Anatomy OF External Ear and its Diseases

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.

Temporal Bone Anatomy

• The temporal bone is made up of five parts. They are -
  • Part 1: Squamous: It is one of the biggest parts and lies at the upper end of the temporal bone.
  • Part 2: Tympanic: It is present between the styloid and the zygomatic Part. It contains the middle ear.
  • Part 3: Styloid: It is the elongated projection at the base of the temporal bone.
  • Part 4: Petromastoid: On the lateral surface, the mastoid part is present, and on the medial surface is the petrous Part. 
  • Part 5: Zygomatic: It projects anteriorly from the squamous Part.
• The petrous part has two slants - anterior and posterior slants.
• The anterior slant articulates with the squamous temporal bone, and the posterior slant articulates with the occipital bone.
• This petrous bone continues as the mastoid temporal bone posteriorly, thus forming the petromastoid complex.
• On the posterior slant, there is a canal present known as the internal auditory canal or internal auditory meatus. 
• The petrous apex lies in very close relation to the brain stem, which continues downwards as the spinal cord. From the brain stem, there exist the 5th, 6th, 7th, and 8th nerves coming from the Pons. The 5th and the 6th cranial nerve go anteriorly toward the petrous apex, which is present medially towards the brain stem. 7th and the 8th cranial nerves go into the internal auditory canal.

Anatomy of the Ear

The ear is divided into three parts. Going from lateral to medial, they are -

1. External ear
2. Middle ear
3. Inner ear

External Ear

The external ear is divided into three parts:

1. Pinna
2. External auditory canal
3. Tympanic membrane

Pinna

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 - 

1. The area between the tragus and the beginning of the helix does not have cartilage. This area is called incisura terminalis.
2. The lobule of the ear is also devoid of cartilage.

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.

External Auditory Canal

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.

• There are some hair follicles, sebaceous glands, and ceruminous glands present on the cartilaginous part of the external auditory canal thus otitis externa or folliculitis (staphylococcus infection) only happens in the outer 1/3rd part of the canal. Communications: There are two communications presents between the external auditory canal and the parotid gland, which can cause to and fro infections. They are –
  • Fissure of Santorini: It is present between the underlying parotid gland and the cartilaginous part of the canal.
  • Foramen of Huschke: It is present between the parotid gland and the bony part of the canal.
• These two communications usually disappear by the age of 5-7 years. The narrowest portion of the external auditory canal is called the isthmus and is present 6mm lateral to the tympanic membrane. As the isthmus is the narrowest part, there are chances of foreign bodies or wax impaction in this area.
• While extracting wax or a foreign body from the isthmus using a probe, there are chances of tympanic membrane perforation as the distance between the two is very small, and the visualization  is poor, and due to discomfort, the patient may move suddenly. This is why it is preferred to give local anaesthesia in adults and sedation/short general anaesthesia in children before extraction to prevent any movements. Also, an endoscope or microscope is used to magnify the space between the foreign body and the tympanic membrane which helps in preventing any trauma to the tympanic membrane.

Nerve Supply of Pinna And External Auditory Canal

The mnemonic is LAG 7 & 10. The nerve supply is:

1. Lesser occipital nerve
2. Auriculotemporal nerve
3. Greater auricular nerve
4. 7th and 10th cranial nerves (Facial and vagus nerve)

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.

Tympanic Membrane

Parts of Tympanic Membrane 

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 –

• Pars Tensa: It is tense and tight in nature.
  • It makes up the lower portion of the tympanic membrane.
  • There is a fibrous cartilaginous ring around the membrane known as the annulus. The cartilage stretches the membrane making it taut.
  • It has three parts: The outer epithelial layer, the middle fibrous layer, and the inner endothelial layer.
  • The fibrous layer provides tensile strength to the membrane.
• Pars Flaccida: It is loose and lax in nature.
  • It makes up the upper portion of the tympanic membrane.
  • The annulus is absent in this portion.
  • It has two parts: The outer epithelial layer and the inner endothelial layer.
  • There is no fibrous layer present.
• Projections on the tympanic membrane:
• These are –
  • The handle of the malleus: It is seen centrally on the tympanic membrane.
  • Umbo: The handle of the malleus lies medially to the tympanic membrane. The point at which the tip of the malleus attaches to the membrane is known as the umbo.
  • Malleolar folds: There are two folds that come out of the malleus, known as the anterior and posterior malleolar folds. The shorter fold is the anterior malleolar fold, and the posterior malleolar fold is the longer one.
  • Quadrants of the pars tensa: The pars tensa is divided into four sections with the help of two imaginary lines. These lines pass through the umbo horizontally, and the other passes through the handle of the malleus vertically. 
• This divides the pars tensa into - anterosuperior quadrant, anteroinferior quadrant, posterosuperior quadrant, and posteroinferior quadrant.
  • Cone of light: It is present in the anteroinferior quadrant of the pars tensa.

