Traumatic bilateral internal carotid artery dissection following airbag deployment in a patient with fibromuscular dysplasia

M. A. Duncan*, N. Dowd, D. Rawluk and A. J. Cunningham

Department of Anaesthesia, Intensive Care Medicine and Neurosurgery, Beaumont Hospital, Beaumont Road, Dublin 9, Ireland

Accepted for publication: April 14, 2000


    Abstract
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 Abstract
 Introduction
 Case report
 Discussion
 References
 
This case describes a 39-yr-old male, presenting with left hemiplegia after a road traffic accident involving frontal deceleration and airbag deployment. Brain computerized tomography (CT) scan revealed a right parietal lobe infarct. Contrast angiography demonstrated bilateral internal carotid artery dissection and fibromuscular dysplasia. The patient was treated with systemic heparinization. Neurological improvement, evidenced by full return of touch sensation, proprioception and nociception began 10 days after the injury. To our knowledge, this is the first case report of carotid artery dissection associated with airbag deployment. Forced neck extension in such settings may result in carotid artery dissection because of shear force injury at the junction of the extracranial and intrapetrous segments of the vessel. Clinicians should consider carotid artery injury when deterioration in neurological status occurs after airbag deployment. We propose that the risk of carotid artery dissection was increased by the presence of fibromuscular dysplasia.

Br J Anaesth 2000; 85: 476–8

Keywords: complications, accidents; complications, trauma; complications, fibromuscular dysplasia; arteries, carotid


    Introduction
 Top
 Abstract
 Introduction
 Case report
 Discussion
 References
 
Airbags were developed to decrease the incidence of death and severe injury following road traffic accidents.1 Airbags are reported to cause injuries in 43% of deployments. The majority of these are minor (abrasions and contusions), but severe injury such as upper limb fracture occurs in 4% of cases.1 This case report describes bilateral internal carotid artery dissection, associated with airbag deployment, in a patient with fibromuscular dysplasia.


    Case report
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 Abstract
 Introduction
 Case report
 Discussion
 References
 
A 39-yr-old male driver, height 165 cm, was involved in an acute deceleration, frontal-impact collision. He was restrained by both a seatbelt and an airbag. He was transferred by road ambulance to the Accident & Emergency unit at our institution. On initial examination the patient was haemodynamically stable. His Glasgow Coma Score (GCS) was 10/15 at the time of initial assessment but improved to 13/15 thereafter. Neurological examination revealed a left homonymous hemianopia, left hemiplegia and an upper motor neurone left 7th nerve palsy. Other injuries sustained included metatarsal fractures and anterior neck abrasions. Standard haematological and biochemical investigations and chest and cervical spine radiographs were normal. A brain computerized tomography (CT) scan showed a right parietal lobe infarct.

The patient was transferred to the neurosurgical intensive care unit for invasive arterial pressure monitoring and neurological observations. Supplemental oxygen was administered by facemask. Aspirin 300 mg once daily by mouth was prescribed for its antiplatelet effect. A second brain CT on hospital day 2 demonstrated haemorrhagic transformation of the right parietal lobe infarct. Duplex scan and magnetic resonance angiogram of the carotid arteries was inconclusive. Contrast angiography revealed bilateral internal carotid artery dissection, fibromuscular dysplasia of the internal carotid arteries and thrombus in the right internal carotid artery (Fig. 1). Heparin was commenced with a target activated partial thromboplastin time of 60 s. Warfarin was commenced with a target prothrombin time of 26 s.



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Fig 1 Right carotid angiogram showing intimal dissection (1) at the junction of the extracranial and intrapetrous segments of the internal carotid artery, and the ‘string of beads’ appearance (2) that is characteristic of fibromuscular dysplasia.

 
Recovery of neurological function began with the return of normal GCS on hospital day 3. By day 10, touch sensation, proprioception and nociception in the left upper and lower limbs were evident. Left lower limb power had improved to grade 3/5 on day 24. However, the left facio-brachial palsy persisted. The patient was transferred to a rehabilitation hospital on day 26.


