Anatomy of Middle ear

Anatomy of the Middle Ear: A Comprehensive Guide for MBBS and ENT PG Students

The middle ear is a fascinating, air-filled chamber within the temporal bone, acting as a crucial bridge for sound transmission to the inner ear. Understanding its intricate anatomy is paramount for both MBBS and ENT PG students, as it forms the basis for diagnosing and managing a wide array of otological conditions. This comprehensive chapter, aligned with the CBME curriculum, offers a detailed yet student-friendly exploration of middle ear anatomy, ideal for university theory exams, viva questions, practical exams, and NEET PG MCQs.

Introduction to the Middle Ear Cleft

The middle ear, also known as the tympanic cavity, is an irregular, air-filled space in the petrous part of the temporal bone. A thin mucous membrane lines this cavity. It lies laterally to the tympanic membrane and medially to the lateral wall of the inner ear.

Importantly, the middle ear does not exist in isolation. It forms part of a larger interconnected system called the middle ear cleft. This cleft comprises:

• The Eustachian tube (anteriorly)
• The tympanic cavity (middle ear proper)
• The attic (epitympanum)
• The aditus ad antrum
• The mastoid antrum
• The mastoid air cells (posteriorly)

Within the tympanic cavity, you find several critical structures: the ear ossicles (malleus, incus, stapes), the stapedius muscle, the tensor tympani muscle, the chorda tympani nerve, and the tympanic plexus. The primary function of the middle ear is to transmit vibrations from the tympanic membrane to the inner ear.

I. Divisions of the Middle Ear

The middle ear is traditionally divided into three parts: the epitympanum (upper compartment), the mesotympanum (middle compartment) and the hypotympanum (lower compartment).

1. Epitympanum or the Attic – This is the upper compartment. It lies above the level of pars tensa and malleolar folds but medial to pars flaccida and the bony lateral attic wall (also known as scutum). It is separated from the mesotympanum and hypotympanum by a series of mucosal membranes and folds.
2. Mesotympanum or the tympanic cavity – This is the middle compartment, directly opposite the pars tensa of the tympanic membrane.
3. Hypotympanum – This is the lower compartment, located below the level of the pars tensa and the tympanic sulcus. 

Beyond these main divisions, we also recognise specific anterior and posterior areas:

• Protympanum: This area lies in the anterior wall of the tympanic cavity, close to the opening of the Eustachian tube.
• Retrotympanum: This area occupies the posterior wall of the tympanic cavity.

Diagram showing Retrotympanum and Protympanum area

 

II. Boundaries of the middle ear.

The middle ear can be visualised as a six-sided box with a roof, a floor, anterior, posterior, lateral, and medial walls.

 

1. Roof (Tegmental Wall)

The roof of the middle ear, also known as the tegmental wall, is a thin bony plate called the tegmen tympani. This structure forms part of the petrous portion of the temporal bone.

• Separation: Crucially, it separates the middle ear cavity from the middle cranial fossa, which houses the temporal lobe of the brain.
• Extension: The tegmen tympani extends posteriorly to form the roof of the aditus ad antrum and the mastoid antrum (tegmen antri), providing continuity to the mastoid air cells.
• Clinical Significance: Because of its thinness, a middle ear infection (otitis media) can easily erode the tegmen tympani, leading to severe intracranial complications like extradural abscess, meningitis, or temporal lobe abscess.
• Cog: A bony crest, the cog, projects caudally from the roof, lying anterior to the malleus head. The cog divides the epitympanum into a larger posterior and smaller anterior epitympanic space. Surgeons meticulously inspect the anterior epitympanic space during cholesteatoma surgery (e.g., canal wall-up procedures) to ensure complete disease removal.

2. Floor (Jugular Wall)

The floor of the middle ear, also called the jugular wall, is also a thin bony plate.

• Relationship: It separates the hypotympanum from the underlying jugular fossa, which contains the dome of the internal jugular vein (jugular bulb).
• Variations: Occasionally, the floor may have a congenital dehiscence (a bony deficiency), allowing the jugular bulb to project directly into the middle ear, separated only by fibrous tissue and mucous membrane. This makes the jugular bulb vulnerable to injury during surgery.
• Jacobson’s Nerve: Jacobson’s nerve (tympanic branch of glossopharyngeal nerve, CN IX) enters the middle ear through the floor. Surgeons must remember its presence when elevating the tympanomeatal flap inferiorly.

3. Anterior Wall (Carotid Wall)

The anterior wall, or carotid wall, is a wafer thin bony plate (up to 3mm thin), separating the middle ear cavity from the pulsating internal carotid artery.

• Openings: It features two important openings:
  • A larger, lower opening for the entry of the Eustachian tube into the middle ear.
  • A smaller, upper opening for the canal housing the tensor tympani muscle.
• Chorda Tympani: The foramen (anterior canaliculus) for the exit of the chorda tympani nerve from the middle ear is also associated with this wall.

