Clinical
anatomy and physiology
The
pharynx
The pharynx is a fibro muscular tube forming the upper part of the
respiratory and digestive passages. It extends from the base of the skull to the
level of the sixth cervical vertebra at the lower border of the cricoid
cartilage where it becomes continuous with the oesophagus. It opens anteriorly
into the nose, mouth and larynx from above downwards, and is therefore divided
into three parts, the nasopharynx, oropharynx and hypo pharynx (Fig.
43.1).
Nasopharynx
The nasopharynx lies anterior to the first cervical vertebra and has the
openings of the eustachian tubes in its lateral wall, behind which lie the
pharyngeal recesses, the fossae of Rosen Muller. The adenoids are situated
submucosally at the junction of the roof and posterior wall of the nasopharynx.
The nasopharynx is closed off from the oropharynx during swallowing by the
raising of the soft palate and contraction of the palatopharyngeal sphincter.
Oropharynx
This is bounded above by the soft palate, below by the upper surface of
the epiglottis and anteriorly by the anterior faucial pillar which contains the
palatoglossus muscle. The oropharynx therefore contains the palatine tonsils
situated in the lateral wall between the anterior and posterior pillars of the
fauces and the posterior third of the tongue. These palatine tonsils are
The
tissue of Waldeyer’s ring undergoes physiological hypertrophy during early
childhood as the child is exposed to increasing amounts of antigenic stimuli;
there is often a similar hypertrophy of the cervical lymph nodes and, indeed,
the abdominal lymph nodes (the aetiology of mesenteric adenitis). The tonsils
contain tortuous crypts which can harbour pus and microorganisms. Clothing the
lateral two-thirds of each tonsil is the capsule, a well-defined structure
composed of fibrous and elastic tissue, and muscle fibres. The tonsil has an
exceptionally good blood supply. It is well to bear in mind that a tortuous
facial artery may be closely related to the lower pole. On the lateral aspect of
the tonsil is a varying number of paratonsillar veins which may be the source of
serious venous bleeding following tonsillectomy. This may particularly occur
when the bleeding end retracts into the upper part of the tonsillar fossa, and
this must be found and ligated before the patient leaves the operating room.
Hypo pharynx
The hypopharynx is bounded above by the upper
border of the epiglottis and anteriorly by the sloping laryngeal inlet. Its
inferior border is the lower border of the cricoid cartilage where it continues
into the oesophagus. The hypopharynx is commonly described anatomically of being
composed of three areas: the piriform fossae, the posterior pharyngeal wall and
the postcricoid area. The mucosa of these areas is in direct continuity with no
distinct barriers, and disease processes, such as malignant neoplasms, can
easily involve more than one area.
Swallowing
Swallowing is a complex neuromuscular act.
Trauma and disease may result in dysphagia and at times aspiration of food and
fluid into the airway. In considering the diseases which involve the pharynx and
larynx, it is important to have a basic understanding of swallowing and the
functions of the larynx. Swallowing consists of three stages: oral, pharyngeal
and oesophageal (Fig. 43.3). Knowledge of the physiology of normal swallowing
and the problems as a consequence of disease has been enhanced in the last two
decades by use of video fluoroscopic techniques. This is the radio graphical
evaluation
of the passage of a bolus of radio-opaque liquid or solid from the point at
which it enters the oral cavity down to its passage within the stomach. This
investigation is considerably more accurate than the older-fashioned
radiological examination of barium swallow, where the object was to concentrate
on the plain X-ray examination of the oesophagus, rather than the new technique
which shows a complete video of all stages of swallowing. This can be reviewed
on many
Swallowing
is mediated via efferent fibres passing to the medulla oblongata through the
second division of the trigeminal nerve (V), glossopharyngeal (IX) and vagus
nerves (X). The afferent pathway is from the nucleus ambiguous, and is mediated
via the glossopharyngeal (IX), vagus (X) and hypoglossal (XII) nerves.
Damage
to these major cranial nerves at any point along their pathway, by trauma or
disease, may cause dysphagia with or without aspiration.
In
the oral voluntary phase of swallowing the lips, cheeks, tongue, floor of mouth,
teeth and palate participate in preparing the food. The food is held in the
oral cavity, lateralised for mastication and then formed into a bolus. The
tongue propels the formed bolus posteriorly into the oropharynx in the second
involuntary pharyngeal phase. The soft palate is elevated to prevent
nasopharyngeal escape, and the lateral and posterior walls contract to propel
the food downwards. The larynx moves upwards and forwards as the posterior
tongue moves backwards and downwards.
The
main function of the larynx is in fact not the production of voice but the
protection of the tracheobroncheal airway and lungs. It is basically a
three-tiered sphincter mechanism: the first tier consisting of the epiglottis,
aryepiglottic folds and arytenoids; the second the false cords; and the third
level the true vocal folds. The whole larynx not only moves upwards and forwards
but the three-tier sphincter mechanism closes on every occasion that swallowing
occurs.
As
the food enters the piriform fossa there is an anticipatory relaxation of the
upper oesophageal sphincter and the food enters the oesophagus. Oesophageal
peristaltic waves then convey the food down into the stomach. Gravity aids both
the involuntary pharyngeal and oesophageal phases of swallowing.
