Traumatic dissection of the parent cerebral arteries

Summary

Objective of the thesis: This summary statement describes epidemiology, etiopathogenesis and management of not only traumatic dissections of the parent cerebral arteries.

Content: Craniocervical arterial dissection is a rare cause of CVA in younger individuals. It develops on the basis of a rupture in the vascular wall with the formation of occlusive stenosis or dissecting aneurysm. As a rule, the primary symptom is headache with associated neurological symptoms (typically partial Horner’s syndrome or paresis of the head nerves) or manifestations of acute ischaemia. The basis of the diagnostics is in the acute phase of ultrasonography, usually with the addition of subsequent angiography; magnetic resonance is also diagnostically valuable. Therapy of extracranial dissections is usually medicamental with acute heparinisation; in intracranial dissections, interventional treatment with stenting of the affected segment is preferred due to high risk of subarachnoid haemorrhage. The last option is the surgical treatment. The prognosis of patients is relatively favourable, with a complete recovery in 75-85% of patients with extracranial dissection; the prognosis for intracranial dissections is significantly worse.

Conclusion: Acute craniocervical arterial dissection is a serious condition requiring prompt diagnosis and therapy, especially where intracranial arteries are affected. However, the expanding possibilities of intervention therapy bring new therapeutic possibilities.

Keywords:

interventional radiology – Traumatic dissection – brain arteries – head trauma

EPIDEMIOLOGY

Cervicocerebral artery dissection accounts for approximately 2 % of all cerebrovascular accidents (CVA), but is one of the most significant causes of CVA in younger individuals. The majority of patients with arterial dissection are aged between 30 and 50 years, with an average of approximately 40 years. In patients under 45 years of age, arterial dissection is the second most common cause of CVA and accounts for 10–25 % of ischaemic cerebral accidents. Although there is no predilection of any gender in adult patients, women are on average 5 years younger at the time when the disease occurs. In childhood, arterial dissections are rare; they mostly occur in boys. The incidence of this disease in the population is reported between 2.6 and 2.9 cases per 100,000 inhabitants per year. Dissection of a. carotis interna (ACI) in (Mayo Clinic Series) was observed in 3.5 cases per 100,000 patients over 20 years of age. However, this disease is often „underdiagnosed“ due to its asympto­matic course.

Patients with intracranial dissection are mostly younger than patients with a disease in cervical area. Dissection in the vertebral artery area accounts for about one-third of the number of ACI dissections, i.e. an incidence of 1.0 per 100,000 inhabitants. Most vertebral artery dissections are extracranial in localisation and account for approximately 15 % of cervicocerebral dissections, while the intracranial segment is affected in 5 %. The age average age of patients with intracranial vertebral dissection in an isolated lesion is around 40 years, while in patients with an extension into the basilar artery it is 30 years. Unlike extracranial dissections in the carotid and vertebral circulation, intracranial dissections of the vertebral artery occur mainly in men [9].

PATHOLOGY

Arterial dissection usually begins with a tear through the intima, which leads to formation of an intramural haematoma with formation of a false lumen. The intramural haematoma can be localized between the layers of tunica media, but it can also be situated eccentrically, either under the tunica intima line (subintimal dissection) or under the tunica adventitia layer (subadventitial dissection). Subintimal dissections are usually responsible for the stenotising nature of the lesion, while subadventitial dissection tends to result in aneurysmal dilations. These are often incorrectly referred to as „false aneurysms“ or „pseudoaneurysms“; however, these are genuine aneurysms because their wall is formed by layers of vascular wall (i.e. media and adventitia). Therefore, „dissecting aneurysm“ is a more appropriate name [18].

In intracranial arteries, the missing lamina elastica external and thin adventitia in the case of subadventitial dissection lead to subarachnoid haemorrhage. This occurs in one fifth of the patients with am intracranial carotid dissection and in more than a half of patients with intracranial vertebral artery dissection.

PATHOGENESIS

Pathogenesis of most arterial dissections remains unknown. They can be iatrogenic, or caused by a vessel trauma. However, most arise spontaneously or after previous minimal wall trauma. The invoking cause may be previous sharp head movement, sneezing, vomiting, chiropractic manipulation, yoga exercises, painting, sexual activities, resuscitation, and numerous sports activities [14].

