Health & Medical Neurological Conditions

Surgical Management of Meningoencephaloceles and CSF Leaks

Surgical Management of Meningoencephaloceles and CSF Leaks


Patient Outcomes

The occurrence of temporal meningoceles and/or meningoencephaloceles in the middle ear or mastoid is often insidious in onset and usually only occurs with ipsilateral aural fullness or CSF egress from a disrupted tympanic membrane or through the eustachian tube. Once this fluid is determined to be CSF, usually by testing for β-2 transferrin, and not a serous middle ear fluid collection, the cranial base should be examined radiologically to identify a cortical dehiscence. Imaging should include both thin-cut CT scanning of the temporal bone and MRI to evaluate for the presence of meningoencephaloceles (Figs. 7 and 8). Any abnormalities should be surgically addressed to prevent persistent leakage and the associated risk of meningitis, intracranial abscess, and seizures. With a combined mastoid/middle fossa approach, we were able to achieve a high success rate (96%) of CSF fistula closure, comparable to rates in previously published reports.

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Figure 7.

Fine-cut coronal CT of the temporal bone demonstrating a defect of the tegmen cortex and opacification of the mastoid air cells.

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Figure 8.

Coronal T2-weighted MR image revealing a right-sided meningoencephalocele herniating through a defect in the tegmen tympani and into the middle ear.

Our surgical technique involves a robust dural closure following extradural dissection and encephalocele reduction/resection. We use a multilayer closure for direct repair of the dural and cranial base defects. Using both a synthetic dural inlay and an epidural autologous graft along the tegmen helps to ensure that the areas of dural and osseous disruption are fully covered and reinforced. As mentioned above, when the middle ear ossicles are exposed, we use a concave calvarial bone graft cut from the temporal craniotomy flap to protect these structures prior to placing a piece of pericranium extradurally. Despite this precaution, we did have 1 patient who required an ossicular chain reconstruction after suffering postoperative hearing loss when the head of the incus became fixed to the surgical repair. Following his revision procedure, his hearing improved dramatically but remained depressed as compared with the contralateral side. Subsequently, we now take care to ensure that the graft is shaped so that the concave side faces the tegmen defect and that there is sufficient space between the middle ear and bone graft to allow for normal mobility of the ossicles (Fig. 4).

Impact and Management of Intracranial Hypertension

Although thinning of the tegmen cortex appears to be fairly common in autopsy studies, ranging from 15% to 34%, the occurrence of CSF otorrhea is fairly infrequent. The predisposing factor to the formation of cranial base (meningo)encephaloceles is thought by many to be intracranial hypertension. It is believed that the pathogenesis of tegmen thinning shares many characteristics with benign intracranial hypertension, or pseudotumor cerebri. Although not our experience, a female preponderance in middle fossa CSF leaks has been reported by many groups. Additionally, a patient's body habitus appears to play a significant role, as these patients tend to be obese (BMI > 30 kg/m). Other signs of intracranial hypertension may also be evident, such as the radiographic finding of an empty sella, which was noted in 17% of the patients in our series, a higher rate than the 5%–6% seen in the normal population. Furthermore, it is likely that the rate of intracranial hypertension is underestimated in this population if the ICP is measured while CSF is actively leaking or at least before the defect(s) is fully repaired. Unrecognized intracranial hypertension may be a reason for recurrent CSF leakage, either from the same site or from a remote cranial base defect, after surgical repair.

Thus, our treatment of this disorder involves not only repair of the disrupted dura and reinforcement of the middle fossa floor but also an assessment of intracranial hypertension and CSF diversion, if present. We use an intraoperative lumbar drain to aid temporal lobe relaxation during evaluation of the tegmen cortex. The drain is then left in place for 3 days postoperatively to allow for decompression of the dural closure during early healing of the repair. The drain is always placed immediately preoperatively under general anesthesia to record the most accurate OP. In our review, the measured preoperative ICPs averaged 21.8 ± 6.0 cm H2O, with 10 patients (43%) demonstrating ICP > 20 cm H2O.

Although a CSF fistula develops through a single site in these patients, the disease process more likely represents a global intracranial problem. We found that 43% of our patients had bilateral tegmen defects and thus were at risk for a recurrent CSF leak through the same site on the contralateral side. For this reason, we have selectively used long-term CSF diversion via VP shunting in patients with significant risk factors for recurrence. We propose that those risk factors include a spontaneous CSF leak not caused by a predisposing condition (that is, trauma, chronic infections, or prior surgery), high-volume leaks, CSF OP > 20 cm H2O, BMI > 30 kg/m, preoperative imaging demonstrating multiple cranial base cortical defects and/or an empty sella turcica, and any history of an event that leads to inflammation of the arachnoid granulations and impairment of CSF absorption (that is, meningitis, intracranial hemorrhage, significant closed head injury, and so forth).

Utilizing these criteria, we suggested VP shunt placement to 8 of the 10 patients with an ICP > 20 cm H2O, 3 of whom refused this treatment. A recurrent leak developed in 1 of these patients within 1 week of surgical repair. Another patient with a normal OP received a shunt given the presence of other risk factors for recurrence. In general, the decision for VP shunt placement is made on an individual basis. Although we are aggressive with long-term CSF diversion in this group of patients, we believe that the prevention of recurrent or additional leaks and the associated risk of meningitis outweigh the risks related to VP shunts.

Critique of Current Study

The limitations of this study include its retrospective nature and limited size. The duration of postoperative follow-up was also variable, with 1 patient not returning at all postoperatively and 6 patients lost to follow-up after only 5 months of monitoring. This follow-up may be long enough, however, to identify most recurrent CSF leaks, despite their insidious nature. The 1 recurrence in our series occurred in a patient within a week of his initial tegmen repair, and other reports have indicated that relapses occur most often within a few months of surgery. Note, however, that rare cases of recurrent CSF leakage have been reported up to 2–4 years after surgery. The development of new CSF fistulas at remote sites of the cranial base likely occurs years, or even decades, after an initial leak, and further follow-up of this group of patients is needed.

Relying on an OP measurement at the time of an active CSF leak to determine intracranial hypertension may not always provide an accurate assessment. Some patients with a normal pressure may demonstrate recurrent CSF leakage at the repair site or elsewhere in the cranial base as a result of continued unrecognized intracranial hypertension. In those patients for whom this may be a concern, it may be prudent to perform a lumbar puncture for OP measurement at a later postoperative date.

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