Historical Perspective

CSF rhinorrhea was first reported in the 17th century.¹ In the early 20th century, Dandy² reported the first successful repair, which used a bifrontal craniotomy for placement of a fascia lata graft. Although this surgical strategy provided direct access for the repair, reported failure rates were quite high and the procedure entailed the morbidity of craniotomy. In fact, reported recurrent rates were as high as 27%,³ and in one series only 60% of leaks were successfully repaired.⁴

Extracranial approaches were introduced in the mid-20th century. In 1948, Dohlman⁵ presented a patient whose CSF leak was repaired through a standard naso-orbital incision. Several years later, Hirsch⁶ reported the successful closure of two sphenoid sinus CSF leaks through a pure endonasal approach. In 1964, Vrabec and Hallberg⁷ described the repair of a cribriform defect through an endonasal route. All of these endonasal procedures were performed before the advent of surgical nasal endoscopy.

Endoscopic approaches were introduced and popularized in the 1980s and early 1990s. Both Wigand⁸ and Stankiewicz⁹ described closure of incidental CSF leaks during endoscopic sinus surgery. In 1989, Papay and colleagues¹⁰ introduced rigid transnasal endoscopy for the endonasal repair of CSF rhinorrhea, and in 1990, Mattox and Kennedy¹¹ presented another series of cases in which the CSF rhinorrhea was addressed with use of endoscopic visualization. Since then, numerous series have been published,^12–14 and endoscopic repair has emerged as a mainstay of surgical management.¹⁵

Classification

Box 54-1 summarizes a classification system for all cases of CSF rhinorrhea. This approach, which is based on the established pathophysiology of CSF rhinorrhea, has important clinical implications for the selection of treatment strategies as well as patient counseling about prognosis.

The importance of accurate classification was first recognized by Ommaya and associates,¹⁶ who proposed dividing CSF rhinorrhea into traumatic and nontraumatic forms. These researchers believed that the application of the term “spontaneous” to cases of CSF rhinorrhea was inappropriate because comprehensive investigations of all cases of CSF rhinorrhea should reveal the true proximate cause. Most cases of so-called spontaneous rhinorrhea have a specific etiology, so the term “spontaneous” is probably best reserved for cases of true idiopathic CSF rhinorrhea, in which various investigations cannot determine a specific cause.

Data about the incidence of CSF rhinorrhea are sparse. Only 4% of all CSF leaks are nontraumatic, and 16% occur as a direct result of intracranial and extracranial procedures.¹⁷ The vast majority result from accidental or surgical trauma. Approximately 80% of all cases of CSF rhinorrhea occur in the setting of accidental trauma, mostly in the form of closed-head injury. Conversely, CSF rhinorrhea is noted in only 2% to 3% of cases of serious head trauma.¹⁷ The presence of a skull base fracture is associated with a CSF fistula in 12% to 30% of cases.¹⁸ More than 50% of CSF fistulas resulting from accidental head trauma are located at the anterior cranial base, most of them involving the cribriform plate.^19,20 The majority of traumatic CSF leaks become clinically evident within 2 days, and almost all manifest within 3 months after the traumatic event.²¹ Most CSF fistulas resulting from accidental head trauma resolve spontaneously or with conservative management, including lumbar drainage and bed rest.

Pathophysiology

CSF is produced by the choroid plexus in the ventricles at a rate of 20 mL per hour in adults. The CSF circulates from the ventricles through the foramina of Luschka and Magendie to the subarachnoid spaces around the cerebral hemispheres, cerebellum, and spine. Total CSF volume is 140 mL, consisting of 20 mL in the ventricles, 50 mL in the intracranial subarachnoid space, and 70 mL in the paraspinal subarachnoid space. The typical upper limit of normal CSF pressure ranges from 40 mm H₂O in infants to 140 mm H₂O in adults. CSF pressure fluctuates with respirations and arterial pulse pressures as well as with changes in head position. CSF pressure is maintained by a relative balance between CSF secretion (from the choroid plexus) and CSF resorption (by the arachnoid villi). Because CSF secretion occurs at a steady rate, the rate of CSF resorption plays the major role in determining CSF pressure.²² Processes that disrupt CSF resorption tend to lead to increased intracranial pressure (ICP).

The presence of active CSF rhinorrhea requires a disruption of the barriers that normally separate the contents of the subarachnoid space from the nose and paranasal sinuses; that is, the leak incorporates defects of the arachnoid and dura mater, paranasal sinus mucosa, and the intervening bone. Furthermore, a pressure gradient is also required to produce flow of CSF.

