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Extracranial Internal Carotid Artery Dissection


KEY FACTS

Terminology

  • Internal carotid artery (ICA) dissection (ICAD)

  • ICAD: Tear in ICA wall allows blood to enter & delaminate wall layers

Imaging

  • Pathognomonic findings of dissection: Intimal flap or double lumen (seen in < 10%)

  • Aneurysmal dilatation seen in 30%

    • Commonly in distal subcranial segment of ICA

    • Focal pseudoaneurysm unusual

  • Flame-shaped ICA occlusion (acute phase)

  • ICAD most commonly originates in ICA 2-3 cm distal to carotid bulb & variably involves distal ICA

  • Stops before petrous ICA

  • MR T1 with fat suppression best sequence for hyperintense mural hematomas

Top Differential Diagnoses

  • Fibromuscular dysplasia

  • Carotid artery fenestration

  • Traumatic ICA pseudoaneurysm

  • Atheromatous plaque

  • Glomus vagale paraganglioma

  • Carotid space schwannoma

Clinical Issues

  • Ipsilateral pain in face, jaw, head, or neck

  • Oculosympathetic palsy (miosis and ptosis, partial Horner syndrome)

  • Ischemic symptoms (cerebral or retinal TIA or stroke)

  • Bruit (40%)

  • Lower cranial nerve palsies (especially CN10)

  • Pulsatile tinnitus

Lateral graphic depicts typical internal carotid artery (ICA) dissection. Note dissection begins above bifurcation
& ends at skull base
. Cross section of subintimal hematoma
is also shown.

Clinical photograph of a patient with an acute postganglionic Horner syndrome shows ptosis
, “upside-down” ptosis (lower lid is up
), and meiosis (constricted pupil
).

Axial T1WI MR in a 47-year-old man who fell skiing 3 weeks prior to developing left frontotemporal headache shows T1 shortening within the crescentic subacute clot
in the false lumen of the dissected left ICA. Note the high signal thrombus
within the true lumen of the vessel, which was occluded.

Axial MRA source image in the same patient shows the high signal thrombus in the false lumen
as well as the thrombosed true lumen
. Compare to normal flow signal of the right ICA
.

TERMINOLOGY

Abbreviations

  • Carotid artery dissection (CAD), internal carotid artery dissection (ICAD)

Definitions

  • ICAD: Tear in internal carotid artery wall allows blood to enter & delaminate wall layers

IMAGING

General Features

  • Best diagnostic clue

    • Pathognomonic findings of dissection: Intimal flap or double lumen (seen in less than 10%)

    • Aneurysmal dilatation seen in 30%, commonly in distal subcranial segment of ICA

    • Flame-shaped ICA occlusion (acute phase)

  • Location

    • ICADs most commonly originate in ICA 2-3 cm distal to carotid bulb & variably involve distal ICA

  • Size

    • ICAD extends variable length along distal ICA

    • Stops before petrous ICA

  • Morphology

    • ICA luminal narrowing ± focal aneurysmal dilatation

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