Pituitary apoplexy pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Akshun Kalia M.B.B.S.[2]

Pituitary apoplexy is an acute clinical syndrome caused by hemorrhage and necrosis in the pituitary gland. Most commonly, pituitary apoplexy is associated with pituitary adenoma. Pituitary adenoma predisposes the patient to an increased risk of bleeding within the pituitary gland. Pituitary adenoma has fenestrated endothelium surrounded by a variable number of smooth muscle cells which are not found in the normal pituitary gland, leading to increased susceptibility to pituitary apoplexy in these tumors. Pituitary apoplexy can result from a mutation in AIP gene which is a tumor suppressor gene located on chromosome 11q13.2. On gross pathology, pituitary apoplexy presents with hemorrhage with or without necrosis. Electron microscopy shows evidence of abnormal fenestration of tumor vessels (pituitary adenoma) with fragmented basal membranes that may predispose the patient to hemorrhage.

Pituitary apoplexy is caused by bleeding into the pituitary gland. Most often, pituitary apoplexy is seen with a pituitary adenoma. Pituitary adenoma predisposes the patient to an increased risk of bleeding within the pituitary gland.^{[1][2][3][4][5][6][7][8]}

• Pituitary adenomas have decreased blood supply and angiogenesis.
• A pituitary adenoma has fenestrated endothelium surrounded by a variable number of smooth muscle cells, which are not found in the normal pituitary gland.

• VEGF mRNA may be increased in pituitary tumors, especially in non-functioning pituitary adenomas, which could be related to an abnormal vascularity.

• Enlarging pituitary adenomas may outgrow their blood supply, making them susceptible to bleeding and infarction.

• The bleeding may lead to increase in intrasellar pressure. The increased intrasellar pressure may compress the adjoining structures and lead to the clinical symptoms of pituitary apoplexy.
  • An enlarged pituitary tumor may become impacted at the diaphragmatic notch, leading to compression of the hypophyseal stalk and its vascular supply.
  • This may render the anterior pituitary gland and its tumor with reduced blood supply causing ischemia and subsequent necrosis.
  • Reperfusion after infarction may lead to hemorrhage within the pituitary gland or adenoma.

• Gene involved in the pathogenesis of pituitary apoplexy include a mutation in AIP gene, which is located on chromosome 11q13.2.
• The most common mutation site in the AIP gene is p.R304 locus.
• Mutated AIP loses its activity as a tumor suppressor gene and leads to increased cell proliferation.
• The penetration of AIP positive carriers is 12-30%.

Pituitary apoplexy is seen with 0.6 to 10% of pituitary adenomas.

• The predominant finding is hemorrhage with or without necrosis.
• Pale, necrotic material is particularly found when there is a long interval between the acute clinical event and surgery.

Electron microscopic shows evidence of abnormal fenestration of tumor vessels (pituitary adenoma) with fragmented basal membranes that may predispose the patient to hemorrhage.

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