From these apparent observations, the possible etiologies for CSF leaks may be inferred. Various surgical interventions, including routine sinus surgery, can lead to inadvertent disruption of the skull base. Complex intracranial and skull base procedures often directly violate the normally sturdy barrier; however, reconstitution of that barrier may be incomplete. Severe head trauma can lead to skull base fractures with dural laceration. Direct erosion of the skull base by neoplasm or infection can also create a CSF fistula.

The other major factor in the pathogenesis of CSF rhinorrhea is increased ICP. Both an intracranial mass and hydrocephalus are associated with elevated ICP. Strong coughing and the Valsalva maneuver both serve to transiently increase ICP. Elevated ICP is also an important factor in cases of apparent idiopathic CSF rhinorrhea. In a series of publications, Schlosser and coworkers^23,24 have noted that all patients who underwent clinically indicated lumbar puncture or drainage after successful endoscopic repair of nontraumatic CSF rhinorrhea had elevated ICP (mean 26.5 cm H₂O in the first report²³ and 32.5 cm H₂O, in the second report²⁴), suggesting that occult elevation of ICP may be an etiologic factor in even so-called idiopathic or spontaneous CSF rhinorrhea. It could be postulated that in patients with occult elevated CSF pressure, the CSF leak may serve as a release valve that decompresses the elevated pressure. (If the patient has an active leak at the time of lumbar puncture, the opening pressure may be normal—because the leak has decompressed the ICP. Thus, the increased pressure may be apparent only after a site of leakage has been surgically repaired.)

In at least certain instances, nontraumatic CSF rhinorrhea seems to result from abnormally elevated ICP. Given that elevated ICP is a primary characteristic of benign intracranial hypertension (BIH), the pathophysiology of nontraumatic CSF rhinorrhea and that of BIH may be similar. Benign intracranial hypertension, also known as idiopathic intracranial hypertension and pseudotumor cerebri, is a syndrome of increased ICP in the absence of specific causes such as intracranial masses, hydrocephalus, and dural sinus thrombosis. Clinical manifestations of BIH include headache, pulsatile tinnitus, papilledema, and visual disturbances including abducens nerve palsy. Most patients with BIH are obese, middle-aged women. In fact, the demographics of the population with spontaneous CSF leak are quite similar to those of the average population of patients with BIH.²⁵ Thus the diagnosis of BIH must be examined in the setting of spontaneous CSF rhinorrhea. In fact, Schlosser and coworkers²⁶ demonstrated that 8 of 11 patients (72%) with apparent idiopathic CSF rhinorrhea strictly fulfilled the modified Dandy criteria used by neuro-ophthalmologists to make the diagnosis of BIH.²⁶ The other 3 patients fulfilled most but not all the criteria.

In a separate publication, Schlosser and Bolger²⁷ assessed the incidence of an empty sella in 15 patients with apparently spontaneous CSF rhinorrhea and in 9 patients with nonspontaneous CSF rhinorrhea and noted a statistically significant (P = .01) greater incidence of empty sella in the nontraumatic CSF leak group (100% vs. 11%, respectively). An empty sella may therefore serve as a marker of elevated ICP.²⁸ Normally, the pituitary gland fills the entire sella turcica; however, if arachnoid and CSF herniate through the sellar diaphragm, this CSF-filled sac may partially or completely compress the pituitary gland. When this compression occurs, an “empty sella” results. The clinical manifestations and demographic profile of patients with empty sella syndrome (ESS) are highly similar to those for patients with BIH and patients with nontraumatic CSF leaks. The clinical presentation of ESS includes headache, memory losses, cerebellar ataxia, papilledema, and visual field defects. In addition, many patients with ESS are obese, middle-aged women with elevated body mass index (BMI). In a later report, Silver and colleagues²⁹ demonstrated that the radiographic signs displayed in 14 patients with nontraumatic, apparently idiopathic, CSF rhinorrhea were largely similar to those seen in patients with ICP and BIH. The signs included arachnoid pits in 79% of patients, empty sella in 50% of patients, meningoencephaloceles in 50% of patients, and dural ectasias in 35% of patients. Because ESS is associated with altered CSF circulation dynamics,³⁰ treatment of nontraumatic CSF rhinorrhea, which has a demonstrated association with ESS, should include consideration of the concomitant diagnosis of ESS as well as the potential clinical impact of ESS.

These associations among nontraumatic CSF rhinorrhea, BIH, and ESS have important clinical implications, because these three entities may all be manifestations of the same underlying pathophysiologic derangement that leads to elevations in intracranial and CSF pressures. Persistent headache after successful surgical repair may indicate occult ICP hypertension. Similarly, recurrent or persistent CSF rhinorrhea often represents decompression of abnormally high ICP. Thus, the issue of abnormal CSF dynamics should be considered in instances of apparently idiopathic CSF rhinorrhea.

