Summary
This chapter discusses the head and neck examination with particular attention to neuro-otologic diagnosis. The physical examination is conducted in a systematic fashion to avoid missing important findings. The cranial nerves are examined carefully, because pathology often produces subtle findings. Cranial nerve anatomy and syndromes are tabulated for easy reference. Special tests for assessing hearing and balance are discussed, with particular attention to findings that suggest acoustic neuroma.
4 Head, Neck, and Neuro-otologic Assessment of Patients with Skull Base Tumors
4.1 Introduction
The art of history taking, physical examination, and creation of a differential diagnosis develops through practice. Key to this art is an understanding of the subtleties of symptoms and signs, especially those associated with neurologic diseases. This chapter discusses the basics of the neuro-otologic examination. Site-specific symptoms and signs will be explored to help the physician learn the cause of these maladies. This chapter is meant to be a foundation from which to work toward a proper differential diagnosis and treatment plan for each patient.
This interaction between physician and patient, which establishes the basic rapport and tenor of the physician–patient relationship, is supplanted and not replaced by technology. The daily and long-term outcomes of treatment are readily measured and tracked by noting the symptoms and signs of disease, whether at the bedside or in the outpatient setting.
It is assumed that the reader, being either a resident or a well-seasoned practitioner, is already familiar with the basics of history and physical examination. This chapter’s objectives are to discuss the physical signs associated with neuro-otologic disease and to discuss the ancillary audiometric, vestibular, and electrophysiologic tests used to discern disease processes. Special attention is paid to the cranial nerve (CN) examination. This chapter will not discuss individual disease states except to discuss the signs and symptoms that are indicative of a particular disease process.
4.2 Physical Examination
Owing to the compact and complex regional anatomy of the head and neck, the neuro-otologic examination requires practice and experience to refine. As with a general physical examination, a head-to-toe organization is systematic and simple to perform for completeness. In doing so, CNs are checked when moving from site to site, although a dedicated and rigorous CN examination requires additional techniques and observation.
On initial introduction to the patient, one might identify obvious facial paralysis or a wet, weak, or hoarse voice. Regardless, the examining physician should avoid being sidetracked by these overt signs and should instead conduct a systematic review to look for all abnormalities. The reader probably has experienced a patient who has long-standing facial paralysis but whose presenting complaint is totally unrelated to that finding. Additionally, patients frequently present with a complaint of ear pain whose cause is discovered only after a careful history and physical examination: vocal fold malignancy.
4.2.1 Head, Scalp, and Skin Exams
Occasionally, the obvious does escape our attention. The head and neck are covered by skin, but sometimes this skin is overlooked to examine the ear canals or nasal passages instead. The posterior surface of the pinna is often overlooked but can harbor malignant disease. The sun-exposed portions need to be examined for premalignant or malignant conditions. Patients who have already had skin excisions need to be queried about the pathologic diagnosis from these sites considering melanoma’s and squamous cell carcinoma’s propensity for metastatic and perineural spread (Fig. 4.1).
At times, the skin of the head and neck provides the diagnosis, as in the case of adenoma sebaceum and tuberous sclerosis or port-wine stain and Sturge-Weber syndrome. A list of neurocutaneous disorders that affect the head and neck, as well as their constituent findings and genetic causes, is given in Table 4.1.1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9
4.2.2 Eye, Orbit, and Eye Movement Exams
Patients who have primary eye complaints are typically seen first by an ophthalmologist. Certainly patients who present with skull base tumors that affect the orbit, eye movements, or visual pathways should have a rigorous ophthalmologic evaluation. A close working relationship with a neuro-ophthalmologist is necessary for any skull base team. The following description of the eye examination is provided to highlight the important signs and symptoms to discover and note in patients who have skull base tumors.
Eye and Orbit
The symmetry of the orbits and eyes should be compared. The globes should be compared to look for proptosis. The status of the lids should be examined, not only to identify lesions but also to inspect their conformity to the globe. Ectropion is very common with facial paralysis, and corrective measures can be performed to minimize its effects. The status of the conjunctiva should be noted for inflammation or irritation: this, too, is a frequent sign accompanying facial paralysis. The size and reactivity of the pupils should be documented: this is done both with a flashlight, looking for direct and indirect responses, and with convergence. Visual fields can be estimated by testing peripheral vision. Finally, an estimate of vision can be gained by testing each eye separately using a handheld Snellen eye chart held about 14 inches from the eyes.
Eye Movements
Normal eye movements depend on the equal function of CNs III, IV, and VI and their innervated muscles. A basic test of eye movements involves having the patient follow the examiner’s finger. All the extraocular muscles are tested in nine different positions (straight ahead, right, left, up, down, as well as diagonally right up, right down, left up, and left down).10 Sixth nerve palsy is common with disease in the petrous apex (Fig. 4.2). The CNs, with their muscles and their actions, are listed in Table 4.2.11
Nystagmus
Nystagmus is an involuntary, rhythmic movement of the eyes. The term is derived from the Greek word nystagmos, for nodding.12 Nystagmus can be generally divided into two broad categories: jerk nystagmus and pendular nystagmus.13 In pendular nystagmus, the two phases of nystagmus are of equal length. Jerk nystagmus, the more relevant of the two in this discussion, has two components: a slow phase followed by a fast phase. Its direction is named for the direction of the fast component. The primary plane or axis of nystagmus is described as horizontal, vertical, rotatory, or direction-changing. Classically, horizontal nystagmus is associated with peripheral lesions. The fast component is toward the unaffected ear. Vertical and direction-changing nystagmus are generally signs of central pathology. The time of onset can be described as spontaneous (occurring without provocation), latent (some delay in onset, usually after a change in position), gaze-evoked (brought out with certain eye movements), or positional (brought out by certain positions).
