Leakage of cerebrospinal fluid (CSF) though the ear structures is a rare but potentially life-threatening situation that requires rapid intervention. The presence of an abnormal communication of the sterile subarachnoid space with the flora of the sinonasal tract places the patient at great risk for meningitis. Indeed, an episode of meningitis may be the presenting problem for a person with an otologic CSF leak.
Even though a leakage of CSF is occurring through otologic structures, actual leakage of the fluid from the ear is not always present. CSF otorrhea occurs only if a perforation in the eardrum or a defect in the external ear canal is present. This is often the case when the leakage results from trauma or previous ear surgery. However, in the absence of such a defect, the fluid flows down the eustachian tube and manifests as a clear rhinorrhea. In this situation, it must be differentiated from a spinal fluid leak from other areas of the skull base, such as the sinuses. The reverse is also important to remember; just because the leak is through the nose does not mean that an otologic source is not a possibility.
The subject of CSF otorrhea covers a broad range of potential pathologies. Most of such leaks are postoperative and are a recognized complication of acoustic neuroma surgery. Some occur as a result of middle ear surgery or erosive disease, such as cholesteatoma, sometimes many years later. Some may be the result of congenital abnormalities in the formation of the inner ear and the mastoid. In this article, the authors attempt to discuss all these related pathologies.
See the image below.
Because this problem is so rare, the exact frequency with which it occurs is unknown. Leaks as a postoperative complication of skull base surgery represent the bulk of cases. This complication has been reported to occur in 6-12% of such cases. Leakage as a result of temporal bone fracture is the second most common etiology and occurs in 21% of patients with temporal bone fractures. Spontaneous leakage is rare, with less than 500 cases having been reported in the literature worldwide. Such leakage is more common in children (72%) than adults. Although rare, spontaneous leakage represents the greatest challenge to the clinician because the source of the leakage is not readily obvious. 
Meningitis is often the presenting symptom. It is found in 93% of children and 36% of adults with spontaneous CSF leakage. Sensorineural hearing loss is another significant morbidity associated with spontaneous leaks in children and is present 82% of the time. Seizures are also a potential morbidity. [2, 3]
The underlying etiology of a spinal fluid leak through the temporal bone is a violation of the bony and meningeal barriers that separate the subarachnoid space from the middle ear and mastoid. This means that a defect must exist not only in the bone, but also in the dura mater. Such problems may be postsurgical, posttraumatic, congenital, or related to otologic disease.
CSF leakage can result from a number of underlying pathologies. Such leaks can broadly be categorized into acquired and congenital.
Congenital cerebrospinal fluid leak
Congenital causes can be due to defects in the otic capsule itself, abnormal patency of pathways associated with the otic capsule, and defects distant from the otic capsule. Although congenital sources are more common in children, they can occur in people of any age and can even be observed in the geriatric population. 
Acquired cerebrospinal fluid leak
Acquired leaks result from temporal bone trauma, surgery, or infectious or neoplastic causes.  Acquired spinal fluid leakage is far more common than congenital leakage. Postoperative leakage following surgery is probably the most common cause of acquired CSF leaks. It is a recognized complication of acoustic neuroma removal and other skull base surgery. These leaks are usually evident in the early postoperative period. They rarely occur more than 2 months postoperatively.
Mastoid surgery for chronic ear disease is also a potential cause of an acquired CSF leak. When the dura is violated intraoperatively, the defect should be repaired immediately if possible. Frequently, however, the dura is not injured, but a defect is left in the bony plate of the tegmen. Over the years, the continuous pulsations of the CSF cause the dura to thin, allowing the arachnoid or brain to prolapse through this defect. This dura may become thin and spontaneously rupture, resulting in a leak of CSF many years after the initial surgery. In addition to dura, portions of brain tissue may also prolapse through the defect, resulting in an encephalocele.
Even in the absence of surgical intervention, similar problems may result from middle ear disease, most notably cholesteatoma. Cholesteatoma may erode the tegmen plate and allow herniation of dura or brain to occur over time. 
Spontaneous cerebrospinal fluid leak
Spontaneous leakage is leakage that occurs without an obvious antecedent pathology. Such leakage is usually due to some congenital defect in the temporal bone. Understandably, such defects are usually evident in childhood.
Spontaneous CSF leakage may result from a number of congenital deformities of the ear. Mondini deformity, an abnormal development of the cochlea, is frequently associated with CSF leakage. Such patients often have a patency at the lateral aspect of their internal auditory canal, allowing direct movement of CSF into the inner ear. A second defect, usually of the annular ring of the stapes footplate, then results in drainage of CSF into the middle ear. This usually causes loss of the remainder of hearing. A similar presentation may be observed in a patient with a widely patent cochlear or vestibular aqueduct.
