Functional and magnetic resonance imaging correlates of corpus callosum in normal pressure hydrocephalus before and after shunting

Background

Normal pressure hydrocephalus (NPH) is associated with corpus callosum abnormalities.

Objectives

To study the clinical and neuropsychological effect of callosal thinning in 18 patients with idiopathic NPH and to investigate the postsurgical callosal changes in 14 patients.

Methods

Global corpus callosum size and seven callosal subdivisions were measured. Neuropsychological assessment included an extensive battery assessing memory, psychomotor speed, visuospatial and frontal lobe functioning.

Results

After surgery, patients showed improvements in memory, visuospatial and frontal lobe functions, and psychomotor speed. Two frontal corpus callosum areas, the genu and the rostral body, were the regions most related to the clinical and neuropsychological dysfunction. After surgery, total corpus callosum and four of the seven subdivisions presented a significant increase in size, which was related to poorer neuropsychological and clinical outcome.

Conclusion

The postsurgical corpus callosum increase might be the result of decompression, re‐expansion and increase of interstitial fluid, although it may also be caused by differences in shape due to cerebral reorganisation.Ventricular dilatation and corpus callosum abnormalities are the anatomical changes most often reported in association with normal pressure hydrocephalus (NPH). Callosal abnormalities include changes in the morphology and the magnetic resonance imaging (MRI) signal. The most consistent findings are stretching, uniform and focal thinning, and upward elevation.^1,2,3,4 Callosal damage has been primarily attributed to lateral ventricle dilatation¹ and to the impingement of the corpus callosum against the falx.²Two studies indicated a partial or complete recovery of different callosal parameters after shunt surgery.^4,5 However, in these studies, only five and eight patients with different types of hydrocephalus were analysed postsurgically. Other studies have reported corpus callosum abnormalities after surgery in 3–17% of cases, including signal changes,^6,7,8,9,10 a transient scalloping deformity⁶ and increased thickness.^7,8 Although the nature of the postsurgical changes in the corpus callosum remains unclear, several causes have been suggested, including callosal compression against the falx, decompression and overdrainage.^6,7,8,9To our knowledge, no morphological MRI quantitative studies of corpus callosum in NPH have been performed to date, nor has the possible involvement of the corpus callosum in the neuropsychological deterioration in NPH been investigated in depth. As damage to the corpus callosum can affect cognition,¹¹ the aim of this study was to investigate the contribution of corpus callosum thinning to the neuropsychological deficits in NPH and to determine the postsurgical callosal changes and their relationship with cognitive outcome.