• An intimal tear allows blood to enter the arterial wall and separate the intimal layer of the artery from the media, forming a hematoma
• Most commonly occur in the internal carotid artery 2-3 cm away from the bifurcation of the common carotid
• Will show both luminal narrowing and aneurysmal dilatation on imaging
• On CT: contast will show double lumen, luminal narrowing, flap formation, and/or aneurysmal dilatation
• On MR:
  • T1 with fat-suppression will show intramural hematoma as a crescent
  • Hematoma also visualized on T2
  • MRA shows vessel tapering and aneurysmal dilatation 
• Most commonly occurs spontaneously, etiology unknown
• May also occur in setting of trauma, although vertebral dissection is more common
• Some with familial connective tissue diseases may be predisposed

References

Hakimi R, Sivakumar S. Imaging of Carotid Dissection. Curr Pain Headache Rep. 2019;23(1):2. Published 2019 Jan 19. doi:10.1007/s11916-019-0741-9

Schievink WI. Spontaneous dissection of the carotid and vertebral arteries. N Engl J Med. 2001;344(12):898-906. doi:10.1056/NEJM200103223441206