Specialist ENT MIDDLE EAR CLEFT

MIDDLE EAR CLEFT

Definition: The middle ear cleft is a space which consists of the middle ear cavity or tympanic cavity, the Eustachian tube, the mastoid air cell system and the mucosal lining the system.

Specialist ENT Screenshot 2020 11 18 Ear final book document

Middle Ear Cavity

The tympanic cavity is irregular, air-filled space within the temporal bone, between the tympanic membrane laterally and the osseous labyrinth of inner ear medially. It is six-sided cavity having:
  • Roof.
  • Floor.
  • Anterior Wall.
  • Posterior Wall.
  • Medial Wall.
  • Lateral Wall.
It contains auditory ossicles (Malleus, Incus and Stapes) and intratympanic muscles (Tensor tympani muscle and Stapedius). Division of Middle Ear Cavity Epitympanum / Attic- It is a space in middle ear cavity above the level of anterior and posterior malleolar folds (above the upper margin of tympanic annulus). It contains head of malleus, body of incus, ossicular ligaments and mucosal folds. Prussack Space is a space between Pars flaccida laterally, neck of malleus medially, lateral malleal fold superiorly and lateral process of malleus inferiorly. It is the primary site of Acquired Cholesteatoma. Mesotympanum- It is a part lying medial to Pars Tensa, between epitympanum superiorly and hypotympanum inferiorly. It is an air-filled space, contains handle of malleus, long process of Incus and stapes. Hypotympanum– It is a part lying below the lower margin of tympanic annulus. It contains a bulge produced by the jugular bulb. If the floor of hypotympanum is deficient thus jugular bulb may project into tympanic cavity.
Specialist ENT ear 5
  1. Roof 
      ● Is a thin bony plate which separates the middle ear from the middle cranial fossa called as Tegmen tympani, formed by both the petrous and squamous portions of the temporal bone.
      ● Petrosquamous suture line, does not close until adult life and can provide a route of access for infection into the middle cranial fossa from middle ear in children.
  2. Floor
      • ● It is a thin bone separates the cavity from the dome of the Jugular bulb.
      ● In some case the floor may be deficient and the jugular bulb is then covered only by fibrous tissue and a mucous membrane.
  3. Lateral Wall
      ● Main part is formed by the tympanic membrane.
      ● Superiorly an area of bone called Scutum (outer attic wall).
      ● Three holes are present in the bone of the medial surface of the lateral wall of the tympanic cavity. The petrotympanic fissure is a slit about 2 mm long which opens anteriorly just above the attachment of the tympanic membrane. It receives
      • ➣ Anterior malleolar ligament.
        ➣ Anterior tympanic branch of the maxillary artery to the tympanic cavity.
        ➣ Chorda tympani nerve enters the medial surface of the fissure through a separate anterior canaliculus called the canal of Huguier.
  4. Medial Wall
      ● It separates the Middle ear from the Inner ear.
      ● Promontory is a bulging of on the medial wall which overlies the basal turn of the cochlea. It has a small groove on its surface containing the nerves which form the tympanic plexus.
      ● Oval Window lies behind and above the promontory and it connects the tympanic cavity with the vestibule, closed by the footplate of the stapes. It is 3.25 mm long and 1.75 mm wide.
      ● Round window- Round window membrane is usually out of sight, obscured by the overhanging edge of the promontory. It is 2.3 x 1.9 mm in dimension and lies in a plane at right angles to the plane of the stapes footplate.
      ● Facial Nerve canal (or Fallopian canal) runs above the promontory and oval window in an anteroposterior direction.
      ● Processus cochleariformis is a curved projection of bone on which the tendon of the tensor tympani muscle hooks and turns laterally to get attached to neck of malleus. This forms the landmark for 1st genu of facial nerve, which is posterosuperior to processus cochleariformis.
      • ● The upper-third is usually pneumatized and may house the anterior epitympanic sinus, a small niche anterior to the ossicular heads, which can hide residual cholesteatoma in canal wall up surgery.
      Anterior Wall
        ● The anterior wall of the tympanic cavity is rather narrow as the medial and lateral walls converge.
        ● The lower-third of the anterior wall consists of a thin plate of bone covering the internal carotid artery. This plate is perforated by the superior and inferior caroticotympanic nerves.
        ● The middle-third comprises of the tympanic orifice of the Eustachian tube, which is oval and 5 x 2mm in size.
        ● Just above this is a canal containing the tensor tympani muscle.
Specialist ENT Screenshot 2020 11 18 Ear final book document
vi Posterior Wall
  • The posterior wall is wider above than below.
  • Aditus is a large irregular opening in its upper part connecting middle ear to mastoid antrum.
  • Fossa incudis – A small depression below the aditus, it houses the short process of the incus and its suspensory ligament.
  • Pyramid is a small hollow conical projection with its apex pointing anteriorly. It houses the stapedius muscle and tendon, the tendon of which comes out of the pyramid and inserts into the posterior aspect of the neck of stapes.
  • Nerve to stapedius runs through the hollow canal within the pyramid.
  • Sinuses of Middle ear- The Posterior Tympanum is divided into four sinuses in relation to Facial nerve and Pyramidal process.
      ➣ Facial sinus- It is a sinus situated lateral to facial canal and above the pyramidal process.
