Neurosurgery notes/Spontaneous Cerebral Arterial Dissections

Spontaneous Cerebral Arterial Dissections

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Arterial dissection
General
  • ICA dissection following blunt cervical trauma is much more common
    • Not discussed here
  • Nomenclature
    • Dissection:
      • Extravasation of blood between the intima and media, creating luminal narrowing or occlusion.
    • Dissecting aneurysm
      • Dissection of blood between the media and adventitia, or at the media, causing aneurysmal dilatation, which may rupture into the subarachnoid space.
    • Pseudoaneurysm
      • Rupture of artery with subsequent encapsulation of the extravascular hematoma, may or may not produce luminal narrowing.
Pathophysiology
  • All dissections is caused by a haemorrhage outside of the vascular lumen due to pathological trans-intimal extravasation of blood from the true lumen into the vessel wall.
    • Hematoma can dissect the
      • Internal elastic membrane from the intima causing narrowing of the true lumen,
      • Dissect into the subadventitial plane producing an adventitial outpouching from the vessel wall (pseudoaneurysm).
    • Rupture through the vessel wall producing SAH
    • Subintimal dissection is more common with intracranial dissections, whereas extracranial vessels (including the aorta) usually dissect at the media or between media and adventitia.
  • “Spontaneous” dissections have been associated with:
    • Fibromuscular dysplasia (FMD):
      • Found in ≈ 15% of cases
    • Cystic medial necrosis (or degeneration):
      • Originally thought to be a common finding, now thought to perhaps be linked to a higher likelihood of fatal dissection
    • Saccular aneurysm
    • Marfan syndrome:
      • Autosomal dominant inherited disorder of connective tissue.
      • Phenotypic manifestations are due to production of abnormal fibrillin,
        • Main component ofextracellular microfibrils,
        • Component in the media of certain blood vessels, encoded by the FBN1 gene on chromosome 15q21
    • Ehlers-Danlos syndrome
    • Atherosclerosis:
      • Only rarely implicated as an etiology.
      • More likely to be a factor with subintimal dissection of extracranial arteries
    • Takayasu’s disease
    • Medial degeneration
    • Syphilitic arteritis
      • More common in the past, associated with 60% of dissections before 1950
    • Autosomal dominant polycystic kidney disease:
      • Associated with a higher incidence of cerebral aneurysms
    • Variant periarteritis nodosa
    • Allergic arteritis
    • Homocystinuria
    • Moyamoya disease
    • Strenuous physical activity
Epidemiology
  • Age of ≈ 45 yrs
    • Average age of traumatic dissections is slightly younger
  • More frequent in men.
  • Incidence is unknown
    • Often times the condition produces mild, transient symptoms. Increased awareness of the condition has resulted in an increased rate of diagnosis. ICA dissection accounts for 1–2.5% of first strokes.5 However, in middle aged and young adults it comprises 10–25% of strokes.6
Sites of dissection
  • Multiple dissections occur in ≈ 10% (the most common: bilateral vertebrobasilar lesions).
  • Spontaneous intracranial dissections by site
      • Location
      Left
      Right
      Total
      Vertebral
      122
      82
      204
      Basilar
      N/A
      N/A
      35
      Internal carotid
      17
      13
      30
      Middle cerebral
      16
      10
      26
      Anterior cerebral
      10
      3
      13
      Posterior cerebral
      7
      9
      16
      PICA
      4
      10
      14
      Total
      176
      127
      338
    • Previously, it was believed that the ICA was the most common site. This change may be due to the recent increased recognition of arterial dissections as a source of SAH (and vertebral dissections most often present as SAH).
Clinical presentation
  • Cerebral arterial dissections may cause symptoms by:
    • Embolization secondary to:
      • Platelet aggregation stimulated by the exposed surfaces
      • Dislodged thrombus (formation of which is enhanced by reduced flow)
    • Reduced distal flow secondary to:
      • Thrombosis due to reduced flow
      • Occlusion of the true lumen by the expansion of the mural hematoma
    • Subarachnoid haemorrhage (atypical presentation, may be more common with posterior circulation dissection than with anterior circulation)
  • <30 yrs
    • Most common cause due to internal carotid dissection without SAH.
  • >30 yrs
    • Vertebrobasilar artery (VBA) dissection with SAH was the most common.
  • Headache
    • Severe
    • Predates neurologic deficit by days or weeks.
Evaluation
  • CT. More useful for evaluating brain for infarction. Dissection can sometimes be visualized directly.8
  • CT angiogram (CTA). Often obviates the need for cerebral angiography since CTA scanners with ≥ 16 detectors are equal in predictive value and have an accuracy near 99%.
  • Angiography.
