Traumatic Cerebrospinal Fluid Fistulas

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CHAPTER 341 Traumatic Cerebrospinal Fluid Fistulas

Peter L. Reilly, Peter J. Wormald, Lawrence F. Marshall

Traumatic cerebrospinal fluid (CSF) fistulas result from a tear in the dura and arachnoid and are most often found in association with a skull base fracture that communicates with the nasal cavity, paranasal sinuses, or middle ear.

CSF fistulas may also be iatrogenic, such as after pituitary transsphenoidal surgery or sinus surgery, or may be spontaneous. In addition, CSF leakage can occur after compound vault wounds. These injuries are treated by repair of the dural tear and careful wound closure (see Chapter 339). Fistulas associated with skull base fractures form the subject of this chapter.

The most common sign of a fistula is leakage of CSF from the nose or ear. A fistula may also be indicated by intracranial air (pneumocephalus), with or without leakage of CSF, and be implied by a cranial infection (meningitis or abscess) occurring at any time after a skull base fracture. The frequency of skull base fractures increases with the force applied to the cranium.¹ Consequently, CSF fistulas are more common after severe head injuries, and for this reason they may be overlooked initially. It is therefore important to have a high degree of suspicion with head injuries associated with skull base fractures, whether closed or penetrating. Fistulas may also occur with midface fractures of the Le Fort III pattern, without an associated head injury. Most fistulas heal spontaneously, particularly when the primary impact is to the facial skeleton.² The advice of earlier neurosurgeons that “dural repair should be considered in all cases of paranasal sinus fracture with rhinorrhea, whether this is of early onset, or brief or long duration”³ no longer holds true.

The most important complication of a fistula is infection, and treatment protocols are designed to prevent this. Healing is not always reliable and infection may occur many years later, even without any history of CSF leakage. Hence a history of head injury or severe facial fracture in a patient with meningitis or a brain abscess should raise the question of a skull base fracture and fistula. Fistulas that do not heal or recur require surgical treatment. Surgical treatment is now most often performed endoscopically.

Epidemiology

The causes of CSF fistula reflect the causes of neurotrauma in the community. In general, the most common causes in order of frequency are motor vehicle accidents, falls, and assaults.^4,⁵ In series in which facial fractures dominate, there is a higher frequency of assaults and motor bike accidents. The reported incidence of skull base fractures after nonpenetrating head injury ranges from 7% to 24% and that of associated CSF fistulas from 2% to 20.8% after head injury.^6,⁷ The incidence of skull base fractures increases with the severity of head injury; however, rhinorrhea can develop after minor head injury or primary facial impact in which there has been little or no loss of consciousness.⁸ Cranionasal fistulas are more common than cranioaural fistulas and less likely to cease spontaneously.⁹

Pathophysiology

Blunt Injury

Traumatic CSF fistulas usually occur with fractures of the anterior and middle cranial fossae. Less commonly, a posterior fossa fracture may extend through the petrous bone to the middle ear or through the clivus to the sphenoid sinus.

Anterior Fossa

Rhinorrhea is most often caused by a fracture of the frontal, ethmoid, or sphenoid bones. The dura is firmly adherent to the thin bone of the anterior fossa floor and is readily torn by fractured bone edges. The most frequent site of rhinorrhea is the cribriform/ethmoid junction and the ethmoid bone itself.¹⁰ The anterior ethmoidal artery penetrates the skull base at the lateral margin of the cribriform plate, thereby creating a natural weakness at that point (Fig. 341-1).¹¹ Fistulas in this region communicate with the nasal cavity directly or via the ethmoid air cells.

FIGURE 341-1 Fractures of the cribriform plate (A) and fracture through the ethmoid air cells (B), the most common fracture type. 1, crista galli; 2, cribriform plate; 3, ethmoid roof.

