Differential considerations included sarcoidosis, lymphoma, metastatic disease, and lymphocytic hypophysitis.

The diagnosis in this case was confirmed via transsphenoidal 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.