Diagnosis: Spontaneous CSF Leak
Persistent fluid in the middle ear without a precedent allergic rhinitis, upper respiratory infection, or some type of process that causes Eustachian tube dysfunction should always be met with suspicion. The question that must come to mind is whether a sinister process may be causing the fluid. This worrying process is often related to malignancies in the nasopharynx or skull base that could cause a blockage in the Eustachian tube. Therefore, it is important to evaluate the nasopharynx with endoscopy and, if suspicion is high, examine the skull base with imaging. Evaluation of the nasopharynx is a must for Asian patients who are usually at a higher risk for nasopharyngeal carcinoma. This examination can be easily done in the office using a flexible scope through the nose.
Elderly patients have a higher risk of developing Eustachian tube dysfunction and serous effusion. This is partly due to the atrophy of the tensor veli palatini that usually occurs in patients with a history of Eustachian tube dysfunction. Atrophy of this muscle impairs the eustachian tube opening and can lead to middle ear effusion. This process tends to occur bilaterally. While unilateral Eustachian tube dysfunction can certainly happen without any precedent event, it may be prudent to hold off the tube placement until the patient's workup is completed.
The second sinister process to be concerned about is spontaneous cerebrospinal fluid (CSF) leakage. This condition usually occurs in obese patients, particularly women. Chronic pressure from the abdominal weight is believed to increase the central venous pressure, which then increases intracranial pressure.
A congenital defect on the roof of the temporal bone (tegmen) or the gradual thinning and destruction of the tegmen allow for herniation of the meninges (dura) and sometimes of the brain into the temporal bone. It has also been found that patients with intracranial hypertension have a thinner tegmen, which may be caused by the chronic high-pressure pulsation of the dura against the roof of the temporal bone. When the bone breaks and the dura weakens from the high pressure, a small hole can develop in the roof of the temporal bone. This causes a slow leakage of CSF into the temporal bone. While one would expect the fluid to flow through the Eustachian tube, this doesn't usually happen. The fluid tends to cause an inflammation in the middle ear and mastoid mucosa that leads to Eustachian tube dysfunction and fluid accumulation in the middle ear. This is not to say that SF does not come out of the Eustachian tube into the nose. However, spontaneous CSF leakage from the temporal bone tends to begin slowly as the opening in the dura is very small. This is in contradistinction with traumatic CSF leakage, which tends to rapidly flow out into the Eustachian tube and nose. Unlike a CSF leakage that originates from the nose (roof of the nose), it is usually difficult to obtain a proper sample for testing by asking the patient to bend over to collect a specimen from the nasal drainage.
The best way to diagnose CSF leakage is by getting a beta-2-transferrin test of the fluid. However, most laboratories require a minimum of 3 mL of fluid for testing, which is impossible to obtain. A limited number of laboratories can perform the test with 0.5 mL of fluid, but even then, obtaining this amount of fluid from the middle ear is not always easy since the entire volume of the middle ear is approximately 0.5 mL. In addition, some of the fluid can be lost in the suction process when obtaining the sample. Finally, not all fluid in the mastoid can be suctioned, given the inflammation and blockage in the middle ear.
This patient's persistent clear drainage from the middle ear after tube placement and the current effusion are most concerning for CSF leakage. The CT imaging showed fluid in the mastoid and a mass from the tegmen through a defect that is likely a meningocele (dura and CSF) or encephalocele (dura and brain; Fig. 2). The right temporal bone showed a thin tegmen with a small defect and no encephalocele (Fig. 3). The patient's imaging from 2014 showed that the intracranial contents had a defect and a herniation into the mastoid (Fig. 4). The MRI confirmed that the small mass in the mastoid is continuous with the intracranial content (Fig. 5).
Treatment of spontaneous CSF leakage is surgical. We usually attempt to close all defects with a post-auricular mastoidectomy. Multiple layers of tissue (usually fascia) are used to close the isolated defect. The mastoid is obliterated with abdominal fat. This approach reduces the morbidity of a middle cranial fossa and temporal lobe retraction for small to medium mastoid tegmen defects. If the defect is very large (>1 cm) or the site of the leak is on the roof of the middle ear (tegmen tympani) or petrous apex, then a middle cranial fossa approach is warranted. If the mastoid approach doesn't work for a patient, a middle cranial fossa approach is done instead. Older patients and those with spontaneous CSF leakage tend to have a very thin dura that adheres to the temporal bone, which makes the middle fossa approach more difficult as separating the dura from the temporal bone can result in a dural tear. In rare cases involving elderly patients who cannot tolerate an extensive procedure, a transcanal or transnasal operation can be performed to obliterate the Eustachian tube and prevent any leakage into the nose. This also prevents meningitis but leaves the patient with conductive hearing loss from the persistent middle ear fluid.
BONUS 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. Axial (horizontal) CT of the left temporal bone showing the fluid in the mastoid and the encephalocele.
- Video 2. Axial (horizontal) CT of the right temporal bone showing the normal mastoid with the dominant jugular bulb.
- Video 3. Coronal (parallel to the face superiorly-inferiorly) CT of the left temporal bone showing the tegmen mastoideum (roof of mastoid) defect with meningocele or encephalocele in antrum.
- Video 4. Coronal (parallel to the face superiorly-inferiorly) CT of the right temporal bone showing a thin tegmen mastoideum (roof of mastoid) with no encephalocele.
- Video 5. Sagittal (looking outside-in from laterally) CT of the temporal bone showing the sagittal anatomy of the encephalocele and its relationship with the ossicles.
- Video 6. Coronal (parallel to the face superiorly-inferiorly) T1 MRI showing that the contents of the mastoid are in continuity with the brain.
All videos can be found exclusively on our website at thehearingjournal.com https://journals.lww.com/thehearingjournal/Pages/collectiondetails.aspx?TopicalCollectionId=23.Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.