Relations of
the pharynx (Fig. 43.4)
The
parapharyngeal space — this potential space lies lateral to the pharynx and is
of importance when understanding disease of the pharynx and neck. It is a
potential space which extends from the base of the skull above to the superior
mediastinum below, and it is occupied by the carotid vessels, internal jugular
vein, deep cervical lymph nodes, the last four cranial nerves and the cervical
sympathetic trunk. Infection and suppuration of the cervical lymph node in the
parapharyngeal space most commonly occurs from infections of the tonsils or
teeth (particularly the third lower molar tooth). It may then spread throughout
the parapharyngeal space up to the skull base or down to the paraoesophageal
region and superior mediastinum. Retropharyngeal space — this potential space
lies posterior to the pharynx bounded anteriorly by the posterior pharyngeal
wall and its covering buccopharyngeal fascia and posteriorly by the cervical
vertebrae and their covering muscles and fascia. It contains the retropharyngeal
lymph nodes, which are usually paired lateral nodes, but which are separated by
a tough median partition which connects
Larynx
The larynx is the protective sphincter which
closes off the airway during swallowing. In humans and some other mammals it
is also responsible for the generation of sound, which in humans is modified by
the pharynx, oral cavity, nasal passages, sinuses, tongue, lips and teeth to
produce speech. The larynx has a mainly cartilaginous framework which may ossify
in later life and which consists of the hyoid bone above, the thyroid and
cricoid cartilages, and the intricate arytenoid cartilages posteriorly.
The
cricoid cartilage is the only complete ring in the entire airway and bounds the sub glottis
which is the narrowest point of the airway. This is the commonest
site for damage from endotracheal tubes, occasionally causing laryngotracheal
stenosis.
An
anatomical description of the larynx divides it into the supraglottis, glottis
and subglottis (Fig. 43.5).
The true
vocal folds (often incorrectly called the vocal cords) are normally white in
contrast to the pink mucosa of the rest of the larynx and airway. The true vocal
folds meet anteriorly at the mid-level of the thyroid cartilage, whereas
posteriorly they are separate and attached to an arytenoid cartilage. This
arrangement produces the ‘V’ shape of the glottis (Fig.
43.6).
Nerve supply
The sensory nerve supply to the larynx above
the vocal folds is from the superior laryngeal nerve and below the vocal
folds from the recurrent laryngeal nerve. Both
of these nerves are branches of the vagus (X). The motor nerves supply to the
larynx is from the recurrent laryngeal nerve, which is a branch of the vagus and
which supplies all intrinsic muscles. Only one of these intrinsic muscles, the
posterior cricoarytenoid, abducts the vocal folds during respiration. All
other intrinsic muscles adduct the cords.
Lymphatics
The lymphatic drainage of the supraglottis
above the vocal folds is to the upper deep cervical nodes, whilst in contrast
that of the subglottis is to inferior deep cervical nodes and to the
paratracheal and mediastinal nodes.
•The
vocal folds themselves have a very sparse lymphatic drainage. The commonest form
of malignant disease affecting the true vocal folds is squamous cell carcinoma,
and tumours confined to the true vocal folds do not metastasise to lymph nodes
unless they spread into supraglottic or subglottic tissue.
All
of the intrinsic muscles of the larynx are supplied by the recurrent laryngeal
nerve, and therefore damage to this nerve or to the vagus nerve will cause
paralysis of the vocal fold on the side of the damage.
Phonation/speech
During expiration air from the lungs passes
out through the larynx under pressure and the vocal folds channel this into a
column of high-speed vibrating air, thus producing sound. This sound is
converted into intelligible speech by the remainder of the vocal tract, i.e. the
pharynx, tongue, lips, teeth and the resonating chambers of the nose and
sinuses. The larynx functions by closing the vocal fold against the air being
exhaled from the lungs but the rise in subglottic pressure forces the vocal
folds apart slightly for an instant with accompanying vibration of the vocal
fold epithelium. The opening and closing occurs in rapid sequence to produce a
vibrating column of air which is the source of sound. The pitch of the sound is
controlled by the frequency of the vocal fold epithelial vibration, which in
turn is determined by the thickness, length and tension of the vocal folds
controlled by the intrinsic musculature. The loudness or intensity of the sound
is governed by the expiratory air pressure and the amplitude of the vocal fold
vibrations.
Paralysis
or overt disease of the vocal folds or closely associated laryngeal structures
will give rise to disturbance of the sound and creation of the symptom of
hoarseness (Table 43.1).
The neck
The neck is divided into anterior and
posterior triangles by the sternocleidomastoid muscle. The anterior triangle
extends from the inferior border of the mandible to the sternum below, and is
bounded by the midline and the sternocleidomastoid muscle. The posterior
triangle extends backwards to the anterior border of trapezius and inferiorly
to the clavicle. The upper part of the anterior triangle is commonly subdivided
into the submandibular triangle above the digastric muscle and the submental
triangle below. The lymphatic drainage of the head and neck is of considerable
clinical importance (Fig. 43.7). The most important chain of nodes is the deep
cervical nodes which run adjacent to the internal jugular vein. The other main
groups are the submental, submandibular, preauricular and postauricular,
occipital and posterior triangle nodes.
The
upper deep cervical nodes, which contain the large jugulodigastric node, drain
the oropharynx, including the tonsils, posterolateral aspects of the oral
cavity, superior aspects of the larynx and piriform fossae, and are the
commonest site of enlargement due to disease in these areas.
The
upper deep cervical nodes may be palpated along the anterior border of the
sternocleidomastoid muscle but when the muscle is well developed or the neck is
obese it may be difficult to evaluate their true size and under these
circumstances
clinical examination may be unreliable.
Metastatic spread of squamous cell carcinoma,
which accounts for 80 per cent of malignant disease of the head and neck, most
commonly
Metastatic spread to regional lymph nodes in the neck is managed surgically in many cases by resection of the neck nodes, and a detailed knowledge of their anatomy is thus required. The parotid and submandibular salivary glands, and the thyroid and parathyroid glands, are additional important neck structures which will be covered separately in their respective chapters.