CLINICALLY
NONFUNCTIONING PITUITARY TUMOR
Clinically nonfunctioning pituitary tumors are identified either incidentally (e.g., on head magnetic resonance imaging [MRI] to evaluate unrelated symptoms) or because of sellar mass-related symptoms (e.g., visual field defect). On the basis of autopsy studies, pituitary microadenomas (≤10 mm in largest dimension) are relatively common, present in approximately 11% of all pituitary glands examined. However, pituitary macroadenomas (>10 mm in largest dimension) are uncommon. Immunohistochemical studies on resected pituitary adenomas can determine the adenohypophyseal cell of origin. The most frequent type of pituitary macroadenoma is the gonadotroph cell adenoma; most do not hypersecrete gonadotropins; thus, affected patients do not present with a hormone excess syndrome. The second most common clinically nonfunctioning pituitary macroadenoma is the null cell adenoma that is not basophilic or acidophilic (chromophobe adenoma); this is a benign neoplasm of adenohypophyseal cells that stains negatively for any anterior pituitary hormone on immunohistochemistry. Rarely, lactotroph, somatotroph, and corticotroph pituitary adenomas may be clinically silent.
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| Plate 1-24 |
The mass-effect symptoms in patients
with clinically nonfunctioning pituitary macroadenomas usually prompt
evaluation with head MRI. Suprasellar extension of the pituitary adenoma causes
compression of the optic chiasm, resulting in the gradual onset of superior
bitemporal quadrantopia that may progress to complete bitemporal hemianopsia
(see Plate 1-11). Because the onset is gradual, patients may not recognize
vision loss until it becomes marked. Additional mass-effect symptoms from an
enlarging sellar mass include diplopia (with cavernous sinus extension and
oculomotor nerve compression), varying degrees of pituitary insufficiency (related
to compression of the normal pituitary gland by the macroadenoma), and
headaches.
MRI is the imaging of choice to
evaluate the sella and surrounding structures. MRI clearly shows the degree of
suprasellar and parasellar extension of pituitary macroadenomas. All patients
with pituitary macroadenomas should be assessed for tumoral hyperfunction,
compression-related hypopituitarism, and visual field defects. Nonfunctioning
pituitary macroadenomas are often associated with mild hyperprolactinemia
(e.g., serum prolactin concentration between 30 and 200 ng/mL) because of
pituitary stalk compression and prevention of hypothalamic dopamine (prolactin
inhibitory factor) from reaching all of the anterior pituitary lactotrophs.
Pituitary lactotrophs are the only anterior pituitary cells that are under
continuous inhibitory control from the hypothalamus. Additional
pituitary-related hormones that should be measured in all patients with
pituitary macroadenomas include luteinizing hormone, folliclestimulating
hormone,α-subunit of glycoprotein hormones, target
gonadal hormone (estrogen in women and testosterone in men), insulinlike growth
factor 1, corticotropin, cortisol, thyrotropin, and free thyroxine. Diabetes
insipidus is rare in patients with benign tumors of the adenohypophysis.
The goals of treatment are to
correct mass-effect symptoms (e.g., vision loss) and to preserve pituitary function. Currently, no effective pharmacologic
options are available to treat patients with clinically nonfunctioning
pituitary tumors. Observation is a reasonable management approach in elderly
patients who have normal visual fields. However, intervention should be
considered in all patients with vision loss. Transsphenoidal surgery (see Plate
1-31) can provide prompt resolution of visual field defects and a permanent
cure. If present preoperatively, pituitary insufficiency may recover in some patients after operation.
Effectiveness of transsphenoidal surgery is assessed by the findings on
postoperative MRI (typically performed 3 months after surgery) and by blood
levels of adenoma secretory products that may have been increased before
surgery (e.g., α-subunit of glycoprotein
hormones). Recurrence of the pituitary adenoma after transsphenoidal surgery
can be treated with stereotactic Gamma knife radiotherapy.