4. Posterior Wall (Mastoid Wall)

The posterior wall, or mastoid wall, is not entirely complete.

• Inferiorly: Its lower part forms a bony partition between the middle ear and the mastoid air cells.
• Superiorly: The epitympanum (attic) continues superiorly into the aditus ad antrum, which then connects directly to the mastoid antrum.
• Pyramid: A small bony elevation called the pyramid projects from this wall. The stapedius muscle’s tendon emerges from the apex of the pyramid and attaches to the neck of the stapes. The aditus lies superior to the pyramid.
• Facial Nerve: The facial nerve (CN VII) runs in the posterior wall, typically just behind the pyramid. Its bony canal (fallopian canal) may be dehiscent, leaving the nerve exposed and vulnerable.
• Facial Recess (Posterior Sinus): This is a crucial surgical depression in the posterior wall, lateral to the pyramid.
  • Boundaries: It is bounded medially by the vertical part of the facial nerve, laterally by the chorda tympani nerve, and superiorly by the fossa incudis.
  • Surgical Importance: The facial recess provides a direct surgical access route to the middle ear (especially the retrotympanum) and mastoid without disrupting the posterior bony ear canal wall, which is vital in procedures like cochlear implantation or mastoidectomy. 
    
    

5. Lateral Wall (Membranous Wall)

The lateral wall, or membranous wall, primarily comprises three parts:

• Superiorly: The bony lateral wall of the epitympanum, known as the scutum. The scutum is a thin, wedge-shaped bone particularly susceptible to erosion by cholesteatoma, creating a characteristic appearance on HRCT scans.
• Centrally: The tympanic membrane (eardrum). This semi-transparent structure acts as a “window” into the middle ear. Through a normal tympanic membrane, you can sometimes visualize parts of the long process of incus, incudostapedial joint, round window niche, and the opening of the Eustachian tube.
• Inferiorly: The bony lateral wall of the hypotympanum.

6. Medial Wall (Labyrinthine Wall)

The medial wall, or labyrinthine wall, separates the middle ear from the delicate inner ear (labyrinth).

• Promontory: A prominent rounded bulge, the promontory, dominates the central portion of this wall. The basal coil of the cochlea produces this bulge.
• Tympanic Plexus: The tympanic plexus, a network of nerves, lies on the promontory. It receives contributions from the tympanic branch of the glossopharyngeal nerve (CN IX) and sympathetic fibers from the internal carotid plexus. The tympanic plexus innervates the mucous membrane of the middle ear, mastoid, and Eustachian tube.
• Windows: Two crucial openings connect the middle ear to the inner ear:
  • Oval Window (Fenestra Vestibuli): This kidney-shaped opening lies superior and posterior to the promontory. The footplate of the stapes is attached to it by the annular ligament, transmitting vibrations to the cochlea.
  • Round Window (Fenestra Cochleae): This round opening lies inferior and posterior to the promontory, covered by the secondary tympanic membrane.
• Facial Nerve Canal: Superior to the oval window is the bony canal for the facial nerve. This canal’s bony covering can sometimes be congenitally dehiscent, leaving the nerve exposed and highly vulnerable to injury or infection.
• Lateral Semicircular Canal: Above the facial nerve canal, a broader bony prominence indicates the underlying lateral semicircular canal of the inner ear.
• Processus Cochleariformis: Just anterior to the oval window, the medial wall presents a hook-like projection called the processus cochleariformis. The tendon of the tensor tympani muscle takes a sharp turn here before attaching to the malleus. This process also marks the level of the first genu (bend) of the facial nerve, serving as an important surgical landmark.
• Sinus Tympani: This complex depression lies on the medial wall in the posterior part of the middle ear. It is bounded medially by the pyramid, laterally by the posterior semicircular canal, superiorly by the ponticulus (bony ridge between pyramid and promontory), and inferiorly by the subiculum (bony ridge between round window niche and styloid eminence). The sinus tympani is a common site for cholesteatoma remnants due to its deep and hidden nature.

 

III. Mastoid Antrum and Air Cell System

The mastoid is an integral part of the middle ear cleft, serving as a reservoir for air and a common site for ear infections to spread.

1. Mastoid Antrum

The mastoid antrum is a relatively large, air-containing space located in the upper part of the mastoid process.

• Dimensions: It typically measures approximately 9 mm in height, 14 mm in width, and 7 mm in depth in adults.
• Communication: The antrum directly communicates with the epitympanum of the middle ear via the aditus ad antrum.
• Development: Unlike the mastoid air cells, the antrum is well-developed at birth. In adults, its average volume is about 2 ml.
• Mucosal Continuity: The mucous membrane lining the mastoid air cells is continuous with the mucous membrane throughout the entire middle ear cleft. Therefore, infections in the middle ear can easily spread into the mastoid area. 