Spontaneous nystagmus represents an imbalance in the vestibular–ocular reflex (VOR) and can be either central or peripheral in origin.14 Spontaneous nystagmus is best evaluated by examining the eyes through Frenzel lenses. These 10 + diopter lenses not only magnify fine movements but also eliminate visual fixation that could overpower a vestibular nystagmus.14 Spontaneous nystagmus that does not abate with visual fixation probably represents central pathology. Pure vertical, torsional, or linear nystagmus cannot be explained by involvement of a single canal or single labyrinth and implies a central etiology.14
Gaze nystagmus can be elicited by having the patient follow the examiner’s finger as it performs a + -type movement, thus evoking either lateral gaze or upward or downward gaze nystagmus. Gaze-evoked nystagmus most often occurs as a side effect of medications or toxins.10 Horizontal gaze-evoked nystagmus usually indicates a lesion in the brainstem or cerebellum; vertical gaze-evoked nystagmus is found in midbrain lesions that involve the interstitial nucleus of Cajal.15 Gaze nystagmus has been described as first-degree (occurs only with gazing in the direction of the fast component), second-degree (occurs in the direction of the fast component and straight ahead), and third-degree (occurs in all three directions of gaze). The significance of these distinctions is that first-degree nystagmus is seen with a peripheral lesion but second- and third-degree with central pathology.16
Congenital nystagmus generally beats horizontally at various frequencies and amplitudes and increases with fixation.10
Bruns’s nystagmus is associated with large posterior fossa tumors. This nystagmus involves a coarse, large-amplitude horizontal gaze nystagmus toward the tumor side and a fine, high-frequency gaze nystagmus away from the tumor side,14 thought to result from bilateral compression of the flocculus.17
Dynamic vestibular imbalance can be assessed by passive head movement and observation of the patient’s eyes. Dynamic visual acuity is assessed by passively rotating the patient’s head at or above 2 Hz while he or she reads a Snellen eye chart at the standard distance. A drop in visual acuity of more than one line indicates abnormal gain in the VOR.18 A computerized form of this test has also been developed19 and might be useful as a clinical tool for separating unilateral from bilateral vestibular hypofunction.
Positional nystagmus is provoked using the Dix-Hallpike maneuver.20 In this test the patient is seated on an examining table or bed and is instructed to turn the head to the right side, then recline backward as quickly as possible. The examiner watches the patient’s eyes for any nystagmus and asks the patient whether he or she feels dizzy. If nystagmus is present, then its length of latency and duration should be noted. After this nystagmus or dizziness disappears, the patient is asked to return to an upright sitting position; again the eyes are examined for nystagmus. Patients who have benign paroxysmal positional vertigo will have a latent (usually 2–5 s), geotropic (nystagmus beats toward the ground), rotatory nystagmus that reverses (reversibility) when seated upright. The duration and strength of the nystagmus lessens with each subsequent test when performed in repetition (fatigability).
Head Thrust Test
The head thrust test (HTT) is a bedside test with which to assess the VOR.21 The test is performed by asking the patient to focus on a target. The examiner gently grasps the head, and a small-amplitude (5–10°), high-acceleration (3,000–4,000°/s/s) thrust is applied. The examiner watches the eyes at the end of the head thrust for a corrective saccade. Normal individuals do not use a corrective saccade: their eyes stay fixed on the target. Patients who have vestibular hypofunction use a corrective saccade after the head thrust, and the saccade is toward the side of the lesion. This corrective saccade returns the eye to the target and indicates a decreased gain (eye velocity/head velocity) of the VOR.22 The specificity of HTT for identifying lateral semicircular canal pathology is very high (95–100%), and it correlates 100% with surgical vestibular nerve section.23 In patients who have lesser degrees of unilateral hypofunction, the sensitivity is as low as 34 to 39% but the specificity remains as high as 95 to 100%.24 , 25 , 26 The sensitivity of this test can be improved by 30° of cervical flexion (making the horizontal canal horizontal).22
Head-Shaking Nystagmus
Head-shaking nystagmus (HSN)27 is used to demonstrate asymmetry in the velocity storage that can occur with either central or peripheral lesions. In this test, the patient’s head is shaken either actively or passively in the horizontal plane for 10 to 15 seconds with the eyes closed. After stopping and opening the eyes, nystagmus will be seen beating away from the side of the lesion.14 In this test, Frenzel lenses are indispensable, because the nystagmus is often fine and fleeting. HSN can also be performed with electronystagmography (ENG) and is discussed in the Electronystagmography section, following.
4.2.3 Ear Exams
Pinna and External Auditory Canal
The external ear includes the pinna, the membranous external auditory meatus, and the bony ear canal. In one’s eagerness to examine the eardrum, the pinna might be overlooked. Fully 15 to 20% of head and neck skin cancers occur on the external ear, and 55% are along the helix.28 , 29 , 30 The examination should not be limited to the protruding parts of the pinna but rather should also include the postauricular skin (Fig. 4.3).
