Friday, May 5, 2017

Introduction to Pituitary Tumors



Constituting 10% of intracranial neoplasms, pituitary tumors typically originate in the anterior pituitary (adenohypophysis). They occur in adults of both sexes, usually during the third and fourth decades of life. The three tissue types of pituitary tumors are chromophobe adenoma (90%), basophil adenoma, and eosinophil adenoma.
The prognosis is fair to good, depending on the extent to which the tumor spreads beyond the sella turcica.

Causes
Although the exact cause is unknown, a predisposition to pituitary tumors may be inherited through an autosomal dominant trait. Some are part of a hereditary disorder called multiple endocrine neoplasia 1. Pituitary tumors aren’t malignant in the strict sense; however, because their growth is invasive, they’re considered a neoplastic disease.
Chromophobe adenoma may be associated with the production of corticotropin, melanocyte-stimulating hormone, growth hormone, and prolactin; basophil adenoma, with evidence of excess corticotropin production and, consequently, with signs of Cushing’s syndrome; and eosinophil adenoma, with excessive growth hormone.
Signs and symptoms
As pituitary adenomas grow, they replace normal glandular tissue and enlarge the sella turcica, which houses the pituitary gland. The resulting pressure on adjacent intracranial structures produces typical clinical features.
Neurologic features
  • Frontal headache
  • Visual symptoms, beginning with blurring and progressing to field cuts (hemianopias) and then unilateral blindness
  • Cranial nerve involvement (III, IV, VI) from lateral extension of the tumor, resulting in strabismus; double vision, with compensating head tilting and dizziness; conjugate deviation of gaze; nystagmus; lid ptosis; and limited eye movements
  • Increased intracranial pressure (secondary hydrocephalus)
  • Personality changes or dementia, if the tumor breaks through to the frontal lobes
  • Seizures
  • Rhinorrhea, if the tumor erodes the base of the skull
  • Pituitary apoplexy secondary to hemorrhagic infarction of the adenoma. Such hemorrhage may lead to both cardiovascular and adrenocortical collapse.
Endocrine features
  • Hypopituitarism, to some degree, in all patients with adenoma, becoming more obvious as the tumor replaces normal gland tissue; signs and symptoms include amenorrhea, decreased libido and impotence in men, skin changes (waxy appearance, decreased wrinkles, and pigmentation), loss of axillary and pubic hair, lethargy, weakness, increased fatigability, intolerance to cold or heat, and constipation (because of decreased corticotropin and thyrotropin production)
  • Addisonian crisis, precipitated by stress and resulting in nausea, vomiting, hypoglycemia, hypotension, and circulatory collapse
  • Diabetes insipidus, resulting from extension to the hypothalamus
  • Prolactin-secreting adenomas (in 70% to 75%), with amenorrhea and galactorrhea; growth hormone-secreting adenomas, with acromegaly; and corticotropin-secreting adenomas, with Cushing’s syndrome.
Diagnosis
  • Magnetic resonance imaging (MRI), cranial computed tomography (CT) scanning, or skull X-rays with tomography show enlargement of the sella turcica or erosion of its floor; if growth hormone secretion predominates,
  •  X-ray films show enlarged paranasal sinuses and mandible, thickened cranial bones, and separated teeth. 
  • MRI and CT scan show the location and size of the adenoma.
  • Carotid angiography shows displacement of the anterior cerebral and internal carotid arteries if the tumor mass is enlarging; it also rules out intracerebral aneurysm.
  • Cerebrospinal fluid analysis may show increased protein levels.
  • Endocrine function tests may contribute helpful information, but results are often ambiguous and inconclusive.
Treatment
Surgical options include transfrontal removal of large tumors impinging on the optic apparatus and transsphenoidal resection for smaller tumors confined to the pituitary fossa.  

Radiation is the primary treatment for small, nonsecretory tumors that don’t extend beyond the sella turcica and for patients who may be poor postoperative risks; otherwise, it’s an adjunct to surgery.
Postoperative treatment includes hormone replacement with cortisone, thyroid, and sex hormones; correction of electrolyte imbalance; and, as necessary, insulin therapy.
Drug therapy may include bromo-criptine, an ergot derivative that shrinks prolactin-secreting and growth hormone-secreting tumors. Antiserotonin drugs can reduce increased corticosteroid levels in the patient with Cushing’s syndrome.
Adjuvant radiotherapy is used when only partial removal of the tumor is possible. 

Cryohypophysectomy (freezing the area with a probe inserted by transsphenoidal route) is a promising alternative to surgical dissection of the tumor.

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