Olfactory Nerve: Cranial Nerve I

Olfactory nerve function is rarely impaired in childhood. Cranial nerve I can be evaluated by having the child smell pleasant aromas (e.g., chocolate, vanilla, peppermint) through each nostril while the other is manually occluded. Olfactory sensation is intact if the child appreciates a change in odor; precise identification is often impracticable. Anosmia occurs most commonly in children with upper respiratory infections or after head trauma, often occipital. Neoplasms in the inferior frontal lobe or cribriform plate regions can cause anosmia. Unilateral anosmia is more worrisome than bilateral anosmia because of the possibility of a unilateral neoplasm.

Optic Nerve: Cranial Nerve II

Examination of cranial nerve II, the optic nerve, is one of the critical portions of the neurologic examination because of the long anterior-to-posterior span of the visual pathways within the brain. Formal visual acuity testing is possible with a Snellen chart or a “near card” in older children. Visual acuity and visual field testing should be performed in an appropriately lit room. The visual test objects should be easily visible and without glare. Occasionally, when subtle changes are being investigated, it is efficacious to hold the visual field test object against a background of less contrast, increasing the difficulty of identification.

Function can be difficult to evaluate in the very young child. Gross vision can be assessed in children younger than 3 or 4 years of age by their ability to recognize familiar items of various sizes, shapes, and colors. Beyond 4 years of age, the E test is useful. The child is taught to recognize the E, and to discern the direction in which the three “arms” are pointing and point a finger accordingly. Most older children can be taught the essentials of the test in less than a minute. During the acuity evaluation, Es of different sizes, rotated in different directions, are presented to the child.

For each eye, the visual field (range of vision) is assessed by confrontation with an object that is moved from a temporal to nasal direction along radii of the field. A small (3-mm), white or red test object or toy can be used. A modification of the same procedure can be used for double simultaneous testing by moving two test objects or penlights simultaneously from the temporal to the nasal fields and then from the superior and inferior portions of the temporal and nasal fields while the child looks directly at the examiner’s nose. Finger counting can be used if acuity is grossly distorted. In cases of extreme impairment, perception of a rapidly moving finger can be used.

Visual acuity is rarely affected by papilledema until there is scarring of the optic nerve head. This lack of acuity change is in marked contrast to the early loss of visual activity that accompanies inflammation of the optic nerve.

The optic disc (i.e., optic nerve head) of the older child is sharply defined and often salmon-colored, which differs from the pale gray color of the disc in an infant. In the presence of a deep cup in the optic disc, the color may appear pale, but the pallor is localized to the center of the disc. The pallor of optic atrophy occurs centrally and peripherally, and is accompanied by a decreased number of arterioles in the disc margins. Most commonly, papilledema is associated with elevation of the optic disc, distended veins, and lack of venous pulsations. Hemorrhages may surround the disc. Before papilledema is obvious, there may be blurring of the nasal disc margins and hyperemia of the nerve head.

Pupils should be observed in light that allows them to remain mildly mydriatic. The diameter, regularity of contour, and responsivity of the pupils to light should be examined. When the pupil is dilated and is minimally reactive or unresponsive to light, the patient may suffer from Adie’s pupil. The upper lid is usually at the margin of the pupil. In Horner’s syndrome, impairment of the sympathetic pathway results in a miotic pupil, mild ptosis, and defective sweating over the ipsilateral side of the face (Figure 2-1). Dragging a finger over the child’s forehead may aid in the recognition of anhidrosis. The fixed, dilated pupil usually is associated with other signs of oculomotor nerve dysfunction and may signify cerebral tonsillar herniation.

Fig. 2-1 Bilateral oculomotor nerve paralysis.

(Courtesy of the Division of Pediatric Neurology, University of Minnesota Medical School.)

The presence or absence of the pupillary light reflex differentiates between peripheral and cortical blindness. Lesions of the anterior visual pathway (i.e., retina to lateral geniculate body) result in the interruption of the afferent limb of the pupillary light reflex, producing an absent or decreased reflex. Anterior visual pathway interruption can cause amblyopia in one eye. In this situation, the pupil fails to constrict when stimulated with direct light; however, the consensual pupillary response (i.e., response when the other eye is illuminated) is intact. Various degrees of visual loss may modify this phenomenon so that the full response to direct stimulation is delayed, but the consensual reflex is brisk. The deficient pupillary reflex is revealed by alternately aiming a light source toward one eye and then the other. In the eye with decreased vision, consensual pupillary constriction is greater than the response to direct light stimulation (Marcus Gunn pupil); the pupil of the affected eye may dilate slightly during direct stimulation.

