Nigrosome 1 absence in de novo Parkinson disease.

A 63-year-old man with 6 months of mild left hand rest tremor and bradykinesia and subtle left wrist cogwheel rigidity was diagnosed with idiopathic Parkinson disease (PD). The most profound neuronal degeneration in PD occurs in nigrosome 1, a lens-shaped substructure of the substantia nigra containing approximately 22,000 cell bodies in each hemi-midbrain, measuring 6 × 6 × 1 mm.1,2 A 7T MRI at the caudal level of red nucleus (figure, A) shows nigrosome 1 signal present in the left nigra and absent in the right, consistent with the clinically affected side. 7T MRI of a healthy 63-year-old with normal bilateral nigrosome 1 signal is shown for comparison (figure, B).