AssessmentsAnatomy clinical correlates: Ear
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 57-year-old woman presents to her primary care physician for evaluation of chronic tinnitus of her right ear. The patient reports insidious onset of symptoms over the past three to four months with associated “balance issues.” The patient has not had other significant medical history. This patient’s Weber test demonstrates lateralization of sound to the left ear, while Rinne testing demonstrates air conduction greater than bone conduction in the right ear. Which of the following is the most likely anatomic site of this patient’s primary pathology?
Content Reviewers:Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.)
Contributors:Sam Gillespie, BSc
The ear has many roles, from hearing and maintaining balance, to showing off jewelry and piercings. But just like the rest of our body, there are a variety of conditions that can affect them, so understanding the anatomy of the ear can help us better understand the clinical conditions that affect it!
Let’s start with the auricular hematoma, also known as a cauliflower or boxer’s ear. You may have guessed from its name - this condition is most common in professional boxers and wrestlers. Boxer’s ear is a deformity caused by blunt trauma to the auricle, in which blood accumulates between the perichondrium and auricular cartilage, resulting in a hematoma. If left undrained, fibrosis can develop in the overlying skin which causes deformity of the auricle. This results in the auricular deformity known as the cauliflower or boxer’s ear.
Next up, let's look at ear pain. The ear receives cutaneous innervation from multiple nerves of the head and neck which makes it prone to referred pain. This is called secondary otalgia, which means that the ear perceives pain when the primary issue is in another anatomical site.
Now, the majority of the external auditory canal innervation comes from the auriculotemporal nerve, which is a branch of the trigeminal nerve. It provides sensory innervation to the anterior portion of the preauricular skin, anterior auricle, and the anterior portions of the external auditory canal. Conditions such as dental infections, maxillary sinusitis, as well as temporomandibular joint disease can cause referred pain in these parts of the ear.
Along with the auriculotemporal nerve innervating the ear, a small auricular branch of the vagus nerve and parts of the glossopharyngeal nerve go on to innervate a small portion of the posterior external auditory canal and tympanic membrane. As these two nerves also innervate portions of the pharynx and larynx, pathologies irritating these areas can be referred to the ear. Examples include hypopharyngeal and laryngeal cancer, as well as oropharyngeal infections, which can all cause otalgia.
The ear also receives a large portion of cutaneous innervation from the lesser occipital and the greater auricular nerves, which come from the C2 and C3 nerve roots of the cervical plexus and innervate the posterior auricle, the skin overlying the parotids, and the mastoid. Referred pain from these nerves is rare, and causes include cervical spine tumors and neck trauma.
Finally there’s also the posterior auricular nerve, which is a branch of the facial nerve. This nerve supplies a small part of the posterior wall and auricle. Referred pain in these areas can result from facial nerve pathology.
Now, this intricate innervation is also the reason for why stimulating the ear region can stimulate the vagus nerve - since the posterior aspects of the external auditory canal are innervated by the vagus nerve via its small auricular branch. When these parts of the ear are stimulated, this can produce a vagal reflex which can include symptoms such as vomiting, bradycardia, coughing, and syncope. This can occur when getting your ears checked at the doctor's office, as the otoscope can irritate these areas.
Now let’s switch gears and look at middle ear effusions caused by obstruction of the pharyngotympanic tube, also known as the auditory or Eustachian tube. Remember that the pharyngotympanic tube is a canal that opens up posterior to the inferior nasal meatus and connects the nasopharynx to the middle ear and mainly functions to equalize the pressure in the middle ear with the atmospheric pressure. This is why you swallow on an airplane so your ears don't feel like they want to pop!
When this tube is not working properly, it causes pressure to build up in the middle ear, leading to transudative middle ear effusions. Symptoms of middle ear effusion include a feeling of fullness and pressure in the ear, hearing loss, and tinnitus. Pathologies associated with pharyngotympanic tube obstruction include rhinosinusitis, allergic rhinitis, or infections like the common cold. The tube can also be anatomically obstructed by tumor or by enlarged adenoid tonsils that cause a mass effect.
Next up, there’s otitis media, which is a painful infection of the middle ear, generally caused by bacterial upper respiratory infections. Common bacteria involved in the pathogenesis of otitis media include Streptococcus pneumoniae or Haemophilus influenzae. Now, the middle ear is in close proximity to the mastoid process of the temporal bone, and the mastoid bone contains air spaces called mastoid air cells which communicate with the middle ear through the mastoid antrum. So any infection of the middle ear can spread to the mastoid bone, causing mastoiditis. Left untreated, mastoiditis can cause osteomyelitis of surrounding bone, or even progress and invade into the adjacent cerebellum or temporal lobe of the brain, causing a brain abscess. This outlines the importance of early recognition and treatment of mastoiditis, where the mainstay of treatment is antibiotics.
Okay, now, let’s take a look at hyperacusis, which is an increased sensitivity to sound where normal noises can seem painfully loud. Normally, the stapedius muscle, which is innervated by the facial nerve, helps dampen the excessive vibrations caused by loud noises on the stapes by pulling on it. This prevents excess movement of the stapes, which helps control the amplitude of sound waves. With damage to the facial nerve, the stapedius muscle is unable to contract and properly dampen the oscillations of the ossicles. This results in the individual perceiving sound as abnormally loud on the affected side.
So far so good!! Before we move on, feel free to take a quick break and see if you can remember the major complications of otitis media.