The structural and functional mechanisms of motor recovery: complementary use of diffusion tensor and functional magnetic resonance imaging in a traumatic injury of the internal capsule

Objectives-Recovery from focal motor pathway lesions may be associated with a functional reorganisation of cortical motor areas. Previous studies of t he relation between structural brain damage and the functional consequences have employed MRI and CT, which provide Limited structural information. Th e recent development of diffusion tensor imaging (DTI) now provides quantit ative measures of fibre tract integrity and orientation. The objective was to use DTI and functional MRI (fMRI) to determine the mechanisms underlying the excellent recovery found after a penetrating injury to the right capsu lar region. Methods-DTI and fMRI were performed on the patient described; DTI was perfo rmed on five normal controls. Results-The injury resulted in a left hemiplegia which resolved fully over several weeks. When studied 18 months later there was no pyramidal weakness , a mild hemidystonia, and sensory disturbance. fMRI activation maps showed contralateral primary and supplementary motor cortex activation during tap ping of each hand; smaller ipsilateral primary motor areas were activated b y the recovered hand only. DTI disclosed preserved structural integrity and orientation in the posterior capsular limb by contrast with the disrupted structure in the anterior limb on the injured side. Conclusions-The findings suggest that the main recovery mechanism was a pre servation of the integrity and orientation of pyramidal tract fibres. The f MRI studies do not suggest substantial reorganisation of the motor cortex, although ipsilateral pathways may have contributed to the recovery. The ini tial deficit was probably due to reversible local factors including oedema and mass effect; permanent damage to fibre tracts in the anterior capsular limb may account for the persistent sensory deficit. This study shows for t he first time the potential value of combining fMRI and DTI together to inv estigate mechanisms of recovery and persistent deficit in an individual pat ient.