Dr. T. Balasubramanian M.S. D.L.O.
Eustachean tube is otherwise known as pharyngotympanic tube,
middle ear ventilation tube. It is bony cartilagenous in nature. It
connects the middle ear with the nasopharynx. In adults it lies at an
angle of 45 degrees to the horizontal plane. In infants this
inclination is about 10 degrees. In adults its length is 38mm. For
descriptive purposes it can be divided into posterior 1/3 which is
osseus in nature and anterior 2/3 which is cartilagenous in nature.
This eustachean tube is shorter straighter and wider in
infants predisposing middle ear infections through this tube. The
osseus portion of the eustachean tube also known as protympanum lies
completely within the petrous portion of the temporal bone. The lumen
of the osseus portion of the eustachean tube is triangular and is open
always in contrast to the fibrocartilageous portion which is kept
closed at rest, and opens during swallowing, or during a valsalva
manuver. The osseous and cartilagenous portion of the eustachean tube
meet at an irregular bony portion and form an angle of about 160
degrees with each other. The cartilagenous tube courses anteromedially
and inferiorly, angled between 30 and 40 degrees. The cartilagenous
portion of the tube is not completely surrounded by cartilage, but is
deficient inferolaterally where it is covered by a membrane. The
cartilage is crook shaped covering the medial, lateral and superior
walls of the cartilagenous portion of the tube. The tubal lumen is
shaped like two cones joined at their apices. The junction of the cones
is the narrowest portion of the lumen and is known as the isthumus, and
is usually situated at the junction of the cartilagenous and bony
portion of the tube.
Fig showing the various portions of eustachean tube
The cartilagenous portion of the eustachean tube
doesnot follow a straight course in the adult but extends along a curve
from the junction of the osseous and cartilagenous portions to the
medial pterygoid plate, approximating the skull base during most of its
course. The eustachean tube crosses the superior border of the superior
constrictor muscle to enter the nasopharynx. The medial cartilagenous
portion of the tube presses against the pharyngeal wall to form a
prominent fold, the torus tubaris. The torus is the site of origin of
the salpingopalatine muscle and is the point of origin of the
The mucosal lining of the eustachean tube is
continuous with that of the nasopharynx and middle ear (ciliated
columnar epithelium). Certain differences in the mucosal lining is
evident, mucous glands predominate at the nasopharyngeal orifice, and
this gradually changes into a mixture of goblet cells at the tympanum.
Muscles associated with eustachean tube: The
muscles associated with the eustachean tube are 4 in number. They are
tensor veli palatini, levator veli palatini, salpingopharyngeus, and
Usually the eustachean tube is closed; it opens
during such actions like swallowing, yawning thus equalising the middle
ear pressure. Active dilatation of the tube is induced by the tensor
veli palatini muscle. Closure of the tube has been attributed to
passive reapproximation of tubal walls by extrinsic forces exerted by
surrounding elastic fibres.
Blood supply: The eustachean tube is supplied by
the ascending palatine artery, pharyngeal branch of internal maxillary
artery, the artery of the pterygoid canal, ascending pharyngeal artery,
and the middle meningeal artery. The venous drainage is via the
Nerve supply: The pharyngeal orifice of the
eustachean tube is supplied by a branch from the otic ganglion, the
sphenopalatine nerve, and the pharyngeal plexus. The reminder of the
tube receives its sensory supply from the tymapnic plexus and the
pharyngeal plexus. The glossopharyngeal nerve has an important role in
the innervation of the eustachean tube.
Functions of the eustachean tube:
Ventilation: It ventilates the middle ear cavity via the nasopharyngeal
Fig showing the ventilatory functions of middle ear
Protection: It protects the middle
ear cavity from microbes of nasopharynx.
Fig showing the protective function of eustachean tube
Drainage: Drains the secretions from the middle ear
cavity into the nasopharynx.
Fig showing the drainage functions of eustachean tube
Features of Infant eustachean tube: In infants the eustachean tube is
about half as long as in the adults, averaging about 18 mm. The osseous
portion is longer than the cartilagenous portion. It is shorter,
straighter, and wider than that of adults. The tensor veli palatini
muscle is less efficient in infants. The tube is also mostly horizontal
in infants. Hence infants are more prone for middle ear infections
arising from the eustachean tube.
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