ENT (Otorhinolaryngology) · MU Sofia

1. Clinical anatomy of the external and middle ear.

Covers the clinical anatomy of the external ear, namely the auricle and external auditory canal, then the tympanic membrane, and moves on to the middle ear cavity, its boundaries, ossicles, middle ear muscles, passing nerves and the Eustachian tube. Blood and nerve supply, clinical presentations such as perichondritis, otitis externa and otosclerosis, and the relevant clinical significance are noted throughout, with landmark lists and a regional breakdown of the tympanic cavity.

Inside: 3 sections · 6 labelled pictures · 15 flashcards · 6 min

Topic 1 of 52 in the MU Sofia syllabus for ENT (Otorhinolaryngology) (Medicine, Year 4). The free AceMed note covers it in 3 sections, about 924 words (6 min of reading), with 15 flashcards.

In this note

  1. Clinical anatomy of the external and middle ear.
  2. Clinical anatomy of the external ear
  3. Clinical anatomy of the middle ear (tympanic cavity)

Clinical anatomy of the external ear

The external ear includes the auricle (pinna) and the External Auditory Canal (EAC), terminating at the lateral surface of the tympanic membrane (eardrum).

A. Auricle (Pinna)

  • Structure: Primarily composed of elastic cartilage, covered by skin. The lobule is the only part without cartilage. Key landmarks include the helix, antihelix, tragus, antitragus, and concha.
  • Clinical Significance:
  • Auricular Hematoma: A collection of blood between the perichondrium and cartilage, often due to trauma. If untreated, it can lead to avascular necrosis of the cartilage, resulting in a permanent deformity known as "Cauliflower Ear."
  • Perichondritis: Infection of the perichondrium, potentially destroying the cartilage framework.
  • Basal cell carcinoma (sun-exposed areas)
  • Blood supply: superficial temporal + posterior auricular aa (branches of ECA)
  • Rich anastomoses → auricle bleeds heavily but heals well.
  • Nerve supply:
  • Sensory: Great auricular nerve→ most of pinna
  • Auriculotemporal nerve→ tragus & anterior part (clinical: TMJ disease can produce ear pain).
  • Arnold’s nerve (X auricular branch) → posterior canal & concha (clinical: stimulation causes cough reflex during ear exam (vasovagal response)).

B. External Auditory Canal (EAC)

  • Structure: A sigmoid (S-shaped) tube, about 2.5 cm long in adults.
  • Outer 1/3 is cartilaginous, containing hair follicles, sebaceous glands, and specialized ceruminous glands (producing earwax/cerumen). Narrowestpartis the isthmus.
  • Inner 2/3 is bony, formed by the temporal bone (tympanic plate). This area is highly sensitive.
  • Epithelial Migration: The skin lining the EAC has a unique ability to migrate laterally, moving cerumen and debris out of the canal. Failure of this mechanism can lead to cerumen impaction or cholesteatoma formation.
  • Innervation (Clinically Critical): same as auricle
  • Clinical Significance:
  • Due to the S-shape, the canal must be straightened (pulling the auricle upward and backward in adults or downward & backward (children) to straighten.) for proper visualization.
  • Otitis Externa: Inflammation/infection often confined to the cartilaginous part.
  • Bony Exostoses: Benign bony growths in the inner EAC, common in cold water swimmers.

C. Tympanic Membrane (TM)

  • Structure: Separates the EAC from the middle ear cavity. It has three layers: outer epithelial, middle fibrous, and inner mucosal. Oblique position, 1 cm in diameter.
  • Pars Tensa: Most of the TM, which is tense and has all three layers. The cone of light is visible in the anteroinferior quadrant upon otoscopy.
  • Pars Flaccida (Shrapnell's membrane): A small, superior area where the fibrous layer is deficient.
  • Landmarks: Handle of Malleus (manubrium), Lateral Process of Malleus, and the Umbo (center).
  • Clinical Significance:

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