May 03, 2023
When talking about the anatomy of the ear, the first important concept is that of the temporal bone.
Read this blog further to get a quick overview of this important topic for ENT and ace your NEET PG exam preparation.
The ear is divided into three parts. Going from lateral to medial, they are -
The external ear is divided into three parts:
It is also called the auricle. The pinna is made up of elastic cartilage. There are various elevations and depressions present over the pinna. The first and most prominent elevation is known as the helix. It is present on the outermost part of the pinna
.Along the helix, in the reverse direction, another smaller projection is present, which is known as the anti-helix. A triangular projection is a present medial to the anti-helix known as the tragus. In the reverse direction of the tragus, there is another projection present which is called the anti-tragus. A depression is present, which is surrounded by the anti-tragus, tragus, and anti-helix. This depression is known as cavum concha. This is the biggest depression on the pinna. Above the concha, there is a triangular depression known as the triangular fossa. The elastic cartilage is present all over the pinna except for two sites -
The importance of area devoid of cartilage is the incisura terminalis. The incisura terminalis is the site of incision in an endaural surgery (like taking a surgical approach from the external auditory canal). Incisura terminalis is chosen because, in case of post-operative infection, the lack of cartilage prevents the chances of underlying cartilage necrosis which further causes deformity of the pinna. This incision is known as Lempert endaural incision. The lobule of the pinna has high-fat content, due to which it becomes the site of fat graft harvest.
It is the continuation of the pinna. The length of the external auditory canal is 24mm. It is divided into two parts - The cartilaginous part and the bony part. The lateral section is the cartilaginous or the outer Part. It accounts for 1/3rd of the external auditory canal, i.e., 8mm. The medial section is the bony or the inner Part. It accounts for the rest of the 2/3rd portion of the external auditory canal, i.e., 16mm.
The canal is not straight. In fact, the canal is S-shaped. This shape makes visualizing the tympanic membrane from the outside difficult. So, it is necessary to straighten the canal before visualizing. To do so, the pinna is stretched upwards, backward, and outwards in adult patients. In children, the pinna is stretched downwards and backward because the bony portion of the external auditory canal has not been fully developed.
The mnemonic is LAG 7 & 10. The nerve supply is:
The major portion of the pinna is supplied by the greater auricular nerve (mainly, the lower portion).
The auriculotemporal nerve supplies the anterior portion in the upper half of the pinna.
The lower occipital nerve supplies the medial portion of the upper half pinna (near the mastoid).The concha is supplied by the 7th and 10th cranial nerves.
The auriculotemporal nerve will extend into the canal and supply the roof and the anterior wall of the external auditory canal.
Arnold’s nerve is the auricular branch of the vagus nerve and supplies the posterior wall and the floor of the external auditory canal.
Stimulation of Arnold's nerve during any procedure will cause a cough reflex. This is because Arnold’s nerve is part of the vagus nerve, which innervates the larynx as well and thus causes the cough on stimulation.
Also, Arnold’s nerve can precipitate a vasovagal attack or syncope on stimulation.
Both the auriculotemporal nerve and Arnold’s nerve supply the lateral surface of the tympanic membrane.
Parts of Tympanic Membrane
|Paras Tensa||Pars Flaccida|
|No. of layers||3||2|
|Umbo and cone of light||Umbo in center and cone of light in antero-inferior part|
It is a partition/curtain between the external ear and the middle ear. It is obliquely placed to the canal at an angle of 45 degrees to the floor of the canal. It is an oval-shaped structure, so it has a longer vertical axis and a shorter horizontal axis which are 10mm long and 9mm wide, respectively. It is 0.1mm in thickness.
The total surface area of the tympanic membrane is 90mm2. The vibrating area of the tympanic membrane is the peripheral portion. This is because, in the center, the handle of the malleus bone rests medially on the membrane, which prevents vibrations. So, the effective vibrating area is half of the total surface area, i.e., 45mm2 Parts of the tympanic membrane: The tympanic membrane has two parts –
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It is Inflammation in the perichondrium is perichondritis.The causes are trauma and surgical trauma. And from the extra auditory canal, there can be a source of infection. Organisms responsible for its causes are mostly pseudomonas, staphylococcus streptococcus.
Waxes are the secretions coming from the sebaceous gland, ceruminous gland, squamous epithelium, and keratin debris. The Color of the wax may vary according to race. They are acidic in pH, bacteriostatic and fungistatic. It is a Protective structure in the auditory canal. Wax retention can occur when there is a small external auditory canal or epithelial migration defect also Conductive hearing loss may be there. Ringing sensation is present in the ear along with Pain and giddiness. Jobson horn probe can be used for the removal of wax.
It is also called swimmer’s ear, tropical ear, and telephonist ear. It is a pseudomonas infection. Because of the constant humidity and swimming pH of the wax changes from acidic to alkaline. Alkaline pH favors the group of bacteria. It is seen in immunocompetent individuals. Pain, discharge, swelling, and obliteration of the retro auricular groove. These symptoms increase with the movement of the jaw. Systemic Antibiotics, topical ear packs, antibiotic ear drops, and glycerine packs are used for treatment.
It is Caused by pseudomonas and the patient is immunosuppressed. Severe excruciating ear pain will occur in this condition. Anteriorly this infection can go to TMJ causing pain and limitation of movement in TMJ. It can spread exclusively because the patient’s immunity is low. Cranial nerves may get involved, first, the cranial nerve involved is the 7th cranial nerve causing facial nerve palsy, then the lower cranial nerves and the jugular foramen get involved.
Red granulation tissues are diagnosed at the bony cartilaginous of the external auditory canal. Biopsy and culture can be done to diagnose. TC99 can be used for early diagnosis of the disease. For checking whether the infection is resolved or not gallium 67 is used. For assessing intracranial spread MRI is used and a CT scan is used to assess erosion of bone. Antipseudomonal antibiotics are used for treatment.
It is caused by the Aspergillus species. It can occur in both immunocompetent and immunosuppressant persons. But it is most often seen in immunocompromised people. Whitish discharge is there and black spores on this white discharge are seen. Wet newspaper appearance is there. There is itching in the extra auditory canal. Local toileting is done along with antifungal ear drops and oral antifungals can also be given.
In this there is Unilateral Foul-smelling discharge. It is Most common in toddlers. Foreign bodies can be removed by syringing, crocodile forceps, lidocaine solution, or any form of an ear drop. Syringing is contraindicated for an organic foreign body removal. Commonly extracted Foreign Bodies are:
If a patient has ciliary motility defect, movement of squamous epithelium will not occur. It will get retained on the extra auditory canal and several layers of squamous epithelium will form like an onion skin, that pattern is called onion skin laminar arrangement. It also Cause widening of the adjacent extra auditory canal. It can be associated with other ciliary motility disorders such as sinusitis, bronchiectasis. In this Facial nerve can be involved. Removal is done under general anesthesia and sedation.
In this syndrome the Herpes zoster virus becomes latent in the geniculate ganglion. Whenever there is the reactivation of this virus there is a pain and vesicles distribution along with facial nerves, and facial nerve palsy occurs along with sensorineural hearing loss. Antiviral acyclovir is given along with steroids.
Haemorrhagic bullae on the tympanic membrane is called myringitis bullosa haemorrhagic. It occurs due to streptococcus pneumonia, mycoplasma, and influenza virus. It causes Severe pain in canal.Systemic antibiotics should be given.
High pressure trauma cause perforation in tympanic membrane
We need to wait and watch for 4 to 6 weeks as it will heal spontaneously. If it fails to heal, myringoplasty is done. In this condition the Ear canal should be kept dry.
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