An Uncommon Differential for Mass in the Middle Ear Cleft-Temporal Meningoencephalocele

Abstract

Meningoencephalocoele (ME) of the temporal bone is otherwise known as brain fungus. It is a rare and potentially life-threatening condition. It occurs in cases of chronic otitis media either as a complication or iatrogenically induced following mastoid surgeries. It requires prompt surgical intervention. High-resolution Computer tomography of Temporal bone and Magnetic resonance imaging of the brain are needed to detect these cases. Surgery can be otological, neurosurgical, or combined. We discuss a case of Iatrogenic Temporal meningoencephalocele and its management along with a review of the literature.

Introduction

Brain fungus or Fungus cerebri is herniation of dura mater and brain tissue into the middle ear and mastoid cavity. Caboche first described it in 1902. In the past, they commonly occur in patients with brain abscesses following drainage [1]. However, now with the advent of modern surgical procedures, it has become a rarity. It is seen in less than 1% of the cases. This condition generally occurs due to the defect in the tegmen tympani or the tegmen antri caused by cholesteatoma, increased intracranial pressure, or following mastoid surgery [2, 3]. The herniation is accompanied mainly by leakage of cerebrospinal fluid(CSF). Management consists of wide surgical exposure, amputation of necrotic and herniated brain tissue, watertight dural closure, and closure in layers of the overlying soft tissues.

Case Report

A 50 years old female presented with recurrent episodes of right ear discharge and right-sided headache for 6 months. She was diagnosed with Right ear Chronic Otitis Media with Cholesteatoma 10 years ago. She was operated on the right ear twice in a different hospital, the first time 8 years back and the second time 2 years after the first surgery. The records of the type of surgery performed were missing.

On her current visit, she had pain in the right ear and a dull aching headache along with occasional watery ear discharge from the right ear for 6 months. She has had hearing loss in the right ear since the second surgery. No history of fever, seizures, vomiting, vision loss, or weakness of limb. She had no other ear complaints like tinnitus, vertigo, or facial weakness. Otologic examination on the right side revealed a postoperative cavity with narrow meatoplasty along with a smooth surfaced, soft, pale, pulsatile swelling arising from the roof of the external auditory canal(EAC). Bilateral facial nerve examination and neurotological examination were normal. The ophthalmic evaluation showed normal fundus in our patient.

Pure tone audiometry (PTA) revealed a right 91.5 dBHL(profound Hearing loss) and left 17.5 dBHL. High-resolution computer tomography(HRCT) of Temporal bone showed a non-enhancing hypodense lesion with smooth bulging margins occupying the middle ear cavity, mastoid and external auditory canal, and communicating with the middle cranial fossa a defect in the tegmen tympani measuring 4 mm × 3 mm. Magnetic Resonance Imaging (MRI) T2 weighted images showed an isointense lesion arising from the middle cranial fossa and protruding into the middle ear cavity, which had continuation with the intracranial contents(Fig. 1a and b).The patient was planned for Right Trans mastoid repair of the defect under general anaesthesia. Intraoperatively a pale pink soft tissue mass was visualized in the roof of the EAC, which was herniating through a defect in the tegmen tympani (Fig. 2a and b). The herniated brain tissue was debulked using bipolar cautery, and the entire mass shrunk in size. No cerebrospinal fluid leak occurred during the procedure. No residual cholesteatoma was present. Malleus, Incus and Stapes suprastructure were missing. The tegmen defect was reconstructed using the Conchal cartilage and the fascia lata graft, placed by underlay technique (Fig. 3a and b). The repair was supported with gel foam. Fascia lata graft was placed over the stapes footplate. The cavity was packed with gel foam soaked in ciprofloxacin drops. The postoperative period was uneventful.

Fig. 1.

a T2 weighted MRI showing herniation of isodense brain tissue along with CSF into the right middle ear and mastoid cavity. b HRCT coronal cut showing eroded tegmen plate in right side

Fig. 2.

a Herniated part of the brain in the right mastoid and middle ear cavity(White arrow). b Middle ear cavity after removal of the meningoencephalocele showing the defect in the Tegmen(Black arrow)

Fig. 3.

a Tegmen defect after being repaired using conchal cartilage. b Placement of the fascia lata graft over the defect and the middle ear cavity(Black arrow)

Discussion

Temporal bone ME is the herniation of brain and meningeal tissue into the middle ear and mastoid cavity. They occur due to a defect in the bony plates separating the middle ear and mastoid from the middle or posterior cranial fossae. Middle cranial fossa herniation into the middle ear is much more common than posterior fossa herniation [4].