    • The definitive diagnostic study.
    • Diagnosis of dissection may be delayed if it is misinterpreted as:
      • An unusual saccular aneurysm
        • Most common error
      • Atherosclerotic lesions:
        • With dissections, the location is unusual, the lesion may be isolated, the age is usually younger, and the stenosis is smooth.
        • Cervical ICA dissection typically spares the carotid bulb whereas cervical ICA atherosclerosis tends to involve the bulb.
      • Vasospasm following SAH:
        • However, the narrowing with vasospasm is delayed in onset vs. the changes with dissection which are present from the beginning
    • Angiographic findings may include:
      • Luminal stenosis:
        • Irregular stenosis over long segments of the artery often with focal areas of near total stenosis (“string sign”)
      • Fusiform dilation with proximal or distal narrowing (string and pearl sign)
      • Occlusion:
        • Artery usually tapers to a point
      • Intimal flap:
        • When seen, usually found at proximal end of dissection
      • May see proximal beading (“string of beads” configuration, indicative of FMD)
      • “Double lumen sign”:
        • True vessel lumen and an intramural false lumen with an intimal flap. Usually with retention of contrast within the false lumen well into the venous phase. The only pathognomonic sign
      • Wavy “ripple” appearance
      • Severe kinking
        • Frequently bilateral.
        • With vertebrobasilar artery lesions: dolichoectasia
    • A characteristic of arterial dissections is that they often change configuration on repeat angiography (some resolve, and some worsen).
    • Forceful intra-arterial contrast injection during the performance of angiography carries a potential for worsening the dissection.
  • MRI
    • Probably not as accurate as CTA or angiography.
    • Optimal MRI study is source T1WI axial images with fat suppression (“fat sat”),
      • Look for loss of visualization over several slices, with good visualization above and below.
      • May visualize intimal flap and distinguish a dissection from a fusiform aneurysm.
      • Crescent sign:
        • Bright signal in wall of ICA on T2WI axial images (hematoma in vessel wall).
Overall outcome
  • Overall mortality of 26%
    • Mortality in first few weeks of presentation with vertebrobasilar artery (VBA) dissection can be as high as 83% .
    • Mortality by location
      • ICA lesions 49%
      • VBA lesions 22%
    • Mortality by presentation
      • SAH 24%
      • Non SAH 29%
  • 70% had a favourable outcome (assessed using Glasgow Outcome scale), 5% poor.
Vessel specific information
  • Internal carotid dissection
    • Posttraumatic ICA dissection is much more common than spontaneous.
      • Some cases considered “spontaneous” may actually be due to trivial trauma, including violent coughing, nose blowing, and simple neck turning.
    • Usually seen in young women.
    • Clinical presentation (for spontaneous dissection)
      • Pain
        • Ipsilateral headache (Most common)
          • Orbital or periorbital (60%)
          • Auricular or mastoid (39%),
          • Frontal (36%)
          • Temporal (27%).
        • Carotidynia: Sudden onset of severe pain over carotid artery
      • Incomplete Horner syndrome (oculosympathetic palsy):
        • Ptosis and miosis without anhidrosis (due to involvement of plexus around the ICA, sparing the ECA plexus which innervates facial sweat glands) may occur.
      • Bruits
      • Clinical features of spontaneous ICA dissection
          • Feature
          %
          Focal cerebral ischemia
          76
          Headache
          59
          Oculosympathetic palsy
          30
          Bruit
          25
          Amaurosis fugax
          10
          Neck pain
          9
          Syncope
          4
          Scalp tenderness
          2
          Neck swelling
          2
      • May be a cause of some cases of infantile and childhood hemiplegia and hemiparesis.
  • Vertebrobasilar system artery dissection
    • General information
      • Less common than carotid.
      • Extracranial lesions outnumber intracranial.
      • Traumatic dissections located
        • Where VA crosses bony prominences
          • At the C1–2 junction or where it enters the foramen transversarium (usually at C6).
      • Spontaneous dissections
        • Located intracranial
        • Commonly occur on the dominant VA.
        • Unlike cervical ICA dissections, which tend not to propagate intracranially through the carotid canal, high cervical VA dissections can readily propagate intracranially through the foramen magnum.
        • Associated with
          • FMD
          • Migraine
          • Oral contraceptives.
        • Unrecognized or forgotten trauma or sudden head motion may have occurred in some cases reported as spontaneous.
        • Commonly occurs in young adults (mean age: 48 yrs).
        • 36% of patients have dissections at other sites, 21% of cases have bilateral VA dissections.
        • Dissecting aneurysms of the VA (possibly a distinct entity) are also described.
          • Fusiform
          • May be amenable to clipping,
          • As of 1984, only ≈ 50 cases of dissecting aneurysms were published.
