A 21-year old man is brought to the emergency department due to head trauma sustained during a boxing match. During the fight, he had a brief loss of consciousness after a hard hit to the right side of his face. He has a headache and muffled hearing in his right ear. On examination, the patient is alert and oriented. Palpation of the head does not reveal any step-offs. Cervical spine examination is normal. Otoscopic examination reveals hemotympanum in the right ear. This patient is at greatest risk for injury involving which of the following cranial nerves?

Question

A 21-year old man is brought to the emergency department due to head trauma sustained during a boxing match.  During the fight, he had a brief loss of consciousness after a hard hit to the right side of his face.  He has a headache and muffled hearing in his right ear.  On examination, the patient is alert and oriented.  Palpation of the head does not reveal any step-offs.  Cervical spine examination is normal.  Otoscopic examination reveals hemotympanum in the right ear.  This patient is at greatest risk for injury involving which of the following cranial nerves?

Quizplus · Accepted Answer

11ec160b_35c6_4441_9249_d9e940a9d259_MD0001_00 This patient who sustained trauma to the head now has hearing loss and hemotympanum, which is concerning for a temporal bone fracture. Contained within the temporal bone are many structures involved in hearing, including the external auditory canal, tympanic membrane, ossicular chain, cochlea, and vestibulocochlear nerve (CN VIII). Injury or disruption to any of these structures can cause hearing loss, as in this patient. The temporal bone also contains the facial nerve (CN VII), which originates in the brainstem and then enters the temporal bone at the internal auditory meatus. It travels through the internal auditory canal with the vestibulocochlear nerve (CN VIII) and then takes a complicated route through the temporal bone itself, traveling near the otic capsule, through the middle ear, and then through the mastoid portion to exit at the stylomastoid foramen. Because of its location, the facial nerve is at risk of injury in temporal bone fractures. Deficits can be diverse and significant because the facial nerve has many functions, including: (Choice A) Axons of chemoreceptor cells make up the olfactory nerve (CN I) rootlets, which project through the cribriform plate of the ethmoid bone. Acceleration-deceleration head injuries can lead to avulsion of the olfactory nerve rootlets, but this would not be associated with hearing loss or hemotympanum. (Choice B) The oculomotor nerve (CN III) exits the skull base from the superior orbital fissure and is at risk with trauma to the orbit or anterior face. (Choice C) The trigeminal nerve (CN V) divides into V1, V2, and V3, which exit the skull base from the superior orbital fissure, foramen rotundum, and foramen ovale, respectively, which are all located in the sphenoid bone. These branches are at risk with trauma to the orbit or anterior face. (Choice E) The hypoglossal nerve (CN XII) exits the skull base through the hypoglossal canal of the occipital bone. It could be injured by fractures involving the occipital bone, but it is more commonly injured due to penetrating neck trauma. Educational objective: In addition to much of the hearing apparatus (eg, ossicles, cochlea, vestibulocochlear nerve), the temporal bone also contains the facial nerve, which can be injured in temporal bone fractures. __________ References: Facial Nerve Anatomy and Clinical Applications (http://www.ncbi.nlm.nih.gov/pubmed/32119456)

A 21-Year Old Man Is Brought to the Emergency Department