Boundaries of mastoid antrum

2. Boundaries of Mastoid Antrum:

• Roof: It is formed by a thin layer of bone called the tegmen antri, which separates the mastoid antrum from the middle cranial fossa, where the brain’s temporal lobe resides. If an infection in the middle ear cleft breaches this thin wall, it can travel to the brain. This can result in serious complications such as extradural abscess, meningitis and temporal lobe abscess.
• Lateral wall: The lateral wall of the antrum is formed by a plate of bone, which is on average 1.5 cm thick in the adult. It is marked externally on the surface of the mastoid by the suprameatal (MacEwen’s) triangle. It is covered by postaural skin. 
• Medial wall: It is formed by the petrous bone and related to the Posterior semicircular canal, Endolymphatic sac and Dura of the posterior cranial fossa
• Anterior: Anteriorly, the mastoid antrum communicates with the attic through the aditus ad antrum.
• Posterior wall: It is primarily formed by the mastoid bone and has an important role in connecting the middle ear to the mastoid air cells. The posterior wall separates the mastoid antrum from the sigmoid sinus, a major venous channel that drains blood from the brain. If an infection in the middle ear cleft spreads and breaches the posterior wall, it can extend to the sigmoid sinus. This can lead to a severe condition known as sigmoid sinus thrombophlebitis. In this condition, the drainage of blood from the central nervous system becomes impaired and infection may spread further into the cerebellum or the brainstem, leading to life-threatening issues.
• Floor: It is formed by the mastoid bone and communicates with the mastoid air cells.

3. MacEwen’s Triangle (Suprameatal Triangle)

MacEwen’s triangle is an important external landmark for the mastoid antrum. You can define its boundaries:

• Superiorly: The linea temporalis (temporal line), a ridge of bone extending posteriorly from the zygomatic process, which marks the lower border of the temporalis muscle and approximates the floor of the middle cranial fossa.
• Anteriorly: The posterosuperior margin of the external auditory canal (EAC).
• Posteriorly: A tangent to the posterior margin of the EAC.

Boundaries of Macewen’s triangle

4. The Mastoid Air Cell System

The mastoid process itself contains a “honeycomb” of air cells beneath its bony cortex. The extent of this pneumatization varies significantly among individuals.

• Types of Mastoid Pneumatization:
  1. Well-pneumatized (Cellular): Characterised by well-developed air cells with thin intervening bony septa. This is the most common type.
  2. Diploetic: Contains marrow spaces and only a few scattered air cells.
  3. Sclerotic (Acellular): Lacks both air cells and marrow spaces, appearing as dense bone. This type is often associated with chronic mastoid infections.
• Antrum Presence: Regardless of the pneumatization type, the mastoid antrum is always present. In sclerotic mastoids, the antrum is usually small, and the sigmoid sinus may be anteposed (positioned more anteriorly), increasing surgical risk. Abscesses can form in relation to these air cells, sometimes far from the main mastoid region.

5. Classification of Mastoid Air Cells by Location

Mastoid air cells are named based on their anatomical location:

• Zygomatic cells are present in the root of zygoma.
• Tegmen cells are present in the tegmen tympani.
• Perisinus cells are present in the the sinus plate.
• Retrofacial cells are present around the facial nerve.
• Perilabyrinthine cells are present above, below and behind the labyrinth.
• Peritubal are present around the eustachian tube.
• Tip cells are present medial and lateral to the digastric ridge in the tip of mastoid.
• Marginal cells are present behind the sinus plate and may extend into the occipital bone.
• Squamosal cells are present in the squamous part of temporal bones.

6. Korner’s Septum (Petrosquamosal Suture)

Squamous and petrous parts of temporal bone together form the mastoid.

• Description: In some individuals, the petrosquamosal suture persists as a distinct bony plate known as Korner’s septum. This septum separates superficial squamosal cells from deeper petrosal cells.
• Surgical Importance: Korner’s septum causes difficulty in locating the antrum and the deeper cells. Removal of Korner’s septum is a must in order to reach the mastoid antrum during surgery. Otherwise, it will lead to incomplete removal of the disease at mastoidectomy.

EAR OSSICLES.

There are three ossicles in the middle ear – the malleus, incus and stapes. The ossicles form a semi-rigid osseous chain across the middle ear from the tympanic membrane to the oval window of the internal ear. The malleus is the most lateral ossicle and it is attached to the tympanic membrane, whereas the stapes ossicle is attached to the oval window. The ossicles conduct sound energy from the tympanic membrane to the oval window. Muscles related to the auditory ossicles modulate movement during the transmission of vibrations from the tympanic membrane.