(Reproduced with permission from Markam JW. Pneumocephalus. In: Vinken PJ, Bruyn GW, eds. Injuries of the Brain and Skull, vol 24, Handbook of Clinical Neurology. New York: Elsevier; 1976:201.)

Frontal or lateral vault impact may result in fractures that cross the anterior fossa floor to the frontal sinus, cribriform-ethmoid area, planum sphenoidale, or the pituitary fossa. With impact to the facial skeleton, fracture lines usually run through the thin bone of the cribriform plate and ethmoid area (the upper-third fracture pattern of Le Fort III or “craniofacial dislocation”).

Avulsion of olfactory fibrils from the cribriform plate by the shearing forces of a blunt impact can rarely cause rhinorrhea in the absence of a fracture. Fracture of the posterior wall of the frontal sinus may allow CSF to track through the frontonasal duct.

Middle and Posterior Fossa

Fractures through the petrous bone that extend to the middle ear may lead to otorrhea if the tympanic membrane is torn or to otorhinorrhea if leakage occurs via the eustachian tube into the nasopharynx.

Between 70% and 90% of temporal bone fractures are parallel to the long axis of the petrous ridge. These longitudinal fractures may damage the ossicular bones and result in conductive hearing loss, as well as damage to the seventh nerve. The tympanic membrane is often torn. A transverse fracture (10% to 30%) is more commonly associated with eighth nerve deficits, sensory neural hearing loss, and facial palsy.¹² The tympanic membrane is usually intact and CSF will leak via the nose (otorhinorrhea).

CSF fistulas occur with equal frequency with either type of fracture.

A middle fossa fracture that extends to the greater wing of the sphenoid may enter a lateral extension of the sphenoid sinus, which is present in nearly a third of skulls, and result in rhinorrhea.¹³

Oculorhinorrhea

Rarely, a cranio-orbital fracture together with a laceration of the conjunctival sac may allow CSF to leak from the eye.^14,¹⁵

Penetrating Injury and Gunshot Wounds

Traumatic CSF leaks may also result from penetrating injuries, including gunshot wounds. Penetrating missile injuries of the skull vault have a high incidence of skull base fractures, 30% of which are discontinuous (i.e., not in continuity with the vault fractures).¹⁰ Either rhinorrhea or otorrhea may develop in approximately 50% of these injuries.¹⁶ High-velocity missile injuries can cause substantial bony and soft tissue loss and disruption, and repair and reconstruction are often complex (see Chapter 339).

Cerebrospinal Fluid Fistulas in Children

CSF fistulas are less common in childhood, with only 15% occurring in children younger than 15 years. The low frequency in children is due partly to a lower frequency of frontal impact but also to the greater flexibility of the cartilaginous components of the skull base and underdevelopment of the sinuses.¹⁷ The frontal sinus is not developed until the age of 4 years or older. The ethmoid sinuses are present at birth and enlarge rapidly, but the ethmoid component of the anterior fossa is cartilaginous and therefore flexible at birth. By the age of 3 years, the nasoethmoid cavities are proportionately equivalent to their size in adults. The sphenoid sinus is very small at birth and becomes related to the anterior fossa between 5 and 10 years of age. The tegmen tympani is thin and rigid at birth, and a fistula to the middle ear is possible. Mastoid air cells are very small at birth but increase up to the age of 5 years (Fig. 341-2).

FIGURE 341-2 Surgical relationships of the pneumatized cavities in the skull base drawn from postmortem photographs. Left, 5 months of age; center, 5 years of age; right, adult.

(Reproduced with permission from Caldicott WJ, North JB, Simpson DA. Traumatic cerebrospinal fluid fistulas in children. J Neurosurg. 1973;38:1.)

