Clinical manifestations of hydrocephalus caused by impingement of the corpus callosum on the falx: an MR study in 40 patients.

The clinical features of patients with hydrocephalus include generalized reductions in coordinated motor and cognitive functions. Although some group similarities have been noted, the outward manifestations of this dysfunction vary in degree and character, with some subjects revealing no overt signs of the underlying hydrocephalus. A retrospective review of subjects with MR criteria of hydrocephalus was undertaken to reevaluate the specific imaging correlates of the signs and symptoms associated with this pathologic process. Forty adults with hydrocephalus on MR evaluation were carefully scrutinized in an effort to elucidate specific clinicoradiologic patterns of abnormality. Spin-echo MR techniques were used with T1 and/or T2 weighting in three orthogonal planes. MR criteria of hydrocephalus encompassed dilated lateral ventricles to include the temporal horns, a pronounced upward elevation of the corpus callosum, and an outward expansion of the cerebral hemispheres at the expense of the subarachnoid space overlying the convexities. The significant related morphologic change on MR that has not been previously described in hydrocephalus was a localized dorsal flattening and thinning of the posterior body of the corpus callosum. Importantly, all but three of the 24 patients with this phenomenon manifested varying combinations of imbalance, gait disturbance, incontinence, short-term memory deficits, and global dementia. In the presence of hydrocephalus, but in the absence of this specific callosal configuration, only one of the remaining 16 subjects revealed symptoms that might suggest the presence of hydrocephalus (i.e., profound dementia). The structure responsible for this focal callosal flattening and thinning in hydrocephalus is the rigid free surface of the falx cerebri as it impinges on the caudal extent of the upwardly expanding corpus callosum and supracallosal hippocampal formation. This mechanical insult hypothetically causes variable axonal dysfunction, ranging from decreased to increased neurophysiologic activity. In summary, it is postulated that callosal impingement represents a dynamic partial hemispheric disconnection and accounts, in part, for the complex clinical state associated with hydrocephalus.