A distinction is made here between the external auditory meatus, which is the cartilaginous outer third of the ear canal, and the bony ear canal, which is the bony two-thirds of the external ear canal. The membranous meatus has a thick squamous epithelium, is hair-covered, and contains the cerumen glands (Fig. 4.4a), whereas the bony canal is lined by a thin squamous epithelium without any modified sweat glands or hair (Fig. 4.4b).
Tympanic Membrane and Middle Ear
These structures are best evaluated with a handheld otoscope, an otomicroscope, and an otoendoscope. Each modality gives a slightly different but complementary view of the ear canal and tympanic membrane (TM). Each also allows testing of TM movement, either with a bulb attachment to the otoscope or through a Siegle otoscope viewed through the microscope. Occasionally patients have a narrowed or oddly shaped ear canal that cannot be adequately evaluated using an oval or round speculum. In such circumstances, a pediatric or adult nasal speculum can be helpful.
Ear endoscopes have been available for the past few decades and have become a part of the surgical treatment of many middle ear diseases. These endoscopes are 6 cm long and are 2.7 or 4 mm in diameter; 0 and 30° varieties are available. These endoscopes can provide an unparalleled view of middle ear structures, surpassing that available through a microscope or a handheld otoscope. Additionally, high-quality photodocumentation of ear canal, eardrum, and middle ear pathology can be captured easily using an endoscope (Fig. 4.5).
Tuning Fork Examination
In a bygone era, tuning fork examination represented the state of the art in audiometric assessment. With the advent of calibrated audiometers, the tuning fork examination has lost its centrality in measuring a patient’s hearing. It has not lost its importance, however, in giving the attentive clinician valuable information regarding hearing. Although the history of otology and audiometry includes several tuning fork tests, only the Weber and Rinne tests are performed routinely.
The Weber test is performed by striking the tuning fork and then placing it on the patient’s forehead, philtrum, or upper incisors and asking the patient where the sound is heard best: right side, left side, or midline (or equally in both ears). The sound is perceived as louder in an ear that has a conductive loss or in an ear that has better sensorineural hearing when no conductive component is present in the other ear. Interestingly, patients who have unilateral, congenital conductive hearing loss do not have lateralization to that side.
The Rinne test is performed by striking the tuning fork and then asking the patient to compare for loudness the sound produced with the fork on the mastoid versus in front of the ear canal. A normal result (also called a “positive Rinne”) is that the loudness is greater in front of the ear, by air conduction (AC), than it is by bone conduction (BC; also noted as AC > BC). In a conductive loss larger than about 25 dB with a 512 Hz fork, the sound is louder on the bone than it is through air conduction (noted as a “negative Rinne” or as BC > AC).
These tests are easy to perform in the outpatient clinic or at the bedside. They provide a quick assessment of hearing and can be used to check audiometric findings.31 , 32
4.2.4 Nose and Nasopharynx Exams
Anterior rhinoscopy demonstrates the health of the nasal mucosa, the status of the turbinates, and the anatomy of the septum. Boggy, purplish, congested turbinates with thin, clear nasal mucus are often an indicator of allergic or irritant rhinitis. Polyps and other masses are noted. Pathology in the nose should be more closely examined using rigid nasal endoscopes. Doing so allows evaluation of the paranasal sinus meati and permits an adequate measurement of the extent of the disease (Fig. 4.6).
The nasopharynx can be examined indirectly using a heated mirror through the oral cavity; however, only a few patients permit an adequate examination with this approach. The nasopharynx is much better assessed using an endoscope. In this circumstance, the Eustachian tube orifice, posterior and lateral pharyngeal wall, and palate movement can be examined. Palatal myoclonus is best examined using nasopharyngeal endoscopy, because the mouth opening required for a peroral examination eliminates this tremor.
Fine Eustachian tube endoscopes are developed and are being evaluated. They could help shed light on and aid in the treatment of disorders such as patulous or obstructed Eustachian tube.33
4.2.5 Oral Cavity and Oropharynx Exams
Even a cursory evaluation of the oral mucosa allows examination of the state of the oral mucosa, teeth, and tongue. Pathologies in the oral cavity are a frequent cause of referred otalgia. Tongue protrusion and movement from side to side adequate denotes normal hypoglossal nerve function, whereas fasciculations and atrophy are indicators of abnormal hypoglossal function. The protruding tongue will point to the side of the lesion. The parotid and submandibular ducts are easily assessed by examining their drainage while massaging the respective gland.
The oropharynx is separated from the oral cavity by an imaginary plane through the hard–soft palate junction superiorly and the circumvallate papillae inferiorly. It contains the palatine tonsils, if still present, the lingual tonsils, the soft palate, and the mucosa of the lateral and posterior pharyngeal walls. The examiner should note the status of this mucosa. Frequently, chronic postnasal drainage will produce cobblestoning of the posterior pharyngeal wall. The movement of the palate should be noted. Unilateral palate weakness, from a glossopharyngeal injury, will allow the uvula to be pulled toward the intact (normal) side. Gag reflex can be elicited by touching the base of the tongue or the lateral pharyngeal walls. A uvula that is bifid or that contains a thin membrana pellucida might be indicators of a submucous cleft palate. This finding warrants digital palpation of the hard palate to assess for occult cleft.
