Giant pituitary tumors are defined as pituitary adenomas ≥ 4 cm in diameter, which is one way to classify pituitary tumors. In addition to giant pituitary tumors, they can also be classified as pituitary macroadenomas as well as microadenomas of the pituitary gland. Microadenomas of the pituitary gland are one of the more frequent clinical types. Giant pituitary tumors often have symptoms of tumor compression. If the tumor grows toward the front of the skull, it often compresses the optic nerve and the optic cross, so a large percentage of cases will have varying degrees of vision loss, and more than half of patients will have accompanying visual field loss. More than half of the patients will have visual field loss. The loss of vision can be in one eye or both eyes, and in severe cases, patients may become blind, and may have temporal hemianopia on one or both sides.