Important Points

• Any perforation in the pars tensa is known as a central perforation.
• Any perforation in the pars flaccida is known as an attic perforation.
• A perforation involving only one quadrant is called a small central perforation.
• If a perforation involves more than one quadrant, then it is called a large central perforation.
• If a perforation involves all the quadrants of the pars tensa, but the annulus is intact, then it is called a subtotal perforation.
• If a perforation involves all the quadrants and the annulus, then it is called total perforation.
• Side of the tympanic membrane: This is the way to identify the side of the tympanic membrane.
• Cone of light: If the cone of light is present in the 3 o’clock to 6 o’clock position, then it is the right tympanic membrane. If it is present in the 6 o’clock to 9 o’clock position, then it is the left tympanic membrane.

Related Anatomy Articles :

DISEASES OF THE EXTERNAL EAR

Congenital abnormalities of the Pinna

Abnormalities of the middle ear and inner ear:

• Macrotia- The size of the pinna is larger or not proportional to the skull.
• Microtia- Small pinna
• Anotia - Complete absence of the pinna
• Bat ear- Protruding ear

Peri auricular sinus / appendages

• It is a congenital malformation that is cause by incomplete fusion of first hillock and other five hillocks. As pinna develops from six hillocks, the first hillock give rise to tragus and other five forms the rest of pinna.
• Outside it can present as a pit but inside it has a large tract and a sac.
• Recurrent infection, with cheesy discharge and can progress to become an abscess.
• Not all peri auricular sinus requires treatment but if recurrent infection is there , surgery can be done. In surgery entire sac is removed. methylene blue is used to demarcate the borders of sac.
• Peri auricular appendages are small skin tags which are present from tragus to the angle of mandible.     

Acquired Abnormalities

Hematoma Auris – 

• Accumulation of blood between the cartilage and overlying perichondrium.
• If there is a history of direct trauma or hit that causes hematoma, mainly it occurs in boxers that’s why it is called BOXERS EAR.
• It can also be acquired iatrogenic. Here depressions and elevations are not seen so this is also called cauliflower ear.
• For small hematomas just aspirate and for larger hematomas, incision, and drainage are required along with antibiotics.

Perichondritis 

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.

Clinical Features:

• Severe pain
• Red swollen ear pinna  
• Sparing of the lobule is a very important feature of the perichondrium.  
• Anti-pseudomonal antibiotics and topical antibiotics are given as a line of treatment.
• Relapse polychondritis is an autoimmune condition which involves multiple cartilages in body. 

Keloid

• Common causes are trauma and ear piercing.
• Trauma will result in excessive collagen production during healing and will lead to irregular scarring which is a keloid.
• Disfigure appearance. It is not a malignancy.
• Treatment- Steroids, Excision, Radiotherapy, Radiofrequency currents
• There are high chances of recurrence. 

Also Read:

How do BRAINSTEM LESIONS affect the brain? 

Anatomy of Upper Limb

Congenital Abnormalities of the External Auditory Canal

Atresia

• Complete non-development of the external auditory canal.
• There is no opening, the tympanic membrane is present in some cases and in some cases, it is not there.
• Some patients can have oral atresia associated with normal tympanic membrane in the middle ear.
• Some of them can have abnormal tympanic membranes at the middle ear.
• Patient’s hearing can be rehabilitated by using BAHA (Bone anchored hearing aid).

Acquired abnormalities of the external auditory canal

Wax/Cerumen

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.

Localised Otitis Externa

• Also called furunculosis.
• Causes of the otitis externa is a staphylococcal infection of the hair follicle.
• Extreme or severe pain with certain amount of hearing loss.
• Pain during chewing and jaw actions.
• Tragal sign is positive.
• Purulent discharge because the external auditory canal has squamous epithelium, there is no mucoid cell. Whenever there is mucoid discharge, it is from the middle ear not from the canal.
• There is an obliteration of the retro auricular groove.
• If the patient is immunocompromised or diabetic there is recurrent furunculosis.

Diffuse Otitis Externa 

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.

Malignant Otitis Externa

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 7^th 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.

Otomycosis

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.

Foreign Body

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:

• Inorganic (beads / pellets)
• Graspable non-living
• Living insects
• Organic and button batteries 

Commonly extracted Foreign Bodies

• Inorganic (beads / pellets)
• Graspable non-living
• Living insects
• Organic and button batteries 

• Simpsons aural syringe is directed toward posterior superior canal wall to avoid any direct trauma. The temperature of water should be like body temperature to avoid any stimulation of labyrinthine which can cause vertigo or nystagmus.

Complications

• Tympanic perforation
• Labyrinthine stimulation
• Stimulation of Arnold’s nerve or vagus nerve causing syncopal attacks.

Keratosis Obturans

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.

Ramsay Hunt Syndrome/Herpes Zoster Oticus

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.

Diseases of the Tympanic Membrane

Myringitis Bullosa Haemorrhagica

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.

Traumatic Perforation of Tympanic Membrane

High pressure trauma cause perforation in tympanic membrane 

• Hearing loss
• Some bleeding
• Fresh edges

Treatment of perforation of 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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