Assessment of Cranial Nerve Damage in Head Trauma Patients

Abstract

This study was initiated upon admission of subject A to the emergency room after being involved in a bicycle accident. The patient presented several signs of cranial nerve damage such as inability to keep their balance, difficulty hearing and weakness in their eyelids. After conducting extensive neurological tests between the patient and a control subject, this study was able to indeed confirm damage to two cranial nerves.

The purpose of this study is to assess the extent of the head trauma suffered by subject A upon being involved in a bicycle accident, and to determine whether any of their cranial nerves have been damaged.

The human being has a total of twelve pairs of cranial nerves. Some of them are primarily sensory nerves, which will send sensory information from the body towards the central nervous system (CNS, brain and spinal cord), some are primarily motor nerves, which will carry motor information from the CNS to other parts of the body, some have both sensory and motor functions, which are known as mixed cranial nerves.

There is a total of two pairs of pure sensory nerves. The first one is the olfactory nerve (CN I), which goes through the cribriform plate and is associated with the sense of smell. The second one is the optic nerve (CN II), which goes through the optic canal and is associated with vision. The vestibulocochlear nerve (CN VIII), which goes through the internal acoustic meatus and is associated with hearing is considered a primarily sensory nerve. Although the vestibulocochlear nerve shows some characteristics of motor nerve and can be associated with balance, it is still considered a primarily sensory nerve.

There is a total of five pairs of pure motor nerves. The first one is the oculomotor nerve (CN III), which goes through the superior orbital fissure and is responsible for most of the eye movements. It innervates eye muscles such as the medial rectus muscle. The second one is the trochlear nerve (CN IV), which also goes through the superior orbital fissure and plays a role in eye movement.  It innervates the superior oblique muscle of the eye. The third pure motor nerve is the abducens nerve (CN VI), which like the previous ones goes through the superior orbital fissure and plays a role in eye movement. It innervates the lateral rectus muscle of the eye. The fourth motor nerve is the accessory nerve (CN XI), which goes through the jugular foramen and innervates both the sternocleidomastoid and trapezius muscle. The last pure motor nerve is the hypoglossal nerve (CN XII), which goes through the hypoglossal canal. It innervates the intrinsic muscles of the tongue and controls tongue movements.

Cranial Nerves of the Human Brain

Lastly, the human brain also has four pairs of mixed cranial nerves. These nerves function both as sensory and motor nerves. The first one is the trigeminal nerve (CN V), which can go through the superior orbital fissure, inferior orbital fissure, foramen rotundum and foramen ovale. The trigeminal nerve is involved in the general sensation of the face and controls the muscles of mastication including the temporalis and masseter. The second one is the facial nerve (CN VII), which goes through the internal acoustic meatus. As a sensory nerve it can be associated with taste in the anterior half of the tongue. As a motor nerve it controls facial expressions such as smiling, closing the eyes and frowning. The third mixed nerve is the glossopharyngeal nerve (CN IX), which goes through the jugular foramen. As a sensory nerve it can be associated with taste, as a motor nerve it innervates the muscles of swallowing and controls gag reflex. The last mixed nerve is the vagus nerve (CN X), which also goes through the jugular foramen. As a sensory nerve it is associated with taste, as motor nerve, like the glossopharyngeal, it also innervates muscles of swallowing and controls gag reflex.

Based upon the symptoms presented from subject A: unable to keep their balance, hearing impairment on the right ear, weakness in the eyelids, eyebrows, lips and forehead on the right side, and inability to distinguish between sweet and salty tastes on the anterior right side of tongue, there is a high possibility that the following cranial nerves have been damaged: vestibulocochlear nerve (CN VIII) and the facial nerve (CN VII). The vestibulocochlear nerve is the one responsible for hearing and balance. Because the patient  seems to be unable to hear through their right ear and keep their balance, their right vestibulocochlear nerve might be damaged. The facial nerve controls symmetry and taste in the anterior aspect of the tongue. Because the patient showed weakness in their right eyelid, eyebrow, lip, forehead and inability to taste on the right anterior side of their tongue, their right facial nerve seems to be damaged. If that is the case, they might need to undergo surgery to repair their right vestibulocochlear and facial nerves. Upon surgery, then her right vestibulocochlear and facial nerves should function properly.

