Growths on the pituitary gland are usually benign tumors although a malignancy is possible yet rare. The most common growth on the pituitary gland is a pituitary adenoma. Other benign tumors may stem from areas around the pituitary gland and invade the pituitary parenchyma or apply pressure on the gland. Benign pituitary hyperplasia is where the pituitary gland enlarges but this is not a result of any mass (tumor, abscess, cyst). It does however mimic a secretory adenoma and result in hyperpituitarism (overactive pituitary functioning). These masses can lead to a host of pituitary gland disorders or remain silent for long periods.
Types of Pituitary Tumors
Pitiutary adenomas are slow-growing benign tumors of the pituitary gland and the most common type of pituitary tumor. These tumors may be referred to as macroadenomas or microadenomas based on the size of the mass – either less than 10mm in diameter (microadenoma) or greater than 10mm in diameter (macroadenoma).
Pituitary adenomas may be described as functional or non-functional. This means that the tumor is secretory or non-secretory which describes the effect on the pituitary hormones.
- A non-secretory adenoma (also referred to as null-cell tumor) destroys normal pituitary tissue and results in hypopituitarism. Non-secretory adenomas are usually found as macroadenomas mainly because it is missed in the early stages as its size and nature does not cause any clinical features. At best estimates, up to 75% of the pituitary gland parenchyma has to be destroyed before there is a significant deficiency in the pituitary function (hypopituitarism).
- A secretory adenoma may cause an excess of one or two pituitary hormones thereby causing endocrine diseases that are detected early. Secretory adenomas are therefore more likely to be detected in the early stage, while still a microadenoma.
Cancer of the pituitary gland (primary pituitary carcinoma) is exceptionally rare and invades the parenchyma resulting in hormone deficiency (hypopituitarism). Secondary carcinoma (metastasis) is more likely to be seen with lymphoma or leukemia.
Other Tumors Around the Pituitary Gland
Other masses in and around the sella turnica, the groove where the pituitary gland sits in the skull, may compress or invade the pituitary gland usually resulting in hypopituitarism, especially anterior hormone deficiency. Refer to the location of the pituitary gland for more information on surrounding structures.
The two most common tumors that arise from structures lying in close proximity to the pituitary gland is a craniopharyngioma and meningioma .
This is a benign tumor that develops from the vestigial remnants of the Rathke’s pouch. It is the most common suprasellar mass and tends to be cystic (hollow cavities) rather than entirely solid like a pituitary adenoma.
These tumors stem from the meninges (lining of the brain) and is the most common parasellar mass. In most cases, a meningioma is benign and results in hypopituitarism.
A chordoma and pinealoma (germinoma) are other tumors that may affect the pituitary gland resulting in hypopituitarism. This is rare compared to craniopharyngiomas and meningiomas.