6400 An Unusual Presentation of Silent Corticotroph Pituitary Macroadenoma

Abstract Disclosure: N. Mon: None. V. Lohano: None. B. Williams: None. N. Lehman: None. R. Kulkarni: None. S.L. Mokshagundam: None. Silent Corticotroph Pituitary Adenomas (SCA) are a rare group of nonfunctioning pituitary adenomas (NFA) comprising 3-6% of all pituitary adenomas and up to 20% of corticotroph adenomas. SCA are biologically and clinically distinct from Cushing disease and NFA. SCA present with headache, visual field impairment, hypopituitarism, and pituitary apoplexy. We present a case of SCA with the initial presentation of syncope with undetectable ACTH and very low AM cortisol level.A 67 year-old-female was incidentally found to have a pituitary macroadenoma in MRI brain for syncope work up in 2017. MRI reported 1.4 x 1.2 x 1.3 cm sellar mass with suprasellar extension, minimal mass effect on the optic chiasm and no cavernous sinus invasion. Initial labs showed ACTH <5 (7.2-63.3 pg/mL), AM cortisol 0.8 (6-28ug/dl), Prolactin 101.1 (3.3-27 ng/mL), TSH 0.08 (0.34-5.60 uIU/mL), Free T4 0.6 (0.58-1.64 ng/dL), FSH 1.7 (2-5 mIU/mL), LH <0.2 (1-13 mIU/mL), IGF-1 33 ( 41-279 ng/mL). ACTH stimulation test: cortisol 0.5 ug/dl at baseline, 5.8 ug/dl at 60min. She was diagnosed with panhypopituitarism and hyperprolactinemia due to stalk effect. Hydrocortisone and Levothyroxine (LT4) were started. She underwent pituitary macroadenoma resection for optic chiasm decompression in 2017. Pathology reported pituitary neuroendocrine tumor (pitNET), but no immunostaining was done at that time. Follow up MRI in 2019 showed residual pituitary tumor. In 2023, she endorsed headaches, mood changes, fatigue and weight gain. Physical exam was unremarkable except BMI 34.75. Prolactin, Free T4, IGF-1 were normal. MRI in 2023 revealed recurrent and enlarging pituitary adenoma (1.9 x 1.4 x 1.6 cm) with suprasellar extension, abutting the optic chiasm, and left cavernous sinus invasion with internal carotid artery encasement. She underwent revision transsphenoidal resection of pituitary tumor to decompress the optic chiasm with plan for subsequent focused radiation to the cavernous sinus portion. Postoperative period was uneventful and hydrocortisone and LT4 were continued on discharge. Final pathology reported silent corticotroph lineage pitNET with low Ki67, immunostaining positive for TPIT, CAM5.2, and negative for ACTH. ACTH-negative SCA are a rare subtype and more likely to have lower ACTH levels, and multiple microcysts on MRI than ACTH-positive SCA. New WHO classification of pitNET highlights the histological typing and subtyping based on immunostaining of pituitary lineage transcription factors as the cornerstone for accurate classification. SCA are more biologically aggressive tumors with a high propensity of recurrence and resistance to conventional treatment. TPIT and ACTH immunostaining significantly improved the diagnosis of SCA and thereby close clinical follow up for early recognition and management of SCA recurrence. Absence of serum markers of recurrence makes this challenging. Presentation: 6/1/2024