Presentation: Monday, July 14, 2025