External Acoustic Meatus

1. External acoustic meatus
Dr Somnath Saha

3. What is it?
lIt is a tube that extends
from the concha of
auricle to tympanic
membrane medially

4. Parts and dimensions
lAverage:24 mm long
l cartitaginous part
lOuter
l8mm long
Bony part
lInner
l16 mm long

6. Shape
l's' shaped because of differing orientations of its
parts
lCartilaginous part runs inwards,slightly downards
and forwards
lBony part is directed backwards,upwards and
medially
lHence,canal is to be straightened in adults by
pulling the pinna backwards,upwards,and
outwards

7. Relations
lSuperior: Middle Cranial Fossa
lInferior:Parotid Gland
lAnterior:Temporomandibular joint
lPosterior:Mastoid air cells+Facial Nerve

10. Skin of the external acoustic meatus
lCartilaginous part
lThick
lWax secreting
ceruminous/pilosebaceo
us glands present
lBony part
lThin
lNo glands present

11. Functions
lAcoustic
lProvides the mechanism
for transmission of
sound to middle ear
lResonance of the
sound(particularly at the
frequency of 2kHz)
lNon acoustic
lProvides protection of
middle ear and inner ear
from trauma and
environmental insults

12. Routes for entry of infections
lCartilaginous Part
l2 fissures of santorini
lParotid/superficial
mastoid infections can
appear in canal/vice
versa
lBony part
lForamen of Huschke
lPermits infections to and
from the parotid

13. Nerve Supply
Auriculotemporal
nerve(from V3)
Auricular Branch of
Vagus(CN X,CN VII)
Anterior wall+roof
Posterior wall+floor

15. Blood supply-arterial
Laterally supplied by
the post auricular and
superficial temporal
arteries.
Medially it is supplied
by deep auricular artery
which is a branch of first
portion of the internal
maxillary artery

17. Drainage-Venous
Drainage occurs into
external jugular veins
Maxillary veins
Pterygoid venous
plexus

19. Drainage-Lymphatic
Preauricular nodes
Postauricular nodes
Cervical nodes

21. Thank you