Which cause of hyperthyroidism is associated with bitemporal hemianopsia due to a pituitary mass?

Which cause of hyperthyroidism is associated with bitemporal hemianopsia due to a pituitary mass?

• A. Graves disease
• B. Toxic multinodular goiter
• C. TSH-secreting pituitary adenoma
• D. Toxic adenoma

Answer: (C)

This item tests recognizing a pituitary source of hyperthyroidism and its mass effect on the optic pathways. A TSH-secreting pituitary adenoma causes secondary (central) hyperthyroidism: the tumor makes thyroid-stimulating hormone, so thyroid hormones (T4 and T3) are elevated while TSH is inappropriately normal or high rather than suppressed. As the adenoma enlarges in the sellar region, it can compress the optic chiasm, leading to bitemporal hemianopsia. In contrast, Graves disease, toxic multinodular goiter, and a toxic adenoma cause primary hyperthyroidism through increased thyroid hormone production; the resulting excess thyroid hormones suppress TSH via negative feedback, and they do not create a pituitary mass that would press on the optic chiasm, so visual field defects are not expected.

This item tests recognizing a pituitary source of hyperthyroidism and its mass effect on the optic pathways. A TSH-secreting pituitary adenoma causes secondary (central) hyperthyroidism: the tumor makes thyroid-stimulating hormone, so thyroid hormones (T4 and T3) are elevated while TSH is inappropriately normal or high rather than suppressed. As the adenoma enlarges in the sellar region, it can compress the optic chiasm, leading to bitemporal hemianopsia.

In contrast, Graves disease, toxic multinodular goiter, and a toxic adenoma cause primary hyperthyroidism through increased thyroid hormone production; the resulting excess thyroid hormones suppress TSH via negative feedback, and they do not create a pituitary mass that would press on the optic chiasm, so visual field defects are not expected.