“When you hear hoof beats think of horses before zebras.”
Adage familiar to most doctors, reminding them that most symptoms come from common problems. Author unknown.

Pituitary gland tumors are common, often found as unsuspected abnormalities in brain scans and in autopsies, and counted as the most common “brain tumors” removed by neurosurgeons. Technically though, the most common pituitary tumors – the horses – are not brain tumors, but gland tumors called adenomas, usually benign and eminently treatable. While more dangerous tumors arising from nearby parts of the brain or skull may closely mimic pituitary adenomas, they are rare – the zebras of pituitary problems. This column is about the horses and for simplicity will refer to pituitary adenomas as pituitary tumors.

What and where is the pituitary gland?

    The pituitary gland hangs like a little globe from the base of the brain. The back half of the gland is neural tissue, connected to the deepest regions of the brain above. The front half is glandular tissue, which, like other glands, makes hormones, secretes them directly into the blood, sends them out to perform many functions in other parts of the body and is prone to adenoma formation as life goes on.

Types of pituitary tumors

    Pituitary tumors which are “non-functioning,” i.e. producing no hormones, may never cause symptoms. Larger tumors or those that produce hormones typically come to attention in midlife, more often in women than men because female reproductive cycles is exquisitely sensitive to hormonal variations. Small, unsuspected tumors turn up in about 10% of MRI scans of the head done for unrelated reasons like sinus disease or head trauma, and in 20-25% of autopsies.

     The factors which determine whether or not a pituitary tumor produces symptoms and requires treatment include its size, its ability to produce hormones of its own, and the degree to which it compresses and damages normal pituitary gland tissue and other surrounding structures. Damage to the normal parts of the gland that diminishes production of pituitary hormones is a condition called pituitary insufficiency. Production of a hormone by a pituitary tumor is called pituitary hypersecretion, which causes predictable signs and symptoms related to the effects of hormonal overdose on the given hormone’s target organs and tissues. Pressure on nearby brain structures by a large pituitary tumor is a phenomenon called tumor mass effect.

Pituitary insufficiency

    Some pituitary hormones such as thyroid stimulating hormone (TSH) prompt other glands to produce their hormones. Other pituitary hormones work directly on many body tissues. Growth hormone, for instance, affects all tissues in the body, controlling growth in early life and many aspects of tissue repair later. Still others control menstrual function, ovulation, and production of sperm, testosterone and breast milk. The rear half of the pituitary gland, which arises from the brain, makes one hormone that helps concentrate urine and another, called oxytocin which stimulates uterine contraction during labor, and has recently been suspected to play a role in some moods and behaviors.

When insufficiency becomes failure

    If a pituitary tumor compresses the normal parts of the gland, causing it to fail, wide-ranging symptoms such as fatigue, headache, weakness, abnormal menstrual cycles, decreased libido, decreasing muscle mass and body hair, weight loss or weight gain and mood alterations may appear long in advance of a correct diagnosis. These are all symptoms which might easily be passed off as lifestyle problems, nutritional deficiencies and aging.

Pituitary Hypersecretion 

    If pituitary tumors are functional, i.e. producing hormones,  symptoms come from excessive hormonal effects on the body. For instance, growth hormone (GH) and the adrenal gland stimulating hormone ACTH are the most common tumor-produced hormones. In someone still growing, too much growth hormone produces a giant – someone whose proportions are normal, but who far exceeds the normal range of sizes. Think Andre the Giant. Once growth ceases, overabundant growth hormone still causes overgrowth in certain bones and tissues, especially the jaw, hands and feet, the nose, heart and tongue, and the heel pads. This condition is called acromegaly.

    ACTH overproduction produces Cushing’s disease, named after Harvey Cushing, the father of neurosurgery in the US, one of the first to try surgically removing a pituitary tumor. Weight increases around the trunk and in the face and neck; muscles and tendons weaken and atrophy. Bones lose calcium. Eyes bulge. Skin bruises and thins. Blood pressure goes up.

Tumor Mass Effect 

    A large tumor in the pituitary may compress not only the normal gland around it but also the surrounding structures in the brain and skull. The gland sits right below the junction of the optic nerves carrying visual information from the eyes to the brain, and in between the bones where the nerves that control eye movements enter the orbits. In addition, the large veins which drain blood from the brain travel beside the pituitary on their way out of the skull. The optic nerves fibers that carry vision from the sides of the visual field are most vulnerable to pressure, which impairs sight on both sides of the patient’s field of vision. Pressure on the nerves to the eye muscles causes double vision. Headache, eye pain, or eye redness comes from mass effect on the large veins coursing beside an enlarged pituitary. Very large tumors may affect the deep brain structures above, resulting in a host of emotional symptoms or seizures.

Diagnosis 

    Symptoms which suggest pituitary gland insufficiency, hypersecretion or tumor mass effect warrant hormonal testing, an ophthalmologist’s examination of the visual fields, and imaging studies of the base of the brain. Tumors found incidentally on scans done for other reasons should prompt a good medical history and physical examination, and possibly some hormonal testing to evaluate the functional status of the tumor.

Treatment 

    Surgical removal of the pituitary tumor is the treatment for functional tumors or those that damage surrounding structures. After surgery, patients might require either temporary or permanent supplementation with pituitary hormones. On rare occasion, abrupt pituitary failure called pituitary apoplexy is the result of a pituitary tumor bleeding. this is a medical emergency, requiring  emergency surgery with meticulous attention to fluid balance and blood pressure because of failure of the hormones that modulate those functions. Non-functioning, small pituitary tumors call for regular follow-up imaging to monitor the tumor size – and should not carry the fearsome designation of brain tumor. They are horses, not zebras.