Massimo Caulo
We have been involved in presurgical brain mapping with task-evoked functional MRI (fMRI) since 2000, and we have observed that brain function reorganizes in different ways in the presence of a tumor or a vascular malformation placed in proximity to eloquent cortex or within a functional network. We were aware that our findings were strongly influenced by mass or other hemodynamic effects induced by brain lesions and by patient compliance with a task-evoked fMRI study. For this reason, we decided to study the functional reorganization of language in patients with epilepsy and no or very small lesions using resting-state fMRI instead of a classic task-evoked approach to limit lesion and task influence.
Interestingly, in patients with epilepsy, we observed an overall (but more pronounced in the left dominant hemisphere) reduction of functional connectivity (FC) within the language network. In addition, in patients with epileptic focus in the left hemisphere, the reduction of FC was coupled with a decline in language performance. These results implicate the possibility of extending the use of FC-MRI results to a clinical context even for patients with epilepsy, and in particular, for an objective assessment of the functional status of the language (or other) network. Indeed, in a subgroup of patients with temporal lobe epilepsy who underwent anterior temporal lobectomy, we demonstrated that the postsurgery language decline was directly correlated with the strength of presurgery inter-hemispheric FC of the language network and thus implicated the validity of FC-MRI for predicting the postsurgery clinical (language) outcome in patients with epilepsy.
In light of these results, an increasing number of neurosurgeons should request a preoperative functional MRI study of the brain, not only for localization and lateralization of language, but also for prognostic information of language performance in the postoperative stage.