      ➣ Lateral tympanic sinus- It is a sinus situated lateral to facial canal and below the pyramidal process.
      ➣ Posterior tympanic sinus- It is a sinus situated medial to facial canal and above the pyramidal process.
      ➣ Sinus tympani- It is a sinus situated medial to facial canal and below the pyramidal process.
Specialist ENT ear 8
Contents of the Middle Ear
Malleus
    • It is largest of the three ossicles (9mm length).
    • It has head, neck, anterior and lateral process, handle of malleus.
    • It is suspended by the superior ligament between head of malleus and the tegmen tympani.
    • Head has saddle-shaped facet on its posteromedial surface to articulate with the body of the incus.
    • An anterior ligament arises from the anterior process to insert into the petrotympanic fissure.
Incus 
    • It has a body, short process, long process and a lenticular process.
    • Body of the incus is suspended by the superior incudal ligament that is attached to the tegmen tympani.
    • Long process extends downwards behind the handle of malleus and articulates with the head of the stapes by its lenticular process.
    • Short process lodges in the fossa incudis.
    • Lenticular process also called the fourth ossicle because of its incomplete fusion with the tip of the long process of incus.
Stapes 
    • It is like a stirrup.
    • It consists of a head, neck, the anterior and posterior crura and a footplate.
    • The Head points laterally and has a small cartilage covered depression for a synovial articulation with the lenticular process of the incus.
    • The foot plate directs medially and closes the Oval window.
    • Stapedius tendon inserts into the posterior part of the neck and upper portion of the posterior crus.
Tympanic Plexus 
  • It lies over the promontory.
  • It is formed by Tympanic branch of Glossopharygeal Nerve (Jacobsons Nerve) and sympathetic fibers from plexus round Internal carotid artery.
  • It supplies Tympanic membrane (mucosal surface), Tympanic Cavity, Mastoid air cells, Bony eustachian tube.
  • Carries secretomotor fibers for the parotid gland.
Chorda Tympani Nerve 
  • It is a branch of Facial Nerve.
  • It carries the taste sensation from anterior 2/3rd of tongue and secretomotor fibers to     sub-maxillary and sub-lingual salivary glands.
  • It enters the medial surface of the petrotympanic fissure through a separate anterior canaliculus called Canal of Huguier.
  • It then runs posteriorly between the fibrous and mucosal layers of the tympanic membrane, across the upper part of the handle of the malleus and then continues within the membrane, but below the level of the posterior malleolar fold. The nerve reaches the posterior bony canal wall just medial to the tympanic sulcus and enters the posterior canaliculus and then runs obliquely downwards and medially through the posterior wall of the tympanic cavity until it reaches the facial nerve.
Tensor Tympani muscle 
  • Origin– cartilaginous part of Eustachian tube, Bony canal over Eustachian tube, greater wing of sphenoid.
  • Lies above the Eustachian tube and enters the middle ear via the canal for tensor tympani in the anterior wall above the Eustachian tube opening.
  • Hooks around the processes cochleariformis on the posterior wall and then changes the direction laterally and get inserted into neck of malleus.
  • Action- It tenses the tympanic membrane, by pulling the malleus medially and protects from barotrauma.
Stapedius Muscle 
  • Origin- From the Pyramid in the posterior wall.
  • Insertion- Neck of Stapes.
  • Supplied by Facial Nerve (Nerve to Stapedius).
  • Action- Pulls the Stapes laterally, thus preventing barotrauma.
Mastoid Process and Air Cells 
  • Mastoid Process is a part of temporal bone and situated behind the ear.
  • Develops by first year.
  • Based on the degree of pneumatisation.
    1. Cellular – 80% – Fully pneumatised
    2. Sclerotic – Cells are replaced by dense bones.
    3. Diploic – Cells are less and small.
  • Mastoid antrum is the biggest and most consistent air cell. It is connected anteriorly to tympanic cavity via the aditus and posteriorly to other air cells.
    1. Roof is formed by Tegmen antri which separates mastoid from middle cranial fossa.
    2. Floor is formed by mastoid portion of temporal bone.
    3. Medial wall is formed by Petrous portion of temporal bone.
    4. Lateral wall is formed by Squamous portion of temporal bone.
  • MacEwens triangle is a consistent landmark for mastoid antrum. It is bounded by Suprameatal crest above, anteriorly posterior margin of External auditory canal and a tangential line from posterior meatal wall cutting the supra meatal crest.
  • Antrum lies postero-superior to spine of Henle.
Eustachian Tube
  • Connects middle ear cavity to nasopharynx.
  • Extends from the anterior wall of middle ear, it passes downwards, forwards and medially.
  • Length is 36mm.
  • Lateral 1/3rd is bony and Medial 2/3rd is cartilaginous.
  • The pharyngeal end is situated 1 cm behind and a little below the end of inferior turbinate.
  • Functions-
    1. In resting stage, it is collapsed. On chewing and yawning it opens up. Helps to equalize air pressure between middle ear and nasopharynx.
    2. Controls ventilation of middle ear cleft.
    3. Helps drainage from middle ear.
  • Muscles attached to Eustachian tube includes Tensor tympani, Tensor veli palati, Levator veli palati and Salpingopharyngeus muscles.

We Are Always Ready to Help You.
Book An Appointment

Specialist ENT section img
Specialist ENT contact img