Time of Onset of Leakage of Cerebrospinal Fluid after Trauma

Early Onset

After nonpenetrating injuries, CSF rhinorrhea usually begins within 48 hours.^4,^5,^7,¹⁸ If the defect is small, the bone may heal, and 60% to 70% of cases will cease spontaneously within 1 week.⁸

The fistula is unlikely to heal spontaneously if

• The bone defect is large with wide separation of the fractures and the torn dural margins or the dura is penetrated by bony spikes

• There is inadequate support for the dura because of extensive loss of bone

• Tissue healing is impaired by metabolic disease

• Intracranial pressure (ICP) is raised ^5,¹⁹

Delayed Onset or Recurrence

A CSF leak may be delayed in onset or recur after a period of cessation. Possible reasons for this are

• Shrinking of blood clot or swollen brain that was adhering to the dural-arachnoid tear and preventing healing ²

• Maturation and shrinkage of the dural scar ^20,²¹

• Devascularization and necrosis of the bone and soft tissue ⁵

Very-Late-Onset Cerebrospinal Fluid Leakage or Infection

CSF rhinorrhea may first develop after a considerable delay, or infection alone may be the first sign of a fistula. Delayed meningitis without a history of CSF rhinorrhea has been reported up to 48 years after the original head injury, which might have been quite minor.²²^–²⁴

Possible explanations for this are

• Contused brain at the site of the fistula forming a cerebral-dural scar that sealed the tear but did not provide a reliable barrier to infection

• Growing fractures of the ethmoid leading to the formation of a herniated encephalocele that stretched and ruptured as a result of intracranial pulsations ²⁵

Cranioaural Fistula

Most cases of traumatic otorrhea and otorhinorrhea cease spontaneously. In a large series, less than 5% persisted more than 14 days.²⁶ Hence, most can be treated conservatively.²⁷ Nonetheless, the incidence of meningitis while awaiting spontaneous healing has been reported to be as high as 18%.⁹

High- and Low-Pressure Leaks

In the early stages after severe head injury, potentially increased ICP may be partly “controlled” by a CSF leak, but in most instances persistent fistulas are not associated with increased ICP. High-pressure leaks are more common with spontaneous, nontraumatic CSF leakage; however, if the leak is accompanied by posttraumatic hydrocephalus, it may be maintained by the high CSF pressure, and the hydrocephalus should be managed by insertion of a lumbar peritoneal shunt as the initial treatment.¹⁹

Intracranial Air (Pneumocephalus)

Intracranial air is present in 20% to 30% of patients with posttraumatic CSF fistulas, but it may also occur without rhinorrhea.²⁸ Alone, it carries the same risk for meningitis as a CSF leak does.²⁹

The mechanism of pneumocephalus is debated.^30,³¹ It may be caused by a ball-valve effect combined with episodic increased pressure within the nasopharynx on coughing or by an “inverted bottle” effect whereby there is a discontinuous exchange of air and CSF when change in posture reduces ICP below atmospheric.

Very small volumes of intracranial air (less than 1 to 2 cc) are common after head injury and usually resolve without treatment. Larger volumes predict a greater likelihood of persistent fistula. A large volume of air occasionally produces a “succussion splash” with head movement.

Tension pneumocephalus is an uncommon but serious complication.³²

Clinical Features

History

The history usually consists of a head or facial injury from a frontal impact. A profuse leak is readily identified, but small and intermittent leaks are often overlooked, particularly if the CSF is mixed with blood and mucus. In an unconscious patient with signs of a skull base fracture, evidence of CSF leakage should be sought actively. A conscious patient may complain of a nasal discharge or a salty taste in the back of the throat (because of the sodium content of CSF) or fullness of the ear with some hearing loss. A large volume of fluid leaking from the nose or ear with change in head position indicates that a CSF-filled sinus has drained (reservoir sign).³³ Patients may complain of nasal dripping in the morning after sitting up, leaning forward, or straining.

Headaches can be either high pressure or low pressure in type. A high-pressure headache may be experienced repeatedly as a steady buildup of pain that is relieved by fluid drainage. Low-pressure headaches are less marked in the recumbent position and are increased by the upright position.