4.2.6 Exams of the Larynx
Laryngeal assessment begins with the interview, noting the patient’s voice quality. Wet, weak, or breathy voices are signs of vocal fold weakness. Speech fluency, by contrast, is directed by higher cortical structures. Expressive aphasia from a lesion in Broca’s area is an example of an abnormal fluency. Dysarthria, or difficult, poorly articulated speech, might result from abnormal hypoglossal or facial nerve function.
A basic examination of laryngeal function includes mirror examination, but only an exceptional patient permits an unhurried examination using this technique. Flexible fiberoptic endoscopy under topical nasal anesthetic is the preferred initial method for assessing vocal fold function. Patients who have or will have vocal fold paralysis should be evaluated by a speech pathologist. Videostroboscopy provides an excellent assessment of vocal fold anatomy and function and can discern various degrees of weakness better than flexible endoscopy can. Additionally, videographic and photographic documentation of vocal fold function and appearance is much better with videostroboscopy than through a flexible fiberoptic scope (Fig. 4.7).
Laryngeal function is controlled by the vagus nerve, a mixed nerve that carries motor, sensory and parasympathetic impulses. Its first branch in the neck is the superior laryngeal nerve, which has two branches: an internal laryngeal branch that carries sensation from the mucosa above the true vocal folds and an external branch that is motor to the cricopharyngeal muscles. This muscle tilts the thyroid cartilage on the cricoid cartilage and produces the tightening of the vocal fold needed to make high-pitch phonation.
The remainder of the laryngeal muscles and the sensation of the vocal folds and mucosa of the tracheobronchial tree are innervated by the vagus and its inferior or recurrent laryngeal nerve. This nerve branch loops under the arch of the aorta on the left side of the neck and the subclavian on the right side. Nonrecurrent nerves (nerves that do not descend into the mediastinum before going to the larynx) have been well described. This situation occurs more commonly on the right side and is constantly on the minds of thyroid surgeons.
The recurrent laryngeal nerve innervates both the adductors and abductors of the vocal folds. Accordingly, recovery from laryngeal neurotmesis might be limited due to synkinesis of laryngeal innervation.
Injury or loss of vagal (and, for that matter, glossopharyngeal) function at the skull base can produce severe dysphagia and aspiration, because both the motor and sensory functions are lost, removing the protective mechanisms of the upper aerodigestive tract.
4.2.7 Neck, Parotid, and Thyroid Exams
The neck and, by extension, the parotid glands should be examined by palpation for any masses or lymphadenopathy. Cervical adenopathy should be reported based on its location and size. For malignant disease, location and size of lymphadenopathy is important for tumor staging. The parotid glands should be palpated for any masses, especially in patients who have facial paralysis (Fig. 4.8; Fig. 4.9). Loss of a single branch of the facial nerve is due to malignant involvement until proven otherwise. Complete facial paralysis can occur from parotid tumors at the stylomastoid foramen. Deep lobe tumors can also cause facial paralysis and can escape palpation; only through imaging studies can these tumors be found.
The thyroid gland sits on top of the trachea, just below the level of the cricoid cartilage and above the sternal notch. Palpating this part of the neck while asking the patient to swallow moves the gland under the examiner’s fingers. A normal gland is usually not able to be palpated. A solitary tumor should be further investigated with ultrasound and fine needle aspiration. Diffuse swelling of the gland might indicate goiter. Vocal fold paralysis associated with a thyroid nodule should be attributed to malignant disease until proven otherwise.
Finally, the spinal accessory nerve (CN XI) function is tested. This nerve innervates the sternocleidomastoid (SCM) and trapezius muscles. To test the SCM muscle, the patient is asked to turn his or her head slightly to the right while the examiner applies an opposite force against the right jaw and face and palpates the strength in the left SCM. The head is turned slightly to the left to test the strength of the right SCM muscle. The patient should be asked to shrug his or her shoulders while the examiner applies resistance to measure trapezius strength.
4.2.8 Exams of the Cranial Nerves
Meyerhoff’s dictum is “any symptom suggestive of cranial neuropathy must alert the clinician to the possibility of a skull base or intracranial space occupying lesion.”34 For the most part, the CN examination is performed while progressing through the head and neck physical examination. Eye, palate, tongue, vocal fold, and shoulder/head movement have been already discussed in the sections related to each organ system.
This space does not permit discussion of the complex anatomy of the CNs or their brainstem and skull base relations, but some of these details have been summarized in Table 4.3.35 , 36 , 37 Here, the nerves that are not readily examined in a routine examination are described as part of a neuro-otologic examination.
Olfactory Nerve Exams
Although taste and smell provide excellent sensory stimulation, they are perhaps the least tested sensory functions.38 The sense of smell occurs when odorants come into contact with olfactory receptors in olfactory receptor neurons (ORN).39 The ORN are bipolar cells that penetrate the cribriform plate to synapse with glomeruli cells in the olfactory bulb. These glomeruli cells then synapse with mitral cells that carry the signal into the piriform cortex. From the piriform, connections with the hippocampus, amygdala, and orbitofrontal cortex combine to give the associated sensory, memory, or hedonic reactions.39 Tests of olfaction are becoming more important as their significance in predicting Parkinson’s disease and Alzheimer’s disease is recognized.39 , 40
Anosmia, or the inability to smell, can be evaluated based on conductive or sensorineural causes.41 Olfactory epithelium is located high inside the nose, on the upper middle turbinate and roof of the nose. Odorants must be able to pass through a patent nasal airway, and the patient must be able to generate sufficient nasal airflow (by sniffing) to bring odorants into contact with the olfactory epithelium. The patient who has severe obstructive nasal polyposis represents a form of conductive anosmia, because the polyps prevent airflow through the nose. Furthermore, a laryngectomee is unable to move any air through the nasal passages, because all his or her airflow is through the tracheostoma.