Traumatic dissections of intracranial parent arteries can occur during a wide range of direct and indirect traumas, typically a direct blow at the neck area. Less common mechanisms include the extension and rotation of head in high-energy injuries. It is reported that about 0.67 % of the hospitalised patients after a major car accident have some kind of internal carotid impairment, of which about 76 % are intimal dissections, pseudoaneurysm or their combination [5]. Dissection can also occur during neck and cervical spine injuries due to opposing forces (whiplash injury); dissection can also occur in a fall; in suicidal attempts, the vertebral artery is typically impaired. There is also a risk of injury in traumas with less energy in case of other associated arterial diseases (see below). More rarely, a blood vessel incarceration between the mandible and cervical spine can also be seen, followed by dissection during hyperinclination; in this case, internal carotid is at particular risk. Other rare causes include intraoral injuries and fractures of the base of the skull. Hughes and Brownell described a higher risk of dissection in sternum fractures or other chest injuries when arteria innominata is extended, increasing the risk of injury to the parent carotid arteries [7]. These mechanisms lead to intimal tear and the development of symptoms of intracranial dissection [6]. Already described cases of possible etiology include falling in sports, at school, snowball injuries, blows at the back of the head, fistfights, etc. [10]. The possibility of developing a symptomatic dissection even with a big delay after primary injury is crucial for the diagnosis; manifestation even after 2 weeks to 6 months after the injury is not excluded [12].

Fibromuscular dysplasia, which is found in 15 % to 20 % of all patients with cervicocephalic dissection and is present in more than a half of patients with bilateral involvement of carotid artery, may be a non-traumatic basis for wall dissection. Approximately 1 % to 5 % of patients have detectable inherited connective tissue disorder such as Ehlers-Danlos syndrome type IV, Marfan’s syndrome, autosomal dominant polycystic kidney disease, bone disease - osteogenesis imperfecta type I, pseudoxanthoma elasticum, or alpha1-antitrypsin deficiency. Dissection also tends to be present in cystic medial necrosis of the arterial wall and Moyamoya disease. A connection with the anomalous course of the artery is also observed, such as a looping and tortuosity of the internal carotid artery or vertebral artery. Five percent of patients with spontaneous dissection have at least one relative with spontaneous dissection of the aorta or originating branches, including carotid and vertebral arteries.

Additional reported risk factors for dissection include: migraine, recent infection, pregnancy, hyperhomocysteinemia [11], smoking, hypertension, and oral contraceptives. No genetic mutation responsible for most of the cervical arterial dissections has been identified. Gene mutation screening for type V procollagen (COL5A1), type III collagen (COL3A1) and tropoelastin (ELN) was negative. However, pathogenesis is mostly multifactorial, the cause being a mechanical factor affecting the impaired artery wall, which is probably genetically or otherwise affected [2, 3].

Localisation of dissections

Dissections of the extracranial segment of the carotid arteries and vertebral arteries account for approximately 80 % to 90 % of all cervical cephalic dissections. This disparity can be explained by the large mobility of the extracranial segments and the potential injury when the vascular wall comes into contact with bone structures such as the transverse process of the upper cervical vertebrae. Extracranial dissection of the internal carotid artery is usually formed 2 cm distally from carotid bifurcation, near the C2 – C3 vertebrae and continues cranially at different lengths of the impairment. Most often, it ends at the entrance of the internal carotid artery into the petrous bone at the place where the wall of the artery is protected. This localization is typically different from atherosclerotic carotid impairment (where there is a typical impairment in the bulb and siphon).

The vertebral artery is the most vulnerable in section C1 – C2, where it leaves foramen transversum and enters the intracranial segment (V3 segment). C1 – C2 section is affected in one half to two thirds of all vertebral artery dissections and in 80 % – 90 % of dissections caused by rotation [18].

Intracranial dissection is more common in children and adolescents than in adult patients. While intracranial dissections in children are more common in the anterior circulation, in posterior circulation they are more common in the adult patient population. The most common site of intracranial impairment is the supraclinoid segment of the ICA and the stem of a. cerebri media. The most common segment of intracranial dissection of the vertebral artery is the V4 segment at or near the origin of the posterior inferior cerebellar artery. In these places, the artery can be compressed during manipulation, the media and adventitia are thinning, the elastic components of lamina elastica externa are disappearing [2, 3].

