Swallow tail sign (substantia nigra)

The swallow tail sign describes the normal axial imaging appearance of nigrosome-1 within the substantia nigra on high resolution T2*/SWI weighted MRI. Absence of the sign (absent swallow tail sign) is reported to have a diagnostic accuracy of greater than 90% for Parkinson disease and dementia with Lewy bodies 1,2

Nigrosome-1 within the posterior third of the substantia nigra returns high signal on axial SWI in a linear or comma shape. It is surrounded anteriorly, laterally and medially by low SWI signal intensity which resembles the distinctive split tail of a swallow. In Parkinson disease the high SWI signal within nigrosome-1 is absent and hence the swallow tail sign is absent. There are two proposed mechanisms for this: increased iron content, or decreased neuromelanin content with decreased iron storage capacity leading to more free iron with paramagnetic properties 3 .

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Article information

rID: 31109
Section: Signs
Synonyms or Alternate Spellings:
  • Swallow tail appearance
  • Absent swallow tail sign

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Cases and figures

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    The tail of the s...
    Figure 1: swallow tail
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    Substantia nigra ...
    Case 1: swallow tail sign - normal
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    Swallow tail sign...
    Figure 2: swallow tail sign - normal
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    Clinical high res...
    Case 2: absent swallow tail sign - Parkinson disease
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    Nigrosome 1 hyper...
    Figure 3: absent swallow tail sign - Parkinson disease
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    In the posterior ...
    Case 3: absent swallow tail sign - Parkinson disease
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