Midbrain to pons area ratio (PSP)

Midbrain to pons area ratio as measured on midline sagittal images has been found useful in confirming a small midbrain in the setting of progressive supranuclear palsy (PSP) 1. This reduction in the size of the midbrain leads to the hummingbird sign

In the method described by Oba et al. the area of the midbrain and pons are calculated on the midline sagittal image and the ratio midbrain: pons obtained 1

The pontomesencephalic junction is defined by a line between the superior pontine notch and the inferior border of the quadrigeminal plate. 

The pontomedullary junction is defined by a line parallel to the first line, at the level of the inferior pontine notch. 

A normal value is approximately 0.24 whereas it is significantly reduced in PSP to 0.12 1

Neurodegenerative diseases

Neurodegenerative diseases are legion and their classification just as protean. A useful approach is to divide them according to underlying pathological process, although even using this schema, there is much overlap and thus resulting confusion.

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Article information

rID: 27992
Synonyms or Alternate Spellings:
  • Midbrain to pons ratio

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Cases and figures

  • Figure 1: annotated cloured image
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  • Case 1: with hummingbird sign
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