Oculomotor, Trochlear, and Abducens Nerves: Cranial Nerves III, IV, and VI

The oculomotor, trochlear, and abducens cranial nerves control extraocular motor movements; these nerves must operate synchronously or diplopia ensues. Cranial nerve III innervates the superior, inferior, and medial recti; the inferior oblique; and the eyelid elevator (levator palpebrae superioris). Cranial nerves IV and VI innervate the superior oblique muscle and the lateral rectus muscle, respectively. Unfortunately for purposes of understanding, the function of extraocular muscles depends somewhat on the direction of gaze. The lateral and medial recti are abductors and adductors of the globe, respectively. The superior rectus and inferior oblique are elevators, and the inferior rectus and superior oblique are depressors. The oblique muscles act in the vertical plane while an eye is adducted. The recti muscles serve this function when an eye is abducted (Figure 2-2). When directed forward (i.e., primary position), the oblique muscles effect torsion around the anteroposterior axis (rotation) of the globes [Cogan, 1966]. The eye position that results from paralysis of each eye muscle is listed in Table 2-2.

Fig. 2-2 Extraocular muscle movement.

A, In primary position. B, In abduction and adduction.

(Courtesy of the Division of Pediatric Neurology, University of Minnesota Medical School.)

Table 2-2 Extraocular Muscle Paralysis

In heterophorias, also called phorias, both globes are directed normally on near or far objects during fixation; however, one or both deviate when one eye is occluded while the other eye fixes. Forcing fixation of the uncovered eye by alternately covering each eye confirms the diagnosis of heterophorias. This predisposition may be evident when the child is febrile or fatigued. Exophoria is a predisposition to divergence, whereas esophoria is a predisposition to convergence.

Eye deviations detectable during binocular vision are heterotropias, also called tropias. Adduction tropias are esotropias; abduction tropias are exotropias. Tropias are most often caused by compromised extraocular muscle innervation. Extraocular palsies can frequently be detected by observation of eye movements. A red glass is placed in front of an eye, and a focused, relatively intense white light is aimed at the eyes from various visual fields while the child fixes on the light. A merged, solitary, red–white image is perceived when extraocular movements are normal; however, when muscle paresis is present, the child reports a separation of the red and white images when looking in the direction of action of the affected muscle. The farthest peripheral image is the one perceived by the abnormal eye; this eye can be identified by the color of the image. Minimal extraocular muscle palsies may be heralded by delayed eye movement to the appropriate final position. Volitional turning of the head accompanies paresis of the lateral rectus muscle to forestall diplopia; the head is deviated toward the paretic muscle, and the eyes are directed ahead. In superior oblique or superior rectus muscle palsies, tilting of the head toward the shoulder opposite the side of the paretic eye muscle occurs.

Extraocular muscle dysfunction is associated with many conditions that affect the brainstem, cranial nerves, neuromuscular junction, or muscles. Among the diseases are ophthalmoplegic migraine, cavernous sinus thrombosis, brainstem glioma, myasthenia gravis, and congenital myopathy. Cranial nerve VI function may be impaired by increased intracranial pressure, irrespective of cause. Squint, usually esotropia, often accompanies decreased visual acuity in infants and young children [Smith, 1967].

Ptosis and extraocular muscle paralysis accompany dysfunction of cranial nerve III. Ptosis resulting from oculomotor nerve compromise is usually more pronounced than is the malposition of the lid associated with Horner’s syndrome. This symptom is a great diagnostic aid because the lid does not significantly elevate when the patient is asked to look up. Complete oculomotor nerve paralysis, although uncommon, causes the eye to position downward and outward. Poor adduction and elevation are also evident (see Figure 2-1).

Version eye positioning may accompany irritative or destructive brainstem lesions and cerebral hemispheral lesions. In destructive brainstem conditions the conjugate eye movement (version) deviation is toward the opposite side. Destructive cerebral hemispheral lesions will cause the eyes to deviate toward the side of the lesion; conversely, an irritative cerebral hemispheral lesion causes the eyes to turn away from the side of the lesion.

