54 Reporting of Facial Nerve Outcome Data for Vestibular Schwannoma

10.1055/b-0039-169208

54 Reporting of Facial Nerve Outcome Data for Vestibular Schwannoma

Matthew L. Carlson, John P. Marinelli, and Neil S. Patel

54.1 Introduction

In the modern era, facial nerve function, hearing status, and tumor control remain the three primary benchmarks used to assess vestibular schwannoma (VS) outcome. Facial nerve paralysis is associated with significant psychological and functional impairment and reduction in quality of life. The widespread acceptance of a convenient, easily reproducible, and accurate facial nerve grading system is critical to facilitate uniform interpretation and clinical outcome reporting. There have been a number of unique instruments that have been developed; however, the House–Brackmann (HB) facial nerve grading scale stands as the most universally accepted system for reporting facial nerve function following VS treatment and has been invaluable toward standardization of facial nerve outcome reporting in the literature.s. Literatur ^, s. Literatur Despite its advantages, several limitations exist and the ideal facial nerve grading system continues to elude clinicians and researchers alike. The observation that at least 19 unique systems have been developed over the last seven decades underscores the importance, complexity, and great difficulty of this task.s. Literatur The objectives of the current chapter are to: (1) provide an overview of functional impairment associated with facial nerve injury; (2) outline the ideal attributes of a facial nerve grading instrument; (3) review the most commonly utilized facial grading systems today including the HB, Facial Nerve Grading Scale 2.0 (FNGS 2.0), and Sunnybrook (SB) systems; and (4) discuss unresolved issues and future direction.

54.2 Facial Nerve Dysfunction following Injury

To understand the workings of facial nerve assessment, it is critical to first review the relevant functions derived from the seventh cranial nerve and the unique set of impairments associated with facial nerve injury (Fig. 54‑1 ). Chiefly, the facial nerve is responsible for special visceral efferent innervation of the 20 ipsilateral muscles of facial expression. In addition, special visceral afferent fibers convey taste from the anterior two-thirds of the tongue, and general visceral efferent pathways supply parasympathetic innervation to the lacrimal, submandibular, and sublingual glands, both via the nervus intermedius. From a practical standpoint, the main categories of impairment following facial nerve injury include early and late motor dysfunction and parasympathetic dysfunction. Within these groupings, “early” refers to immediate loss of function from axonal injury such as reduced facial tone and strength or dry eye, while “late” refers to secondary sequelae associated with aberrant axonal regeneration, such as synkinesis, contracture, or gustatory lacrimation (i.e., crocodile tears). The potential for primary and late sequelae of varying severities, the frequent differential involvement of the five motor divisions of the facial nerve, and varying possibilities of parasympathetic deficits provides an infinite number of permutations a patient may experience. In addition, even between patients with a similar severity of facial nerve injury, there is often tremendous variability in perceived disability. For example, mild motor dysfunction may be career ending for a film actor, but may go nearly unnoticed by others.

**Fig. 54.1** Patient with severe left facial nerve paralysis during rest and maximal effort. Note the loss of forehead rhytids, brow ptosis, lateral eyelid hooding, lower eyelid ectropion, flattening of the nasolabial fold, and drooping of the corner of mouth. During attempted eye closure with maximum effort, upward and outward movement of the eye is noted, termed “Bell’s phenomenon.”

54.3 Attributes of the Ideal Facial Nerve Grading System

54.3.1 General Principles of Instrument Scoring

With regard to summarizing data, an instrument that utilizes a continuous score and results in a relatively normal distribution of outcomes is more conducive to statistical analysis than an ordinal scale utilizing arbitrary levels. For example, the HB scale includes six levels where incremental differences between levels are not necessarily equal—the difference in severity of facial nerve paralysis between HB grades II and III may be significantly greater than the difference between grades V and VI. In this setting, nonparametric analyses may be needed and medians rather than means should be reported. Additionally, the possible number of discrete scores for the instrument should be large enough to capture small changes that may occur longitudinally or with intervention, without being needlessly excessive. Since reliability in reporting for many of these subjective instruments is limited by observer bias, a larger number of scores is not necessarily better—that is, a large point spread assumes a level of precision that is not substantiated.s. Literatur For example, a grading system that only incorporates three levels of motor dysfunction—“normal,” “partial paralysis,” and “complete paralysis”—could fail to detect changes with one of those three broad levels that could potentially be clinically significant. Conversely, a scale with 20 levels may be overly detailed and outside the range of what we can dependably interpret or would consider clinically significant. Finally, the scoring system should offer clinically meaningful information relevant to daily patient care. For example, a single composite score from multiple subdomains, if reported alone, may not convey information that is critical toward patient care, such as status of eye closure to prevent risk of exposure keratopathy.

