Pituitary Structural and Vascular Changes with Preserved Hypothalamic Microstructure in Postmenopausal Women with Primary Sjögren’s Syndrome: An MRI Study

(1) Background: This study aimed to evaluate hypothalamic–hypophyseal (HH) axis involvement in Primary Sjögren’s syndrome (pSS) using MRI and assess its relationship with hypothalamic–pituitary–adrenal (HPA) axis dysfunction. (2) Methods: A total of 22 postmenopausal women with pSS and 17 healthy controls were enrolled. Midline sagittal T1-weighted MRI was used to measure pituitary gland height (PGH). Dynamic contrast-enhanced imaging assessed hypothalamic–hypophyseal (HH) microcirculation, while diffusion tensor imaging (DTI) evaluated hypothalamic microstructure. Biochemical variables, including cortisol and complement factors, were measured. Linear regression analysis was performed to identify predictors of PGH. (3) Results: Patients had a mean disease duration of 11.5 ± 6.7 years. PGH was significantly different in patients than in controls (3.6 ± 1.1 mm vs. 4.4 ± 0.6 mm, p = 0.004). Cortisol levels were also reduced (8.9 ± 4.6 µg/dL vs. 12.6 ± 4.7 µg/dL, p = 0.040), while ACTH levels were not significantly different. Dynamic imaging demonstrated delayed enhancement of the anterior pituitary lobe. DTI revealed no hypothalamic microstructural abnormalities. PGH was positively associated with C3 (p = 0.029). (4) Conclusions: pSS is associated with pituitary structural and functional alterations consistent with HPA axis hypofunction, likely reflecting immune-mediated pituitary involvement with preserved hypothalamic integrity.