Vascular injury following lateral skull base trauma: diagnosis and management

Introduction

Head trauma has been cited as the most frequent clinical presentation in the emergency department. According to a 2013 survey by American College of Surgeons, nearly 800 trauma admissions were reported across different healthcare facilities in the United States. Additionally, skull base injuries were seen in one-third of the patients. The reported incidence is even greater in the developing countries or regions of limited healthcare access. Traumatic brain injury (TBI) therefore represents a global health problem contributing to high rates of in-hospital morbidity and mortality.

Etiology

The etiology can be broadly classified into penetrating and nonpenetrating trauma. Nonpenetrating injuries have been identified as the leading causes of skull base fractures with a prevalence of 7%–16%. This usually includes high-velocity trauma including motorized vehicle collisions (MVCs), blunt cerebrovascular injury (BCVI) via falls, and assaults. Penetrating trauma (mostly gunshot wounds) accounts for less than 10% of the cases. ^, Identification of skull base fractures often prompts assessment of coexisting orbital and facial fractures in addition to intracranial lesions. The extent of potential vascular complications and resulting management depends on the location and pattern of the fracture, which is in turn determined by the mechanism of injury and type of impact.

Skull base anatomy

The skull base is made up of seven bones, the paired frontal and temporal bones, and the unpaired ethmoid, sphenoid, and occipital bones. It is divided into anterior, central, and posterior regions, which form the floor of the anterior, middle, and posterior cranial fossae.

The anterior skull base (ASB), formed by the frontal and ethmoid bones, separates the anterior and inferior frontal lobes and olfactory structures within the anterior cranial fossa from the orbits and the sinonasal cavity. Anterior fossa is bound by important structures: The lateral and anterior borders are formed by the frontal bone and frontal sinus, and floor is formed by the cribriform plates and roof of the ethmoid sinuses. Lesser wing of the sphenoid bone, including the clinoid process, forms the posterior border between the anterior and central skull base. Anterior and posterior ethmoid artery foramina are located in ASB.

The central skull base (CSB), formed by the sphenoid and anterior temporal bones, is closely related to the pituitary gland, cavernous sinuses, and the temporal lobes superiorly, and the sphenoid sinus anteriorly and inferiorly. The anterior border of the CSB is formed by the posterior margin of the lesser wing of the sphenoid bone, clinoid process, and tuberculum sella. The floor is formed by the greater wing and central body of the sphenoid bone, the sphenoid sinus, and the sella. The posterior border between the central and posterior skull base is formed by the superior margin of the petrous ridge of the temporal bone, the basi sphenoid portion of the clivus, and the dorsum sella. Important vascular structure in this par includes the internal carotid artery.

The posterior skull base (PSB) is formed by the posterior temporal bone and the occipital bone. The anterior border is formed by the petrous ridge of the temporal bone superiorly, and the clivus (basi occiput portion) inferiorly. Foramen magnum located in the PSB transmits the vertebral artery.

According to Van Huijzen's classification, extension lines from the suborbital fissure and the petrooccipital fissure intersect at the apex of the nasopharynx inside, pointing outward to the zygomatic bone and posterior margin of the mastoid process, respectively. The triangular area between the two lines is described as a lateral skull base and includes parapharyngeal space, infratemporal fossa, and pterygopalatine fossa. The lateral skull base houses important neurovascular structures including internal carotid artery, the lateral sinus, and sigmoid that will give the vein jugular, and petrosal sinus.

A 5-year retrospective study of 1606 patients with skull base trauma reported the highest frequency of temporal bone (40%) involvement followed by orbital roof (24.1%), sphenoid (22.6%), occipital (15.4%), ethmoid (10.8%), and clival bone (1.03%).

Blunt cerebrovascular injury classification

The diagnosis of vascular injury in association with skull base trauma is closely tied to the screening criteria used for patient evaluation. This then facilitates and determines the choice of diagnostic modalities and subsequent management. Biffl et al. proposed a grading scale, Denver criteria, to assess blunt cerebrovascular injuries (BCVIs) and subsequent neurological outcomes: grade I (mild intimal injury or irregular intima), grade II (dissection with raised intimal flap/intramural hematoma/intraluminal thrombosis with luminal narrowing >25%), grade III (pseudoaneurysm), grade IV (vessel occlusion/thrombosis), and grade V (vessel transection). This is commonly used for classification of blunt injury in carotid and vertebral arteries. A total of 76 patients presenting with blunt carotid arterial injury were included in the analysis. Grade I injuries were associated with the best prognosis, with two-thirds of cases resolving spontaneously. On the other hand, vascular transection (grade V) was shown to be refractory to any intervention. Based on their findings, Biff et al. recommended endovascular repair for grade II, III, IV, and V lesions in addition to systemic anticoagulation. Isolated heparin therapy was associated with progressing dissections (grade II) and less than 10% of pseudoaneurysms (grade III) healing. Another clinically relevant tool is Memphis criteria.

Both Memphis ( Table 10.1 ) and Denver criteria ( Table 10.2 ) have been modified to further improve the utility of these tools in diagnostic settings. Overall, introduction of the screening criteria in combination with advanced imaging has significantly improved the sensitivity of BCVI identification.