Mechanism of the ischaemia

Cervical cephalic dissections can cause ischaemic symptoms due to a haemodynamically significant reduction in flow by narrowing or occluding the artery, thromboembolic complications, or a combination of both. Numerous studies have identified distal embolism in the branches of the median cerebral artery after dissection of the wall of the internal carotid artery as the cause of ischaemic symptomatology.

CLINICAL SYMPTOMS

Extracranial dissection of the internal r carotid artery

Local symptoms: The most frequent symptom of dissection of the extracranial segment of the internal carotid artery is pain with propagation to the neck, face, and head (isolated or together with cerebral or retinal ischaemic symptoms). Incomplete Horner’s syndrome is present in approximately one third of the cases.

Pain is present in more than 80 % of dissection cases and is an initial symptom in one half to two thirds of the patients. In 60 % up to 75 %, it can precede the other symptoms for hours up to weeks. The usually graduating nature of the pain is ipsilateral in localisation, but there can also be bilateral headaches. Pain at the front of the neck is present in 20 % to 30 % of patients, facial and orbital pain in more than 50 % of patients. Ipsilateral partial oculosympathetic paresis occurs in more than 30 % of patients with impairment of sympathetic fibres of the internal carotid plexus. Miosis and ptosis are usually present, while the face remains intact, except for a small area of the forehead, because most sympathetic fibres supplying the face run along the external carotid artery. Head nerve paresis is present in approximately 12 % of patients with impairment of most often the cranial nerve XII, and less often of the cranial nerve IX, X, and XI. Approx. one quarter of patients have pulsatile tinnitus [9].

Ischaemic symptoms: They are described in 50 % to 90 % of the patients. The onset of most ischaemic symptoms occurs around week 1 from the beginning of the pain; according to some studies, the median of the onset of symptoms is approx. 4 days. Most cerebral infarctions are territorial, corresponding rather to embolisation etio­logy. Transient ischaemic symptoms are described in 50 % of patients and are repeated in more than a half of the patients. Transient monocular blindness occurs in one quarter of the patients. Ischaemic symptoms in dissections are more commonly associated with occlusion or stenotisation of the artery, while dissection with aneu­rysms is more often caused by the Horner’s syndrome or cranial nerve impairment.

Intracranial dissection of the internal carotid artery

This type of dissections is observed more frequently in younger individuals; it is mostly accompanied by ipsilateral headache and ischaemic symptoms with significantly shorter delay. Convulsions, syncope, and short-term loss of consciousness are present in one half of the patients. Three quarters of intracranial dissections affect the supraclinoid segment of the internal carotid artery or the stem of the middle cerebral artery. Bila­teral intracranial dissection is less common than in extracranial localisation. Subarachnoid haemorrhage in subadventitial dissection occurs in approximately 20 % of cases of intracranial dissection of the internal carotid artery [2, 3].

Extracranial dissection of the vertebral artery

Local symptoms: Pain occurs in one half to two thirds of patients and is typically ipsilateral and occipital; it may be stabbing or pressure-like pain, usually of an escalating nature. It is usually one-sided, but can be bilateral in one third of cases.

Ischaemic symptoms:Most patients with vertebral artery dissection have ischaemic symptoms. The median of development of ischaemic symptoms from the onset of pain is 14 days. Lateral medullary symptoms can be observed as isolated or in combination with stem symptoms and impairments in circulation of the posterior inferior cerebellar artery or medullary symptoms in cervical localization.

Intracranial dissection of the vertebral artery and basilar artery

Intracranial dissection of the vertebral and basilar artery differs from extracranial impairment due to presence of subarachnoid haemorrhage. This is present in one half to two thirds of adult patients, but it is usually not described in children. Basilar artery dissections are rare; they may be either isolated, or associated with vertebral artery dissection. Clinical signs may be exacerbated by rapidly progressing brainstem ischemia or pain caused by the pressure of the intravascular haematoma. Intracranial dissection may result in subarachnoid haemorrhage or dissecting aneurysm with subadventitial or transmural impairment [4].