54.3.2 Reliability and Validity

Reliability and validity are two technical properties of a clinical assessment tool that indicate the quality and usefulness of the measure. The reliability of an instrument describes the consistency in scoring between repeated measures on the same subject. After brief orientation, an ideal facial grading scale should demonstrate good inter-rater reliability between healthcare professionals, independent of experience or level of training. Additionally, there should be minimal test–retest variability within a single observer at two separate points in time. An ideal assessment tool should also have good validity—it must succeed in quantifying that which it was designed to measure. Because there is currently no gold standard to correlate with, criterion-related validity cannot be assessed; however, expert assessment can assist with determining if the measure appears logical (face validity) and if the items assessed adequately represent all important aspects of the condition (content validity). Most publications emphasize the importance of assessing both static and dynamic facial motor function of various regions compared to the normal side, “nervus intermedius dysfunction” including dysgeusia and dry eye, as well as late sequelae such as synkinesis, contracture, spasm, and gustatory lacrimation.

54.3.3 Convenience and Simplicity

While it is evident that many of the aforementioned attributes drive an instrument toward increasing complexity, the environment of the “end user” must also be strongly considered. For a system to become widely adopted, it must be brief and simple to administer in the office setting without requiring an elaborate setup. The methodology must be easy to learn by all levels of the healthcare team and understood by patients. In the fast-paced clinical setting where the majority of time is given toward patient counseling, an onerous or complex system will likely never be adopted.s. Literatur This issue is demonstrated by the fact that gross scales, such as the HB grading system of facial function, the Glasgow Coma Scale for communicating level of consciousness, and the Hunt-Hess score for assessing patients after subarachnoid hemorrhage, remain the most widely utilized scales today.

54.4 Current Facial Nerve Grading Systems

54.4.1 Classifications

There are several different categories by which facial nerve assessment tools can be classified. Broadly, the method of analysis may be objective or subjective and may include gross, regional, or specific scales.s. Literatur ^, s. Literatur Objective instruments incorporate precisely measurable observations such as distance of oral commissure excursion or linear distance between lateral canthus and angle of mouth at rest and maximal effort. Such measures may include fully automated, semiautomated, or manual determination, depending on the degree of reliance on a computer-based system. Subjective assessment tools can be further divided into provider reported or patient reported. Provider-reported scales commonly interrogate tone at rest, voluntary movement, and synkinesis, while patient-reported outcomes often additionally incorporate questions pertaining to symptomatology and social function in order to determine how facial nerve injury has impacted daily life. Finally, gross, regional, and specific scales refer to instruments that evaluate global function, individual divisions of the face separately, or specific areas of the face with “yes” or “no” responses, respectively.s. Literatur ^, s. Literatur Regional scales may be further subclassified into weighted and nonweighted scales based on whether a particular division is prioritized over another. For example, some systems consider strength of eye closure and oral competence over brow function. Currently, the most widely adopted scales are subjective provider-reported gross and regional systems, which will be the focus of the remaining section. These include the HB (1983 and 1985), modified HB (2003), Sunnybrook (1996), and FNGS 2.0 (2009).s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur It should be acknowledged that several other quality facial grading systems have been proposed, including the Yanagihara (1976), Fisch-Burrow, and Nottingham systems; however, a detailed review of these less frequently used scales is beyond the scope of this chapter.s. Literatur ^, s. Literatur ^, s. Literatur

