Middle ear Anatomy

Middle ear Anatomy


MIDDLE EAR

  • Mesotympanum – part of middle ear lying opposite to pars tensa (narrowest part)
  • Epitympanum or attic – lying above pars tensa but medial to Shrapnell’s membrane
  • Hypotympanum – lying below the level of pars tensa
  • Protympanum – around the tympanic orifice of Eustachian tube

BOUNDARIES OF MIDDLE EAR

Roof (tegmental wall):

  • Tegmen tympani
  • It separates middle ear from middle cranial fossa containing Temporal Lobe of Brain.
  • Floor (jugular wall): bone which separates middle ear from the bulb of internal jugular vein.
  • Lateral wall : formed largely by Tympanic Membrane; To a lesser extent by bony outer attic wall (scutum).
  • The chorda tympani nerve is related to the lateral wall.
  • The distance between tympanic membrane and medial wall of middle ear at the level of center is 4 mm.
  • Anterior wall: Bone which separates middle ear from internal carotid artery. It has 2 openings
  • Upper opening contains canal for tensor tympani
  • Lower Opening contains canal for Eustachian Tube.
  • The Eustachian tube(auditory tube )connects the nasopharynx with the anterior wall.

Posterior wall

  • Pyramid – bony projection where tendon of stapedius arises
  • Facial nerve runs in the posterior wall just behind the pyramid
  • Two recesses – Facial recess (suprapyramidal)and Sinus tympani (infrapyramidal)    
  • These recesses are the most common location of cholesteatoma persistence after ear surgery    
  • Sinus tympani is very difficult to access surgically

Facial recess is lateral to facial nerve and its relations are

  • Medial – pyramid
  • Lateral – posterosuperior meatal wall
  • Below – chorda tympani
  • Above – fossa incudis
  • Facial recess is important in cochlear implant and Middle ear can be approached through it.

 Medial wall: formed by labyrinth  

  • Promontory- formed by basal turn of cochlea.
  • Tympanic plexus formed by the tympanic branch of Glossopharyngeal Nerve is found over the promontory.
  • Sensory nerve supply of middle ear cavity is provided by Glossopharyngeal Nerve.
  • Oval window- foot plate of stapes fixed
  • Round window or fenestra cochlea- covered by secondary TM
  • Canal for facial nerve – above the oval window
  • Processus cochleariformis – anterior to oval window, marks the genu of facial nerve (landmark of surgery)
  • Prussak’s space
  • medially neck of malleus
  • laterally pars flaccida
  • above lateral process of malleus
  • anteriorly, posteriorly and superiorly by lateral malleal ligament

CONTENTS OF MIDDLE EAR

  • Ear ossicles – Malleus, Incus, Stapes (the smallest bone)
  • The joints between ossicles are synovial.
  • Bones of middle ear are responsible for reduction of impedance to sound transmission and conduct sound energy from the tympanic membrane to the oval window and then to the inner ear fluid
  1. Ligaments of ear ossicles
  2. Muscles – Tensor tympani and Stapedius
  3. Vessels of Middle ear
  4. Nerves – Chorda tympani and tympanic plexus.

Referred pain from tonsil to middle ear is due to Glossopharyngeal Nerve.

ARTERIAL SUPPLY OF MIDDLE EAR

  • Anterior tympanic branch – from maxillary artery
  • Posterior tympanic branch – from posterior auricular artery.

CONTENTS OF MIDDLE EAR CLEFT

  1. Eustachian tube
  2. The middle ear (tympanic cavity)
  3. Aditus which leads posteriorly to the mastoid antrum and air cells

LYMPHATIC DRAINAGE OF MIDDLE EAR

  • Retropharyngeal Lymph Nodes-Upper Jugular Chain

CLINICAL SIGNIFICANCE OF MIDDLE EAR.

  • Nitrous Oxide should be avoided during Middle ear Surgery.
  • The structure injured by the primary blast wave, in order of prevalence, are the Middle ear, the lung, and the bowel.
  • Teunissen’s classification is used in classification of congenital anomalies of Middle ear.
  • Middle ear structures which are of adult size at the time of Birth are all three ossicles,the middle ear cavity, the oval window, round window.
  • The conclusion post mortem finding of death by drowning is presence of water in the middle ear.
  • Most common bony tumour of middle ear is Squamous Cell Carcinoma. 
  • Treatment of carcinoma of middle ear is combination of surgery followed by radiotherapy.
  • Surgery of carcinoma of middle ear consists of radical mastoidectomy / subtotal or total petrosectomy depending on the extent of tumor.
  • Treatment of middle ear papilloma is Tympanomastoidectomy.

Exam Question

  • Referred pain from tonsil to middle ear is due to Glossopharyngeal Nerve.
  • Nitrous Oxide should be avoided during Middle ear Surgery.
  • The structure injured by the primary blast wave, in order of prevalence, are the middle ear, the lung, and the bowel.
  • The joints between ossicles are synovial.
  • The chorda tympani nerve is related to the lateral wall of Middle ear.
  • The Eustachian tube(auditory tube )connects the nasopharynx with the anterior wall of Middle ear.
  • Middle ear structures which are of adult size at the time of Birth are all three ossicles,the middle ear cavity, the oval window, round window. 
  • The facial nerve passes in a canal situated in the posterior and medial walls of the middle ear.
  • Teunissen’s classification is used in classification of congenital anomalies of Middle ear.
  • The conclusion post mortem finding of death by drowning is presence of water in the middle ear.
  • Floor of middle ear cavity is in relation with bulb of the internal jugular vein
  • The distance between tympanic membrane and medial wall of middle ear at the level of center is 4 mm.
  • Sensory nerve supply of middle ear cavity is provided by Glossopharyngeal Nerve.
  • Tegmen seperates middle ear from the middle cranial fossa containing temporal lobe of brain by roof of the Middle ear.
  • Narrowest part of middle ear is Mesotympanum.
  • Promontory seen in the middle ear is the Basal turn of Cochlea.
  • Eustachian Tube opens in the Middle ear cavity at the Anterior wall.
  • Lateral wall of middle ear is formed by Tympanic Membrane.
  • Bones of middle ear are responsible for reduction of impedance to sound transmission and and conduct sound energy from the tympanic membrane to the oval window and then to the inner ear fluid.
  • Scutum is present in Lateral Wall of Middle ear.
  • Treatment of middle ear papilloma is Tympanomastoidectomy.
  • Contents of Middle ear Cleft include Eustachian Tube,Middle ear,Aditus which leads to Mastoid Antrum and Air cells.
  • Most common bony tumour of middle ear is Squamous Cell Carcinoma.
  • Treatment of carcinoma of middle ear includes Surgery consisting of radical mastoidectomy / subtotal or total petrosectomy.
  • Tendon of Stapedius muscle passes through the pyramid in middle ear
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