Endoscopic Petrosal Approaches

History

Many lesions of the petrous apex are small benign lesions that may remain asymptomatic for years and are often incidentally diagnosed on imaging done for other reasons. Therefore, symptoms can be vague, but larger lesions may cause the following symptoms:

• 1.

  Diplopia: most commonly due to lateral rectus palsy as a result of compression of cranial CN VI at the level of Dorello’s canal

• 2.

  Headache: often retro-orbital

• 3.

  Hearing loss, imbalance

• 4.

  Facial pain or numbness: involvement of trigeminal ganglion in Meckel’s cave

• 5.

  Lower cranial nerve neuropathies: dysphagia, dysarthria

• 6.

  Gradenigo’s syndrome (otorrhea, diplopia due to ipsilateral lateral rectus palsy and retro-orbital headache)

• 7.

  Meningitis

• 8.

  Syncope, stroke, and amaurosis fugax: secondary to occlusion of the carotid artery

• 9.

  Unilateral nasal symptoms, such as persistent nasal obstruction, epistaxis, and/or rhinorrhea must raise the suspicion of a mass in the nasal cavity.

Physical Examination and Other Tests

• 1.

  Cranial nerve examination: While CN VI is affected most commonly (leading to lateral gaze palsy), any of the cranial nerves may be affected depending on the extent of the lesion.

• 2.

  The neck should always be examined to rule out metastases to the cervical lymph nodes in cases of malignancy.

• 3.

  Rigid or flexible laryngoscopy when lower cranial nerve compromise is suspected

• 4.

  An Ophthalmologist should evaluate any patient with visual symptoms to detect more subtle findings.

• 5.

  Nasal endoscopy: This is usually normal; however, it is important to assess for the presence of the following:

  • a.

    Septal deviations, concha bullosa, and other anatomic variations that can hinder access

  • b.

    Scarring or crusting from prior surgery and/or radiation

  • c.

    Active sinusitis that can increase the risk of meningitis

  • d.

    Viability of a nasoseptal flap: Prior surgery or septal perforation may obviate the use of the flap. In such cases, other reconstructive techniques need to be considered.

• 6.

  Examination of the ears and audiogram: Because of their close proximity to the middle ear, Eustachian tube, and hearing/vestibular apparatus, petroclival lesions can produce abnormalities in hearing and balance.

Imaging

• 1.

  Computed tomography (CT)

  • a.

    Delivers information regarding bone erosion/remodeling, osteitis, and sinusitis

  • b.

    High resolution CT (1 mm) with stealth protocol for image guidance

  • c.

    CT angiography should be used to highlight the course of the ICA for image guidance navigation if CT/magnet resonance imaging (MRI) fusion is not being used.

  • d.

    Contrast is typically not necessary if concurrent MRI with contrast will be performed.

• 2.

  Videofluoroscopy

  If dysphagia is present preoperatively, videofluoroscopic evaluation of swallowing function should be performed.

• 3.

  MRI with gadolinium

  • a.

    Best delineates tumor size, extent, and the intrinsic characteristics of the tumor

  • b.

    CT and MRI are used in complementary fashion.

• 4.

  Vascular and interventional radiology

  • a.

    Angiography, angio-MRI, or angio-CT has a cardinal role in outlining vascular anatomy and ruling out aneurysm, thrombosis, or compromise to adjacent arteries or veins.

  • b.

    Although not common for petrous apex pathology, preoperative embolization of specific pathology can decrease intraoperative bleeding.

• 5.

  Balloon test occlusion (BTO)

  A BTO can be done if the scans are suspicious for carotid invasion. Following a standard angiogram, a temporary balloon is placed in the ICA to be tested. A neurologist evaluates the patient for the next 20–25 minutes. Some centers, in the effort to enhance the prognostic validity of a BTO with clinical surveillance, use additional evaluations, such as hypotensive challenge to mimic physical activity, stump pressure measurements, electroencephalography and evoked potentials, cerebral oximetry by using near-infrared spectroscopy, blood velocity measurements applying transcranial Doppler ultrasonography (TCD), evaluation of cerebral blood flow with xenon-enhanced CT, positron-emission tomography (PET), xenon-enhanced CT, and/or MR perfusion imaging. While a normal BTO reduces the morbidity and mortality associated with permanent ICA occlusion, unfortunately, it does not eliminate it. With BTO there is a risk of 0.4%–1.2% transitory and permanent complications, respectively. The incidence of stroke after permanent ICA occlusion is between 17% and 30%.

• 6.

  PET is often necessary for staging malignant lesions that are prone to regional and distant metastasis.

Indications

• 1.

  It is fundamental to adapt the surgical approach to the patient and not the other way around. Individual risks and benefits based on symptoms, extent of disease, and natural history of the disease must be considered. Small lesions in asymptomatic patients can be followed up every 6 months with serial imaging.

• 2.

  A multidisciplinary team with an experienced Otolaryngologist and Neurosurgeon is necessary.

• 3.

  The EEA is ideal when lesions are located medial to and below important neurovascular structures, namely the ICA ( Figs. 120.2 and 120.3 ).

  
  

• 4.

  Compared to lateral approaches, the advantages of EEA are better access to deeply seated lesions, better exposure of the midline, preservation of hearing, and no manipulation of the facial nerve.

• 5.

  Lesions with lateral extension and those with involvement of critical neurovascular structures should be analyzed for an open or combined approach. Lateralization of the ICA is an option, but it should be reserved only for experienced skull base surgeons.

• 6.

  Stereotactic radiosurgery (SRS) or image-guided intensity modulated radiotherapy are options for patients who are poor surgical candidates or are at high risk for a vascular complication.

Contraindications

• 1.

  If the tumor is encasing vital vascular structures (i.e., ICA or perforating vessels), nonsurgical therapy (i.e., SRS) or an open approach, which allows for better vascular control, should be considered, especially if the tumor is of a hard consistency.

• 2.

  In cases where neurovascular shunting is necessary, an open or combined endoscopic-assisted approach is favored.

• 3.

  A lateral component of the lesion may be better accessed through a lateral approach.

Preoperative Preparation

• 1.

  Patients should be informed about the risks associated with tumor excision, including vascular and neural injury, as well as the possibility of skull base reconstruction and the need to convert to an open procedure.

• 2.

  Concomitant rhinosinusitis should be optimally treated before an EEA is done.

• 3.

  If there is risk of vascular injury, a neurointerventionalist must be available.

• 4.

  Preoperative angiography with BTO should be considered for cases with high risk of ICA injury.

• 5.

  Antiplatelet therapy and anticoagulants should be discontinued prior to surgery at the discretion of the patient’s medical team. Low-molecular-weight heparin can be used as a bridge if indicated. Dietary supplements such as vitamin E, fish oil, Echinacea, aloe, and garlic extract also can be a source of bleeding disorders, and their use should be discontinued.