Fuente: Tracey A. Milligan, MD; Tamara B. Kaplan, MD; Neurología, Brigham y de mujeres / Hospital General de Massachusetts, Boston, Massachusetts, Estados Unidos
El examen del nervio craneal sigue la evaluación del estado mental en un examen neurológico. Sin embargo, la examinación comienza con observaciones sobre saludo al paciente. Por ejemplo, debilidad de los músculos faciales (que son inervados por el nervio craneal VII) puede ser evidente durante el primer encuentro con el paciente. Par craneal VII (nervio facial) también tiene ramas sensoriales que inervan las papilas gustativas de los dos tercios anteriores de la lengua y el aspecto medial del conducto auditivo externo. Por lo tanto, encontrar disfunción ipsilateral del gusto en un paciente con debilidad facial confirma la implicación del nervio craneal VII. Además, el conocimiento de la neuroanatomía ayuda al médico a localizar el nivel de la lesión: debilidad unilateral de los músculos faciales más bajos sugiere una lesión supranuclear en el lado opuesto, mientras que las lesiones que implican la parte nuclear o infranuclear del nervio facial se manifiestan con una parálisis ipsilateral de todos los músculos faciales del lado implicado. Par craneal VIII (nervio de acústica) tiene dos divisiones: la división (coclear) de la audiencia y la división vestibular, que inerva los canales semicirculares y desempeña un papel importante en mantener el equilibrio. Durante un examen neurológico de rutina, pruebas especiales del nervio vestibular generalmente no se realizan.
Par craneal IX (nervio glosofaríngeo) y del nervio craneal X (nervio thevagus) surgen de la médula y tienen la función laríngea y faríngea; su función es probada mediante la evaluación de habla y la movilidad del velo del paladar. Porque los nervios craneales IX y Xform las extremidades sensoriales y del motores de la gag reflex, obtención de reflejo nauseoso puede probar también su función. Par craneal XI (nervio accesorio espinal) inerva el músculo esternocleidomastoideo y la parte superior del músculo trapecio. Estos músculos controlan de lado a lado dando vuelta la cabeza y encogiéndose de hombros. El examen del nervio craneal se concluye por la prueba del nervio craneal XII (nervio hipogloso), que controla el motor de los músculos de la lengua.
Durante la evaluación neurológica, el médico debe siempre estar tratando de vincular los resultados del examen para tener una visión de la enfermedad subyacente. Las importantes pistas de diagnóstico pueden incluir signos de implicación del nervio craneal múltiple y unilateral vs disfunción bilateral del nervio craneal. Ayudará al clínico formular diagnósticos diferenciales para saber si los síntomas del paciente se ha producido repentinamente (como era de esperar con un accidente cerebrovascular), sobre un día (como en la parálisis de Bell), y gradualmente sobre semanas o meses (con una lesión total expansión).
Evaluación de nervios craneales VI está cubierto en otro video de esta colección. Este video muestra el examen sistemático de los nervios craneales VII-XII (tabla 1).
| Me | Olfativo | Olor |
| II | Óptica | Agudeza visual, respuesta pupilar aferente |
| III | Oculomotora | Movimientos de ojo horizontales (aducción), respuesta pupilar eferente |
| IV | Trochlear | Del movimiento de ojo vertical hacia abajo, rotación interna del ojo |
| V | Del trigémino | Sensación facial, movimiento de la mandíbula |
| VI | Abducens | Del movimiento de ojo horizontal (abducción) |
| VII | Facial | Movimiento facial y la fuerza, gusto, amortiguación de sonidos fuertes, sensación; pared anterior del conducto auditivo externo |
| VIII | Acústico | Audiencia, funcionamiento vestibular |
| IX | Glosofaríngeo | Movimiento de la faringe, sensación de faringe, lengua posterior (incluyendo el sabor de la lengua posterior) y la mayoría de conducto auditivo |
| X | Vagal | Movimiento y sensación de paladar, faringe, gag reflex, guturales sonidos |
| XI | Accesorio espinal | Fuerza de los músculos esternocleidomastoideo y trapecio |
| XII | Hipogloso | Protrusión de la lengua y movimientos laterales |
Tabla 1. 12 los nervios craneales y sus funciones básicas
An examiner should develop an orderly approach to going through each nerve in numerical order, and document what test is performed and any findings. Abnormalities found in the cranial nerve exam may impact the remainder of the examination, requiring the examiner to look for other signs of diseases, such as multiple sclerosis (MS), myasthenia gravis, or amyotrophic lateral sclerosis (ALS) on the motor examination. For example, motor dysfunction of the lower cranial nerves, often called bulbar weakness, can be an early sign of muscle weakness, as seen in diseases such as ALS or myasthenia gravis. These findings on the cranial nerve examination will help the clinician focus the rest of the neurologic exam to help reach a possible diagnosis. Knowledge of the anatomy of the cranial nerves, head, and neck is important in both localization and diagnosis.