Examination

An anterior fossa floor fracture may be suggested by periorbital bruising (raccoon sign) and a frontal sinus fracture by a palpable depression in the forehead. Bruising of the scalp over the mastoid process indicates a petrous fracture (Battle’s sign). The external auditory canal should be examined to determine whether the tympanic membrane is intact and to look for bubbles of air or an air-fluid level behind it. If the tympanic membrane is ruptured, flow of blood or clear fluid may be seen.

Neurological examination may provide valuable localizing information. Anosmia suggests a fracture of the anterior cranial fossa at or near the cribriform plate; however, intact olfaction does not exclude the possibility of a cribriform fracture.³² Seventh or eighth nerve palsies and impaired balance suggest a fracture of the temporal bone involving the labyrinth. Defects in vision or visual fields indicating optic nerve injury and sensory loss of the first division of the trigeminal nerve suggest fracture of the anterior fossa.

The side of rhinorrhea cannot be relied on to locate the fistula. Although usually ipsilateral to the fracture site, it is frequently contralateral or bilateral.^3,³²

Investigation

Identifying Cerebrospinal Fluid

Locating the Fistula

Plain Radiographs

Plain radiographs are of limited value, but they may indicate the probable pattern of skull base fractures and show fluid in the paranasal sinuses or intracranial air. These features may also be visible on the scout view of a computed tomographic (CT) scan.

Computed Tomography

A CT scan is the most useful investigation for determining the possible site of a CSF fistula and predicting the likelihood of spontaneous healing.

Fine-Cut Bone Window Scans

For examining the skull base, the standard format consists of fine cuts (0.6- to 1-mm intervals) performed on a helical multislice CT scanner at bone and soft tissue window levels. This protocol results in a box of data that can be sliced by the scanner in any plane. For best definition, the axis of scanning should be at right angles to the plane of the bone being examined. Thus, axial bone scans show the walls of the frontal sinuses, whereas coronal scans show the ethmoid complex, the roof of the sphenoid sinus, and the tegmen of the middle ear. The pattern of fracture lines and the presence of comminuted fractures, spikes, and wide fractures should be noted (Figs. 341-3 and 341-4).

FIGURE 341-3 Fine-cut coronal computed tomographic scan showing fracture of the sphenoid sinus wall lying close to the position of the internal carotid artery, along with intracranial air and fluid in the sinus.

FIGURE 341-4 Fine-cut coronal computed tomographic scan showing a tilted facture of the roof of the ethmoid with fluid tracking into the nasal cavity and the maxillary sinus.

Soft Tissue Scans

Soft tissue scans may indicate fluid in sinuses, intracranial air, and soft tissue dehiscence through fracture lines. Brain windows should be examined for evidence of focal injuries. The presence of brain swelling may influence the timing of surgical exploration.

With use of the preceding techniques, the site of a fistula can be identified in more than 70% of cases.³⁸

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) has been reported to be a useful, noninvasive adjunct in the investigation of CSF rhinorrhea, particularly in the presence of inflammatory sinus disease.³⁹ It may distinguish between mucosal disease with mucopurulent discharge and CSF, which may show the same radiopacity on a CT scan. On T2-weighted images, CSF will appear white and perimucosal discharge and nasal disease will be darker. Mucosal disease can be highlighted by the administration of gadolinium. MRI signs indicative of a CSF fistula include brain arachnoid hernia through the bone defect and a CSF signal in the perinasal sinuses that is continuous with intracranial CSF. A fistula may also be suspected if there is fluid in only one of the paranasal sinuses even though the fluid is not continuous with intracranial CSF. One study found that MRI was 100% successful and superior to CT cisternography in detecting active CSF leaks.⁴⁰ However, another study found the T2 signs reported to be relevant to the identification of a fistula to lack useful specificity.⁴¹

Tracer Studies

Several types of tracers have been used to detect the site of a fistula. Radionuclide tracers are no longer widely used, and when endoscopic skills are available, the preferred tracer technique is intrathecal fluorescein. If this does not identify the fistula, CT cisternography is used. MRI cisternography has been reported to be reliable and may play a bigger role in the future.

