Posterior pituitary bright spot

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The posterior pituitary bright spot is an MRI feature of the normal pituitary gland wherein the posterior pituitary appears bright on non-contrast T1 weighted images.

Pathology

The posterior pituitary bright spot, having intrinsically high signal on T1 weighted images is believed to be from the storage of vasopressin, which has a T1-shortening effect . The hormone is synthesized in the hypothalamus and carried down the axons that form the stalk to the posterior pituitary bound to a vasopressin-neurophysin II-copeptin complex, a macroproteic structure that shortens T1 signal .

It is important to note that a posterior pituitary bright spot is not identified in all patients, but rather somewhere between 50-100% .

Additionally, in individuals with compression or interruption of the stalk the aforementioned downward transport can be halted and brightness can be seen above the compression/interruption. This should not be mistaken for an ectopic posterior pituitary .

Radiographic features

MRI
  • oval/round high T1 signal, best seen on sagittal images in the posterior aspect of the pituitary fossa
  • normal measurements (decreasing size with age) 
    • long axis: 1.2-8.5 mm
    • short axis: 0.4-4.4 mm

Related pathology

The absence of posterior pituitary bright spot should prompt the consideration of the following (noting it may be absent in normal patients):

Differential diagnosis