Systematic cranial nerve testing can sometimes give a clinician early and detailed information about specific pathologic processes affecting the brain. Anatomically, the twelve cranial nerves arise from distinctive locations in the brain and innervate various head and neck structures, as well as several organs in the thorax and abdominal cavity.
The cranial nerve exam part one focused of nerves one through six. In this installment we will briefly review the functions of nerves seven through twelve, followed by demonstration of specific tests that can provide valuable diagnostic information associated with the damage of these specific nerves.
We will start with a short discussion of the anatomy and physiology of cranial nerves VII to XII.
The cranial nerve VII is predominantly composed of motor fibers that supply muscles of facial expression. The facial nerve also carries taste information from the anterior two-thirds of the tongue and provides parasympathetic supply to the lacrimal, sublingual and submandibular glands. Cranial nerve VIII, the vestibulocochlear nerve, consists of cochlear and vestibular divisions, which relay sound and equilibrium information, respectively, from the inner ear to medulla.
Cranial nerve IX, the glossopharyngeal nerve arises from medulla and innervates the posterior one-third of the tongue and soft palate. It also stimulates the parotid gland to secrete saliva, and supplies the stylopharyngeus muscle, which helps in swallowing. Therefore, damage to this nerve may lead to the absence of the normal gag reflex. On the other hand, cranial nerve X, the vagus nerve, which also rises from the medulla, is a widely distributed, complex nerve that innervates various structures in head, neck, thorax and abdomen. However, all the functions of this nerve are not tested during a routine physical exam.
Cranial nerve XI, the spinal accessory nerve, innervates the sternocleidomastoid muscles and the upper portion of the trapezius. These muscles control turning the head to the side and shrugging of the shoulders. The cranial nerve exam concludes by testing cranial nerve XII, the hypoglossal nerve, which provides motor control of the muscles of the tongue involved in speech control and swallowing.
Now let’s review the systematic approach to examine this set of cranial nerves. Begin with the assessment of the facial nerve. Observe the patient’s face for signs of weakness, such as smoothing of nasolabial folds or widening of a palpebral fissure. Then have the patient raise their eyebrows and look for an inability to wrinkle their forehead on the involved side that can be seen in peripheral facial palsy, or the Bell’s palsy, which occurs due to facial nerve damage and manifests with unilateral weakness of both-the upper and lower facial muscles. This differs from the central facial palsy – seen in stroke patients with supranuclear lesion – which only affects the lower portion of one side.
Next, ask the patient to smile. Note an asymmetry in the contour of the smile, which can result from inability to fully raise the lip on the affected side in patients with either peripheral or central facial nerve palsy. Following that, instruct the patient to close their eyes tightly and assess if they “bury” their lashes equally on both sides. Then ask them to close their eyes again, and keep it closed while you try to open them. And, finally, have the patient blow up their cheeks while you try to push the air out of their pursed lips.
The next step is to assess the taste sensation, for which you will need cotton-tipped applicator, sugar water solution, and water for rinsing the mouth. Tell the patient to stick out their tongue, so that you can swab the sides with the sugar solution. Ask the patient to identify the taste. After getting the patient’s response have them rinse their mouth and repeat the testing on the other side of tongue. Then, ask the patient to compare the sense of taste on each side of the tongue.
