Management of tumours of the temporal bone and base of skull is one of the most challenging problems. The intimate association of these tumours with the internal carotid artery, internal jugular vein & jugular bulb and the V through XII cranial nerves has in the past rendered many patients inoperable. The development of the infratemporal fossa approach, as pioneered by Fisch, has allowed the excision of lateral skull base and petrous apex lesions that were previously deemed unresectable.
These approaches are classified as Fisch type A, B and C.
This approach is used for removal of tumours involving the jugular foramen and vertical segment of petrous internal carotid artery, primarily class C and D glomus temporal tumours. This approach is also indicated for meningiomas, cholesteatoma involving the internal carotid artery and petrous apex, for intratemporal neuromas of cranial nerves IX-XII and for lesions reaching the skull base from below (Carotid artery aneurysms, glomusvagale tumors etc).
The key point of this approach is the anterior transposition of the facial nerve, which provides optimal control of the infralabyrinthine and jugular foramen regions, as well as the vertical portion of the internal carotid artery.
A standard, curvilinear post auricular incision is made from the temporal region to the level of cricoid. The anterior flap is elevated superficial to temporalis and sternomastoid muscles. The external canal is transected at the bony cartilaginous junction and the flap continued forward over the parotid for 2-3 cms. The external ear canal skin is undermined from underlying cartilage, everted, and over sewn to create a blind-sac closure of the EAC. The extratemporal facial nerve is dissected out in the parotid upto its bifurcation.
The upper neck is next dissected, vessel loops are placed proximally around the internal and external carotid arteries. Hypoglossal nerve, vagus nerve, spinal accessory nerve and internal jugular vein were indentified. The sternomastoid muscle is dissected from the mastoid tip.
A well bevelled canal wall down mastoidectomy is next performed. The remaining EAC skin, tympanic membrane, malleus and incus are excised, and the sigmoid sinus is completely skeletonised. The entire middle ear and mastoid course of the facial nerve is identified using cochlear form process, horizontal semicircular canal and digastric ridge as landmarks. The facial nerve is decompressed to 2700 of its circumference where possible, from the geniculate ganglion to the stylomastoid foramen. The mastoid tip and the bony EAC are quickly removed with large cutting burr and bone roungeurs while constantly keeping facial nerve in view. The facial nerve is rerouted anteriorly. After ligating the internal jugular vein, the tumour is excised along with the lateral wall of jugular bulb. Whenever possible, the medial wall of the jugular bulb is left intact, thereby protecting the cranial nerves IX through XI.
Tumour is carefully removed from the carotid artery anteriorly, if necessary. Often, a surgical plane between the carotid artery adventia and tumour can be identified. When such a plane is not present and tumour is adherent to the adventitia, residual tumour is left on carotid and later cauterized. Deep infralabyrinthinetumour extension may involve the inferior internal auditory canal, thereby placing the cranial nerves VII and VIII at risk. At times labyrinthectomy may be necessary to permit exposure and safe tumour removal from the IAC.
The management of intracranial tumour extension depends on the size and location of the tumour, and the status of the patient. Small intracranial tumour extension is removed with the jugular bulb because this is typically the site of dural penetration. The decision to remove large intracranial extensions is based on the haemodynamic status of the patient. Blood loss in excess of 3 litres usually prompts a second stage approach to total tumour removal.
The eustachian tube is obliterated with muscle and facial plugs. The surgical cavity is obliterated with abdominal fat. The procedure described above is used for glomusjugularetumours.
In this approach, the skin incision is extended anteriorly at the temporal region, the zygomatic arch is divided and the petrous carotid artery is skeletonized. The temperomandibular join is then disarticulated, the eustachian tube detached anteriorly with associated soft tissue, and the middle meningeal artery and mandibular nerve divided as needed. This provides access to the clivus and petrous apex and is applicable to glomustumours involving the horizontal petrous carotid artery, clivalchordoma, and congenital cholesteatoma of the petrous apex.
This is an anterior extension of type B and allows for exposure of the parasellar region, nasopharynx, pterygomaxillary fossa and eustachian tube. It has been used primarily for recurrent nasopharyngeal carcinoma.
All patients who have undergone infratemporal fossa dissection are monitored overnight in the intensive care unit for evidence of hemorrhage or evolving neurological injury. Postoperative hemorrhage is extremely rare due to the extensive measures taken to ensure intraoperative vascular control.
Considering the complexities of modern skull base surgery and the advanced stage in which most skull base tumours present, postoperative cranial nerve deficits are inevitable. All patients who underwent rerouting of facial nerve during this surgery develop facial palsy. It is usually temporary and most of them regain facial movement. Some will develop mass movement (synkinesis).In all cases of facial paralysis, it is essential that adequate corneal protection be provided by medication and temporary taping. Patients who develop facial palsy before surgery due to tumour infiltration may not recover full facial function. If the paralysis is permanent, placement of gold weights or tarsorrhaphy must be considered.
Jacksons reported that 76% of his patients with extensive skull base neoplasms suffered a new intraoperative cranial nerve deficit, the most common being a glossopharyngeal / vagal lesion. In the later stages of growth, many skull base neoplasms tend to envelop rather than infiltrate the contiguous cranial nerves. Consequently, it may be possible to maintain anatomic continuity of the nerve by microsurgicaltumour dissection. Because such dissection tends to devascularize the nerve, many patients will suffer transient cranial nerve palsy as a result of their surgery and will require temporary supportive care.
Because of the high incidence of transient dysphagia and aspiration, tracheostomy and nasogastric tube feeding may be required for several weeks, particularly if multiple cranial nerve palsies including X, XI, XII have occurred. Early vocal cord medialization, either by endoscopic teflon injection or external thyropalsty, may be necessary to permit decannulation in those cases with new vagal lesion and severe aspiration. Except in those cases with extensive intracrianl extension, cerebrospinal fluid leak and meningitis are rare.
The infratemporal fossa approach, in conjunction with the application of microsurgical technique and improved perioperative care, has permitted significant advances in lateral skull base surgery. The glomus jugular tumour is the typical neoplasm resected by this approach, although this technique can be applied to a host of additional benign and malignant lesions of the skull base. This approach entails identification and control of the cranial nerves and great vessels in the neck, anterior transposition of the facial nerve, and infralabyrinthinepetrosectomy. Intracranial tumour extension and petrous carotid artery involvement remain limiting factors. Significant morbidity, particularly neurological deficit and hemorrhage, may occur due to the nature and location of lateral skull base tumours. Recent advances in preoperative embolization and temporary carotid artery balloon occlusion have advanced the limits of resection via the infratemporal fossa approach.
