Pituitary adenomas are benign tumors of the anterior pituitary gland that cause disease through hormone hypersecretion, mass effect, or both. Functioning adenomas produce excess hormones: prolactinomas (most common, 40%) cause galactorrhea and amenorrhea; GH-secreting adenomas cause acromegaly (adults) or gigantism (children); ACTH-secreting adenomas cause Cushing disease; and TSH-secreting adenomas cause central hyperthyroidism. Non-functioning adenomas (30%) present with mass effect symptoms: compression of the optic chiasm causes bitemporal hemianopsia (loss of peripheral vision in both eyes), while compression of the normal pituitary causes hypopituitarism. Macroadenomas (≥10 mm) are more likely to cause visual field defects and headaches, while microadenomas (<10 mm) typically present with hormonal symptoms alone.