Sensorineural anosmia can result from either damaged olfactory mucosa, such as might occur after a viral upper respiratory tract infection, or shearing of the olfactory nerve as a result of head trauma. Tumors in the sinonasal tract and esthesioblastomas can produce anosmia through obstruction and/or destruction along the olfactory pathway. Olfactory loss from intracerebral tumors (glioma, olfactory meningioma, esthesioneuroblastoma, and adenocarcinoma) has been described.39 For this reason, patients who have anosmia and a normal nasal endoscopic examination should undergo MRI imaging.39
Olfaction can be measured in several ways. A simple test of smell might include waved household products such as coffee, cinnamon, mint, or water under the nose and closed eyes and asking the patient to respond to the question of “Do you smell this item?”13 , 42 Eighty percent of the normal population can identify the odor of coffee.34 A patient who professes not to smell anything can be further tested in a similar fashion using ammonium, which triggers response from V2, being a mucosal irritant. All normal patients sense the nasal irritation of ammonia.34 A “no” response in this circumstance might indicate that the patient is being less than honest.
A better form of testing uses the University of Pennsylvania Smell Identification Test (UPSIT).43 This test uses 40 scratch-and-sniff odors that patients try to identify by matching to a four-option response panel. Patients are required to answer all questions and to guess at an answer even if they smell nothing. The number of correct answers is matched in a nomogram divided by gender and age range to determine the level of olfaction: normal, hyposmia, anosmia, malingering. Because patients have a one-in-four chance of getting any question correct through guessing, a patient who has missed all 40 questions has probably intentionally avoided correct answers.40 This test is performed with both nostrils open and thus cannot give side-specific values. Nonetheless, this method of testing has been widely verified and is valued for its accuracy in providing a qualitative measurement of smell.41
Trigeminal Nerve
The trigeminal nerve is perhaps the most complex nerve of the head and neck. It has origins from four different brainstem nuclei, and it carries both sensory and motor function. Its three main trunks pass through three different foramina in the skull base, and each trunk has an associated parasympathetic ganglion.
The trigeminal nerve has general somatic and general visceral afferent function. The somatic afferents are for cutaneous sensation of the skin of the head and neck. The first division, V1, supplies sensation to the cornea and conjunctiva, the upper eyelid, the eyebrow, and the scalp as far posterior as the vertex. The second division, V2, supplies sensation to the skin of the nose, cheek, and upper lip; to the maxillary teeth; and to the mucosa of the nose and the roof of the mouth. The third division, V3, provides sensation to the skin of the lower lip, chin, and lower third of the face; to the mandibular teeth; and to the mucosa of the cheeks, lower lip, and floor of mouth. The general somatic afferents of CN V are also carried on V3 to the anterior two-thirds of the tongue. Light touch, pinprick, and temperature can be tested for each division of the trigeminal nerve.
The motor function of the trigeminal nerve is carried on V3 to the masticatory muscles (masseter, temporalis, medial, and lateral pterygoid) and to the accessory muscles of mastication (mylohyoid, anterior belly of the digastric, tensor tympani, and tensor veli palatini). Motor strength is difficult to assess clinically, but the tone of the masseter and temporalis can be palpated while the patient grinds his or her teeth.
Corneal Reflex
The description of the corneal reflex rightfully belongs between the discussion of trigeminal and facial nerve function, because it involves both nerves. The corneal reflex arc is composed of afferents from corneal epithelium through the V1 into the brainstem, where it synapses through one or two interneurons and connects to the facial nuclei to produce muscular contraction of the orbicularis oculi muscles. Normally, unilateral corneal irritation produces bilateral orbicularis oculi contraction.
The test is performed by asking the patient to look slightly nasally while a wisp of cotton is placed on the temporal portion of the cornea. Care is taken to prevent the patient from seeing the cotton approach the eye. In the case of a trigeminal nerve lesion, no muscular contraction will be elicited in either eye. In the case of a facial nerve lesion, the muscular contraction will be absent on the side of the lesion but will still be present on the normal side.
Facial Nerve
Being the motor supply to the face, the facial nerve controls several wide-ranging functions. Under control of the facial nerve, the buccinator muscle aids in mastication by helping keep the food bolus on the occlusal surface of the molars and not in the gingivobuccal sulcus. The perioral muscles aid in articulation of speech (for labial and plosive sounds). The orbicularis oculi protects the eye by closing the lids and by moving a lubricating coating of tears over the cornea. Last, and perhaps most important, it allows nonverbal communication of emotion through facial muscle contractions.
