An epidermoid cyst affecting the petrous portion of the temporal bone. It extends beyond the inner ear towards the center of the skull base. Clinical presentation of Petrous Bone Cholesteatoma is often variable and misleading. It can present as a middle ear cholesteatoma, progressive or sudden facial nerve palsy, sensorineural hearing loss or a conductive hearing loss, secretary otitis media or intracranial complication.
Pathophysiology
This disease can be either acquired or congenital. Petrous Bone Cholesteatomas (PBC) are most of congenital. It is believed that the congenital cholesteatoma of petrous apex is caused by the resting squamous cell. The disease is described as congenital when it manifests itself without a past history of trauma or infection with intact and located behind the tympanic membrane. This disease is destructive in nature; most of PBC appear to be asymptomatic and appear to be innocuous keratin pearl. In severe conditions, they can enlarge and caused serious complications that include the ossicular destruction, base of skull complications and facial paralysis.
What are the symptoms?
The commonest presenting symptom is unilateral hearing loss, followed by facial paralysis/ weakness due to involvement of facial nerve. They can also present with vertigo, numbness of face, blurring of vision/ double vision. Rarely, intracranial complications causes seizures/ altered sensorium.
How is it diagnosed?
Otoscopic findings:
· Primary acquired: central perforation with cholesteatoma debris or retraction pocket with squamous epithelium and debris
Fig 1(A): A case of chronic suppurative otitis media with central perforation and cholesteatoma seen in the middle ear cavity. (B): Attic retraction pocket with cholesteatoma.
Congenital and secondary acquired: white or pearly mass behind the intact tympanic membrane
Fig 2: whitish mass behind the intact TM
Imaging:
Fig 3: Diagnosis of Petrous bone cholesteatoma in CT and MRI scan.
Currently, the advances in radiology have greatly improved the detection and diagnosis of PBC. Computer tomography (CT) can clearly show the destruction of bone as well as the anatomic relationship between lesions and relevant surgical marks which will provide direct reference for making appropriate surgical plans. Magnetic resonance imaging (MRI) is more helpful to distinguish PBC from other soft tissue lesions, and the sequence of diffusion weighted imaging (DWI) is the best method to detect residual and recurrence of PBC.
Audiometry:
To assess the degree of hearing loss and to plan for hearing rehabilitation post-surgery.
Management of Petrous Bone Cholesteatomas
Surgery remains the cornerstone for treatment of PBC. The translabyrinthine-transcochlear approach, transotic approach, infralabyrinthine approach, and infracochlear approach represent the most direct surgical approaches. Translabyrinthine-transcochlear approaches are aggressive approaches that require sacrifice of any residual hearing with or without transposition of the facial nerve. The infralabyrinthine approach and infracochlear approach are hearing preservation surgeries. Post-surgery the cavity is closed permanently. Hence hearing rehabilitation can be done using various implantable such as bone anchoring hearing implants and cochlear implantation.
The middle cranial fossa approach, which may allow for hearing preservation, may be performed in patients with good hearing and normal facial nerve function, but requires a craniotomy, affords poor access, and may involve traction on important neurologic structures with potential for injury.
Fig4: Petrous bone Cholesteatoma seen intraoperatively
Fig5: Post-surgery OSIA for hearing rehabilitation