54.5 House–Brackmann and Modified House–Brackmann System

Building upon previous gross ordinal scales, the HB system was initially proposed by John House in 1983 and was subsequently revised by John House and Derald Brackmann.s. Literatur ^, s. Literatur ^, s. Literatur The HB system is a subjective gross scale that incorporates six levels evaluating resting and dynamic motor function and synkinesis (Table 54‑1 ). The primary advantages of this system include ease of use and general good reliability between observers compared to previous systems. Related to its predecessor scales, the HB scale adds one additional category (grade IV, moderately severe) to further differentiate intermediate paralysis and more clearly defines each level to reduce interobserver variability. The HB scale was the first facial grading system to be endorsed by the Facial Nerve Disorders Committee of the American Academy of Otolaryngology in 1985 and was reaffirmed by the 1995 Committee on Hearing and Equilibrium for specific use with VS outcome reporting.s. Literatur ^, s. Literatur To date, the HB scale has made the most headway toward standardized interpretation and universal reporting of facial nerve outcomes following VS surgery.

Table 54.1 The House–Brackmann grading system
Grade	Description	Characteristics
I	Normal	Normal facial function in all areas
II	Mild dysfunction	Gross: slight weakness noticeable on close inspection; may have very slight synkinesis At rest: normal symmetry and tone Motion Forehead: moderate to good function Eye: complete closure with minimum effort Mouth: slight asymmetry
III	Moderate dysfunction	Gross: obvious but not disfiguring difference between two sides; noticeable but not severe synkinesis, contracture, and/or hemifacial spasm At rest: normal symmetry and tone Motion Forehead: slight to moderate movement Eye: complete closure with effort Mouth: slightly weak with maximum effort
IV	Moderately severe dysfunction	Gross: obvious weakness and/or disfiguring asymmetry At rest: normal symmetry and tone Motion Forehead: none Eye: incomplete closure Mouth: asymmetric with maximal effort
V	Severe dysfunction	Gross: only barely perceptible motion At rest: asymmetry Motion Forehead: none Eye: incomplete closure Mouth: slight movement
VI	Total paralysis	No movement
Source: Used with permission from House JW, Brackmann DE. Facial nerve grading system. Otolaryngol Head Neck Surg. 1985; 93(2):146–147.

Despite these contributions, several important limitations of the HB scale have been identified. First, by nature of gross assessment, regional differences are not distinguished, which is problematic as differential facial function often occurs. In studying this limitation, Yen et al found that most clinicians prioritized eye function when discrepancies between regions were present.s. Literatur A second limitation is related to interobserver variability with relatively poor agreement between HB grades III and IV in particular, secondary to subjectivity of level descriptions and the difficulty in separating intermediate dysfunction.s. Literatur ^, s. Literatur Finally, the original HB system failed to quantify “nervus intermedius dysfunction,” which has been shown to significantly impact patient quality of life.

These limitations have led to a modified reporting system by the 2003 Consensus Meeting on Systems for Reporting Results in Vestibular Schwannoma.s. Literatur The major proposed changes included the division of grade III into IIIA and IIIB, separated by the degree of synkinesis and “eye comfortable and in good condition with or without lubricants” versus “eye dry and uncomfortable with evidence of exposure keratitis, requiring lubricants and possibly tarsorrhaphy.” In addition, the presence or absence of crocodile tears (C0 vs. C1), metallic or aberrant taste (T0 vs. T1), and dry eye (E0 vs. E1) became separately documented. At this consensus meeting, it was also recommended that the Iowa Repaired Facial Nerve Recovery Scale supplant the HB scale for assessing outcomes following facial nerve repair.s. Literatur

54.5.1 Sunnybrook Facial Grading System

The SB grading system is a subjective regional weighted instrument proposed by Ross and colleagues in 1996.s. Literatur The SB scale analyzes resting symmetry of the eye, cheek, and mouth, as well as voluntary excursion and synkinesis evaluated during five standard facial expressions to achieve a maximum composite score of 100 (Fig. 54‑2 ). The larger number of discrete scores with the SB instrument confers greater capacity to detect change with time or intervention without significantly compromising reliability. Additionally, the greater range of scores may allow for more flexibility during statistical analysis. Similar to the HB scale, the SB system does not integrate other secondary deficits such as dysgeusia, dry eye, and crocodile tears. Additionally, while the SB evaluation form fits on a single page, it still requires more time and preparation than the HB score, which undoubtedly remains an obstacle toward adoption by surgeons.