Malleus (hammer): The malleus is the largest ossicle. It measures 8-9 mm in length. Parts of malleus include the head of the malleus, neck of the malleus, anterior and lateral processes, and handle of the malleus(manubrium).

1. Head: The head of the malleus is the rounded upper part of the malleus which lies in the attic region. It is suspended by the superior ligament, which runs upwards to the tegmen tympani.  Its saddle-shaped posterior surface articulates with the body of the incus by a synovial joint.
2. Neck: Inferior to the head of the malleus is the constricted neck of the malleus which also lies in the attic region. The chorda tympani and tendon of tensor tympani lie below the neck of malleus, hence amputation of the head of malleus by cutting through the neck leaves both chorda tympani and tensor tympani intact.
3. Anterior process: Below the neck of malleus there are the anterior and lateral processes. The anterior process is attached to the anterior wall of the middle ear by a ligament.
4. Lateral process: The lateral process forms a knob-like projection on the outer surface of the tympanic membrane is attached to the anterior and posterior malleolar folds of the tympanic membrane.
5. Handle of malleus: Below the anterior and lateral processes, is the handle of the malleus, which is embedded in the fibrous layer of the tympanic membrane. Tendon of the tensor tympani muscle inserts on the medial surface of the handle. Chorda tympani crosses the handle of malleus just above the insertion of the tensor tympani muscle.

Incus (Anvil). It is the second bone in the series of ear ossicles. Parts of malleus include the body of the incus and long and short process.

1. Body. It articulates with the head of the malleus and lie in the attic. It is suspended by the superior incudal ligament coming from tegmen tympani.
2. Short process. The short process projects backwards to lie in the fossa incudes. It is attached by a short suspensory ligament to the upper posterior wall of the middle ear.
3. Long process. It hangs vertically downward into the mesotympanum almost parallel to the handle of the malleus. Tip of incus also known as the lenticular process and  is at times been called the fourth ossicle because of its incomplete fusion with the tip of the long process. The lenticular process articulates with the head of the stapes and forms incudostapedial joint.

Stapes (stirrup): The stapes is the third and smallest bone in the ossicular chain. It measures about 3.5 mm.  It is attached to the oval window by annular ligament. Parts of malleus include the head, neck, anterior and posterior crura and footplate.

MUSCLES ASSOCIATED WITH THE OSSICLES. There are two middle ear muscles: tensor tympani and the stapedius.

Muscles associated with the ossicles

• Stapedius muscle. The stapedius arises from the apex of pyramid, which is a small projection on the posterior (mastoid) wall of the middle ear and passes forward to attach to the posterior surface of the neck of the stapes. In response to loud sounds (80 dB and above), the stapedius muscle contracts, pulling the stapes posteriorly, hereby dampens the loud sounds and prevents noise trauma to the inner ear (acoustic reflex). Stapedius is a second arch muscle and is supplied by nerve to stapedius which is a branch of CN VII.
• Tensor tympani muscle. This is a long, slender muscle arising from the bony canal present on the anterior wall of middle ear. It is present above the opening of eustachian tube. Its tendon turns through a right angle round the processus cochleariformis and passes laterally and insert into the medial aspect of the upper end of the handle of malleus.  It tenses the tympanic membrane. Contraction of the tensor tympani pulls the handle of the malleus medially. This tenses the tympanic membrane, reducing the force of vibrations in response to loud noises. The muscle develops from the first arch and is supplied by medial pterygoid branch of mandibular nerve (V3).

TYMPANIC PLEXUS

Tympanic plexus

The tympanic plexus innervates the the medial surface of the tympanic membrane, tympanic cavity, mastoid air cells and the bony eustachian tube.

The tympanic plexus lies on the promontory and is formed by the

• Tympanic branch of glossopharyngeal and
• Caroticotympanic nerves (sympathetic fibres) from the plexus round the internal carotid artery. 

The tympanic plexus also gives off a major branch (the lesser petrosal nerve), which supplies preganglionic para-sympathetic fibers to the otic ganglion. Tympanic branch of glossopharyngeal nerve carries secretomotor fibres for the parotid gland. Section of tympanic branch of glossopharyngeal nerve can be carried out in the middle ear in cases of Frey’s syndrome.

Course of secretomotor fibres to the parotid:

Inferior salivary nucleus → CN IX → Tympanic branch → Tympanic plexus → Lesser petrosal nerve → Otic ganglion → Auriculotemporal nerve → Parotid gland.

CHORDA TYMPANI NERVE

It is a branch of the facial nerve. It enters the middle ear through posterior canaliculus at the junction of the lateral and posterior walls of middle ear. It runs on the medial surface of the tympanic membrane between its mucosal and fibrous layers. On malleus, it runs medially just below the neck of malleus and above the attachment of tendon of tensor tympani. It further continue forwards and leave the middle ear through anterior canaliculus. It carries taste sensation from anterior two-thirds of tongue and supplies secretomotor fibres to the submaxillary and sublingual salivary glands.

