Meningoencephalic herniation is the herniation of meningeal and/or encephalic tissue in the middle ear or mastoid. It occurs in connection with infection, previous surgery, head trauma, or congenital tegmental defects. A patient with meningoencephalic herniation has a high risk of developing meningitis and epilepsy due to epileptogenic focus in the herniating tissues.
The patient may present with a pulsatile retrotympanic mass, cerebrospinal fluid (CSF) leakage, and aphasia. However, the most common manifestation is that of a conductive or mixed hearing loss with a draining ear or serous otitis media.
Herniation of meningeal and/or encephalic tissue into the middle ear is a form of pathology that—even if rarely found by the otologist—can be life-threatening for the patient due to possible infectious intracranial complications. Four different etiological types are possible: infectious, postsurgical, traumatic, and spontaneous. From a pathogenic point of view, all these types are characterized by a bony and dural defect located in the tegmen, through which meningeal and encephalic tissue can herniate. Therefore, once meningoencephalic herniation is suspected, surgical correction is required. The symptoms are often nonspecific, so that some cases are diagnosed during surgery.
When there is strong suspicion of herniation, neuroradiological assessment procedures have to be performed to establish a correct preoperative diagnosis. High-resolution computed tomography (CT) of the temporal bone, in particular, can demonstrate the exact limits and location of the bone defect, while magnetic resonance imaging (MRI) allows the nature of the tissue in the middle ear to be determined. The choice of surgical approach is directed by the etiology, the position and size of the bony defect, preoperative audiometry, the presence of chronic infection in the middle ear, and/or intraoperative active CSF leakage.
In our experience, 5% of revision canal wall down mastoidectomies are complicated by either meningoencephalic or dural herniations. A small herniation (< 1cm2) can be pushed back intracranially and a piece of cartilage then inserted beneath the bone to ensure repositioning of the dura. The cartilage is covered with bone paste and fascia.
Middle-sized herniations (1–2 cm2) can be repaired by a combined approach. The brain tissue is treated with bipolar coagulation. Then, after pushing back the herniation intracranially, a sufficiently large piece of autologous or homologous cartilage is inserted extradurally through a small craniotomy to ensure repositioning. The bony defect is further repaired using bone paste and covered with temporalis fascia from the mastoid cavity.
In cases of large herniation (> 2 cm2), a middle cranial fossa approach is adopted. In this approach, the dura of the temporal lobe is carefully elevated until the neck of the hernia is identified and subjected to bipolar coagulation. The coagulated part is left in the middle ear or mastoid, where it acts as a barrier against infection. The defect is then reconstructed by placing a piece of temporalis fascia between the cerebral tissue and the dura; another piece of fascia is placed extradurally. Next, a piece of cartilage is placed between the bony defect and the dura for reinforcement.
The advantage of this approach is the opportunity to reach bony defects located anteriorly without any manipulation of the ossicular chain.
Subtotal petrosectomy with middle ear obliteration, in our opinion, represents the safest and most definitive treatment for meningoencephalic herniation. Performing a blind sac closure of the external auditory canal, obliterating the Eustachian tube, and filling the surgical cavity with fat completely isolate the middle ear and mastoid cavities from the external environment, minimizing the risks of recurrence and other complications such as CSF leakage. However, due to the resulting conductive hearing loss (generally around 60 dB), it should be reserved for cases with poor auditory reserve or extensive middle ear destruction with a limited possibility for reconstruction. Because of the closure of the external auditory canal, in subtotal petrosectomy postoperative radiologic follow-up is mandatory (CT scan, MRI scan with fat-suppression and diffusion-weighted images) to reveal presence of residual cholesteatoma.
Meningoencephalic herniation is depicted in the following figures ( ▶ Fig. 13.1, ▶ Fig. 13.2, ▶ Fig. 13.3, ▶ Fig. 13.4, ▶ Fig. 13.5, ▶ Fig. 13.6, ▶ Fig. 13.7, ▶ Fig. 13.8, ▶ Fig. 13.9, ▶ Fig. 13.10, ▶ Fig. 13.11, ▶ Fig. 13.12, ▶ Fig. 13.13, ▶ Fig. 13.14, ▶ Fig. 13.15, ▶ Fig. 13.16, ▶ Fig. 13.17, ▶ Fig. 13.18, ▶ Fig. 13.19, ▶ Fig. 13.20, ▶ Fig. 13.21, ▶ Fig. 13.22, ▶ Fig. 13.23, ▶ Fig. 13.24, ▶ Fig. 13.25, ▶ Fig. 13.26, ▶ Fig. 13.27, ▶ Fig. 13.28, ▶ Fig. 13.29).
Fig. 13.1 Left meningoencephalic herniation in a patient who had previously undergone open tympanoplasty. The hernia protrudes into the attic through a small tegmental defect and appears otoscopically as a pulsatile retrotympanic mass.
Fig. 13.2 CT scan of the case described in ▶ Fig. 13.1, coronal view. The osseous defect with the herniating tissue can be clearly visualized (arrow).
Fig. 13.3 MRI of the previous case. The protrusion of the cerebral tissue into the middle ear is visible (arrow).
Fig. 13.4 Postoperative CT scan. The hernia was managed using a middle fossa approach. The bony defect was repaired using cartilage. The temporal craniotomy (green arrow) and the cartilage (yellow arrow) are clearly visible.
Fig. 13.5 Left meningoencephalic hernia. The superior wall of the external auditory canal is dehiscent. A soft, reducible, nonpulsating mass is observed. The patient had a history of head trauma with transverse fracture of the temporal bone that occurred 3 years before presentation. He complained of left hearing loss and the sensation of ear fullness.
Fig. 13.6 Preoperative CT scan of the case in ▶ Fig. 13.5 demonstrating the herniation of cerebral tissue into the middle ear (arrow).
Fig. 13.7 CT scan of the previous case 1 year postoperatively. The hernia was managed using a middle fossa approach, placing a cartilaginous plate to reconstruct the bony defect after having sectioned the neck of the herniating tissue. The cerebral tissue, which is left in the ear during the operation, is resorbed with time as seen in the CT scan
Fig. 13.8 Left ear. Otoscopy 6 months postoperatively in the same patient. The soft mass protruding from above into the external auditory canal has shrunk, indicating progressive atrophy of the herniated tissue left in the attic.
Fig. 13.9 Left meningoencephalic herniation in a patient who had previously undergone multiple ear surgeries. The only manifestation was conductive hearing loss.
Fig. 13.10 CT scan of the case presented in ▶ Fig. 13.9.
Fig. 13.11 Posttraumatic meningoencephalic herniation in a patient with temporal bone fracture. The fracture line is evident with disruption of the posterior wall of the external auditory canal (yellow arrow). A pinkish pulsating retrotympanic mass could be visible in the whole attic (green arrow). Exostoses of the inferior and anterior walls of the external auditory canal are also visible. The patient underwent subtotal petrosectomy with obliteration of the middle ear.
Fig. 13.12 CT scan of the same case. Meningoencephalic herniation is evident at the level of the tegmen antri (arrow).