Management of Skull Base Trauma

General Management

A dedicated, multidisciplinary craniofacial-trauma team is best equipped to manage patients with skull base trauma. Collaborative input with expertise from neurosurgeons; maxillofacial, plastics, and trauma surgeons; and intensivists is required. A multidisciplinary subspecialty team has been shown to reduce costs of care for trauma patients with complex skull base injury through several mechanisms that include a decreased number of consultations, decreased number of transfers to other hospitals, reduced time to operative treatment, and reduced overall length of hospital stay. A universal classification system for skull base fractures is needed to facilitate communication between subspecialty groups and centers, to provide a framework for protocols that guide medical and surgical management, and to enable a systematic approach to prognostication for patients with these injuries.

Anesthesia and Perioperative Considerations

Severe supratentorial head injury usually accompanies skull base trauma, and patients are generally intubated. In the intensive care unit (ICU) they frequently require advanced TBI care to address intracranial pressure (ICP), brain tissue oxygen, cerebral blood flow, and the need for jugular venous saturation monitoring. A central venous pressure line should be inserted to assist fluid management in the ICU and to enable rapid resuscitation in the event of unexpected large artery or venous bleeding during surgery. Intraoperatively, monitoring for air embolus is also indicated for any procedure that exposes over a major venous sinus. Major injury to the neck and upper airway with supraglottic edema frequently accompanies severe skull base trauma, and consideration should be given to performing an early tracheostomy as opposed to endotracheal intubation in these circumstances, as well as involvement with maxillofacial subspecialty teams for combined repairs.

Graft Repair Options

A variety of graft options are available for surgical repair of skull base defects. Autologous grafts are preferred and include vascularized pericranium and rotational flaps of temporalis muscle and fascia. Nonvascularized free grafts of pericranium, temporalis, rectus femoris, and abdominal muscle or fascia lata also can be used. Vascularized pedicle grafts resist infection and incorporate more quickly into the recipient site than free flaps, and they give a watertight seal that is durable for years. ^, In the setting of trauma, defects in the pericranium are common and repair techniques have been described to salvage these grafts. The dura of the anterior falx also can be used to close dural defects.

The accessibility of vascularized, septal mucosal flaps is a valuable adjunct to skull base repairs during endoscopic approaches. The presence of viable tissue in the vicinity chosen for graft placement is important to facilitate graft survival. Fat may be used to fill large defects and is preferred due to its intrinsic hydrophobic properties. Devascularized muscle flaps also may be used. While fat is preferred over muscle for its longer durability, free fat grafts rely on their ability to parasitize blood supply from adjacent soft tissue, and they may resorb when juxtaposed to devitalized bone and dura. ^,

Large bone defects from comminuted fractures in the skull base are best repaired using the patient’s own bone. Large fracture fragments may be debrided, soaked in antibiotic solution, and reapproximated with a titanium craniofacial plating system. Reconstruction by plating of multiple small fragments of the thin bones of the nose and orbit is not recommended, because it carries significant risk of bony resorption of the repair. Fracture defects in the orbital roof should always be reconstructed, either with titanium mesh or with a synthetic prosthesis, to prevent pulsatile exophthalmos. Split calvarium is preferred for autologous repair when large defects cannot be reconstructed primarily with the fracture fragments. Bone also can be harvested from iliac crest and rib. Calvaria bone has a low resorption rate (17% to 19%), whereas the rate of resorption for iliac crest and rib may approach 60% to 80%. Use of oblique angles in the bone cuts can reduce the number of screws and plates required for reapproximation of the bone flap. Septal cartilage also can be used for reconstruction of the ethmoid and sphenoid skull base. Inorganic implants, including both titanium mesh and porous, polyethylene implants, yield excellent cosmetic results for reconstruction of soft tissue and bony defects with a low risk of complications. However, methyl methacrylate and other cranioplasty cements should not be used to repair fracture defects because they do not give a watertight seal and are predisposed to entrapping microbes leading to delayed infectious complications, especially when placed in the vicinity of the paranasal sinuses. Use of monocryl suture, an absorbable copolymer of glycolide and caprolactone, minimizes tissue reaction during healing and slowly hydrolyses over a period of 3 to 4 months.