Other deformities of the inner ear are also associated with spontaneous CSF leak. CSF can leak through a patent Hyrtl fissure, a congenital fusion plane found between the otic capsule and the jugular bulb (also termed the tympanomeningeal fissure). Such leakage may not be associated with any inner ear abnormalities, and the patient may have no evidence of a sensorineural hearing loss. Similar presentations may be observed in an abnormal patency of the petromastoid canal, which normally carries the subarcuate artery. Such patients may present with recurrent bouts of meningitis associated with what appears to be a unilateral serous otitis. Frequently, the true nature of the problem is not realized until a myringotomy is performed, at which time an unceasing flow of clear fluid is returned.
Although spontaneous CSF leakage is more common in children, reports of it occurring in people of greater age are increasing. In adults, spontaneous CSF otorrhea is often associated with a defect in the bone separating the middle ear space and the cranial vault. Such bony dehiscences are most commonly found on the floor of the middle fossa, along the tegmen plate. Tegmen dehiscences are found in up to 30% of autopsy specimens.
Continuous pressure of the CSF over the years results in formation of a meningocele or encephalocele. Defects in the middle fossa are associated with 88% of spontaneous leaks in adults. The remainder of spontaneous leaks are due to posterior fossa defects and arachnoid granulations, normal structures that absorb CSF. These structures are usually associated with the venous sinuses of the dura mater, but they have been found within the temporal bone on some autopsy specimens. Spontaneous leaks have recently been shown to be often associated with increased intracranial pressure. This is often manifested by a partially empty sella on the MRI scan.
The chief presenting symptom one would expect when a CSF leakage through the ear is present is a clear watery drainage from the ear. This, however, is not always present and does not occur unless the eardrum or canal is in some way violated. If this is not the case, the leakage may be evident as a clear watery nasal discharge. This discharge may be positional or intermittent in nature and may only become apparent during straining or leaning forward. Some patients may notice no discharge at all but rather may report a strange salty taste in the back of the throat.
Often, a patient with an otogenic spinal fluid leakage presents with a unilateral hearing loss. The nature of the hearing loss is important. A sensorineural hearing loss suggests an associated abnormality of the inner ear, such as a Mondini deformity. However, the loss may be conductive, suggesting a leak elsewhere in the temporal bone. Such a presentation may be very similar to that of a unilateral serous otitis media and may be mistaken for such. The realization of the true identity of the fluid may only be made at the time of myringotomy, when clear fluid pours unceasingly from the incision. When such an event occurs, the ear canal is often packed to prevent continuous drainage from the ear and allow the eardrum to heal. Other authors think that packing may cause stasis and provide a nidus for infection, hastening meningitis, and they recommend only a loosely placed, frequently changed sterile cotton ball placed in the conchal bowl. A full workup should be immediately undertaken.
A common presentation for a spontaneous spinal fluid leakage is an unexplained episode of meningitis. In such situations, the source of the leakage may not be readily apparent. A history of unilateral hearing loss or chronic ear disease may suggest which side is involved. Absence of otologic symptoms and a history of sinonasal disease may suggest an anterior source of leak. In situations of leakage following surgery and trauma, the source of the leak usually is readily apparent.
Patients suspected of having a spinal fluid leakage should undergo complete otologic, neurologic, and head and neck examination. Use binocular microscopy to examine the ears. Pneumatic otoscopy may be helpful in demonstrating fluid within the middle ear space, especially when that fluid is very clear. Tuning fork evaluations can be used to demonstrate a conductive hearing loss. If possible, perform complete audiometric evaluation.
An important part of the physical examination is an attempt to demonstrate the leak. Usually, the patient is asked to perform for the examiner the maneuver with which they notice the leak, such as straining or leaning forward. With the Dandy maneuver, the patient leans forward with the head pointed down while performing a Valsalva. This maneuver often results in the appearance of clear fluid from the nostril of a person with a CSF leak. The side of the nostril from which the leakage occurs usually agrees with the side of the otologic source.
Leakage of CSF though the ear structures places the patient at great risk of meningitis. Surgery is therefore indicated to repair this problem in most situations. Leaks occurring following trauma or recent skull base surgery can often be treated conservatively using a pressure dressing and a lumbar drain. Surgery is recommended for patients in whom this conservative therapy is unsuccessful.
See Etiology and Pathophysiology.
In patients with postsurgical and traumatic leaks, surgery may not be indicated because it is reserved for those in whom conservative therapy is unsuccessful.