Anatomy clinical correlates: Ear

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Introduction0:00–0:19

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.

Cauliflower (boxer's) ear0:19–0:51

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 article 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 article.
This results in the auricular deformity known as the cauliflower or boxer's ear. Next up.

Referred ear pain0:51–3:09

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 ale 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 C two and C three nerve roots of the cervical plexus and innervate the posterior auricle, the skin overlying the parotid 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 in middle ear effusions caused by obstruction of the pharyngeal tympanic tube, also known as the auditory or eustachian tube.

Pharyngotympanic tube obstruction3:09–4:06

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 trans sedative 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.

Otitis media4:06–4:57

Common bacteria involved in the pathologies 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.
Ok. Now, let's take a look at hyperacusis which is an increased sensitivity to sound where normal noises can seem painfully loud.

Hyperacusis4:57–5:32

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.

Quiz5:32–5:49

Hearing loss5:49–10:15

Great. Finally, let's have a look at hearing loss which can be categorized as conductive sensory neural or mixed hearing loss.
First, let's start with conductive hearing loss, which refers to anything that interferes or limits the amount of sound that gets into the external and middle ear anatomical structures that can be affected in conductive hearing loss include the external auditory canal tympanic membrane and the middle ear ossicles.
In this type of hearing loss, the cochlear nerve is unaffected. So individuals actually perceive their voices to be louder in their own heads and tend to speak quieter.
Some causes include cerumen impaction, which is when earwax builds up and obstructs the external auditory canal tympanic membrane perforation, which is literally what it sounds like infections such as otitis media and externa and Coote atomus, which is an abnormal growth of skin and debris build up in the middle ear which can erode the ossicles or mastoid air cells.
On the other hand, sensory neural hearing loss usually occurs as a result of any lesion, disrupting the transmission of a neural impulse from the cochlea to the brain.
This can result from damage to the inner ear cochlea, cochlear nerve or the brain stem. This means that the outside world as well as the individual's voice are both perceived as quieter.
Common causes include inner ear tumors like a vestibular schwannoma noise induced hearing loss, where excessive chronic noise exposure can damage the stereocilia cells of the organ of Corti presbycusis, which is age related hearing loss, ototoxic medications such as aminoglycosides or chemotherapeutics, congenital viral infections, as well as other diseases of the inner ear like Meniere disease, which is related to excess endolymph and Alport Syndrome.
An X linked disorder of Collagen diagnostic workup of hearing loss involves the Weber and RNA tests. Among others, these tests help determine whether a patient is suffering from conductive or sensory neural hearing loss.
During the Weber test, a tuning fork is struck and placed on the bridge of the forehead. And the individual is asked if the sound is louder in one ear or the other.
As this test is determining the ear's ability to sense bone conducted sound. In individuals with normal hearing or bilateral symmetric hearing loss, there would be no lateralization of sound, meaning the sound will be perceived as equally loud on both sides.
Now, in individuals with unilateral conductive hearing loss, the sound is lateralized towards the affected ear. This means that the sound is perceived as louder on the affected side because that ear now has a relative improvement in the ability to sense bone conducted sound.
This is in contrast to an individual with unilateral sensory neural hearing loss where the sound is lateralized to the unaffected ear as the damaged side has a reduced ability to sense bone conducted sound.
This means that in a positive Weber test where the sound lateralizes to one side, there is either unilateral conductive hearing loss on the side that perceives the sound as louder or unilateral sensory hearing loss on the side that perceives the sound is quieter.
The RNA test. On the other hand, compares the ears ability to sense bone conduction versus air conduction.
Bone conduction is tested by striking the tuning fork and placing it on the mastoid bone and air conduction is tested by striking the tuning fork and placing it next to the person's ear.
After each of these are done, the individual is asked what they think is louder. Normally, air conduction is perceived as louder than bone conduction.
So with a normal RNA test, the individual perceived the tuning fork next to the ear as louder than when placed on their mastoid.
During conductive hearing loss, the sound from the tuning fork beside the ear is blocked from getting into the inner ear.
So bone conduction will be perceived as louder than air conduction. However, in sensory neural hearing loss, both are affected equally.
So air conduction is still louder than bone conduction. Using these two tests together can help localize the side and type of hearing loss.
For example, let's look at right side conductive hearing loss. Using the Weber test, we know that the right side perceives the sound as louder.
Then using the RNA test, bone conduction will be louder than air conduction. Confirming this is a conductive hearing loss and not a sensory neural hearing loss.
If the RNA test had air conduction is louder, then we know the results of the Weber test was due to sensory neural hearing loss of the other side.
All right. As a quick recap cauliflower ear or Boxer's ear occurs as a result of accumulation of blood in the space between the perichondrium and auricular cartilage.

Review10:15–11:43

Resulting in deformity, referred ear pain or secondary otalgia is caused by a lesion somewhere outside the ear which affects a nerve providing cutaneous innervation to the ear which are cranial nerves 579 and 10 in the cervical plexus, pharyngotympanic tube obstruction can cause middle ear effusions because of inflammatory or infectious processes or compression for masses such as a tumor, otitis media is typically caused by a middle ear bacterial infection which can lead to mastoiditis left untreated.
It can progress and result in surrounding osteomyelitis or local brain abscess with hyperacusis. There's increased sensitivity to sound due to stapedius muscle dysfunction, which is usually due to facial nerve lesions.
Finally, hearing loss can be conductive sensory neural or mixed conductive hearing loss occurs because of disruption in the transmission of sound from the outside world to the inner ear.
While sensory neural hearing loss occurs as a result of any lesion disrupting the transmission of neuronal input to the central nervous system.
Diagnostic workup of hearing loss involves the weber and Rinne tests