The causes of pituitary apoplexy is unknown, possibility is caused by the following factors.

1. Ischemic factors:
1) When the pituitary adenoma growth faster than the capacity of the blood supply, the tumor tissue area appear avascular necrosis, and subsequent bleeding.

2) The pituitary gland has a unique vascular supply, only through supply from the the pituitary portal system on the pituitary stalk, when the suprasellar pituitary adenoma growth, it can embed incisure diaphragma sellae and the pituitary stalk in the middle of the narrow site, blocking the pituitary pars distalis of nutrition and tumor blood vessels, lead to anterior leavess and the whole tumor ischemia, necrosis and hemorrhage. Pituitary adenoma side growth to suppression cavernous sinus, and make to raise the pressure of cavernous sinus. Cause increased venous pressure within the tumor so that tumor supply artery damage and infarct.

2. Vascular factors: pituitary adenoma with abundant blood vessels, forming irregular sinusoids, thin-walled sinusoids, tumor volume increased pressure to cause blood vessel bursting and bleeding. Modern angiography confirmed that blood vessel in pituitary adenoma is smaller than normal blood vessels and diameter mixed. Electron microscopy in these blood vessels do not fully mature, the membrane was ruptured or segment-shaped, perivascular space has been compressed plasma protein and red blood cells, which are the basis of pituitary adenoma hemorrhage.

3. Certain Tumor: more see in prolactinomas, not only because it is more see in pituitary adenomas, and in general due to the larger tumor size, easy to cause the obstacles of local blood circulation and blood supply. Pituitary apoplexy was particularly prevalent in the larger adenomas, but that may also occur in small adenomas, and many small adenoma post-stroke, no significant clinical symptoms, known as subclinical pituitary apoplexy.

4. Induced factors:
1) trauma: in suffering from pituitary adenoma, if the head by the external force, tumor and neurocranium occurred extrusion or stretch moment in sports, causes tumor vascular hemorrhage, especially in tumor blood vessels.

2) radiation therapy: Radiation therapy of pituitary adenoma can increase tumor blood vessels bleeding.

3) estrogen: estrogen can lead to pituitary hyperemia, prone to pituitary apoplexy.

4) upper respiratory tract infection, sneeze that increased pressure within the cavernous sinus, such as the adenoma into the cavernous sinus, the tumor is increased venous pressure, cause insufficient blood supply to tumor or artery embolization.

5) certain drugs and other: such as bromocriptine, chlorpromazine, anticoagulant therapy, alcoholism, angiography, dynamic pituitary function checks after surgery, as well as sphenoid sinusitis, atherosclerosis embolism, thrombocytopenia can cause pituitary apoplexy .

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