THE MATRIX OF FACIAL NERVE PRESERVATION IN VESTIBULAR SCHWANNOMA SURGERY A young beautiful lady gives a damn care to intra operative anatomic preservation of facial nerve if she finds a disfigured face in recovery room. For her, the most important part postoperatively is facial nerve preservation followed by complete tumor removal and hearing preservation. Microsurgical neurosurgery and improved expertise has reduced facial paralysis rate from nearly 100% to 10%, but still the goal of cent percent facial nerve preservation is farfetched. HISTORY OF FACIAL NERVE PRESERVATION (FNP) • Cairns 1931, the first report of FNP. • Olivercrona, McKissok and House advocated the importance of FNP • Md Samii, advocated and pionerred the technique of FNP. GRADING OF FACIAL NERVE FUNCTION- HOUSE AND BRACKMANN • GRADE 1 Feature-> Normal symmetrical function in all areas • GRADE 2 Feature-> Slight weakness noticeable only on close inspection, Complete eye closure with minimal effort Slight asymmetry of smile with maximal effort (Synkinesis barely noticeable, contracture or spasm absent) • GRADE 3 Feature-> Obvious weakness, but not disfiguring. May not be able to lift eyebrow. Complete eye closure and strong but asymmetrical mouth movement with maxilla effort. Obvious but not disfiguring synkinesis, mass movement or spasm • GRADE 4 Feature-> Obvious disfiguring weakness. Inability to lift brow. Incomplete eye closure and asymmetry of mouth with maximal effort. Sever synkinesis, mass movement or spasm • GRADE 5 Feature-> Motion barely perceptible. Incomplete eye closure, slight movement corner mouth. Synkinesis, contracture ans spasm usually absent. VASCULAR SUPPLY OF FACIAL NERVE • Labyrinthine artery of AICA • Greater superficial petrosal branch of middle meningeal artery • Stylomastoid branch of external carotid artery FACTORS AFFECTING FACIAL NERVE PRESERVATION A. TUMOR SIZE- Cerullo et.al • 4 cm-64% B. INTRAOPERATIVE USE OF NERVE MONITORING • Used-> Better results • Not used-> Worse C. SOLID VS CYSTIC – Samii et al • Solid -> 93% • Cystic-> 88% MANEUVRES TO PRESERVE FACIAL NERVE • Compress and retract the tumor capsule rather than the nerve by debulking the tumour prior to nerve dissection is of major importance particularly in the case of large tumours. • Excessive pressure on the facial nerve should be avoided. Cotton and microsuction devices should be used all the times. Sharp dissection should be used until a clear dissection plane is established to avoid unnecessary stretch injury. • It is important to avoid excessive cerebellar traction to minimise the tension placed on the facial nerve. • Proceed the dissection from the known to unknown structures. Always, localize the vessel at the lateral end of IAC first and then proceed for dissection. • If hearing preservation is not a consideration, early identification of facial nerve near the lamina spiralis allows better appreciation of its relationship with the tumor. • Avoid vascular injury to facial nerve by i. Cautious use of a bipolar cautery ii. When possible, blunt dissection near all vascular structures iii. Topical application of papaverine after tumour resection to prevent vasospasm iv. As most of the microvascular blood supply is in subarachnoid space, it is essential to proceed dissection in the correct plane between tumour capsule and the underlying arachnoid. v. Overly aggressive dissection of the tumour capsule from the facial nerve may strip the facial nerve of its vital microvascular supply and lead to postoperative nerve dysfunction. • Avoid thermal injury to the nerve i. Overly cold irrigation may stun the nerve and is avoidable with the use of warmed saline. This phenomenon may be transient but occasionally it may lead to local vasoconstriction and cause secondary ischemic injury to the nerve. ii. Thermal injury can be more permanent if laser is used for tumor vapourization esp Potassium titanium phosphate and CO2 lasers iii. Suction irrigation should be done while drilling near meatus • Cystic tumours have lesser chances of facial nerve preservation as compared to their solid counterparts. The one possible explanation is the more variable anatomy of the cystic component of the tumor in relation to the VII nerve as compared to solid tumors. Samii and Matthies found that the anatomic preservation rate of the facial nerve decreased from 93% to 88% in patients with cystic tumors. However, what exactly defines a cystic vestibular schwannoma is still not sure! MYTHS OF FACIAL NERVE PRESERVATION 1. SOME PARTICULAR APPROACHES HAVE HIGHER PRESERVATION RATES! Literature mentions various reports comparing FNP rates with various approaches. These are not standardized as • There is a size bias • There is expertise bias in any particular approach and its practise • Most of the large vestibular schwannomas have cystic component. (There is no standard definition of a cystic schwannoma, till date)If this cystic component part is removed, then there is no difference in FNP rates in various approaches. • Solution-Comparison of different series must eliminate tumor size as a confounding variable. 2. MIDDLE FOSSA APPROACH HAS A HIGHER FACIAL NERVE PRESERVATION RATE! The answer is NO. Facial nerve preservation rate is comparatively lower with middle fossa approach as compared to suboccipital or translabyrinthine approach. In middle fossa approach, facial nerve is seen in front of the tumor and sustains prolonged traction while removal. Various previous series reported better FNP rate with middle fossa approach but those were small (
Posted on: Thu, 12 Sep 2013 06:04:21 +0000
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