MIDDLE EAR CLEFT MUCOSA

The middle ear mucosa is essentially mucus-secreting respiratory mucosa bearing cilia on its surface. Mucosa of the nasopharynx is continuous with that of the middle ear cleft. The mucosa wraps ossicles, muscles, ligaments and nerves in a similar way as peritoneum wraps various viscera in the abdomen – raising several mucosal folds and dividing the middle ear into various compartments. So, all the middle ear structures lie outside the mucous membrane. Middle ear contains nothing but the air; all the structures lie outside the mucous membrane. Mucous membrane of the nasopharynx is continuous with that of the middle ear cleft.

Histologically, the eustachian tube is lined by ciliated epithelium, which is pseudostratified columnar in the cartilaginous part, columnar in the bony part with several mucous glands in the submucosa. Tympanic cavity is lined by ciliated columnar epithelium in its anterior and inferior part which changes to cuboidal type in the posterior part. Epitympanum and mastoid air cells are lined by flat, non-ciliated epithelium.

COMPARTMENTS AND FOLDS OF MIDDLE EAR. Ossicles and their mucosal folds separate mesotympanum from epitympanum (attic).

 

1.	Compartments of Epitympanum	a. Prussak’s space: Its boundaries, which limit spread of infection to other compartments, are following: – Lateral: Pars flaccida – Medial: Neck of malleus – Floor: Lateral process of malleus – Roof: Ligament arising from neck of malleus
		b. Attic compartments: Cog divides attic into two compartments – smaller anterior epitympanum and larger posterior epitympanum. The space between the lateral malleolar fold and lateral incudal fold provides communication with Prussak’s space.
2.	Compartments of Mesotympanum	Inferior incudal space: Its boundaries are following – Superior: Lateral incudal fold – Medial: Medial incudal fold – Lateral: Posterior malleolar fold – Anterior: Interossicular fold
		Anterior pouch of von Troeltsch: It lies between the following boundaries:  – Medial: Anterior malleolar fold – Lateral: Portion of the tympanic membrane anterior to handle of malleus
		Posterior pouch of von Troeltsch: It is situated between the following boundaries: – Medial: Posterior malleolar fold – Lateral: Portion of the tympanic membrane posterior to handle of malleus.

BLOOD SUPPLY OF MIDDLE EAR

Middle ear is supplied by eight arteries, out of which two are the main, i.e.

1. Anterior tympanic branch of maxillary artery which supplies tympanic membrane, malleus, incus and anterior part of tympanic cavity.
2. Stylomastoid branch of posterior auricular artery which supplies stapedius muscle and posterior part of tympanic cavity.

Six minor vessels are:

1. Mastoid branch of stylomastoid artery which supplies mastoid air cells.
2. Petrosal branch of middle meningeal artery (runs along greater petrosal nerve) which supplies the roof of mastoid and epitympanum.
3. Superior tympanic branch of middle meningeal artery which supplies the canal for tensor tympani muscle, malleus and incus.
4. Inferior tympanic branch of ascending pharyngeal artery which supplies the mesotympanum.
5. Branch of artery of pterygoid canal (runs along eustachian tube) which supplies the mesotympanum and hypotympanum
6. Tympanic branch of internal carotid which supplies the mesotympanum and hypotympanum

Branch	Parent artery	Region supplied
Anterior tympanic	Maxillary artery	Tympanic membrane Malleus and incus Anterior part of tympanic cavity
Stylomastoid	Posterior auricular	Posterior part of tympanic cavity Stapedius muscle
Mastoid	Stylomastoid	Mastoid air cells
Petrosal	Middle meningeal	Roof of mastoid Roof of epitympanum
Superior tympanic	Middle meningeal	Malleus and incus Tensor tympani
Inferior tympanic	Ascending pharyngeal	Mesotympanum
Branch from artery	Artery of pterygoid canal	Meso- and hypotympanum
Tympanic arches	Internal carotid	Meso- and hypotympanum

Veins drain into pterygoid venous plexus and superior petrosal sinus.

LYMPHATIC DRAINAGE OF EAR

The lymphatics of middle ear drain into retropharyngeal and parotid nodes. Eustachian tube lymphatics drain into retropharyngeal group of lymph nodes. Internal ear does not have any lymphatics.