Eye-movement deviations of the binocular disconjugate (nonparallel) type caused by brainstem dysfunction also occur in children. Vertical gaze paresis results from dysfunction of the tectal area of the midbrain. Patients with a pineal tumor or hydrocephalus may be unable to elevate the eyes for upward gaze.

Brainstem lesions, especially those in the midbrain or pons, may disrupt the medial longitudinal fasciculus. The resultant impairment of conjugate eye movement is referred to as an internuclear ophthalmoplegia. These lesions engender weakness of medial rectus muscle contraction of the adducting eye, which is accompanied by a monocular nystagmus in the abducting eye. Occasionally, paresis of lateral rectus muscle movement in the abducting eye may occur. Medial longitudinal fasciculus involvement may be unilateral or bilateral, and may be associated with a number of brainstem conditions, including hemoglobinopathies, demyelinating disease, or brainstem vascular disease [Cogan, 1966].

Internal ophthalmoplegia consists of a fully dilated pupil that is unreactive to light or accommodation. Extraocular muscle function is normal when each muscle is tested separately. The oculomotor nerve, nucleus, or ciliary ganglion may be a site of involvement.

External ophthalmoplegia results in ptosis and paralysis of all extraocular muscles. Pupillary reactivity is normal. This pattern of involvement may accompany myasthenia gravis, hyperthyroidism, ocular myopathy, Möbius’ syndrome, tumors or vascular lesions of the brainstem, Wernicke’s disease, botulism, and lead intoxication.

Opticokinetic nystagmus is a useful test in evaluating the eye movements of children. A drum or tape with stripes or figures is slowly rotated or drawn before the child’s eyes in horizontal and vertical directions. With fixation, the child should visually track the object in the direction the tape is being drawn, with a rapid, rhythmic movement (refixation) of the eyes in the reverse direction to enable fixation on the next figure or stripe. Absence of such a response may result from failure of fixation, amaurosis, or disturbed saccadic eye movements.

The child who appears clinically blind because of a conversion reaction usually exhibits a normal opticokinetic nystagmus response. Children who manifest congenital nystagmus and have an opticokinetic nystagmus response in the vertical plane likely have adequate functional sight. Absence of opticokinetic nystagmus in the presence of congenital nystagmus heralds reduced visual acuity. If asymmetry of an opticokinetic nystagmus response is evident, lateral lesions in the posterior half of the cerebral hemisphere are likely present. The lesion is on the side that manifests reduced or absent opticokinetic nystagmus reactivity. The area of involvement is generally in the posterotemporal, parietal, or occipital areas. Hemianopic field defects may exist.

Spontaneous nystagmus (i.e., involuntary oscillatory movements of the eye) may be horizontal, vertical, or rotary; a patient can exhibit all three types. The movements may consist of a slow and a fast phase, giving rise to the term jerk nystagmus. However, the phases may be of equal duration and amplitude, appearing pendular.

Nystagmus, especially vertical nystagmus, is most commonly induced by medications (e.g., barbiturates, phenytoin, carbamazepine, benzodiazepines). Such nystagmus often has a jerk component and is usually most prominent in the direction of gaze. Vertical nystagmus that is not associated with medications indicates brainstem dysfunction. A few beats of horizontal nystagmus with extreme lateral gaze are usually normal. Persistent horizontal nystagmus indicates dysfunction of the cerebellum or brainstem vestibular system components; the nystagmus is coarser (i.e., the amplitude of movements are greater) when the direction of gaze is toward the side of the lesion. A rare condition, seesaw nystagmus, is characterized by disconjugate (alternating) movement of the eyes, which move upward and downward in a seesaw motion. This type of nystagmus accompanies lesions in the region of the optic chiasm (see Chapter 6).