    Discussion
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 Abstract
 Introduction
 Case report
 Discussion
 References
 
Blunt carotid injury presents typically with neck abrasions and neurological sequelae, including hemiplegia, low GCS and a co-existing Horner’s syndrome when the sympathetic chain is stretched across the transverse process of the first cervical vertebrae.2 3 Road traffic accidents are the most frequent cause of blunt carotid injury.3 The mechanism of injury to the internal carotid artery is thought to be a shear force applied to the vessel during forced neck extension, causing intimal dissection at the junction of the immobile intracranial and relatively mobile extracranial portions of the internal carotid artery.2

Fibromuscular dysplasia is an arterial developmental abnormality of unknown aetiology affecting medium-sized arteries.4 5 The incidence of the disorder based on a series of 20 244 post-mortems is two per 1000 population.4 There are four known subtypes, each with its own unique histological appearance (intimal fibroplasia, medial fibroplasia, medial hyperplasia and perimedial dysplasia).5 Affected vessels are elongated, kinked and punctuated with stenoses and microaneurysms.5 These abnormalities produce unique angiographic features which radiologists call the ‘string of beads’ appearance (Fig. 1). The presence of fibromuscular dysplasia may compromise the structural integrity of the affected vessels, including the carotid artery, and therefore predispose to vessel dissection after traumatic injury.

Patients with fibromuscular dysplasia are asymptomatic until they sustain a vessel dissection. They then present with ischaemia of the organs supplied by the affected vessel, for example cerebrovascular accident. Fibromuscular dysplasia is found in 15% of cases of spontaneous carotid dissection.2 6 A report of bilateral internal carotid and vertebral artery dissection in a patient with fibromuscular dysplasia after a road traffic accident has been described.7 Arteriography is the gold standard diagnostic test for both fibromuscular dysplasia and blunt carotid injury.5 8

The management of carotid artery dissection is controversial. Heparinization was associated with an improved outcome in the largest series of blunt carotid injuries.3 However, the safety and efficacy of anticoagulation in the management of stroke following carotid injury has not been demonstrated.9 In our patient, the apparent benefit of heparinization had to be balanced against the risks of a worsening stroke.

Airbag usage is increasing worldwide and is now mandatory in new cars in some countries.1 Airbags function by preventing traumatic impact between the vehicle occupant and the vehicle interior. During a road traffic accident, sensors in the vehicle body detect deceleration and trigger airbag deployment.1 To protect against injury, airbags must be fully expanded before the vehicle occupant is propelled forward by the deceleration of the accident. An airbag expansion speed of 200 mph is necessary. This rapid forceful expansion causes airbag-associated injury in 43% of deployments. In addition, fatal rupture of the ventral ligaments of the cervical spine and brain stem has been described secondary to forced neck extension.10

An increase in the incidence of airbag-associated injury is predicted.1 Drivers of short stature, as in this case, are at increased risk of these injuries.8 9 Their short stature makes it necessary to move the vehicle seat forward in order to reach the foot pedals, thereby bringing the upper body into the path of the expanding airbag. In the USA it is now recommended that airbags should be decommissioned if drivers cannot keep a wheel–chest distance of 10 inches.1

The evidence for airbag-mediated blunt carotid injury by means of forced neck extension is compelling in this case. A less likely explanation is that the patient initially sustained spontaneous carotid artery dissection because of fibromuscular dysplasia and then crashed. However, spontaneous dissections of the carotid artery typically present initially with minor clinical manifestations (e.g. headache),10 and only develop neurological signs after several days.11 12

In summary, this is the first case report of bilateral internal carotid artery dissection, in a patient with fibromuscular dysplasia, associated with airbag deployment. The report suggests that clinicians should consider the possibility of carotid injury when neurological deterioration occurs after a road traffic accident with airbag deployment. Associated conditions, such as fibromuscular dysplasia, may increase the risk of carotid artery injury in this setting. Early carotid angiography is warranted to make the diagnosis.


    Footnotes
 
* Corresponding author Back


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 Abstract
 Introduction
 Case report
 Discussion
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