 

———— End of the chapter ————

High-Yield Points for NEET PG and University Exams

Memorize these key facts for quick recall during exams and vivas:

• Middle Ear Cleft: Always remember it’s one continuous space (Eustachian tube to mastoid air cells).
• Tegmen Tympani: Roof of middle ear, separates from middle cranial fossa. Very thin, risk of intracranial complications if breached.
• Jugular Wall: Floor of middle ear, related to internal jugular vein. Potential for dehiscence.
• Anterior Wall: Related to internal carotid artery and has openings for Eustachian tube and tensor tympani.
• Posterior Wall: Features pyramid (for stapedius), facial nerve course, and the surgically important facial recess.
• Lateral Wall: Formed by tympanic membrane and scutum. Scutum erosion is a hallmark of cholesteatoma.
• Medial Wall: Dominated by promontory (over cochlea), oval window (stapes footplate), round window, and facial nerve canal.
• Processus Cochleariformis: Landmark for tensor tympani turn and 1st genu of facial nerve.
• Sinus Tympani: A deep, hidden recess in the posterior medial wall, common site for cholesteatoma recurrence.
• MacEwen’s Triangle: External landmark for mastoid antrum.
• Korner’s Septum: Persistent petrosquamosal suture, important surgical landmark in mastoidectomy, can hide disease.
• Malleus & Incus: Move as a unit, articulate with each other. Malleus handle embedded in TM.
• Stapes: Smallest bone, footplate in oval window.
• Stapedius Muscle: Innervated by Facial Nerve (CN VII), dampens loud sounds (acoustic reflex). Originates from 2nd arch.
• Tensor Tympani Muscle: Innervated by Mandibular Nerve (V3 of CN V), tenses TM. Originates from 1st arch.
• Chorda Tympani Nerve: Branch of CN VII, carries taste (ant. 2/3 tongue) and secretomotor to submandibular/sublingual glands. Crosses medial to malleus neck/handle.
• Tympanic Plexus: On promontory, formed by Jacobson’s nerve (CN IX) and sympathetic fibers. Innervates middle ear mucosa. Gives off Lesser Petrosal Nerve (to parotid).
• Mucosa: Continuous from nasopharynx. Variable histology (ciliated columnar to flat cuboidal).
• Prussak’s Space: Clinically vital, location of pars flaccida cholesteatoma origin.

 

MCQs – Anatomy of Middle Ear

Test your knowledge with these practice questions.

Q1. A 10-year-old boy presents with a 2-month history of ear discharge and hearing loss. HRCT temporal bone reveals scutum erosion and a soft tissue mass in the attic. Which compartment is most likely involved?

1. Hypotympanum
2. Epitympanum
3. Mesotympanum
4. Protympanum

Q2. During middle ear surgery for cholesteatoma, a surgeon carefully inspects the anterior epitympanum. What structure divides the attic into anterior and posterior compartments?

1. Promontory
2. Ponticulus
3. Cog
4. Processus cochleariformis

Q3. A child presents with congenital dehiscence of the floor of the middle ear, exposing the jugular bulb. Which wall of middle ear is deficient?

1. Roof (tegmental wall)
2. Floor (jugular wall)
3. Anterior wall (carotid wall)
4. Medial wall (labyrinthine wall)

Q4. The nerve that enters through the floor of the middle ear is:

1. Chorda tympani
2. Facial nerve
3. Jacobson’s nerve
4. Lesser petrosal nerve

Q5. A cochlear implant surgeon accesses the middle ear through facial recess approach. The facial recess is bounded:

1. Laterally by facial nerve, medially by chorda tympani
2. Medially by facial nerve, laterally by chorda tympani
3. Superiorly by oval window, inferiorly by pyramid
4. Superiorly by eustachian tube, inferiorly by promontory

Q6. A patient has taste disturbances and dry mouth following middle ear surgery. The likely injured structure is:

1. Jacobson’s nerve
2. Lesser petrosal nerve
3. Chorda tympani nerve
4. Greater petrosal nerve

Q7. The stapedius muscle originates from which bony projection of the posterior wall?

1. Pyramid
2. Ponticulus
3. Subiculum
4. Fossa incudis

Q8. In a child with recurrent acute otitis media, infection can spread directly to the brain due to thin bone separating middle ear from cranial cavity. This bone is called:

1. Tegmen tympani
2. Scutum
3. Promontory
4. Processus cochleariformis

Q9. In a HRCT scan of the mastoid, a large, well-developed mastoid antrum is seen communicating with attic via:

1. Sinus tympani
2. Aditus ad antrum
3. Facial recess
4. Round window niche

Q10. Which of the following is the smallest ossicle?

1. Malleus
2. Incus
3. Stapes
4. Lenticular process

Q11. A patient develops sigmoid sinus thrombosis as a complication of mastoiditis. Which mastoid wall separates mastoid antrum from sigmoid sinus?

