Cholesteatoma is an abnormal collection of skin deep inside the ear. Petrous bone cholesteatoma (PBC) refers to an epidermoid cyst occurring in the petrous portion of the temporal bone. It is an unusual entity occurring in about 4-6% of all temporal bone lesions1. It is slow growing and hence can remain undetected until it involves the facial nerve or labyrinth.
Why does a Petrous bone Cholesteatoma occur?
PBCs can be Congenital, Acquired, or Iatrogenic2. Congenital PBC occurs due to the epidermal cells resting within the temporal bone and presenting as a pearly white mass behind an intact tympanic membrane. A diagnosis of congenital PBC is considered when there is no previous history of otorrhea, trauma, or surgery. A large primary acquired cholesteatoma occurring in a well-pneumatized temporal bone can extend above or below the labyrinthine compartment to form a PBC. The iatrogenic type happens due to the implantation of squamous epithelium after ear surgery.
Clinical Presentation of a PBC
PBCs are locally destructive lesions yet patients remain asymptomatic until the disease involves vital structures. The commonest presenting symptom is progressive conductive or sensorineural hearing loss. Progressive or sudden facial weakness can cause alarm. Patients can also present with vertigo, tinnitus, imbalance, foul smelling ear discharge. Headache, vomiting, and seizures occur in case of intracranial extension/complications. Involvement of other cranial nerves can cause numbness of the face, Double vision, and Trigeminal neuralgia.
How do we diagnose a PBC?
Diagnosis would involve a complete neurotological examination and imaging. A high-resolution computed tomography of the temporal bone with 1mm cuts will help delineate the extent of the lesion and aid in surgical planning. With the advent of Magnetic Resonance imaging, it has become increasingly easier to distinguish PBCs from other temporal bone lesions. Diffusion Weighted images are particularly useful in identifying residual/recurrent PBCs. Audiometric tests are performed to assess the type and degree of hearing loss. They are also needed for planning hearing rehabilitation after surgery.
How to treat?
Surgery remains the mainstay of treatment for Petrous bone Cholesteatoma. The main goal of surgery is the full eradication of disease and to give a dry, trouble-free ear. Advances in Neuroradiology and neuromonitoring have made it possible to achieve good results with minimum morbidity. The surgical approach depends on the site and type of the lesion, degree of hearing loss, and integrity of the facial nerve. Sanna et al.,3 have classified PBCs into 5 types namely Supralabyrinthine, Infralabyrinthine, Infralabyrinthine-apical, Massive and Apical. Subclasses were added by Sampath et al.,2 vis-à-vis extension to clivus, sphenoid sinus, nasopharynx, and intradural. Commonly used approaches are Transotic ( preferred ), Modified transcochlear Type A and B, Subtotal Petrosectomy, Translabyrinthine, and Infratemporal fossa type B approach.
Management of the Facial nerve
Transotic approach is preferred in cases of preoperative preserved facial nerve function. Some form of facial nerve management would be essential in all cases and can range from skeletalization or decompression of the nerve to Active management. The latter can involve
1. Partial / Total Posterior re-routing of the nerve
2. Posterior re-routing and end-end anastomosis
3. Nerve sectioning and end-end anastomosis
4. Nerve sectioning and cable nerve grafting (Sural nerve is used)
5. Facial- Hypoglossal or Facial- Trigeminal anastomosis.
Hearing Rehabilitation
Hearing preservation surgery can be performed in limited Supralabyrinthine (Transmastoid - Middle cranial fossa approach) or Infralabyrinthine (Transmastoid- Retrofacial approach / Subtotal Petrosectomy) PBCs.
However, in the presence of a fistula in the cochlea, the Middle cranial fossa approach cannot preserve hearing.
Generally, complete disease removal and preservation of facial nerve function take precedence over hearing preservation. Hearing can be rehabilitated in such cases with bone-anchored hearing aids or cochlear implants or Soundbridge in the same sitting.
PBCs are surgically challenging and management requires meticulous preoperative evaluation, planning, execution, and strict follow-up. Radical surgery to eradicate the disease and preserve facial nerve function remains a cornerstone of management.
References
1. Omran A, De Donato G, Piccirillo E, Leone O, Sanna M: Petrous bone cholesteatoma: management and outcomes. Laryngoscope 2006;116: 619–626.
2. Prasad SC, Piras G, Piccirillo E, Taibah A, Russo A, He J, Sanna M. Surgical strategy and facial nerve outcomes in petrous bone cholesteatoma. Audiology and Neurotology. 2016;21(5):275-85.
3. Sanna M, Zini C, Gamoletti R, et al. Petrous bone cholesteatoma. Skull Base Surg 1993;3:201-13.