DIAGNOSTICS

The combination of non-invasive MRI and MRA examinations is currently indicated as a diagnostic method of choice in case of clinical suspicion of dissection of the parent cerebral arteries (whether spontaneous or traumatic). Duplex Doppler ultrasonography and transcranial Doppler examination are also used for traumatic dissections. More recent techniques include computed tomography angiography. Conventional digital subtraction angiography, possibly supplemented by digital rotational angiography, plays an important role in determining a number of accompanying complications: formation of a false lumen, pseudoaneurysm or dissecting aneurysm, as applicable, and the presence of intraluminal thrombus or the occurrence of distal cerebral embolisation. Endovascular neurointerventional procedure may, in indicated cases, follow directly after the diagnostic angiographic examination.

Ultrasonography

Information about dissection on the cervical extracranial segment of the internal carotid artery is mostly indirect (flow alteration, visibility of an intimal tear) due to the frequent beginning of dissection 2 cm distally from the carotid bulb. Decrease or absence of flow, retrograde flow in supraorbital arteries or bidirectional flow in ICA give suspicion of dissection of the distal segment of the internal carotid artery or pre-occlusive stenosis or closure of the internal carotid artery. The presence of conical narrowing above the bulb of the internal carotid artery or the visibility of the true and false lumen are available in 15 % of patients.

Extracranial colour Doppler examination of vertebral arteries may also detect weakening or disappearing of flow or bidirectional flow. TCCD examination provides information about the flow distally from the place of dissection or the occurrence of distal arterioarterial embolisation to the circulation of the middle cerebral artery or basilar artery. Repeated examinations during conventional anticoagulant therapy allow for determining the development of the disease, regression of the finding of stenosis, or the recanalization of the occlusion caused by the intimal „flap”.

Angiography

Although MRI, MRA and US are usually sufficient to dia­gnose extracranial carotid dissections and sometimes extracranial vertebral dissections, angiography is usually the definitive test in the diagnosis of intracranial impairment, as well as of extracranial vertebral dissections. Although it is an invasive examination, as compared with other methods it provides an additional accurate depiction of the shapes of abnormalities associated with the dissection, including the intimal tear, intraluminal thrombus, „tapered-flame-like“ occlusion, double lumen, „string-like” stenosis of arteries, and formation of dissecting aneurysm. Double lumen and intimal tear are characteristic angiographic findings. Intracranially, angiography can reveal cerebral aneurysms (typically located outside the branching in a straight segment of the arteries and causing subarachnoid haemorrhage) and irregularly narrowed course of arteries. Fibromuscular dysplasia occurs in up to 15 % of multifocal dissections.

Computer tomography

Advanced CT applications – such as multidetector spiral CT – angiography (CTA) – can be very useful in traumatic dissections. CTA examination is fast, allowing exa­mination of unstable, monitored patients. Experience is limited so far, but it turns out that CTA can provide information similar to that of classical angiography with high sensitivity and specificity.

Magnetic resonance

Simultaneous examination of the brain and large vessels is carried out by the standard technique of T1 and T2 weighted images supplemented by FLAIR axial MRI images with three-dimensional (TOF) MRA. A characte­ristic MRI finding in the extracranial section is the reduction or disappearance of the flow signal, the narrowing of the artery lumen marginally lined with hyperintensive crescent of the present intramural haematoma in the wall typically in T1 and FLAIR images. The intensity at the haematoma site in T1 and T2 weighted images depends on the age of dissection with the presence of methemoglobin. However, in some cases the signal at the thrombus site may be hypointense due to the presence of deoxyhemoglobin or hemosiderin in chronic types. The presence of cerebral ischaemia in the dissections of cervical segment of the internal carotid artery is observed in 83 % cortically, in 60 % subcortically with MCA circulation impairment in 99 %, ACA in 4 %, PCA in 3 % and interteriorial areas in 5 %. Intracranial dissections give a less specific picture in MRI and MRA examinations; the intramural haematoma can also be captured here, but digital subtraction angiography is dominant for the diagnosis.

Extracranial vertebral dissection typically occurs in the C1–C2 section, typical T1 and T2 modalities including FLAIR are less sensitive in this localization. A native MRI scan may show the occurrence of early ischaemia in the cerebellum and brain stem area.

