VOCAL CORD PARALYSIS
Depending upon the cause, vocal cord paralysis may be unilateral or bilateral,
complete or incomplete, giving four possible combinations, namely: (a)
unilateral incomplete; (b) unilateral complete; (c) bilateral incomplete; and
(d) bilateral complete. Each of these presents a different clinical picture and
each requires a different management.
PATHOLOGY. The recurrent laryngeal nerve is the motor nerve to all the
laryngeal muscles except the cricothyroid muscle which is supplied by the
external branch of the superior laryngeal nerve. This latter muscle has an
adductor effect on the vocal cords, and thus a lesion which spares the superior
laryngeal nerve will leave the cord lying nearer the midline than one which
paralyses both the recurrent and superior laryngeal nerves. This, in effect,
means that a high lesion of the vagus nerve will leave the paralysed cord
further from the midline than a paralysis of the recurrent laryngeal nerve.
Three positions of paralysed vocal cords are described: (a) paramedian;
(b) intermediate; and (c) cadaveric. There is little point in differentiating
between the first two as it is of little diagnostic significance and the difference
is one of only a few millimetres. Reference will only be made therefore to the
paramedian and the cadaveric positions.
Another factor which controls the position of the paralysed cord is the
curious fact described by Semon—'in all progressive organic lesions of the
centres and trunks of the motor laryngeal nerves, the fibres supplying
the abductors of the vocal cords become involved much earlier than do the
adductors'. What this means, in fact, is that a partial lesion will leave the cord
in the paramedian rather than the cadaveric position. Neither Semon's Law
nor the site of the lesion decide the position of the cord absolutely, but both
are useful guides.
The most commonly affected nerve is the left recurrent laryngeal nerve due
mainly to the high incidence of bronchial carcinoma.
AETIOLOGY. Vocal cord paralysis arises as a rule from remote causes. The
lesions which affect either vagus nerve are: (1) tumours at the base of the skull,
e.g. glomus jugulare tumours and nasopharyngeal carcinoma, (2) bulbar
paralysis, (3) peripheral neuritis due to influenza, herpes or the Epstein-Barr
virus, (4) high neck injuries, e.g. trauma or surgical complication of radical
neck dissection, (5) metastatic glandular enlargement, (6) basal meningitis,
and (7) vagal tumours, e.g. glomus vagale or neurilemmoma.
The lesions affecting the left recurrent laryngeal nerve include: (1) carcinoma
of the bronchus, (2) carcinoma of the cervical or thoracic oesophagus, (3)
carcinoma of the thyroid gland, (4) operative trauma from thyroidectomy,
radical neck dissection, pharyngeal pouch removal, cricopharyngeal myotomy,
ligation of a patent ductus and other cardiac and pulmonary surgery, (5)