Intrathecal Fluorescein

Fluorescein injected intrathecally may be detected on cottonoid pledgets placed in the nasopharynx or during endoscopic examination.⁴²^–⁴⁷ Ten milliliters of CSF is withdrawn by lumbar puncture, mixed with 0.2 to 0.5 mL of 5% fluorescein, and slowly reinjected through a lumbar drain filter over a 10-minute period.^42,^45,⁴⁶ This is done while the patient is awake so that any adverse effects are apparent immediately. The patient is placed in the reverse Trendelenburg position to facilitate diffusion of the fluorescein intracranially. In most cases this is done in the anesthetic recovery room at the beginning of the operating schedule, which allows the patient to remain in recovery for a few hours before surgery. This approach allows time for diffusion of the fluorescein into the intracranial cavity. If this is not possible, at least 30 minutes should be allowed for diffusion to occur before surgery is undertaken. Before endoscopic sinus surgery, the eustachian tube orifice needs to be inspected to ensure that CSF is not draining from the middle ear to the eustachian tube. The patient is then taken to the operating room.

A complete sphenoethmoidectomy is then performed and the skull base inspected. Fluorescein-stained CSF can be seen as bright yellow to green. If fluorescein is not seen immediately, saline can be injected in 10- to 20-mL increments via the lumbar spinal catheter while monitoring CSF pressure with a pressure transducer. Depending on CSF pressure, up to 100 mL can be injected. This technique is highly successful and accurate in diagnosing and localizing an active CSF leak.

Although intrathecal fluorescein has been reported to be safe at these concentrations,⁴²^–⁴⁶ there have been reports in the past of numbness and weakness of the lower extremities, opisthotonos, and seizures when higher concentrations were used. If an adverse reaction does occur, saline irrigation to clear the lumbar CSF and elevation of the head to limit side effects to the lower extremities have been recommended.

Computed Tomographic Cisternography

If there is an active leak, CT cisternography can demonstrate a fistula in 76% to 100% of cases. If no leak is present at the time of the investigation, the rate of detection is lower.^48,⁴⁹ After a baseline scan, 6 to 7 mL of metrizamide or iopamidol is injected via a lateral C1-2 puncture or lumbar puncture in the screening room with the patient prone. The contrast medium is then manipulated into the basal subarachnoid space. Coronal images are obtained from the frontal sinuses to the dorsum sellae and, if indicated, the petrous bone. The site of the leak is indicated by bone dehiscence, contrast agent in the adjacent paranasal sinus, and distortion of the subarachnoid space, findings indicative of brain herniation.^40,^50,⁵¹

Magnetic Resonance Imaging with Intrathecal Gadolinium Enhancement

Intrathecal gadolinium-enhanced MRI cisternography has recently been reported to localize CSF fistulas with a high rate of success.⁵²^–⁵⁴

Management

Infection

Meningitis is the most serious complication of CSF fistulas. Untreated, CSF rhinorrhea has been associated with a 25% risk for meningitis.³ Early leaks have been associated with a 6% to 20% incidence of meningitis and delayed leaks with up to a 57% incidence.^3,^5,^9,⁵⁵^–⁵⁸ Daudia and colleagues calculated an overall risk of 19% for those with persisting leakage, the risk being greatest in the first year and progressively decreasing with time.⁵⁵

Although most fistulas heal spontaneously, the incidence of meningitis while awaiting a decision on surgical repair is about 11%.⁵⁹ The mortality rate for meningitis resulting from a traumatic CSF fistula has been reported to be 10%.⁶⁰ Risk for meningitis is greater with

• Delayed CSF leakage

• Longer duration of CSF leakage ⁵⁹

• Concurrent infection

Any basal skull fracture potentially allows direct communication between the subarachnoid space and the exterior. There is a 2.6 times greater rate of intracranial infection with basal skull fractures when a ventricular catheter is used.⁶¹ Because the risk of infection is considerably lower with lumbar catheters, the use of ventricular catheters in patients with basal fractures must have a sound clinical indication.