    • Presentation
      • Neck pain (most)
        • Located over the
          • Occiput
          • Posterior cervical
      • Headache
        • Severe
      • TIAs or stroke
        • In the form of
          • Lateral medullary syndrome
          • Cerebellar infarction
        • Especially in patients with occlusion of the third or fourth portion of the VA
          • None of 5 patients developed new neurologic symptoms after the original stroke in an average of 21 months follow-up.
          • In 3 of these 5, VA dissection was bilateral.
      • Altered consciousness
      • SAH
        • Seen in 6 of 30 cases of vertebrobasilar complex dissections.
        • Rebleeding
          • In 24–30% of those cases presenting with SAH,
          • Causes a very high mortality.
        • Traumatic extradural dissections or pseudoaneurysms may have a similar presentation, but can also produce massive external hemorrhage or neck hematomas.
    • Evaluation
      • Angiography.
        • May be difficult in many cases
          • The most common misdiagnosis is ruptured saccular aneurysm of unusual shape
        • In posttraumatic dissections, the most common finding is irregular stenosis of horizontal loops of distal extracranial VAs as they pass behind C1, often bilateral.
          • In 14 of 15 posttraumatic VA dissections, the lesion was located posterior to the atlas (distal extracranial 3rd segment),
            • Single exception being a patient with direct trauma causing proximal VA involvement.
          • This predilection is possibly explained by the fact that the first and third portions of the VA are movable, whereas the second and fourth are relatively immobilized by bone.
    • Treatment
      • Medical treatment
        • Unless has hemorrhage or large ischemic stroke, medical therapy should be started ASAP.
        • Anticoagulation
          • Start heparin
          • Followed by oral agents (e.g. Coumadin) probably for a total of 6 months.
            • Recent preliminary study showed antiplatelet therapy was equally as effective.
      • Endovascular treatment.
        • Indications for surgical or endovascular intervention.
          • SAH (due to their propensity to rebleed) + Intradural dissections.
          • Extradural lesions with
            • Dissections that progress (angiographically) OR
            • Persistent symptoms in spite of adequate medical therapy.
          • Medical therapy is
            • Ineffective
            • Contraindicated
          • Dissection causes symptomatic flow-limiting stenosis.
        • As with traumatic dissections, endovascular techniques are now assuming a more prominent role in management of spontaneous dissections
          • Given the small number of patients treated and the fact that medical therapy is generally effective, the role of stenting for dissection remains to be defined.
        • Techniques
          • Stents (mainly)
            • Types of stents used
              • Balloon-mounted
              • Self-expandable
              • Covered stents
          • Occlusion
          • Angioplasty
      • Surgical treatment.
        • Indicated
          • Medical and endovascular tx is not possible and further progression of clinic symptoms
        • Intraoperative identification of site of dissection:
          • Fusiform or tubular enlargement of the artery with discoloration due to blood within the arterial wall (the discoloration has been described as black, bluish, purple, purple red, or brown).
        • Surgical treatment of intradural dissection when endovascular techniques are not an option includes the following alternatives:
          • Non-clippable aneurysms may be candidates for Hunterian occlusion of the VA proximal to the BA
            • Either by microsurgical technique, or by endovascular techniques which may not be as precise
            • Some may not tolerate clipping the dominant VA, especially if the contralateral VA is hypoplastic. Conversely, some may tolerate bilateral VA occlusion.
            • Balloon test occlusion is recommended:
              • If the dissection involves the PICA origin, then clip proximal to dissection.
                • PICA then fills from retrograde flow, and the reversal of flow across the site of dissection should push the intima back against the wall
              • If the dissection is proximal to PICA and doesn’t involve PICA, then trap the aneurysm between clips. PICA fills by retrograde flow
              • If the aneurysm begins distal to the PICA origin, occlude the VA distal to the PICA takeoff
          • Combining VA clipping (non-clippable aneurysms may be candidates for Hunterian occlusion of the VA proximal to the aneurysm) + Vascular bypass, options:
            • Side-to-side PICA-PICA anastomosis
            • Transplantation of the PICA origin to the VA outside the aneurysm
            • Occipital artery-to-PICA bypass
          • Resection accompanied by autogenous interposition vein graft
          • Non-occlusive surgical techniques
            • Clipping with specially designed clips for fusiform aneurysms (e.g. Sundt-Kees clip)
                • notion image
            • Wrapping: of dubious benefit
    • Vertebrobasilar system dissections excluding the VA
      • Basilar artery dissections tend to present with brainstem infarction and more rarely with SAH.24 The prognosis is generally regarded as poor. Endovascular techniques may be able to treat some.