Abstracts

Rationale: Functional MRI assist in determining the neuroanatomical regions involved in critical cortical functions such as motor, sensory, and language (the eloquent cortex). Passive movement, which has been shown to have the same neuro-anatomical distribution as active movement, may be used in young children whom cannot actively participate in the procedure. More recently tractography, a novel technique is used to investigate the trajectories of cerebral white matter tracts. It is extremely useful in cases of lesions involving or approximating the eloquent cortex, or deeper lesions in the cerebral white matter that may disrupt major functional motor, visual, and sensory pathways. Direct cortical stimulation using intracranial electrodes is however the gold standard for determining cortical functions, therefore defining the eloquent cortex. Methods: In an attempt to determine the complimentary role of fMRI and tractography in children with symptomatic intractable epilepsy unable to actively cooperate during testing, we retrospectively reviewed epilepsy surgical cases done between January 2007 and present. Only cases in whom, both DTI and fMRI were carried out were included. Motor activity was assessed in all patients but testing sensory and language was determined by the patient’s ability to cooperate. In young uncooperative children passive movement was used to localize motor function with fMRI. Results: 34 children, all of whom were potential epilepsy surgical candidates and who received fMRI and DTI were included. One patient with child’s assent and parental consent refused surgery. Another patient with somewhat late onset symptomatic seizures associated with clinical and MRI findings suggestive of Rasmussen syndrome had both motor, sensory and language function correctly positioned in the affected hemisphere and tractography revealed that tracts were symmetrical in both the affected and non-affected hemispheres. 22 of these patients had surgery, 13 of whom had cortical mapping. In all but one case, in which cortical mapping was done, the findings on fMRI were concordant. The case with discordance was a tumor case with a causative change in neuro-anatomical vasculature. DTI tractography correctly revealed motor and other functional tract being redirected in cases in which tumors were the reason for seizure intractability, and in most cases of cortical dysplasia. Passive motor was also successfully done using Magnetoencephalography in two patients and were concordant with fMRI. Conclusions: Both fMRI and DTI are useful complimentary test to cortical mapping in planning for epilepsy surgery. This is especially relevant in assessing motor function in children unable to cooperate. In some case both procedures may affect the decision making process in proceeding to a phase two evaluation and may assist in avoiding critical cortical functional areas. fMRI results may however be dependant on blood flow which may limit its sensitivity if the vascular anatomy has.