Like the trigeminal nerve, the facial nerve has an intricate anatomy, including the longest bony course of any CN; conveys motor, general sensory, and special sensory functions; and is the primary pathway for two parasympathetic ganglia (sphenopalatine and submandibular). Because the facial nerve has many different branches along its course, each having a testable function, a topographic method of testing was previously used to determine the site of lesion, so that testing lacrimation (Shirmer’s test), taste (electrogustometry), salivation, stapedial reflexes, and facial muscle function could provide the examiner with the location of the lesion. However, this topographic testing has largely been supplanted by modern imaging techniques and thus is no longer in wide use. Acoustic reflex testing is performed and will be discussed in the section on audiometric testing.
Facial muscle function is tested by asking the patient to “raise your eyebrows”; “close your eyes tightly,” even against resistance; “wrinkle your nose”; “puff out your cheeks”; “pucker your lips”; and “show your teeth” (Fig. 4.6). In cases of complete paralysis, the examiner presses his or her thumbs on the midline of the patient’s face to prevent the unopposed normal side from distorting the examination of the paralyzed side.
Facial function should be reported for each area of the face, because just one branch might be paralyzed. Single-branch facial paralysis strongly suggests tumor.44 Any individual who has progressive facial weakness should be considered to have a tumor of the facial nerve until proven otherwise.44 The American Academy of Otolaryngology has approved the House-Brackmann scale as a measure of facial function for reporting results in its publications (Table 4.4).45
The constellation of CN abnormalities can be grouped according to recognizable patterns. These patterns, which are often eponymous, can help in deducing the underlying pathologic process. Several such syndromes are listed in Table 4.5.41 , 46 , 47 , 48 , 49 , 50 , 51 , s. Literatur
4.2.9 Gait and Balance Testing
A general neurologic examination of upper and lower body strength and sensation and of cerebellar function should be performed, looking for light touch, vibratory sensation, fine and rapid motor skills, and finger-to-nose testing.13
Gait
Patients are asked to walk for 15 feet and then return, allowing assessment of gait. The observer should note the posture, head position, arm motion, and gait. Foot drop or poor posture might be indicators of imbalance. One should note how the patient turns around: does he or she use a quick method without needing to stop, or does he or her make several small steps to turn around? The latter might be an indication of a vestibular pathology.
Next the patient is asked to walk heel to toe (tandem gait) for 15 feet. The examiner should accompany the patient to guard against fall. An abnormal tandem gait is loss of balance more than three times within 15 feet.
Stance
Moritz Heinrich Romberg first published his description of tabes dorsalis in 1846.53 Romberg test is performed with eyes closed, feet together, arms folded across the chest, and head extended.54 A sharpened Romberg test is performed with feet tandem (heel to toe), eyes closed, arms folded across the chest, and head extended. A simplified Romberg test is performed with feet together, arms at the side, head in a neutral position, and eyes closed. The examiner looks for increased body sway and protects the patient from falling. This can be done by asking the patient to stand between two chairs with his or her back about 50 cm from the wall. Normal individuals can maintain a Romberg posture for 30 seconds with eyes closed. Romberg posture relies on normal proprioception (dorsal columns), and an abnormal Romberg often indicates disease outside of the labyrinths.54
Patients are then asked to stand on one leg with eyes open and then with eyes closed. Normal patients can easily stand on one leg for 15 seconds. Inability to stand on one leg indicates imbalance and highlights the need for normal muscle and joint strength and normal proprioception to maintain balance.
Fukuda Test
The Fukuda55 (also called Unterberger56) stepping test is performed with eyes closed and arms outstretched while the patient marches in place. The examiner watches the patient’s movement during 50 marched steps. Forward movement (> 1 meter) or turning movement (> 45°, usually toward the side of the lesion) are significant findings in the Fukuda test.57 This is a test of vestibulospinal and proprioceptive contributions for balance control.58 Some reports have shown good sensitivity of this test,57 but others have discounted its usefulness.56 , 59
Clinical Test of Sensory Integration and Balance
The Clinical Test of Sensory Integration and Balance (CTSIB) series of tests uses simple objects to test static and dynamic equilibrium.54 , 60 Romberg postures with eyes open and closed are used to mimic test situations 4 and 5 as found in computerized dynamic posturography (CDP).54 Thick upholstery foam, a rigid cover, and a lampshade are used to create the “foam and dome” test modalities. These simple clinical tasks of static and dynamic equilibrium can reliably distinguish vestibular disorder patients from normal subjects.61
4.3 Audiometric, Vestibular, and Electromyographic Tests
These tests provide valuable insight into the disease process and help in measuring function. The following text is not meant to describe how to perform each test; where indicated, a rudimentary description is given to familiarize the reader with how the test is performed as well as, more important, how to interpret its results and place them into the framework of the entire clinical picture.
Electrodiagnostic testing is a wide field of medical practice. Audiologists, neurologists, neuromuscular specialists, and physiatrists perform one or more of these tests as part of their regular practice and are the recognized experts in performing these tests. Liberal use of these consultants is necessary for evaluation of patients who have skull base tumors. The allotted space does not permit this chapter to be an exhaustive resource; accordingly, certain tests are eliminated even if they might provide insight into disease processes (e.g., electrogustometry).