The bony architecture of the skull base plays a role in the development of CSF rhinorrhea. Certainly bony dehiscences or even partial thinning weakens the normal barrier that separates the subarachnoid space from the paranasal sinus space. Alternatively, these weaknesses can be considered congenital anomalies. In addition, specific areas of the skull base are normally quite thin. In particular, the lateral lamella of the cribriform plate (LLCP) has been well recognized as an area of potential weakness (Fig. 54-1). The length of the LLCP shows considerable variation; if the LLCP is especially long, this anatomic variation weakens a significant portion of the skull. Congenital dehiscences in the lateral sphenoid roof, occurring from persistence of the lateral craniopharyngeal canal (Sternberg’s canal), have also been implicated in the pathogenesis of sphenoid CSF leaks and meningoencephaloceles.^31,32 In all instances of thinning of the bony skull base, the pressure from the overlying intracranial contents coupled with constant dural pulsations may further erode the weakened area with the resultant development of CSF rhinorrhea.

Figure 54-1. The lateral lamella of the cribriform plate (indicated by an arrow in this coronal sinus computed tomography scan) forms the weakest part of the skull base. The length of the lateral lamella is quite variable. In this example, it is quite long; hence, the skull base is at increased risk of inadvertent injury.

Although skull base trauma leading to CSF rhinorrhea during or after routine endoscopic sinus surgery is a rare event, the frequency of this procedure makes this complication an important cause of CSF rhinorrhea today.^9,33,34 Inadvertent pressure along the thin skull base may fracture the skull base and lacerate the dura. Because the LLCP is the weakest part of the skull base, even minor trauma in this region may cause CSF rhinorrhea. Aggressive middle turbinate retraction or resection (Fig. 54-2) may be associated with LLCP injury. The mechanism of injury during the procedure should also be considered. It is likely that powered instrumentation produces a greater skull base injury than the standard sinus forceps and through-cutting forceps. Powered instrumentation is invariably associated with greater removal of tissue; as a result, the resultant skull base defect may be quite extensive. Later generations of powered instrumentation may increase the risk of this complication, because they can remove tissue more quickly and easily. CSF rhinorrhea may occur both intraoperatively and postoperatively. When patients report symptoms that are consistent with CSF rhinorrhea after sinus surgery, the diagnosis of CSF rhinorrhea should be considered, even if the procedure itself was seemingly uneventful.

Figure 54-2. Intraoperative images from endoscopic surgery using an image-guided navigation system for repair of bilateral cerebrospinal (CSF) leaks. The cross hairs on the reformatted three-dimensional computed tomography scans (top, bottom left) denote placement of the probe as seen in the endoscopic view (bottom right). Middle turbinate resection may result in inadvertent skull base trauma and CSF leak. The instrument tip rests on the anterior skull base defect. The coronal sinus CT shows bony loss of the skull base and middle turbinate on both the left and right sides.

A meningocele or meningoencephalocele may occur in association with CSF rhinorrhea, although each of these lesions may occur independently. Meningoceles and meningoencephaloceles develop from the constant pressure exerted by the dura over a weakened portion of the skull base. Over time, a portion of dura may protrude through the bony defect into the paranasal sinuses and nose. If the defect is large enough and sufficient time has elapsed, meningoencephalocele may eventually develop. Often CSF rhinorrhea is the presenting symptom of a meningocele or meningoencephalocele, but not universally so.

In many patients, it is difficult to determine a precise etiology. Conceivably, multiple factors may play a role in the pathogenesis. A long LLCP increases the risk of a spontaneous leak, although most individuals with this skull base feature do not have such a leak. However, the combination of a long LLCP and elevated ICP—perhaps owing to a variant of ESS and/or BIH—may lead to CSF rhinorrhea. It is important to remember this multifactorial etiology, especially in patients with recurrent or persistent CSF rhinorrhea after surgical repair. Of course, surgical failure may result from other unrecognized factors.

Diagnosis

Intuitively, the diagnosis of CSF rhinorrhea may seem simple; in practice, however, it may be problematic. In selected instances, the presence of CSF rhinorrhea may be obvious. For instance, the development of unilateral watery rhinorrhea after head trauma with resultant anterior skull base fracture warrants little effort for diagnosis confirmation. However, the establishment of the diagnosis of a CSF leak as well as its precise localization often represents a major clinical challenge for a number of reasons. First, CSF rhinorrhea is relatively rare, but other rhinopathies, including seasonal allergic rhinitis, perennial nonallergic rhinitis, and vasomotor rhinitis, are relatively common. These more innocuous conditions may mimic some of the signs and symptoms of CSF rhinorrhea or may occur simultaneously with CSF rhinorrhea. Second, CSF rhinorrhea is often intermittent. As a result, a diagnostic test performed at a time when the CSF rhinorrhea is quiescent may lead to a false-negative result. Finally, the CSF drains from a low-pressure system; therefore, the quantity and duration of drainage may be quite low, because the pressure gradient that drives the CSF flow is intrinsically low, even in the presence of relative increases in CSF rhinorrhea.