The most common organisms are Streptococcus pneumoniae and Haemophilus influenzae. S. pneumoniae meningitis may be rapidly fatal. A variety of other organisms have been reported, and infections with multiple organisms, often including anaerobes, are common. Penetrating injury may introduce a range of pathogens.

Antibiotic Prophylaxis

The value of antibiotic prophylaxis continues to be debated,⁶² with some reports showing increased infection with antibiotic treatment.^63,⁶⁴ A review of the Mayo Clinic experience found that infection was halved in those treated with prophylactic antibiotics.⁶⁵ Although one meta-analysis recorded a 2.5% incidence of infection with antibiotics and 10% without,⁶³ another found no benefit.⁶⁶ Only two double-blind studies have been conducted; they were inconclusive regarding the incidence of meningitis but showed no increase in other significant infections.^67,⁶⁸

Arguments against antibiotic prophylaxis are as follows:

1 The antibiotics commonly used penetrate CSF poorly.

2 The period of risk and hence the duration of prophylactic treatment beyond cessation of the CSF leak are uncertain.

3 Antibiotics may promote resistant strains of organisms within the nasopharynx and consequently lead to infection with resistant or unusual organisms.⁶⁴

At present, there seems to be no compelling evidence of either benefit or harm from the use of prophylactic antibiotics.

Choice of Prophylactic Antibiotics

Because the principal source of infection is the nasopharynx, antibiotic prophylaxis aims to sterilize the nasopharynx of potential pathogens. Consequently, if antibiotics are used, a combination of co-trimoxazole (trimethoprim-sulfamethoxazole), which is bactericidal in CSF, and amoxicillin or penicillin, which are bactericidal in nasal mucosa, is recommended.

Definitive Treatment

Conservative Care versus Surgery

Initial conservative treatment is indicated if CT scans show undisplaced and linear fractures because spontaneous healing is likely. Patients with a facial impact but without a vault fracture may be treated by reduction of the facial fractures and initial conservative treatment of the rhinorrhea.²

Conservative treatment consists of the following:

1 Bed rest with the head elevated moderately (e.g., 30 degrees).

2 Avoidance of actions that might cause a sudden increase in ICP, such as nose blowing, straining of stool, coughing, and sneezing. The patient should be placed on a bowel regimen that includes laxatives and stool softeners.

3 CSF drainage.

If the leak does not cease within 3 days, intermittent or continuous drainage of lumbar fluid may be considered.^6,⁶⁹^–⁷¹ Continuous CSF drainage is potentially hazardous and should be used with caution. Overdrainage can lead to intracranial aeroceles, severe brain displacement, and coma^72,⁷³ and require emergency drainage of the aerocele.⁷⁴ Intermittent drainage of 20 to 30 mL over an 8-hour period into a closed system is safer. If continuous drainage is used, the drain should be placed no lower than shoulder height with the head elevated about 10 to 15 degrees. It has been suggested but not proved that lumbar drainage may promote the entry of bacteria through the fistula, as well as impose its own risk for infection at the site of the spinal catheter; however, it is still preferable to ventricular drainage.