Trigeminal Nerve: Cranial Nerve V

Cranial nerve V, the trigeminal nerve, has motor and sensory functions. The motor division of the trigeminal nerve innervates the masticatory muscles: masseter, pterygoid, and temporalis. Temporalis muscle atrophy manifests as scalloping of the temporal fossa. The masseter muscle bulk may be assessed by palpation while the patient firmly closes the jaw. Pterygoid muscle strength is evaluated by having the patient open the mouth and “slide” the jaw from one side to the other while the examiner resists movements with the hand to assess muscle strength. The jaw reflex is elicited when the examiner places a finger on the patient’s chin while the mouth is slightly open and taps the finger to stretch the masticatory muscles. A rapid muscle contraction with closure of the mouth is the reflex response. This stretch reflex receives its afferent and efferent nerve control from cranial nerve V; the segmental level is located in the midpons. The expected reflex reaction is absent with motor nucleus and peripheral trigeminal nerve compromise. Conversely, this reflex is overactive in the presence of supranuclear lesions; rarely, jaw clonus may be evident. Because of weakness of the ipsilateral pterygoid muscles, unilateral impairment of the trigeminal nerve causes deviation of the jaw toward the side of the lesion.

Cranial nerve V is also responsible for sensation involving the face and the anterior half of the scalp (Figure 2-3). Brainstem compromise can effect clearly delineated laminar sensory deficits; however, mapping of such deficits is difficult in children. The corneal reflex, provided its sensory input by the trigeminal nerve, may be diminished or absent after trauma, in cerebellopontine angle tumors, brainstem tumors, cavernous sinus thrombosis, Gradenigo’s syndrome, or childhood collagen–vascular diseases.

Fig. 2-3 Facial sensation supplied by the trigeminal nerve.

(Courtesy of the Division of Pediatric Neurology, University of Minnesota Medical School.)

Facial Nerve: Cranial Nerve VII

Taste sensation over the anterior two-thirds of the tongue, secretory fibers (parasympathetic) innervating the lacrimal and salivary glands, and innervation of all facial muscles are accomplished by cranial nerve VII. Complete motor dysfunction on one side of the face ensues when the cranial nerve VII pathway is disrupted in the nucleus, pons, or peripheral nerve. The patient is unable to move the forehead upward, close the eye forcefully, or elevate the corner of the mouth on the side of the affected nerve (Figure 2-4 and Figure 2-5).

Fig. 2-4 Right facial paralysis of the peripheral type.

(Courtesy of the Division of Pediatric Neurology, University of Minnesota Medical School.)

Fig. 2-5 Möbius’ syndrome is manifested by bilateral palsy of cranial nerves VI and VII.

Central (supranuclear) facial nerve impairment produces only paresis of the muscles involving the lower face, with resultant drooping of the angle of the mouth, disappearance or diminution of the nasal labial fold, and widened palpebral fissure. The muscles of the forehead, which are innervated bilaterally, are unaffected. Cardiofacial syndrome is a congenital weakness that causes failure of depression of the angle of the mouth and is unrelated to facial nerve palsy (see Chapter 4).

Taste sensation in the anterior two-thirds of the tongue is in part provided by the chorda tympani nerve, which traverses the path of the facial nerve for a short distance. Testing of taste sensation is difficult. Evaluation of taste requires that the patient extend the tongue and that the examiner hold the tip of the tongue with a piece of gauze and place salty, sweet, acidic, and sour and bitter materials, usually represented by salt, sugar, vinegar, and quinine, on the anterior portion of the tongue. The patient’s tongue must remain outside of the mouth until the test is completed. An older patient should be able to identify each substance.

Auditory Nerve: Cranial Nerve VIII

Function and evaluation of cranial nerve VIII are discussed in detail in Chapters 7 and 8. Although cranial nerve VIII is known as the auditory nerve, it has auditory and vestibular functions. Gross auditory impairment may be suspected during the history-taking session while the child is in the room. The child may not respond directly to questions or to directions from the caregivers. More specific testing with whispered language, the ticking of a watch, a party noisemaker, or a tuning fork may be used to gain more information.

Patients who fail to develop speech or who have slow speech development, as well as those who have difficulty with fluency and articulation, may have hearing impairment. Older children can cooperate with formal audiometric testing. Such testing may not be possible in younger infants, but brainstem auditory-evoked potentials may provide the necessary information concerning hearing impairment and the level of dysfunction within the nervous system.

