Intracranial artery dissection (IAD)

  • Unknown incidence, probably lower than cervical artery dissection (2.6 - 5 per 100,000 people).
  • Affects posterior circulation more often (75-93%) than anterior.
  • Intradural arteries lack elastic fibers in tunica media, have no external elastic lamina and have proportionately thinner tunica adventitia than cervical vessels. Weaker support tissues make them prone to adventitial dissection and subsequent subarachnoid hemorrhage.
  • 30-78% of patients present with signs of cerebral ischemia.
  • 50-60% present with subarachnoid hemorrhage.
  • 80% of patients have a prodromal headache before SAH or cerebral ischemia.
  • Isolated headache, mass effect on cranial nerves or brainstem, and, rarely, intracerebral hemorrhage (even without SAH) have been reported.

Imaging

  • Mural hematoma, double lumen or intimal flap are pathognomonic but challenging to detect due to the small size of the vessels.
  • Mural hematoma detected as a crescent-shaped eccentric thickening of the arterial wall.
  • On fat-saturated T1 sequence, hematoma is hyperintense 48-72h after onset.
  • Hemorrhagic atheromatous plaque or partially recanalized thrombus may mimic the imaging pattern but do not usually cause eccentric thickening of the vessel wall.
  • Intimal flap best detected on DSA.
  • Aneurysmal dilatation, segmental stenosis or occlusion are non-specific possible presentations, with wide reported variability in different studies.
  • Aneurysmal dilatation may be more commonly associated with SAH.

Imaging differential

  • Atherosclerosis
    • Unusual location, absence of atheromatous changes and/or calcification in other arteries, dynamic change in morphology on serial imaging favor dissection.
  • Vasospasm after SAH
    • Focal narrowing in one rather than multiple arteries, seen on day of onset of SAH (vasospasm takes between 4 days to 3 weeks to manifest after SAH) favor dissection.
  • Reversible cerebral vasoconstriction syndrome
    • Focal narrowing in one rather than multiple arteries, absence of trigger for RCVS, residual stenosis after 3 months on serial imaging favor dissection.
  • Vasculitis
    • Focal narrowing in one rather than multiple arteries and absence of focal wall enhancement on vessel wall imaging favor dissection.
  • Fibromuscular dysplasia
    • Absence of string-of-beads appearance, long stenotic segment, string sign on DSA, and dynamic change on serial imaging favor dissection.
  • Fusiform aneurysm
    • Mural hematoma, intimal flap, double lumen or dynamic change in shape on serial imaging favor dissection.
  • Dolichoectasia
    • Mural hematoma, intimal flap, double lumen or dynamic change in shape on serial imaging favor dissection.
  • Thromboembolic occlusion
    • Mural hematoma, intimal flap or double lumen, recanalisation showing long filiform stenosis, fusiform aneurysm, and string-and-pearl sign favor dissection.
  • Transient cerebral arteriopathy
    • TCA mostly seen in children while IAD mostly seen in adolescents.
    • Infarcts in TCA most often involve the lenticulostriate territory. Large infarct size favors dissection
    • Progression of stenosis might happen in TCA during the first 3-6 months, followed by stabilization or normalization.
    • TCA frequently shows concentric stenosis and wall enhancement on vessel wall imaging. Eccentric stenosis, wall hematoma, irregular arterial lesion favor dissection.
  • Fenestration (anatomic variant)
    • No distinct adventitial layers, dynamic change in shape on follow-up examinations favor dissection.

Management

No evidence-based recommendations exist.

  • Patients with SAH are treated with surgery or endovascularly because of high (up to 40%) rebleeding risk
  • Endovascular treatment is considered in patients without SAH that suffer recurrent ischemic events despite appropriate medical treatment, if aneurysm size increases or to reduce mass effect
  • In patients without SAH presenting with cerebral ischemia, thrombolysis may be considered but its efficacy and safety are unknown.
  • Currently existing data do not show significant difference in the efficacy or safety of antiplatelet vs anticoagulation treatment.
  • In patients with IAD and no signs of cerebral ischemia or in cases with both SAH and cerebral ischemia, no antithrombotic treatment and close monitoring have been proposed.