5086 Approaching the Enigma: Unveiling a Pituitary Stalk Lesion with Imaging and Hormonal Patterns

Abstract Disclosure: N. Rodriguez-Morales: None. P. Guido: None. Background: Pituitary stalk lesions (PSL) pose a diagnostic dilemma for endocrinologists. Multiple studies have attempted to associate hormonal imbalances and imaging patterns to a specific etiology (1,2). However, the diagnosis remains a mystery on many occasions. We describe a case of secondary hypogonadism and central DI attributed by a PSL. Clinical Case: A 39-year-old male presented with symptoms of hypogonadism and polyuria. Initial workup was consistent with secondary hypogonadism; decreased free and total testosterone levels (1.8 pg/dL and 9 ng/dL, n>35 pg/dL, n>250 ng/dL), LH (0.2 mIU/mL, n>1.5 mIU/mL), and FSH (<0.7 mIU/mL, n>1.6 mIU/mL). The remaining anterior pituitary hormones were within normal limits. The patient was also polyuric (6.5L urine output in 24hr). HgbA1c was normal. Urine Na, urine Osm demonstrated water diuresis (13 mmol/L and 54 mOsm/kg, respectively). A water deprivation test was performed. Initial urine Osm after water restriction was 119 mOsm/kg, which more than tripled to 575 mOsm/kg after administration of desmopressin, diagnostic of central DI. Pituitary MRI showed a well-circumscribed thickening of the pituitary stalk (6x6x5mm), with uniform enhancement. Evaluation for etiology to rule out germ cell tumor, lymphoma, sarcoidosis, opportunistic infection, tuberculosis, Langerhans cell histiocytosis showed a normal serum hCG, HIV, ACE, LDH, AFP. A lumbar puncture demonstrated normal cytology and was negative for AFB. Whole body bone scintigraphy and chest X-ray were normal. Pituitary deficits were treated with hormone replacement (testosterone and desmopressin), and a repeat MRI showed a stable lesion. Conclusion: Noninvasive testing is key to the evaluation of a pituitary stalk lesion. Careful consideration of inflammatory, infectious, and neoplastic etiologies along with attention to pituitary deficits is very important. Our patient most likely has a craniopharyngioma based on data from other case series (1,2). This case serves to bring additional data to the body of literature on this complicated clinical scenario. References: 1. Turcu AF, Erickson BJ, Lin E, et al. Pituitary stalk lesions: The mayo clinic experience. Journal of Clinical Endocrinology and Metabolism. 2013;98(5):1812-1818. doi:https://doi.org/10.1210/jc.2012-41712. 2. Sbardella E, Joseph R, Bahram Jafar-Mohammadi, Isidori AM, Cudlip S, Grossman A. Pituitary stalk thickening: the role of an innovative MRI imaging analysis which may assist in determining clinical management. European journal of endocrinology. 2016;175(4):255-263. doi:https://doi.org/10.1530/eje-16-0455 Presentation: 6/1/2024