TREATMENT

Medicamental treatment

The treatment of extracranial carotid dissections is controversial and is based mainly on empirical and clinical observations (major randomized clinical trials are missing). Most acute cerebral ischaemiae associated with carotid artery dissection are caused by arterio-arterial embolisation into distal cerebral circulation. Therefore, the most common generally recommended treatment is acute heparin anticoagulation followed by warfari­nization, with repeated ultrasonography or MRI-MRA checks, as appropriate. If the dissection is healed after three months, anticoagulation is replaced by anti-aggregation therapy. If irregular narrowing of the lumen of the arteries persists or a dissecting aneurysm is present, warfarinization is prolonged for another 3 months.

However, anticoagulation is contraindicated in intracranial dissections due to the high risk of subarachnoid haemorrhage (SAH). This limitation is typical for intracranial vertebral dissection, where the risk of SAH is up to 50 %. Other contraindications to heparinisation include the expansive effect and haemorrhagic transformation of the large infarction deposit and the presence of an intracranial dissecting aneurysm.

Intervention treatment

Endovascular treatment is becoming increasingly important especially in patients: (1) where conservative anticoagulant therapy has failed; (2) in patients with persistent ischaemic symptoms; (3) in patients contraindicated to anticoagulant therapy; (4) in unavailable lesions; (5) in patients with narrow stenosis persistence and/or progression of expanding dissecting aneurysm. In these cases, endovascular treatment with balloon angioplasty and implantation of a self-expandable stent or a balloon-expandable stent can reconstruct the true lumen with flow restoration and obliteration of the false lumen.

In dissecting aneurysms, the application of coated stents (stent grafts) or the implantation of spirals in combination with the introduction of a stent to remodel the lumen of the artery is a method of choice. After stent implantation, anti-aggregation therapy is recommended for a period of 3 months. In intracranial dissections of the vertebral arteries associated with subarachnoid haemorrhage, dissecting aneurysms are at high risk of new haemorrhage. In these cases, the method of choice is the therapeutic occlusion of the artery using detachable balloons or embolisation by spirals after performing occlusive tests to verify sufficient collateral flow [8].

Surgical treatment

At the present time of incoming intervention therapy, the need for surgical treatment is decreasing. Surgical approaches consist in tying the carotid artery, resection of the aneurysm with artery reconstruction, or bypass procedures with the suture of high-flow bypass on petrous or supraclinoid segment of the internal carotid artery. Clipping of aneurysms is usually difficult due to the fusiform shape of dissecting aneurysms. Resection of extracranial dissecting aneurysm with venous graft replacement or primary re-anastomosis is a surgical approach technique. However, it tends to be associated with a higher incidence of transient nerve impairment resulting from dysphonia or dysphagia, especially in dissecting aneurysms near the base of the skull. Due to the occurrence of recurrent dissections in contralateral arteries, flow-maintaining approaches are currently preferred, whether using the bypass procedure or endovascular therapy, or combination therapy, as appropriate.

COURSE AND PROGNOSIS

Clinical prognosis of extracranial dissections of carotid and vertebral arteries depends on initial ischaemic impairment, but is favourable in most cases. Complete improvement is described in 75 % to 85 % of cases. Mortality associated with dissection of the extracranial segment is less than 5 % and significant persistent neurological deficit occurs in 5 % to 10 % of patients. The neurological finding is less favourable in occlusions of carotid arteries, traumatic dissections, or intracranial dissections associated mainly with the occurrence of SAH. Roughly one half of patients with intracranial impairments have a major neurological deficit. Dissection of the basilar artery is associated with mortality of about 60 %.

The risk of recurrent dissection is highest during the first year and is described in 2 % of patients within the first month and in 1 % in an annual follow-up. Patients under 45 years of age are the ones most often affected by recurrent dissection in up to 17 %. Arterial occlusions of the carotid arteries recanalize in more than a half of patients, and complete curing is described in more than 20 % of dissecting aneurysms. Persistent dissecting aneurysms usually do not rupture, if they regress, then mostly within 3 months, but only rarely after 6 months [1, 17].

MUDr. František Jalůvka

frantisek.jaluvka@fno.cz