The next group of tests evaluates the cochlear division of the cranial nerve VIII, the acoustic nerve. The assessment of hearing function starts with observing whether or not the patient can hear you during the interview. Note if they are wearing hearing aids. First perform a quick hearing assessment by holding your fingers a few inches away from the patient’s ear and softly rubbing them together. Ask the patient if they can hear the finger rub, then repeat on the other side, and inquire if the perceived sound is same for both sides.
Next, if the patient shows signs of hearing impairment, move onto the Weber and Rinne tests, also known as the tuning fork tests. These are performed to distinguish between conductive hearing loss and sensorineural hearing loss. Conductive hearing loss results from the external or middle ear disorders, such as otitis media or perforation of the eardrum. And sensorineural hearing loss occurs due to the damage of the cochlear nerve or the auditory pathways in the brain, which may result from aging, acoustic neuroma, or constant exposure to loud noises.
First let’s review the Weber test. Hit tuning fork tines with the heel of your hand and place the stem at the vertex of the patient’s head. Now ask the patient where they hear the sound. The sound produced by a tuning fork is conducted through both-air and vibration in the bones. Patients with normal hearing will hear the sound in the center of their head and equally in both ears. If the patient is experiencing hearing loss on one side, and if the nature of loss is sensorineural, then the sound lateralizes, or is perceived louder on the “good” side. Whereas, if the nature of loss is conductive, then the sound lateralizes to the “bad” side, since the well-functioning inner ear on this side might pick up the sound transmitted by the skull bones, causing it to be perceived as louder than the unaffected side.
If the Weber test is abnormal, move onto performing the Rinne test. For this, hit the tuning fork tines and place stem on the mastoid bone. Instruct the patient to say “now” when they no longer hear the tone and quickly move the tines adjacent to the outer ear canal. Ask the patient if they can still hear the sound. In the case of conductive hearing loss, the patient will hear the sound for a longer time when the tuning fork is on the bone, compared to when it is in the air near the external ear canal.
Next, evaluate the cranial nerves IX, the glosspharyngeal nerve and cranial nerve X, the vagus nerve, together. Begin by asking the patient to say one full sentence to determine if their speech has nasal quality, which is characteristic to palatal weakness.
After that, ask the patient to open their mouth and say, “AAH”. While the patient is doing so, observe the elevation of their soft palate and note if any asymmetry is present. In the cranial nerve X paralysis, the soft palate fails to rise and the uvula deviates towards the opposite side.
Following that, move to cranial nerve XI or the spinal accessory nerve evaluation. Start by asking the patient to shrug their shoulders upward. Then instruct them to repeat the movement, while you provide resistance by pushing the shoulders down to check for weakness or asymmetry. Next, instruct the patient to turn their head to one side, and ask them to resist your attempt to push their chin in the opposite direction. Repeat the test with the patient turning their head to the opposite side. This is done to assess the strength of the sternocleidomastoids muscle.
Conclude the examination by testing cranial nerve XII, the hypoglossal nerve. For this, ask the patient to open their mouth and first observe their tongue at rest. Look for fasciculations, as may be seen with amyotrophic lateral sclerosis and other motor neuron diseases. Then instruct the patient to stick their tongue out straight; it should be in midline. Unilateral weakness may cause it to deviate towards the weak side.
For the final test assessing the strength of tongue muscles, ask the patient to push their tongue against their cheek, and instruct them to resist while to try to push it back in. Repeat on the other side, each time looking for weakness or asymmetry. This concludes the examination of all the cranial nerves.
You’ve just watched a JoVE video on examination of the cranial nerves from VII to XII. You should now have an understanding of the orderly approach that a clinician should follow while going through a comprehensive cranial nerve exam. The practice of tying together the findings of this exam with the patient history can help a physician gain an insight into the underlying neurological disease. As always, thanks for watching!
