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What is Absent swallow tail sign is seen in and explain in detail?
SWALLOW TAIL SIGN: 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 repoed to have a diagnostic accuracy of greater than 90% for Parkinson disease. Figure showing normal swallow tail. Figure showing absent swallow tail Figure showing absent swallow tail sign in Parkinsonism.