Pituitary Adenomas

OVERVIEW:

Pituitary adenomas arise from the pituitary gland itself, account for 15-20% of primary brain tumors and are the third most common intracranial tumor after gliomas and meningiomas. Over 99% of pituitary adenomas are benign (not malignant or cancerous) and are slow growing. From autopsy studies and MRIs of normal individuals, it is known that 10-20% of the general population has a pituitary adenoma. Most of these tumors remain small and do not cause significant harm or symptoms. However many do progress and grow to cause major hormonal and neurological problems.

Adenomas are classified by size and whether they produce pituitary hormones; those less than 1 cm in diameter are called microadenomas, those over 1 cm in diameter are called macroadenomas. Adenomas that make excess hormones (endocrine-active adenomas) include prolactin secreting adenomas known as prolactionomas, adrenocorticotropic hormone (ACTH) secreting adenomas causing Cushing’s disease, growth hormone (GH) secreting adenomas causing acromegaly, and the least common endocrine-active adenoma, thyroid stimulating hormone (TSH) secreting adenomas causing hyperthyroidism. Adenomas that do not make excess hormones are called endocrine-inactive or non-functional adenomas.

Most adenomas are not genetically inherited; cases of familial pituitary tumors are rare. Multiple Endocrine Neoplasia (MEN) type I accounts for less than 5% of cases of pituitary adenomas. This autosomal dominant condition is characterized by multiple and sometimes simultaneous tumors of the pituitary, pancreas and parathyroid glands. Pituitary adenomas develop in 25% of patients with MEN I.

SYMPTOMS:

Pituitary adenomas may cause problems because of hormonal hypersecretion, pituitary hormonal failure, vision loss, headaches and/or bleeding into the tumor (apoplexy).

Hormonal hypersecretion: The three most common hormonally active adenomas are prolactinomas, GH-secreting tumors causing acromegaly, and ACTH-secreting tumors causing Cushing’s disease. Thyroid stimulating hormone (TSH) tumors are rare.
Pituitary failure (hypopituitarism): This problem typically occurs only in larger tumors (macroadenomas) and results from compression and damage to the normal pituitary gland from the enlarging adenoma. Manifestations may include hypogonadism (sexual dysfunction, loss of libido, and impotence), hypothyroidism (fatigue, weakness, weight gain, coarse dry hair and dry skin, cold intolerance, depression), adrenal insufficiency (fatigue, weakness, loss of appetite, dizziness, nausea and vomiting), growth failure (in children and adolescents), hyperprolactinemia due to "stalk effect" (seen in diseases within or near the pituitary gland and stalk, interfering with the delivery of dopamine, a neuron-transmitter, from the hypothalamus to the prolactin secreting cells of the pituitary gland), which can result in hypogonadism and its associated problems. Rarely posterior pituitary gland damage occurs with diabetes insipidus, which is caused by the inability of the kidneys to conserve water leading to frequent urination and thirst. Learn more.
Neurological problems: The most common neurological problems from a pituitary macroadenoma are loss of visual acuity and loss of peripheral vision termed a bitemporal hemianopsia. This visual loss results from pressure on the optic nerves and optic chiasm which is directly above the pituitary gland. Visual loss is typically seen only with larger macroadenomas (> 1 - 2 cms in size). Macroadenomas may on occasion also result in ocular palsies (double vision).
Headache: Typically headaches are seen in patients with macroadenomas and they are usually located in the frontal/ forehead and temporal area.
Bleeding (pituitary apoplexy): This condition develops over hours to several days from hemorrhage and/or infarction of a macroadenoma. Symptoms may include headache, nausea, visual loss, double vision and confusion. Most patients have undiagnosed hormone insufficiency prior to the apoplectic event. Apoplexy is best confirmed by MRI. A head CT will also show an abnormality in the majority of cases. Other conditions to consider that might mimic pituitary apoplexy are a ruptured aneurysm, meningitis, a stroke, intracerebral hemorrhage and migraine headache. The treatment for most patients with pituitary apoplexy is urgent transsphenoidal surgery as well as replacement of the stress hormone cortisol.

DIAGNOSIS:

Pituitary adenomas are best diagnosed by imaging studies and hormonal testing.

Imaging:The imaging study of choice is an MRI of the pituitary gland without and with gadolinium (a contrast agent). A brain MRI or CT scan will also reveal most pituitary macroadenomas but may not reveal smaller microadenomas. In a minority of patients it may be difficult to distinguish an adenoma of the pituitary from other masses which may include Craniopharyngioma, Rathke’s Cleft Cyst, Meningioma, Hypophysitis (pituitary inflammation), Glioma of the suprasellar region, Metastatic tumor or Chordoma.
Hormonal Testing: Evaluation of pituitary gland function either for under-production (hypopituitarism, or pituitary failure) or over-production of hormones should include blood levels of ACTH, cortisol, TSH, free T4 (thyroid function), LH (luteinizing hormone), FSH (follicle-stimulating hormone), estradiol in women, testosterone in men, GH (growth hormone), IGF-1 (insulin-like growth factor, growth hormone's target hormone, also known as somatomedin-C), and prolactin. Given that some tests need to be performed at a certain time of the day, and stimulation tests may be needed to diagnose some endocrine-active tumors (Cushing’s disease or acromegaly), this testing should be overseen by an endocrinologist.
Ophthalmological Evaluation: Patients with visual complaints or those whose tumors that contact the optic nerves or optic chiasm should receive a full ophthalmological evaluation. This evaluation should include acuity (vision quality) testing of each eye and formal visual field testing to determine if there is loss of peripheral vision.

TREATMENT:

Transsphenoidal surgery: Endonasal transsphenoidal surgery is considered the first-line treatment for all pituitary adenomas except prolactinomas. The operation is performed through a nostril without incisions on the face or nose and no nasal packing is used. The operating microscope, an endoscope or both are used to provide high resolution and panoramic visualization during the procedure. Complete tumor removal rates are generally high (80-90%) with smaller and non-invasive tumors, and lower with larger and/or invasive tumors (30-70%). Complications such as vision loss, bleeding, stroke, cerebrospinal fluid leak and meningitis are relatively rare when performed by experienced transsphenoidal neurosurgeons.
Transcranial surgery: A craniotomy is rarely required (in less than 1% of cases) for removal of a pituitary adenoma. .
Medical and Radiation therapies: Please see specific tumor types. Acromegaly, Endocrine-Inactive, Cushing’s disease, Prolactinoma