Timing of Surgery

Delayed Surgery

Delayed surgery is indicated for

1 Failed conservative management, such as a CSF leak persisting beyond 10 days

2 Recurrent or delayed CSF leakage after 10 days

3 Recurrent aerocele after 10 days

4 Meningitis or abscess at any time after injury

Intracranial versus Endoscopic Repair

Endoscopic surgery is the first choice for repair of CSF fistulas, but it depends on accurate identification of the fistula before definitive surgery. Advantages of endoscopy are

• No brain retraction

• No risk of inducing anosmia

• Better access to the sphenoid, parasellar, and posterior ethmoid regions

• A high success rate in skilled hands

Intracranial Repair

Intracranial surgery is indicated when

• Operating for associated craniofacial injuries

• There are large bone defects that may be difficult to repair endoscopically

• The fistula site cannot be identified by endoscopic inspection

Multiple fractures of the ethmoid and posterior frontal sinus can be repaired endoscopically, but in some situations transcranial repair may be preferred.

Repair of Anterior Fossa Fistulas

Patient Positioning

The patient is placed supine with the head moderately extended to allow elevation of the frontal lobes with light retraction. The head is elevated relative to the heart to reduce venous pressure. Cranial fixation and fixed brain retraction are preferred. Twenty percent (1 g/kg) mannitol is given before the scalp incision. This may be combined with spinal CSF drainage.

Exposure

The standard flap is bicoronal, placed behind the hairline, and taken lateral to the level of the superior orbital margins. A full-thickness scalp flap is turned down and the periosteum is separated from the galea. Bur holes are placed laterally behind the temporal crest for cosmetic reasons after separating the temporalis muscle. The bone flap may be larger if a graft of split calvarial bone is required.

The inferior margin of the craniotomy is cut low across the frontal sinuses to avoid a midline inferior bur hole if possible. This must be done with care and in stages, depending on the size and extent of the frontal sinuses. If the site of the leak is known to be unilateral, an ipsilateral craniotomy is sufficient.

Operative Procedure

Some authors recommend first identifying the dural tear extradurally or a combined intradural-extradural approach ⁷⁵; however, in general, intradural exploration allows clearer delineation of the dural tear, does not risk creating false tears, and permits more definitive repair.

The dura is opened horizontally on either side, with small flaps turned adjacent to the superior sagittal sinus. It is not usually necessary to divide the sinus, but if divided, it should be done so well forward to preserve all draining veins. Each frontal lobe is then carefully elevated while taking care to avoid excessive retraction pressure and attempting to preserve at least one olfactory nerve. The olfactory tracts can be dissected from the frontal lobe and preserved. The crista galli varies considerably in size and shape, and the cribriform fossa may be quite deep.

A systematic intradural search is conducted under magnification. The first intradural sign may be an area of adherence of brain and arachnoid to the site of the fistula. Defects into the posterior planum sphenoidale and supradiaphragmatic pituitary fossa may need to be probed carefully to establish their full extent. A small bone defect should be plugged with muscle or fat. If large, it should be filled with a bone graft, which may be taken from the inner calvaria. Primary suturing of a dural tear is rarely possible, and thus a graft of temporalis fascia or fascia lata is placed intradurally and held in place with nonabsorbable sutures and tissue glue. The intradural repair will be made additionally secure by tamponade of the dural patch by the brain.

The dural incision is sutured. The transected frontal sinus is stripped of mucosa and the frontonasal duct plugged with muscle and fat. A pericranial flap (or galeal flap if pericranium is not available) is turned over the frontal sinus and sutured to the dura. Frontal sinus mucosa is stripped from within the bone flap, and the craniotomy is reconstructed with titanium miniplates. The scalp is closed in two layers without drains.

If no fistula is found after careful exploration, the operation should cease and radiographs should be thoroughly reviewed for any other possible sites, such as the middle or posterior fossa. Avulsion of intact olfactory nerves and covering the entire anterior fossa floor with fascia are not recommended. If no other site is suggested by review and the leak is small, it may be treated indirectly with a lumbar peritoneal shunt.⁷⁰

Postoperative Care

Antibiotics are not continued postoperatively. Postoperative CSF drainage is not performed unless the quality of the repair is in doubt. If an early leak recurs, a period of lumbar drainage may be undertaken.

