Differential Diagnosis:
In this case, differential diagnoses include primary hypothyroidism with
pituitary hyperplasia, as chronic elevated TSH from untreated
hypothyroidism can cause pituitary enlargement. A TSH-secreting
pituitary adenoma (TSHoma) is less likely, as thyroxine therapy
normalized TSH, which wouldn’t occur with a true TSHoma. The stable,
non-enhancing lesion may represent a non-functional pituitary
microadenoma coexisting with hypothyroidism, while secondary
hypothyroidism due to compression by the lesion is improbable given the
lesion’s small size and lack of compression. Granulomatous diseases,
like sarcoidosis, can involve the pituitary, causing headaches and
endocrine dysfunction, though they often present with more extensive
hormonal deficiencies than isolated TSH elevation.