Neurological tests will be applied to subject A and a control subject in order to confirm or deny these suspects.

Suspected Cranial Nerves Damage in Subject A

Olfactory nerve (CN 1): This test was applied in order to determine the patient’s ability to identify an unknow scent. With both eyes closed and one of the nostrils blocked, patient was presented with an unknown vial placed 10 cm below the unblocked nostril and asked to identify the scent. Both nostrils were tested (Howard Community College, 2019, 142).

Optic nerve (CN II): This test was applied to determine visual acuity and peripheral vision. For the visual acuity test a Snellen eye chart was used. Patient was asked to stand 20 ft away from the chart, cover one eye and read the letters on the chart.

For the peripheral vision test, patient was asked to sit 2ft away at eye level with tester. With one eye covered and staring straight ahead, tester held a finger on the side of the face that had un uncovered eye and asked subject if they could see the finger (HCC, 2019, 143).

Oculomotor nerve (CN III), Trochlear nerve (CN IV), Abducens nerve (CN VI): Because all of these three nerves control voluntary eye movement, the same procedure was applied in order to determine eye movement and pupillary constriction.

For the voluntary motor test, tester stood in front of the patient and asked patient to follow with their eyes as the tester drew the letter H into space.

For the pupillary constriction test, with the patient staring straight ahead, a light was shone into their pupils from a short distance of 20 cm.

Trigeminal nerve (CN V): Because this one is a mixed nerve; the patient was tested for general sensation and strength of motor nerves.

For the sensation test, the subject was touched lightly on the side of the forehead, the buccal (cheek) region and mental (chin) region with a Von Frey hair and asked if they felt the touch. They were also touched with a warm and a cold metal probes on the same areas to determine if they could feel the different temperatures.

For the motor function test, the subject was asked to clench their teeth in order to determine the strength of their temporalis and masseter muscles.

Facial nerve (CN VII): Because this too is a mixed nerve, again the subject was tested for both sensory and motor functions.

For the sensory test, the subject was asked to close their eyes and stick out their tongue. The tester then placed a few drops of both sugary and salty solutions in the first half of the tongue to determine whether the subject could distinguish between sugary and salty tastes (HCC, 2019, 148).

For the motor test, the subject was asked to smile, raise eyebrows, open and close eyelids, pucker their lips, frown and wrinkle forehead to determine symmetry and facial expressions.

Vestibulocochlear nerve (CN VIII): For this nerve the subject was tested to determine the senses of hearing and equilibrium (balance).

For the hearing test, the subject was asked to cover one ear. The tester then stood 12 inches away from the uncovered ear, whispered a phrase and asked the subject to repeat it.

For the equilibrium test a Romberg test was followed. The tester asked the subject to stand up right, facing forward with both eyes open for 2 minutes. Tester watched for swaying of the subject’s body.

Glossopharyngeal nerve (CN IX), Vagus nerve (CN X): Both of these mixed nerves have the same sensory and motor functions. They were tested simultaneously.

For the sensory test, the tester placed drops of sugary and salty solutions in the second half of the subject’s tongue to determine whether the subject could distinguish between sugary and salty tastes.

For the motor test, the subject was asked to make the sound “ahh” and the tester checked the position of the soft palate. The subject was then asked to swallow, and the tester checked if the subject had any difficulty doing so. Lastly, the tester checked the subject’s gag reflex by asking the subject to stick out their tongue upon which the tester depressed the tongue using a tongue depressor and touched the back of the throat with a cotton tip.

Accessory nerve (CN XI): This motor nerve innervates the sternocleidomastoid and trapezius muscles. Subject was tested on the strength of both muscles.

For the sternocleidomastoid the tester placed their hand on the subject’s cheek and asked the subject to turn their head against the resistance of the tester’s hand.

For the trapezius muscle, with the subject sitting down, the tester placed both hands on the subject’s shoulder and asked the subject to try to lift up their shoulder against the resistance.

Hypoglossal nerve (CN XII): This nerve was tested for motor function.

For this test the tester asked the subject to protrude their tongue out of their mouth (HCC, 2019, 151).