Traumatic Skull Base Cerebrospinal Fluid Fistula

In the setting of an associated dural tear, fractures of the skull base traversing the paranasal sinuses or middle ear may be accompanied by a CSF fistula. Approximately 10% to 20% of patients with skull base fractures develop a CSF fistula. ^{, ,} In a series of 625 patients with severe skull base trauma, the incidence of CSF leak was 12% (75 patients). In young children, a CSF fistula is unusual due to the late development and maturation of the paranasal sinuses. CSF leaks are more common in anterior as compared to middle fossa and posterior skull base fractures. The site of the CSF fistula most commonly localizes to a fracture through the ethmoid/cribriform plate and manifests as rhinorrhea. Less frequently, CSF may arise from a fracture of the frontal sinus, ethmoidal cells, or sphenoid sinus. CSF may also leak through the foramina in the cribriform plate following olfactory nerve avulsion. Rhinorrhea also can occur from a temporal bone fracture with an intact tympanic membrane. In this setting, CSF escapes through the fracture and along the eustachian tube into the posterior nasopharynx. Rhinorrhea may present in a delayed fashion, possibly due to unmasking of fistula sites as brain swelling from the injury resolves. The risk of meningitis from untreated CSF leakage is as high as 85% in long-term follow-up. ^, Dural tears, whether masked or occult, may not be diagnosed until they present with meningitis, CSF rhinorrhea, or a mucocele, sometimes years following the injury.

Otorrhea, drainage of CSF from the ear, requires both a dural laceration with an underlying fracture in the petrous bone and a perforation of the tympanic membrane. Otorrhea occurs in approximately 15% to 25% of all temporal bone fractures. ^, In longitudinal fractures, CSF may leak through a bony fracture that directly communicates with the external auditory meatus, or it may egress through a disrupted tympanic membrane. By comparison, in transverse temporal bone fractures, CSF passes down the eustachian tube, leading to rhinorrhea, because the tympanic membrane is often intact. Otorrhea usually resolves spontaneously and rarely persists beyond 7 days from time of injury. Delayed otorrhea is uncommon.

Most CSF leaks resolve spontaneously. Approximately 85% of patients with rhinorrhea and more than 90% with CSF otorrhea resolve spontaneously within 1 week after injury. ^, In a series of 54 patients with anterior fossa CSF rhinorrhea, Mincy found that 35% resolved spontaneously within 24 hours, 68% within 48 hours, and 85% within 7 days. In the first week of CSF leakage, the risk of meningitis is low. The risk of meningitis increases 8 to 10-fold, with an incidence of more than 20%, if the CSF leakage persists beyond 7 to 10 days. ^{, ,} To facilitate spontaneous closure, the patient should be maintained with the head of the bed elevated, stool softeners, antiemetics, and avoidance of Valsalva maneuvers such as nose blowing or drinking through a straw. If the CSF leak does not resolve spontaneously within approximately 72 hours with these conservative measures, and if there are no risks of cerebral herniation, then a lumbar drain should be inserted to remove CSF (10 to 15 mL/h). Reduction and repair of concomitant naso-ethmoid, supraorbital, and glabellar fractures can facilitate spontaneous resolution of CSF leaks from the anterior frontal floor and cribriform region.

The use of prophylactic antibiotics for CSF fistula is controversial and generally is not advised. ^{, ,} A recent Cochrane review of antibiotic prophylaxis for patients with basilar skull fractures evaluated 208 patients in four randomized, controlled trials by meta-analysis, and a further 2168 patients in nonrandomized, controlled studies. This review concluded that prophylactic antibiotics were not supported, whether or not CSF leakage was present. In this analysis, early surgical repair was found to reduce the risk of meningitis.

