Interpeduncular angle

The interpeduncular angle is defined as the angle formed by the posterior half of the cerebral peduncles on axial images. The interpeduncular angle has been proposed as a sensitive and specific measure of intracranial hypotension (reduced) and progressive supranuclear palsy (PSP) (increased).

Usage

This measurement seeks to quantify what has been recognized for some time morphologically, namely, that the interpeduncular cistern becomes widened in PSP as the midbrain shrinks and narrowed in intracranial hypotension. It has, however, only been recently described and has not yet entered common usage.

Measurement

The angle has been defined as the angle formed by the posterior half of the cerebral peduncles obtained on an axial T2-weighted image at the level of the mammillary bodies or the slice immediately below it, whichever yields a lesser value. For cases with a U- instead of V-shaped apex, it has been proposed to measure the linear portion of the cerebral peduncles .

Interpretation

The interpeduncular angle is narrower in patients with intracranial hypotension. In adults, an optimal threshold of 40.5° has yielded a sensitivity of 80.0% and a specificity of 96.7%. Pediatric patients were excluded from the original study .

In the setting of progressive supranuclear palsy, a threshold of 57° yielded a sensitivity of 100% and specificity of 90% in distinguishing these patients from those with Parkinson disease and multiple system atrophy Parkinsonian subtype .