Clinical evaluation and caloric testing can be used for gross assessment of vestibular function. More complex evaluation should be undertaken if the screening tests or the complaint indicate a need for more detailed assessment. Complaints of nausea, ataxia, vertigo, or unexplained vomiting, singly or in combination, may indicate labyrinthine and vestibular pathologic origins. Caloric testing can be performed with relative ease. While the patient is in the supine position, the head is flexed at 30 degrees. Ice water (10 mL) is injected over 30 seconds into one external auditory canal at a time. The conscious patient develops coarse nystagmus toward the ipsilateral ear; no eye deviation occurs. If the patient has some degree of obtundation, there is a modification of the response. The eyes become tonically deviated ipsilaterally, with accompanying nystagmus occurring contralaterally. If the patient is comatose, cold water stimulation usually causes tonic deviation ipsilaterally and no nystagmus; if the coma is profound or the patient is brain-dead, no eye changes occur.

Glossopharyngeal and Vagus Nerves: Cranial Nerves IX and X

Examination of the larynx, pharynx, and palate provides most of the desired information concerning the function of cranial nerves IX and X. Unilateral paresis of the soft palate causes an ipsilateral droop, even when the patient is expelling air through the open mouth or gagging in response to a tongue blade. Bilateral involvement causes a flaccid soft palate bilaterally. With bilateral paresis, the voice becomes nasal, and regurgitation of fluids occurs during drinking. During evaluation of swallowing, the child should be asked to swallow up to ten times to determine the efficacy of swallowing and stamina. The examiner can evaluate the difficulty and the relative movements of the hyoid during swallowing.

The gag reflex is mediated through cranial nerve IX and is elicited by touching the posterior pharyngeal mucosa with a tongue blade. Normal individuals may have absence or a seemingly disproportionately violent response; assessing the importance of changes in the gag reflex is difficult in the absence of other findings. The integrity of cranial nerves IX and X is necessary for a gag response. Although the larynx can be studied under direct or indirect laryngoscopy, the presence of stridor, hoarseness, or dystonia suggests the need for more detailed examination of the brainstem and cranial nerve IX integrity.

Spinal Accessory Nerve: Cranial Nerve XI

Cranial nerve XI provides innervation for the trapezius and sternocleidomastoid muscles. Cranial nerve XI comprises some fibers from C1 and C2, and some from the motor nucleus in the brainstem, and is unique in combining brainstem and cervical cord origins. The trapezius muscles are assessed when the patient is asked to shrug the shoulders against resistance exerted by the examiner. Atrophy of the muscle and drooping of the shoulder provide further information on the status of the trapezius. The sternocleidomastoid muscle is tested by exerting resistance against the child’s head while the child attempts rotation to one side. Weakness of the sternocleidomastoid muscle results in an inability to rotate the head to the contralateral side. Muscle bulk of the sternocleidomastoid muscle is readily palpable and is readily visible in the presence of moderate to severe atrophy. Congenital or acquired lesions in the area of the foramen magnum most commonly cause difficulties of cranial nerve XI.

Hypoglossal Nerve: Cranial Nerve XII

The tongue muscle is the primary responsibility of cranial nerve XII. Atrophy and fasciculation of the tongue occur when the ipsilateral hypoglossal nucleus or hypoglossal nerve is involved. The protruded tongue deviates toward the involved side because contraction of the normally innervated tongue muscle causes protrusion and is unopposed. The child cannot push the tongue against the cheek of the unaffected side. Speech may be muffled or dysarthric. Bilateral involvement of hypoglossal nuclei or cranial nerve XII may be severely incapacitating. The tongue muscle may be markedly atrophied, and fasciculations of the tongue may be very prominent (Figure 2-6). The patient may be unable to protrude the tongue beyond the lips, and there is marked dysarthria with unintelligibility of speech. Although chewing and swallowing are somewhat affected by unilateral tongue weakness, bilateral involvement results in gross difficulty.

Fig. 2-6 Fasciculation of the tongue, especially of the right lateral border, in a patient with group 2 Werdnig–Hoffmann disease.

(Courtesy of the Division of Pediatric Neurology, University of Minnesota Medical School.)

Cranial nerve XII dysfunction may result from supranuclear bulbar palsy from unilateral or bilateral corticobulbar tract involvement. Although the signs and symptoms may resemble those of involvement of the hypoglossal nucleus or nerve, lower motor unit signs such as fasciculations and atrophy are absent. Certain movement disorders, particularly dystonia, may interfere with normal tongue movements and confound the examiner.