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

Abstract

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.

fig 1.

Photomicrograph of the midbrain shows the white matter between the red nucleus and substantia nigra, where the nerve fibers (arrow) extend in the obliquely ventrodorsal direction (Klüver-Barrera stain; original magnification, ×40). R indicates red nucleus; SN, substantia nigra; arrowhead, pigmented neurons

fig 2.

41-year-old male control subject. A, Axial T2-weighted image (3540/105) of the midbrain barely depicts the substantia nigra (arrow). The red nucleus (arrowhead) is depicted as a round area of low intensity resulting from the accumulation of iron. B, Diffusion-weighted image with a left-right direction diffusion-sensitizing gradient shows a distinct crescent of low signal intensity (arrow) between the cerebral peduncle and the tegmentum. Large arrowhead indicates substantia nigra; small arrowhead, mammillary body.

fig 3.

Thickness of the substantia nigra in the control subjects, the patients with Parkinson's disease, and the patients with secondary parkinsonism. The mean (± SD) thickness of the substantia nigra in the control group (n = 72) was 5.1 ± 0.89 mm, that in the group with Parkinson's disease (n = 47), 4.8 ± 0.75 mm; and that in the group with secondary parkinsonism (n = 10), 3.4 ± 0.53 mm. There was a significant difference between the group with Parkinson's disease and the group with secondary parkinsonism by unpaired Student's t-test (P < .01)

fig 4.

67-year-old man with Parkinson's disease (Hoehn and Yahr scale, 4). A, On T2-weighted image (3540/105), the substantia nigra is difficult to identify. There are no abnormal signal changes in the midbrain. B, On diffusion-weighted image, the substantia nigra (arrow) is depicted clearly as a crescent of low signal intensity. No atrophy of the substantia nigra is seen.

fig 5.

19-year-old man with secondary parkinsonism (carbon monoxide intoxication) 3 years after onset. A, On T2-weighted axial image (3540/105), a hyperintense lesion (arrow) is observed in the globus pallidus; a result of carbon monoxide poisoning. B, Diffusion-weighted axial image of the midbrain shows atrophy of both substantia nigra (arrow). The signal intensity is relatively higher than that in the control subjects.

fig 6.

75-year-old man with secondary parkinsonism after bilateral putaminal hemorrhage. A, T2-weighted image shows a large hyperintense area in the left putamen and a slitlike hyperintensity in the right putamen. Multiple spotty areas of hyperintensity are also seen in both putamen. The margins of the large area of hyperintensity and of the slitlike hyperintensity are hypointense owing to susceptibility effects resulting from the accumulation of iron (hemosiderin). B, On T2-weighted image (3540/105) of the midbrain, the substantia nigra is not distinguishable. There are no abnormal signal changes in the midbrain. C, On diffusion-weighted image, both substantia nigra are reduced in size. This image shows hyperintensity in the substantia nigra, which might reflect neuronal degeneration and gliosis.

fig 7.

65-year-old man with progressive supranuclear palsy. A, T2-weighted image (3540/105) shows atrophic changes of the midbrain; however, no abnormal signal intensity is evident. B, Diffusion-weighted image shows the substantia nigra to be reduced in size.