Indications for Surgery

Indications for operative repair of CSF fistula include: (1) failure of conservative therapy to resolve the CSF leak; (2) penetrating injury with CSF leak; (3) pneumocephalus with persistent CSF leak; (4) development of meningitis during nonoperative treatment of a CSF leak; (5) a CSF leak that presents in a delayed fashion; (6) a recurrent, intermittent CSF leak, especially one timed to clamping of a lumbar drain; and (7) a severe anterior skull base defect with evidence on computed tomography (CT) scan or endoscopy that the brain is externally herniating through the skull defect. ^, Persistent or recurrent CSF leak despite lumbar drainage beyond 7 to 10 days from the time of injury is deemed long enough to establish that nonoperative therapy has failed. Early surgery should be considered for patients with high-risk features for development of meningitis during a trial of nonoperative therapy. CSF leakage that presents in a delayed manner; pneumocephalus that persists on serial CT scan, indicating a large dural tear; and patients with external brain herniation through the skull defect are less likely to resolve their CSF fistulae spontaneously and should be considered for early surgical repair. Penetrating injuries with CSF leak carry a very high risk of developing gram-negative meningitis and should not be managed nonoperatively. ^,

Timing of surgical repair depends on the ongoing risk of meningitis during a nonoperative treatment course; the likelihood of spontaneous resolution, thereby obviating the need for surgery; and in many cases, the risks of frontal lobe retraction for skull base exposure in the setting of traumatic brain swelling. In general, frontal lobe swelling dissipates to allow adequate brain retraction for exposure of the anterior skull base by 10 days following injury. Traumatic otorrhea resolves spontaneously within 2 weeks of injury in almost all cases, and the need for operative repair is uncommon. Indications for operative repair of CSF otorrhea are similar to those for rhinorrhea from anterior skull base fractures, although the high likelihood of spontaneous resolution may lead to a somewhat longer trial of nonoperative management.

Methods of Surgical Repair

There are two surgical approaches to the operative repair of traumatic skull base CSF fistulae: (1) craniotomy with intradural and extradural exposure and (2) extracranial paranasal sinus exposure. In addition, consideration should be given to the possible need for ancillary CSF diversion procedures. Localization of the site of the dural fistula helps guide the surgical approach. Metrizamide CT cisternography and radioactivity studies can be used to localize the fistula site. Metrizamide CT requires an actively leaking fistula. Radioactive studies are more labor intensive and require placement and radioactive counting of pledgets in different sites within the paranasal sinuses following lumbar puncture and CSF administration of a radiolabeled substance. For complex fractures of the anterior skull base involving the cribriform plate and ethmoid sinus, a bifrontal craniotomy is the most effective approach ( Fig. 124.1 ). Extradural dissection is associated with less brain retraction and is employed for simple anterior skull base, as well as for middle cranial fossa dural repairs. Direct paranasal sinus approaches are best suited for localized fractures of the frontal, ethmoid, and sphenoid sinuses.

Perioperative Considerations

Perioperative antibiotics are generally administered and continued for 5 to 7 days postoperatively. If not already present, a lumbar drain with CSF diversion for a period of approximately 1 week postoperatively facilitates healing of the repair site. With an open CSF fistula, intracranial air can exchange freely and does not build up pressure. As the fistula site closes down, tension pneumocephalus can develop and be exacerbated by negative pressures induced by CSF drainage through a lumbar drain. During closure of the fistula and weaning of the lumbar drain, patients should be observed for signs of hydrocephalus that may have been masked earlier by the ongoing leakage of CSF, by lumbar CSF drainage, or both.

Craniotomy for Open Repair of Traumatic Anterior Cranial Skull Base Cerebrospinal Fluid Fistula

Open craniotomy allows both intradural and extradural exploration of the fistula site, treatment of associated intracranial mass lesions, and repair of cranial fractures in a single procedure. A dural tear at the fistula site can be repaired by direct suture more easily through an intradural exposure. The extradural approach offers the advantages of less brain retraction. For complex skull base fistula, some surgeons recommend first exploring and repairing the fistula site intradurally. If both olfactory nerves have been disrupted by the trauma, the intradural procedure can then be augmented with extradural repair over the cribriform and olfactory fossa. ^,