The differential diagnosis of nonpituitary sellar masses is broad; differentiating among potential etiologies may not always be straightforward because many of these lesions, tumorous and nontumorous, may mimic the clinical, endocrinologic, and radiologic presentations of pituitary neuroendocrine tumors
((Freda PU, Post KD. Differential diagnosis of sellar masses. Endocrinol Metab Clin North Am. 1999 Mar;28(1):81-117, vi. doi: 10.1016/s0889-8529(05)70058-x. PMID: 10207686.)).

The differential diagnosis of pituitary metastases is broadly that of pituitary region masses, and generally can be narrowed depending on the morphology of the lesion. 

Solid and enhancing pituitary region masses has a differential which includes: 

    pituitary neuroendocrine tumor
    craniopharyngioma (papillary type)
    meningioma
    lymphocytic hypophysitis
    lymphoma

Nodular thickening and enhancement of the infundibulum have a differential that includes 1: 

    CNS tuberculosis
    Langerhans cell histiocytosis (Eosinophilic granuloma)
    sarcoidosis
    lymphocytic hypophysitis