The diagnosis of CSF rhinorrhea is typically a two-step process: First, the presence of a CSF leak must be confirmed through the documentation of objective evidence of extracranial CSF. Second, the position of the skull base defect or defects through which the CSF is draining must be determined.

Differential Diagnosis

Occasionally, CSF otorrhea may manifest as CSF rhinorrhea. In this circumstance, a skull base defect communicates between the intracranial space and pneumatized spaces of the middle ear and mastoid behind an intact tympanic membrane. The CSF collects in the middle ear space and then drains down the eustachian tube to the nose, where it appears as watery nasal drainage.

Patients who perform sinonasal saline irrigations may note watery nasal drainage that occurs even hours after they have completed the irrigation. Retained irrigation fluids may be more problematic when the surgically opened sinuses hold the saline until the patient tips the head. When this situation occurs in the immediate postoperative period, distinguishing between a true CSF leak and the release of retained saline irrigation fluid can be somewhat challenging; however, discontinuing the irrigations quickly eliminates any problems caused by them, but will not diminish a true CSF leak.

A large number of sinonasal inflammatory conditions, including both seasonal and perennial allergic rhinitis, and noninflammatory conditions, including vasomotor rhinitis, may produce watery rhinorrhea. Associated features typically serve to separate these conditions from true CSF rhinorrhea.

History

The patient’s clinical history provides important cues about CSF rhinorrhea. A patient with active CSF rhinorrhea reports unilateral watery nasal discharge that occurs on the side of the presumed CSF leak. Often, the rhinorrhea is associated with a salty taste, but this may not necessarily be so. Of course, the patient with a septal perforation is not able to reliably localize the side of the skull base defect, and the patient with bilateral defects describes bilateral watery rhinorrhea. Rhinorrhea caused by a CSF leak has a typical characteristic of positional variation; that is, the rhinorrhea occurs only when the patient lowers the head. For instance, such a patient indicates that the watery drainage occurs when he or she bends over to tie his or her shoelaces.

In the situation of a traumatic CSF leak, the history of the antecedent event provides obvious cues about the presence of a skull base defect. Unilateral watery drainage that develops after a head injury from a motor vehicle accident or fall or unilateral drainage that is first noted after sinus surgery or skull base surgery must be regarded as possible CSF leak.

CSF leaks that are seemingly idiopathic may be preceded by transient increases in ICP. Clinical anecdotes suggest that some patients experience CSF rhinorrhea after strong nose blowing. In this situation, the CSF leak may best be classified as a traumatic leak.

If the skull base defect involves the cribriform plate, the patient may report hyposmia, anosmia, parosmia, or a combination of these disorders. A skull base neoplasm, causing a skull base defect, may produce remarkably minimal symptoms, aside from those associated with skull base defect, until the lesion is relatively massive and encroaches upon and destroys adjacent cranial nerves and other structures.

A detailed history of nasal and sinus health is also warranted in patients with suspected CSF rhinorrhea. First, the presence of inflammatory paranasal sinus disease may influence the treatment strategy if a true CSF leak is present. Second, inflammatory conditions may mimic the symptoms of a CSF leak, and fluctuating nasal symptoms due to varying inflammation may complicate the clinical history. Finally, many patients with suspected CSF leak may have undergone surgery, although not recently. In such cases, unrecognized skull base injury may manifest as CSF rhinorrhea years or decades after the initial procedure.

A history of headache must be explored in detail. Some patients with idiopathic, nontraumatic CSF rhinorrhea report severe diffuse headache that improves when the rhinorrhea occurs and worsens when the rhinorrhea stops. The pathophysiology of these headaches probably reflects variations in ICP. When the ICP is elevated, the headache occurs; however, when the CSF leak, appearing as watery rhinorrhea, releases the ICP elevation, the headache improves. Chronic headache may also result from other causes of elevated ICP, including BIH and ESS, which have been associated with CSF rhinorrhea (as described previously). Rarely, a chronic headache may result from an unrecognized intracranial neoplasm. Severe chronic headache may also occur from low ICP caused by chronic depletion of CSF through a persistent CSF leak.

A history of bacterial meningitis, especially of multiple episodes of bacterial meningitis, may suggest a possible skull base defect that provides a route for the intracranial extension of bacterial pathogens from the paranasal sinuses.

Physical Examination

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