Pituitary Tumors
The pituitary gland is a half-breed in many ways. It is not really
a part of the brain, but rather hangs beneath it. Half of the gland comes
down from the brain (the posterior lobe which controls the body's water
levels and secretes the hormone ADH -- anti-diuretic hormone). The other
half comes from tissues originating from the roof of the embryonic mouth,
the anterior lobe which controls sex hormone levels, lactation, growth
hormone, body steroids, and the thyroid gland).
The pituitary is responsible for almost all of the body's hormonal systems,
taking all of its cues from the hypothalmus, the hidden and very deeply
located Grand Wizard of the brain. The hypothalmus also controls such activities
as body temperature, sexual drive, appetite, blood glucose levels, and
sleep/arousal behavior patterns.
As elsewhere in the brain, tumors of the pituitary gland behave according
to their cell of origin. Most of these tumor are truly benign, although
on occasion they may prove to be malignant (pituitary carcinomas). The
list of cells of the pituitary determines the tumor types, as well as the
clinical syndromes related to each. Almost all have the good prognosis
which calls for total removal. On the other hand, almost all can eventually
become "malignant by position."
This is especially true when the tumors grow off to either side, involving
the jam packed structures behind both eyeballs, called the "cavernous sinuses."
The pituitary gland is located exactly between these two structures, which
contain the nerves that control eye movement and the major arteries that
feed the brain (carotid arteries, the veins that drain the eyes and other
nerve related structures). Therefore, these tumors may occasionally present
the patient with double vision, or even something called "Pituitary Apoplexy"
(severe sudden headache, loss of and/or double vision, protruding eyeball).
Each tumor, because of its extraordinarily high hormonal output, creates
a characteristic clinical syndrome that brings attention to the tumor.
Because the pituitary gland is located directly beneath the place where
the nerves cross, coming from the eyes to the brain (the optic chiasm),
many tumors also present -- along with the hormonal problems listed below
-- loss of peripheral vision.
Hormonal Problems
Gigantism: This syndrome is caused by pituitary tumors on
the growth hormone secreting cells of the pituitary gland. Remember Lurch
from the James Bond movie -- large hands, protruding jaw, severe arthritis,
huge size, protruding eyebrows, plus other systemic problems -- a classic
example of gigantism.
Cushings Disease: This syndrome is caused by tumors on
the ACTH (Adrenal Corticotrophin Hormone) secreting cells of the pituitary
gland. Patients with this problem develop fat deposits in strange places
(Moon face, Buffalo hump on the back of the neck), spontaneous scarring
of the skin along the belly that look striated, pimples in adults, high
blood pressure and elevated body temperature. These tumors are usually
so small that the surgeon might have a difficult time finding the little
"bad pearl" in the gland during surgery. This is the one time when small
can be bad, especially if the surgeon is unable to locate and remove the
tumor! ACTH secreting tumors, although small and troublesome, are readily
cured by surgery alone.
Prolactin Syndrome: This syndrome is caused by tumors
on the prolactin secreting cells of the pituitary gland. The tumors are
the most common of all the pituitary tumors. Production of breast milk
in women who are not pregnant, loss of menstrual cycle, and loss of bone
calcium are all hallmarks of this tumor. When small, it may be cured; when
large, it may cause visual problems and require other (e.g. radiation)
therapy. Many women with this tumor visit their gynecologist thinking that
they might be pregnant.
Growth hormone secreting tumors may very occasionally be treated with
drugs, but most often must be removed surgically.
Non-Secreting Tumors: Can be treated by surgery and/or
radiation. These patients almost always have problems with vision, as the
hormonally quiet tumor grows to oversized proportions, actually growing
to the point of lifting up and stretching the optic nerves (especially
where the nerves from both eyes cross as they travel to the brain). The
treatment of these tumors is variable. Prolactinomas are most often treated
non-surgically with drugs that inhibit prolactin production (parlodil).
Microprolactinomas sometimes never really grow over long periods of time,
and do not require surgery.
All pituitary tumors can be treated by radiation, especially with the
improvements brought on by focused beam radiation (liner accelerator and
proton beam). The idea of radiosurgery originated in this venue. One serious
problem with radiation has been loss of function in the remainder of the
pituitary gland, requiring patients to depend on hormone supplements for
the continuation of their lives. Another has been the inability to quickly
reverse visual loss in large tumors using radiation. On the other hand,
radiation has been used as a very successful adjunct in larger tumors that
pose a threat to long term survival.
Surgery on Pituitary Tumors
The wonderful surgical achievement of the modern age is the combination
of improved lighting, the surgical microscope, and computer assisted navigational
instrumentation now used in the O.R. The pituitary gland lies just above
the air spaces in the nose (if you'd stick a pencil through your nose hard
enough, you'd end up in your pituitary gland). In fact, the word "pituita"
(like the word "ptuey!") refers to the not so delicate production of "snot."
In medieval times in Europe, and in China today, it is thought that "pituita"
was something good to get rid of, serving as a relief valve for bad humors
of the brain. In other words, spitting was good for the soul as well as
one's health.
Thus, by traversing the structures just beneath the skull through the
nasal cavities, brain surgery can be avoided and the risk of approaching
the pituitary gland can be enormously reduced.
Decision Making for Pituitary Tumor Surgery
It's an Emergency: Patients who have a large pituitary tumor (and often
don't even know about it) will occasionally develop a kind of pituitary
"stroke," called pituitary apoplexy. This occurs after the tumor outgrows
its blood supply and suddenly enlarges (due to swelling) after it infarcts
(a type of local stroke), or begins bleeding within the tumor. The enlargement
causes severe headache and/or double vision, because the nerves that control
the eye located next to the gland are pressed upon. It can also cause loss
of vision (because the gland swells upward, pressing from beneath the optic
nerves above). Surgical decompression is an emergency procedure because
permanent blindness may result if left untreated.
Surgery Is the Best Way to Go
Cushing's Disease: Because the tumor is so small, a cure is possible when
removed. Thus, surgery is the best way to go. Moreover, the remainder of
the gland is left intact, and will function normally thereafter.
Large tumors with liquified (necrotic) centers: In these cases,
the surgery is easy, and the improvement is immediate. Any remaining tumor
beyond the confines of the surgical field can be safely treated by other
standard therapies (e.g. radiation therapy).
Medium sized tumors: Still within the confines of the pituitary gland.
As with the Cushing's tumors, the tumor can be completely removed and the
gland saved for normal function.
A 'Hold' on the Surgery
Prolactinomas: Should always be treated initially with medication
(anti-DOPA agents such as Parlodil, Bromocriptin, etc.). Even large tumors
that most need to be treated by either surgey or radiosurgery should be
pretreated with these drugs to shrink the tumor away from vital brain structures
before surgery should be contemplated.
Microprolactinomas: Surgically, nothing need be done for
as long as possible. Some of these tumors appear to just sit there for
years, even decades.
Extremely large tumors that cause little visual or other brain problems:
In treating these tumors, particularly in older people, the physician should
consider radiation therapy to stop the progression of these tumors. A surgical
cure is usually not an option, for the substantial surgical risk entailed.
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