Frontal Sinus Fractures

A bicoronal scalp flap is turned down and a small craniotomy is cut low across the frontal sinus. The dura is explored extradurally and the tear repaired in watertight manner. The posterior wall of the sinus is excised, the sinus mucosa stripped, and the frontal nasal duct plugged with fat or muscle. The anterior wall is replaced and reconstituted with miniplates (see also Chapter 339).

Middle Fossa Leaks

Persistent CSF otorrhea or otorhinorrhea from a petrous fracture is rare. Longitudinal petrous fractures may disrupt the roof of the middle ear but rarely need repair. If they do require repair because of persistent or recurrent CSF leakage or infection, they are best approached through a subtemporal craniotomy.

Patient Positioning

The patient is placed supine or in the full lateral position to bring the head fully lateral. The head is elevated moderately.

Exposure

A square lateral flap is turned down. A small lateral craniotomy is performed and the inferior margin burred to the floor of the middle fossa. If mastoid air cells have been opened, they are sealed with bone wax.

Operative Procedure

The dura is opened and the flap turned down. Care must be taken to preserve the vein of Labbé, but veins draining to the dura from the inferior temporal lobe can be coagulated and divided. The site of the fistula is sought over the region of the tegmen tympani, and an intradural repair is performed as described earlier.

Posterior Fossa Leaks

Fractures through the posterior petrous surface (transverse fractures) are often associated with hearing loss. If hearing is lost, these fistulas may be repaired through a translabyrinthine approach. If hearing is intact, they should be approached intracranially via the posterior fossa.

Endoscopic Repair

Anterior and Posterior Cranial Fossa Cerebrospinal Fluid Leaks

The first and most important step is to identify the site of CSF leakage.^42,^43,⁴⁵^–⁴⁷ As described earlier, this is done by identifying the most likely site of the leak on fine-cut CT scans and then approaching this region endoscopically and clearly delineating the leak by visualizing fluorescein-stained CSF leaking from the defect.

The probable site of the leak can usually be identified by fractures of the skull base or isolated fluid within a sinus (see Figs. 341-3 and 341-4). Surgical access to this site is then planned. If the site involves the posterior wall of the frontal sinus, an endoscopic modified Lothrop technique (endoscopic frontal sinus drill-out procedure) is performed to expose the frontal sinuses widely and provide access to the posterior wall. If the site is the cribriform plate, a middle turbinectomy with or without ethmoidectomy will give good exposure. If the leak is in the roof of the ethmoids (fovea ethmoidalis), endoscopic ethmoidectomy is needed. If the site is the roof of the sphenoid, lateral wall (middle cranial fossa), or posterior wall (posterior cranial fossa), endoscopic sphenoidotomy provides good exposure to these areas. When the sphenoid is very pneumatized and the leak is from the lateral wall of the sphenoid, a transpterygoid approach is required. After a large middle meatal antrostomy is performed, the posterior bony wall overlying the pterygopalatine fossa is removed to expose the pterygopalatine fossa. In this approach the vidian nerve, pterygopalatine ganglion, and sphenopalatine artery are removed from the pterygopalatine fossa with preservation of the infraorbital nerve. This exposes the anterior wall of the pneumatized sphenoid, which is removed with a diamond bur to provide a direct approach to the lateral wall and CSF leak in a pneumatized sphenoid.

Once the leak is clearly identified, the nasal or sinus mucosa around the site of the leak is removed for about 5 mm to expose the bone around the defect (Fig. 341-5, Video 341-1).^42,^45,⁴⁶ This allows attachment of the free graft to the bone and improves the seal of the repair. If any loose bony fragments are seen around the bone defect, they are gently removed. If the dural defect is significantly smaller than the bony defect, the dural defect is enlarged to the size of the bony defect. Attempting to repair a dural defect without bone support is associated with a high incidence of failure and is not recommended.