1. Roof (tegmen antri)
2. Lateral wall (suprameatal triangle)
3. Posterior wall
4. Medial wall

Q12. Korner’s septum, if not removed completely during mastoidectomy, may lead to:

1. Sigmoid sinus thrombosis
2. Facial nerve injury
3. Incomplete disease clearance
4. Perilymphatic fistula

Q13. A child with congenital cholesteatoma has erosion of lateral attic wall on HRCT. Which structure is primarily involved?

1. Scutum
2. Ponticulus
3. Sinus tympani
4. Fossa incudis

Q14. In middle ear surgeries, which compartment lies directly below pars tensa?

1. Hypotympanum
2. Mesotympanum
3. Epitympanum
4. Protympanum

Q15. Taste sensation from anterior 2/3rd of tongue passes through:

1. Glossopharyngeal nerve
2. Lesser petrosal nerve
3. Chorda tympani nerve
4. Greater petrosal nerve

Answer Key with Detailed Explanations

Q1 → B. Epitympanum. Explanation: Cholesteatomas commonly originate in the epitympanum (attic), particularly when the scutum is eroded.

Q2 → C. Cog. Explanation: The cog divides the attic into anterior and posterior compartments, important during cholesteatoma surgery.

Q3 → B. Floor (jugular wall). Explanation: Congenital dehiscence of the jugular wall may expose the jugular bulb, posing surgical risks.

Q4 → C. Jacobson’s nerve. Explanation: The tympanic branch of glossopharyngeal nerve (Jacobson’s nerve) enters through the floor (jugular wall).

Q5 → B. Medially by facial nerve, laterally by chorda tympani. Explanation: The facial recess is bounded medially by facial nerve and laterally by chorda tympani — key for safe cochlear implant access.

Q6 → C. Chorda tympani nerve. Explanation: Chorda tympani carries taste fibers from anterior 2/3 tongue and secretomotor fibers to submandibular and sublingual glands.

Q7 → A. Pyramid. Explanation: The stapedius arises from the pyramid on the posterior wall, controlling stapes movement.

Q8 → A. Tegmen tympani. Explanation: Thin tegmen tympani separates middle ear from temporal lobe. Its dehiscence can cause intracranial spread of infection.

Q9 → B. Aditus ad antrum. Explanation: The mastoid antrum communicates with the attic through the aditus ad antrum.

Q10 → C. Stapes. Explanation: Stapes is the smallest ossicle (approx. 3.5 mm); it transmits sound vibrations to oval window.

Q11 → C. Posterior wall. Explanation: Posterior wall of mastoid antrum separates it from sigmoid sinus. Infection breach can cause sigmoid sinus thrombophlebitis.

Q12 → C. Incomplete disease clearance. Explanation: Korner’s septum may hide deeper petrosal air cells; failure to remove it leads to incomplete clearance.

Q13 → A. Scutum. Explanation: The scutum, thin bony lateral attic wall, is eroded early in attic cholesteatoma.

Q14 → A. Hypotympanum. Explanation: Hypotympanum lies below pars tensa, mesotympanum lies directly behind it.

Q15 → C. Chorda tympani nerve. Explanation: Chorda tympani (branch of CN VII) carries taste from anterior 2/3rd tongue.

 

Clinical-Based Questions for Practical Exams and Viva

These scenarios help you connect anatomical knowledge to real-world clinical presentations.

1. Scenario: A 45-year-old male with a history of chronic otitis media presents with severe headache, fever, and altered sensorium. Imaging reveals an extradural abscess in the middle cranial fossa, originating from the middle ear.
   • Questions:
     • Which specific anatomical boundary of the middle ear was likely breached, leading to this intracranial complication?
     • Explain the anatomical relationship that allowed this spread.
     • What other intracranial complications could arise from similar breaches of the middle ear boundaries?
2. Scenario: During a radical mastoidectomy for extensive cholesteatoma, the surgeon encounters difficulty locating the mastoid antrum and deeper air cells, finding a dense bony plate obstructing access. The patient has a history of recurrent ear discharge.
   • Questions:
     • What anatomical variant is the surgeon likely encountering?
     • Why is it crucial to identify and remove this structure during mastoidectomy for cholesteatoma?
     • Name one external anatomical landmark you would use to locate the mastoid antrum.
3. Scenario: A patient undergoing tympanoplasty develops a complaint of altered taste sensation on the anterior part of their tongue and reduced salivation immediately after surgery.
   • Questions:
     • Which specific nerve in the middle ear was most likely injured during the procedure?
     • Describe the typical course of this nerve through the middle ear cavity that makes it vulnerable to iatrogenic injury.
     • What are the two main functions of this nerve?
4. Scenario: A 5-year-old child presents with a cholesteatoma originating from the pars flaccida. On examination, the lesion appears to be expanding within a confined space.
   • Questions:
     • Name the specific anatomical space in the epitympanum where this type of cholesteatoma typically originates and expands.
     • List the key boundaries of this space.
     • Why is this space particularly significant in cholesteatoma pathology?