The bulk of medical literature relating to audiometric testing and skull base tumors concerns the diagnosis of acoustic neuroma (AN). ANs account for 5 to 10% of intracranial tumors and 80 to 90% of posterior fossa tumors.62 Since Cushing recognized hearing loss as the presenting symptom of ANs,63 scientists and physicians have tried to develop better audiometric tests to identify their presence. The history of neuro-otologic diagnosis for ANs has included reflex decay, alternate binaural loudness, and Bekesy audiometry,64 , 65 but these modalities have been replaced by auditory brainstem response (ABR) and MRI. The following topics will primarily relate the findings of audiometry and vestibular testing to ANs. The findings of other tumors, such as meningiomas and epidermoids, will be presented where significant differences are found.
4.3.1 Basic Audiometry
The audiogram is the most fundamental element of otologic and neuro-otologic evaluation after the history and physical examination. A basic audiogram consists of pure tone audiometry, speech audiometry, immittance testing (e.g., tympanogram), and acoustic reflex testing. Only a brief description of each test is permitted in this chapter; the interested reader is directed to other reference works for an in-depth discussion of their finer points.66 , 67 , 68 , 69
Pure tone audiometry is the measurement of the lowest threshold at which a tone is heard. A calibrated audiometer delivers sound at a specific frequency (pitch) and specific intensity (loudness). The test is performed by an audiologist in a soundproof booth using either circumaural headphones or ear inserts for air conduction levels and a bone vibrator for bone conduction levels. Masking sound is given to the nontest ear via an ear canal insert and is the physiologic equivalent of covering one eye during a vision test.
The results of pure tone tests are placed on the audiogram, using conventional symbols to designate the ear, the modality (air or bone conduction), and the use of masking. The intensity levels of air conduction at 500, 1,000, and 2,000 Hz (and occasionally 3,000 or 4,000 Hz) are averaged producing a pure tone average (PTA). Hearing loss can be grouped into three different categories: conductive, sensorineural, and mixed.
Conductive hearing loss indicates that the sound-conducting mechanism of the ear is impaired. This condition can occur as a result of any process that blocks the ear canal or impairs the vibration of the TM or ossicles. TM perforations, cholesteatoma, cerumen impaction, otitis media, ear canal cancers (Fig. 4.10), and otosclerosis are common causes of conductive hearing loss (Fig. 4.11).
Sensorineural hearing loss indicates that the defect in hearing lies within either the cochlea or the auditory nervous pathway. Sensorineural hearing loss commonly occurs in cases of presbycusis, noise-induced hearing loss, ototoxicity (Fig. 4.12), and ANs (Fig. 4.13).
Mixed hearing loss means that both conductive and sensorineural hearing loss (SNHL) types are present in an ear.
A threshold for perceiving words can be achieved by using spondaic words. The lowest level, at which 50% of words are perceived, is called the speech reception threshold (SRT). The PTA and SRT should agree within 5 to 10 dB of each other.
Speech audiometry measures word understanding. Phonetically balanced (PB) words are presented via air conduction at a presentation level 40 dB over the SRT or PTA (also called 40 dB sensation level or 40 dB normal hearing level [nHL]). The percentage of words understood is recorded as the speech discrimination score (SDS). Generally speaking, word understanding improves as intensity is increased for cochlear or sensory hearing loss. However, retrocochlear hearing loss might demonstrate a worsening of word understanding with increased intensity in what is called PB rollover. A compilation of differences between sensory or cochlear hearing loss and retrocochlear or neural hearing loss is presented in Table 4.6.70 , 71 , 72 , 73 , 74
Prior to ABR and MRI, site of lesion testing was of paramount importance in discerning patients who might have an AN. However, because up to 20% of AN patients might demonstrate a cochlear rather than a retrocochlear pattern of hearing loss, retrocochlear audiometric testing is of little benefit.75
The American Academy of Otolaryngology Committee on Hearing and Equilibrium76 composed a classification system for reporting hearing results in AN surgery. This classification system uses PTA and SDS to stratify patients into four different classes of hearing level (Table 4.7).
Alternatively, some authors report hearing results as “unchanged,” “serviceable,” “measurable,” or “not measurable.” In this context, serviceable means PTA ≤ 50 dB and SDS ≥ 50%, unchanged means hearing within 15 dB PTA and 15% SDS of preoperative levels, and measurable means any other hearing; not measurable is self-explanatory.77
Immittance testing uses an impedance bridge to measure changes in TM compliance. Compliance of the TM is affected by perforations, middle ear fluid or tumor, and the reflex contraction of middle ear muscles. Several important findings can be made using this type of testing. Immittance testing gives clues to the status of the TM (intact, perforated, or floppy) and the status of the middle ear (aerated or fluid-filled). These findings are denoted on a tympanogram, but this has little significance for the discussion of skull base tumors unless the tumor or spinal fluid invades the middle ear and produces a flat tympanogram.
