Surgical management of large traumatic anterior cranial base defects via craniotomy

Introduction

Major craniofacial trauma can result in numerous comminuted fractures of the frontal and facial bones, and when in-driven, multiple lacerations of the dura mater, laceration and contusion of the underlying frontal lobes, and cerebrospinal fluid (CSF) leak in the form of rhinorrhea, direct leak via open lacerations and tissue defects, or even from the orbit. Surgical management of these injuries requires a thorough understanding of craniofacial anatomy and repair principles that will result in long-lasting repair, healing, and avoidance of complications.

These principles of management of large traumatic anterior cranial base defects include early soft tissue repair, precise anatomic bony fixation, and one-stage reconstruction if possible. ^, The goal of craniofacial repair is restoration of the correct anatomic alignment and positioning of the maxilla relative to the cranial base and mandible. Cranial fractures are generally repaired first followed by reattachment of the maxillofacial skeleton unless there is massive cranial bone loss (in which case the order may need to be reversed). Also key to successful repair are reestablishing dural integrity and removing sinus mucosa during cranialization of the frontal sinus for prevention of future infection and mucocele.

Epidemiology

The majority of patients sustaining traumatic brain injury (TBI) also have maxillofacial injuries ; therefore, a thorough understanding of management of these injuries is required for neurosurgeons treating patients with TBI. The most frequent causes are high-speed motor vehicle crashes, but certainly falls, assault, industrial and recreational mishaps, and other mechanisms of injury occur. As personal safety devices have evolved for automobiles, these mechanisms have decreased over time. Early studies showed that the frontal sinus was fractured in approximately 30% of patients with maxillofacial injury, was associated with higher velocity mechanisms of injury, and represented 5% to 15% of all maxillofacial injuries. When present, unconsciousness associated with TBI was present in 76% of patients with frontal sinus fractures. The anterior table alone is involved in approximately one-third of injuries, and the other two-thirds involve the anterior table, posterior table, or nasofrontal ducts. It is the latter injury pattern that is the main focus of this chapter, with attention to injuries in older teenagers and adults with pneumatized frontal sinuses.

Nasoorbitoethmoidal (NOE) fractures provide additional surgical challenges, as do orbital fractures and orbitozygomatic fractures. NOE fractures associated with CSF leak may involve the ethmoid sinuses, the superior and middle turbinates, or the perpendicular plate of the ethmoid bone, and the nasal bones may be driven into the interorbital space. Given that the medial orbital walls are relatively thin, comminuted fractures are often present. Bony fragments in these fractures are prone to entering the anterior cranial fossa and piercing the dura at the cribriform plate and the roof of the ethmoids. Frontal bone and maxillary fractures need to be stabilized and fixated before fixing NOE fractures, which, if inadequately repaired, can result in significant facial deformity.

Diagnosis and indications for surgery

As with all trauma, the first interventions include the ABCDE method of workup: airway, breathing, and circulation followed by neurologic assessment (disability) and assessment for temperature derangements and critical skin injuries (exposure). Part of every polytrauma assessment for those with head and facial trauma is inspection for CSF per the nares, the external auditory canals, the nasopharynx (if possible given intubation status), and from the orbits or soft tissue defects. Visualization of the tympanic membranes and documentation of soft tissue abrasions, lacerations, ecchymosis, edema, and deformities are also performed. Careful exploration or palpation of lacerations may demonstrate underlying fractures and fracture fragments. It should be noted that CSF leaks are not always seen in the acute stages of assessment because they can be tamponaded by hematoma, brain edema, or soft tissue edema.

Computed tomography (CT) is the imaging modality of choice, with thin cuts and multiplanar reconstructions to thoroughly demonstrate the extent of bony injuries, soft tissue swelling, brain injury, extra- and intraaxial hematomas, pneumocephalus, hydrocephalus, and other acute sequelae of trauma. The presence of pneumocephalus in the ventricles, brain tissue, and CSF cisterns is pathognomonic of dural laceration and should alert the examiner to the high risk of CSF leak and the need for repair. Small air droplets in the epidural space, by contrast, may represent escape from a fractured craniofacial sinus without dural laceration and are managed differently. Other indications for surgery include moderate to severe fractures of the nasofrontal ducts, posterior displacement of the posterior wall (greater than the thickness of bone) or comminuted posterior wall fractures with CSF leak, or minimally displaced posterior wall fractures with persistent CSF leak.

Timing of surgery depends on other life- and limb-threatening injuries, the need for craniotomy for intracranial hematoma evacuation, and the degree of facial and cerebral edema. In general, the sooner the definitive repair can be accomplished, the better for infection prevention, and most major cases should be performed within the first 24 to 48 hours, although other injuries and extent of soft tissue and brain injury often dictate otherwise. Provided the degree of injury is significant, requiring reconstruction of the craniofacial injuries and dural repair, the following techniques may be used to conduct the repair.

Surgical exposure

Preparation

Discussion should be held with the anesthesiology team regarding the potential for air embolism and major rapid blood loss, if there is an injury to the superior sagittal sinus (SSS). The use of a precordial Doppler, central line for air evacuation, and rapid ability to change the position of the operating room table are preventive measures in case air embolism occurs intraoperatively. Likewise, ready availability of blood products in the operating room (OR) should be planned in the case of major rapid blood loss from SSS bleeding. Routine perioperative antibiotics are given. There is considerable controversy surrounding whether antibiotics should be started on admission if surgery is delayed. In general, if prophylactic antibiotics are used, there is a risk of superselection of organisms if the patient develops meningitis. However, vigilance for the development of signs and symptoms of infection is paramount, and antibiotics are started if infection develops. (Signs and symptoms of infection include fever, leukocytosis, meningismus, headache, or enhancement of meninges on CT.)

In the OR, the patient is positioned supine on the operating table, and the patient’s head may be placed in a doughnut, in a horseshoe headrest, or in pins, although the latter are often precluded because of the nature of the incision, soft tissue injuries, or timing. The hair is clipped from the cranium. In general, hair-sparing incisions in major trauma are not used because of the need to assess for occult scalp injuries, including full-thickness lacerations. The planned incision is placed behind the hairline for most patients, extending bicoronally from 1 cm anterior to the tragus on one side to the other and incorporating a curvilinear “widow’s peak” at the midline to aid in cosmetic closure while avoiding tension on the incision at closure ( Fig. 13.1 ). The entire frontal area, extending down to the lateral face and neck and upper face, is sterilely prepped; this often requires creative positioning of the endotracheal tube tape. After the planned incision is marked, self-adhesive drapes are used to include the supraorbital rims in the visualized exposure if possible, taking care not to place strong adhesive on the eyebrows if possible (and when removed, taking care not to pull out eyebrow hairs because they frequently do not grow back.)