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The callosal angle has been proposed as a useful marker of patients with idiopathic normal pressure hydrocephalus (iNPH), helpful in distinguishing these patients from those with ex-vacuo ventriculomegaly (see hydrocephalus versus atrophy).
It should be noted that there is nothing magical about this measurement, but rather it is merely a quantifiable measurement of the morphology of iNPH characterized by enlarged widening of the Sylvian fissures and cisterns with crowding of the gyri at the vertex.
Ideally, the angle should be measured on a coronal image perpendicular to the anterior commissure - posterior commissure (AC-PC) plane at the level of the posterior commissure 1,2.
In general patients with iNPH have smaller angles than those with ventriculomegaly from atrophy or normal controls.
A normal value is typically between 100-120°. In patients with iNPH that value is lower, between 50-80° 2.
In one study, symptomatic iNPH patients who responded to shunting had a significantly smaller mean preoperative callosal angle (59° (95% CI 56°-63°)) compared with those who did not respond (68° (95% CI 61°-75°)) 1. The callosal angle cutoff value of 63° showed the best prognostic accuracy 1.
- 1. Virhammar J, Laurell K, Cesarini KG et-al. The callosal angle measured on MRI as a predictor of outcome in idiopathic normal-pressure hydrocephalus. J. Neurosurg. 2014;120 (1): 178-84. doi:10.3171/2013.8.JNS13575 - Pubmed citation
- 2. Ishii K, Kanda T, Harada A et-al. Clinical impact of the callosal angle in the diagnosis of idiopathic normal pressure hydrocephalus. Eur Radiol. 2008;18 (11): 2678-83. doi:10.1007/s00330-008-1044-4 - Pubmed citation