SUN-039 A Misguided Attack on the Pituitary Stalk: A Case of Isolated Lymphocytic Neuroinfundibulitis with Hypothalamitis

Abstract Disclosure: L. Xu: None. B. Force: None. J. Kaplan: None. Introduction: Pituitary stalk lesions are rare endocrine disorders with varied etiologies, including neoplastic, infectious, inflammatory, drug-induced and idiopathic. Here we present a case of isolated neuroinfundibulitis with hypothalamitis that highlights the critical role of a multidisciplinary approach to diagnosis and management.Case Presentation: A previously healthy 64-year-old woman presented with rapidly progressive bilateral vision loss and panhypopituitarismwith arginine vasopressin deficiency (AVP-D). Magnetic resonance imaging (MRI) brain showed a 2.4 cm homogeneously enhancing sellar/suprasellar mass with infundibular thickening, optic chiasm compression and hypothalamic edema. She was optimized on hydrocortisone, levothyroxine and desmopressin. Given rapid vision loss, she underwent transsphenoidal surgery (TSS) which showed a grossly normal adenohypophysis but a thickened and fibrotic pituitary stalk. Pathology showed robust lymphocytic and few histiocytic infiltrates, without a malignant or infectious process. Extensive laboratory analyses (quantiferon gold, anti-nuclear antibody, anti-neutrophil cytoplasmic antibody, thyroid peroxidase antibody, angiotensin converting enzyme(ACE), and immunoglobulin(IgG)-G4), cerebrospinal fluid (CSF) analyses (ACE, IgG index, protein electrophoresis, flow cytometry) and imaging (chest, abdominopelvic and spinal) did not reveal a systemic process. After a thorough evaluation by endocrinology, neurosurgery, neuropathology and neurology, the patient was diagnosed with isolated lymphocytic neuroinfundibulitis with hypothalamitis.She was started on a high-dose corticosteroid taper with remarkable regression of the lesion in 3 months and stabilization of vision. Due to the high risk of relapse, she was switched to mycophenolate mofetil as a steroid-sparing agent. While her pituitary deficiencies persisted, neuro-ophthalmological surveillance showed continued improvement in vision.Discussion: Pituitary stalk lesions are a diagnostic challenge for clinicians. They can be distinguished from pituitary adenomas by the pre-operative presence of AVP-D and MRI findings (homogenously enhancing symmetric mass, pituitary stalk thickening, hypothalamic edema). Careful evaluation of etiologies is a must, including immunotherapy-induced, metastases, lymphoma, germinoma, craniopharyngioma, tuberculosis, Langerhans cell histiocytosis or neurosarcoidosis,to highlight a few. In patients with rapidly progressive mass effects, TSS can provide a quick diagnostic evaluation. High-dose glucocorticoids are effective in 50% of cases and steroid-sparing agents (azathioprine, rituximab, mycophenolate mofetil, etc.) can be used to reduce risk of relapse. This case emphasizesthe role of a multidisciplinary approach in achieving an accurate diagnosis and optimal management. Presentation: Sunday, July 13, 2025