Substantia nigra

The substantia nigra is one of the brainstem nuclei and part of the extrapyramidal system. While other nuclei such as the red nucleus are as small and contained within an axial slice at the superior colliculi (see figure), the substantia nigra is seen in axial slices at both superior and inferior colliculi.

They are situated in the anterior midbrain and mark the transition point of the tegmentum and cerebral peduncles.

It is an important relay station in the motor system. It consists of a compact part (dark, containing melanin) and a reticular part (reddish, containing iron). Most of its axons are projected diffusely to other brain areas and not arranged into tracts. Numerous axonal tracts terminate in the substantia nigra:

  • caudate nucleus (striatonigral fibres)
  • anterior cerebral cortex (corticonigral fibres)
  • putamen
  • precentral cortex

Nigrosomes are small clusters of dopaminergic cells measuring up to a few millimetres in size within the substantia nigra that exhibit calbindin D28K negativity on immunohistochemistry. Five nigrasomes have been described with the largest labelled as nigrosome-1 positioned in the caudal, medio-lateral portion of the substantia nigra. Nigrasome-1 contains the largest proportion of neurons affected in Parkinson disease 3.

High resolution T2*/SWI weighted MRI is able to identify the distribution of normal signal within healthy and diseased substantia nigra both at 7T and 3T field strength. The healthy nigrosome-1 produces a swallow tail appearance on axial imaging. Absence of the normal swallow tail appearance of nigrosome-1 is reported to be a reliable sign of Parkinson disease 3

Neuroanatomy
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rID: 5813
Section: Anatomy
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    Substantia nigra on MRI
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    Substantia nigra on MRI
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    Brainstem nuclei and their connections
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    Midbrain (axial)
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    Midbrain (axial)
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