Approximately 8 mm to 13 mm above the pituitary gland is the optic chiasm. Upwardly growing pituitary tumors, which reach appropriate sizes, impinge on the anterior notch of the chiasm at its lowest lying aspect. This produces the bitemporal hemianopsia with increased density superiorly. Since tumor growth is usually asymmetrical, the field loss between two eyes is also typically asymmetrical. Mechanical disturbances occur whenever a tumor compresses adjacent structures.
Hormonal manifestations result when hyper-or hyposecretions occur.
Pituitary adenomas are further differentiated by size. Microadenomas have little impact on the visual system or gland function and are defined as intrasellar adenomas that measure up to one centimeter in diameter without sellar enlargement. Macroadenomas present with mass effect symptoms such as headaches and measure larger than one centimeter with generalized sellar enlargement. Secreting tumors are usually diagnosed by general physicians and endocrinologists. Non-secreting tumors are often diagnosed by eye care practitioners because they produce visual symptoms in the absence of systemic signs.