Evaluation of the substantia nigra in patients with Parkinsonian syndrome accomplished using multishot diffusion-weighted MR imaging.

BACKGROUND AND PURPOSE Although it is important to evaluate the substantia nigra in patients with parkinsonian syndrome, it is difficult to depict its anatomy, even by MR imaging. Using anatomic studies of the direction of nerve fibers around the substantia nigra, we attempted to depict this entity with multishot diffusion-weighted MR imaging to evaluate its topographic changes in patients with Parkinson's disease and secondary parkinsonism. METHODS We measured the substantia nigra on 72 diffusion-weighted axial MR images obtained in 36 healthy control subjects, on 47 images obtained in 25 patients with Parkinson's disease, and on 10 images obtained in five patients with secondary parkinsonism. We considered the width of the minor axis of the substantia nigra as its "thickness," which appeared as a crescent-shaped region in the midbrain. RESULTS Diffusion-weighted imaging portrayed the substantia nigra distinctly better than did T2-weighted imaging, because the surrounding white matter appeared as an area of high signal intensity. The mean (+/- SD) thickness values of the substantia nigra were 5.1+/-0.89 mm in control subjects, 4.8+/-0.75 mm in patients with Parkinson's disease, and 3.4+/-0.53 mm in patients with secondary parkinsonism. CONCLUSION Multishot diffusion-weighted imaging is a better imaging technique than T2-weighted imaging for demonstrating a change in size of the substantia nigra in vivo. The substantia nigra is not reduced in size in patients with Parkinson's disease, but it is reduced in patients with secondary parkinsonism.