What is the pathophysiology of pituitary apoplexy?

Answer

Pituitary apoplexy stems from an acute expansion of a pituitary adenoma or, less commonly, in a nonadenomatous gland, from infarction or hemorrhage. The anterior pituitary gland is perfused by its portal venous system, which passes down the hypophyseal stalk. This unusual vascular supply likely contributes to frequency of pituitary apoplexy.

Some postulate that a gradual enlarging pituitary tumor becomes impacted at the diaphragmatic notch, compressing and distorting the hypophyseal stalk and its vascular supply. This deprives the anterior pituitary gland and the tumor itself of its vascular supply, apoplectically causing ischemia and subsequent necrosis.

Another theory stipulates that rapid expansion of the tumor outstrips its vascular supply, resulting in ischemia and necrosis. This explanation is doubtful, since most tumors that undergo apoplexy are slow growing.

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Media Gallery

Enhanced coronal CT showing large pituitary tumor with a "snowman" configuration and heterogeneous density (mixed signal) within the tumor indicative of pituitary apoplexy. Hemorrhage was confirmed at surgery.
Enhanced axial and coronal T1-weighted MRI of a typical large pituitary tumor with a "snowman" configuration (coronal) and marked enhancement with contrast. This tumor has not undergone apoplexy.
Enhanced T1-weighted axial and coronal MRI showing a large pituitary tumor that has recently undergone ischemic apoplexy showing a necrotic (hypointense) center and ring of gadolinium enhancement (hyperintense), ie, the "pituitary ring sign." There is a small area of hemorrhagic blush in the center of the necrosis.
Automated visual field showing a bitemporal field defect due to compression of the optic chiasm from below.
Post-contrast sagittal T1-weighted scan shows sphenoid sinus roof mucosal thickening. The yellow arrow shows the “pituitary ring sign,” while the white arrow shows sphenoid sinus roof mucosal thickening. Courtesy of Taylor & Francis (Vaphiades MS. Pituitary Ring Sign Plus Sphenoid Sinus Mucosal Thickening: Neuroimaging Signs of Pituitary Apoplexy. Neuroophthalmology. 2017 Dec. 41 (6):306-309. Online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5764063/.).

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What is the pathophysiology of pituitary apoplexy?

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