One condition that can result from damage to the pituitary gland is Secondary Hypothyroidism, which isn't always picked up by a simple Thyroid test; as the linked page below mentions, TSH tests sometimes come out normal. I've found that in some clinics, you have to specifically request to have T3 and T4 tests done. You can also get pituitary hormones measured, but I believe you have to see an Endocrinologist for these tests.

There is a helpful write-up here:

http://endocrinesurgery.ucla.edu/pat...secondary.html