Acoustic reflex testing, by contrast, has more significance for neuro-otologic diagnosis of skull base tumors. Using the impedance bridge, compliance of the TM can be measured in response to a tone burst given either ipsi- or contralaterally. In response to loud sound (85–110 dB), a reflex contraction of the stapedial muscle will occur bilaterally. A normal reflex requires an intact TM, an air-filled middle ear, normal movement of the ossicles, no worse than 35 dB hearing loss, and an intact facial nerve (stapedial muscle). A defect anywhere along this pathway can produce an absent or reduced acoustic reflex. The sensitivity of acoustic reflex testing for ANs has been quoted as anywhere between 21 and 90%.75 , 78 , 79 , 80 , 81 , 82 , 83 , s. Literatur
Acoustic reflex decay is defined as a 50% loss of middle ear contractility in response to a tone administered 10 dB above threshold. The sensitivity of reflex decay has been reported to be from 36 to 100% for ANs.75 , 78 , 79 , 81 , 82 , 83 , 84 , s. Literatur
Acoustic Neuroma
Hearing loss is found in up to 95% of patients who have an AN.75 By the same token, normal hearing is reported in 3 to 12% of AN patients.75 , 81 , 86 , 87 , 88 The current level of clinical detection of ANs is approximately 1 in 100,000 persons per year,89 although vastly higher numbers of tumors must be present and escaping detection considering the 1% observed rate of acoustic tumors found at autopsy.90 Indeed, a significant number of ANs are found serendipitously on MRI performed for unrelated complaints.91 In general, degree of hearing loss is significantly linked to tumor size, so that up to 33% of intracanalicular tumors are associated with normal hearing.83 However, there are many reports of individual large tumors (> 2 cm) associated with normal hearing and small tumors (< 1 cm) associated with anacusis.92
Schuknecht calculated that 75% of nerve fibers need to be destroyed before pure tone hearing is affected, given an intact organ of Corti.93 The distribution of high-frequency nerve fibers on the periphery and low-frequency fibers centrally in the acoustic nerve accounts for the high-frequency hearing loss found in early acoustic tumor development: Hearing deteriorates by as much as 2.4 dB per year while ANs are observed.94 Speech discrimination also significantly deteriorates over time in observed ANs.94 In the series of tumors described by Selesnick and Jackler,88 high-frequency asymmetry at 4 KHz was a more sensitive indicator of an AN than difference in either SRT or SDS.
Although the classic presentation of an AN is a unilateral progressive SNHL with poor speech discrimination,95 experts do not agree on what exactly constitutes a significant asymmetry.75 , 96 , 97 As a rule of thumb, a significant asymmetry in hearing is described as an interaural SRT difference greater than 15 dB, an interaural SDS difference greater than 12 to 20%, or an interaural 4 kHz difference greater than 15 dB.75
Obholzer et al,98 seeking to define appropriate audiometric criteria for referral for MRI, reviewed 392 MRIs performed in one year; the 36 ANs found and 92 randomly selected “normals” were included for the analysis. Audiometric data and clinical histories were evaluated to look for findings that might be indicative of AN. The researchers used the published protocols of seven different studies to analyze audiometric data. Their study supports the use of interaural asymmetry at two neighboring frequencies of > 15 dB if the mean threshold in the better ear was ≤ 30 dB (unilateral hearing loss) and an interaural difference of 20 dB if the mean threshold is greater than 30 dB in the better ear (bilateral asymmetric hearing loss). These criteria had a 97% sensitivity and 49% specificity for AN. The most sensitive individual frequency asymmetry was for 15 dB at 2 KHz, with a sensitivity of 91% and a specificity of 60%. The most sensitive criterion was a difference of 15 dB at any frequency (sensitivity 100% and specificity 29%).
Several authors have examined hearing levels as a predictor of hearing preservation in AN surgery. In a multivariate logistic analysis of preoperative hearing variables predictive of hearing preservation, Robinette et al99 examined the audiometric tests results of 104 AN patients. Only word recognition score (WR40) was found to be a significant determinant after accounting for small tumor size (≤ 2.0 cm). Additionally, they found that patients who had hearing preserved had a higher rate of normal acoustic reflexes than those patients who did not have hearing preserved.99
Other Tumors
In 1997, Baguley et al100 published a series of cerebellopontine angle (CPA) meningiomas and performed a review of the literature. In their series, 80% (20 of 25 patients) had abnormal pure tone testing, and 50% (10 of 20) had abnormal SDS (i.e. < 90%). Interestingly, the five patients who had normal audiometry had large tumors (two in the 2.5–3.4 cm range and three > 4.5 cm); similarly, 9 of 10 patients who had normal SDS were found to have large tumors (2.5 cm or larger). In combined with the other series reviewed, 37 of 61 (61%) patients had abnormal PTA and 22 of 42 (52%) had abnormal SDS.100
Doyle and De La Cruz101 reported audiometric results in 13 patients who had CPA epidermoid tumors. Four patients had PTA greater than 30 dB; SDS was reduced out of proportion to pure tone hearing.
Quaranta et al102 described the audiometric features in a report of 11 CPA epidermoid tumors. Their series consisted of tumors that measured 3.5 to 7 cm in maximum diameter. They found symmetric hearing in six patients; another four had asymmetric hearing loss that was worse on the tumor side.
In a report on 10 epidermoid tumors, Kaylie et al103 found normal hearing in three, but the remainder had varying levels of hearing loss, from mild to anacusis.
Related posts:
5 Anesthesia and Intraoperative Monitoring of Patients with Skull Base Tumors
6 Endoscopic Endonasal Skull Base Surgery
10 Management of Benign Skull Base Tumors in Neuro-oncology: Systemic Cytotoxic and Targeted Therapies
9 Clinical Applications of Radiotherapy for Skull Base Tumors
8 Radiotherapy for Skull Base Tumors: Principles and Techniques
15 Pediatric Skull Base Surgery
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