 

Frequently Asked Questions (FAQs)

Here are some common questions about middle ear anatomy, optimized for Google Rich Snippets:

• Q: What are the main divisions of the middle ear cavity?
  • A: The middle ear cavity is traditionally divided into three parts: the epitympanum (attic) superiorly, the mesotympanum centrally, and the hypotympanum inferiorly.
• Q: Which structures form the ossicular chain in the middle ear?
  • A: The ossicular chain consists of three small bones: the malleus (hammer), incus (anvil), and stapes (stirrup), which transmit sound vibrations.
• Q: What is the clinical significance of the tegmen tympani?
  • A: The tegmen tympani is the thin bony roof of the middle ear that separates it from the middle cranial fossa; its breach can lead to intracranial complications like meningitis or brain abscess.
• Q: Which cranial nerve innervates the tensor tympani muscle?
  • A: The tensor tympani muscle is innervated by the medial pterygoid branch of the mandibular nerve (V3), which is a division of the Trigeminal nerve (CN V).
• Q: Where is Prussak’s space located, and why is it important?
  • A: Prussak’s space is a crucial compartment in the epitympanum (attic), bounded by the pars flaccida, neck, and lateral process of the malleus. It is a common site for the origin and initial expansion of pars flaccida cholesteatoma.
• Q: What is the function of the stapedius muscle, and what is its nerve supply?
  • A: The stapedius muscle dampens loud sounds by pulling the stapes posteriorly (acoustic reflex) and is innervated by the nerve to stapedius, a branch of the Facial Nerve (CN VII).
• Q: What are the two main functions of the chorda tympani nerve?
  • A: The chorda tympani nerve carries taste sensation from the anterior two-thirds of the tongue and provides secretomotor innervation to the submandibular and sublingual salivary glands.

 

Practical Tips for Viva and Clinical Exam Scenarios

• Master the Boundaries: Examiners frequently ask you to describe the “six walls of the middle ear.” Know the name of each wall, its key anatomical relations (e.g., roof-temporal lobe, anterior-carotid artery, floor-jugular bulb), and crucial structures on it (e.g., oval window on medial wall, pyramid on posterior wall).
• Clinical Correlates are Gold: For every anatomical structure, think of a clinical pathology.
  • Tegmen tympani breach -> intracranial complications.
  • Scutum erosion -> cholesteatoma.
  • Facial nerve dehiscence -> iatrogenic injury.
  • Prussak’s space -> pars flaccida cholesteatoma.
  • Korner’s septum -> surgical challenge in mastoidectomy.
• Nerves & Muscles: Know the innervation and function of the middle ear muscles (Stapedius-CN VII, Tensor Tympani-CN V3). Be prepared to discuss the course and function of the Chorda Tympani and Tympanic Plexus. Expect questions on Frey’s syndrome related to the tympanic plexus.
• Surgical Landmarks: Identify and describe MacEwen’s triangle and the Facial Recess. Explain their importance for surgical access (e.g., “This is the entry point for the posterior tympanotomy approach”).
• Visualizing on Otoscopy: When describing the lateral wall, connect it to what you see during otoscopy (e.g., “The malleus handle is visible through the pars tensa”).
• “Show me on the model/skull”: In practical exams, be ready to point out all these structures on a temporal bone or a model. Practice tracing nerve courses (e.g., facial nerve, chorda tympani) and identifying ossicles.
• Blood Supply Mnemonic: Remember the two main arteries first (Anterior Tympanic from Maxillary, Stylomastoid from Posterior Auricular).

———— End ————

Download full PDF Link:

Anatomy of Middle Ear Walls Best Lecture Notes Dr Rahul Bagla ENT Textbook

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Anatomy of Ear Best PPT Notes Lectures Dr Rahul Bagla ENT Textbook

Reference Textbooks.

• Scott-Brown, Textbook of Otorhinolaryngology-Head and Neck Surgery.
• Glasscock-Shambaugh, Textbook of Surgery of the Ear.
• P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
• Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
• Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck Surgery
• Hans Behrbohm, Textbook of Ear, Nose, and Throat Diseases With Head and Neck Surgery.
• Salah Mansour, Middle Ear Diseases – Advances in Diagnosis and Management.
• Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
• Rob and smith, Textbook of Operative surgery.
• Anirban Biswas, Textbook of Clinical Audio-vestibulometry.
• Arnold, U. Ganzer, Textbook of  Otorhinolaryngology, Head and Neck Surgery.

Author:

Dr. Rahul Bagla
MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
Fellow Rhinoplasty & Facial Plastic Surgery.
Renowned Teaching Faculty
Mail: msrahulbagla@gmail.com
India

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