Tonsil Anatomy

Palatine tonsils a re two in number. Each tonsil is an
ovoid mass of lymphoid tissue situated in the lateral wall
of oropharynx between the anterior and posterior pillars.
Actual size of the tonsil is bigger than the one that appears
from its surface as parts of tonsil extend upwards into
the soft palate , downwards into the base of tongue and
anteriorly into palatoglossal arch. A tonsil presents two
surfaces-a medial and a lateral, and two poles- an upper
and a lower.
Medial surface of the tonsil is covered by nonkeratinising
stratified squamous epithelium which dips
into the substance of tonsil in the form of crypts. Openings
of 12-15 crypts can be seen on the medial surface of the
tonsil. One of the crypts, situated near the upper part
of tonsil is very large and deep and is called crypta magna
or intratonsillar cleft. It represents the ventral
part of second pharyngeal pouch. From the main crypts
arise the secondary crypts, within the substance of tons il.
Crypts may be filled wi th cheesy material consisting of
epithelial cells, bacteria and food debris which can be
expressed by pressure over the anterior pillar.
Lateral surface of the tonsil presents a well -defin ed
fibrous capsule. Between the capsul e and the bed of tonsil
is the loose areolar tissue which makes it easy to d issect
the tonsil in the plane during tonSillectomy. It is also
the site for cullection of pus in peritonsillar abscess.
Some fibres of palatoglossus and pa latopharyngeus muscles
are a ttac hed to the capsule of the tonsil.
Upper pole of the tonsil extends into soft palate. Its
medial surface is covered by a semilunar fold, extending
be tween anterior and pos terior pillars and enclosing a
po tential space called supratonsillar fossa.
Lower pole of the tonsil is attached to the tongue. A
triangular fold of mucous membrane extends from anterior
pillar to the an te roinfe rior part of tonsil and encloses a
space called anterior tonsillar space. The tonsil is separated
from the tongue by a sulcus called tonsillolingual sulcus
which may be the seat of carcinoma.
Bed of the tonsil. It is formed by the superior constrictor
and styloglossus muscles. The glossopharyngeal nerve
and styloid process , if enlarged, may lie in relat ion to the
lower part of tonsillar fossa. Both these structures can be
surgically approached through the tonsil bed after tonsillectomy.
Outs ide the superior constrictor, tonsil is related
to the facial artery, submand ibular salivary gland, posterior
belly of digastric muscle, medial pterygoid muscle and the
angle of mandi ble.
Blood Supply
The tonsil is supplied by five arteries.
l. Tonsillar branch of fac ial artery. This is the main
artery.
2. Ascending pharyngeal artery from ex ternal caro tid.
3. Ascending palatine, a branch of fac ial artery.
4. Dorsal linguae branches of lingual artery.
5. Descending palatine branch of maxillary artery.
Venous Drainage
Veins from the tonsils drain into paratonsilbr ve in
which joins the common facial vein and pharyngeal
ve nous plexus.
Lymphatic Drainage
Lymphatics from the tonsil pierce the superior constrictor
and drain into upper deep cervical nodes particularly
rhe jugulodigastric (tonsillar) node si ruated below rhe
angle of mandible.
Nerve Supply
Lesse r palatine branches of sphenopalatine ganglion
(CN V) and glossopharyngeal nerve provide sensory
nerve supply.
Functions of Tonsils
Like other lymphoid masses of Waldeyer's ring, palatine
tonsi ls have a protective role and act as sentinels at the
portal of air and food passage. The crypts in tonsils increase
the surface area for contact with foreign substances.
Tonsils are larger in childhood and gradually diminish
near puberty. They are removed when they themselves
become the seat of disease.