Carotid artery dissection
- Incidence: 2.00 cases per 100,000 person-years
- Peak incidence: 50-60 years
- Sex ratio: 1:1
- A small tear occurs in the tunica intima, which is the innermost wall of the carotid artery
- Blood enters the space created by the tear between the outer and inner layer of the artery to form an occlusion or stenosis
- If the occlusion is complete, it can lead to ischaemia
- Some complete occlusions are asymptomatic as the bilateral circulation to the brain keeps it sufficiently perfused
- Over time, blood clots can form at the site of tear and break off to form emboli
- Emboli may then travel through the arterial system and into the brain to reduce the blood supply in the brain
- This can cause an ischaemic stroke or infarction
The mechanism in traumatic carotid artery dissection
- Head and neck trauma are the most common causes of traumatic carotid artery dissection
- For most internal carotid injuries, the most likely mechanism is rapid deceleration that results in neck hyperextension
- This causes stretching of the internal carotid artery over the cervical vertebrae and results in a tear in the tunica intima
The following signs and symptoms occur in carotid dissection:
- Headache (60-75%): usually unilateral, severe and of a gradual onset
- Partial Horner’s syndrome (58%)
- Pulsatile tinnitus (27%)
- Unilateral neck pain (25%)
- Transient monocular blindness (25%)
- Cranial nerve palsy (12%): most commonly cranial nerves IX to XII
These symptoms may occur before patients have a stroke.
- Hemisensory loss
- Vascular bruits
- Only present in one-third of patients with carotid dissection
- Ipsilateral neck pain
- Ipsilateral Horner’s syndrome
There are three main imaging tests that can be used:
- Carotid ultrasound: used as a screening investigation
- Magnetic resonance angiography (MRA) and fat-suppression magnetic resonance imaging (MRI)
- Computed tomography (CT) angiogram
Carotid ultrasound may be used as a screening investigation as it is non-invasive. It has poor diagnostic value in intracranial carotid dissections but has high sensitivity in diagnosing extracranial carotid dissection and ischaemic symptoms. Luminal narrowing may be observed on ultrasound.
Magnetic resonance angiography (MRA) and fat-suppression magnetic resonance imaging (MRI) are the preferred methods to diagnose carotid dissection. These techniques have high specificity and sensitivity, lack exposure to ionising radiation and can visualise intramural haematomas. MRA may show narrowing or vessel occlusion in the carotid dissection and there is often a ‘string sign’ on imaging. A double-lumen sign (a false and true lumen) is seen on fat-suppression MRI in carotid dissection. Intramural haematomas caused by dissection are observed in the presence of luminal narrowing and increased signals.
A computed tomography (CT) angiogram can be used in patients with no contraindications. This may show a double-lumen sign or flame-like taper of the lumen. It can be completed concurrently with a CT scan of the brain to look for signs of an acute stroke or haemorrhage.
- Whether the dissection was spontaneous or caused by trauma
- Whether the patient has had a stroke
- Whether the dissection is extracranial or intracranial
- Whether there is haemorrhage
Treatment is based on preventing infarction and similar to the treatment of an acute cerebrovascular accident. In patients with no contraindications, thrombolysis can be used within three hours of presentation. Outside of this, anticoagulation and antithrombotic treatments can be used if indicated. If ischaemic symptoms continue, endovascular stenting and surgery are possible options. Asymptomatic patients do not usually require treatment.
Antiplatelet and anticoagulation medications are used to reduce the risk of a stroke occurring. They are also used to prevent thrombus formation at the injured site and avoid the formation of embolism into other arteries in the brain. These medications help to restore blood flow and improve neurological outcomes.
The main methods of treatment include:
- Antiplatelet medications such as aspirin
- Anticoagulation with warfarin and heparin
- Endovascular interventions and surgery
Antiplatelet medications such as aspirin can be used in traumatic cases. They are specifically preferred in intracranial carotid dissections and extensive infarcts.
Anticoagulation with warfarin and heparin is used to prevent the progression of neurological symptoms. It is only given to patients who have had an intracerebral haemorrhage ruled out using a CT scan of the head. Contraindications to heparin and warfarin include intracranial dissection and extensive infarcts.
Thrombolysis can be used in patients with a stroke caused by spontaneous extracranial dissection. Contraindications include intracranial dissection and involvement of the aorta due to the risk of aortic rupture.
Endovascular interventions such as stenting have been found to be beneficial in internal carotid dissection and concurrent proximal intracranial occlusion. Urgent surgical interventions may be used in patients who present with subarachnoid haemorrhage. Surgery can also be performed in symptomatic aneurysmal dilatation and chronic carotid dissections. Medical management is usually the first method of treatment due to the risks involved in surgery.
- Transient ischaemic attacks (TIA)
- Subarachnoid haemorrhage (SAH)
Internal carotid dissections account for 20% of strokes in younger patients. Strokes and TIA can be caused by emboli reducing blood flow to the brain. These emboli form from thrombus at the site of injury. Complete occlusion from thrombus formation in the carotid artery may also cause a stroke.
Pseudoaneurysms occurs when a pool of blood collects between the tunica adventitia and tunica media, the two outermost layers of an artery. They are more common in tortuous or coiled arterial segments. Saccular pseudoaneurysms are more common in internal carotid dissections and most pseudoaneurysms decrease in size over time and some resolve completely.
Subarachnoid haemorrhage is a rare complication that occurs in carotid dissection. SAH following internal carotid dissection is more likely after head and neck trauma. In these patients, thin layers in the tunica media and tunica adventitia and an underdeveloped external elastic lamina are the main contributing factors for causing an SAH.