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MR images show a diffusely thickened pituitary stalk and a larger than expected pituitary gland for age, which are otherwise normal in signal intensity on T1 and T2 weighted images. The gland and stalk both demonstrate avid enhancement on post-contrast imaging.
Differential considerations included sarcoidosis, lymphoma, metastatic disease, and lymphocytic hypophysitis.
The diagnosis in this case was confirmed via transphenoidal biopsy, which showed a lymphocytic and plasmacytic infiltrate. IgG4 immunohistochemistry demonstrated staining of numerous plasma cells, which was consistent with IgG4-related hypophysitis.
The patient was treated with prednisone and DDAVP with resolution of the imaging findings and good control of his diabetes insipidus. Bulky mediastinal lymphadenopathy thought to be associated with the patient's IgG4 disease also improved following treatment.