ME can occur due to congenital dehiscence of the tegmen plate, iatrogenic damage during surgery, as a complication of cholesteatoma, and even spontaneously. Congenital dehiscence of the petrosquamous suture in the tegmen plate or the defect in the tegmen can also cause ME formation [5]. The commonest cause is an inadvertent iatrogenic injury to the tegmen plate during mastoidectomy. The tear in the dura and a possible small CSF leak may go unnoticed during surgery. Thus a high index of suspicion must be maintained in evaluating patients with a history of temporal bone trauma or surgery to avoid potential misdiagnosis. In our patient, the past surgeries had led to a tegmen and dural defect, which ultimately led to ME formation. Spontaneous ME's are more common in the elderly and patients with increased intracranial pressure [4]. Rare causes include cranial irradiation [5], vitamin D deficiency with rickets, and ectopic arachnoid granulations [6].

Common signs of ME include CSF otorrhea or rhinorrhea, serous otitis media, hearing loss, and meningitis. Uncommon presentations are temporal lobe epilepsy, facial paralysis, aphasia, tension pneumocephalus[7], and subcutaneous postauricular mass [4]. An examination may reveal clear fluid in the middle ear. The mass is usually soft, pulsatile, and increases in size on performing the Valsalva manoeuvre. In our patient, there was a history of occasional CSF otorrhea and hearing loss. On examination, the pulsatile brain tissue was directly visualized in the mastoid cavity.

The typical presentation of ME is serous middle ear effusion or clear watery otorrhea. In a study, 42% of patients with spontaneous CSF otorrhea presented with otorrhea alone, whereas 33% showed middle ear effusion. Only 24% presented with classical warning signs such as meningitis. [8] Our patient never had any history of meningitis. Since our patient had no active otorrhea at the time of presentation to us, CSF analysis was not done.

CT and MRI play an essential role in the management of these patients. High-resolution CT of the temporal bone in both axial and coronal planes will reveal the tegmen defect. MRI helps in identifying the nature of the pathology. It differentiates fluid from soft tissue masses like cholesteatoma and ME. Brain herniation into the middle ear will appear isointense on T1 /T2, demonstrate continuity with intracranial contents, and be non-enhancing [8, 9]. A classic "teardrop sign" distortion of the temporal lobe due to temporal lobe herniation may be observed. In our patient, a 4 × 3 mm defect was noted in the HRCT, and the teardrop sign was visible in the MRI, which was isointense in T1 and T2 [8].

Repair of a temporal bone encephalocele has three basic steps:[a] management of brain herniation, [b] restoration of dural integrity, and [c] exenteration of mastoid infection and cholesteatoma if present. Brain tissue herniated into the mastoid is felt by most authors to be non-functional and, in general, should be excised. The size of the encephalocele itself is not as important as that of the dural defect. Due to the high risk of recurrence, transmastoid repair is now generally reserved for those cases with small, lateral defects smaller than 1 cm. It can be repaired with temporalis fascia alone [8]. Since our patient had a small defect, we repaired using the transmastoid approach. Due to previous surgeries, we suspected a deficiency in adequate temporalis fascia, and hence we used a fascia lata graft from the ipsilateral thigh. Conchal cartilage was used to close the bone defect. The Underlay technique was used for a watertight closure. In large defects [> 1 cm], depending on ossicular chain involvement, either a middle cranial fossa approach or a combined approach may be needed [10, 11].

Conclusion

Brain fungus or Temporal meningoencephalocele, though a rare condition in the current era of medicine, should always be kept in mind in patients with previous mastoid surgeries. It forms one of the rare differentials when a pulsatile mass is visualized in the middle ear cleft. It can produce life-threatening complications like meningitis due to ascending infection from the ear. Hence meticulous surgical removal along with watertight closure of the defect is essential.

Authors’ Contributions

The first draft of the article was written by SD. The draft was revised by RS and AA. All authors commented on the previous versions of the article. All authors read and approved the final manuscript.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The authors did not receive support from any organization for the submitted work. No funding was received to assist with the preparation of this manuscript. No funding was received for conducting this study. No funds, grants, or other support was received.

Declarations

Conflict of interest

The authors declare that they have no conflict of interest.

Ethics Approval

This study was performed in line with the principles of the Declaration of Helsinki. Our Institute Research Ethics Committee has confirmed that no ethics approval is needed for case reports.

Informed Consent

Informed consent was obtained from the patient.

Consent for Publication

The authors affirm that human research participant provided informed consent for publication of the images.