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Clinical Consultation

Symptom

Hearing Loss After Skull Base Surgery

Djalilian, Hamid R. MD; Sarna, Brooke; Abouzari, Mehdi MD, PhD

Author Information
doi: 10.1097/01.HJ.0000654948.73710.13
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A 48-year-old man presented with a history of hearing loss in the right ear. Three months ago, he underwent a retrosigmoid resection of a meningioma. His records showed that he had a partial retrosigmoid resection of the tumor approximately two years ago. Prior to this, the upper portion of the tumor had been removed via the middle cranial fossa. He noted that when he bent over, watery fluid drained out of his nose on the right side. He denied having any headache or other issues. His otoscopic examination (Fig. 1) showed the presence of fluid in the right middle ear, with a small air bubble (arrows) in the anterior superior quadrant of the tympanic membrane (TM). His audiogram showed a conductive loss.

Figure 1.
Figure 1.:
Image of the patient's right tympanic membrane. Hearing loss, cerebrospinal Fluid, medical education.
Figure 2.
Figure 2.:
Axial (horizontal) T2 MRI showing some fluid in the right mastoid that is most likely CSF (white). Hearing loss, cerebrospinal Fluid, medical education.
Figure 3.
Figure 3.:
Axial (horizontal) CT of the head showing the defect in the posterior right mastoid through which the CSF traveled to get to the middle ear and eventually the nose. Hearing loss, cerebrospinal Fluid, medical education.
Figure 4.
Figure 4.:
Axial (horizontal) CT of the head prior to the recent surgery showing a previously intact mastoid process. Hearing loss, cerebrospinal Fluid, medical education.
Figure 5.
Figure 5.:
Axial (horizontal) T1 post-gadolinium MRI of the head prior to the recent surgery showing the location of the tumor. Hearing loss, cerebrospinal Fluid, medical education.

Diagnosis: CSF Leak

Hearing loss after a skull base surgery can occur for a variety of reasons. The most common cause is blood that enters the middle ear through the mastoid air cells. Over the course of about six weeks, the blood behind the TM is usually replaced by a serous fluid that is eventually removed through the Eustachian tube (ET). Posterior fossa surgery presents a unique risk to the cochleovestibular nerve, which traverses the space between the brainstem and the temporal bone where the surgery is often performed. Removal of tumors within this area carries the risk of stretching or disrupting not only the cochleovestibular nerve but also the internal auditory artery, which feeds the inner ear structures. Also a cause of hearing loss after skull base surgery is bone dust, which can cause conductive hearing loss if it enters the middle ear from the mastoid and gathers around the stapes. Finally, disruption of the posterior semicircular canal can create a third window effect with posterior canal dehiscence, and can lead to conductive or mixed hearing loss.

The patient's audiogram indicated conductive hearing loss in the right ear. The examination also showed the presence of fluid in the middle ear. At three months post-operation, the fluid in the middle ear is unlikely to be the serous fluid from the resolution of blood. Of course, other causes of this fluid should be considered, such as ET dysfunction, which is most likely caused by an upper respiratory infection, allergic rhinitis, or gastroesophageal reflux that can reach the nasopharynx. However, it is unlikely that someone with no previous history of ET dysfunction will suddenly develop this problem immediately following a surgery. Rather, the condition is common in elderly patients, most likely due to an atrophy of the tensor veli palatini muscle—a finding that can be confirmed via temporal bone histopathology. Atrophy of this muscle can cause problems with ET opening and result in middle ear effusion. This process tends to occur bilaterally, but can certainly occur unilaterally as well.

The patient reported that liquid drained out of his nose when he bent over. When presented with this symptom, it is imperative for the clinician to rule out the presence of a cerebrospinal fluid (CSF) leak by obtaining a sample of the fluid for beta-2 transferrin testing. This molecule is found at high concentrations in CSF and perilymph. Given that the volume of perilymph in each ear is approximately 150 µL (a very small amount), if beta-2 transferrin is found in the middle ear fluid, it is almost certainly from CSF. The presence of clear liquid drainage from the nose indicates a high-flow CSF leak, which is rarely found in spontaneous CSF leaks from the temporal bone. High-flow leaks more commonly occur from a surgical disruption in the mastoid or the middle ear that creates a large opening for CSF leakage. Another possible explanation for this clear drainage is retained irrigation fluid within the maxillary sinuses. After a sinus surgery, patients regularly irrigate their nose with saline. This irrigation fluid can occasionally be retained within the maxillary sinus, which has a large opening for drainage through the nose, expelling the fluid when the patient bends forward. Another potential cause of clear rhinorrhea is vasomotor rhinitis, which causes clear watery drainage from the nose, typically when the person is eating or when the environmental temperature changes from warm to cold. Though it generally affects both sides of the nose, it can be unilateral in rare cases. Ipratropium nasal spray is both a treatment for and a method to rule out vasomotor rhinitis. Ultimately, if someone does not have a history of sinus surgery or nasal irrigation use, then the retained fluid within the maxillary sinus is unlikely to be the cause of clear liquid drainage from the nose.

The magnetic resonance imaging (MRI) of the patient a few days post-operation showed some fluid in the mastoid (Fig. 2). A computerized tomography (CT) scan of the head immediately after surgery showed a small defect in the posterior inferior aspect of the mastoid (Fig. 3). This defect was the most likely source of the CSF leakage. A retrospective review of the patient's CT scan before his most recent surgery showed that the mastoid process was intact at that time (Fig. 4). Given the anterior nature of the tumor (Fig. 5), the neurosurgeon most likely extended the craniectomy anteriorly to obtain a better exposure of the tumor. This led to a small opening into the mastoid air cells medially that subsequently allowed CSF to escape into the mastoid air cells and eventually drain into the middle ear and cause conductive hearing loss. The treatment of a post-operative CSF leak can be initially conservative. Depending on the circumstances, patients are sometimes treated with a lumbar drain to decrease CSF pressure intracranially by draining out a small amount of CSF. This allows the small defects in the dura to heal without disrupting the active flow of CSF. If that is not successful, surgery can be performed to close the defect in the mastoid. This is often performed by going through the craniotomy defect or through the mastoid itself. If the patient has no sensorineural hearing, closure of the ET, either through the ear canal or the nasal structures, can suffice in treating the problem. As long as the CSF is not exposed (through the ET or a TM perforation) for bacteria to infiltrate intracranially, the presence of CSF in the mastoid or the middle ear alone does not pose a significant danger to the patient.

BONUS ONLINE VIDEOS: VISUAL DIAGNOSIS

Read this month's Clinical Consultation case, then watch the accompanying videos from Hamid R. Djalilian, MD, to review the patient's imaging for yourself.

  • Video 1. Video of the examination.
  • Video 2. Axial (horizontal) T2 MRI showing a small amount of fluid in the mastoid on the right side and a normal mastoid on the left.
  • Video 3. Axial (horizontal) CT showing the opening in the mastoid and some air intracranially.
  • Video 4. Coronal (vertical parallel to face) CT showing the opening in the posterior of the mastoid.
  • Video 5. Axial (horizontal) T1 post-gadolinium showing the extent of the large petroclival meningioma.
  • Video 6. Axial (horizontal) CT prior to the recent surgery showing an intact mastoid process and a previous titanium plate over the craniectomy.

Watch the patient videos online at thehearingjournal.com.

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