Diagnosis and Multimodality Management of Skull Base Fractures and Cerebrospinal Fluid Leaks

History

The description, diagnosis, and management of skull base cerebrospinal fluid (CSF) leaks has a long, controversial history dating back to the first report of this entity in the 17th century by Bidloo. In his report, the Dutch surgeon described a case of profuse posttraumatic CSF rhinorrhea that resulted in the death of his patient 7 months later from meningitis. Then, in the late 1800s, Chiari was the first to document the link between CSF rhinorrhea and traumatic injuries to the paranasal sinuses with concomitant pneumocephalus. These early cases highlighted the end result modern practitioners aim to prevent and the impetus behind the increasingly sophisticated methods and techniques used to treat this condition.

The early 1900s saw further classification of skull base CSF leaks and the first descriptions of the surgical repair of dural defects causing these leaks. Using his experience with both closed and penetrating brain injuries, Hugh Cairns in a 1937 paper classified CSF rhinorrhea into four categories that are still applicable today (see Table 1.6.1 ). In addition, Walter Dandy visualized and repaired a dural tear at the base of the skull with tensor fascia lata in the same time frame.

Military conflicts since World War I have revealed CSF leaks to be harbingers of significant morbidity and mortality. In the Iran–Iraq War, CSF leaks were an independent variable contributing to deep central nervous system (CNS) infections in military missile head wounds in a regression model. Additionally, as modern protective gear and helmets have improved, the incidence of individuals’ sustaining penetrating injuries to the skull base via transfrontal, transorbital, and transfacial routes have only increased. Finally, the high energy imparted by modern penetrating and nonpenetrating blast injuries creates closed head and paranasal sinus injuries classically associated with CSF rhinorrhea and otorrhea in the civilian population.

Demographics and Associated Injuries

In the general population, head trauma is the major cause of morbidity and mortality between the ages of 1 and 44, with approximately 50,000 Americans dying annually from traumatic brain injury (TBI). Among those sustaining closed head injuries (CHI), 10%–20% have a basilar skull fracture and 1%–3% have CSF leaks. Additionally, approximately 1.7% of individuals with blunt mechanism facial fractures will sustain basilar skull fractures and 9.7% will have cervical spine fractures. Among those experiencing CSF leaks, over 80% present with CSF rhinorrhea and the other 20% with otorrhea. Also, between 20% and 50% of patients with CSF leaks will develop CNS infections if left untreated with no resolution of their leak. Of note, for those sustaining basilar skull fractures, a CSF leak does not have to be present for meningitis to occur and said event can be quite remote from its antecedent trauma.

History, Clinical, and Laboratory Assessment

One must consider several important historical findings in those with skull base fractures and concomitant CSF leaks. In addition to the timing and mechanism of injury, one should also note any reports of loss of consciousness, seizure activity, or periods of hypoxia or hypotension as these can independently affect prognosis and subsequent decision making. While severe craniomaxillofacial trauma can be dramatic at first glance, one should always remember the basic tenets of trauma care and resuscitation. ATLS guidelines and protocol should be followed on presentation and no further neurosurgical treatment planning should commence until it is certain that the patient is stable from a cardiopulmonary standpoint. During this time, one may perform a neurological examination (to attain a Glasgow Coma Score [GCS]) prior to intubation (if possible) and stop any arterial hemorrhage from scalp or facial wounds by simple closure with staples or sutures. In addition to standard trauma protocols utilizing the placement of rigid cervical collars and universal spine precautions, those in which there is a significant concern for cervical spine injury should undergo a full American Spinal Injury Association (ASIA) exam to fully describe and characterize the completeness and neurological level of any potential spinal cord injury. Finally, all cooperative patients should undergo cranial nerve testing to rule out an orbital apex syndrome or optic nerve injury.

The clinical and physical signs of those with skull base CSF leaks typically mimic those with all basilar skull fractures (mastoid ecchymosis [Battle's sign], periorbital ecchymosis [raccoon eyes], etc.). When found clinically and/or radiographically, one should have a high index of suspicion for CSF leakage and perform a detailed physical examination as such. Aside from the obvious signs of CSF rhino/otorrhea, one should attempt to examine the posterior oropharynx for the “glistening” sight of CSF drainage. In addition, CSF accumulation behind the tympanic membrane should be examined for using an otoscope. In the obtunded or sedated patient, endoscopy may be utilized to examine the paranasal sinuses, skull base, posterior oropharynx, and Eustachian tube in a more detailed manner for CSF drainage. Additionally, examination of the orbit may reveal CSF leakage or a pulsatile globe due to an orbital roof fracture that may have a corresponding dural tear. In awake patients, additional symptoms such as positional headaches, the sensation of postnasal drip, a “salty” taste in the back of the mouth, or a feeling of fluid/fullness in the ear should be identified.

For cases in which the clinical diagnosis of CSF rhino or otorrhea is uncertain, certain laboratory findings can assist in confirming what may be a presumptive diagnosis. Glucose and protein levels have been used in the past, utilizing normative values to help establish whether the fluid in question is in fact CSF. One should use caution with this method alone though, as these values can vary in the presence of infection/meningitis and in those with diabetes, which can affect the interpretation of results. Beta-2 transferrin (beta-2 trf), the desialated isoform of transferrin, is only present in CSF and has a sensitivity and specificity of 84% and 100% (respectively) in the diagnosis of CSF leakage. However, most assays require between 2 mL and 5 mL of fluid for successful analysis, which may be problematic for those with low-flow/volume or intermittent CSF leakage (which account for the majority of cases with clinical/diagnostic uncertainty). Additionally, the laboratory assay for beta-2 transferrin is not readily available at all hospital/clinical laboratories and as such may take several days to weeks to process at outside facilities. As a result, laboratory analysis of fluid concerning for CSF leakage serves a limited role and should be used as only one of the factors that seasoned clinicians use in diagnosis.

Computed Tomography (CT)

In modern practice, fine-cut (less than 1 mm) CT scans of the face, sinuses, and head in the axial, sagittal, and coronal planes are the best way to examine for the skull base and sinus fractures typically associated with CSF leakage and pneumocephalus. With regards to the frontal sinus, the status of both the anterior and posterior walls in addition to the patency of the nasofrontal ducts should be assessed. Given the multiplicity and thin bony architecture of the ethmoid sinuses, fractures can often be difficult to detect. However, the presence of ethmoid opacification on CT, air cells appearing to communicate with the intracranial compartment, or frank pneumocephalus are harbingers of injury to this complex.

Basilar skull injuries affecting the middle cranial fossa typically result in either longitudinal or transverse fracture patterns of the petrous pyramid. Of note, longitudinal fractures are more likely to result in CSF otorrhea given their tendency to involve the posterior portion of the external auditory canal and the tegmen tympani. One should also examine for any involvement of the carotid canal, facial canal, cochlea, and semicircular canals in these particular fractures.

The injection of intrathecal contrast in conjunction with CT imaging as specified above is another method to more precisely localize the potential site(s) of CSF leakage. Additionally, the use of intrathecal fluorescein can be of great assistance in localizing the site of CSF leak either pre- or intraoperatively utilizing endoscopic assistance.