Page 102 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 7 · Surgery of the larynx

The laryngeal ventricles are located medial to the cartilages remain in a paramedian position. Upper airway
thyroid cartilage and lateral to the vestibular and vocal obstruction occurs because of the greatly increased
VetBooks.ir control phonation. The slit-like opening is bordered crani- Laryngeal oedema may develop as a consequence of
resistance to airflow at the level of the rima glottidis.
folds. The vocal folds and adjacent laryngeal ventricles
turbulent airflow, causing further obstruction.
ally by the vestibular fold and caudally by the vocal fold
(Basenji dogs have severely reduced or absent laryngeal
ventricles, which fits with the speculation that they cannot • Congenital laryngeal paralysis occurs at a young age
or do not bark). (typically before 1 year of age) in Bouviers des
The recurrent laryngeal nerve is a branch of the vagus Flandres, Bull Terriers, Dalmatians, Rottweilers and
nerve that innervates all intrinsic muscles of the larynx Huskies. Bouviers and Bull Terriers tend to be of
except the cricothyroideus (tensor) muscle. The somatic European lineages, whilst affected Dalmatians and
fibres arise from the nucleus ambiguus before joining the Huskies tend to be reported in the USA. Wallerian
vagus nerve. The recurrent laryngeal nerve branches from degeneration of the recurrent laryngeal nerves and
the vagus nerve at the level of the aortic arch, where the left abnormalities of the nucleus ambiguus are present.
recurrent laryngeal nerve courses around the ligamentum • An inherited laryngeal paralysis has been
arteriosum before ascending cranially. On the right side, it documented in young Bouviers des Flandres. It can be
arises from a similar level and wraps around the right sub- uni- or bilateral and is autosomal dominant, involving a
clavian artery before continuing on its course cranially. The loss of motor neurons in the nucleus ambiguus. Similar
nerve courses over the lateral aspects of the trachea to findings have been reported in young Siberian Huskies
the level of the larynx and oesophagus, and terminates and crosses, and in Bull Terriers.
as the caudal laryngeal nerve bilaterally. The cricothyroid- • A suspected hereditary laryngeal paralysis–
eus muscle is innervated by branches of the cranial laryn- polyneuropathy complex has been reported in
geal nerve, in addition to pharyngeal branches of the vagus Dalmatians, Rottweilers and Leonbergers in which
nerve. Less cited recurrent laryngeal nerve branches form affected dogs manifest signs of a generalized
the pararecurrent laryngeal nerves, which innervate the neuropathy.
cervical and cranial thoracic oesophagus. • There have been several reports of a
neurodegenerative disease in Rottweilers, different
from the above. These dogs demonstrate progressive
Functions of the larynx ataxia, tetraparesis and laryngeal paralysis, and have
widespread neuronal vacuolation and spongiform
changes in their nervous systems.
The functions of the larynx include:
• Myasthenia gravis has been reported with laryngeal
paralysis, and laryngeal paralysis can occasionally be
• Preventing inhalation of food or liquids during
the presenting clinical sign.
swallowing by adduction of the arytenoids and vocal • Four cases of spontaneous laryngeal paralysis in
folds and passive coverage by the epiglottis
juvenile white-coated German Shepherd Dogs have
• Regulating airflow and minimizing resistance to the been reported.
passage of air when demand is increased:
• Traumatic laryngeal paralysis occurs sporadically
• At rest: abduction of arytenoids during inspiration, with injuries to the neck or cranial thorax (e.g. bite
passive during expiration
wounds).
• With vigorous exercise: maximal abduction during • Iatrogenic trauma to the recurrent laryngeal nerve(s),
inspiration and expiration
during procedures such as tracheal surgery, patent
• Vocalization, mediated by the vocal folds and laryngeal ductus arteriosus surgery and pharyngostomy tube
ventricles. This can be important in working dogs. A
placement, could potentially result in temporary or
change in bark may be the earliest sign of laryngeal permanent dysfunction.
paralysis. A loss of purring can be an early sign in the
• Tumours such as thyroid neoplasia and cranial
cat
• The larynx is also important in coughing, parturition, mediastinal masses can disrupt recurrent laryngeal
nerve function, resulting in the condition.
eructation and vomiting.
• Laryngeal paralysis can be a manifestation of any
generalized neuropathy or myopathy, e.g. vagal
These functions are regulated by the intrinsic muscu-
lature and innervation of the larynx. The cricoarytenoideus neuropathy, and is seen associated with
hypothyroidism (up to 17% of hypothyroid dogs have
dorsalis muscle is responsible for arytenoid cartilage been reported to have laryngeal paralysis).
abduction during inspiration. The recurrent laryngeal nerve
• By far the majority of dogs with laryngeal paralysis fall
innervates this muscle. An injury to the recurrent laryngeal into the category idiopathic laryngeal paralysis (ILP).
nerve at any point along its length, or to the cricoarytenoid-
ILP is seen mostly in middle-aged to older, medium to
eus dorsalis muscle, can lead to laryngeal paresis or para- large breeds such as Labrador and Golden Retrievers,
lysis. Laryngeal dysfunction can be unilateral or bilateral.
Irish Setters, pointers, Afghan Hounds, and some giant
breeds. Male dogs seem to be more frequently
affected than bitches, but not all studies support this
Laryngeal paralysis observation.
Aetiology of paralysis istor and e a ination ndin s
Interruption in the transmission of impulses through the Presenting signs are similar for both congenital and
recurrent laryngeal nerves and caudal laryngeal nerves acquired forms of laryngeal paralysis. Signs can be pro-
can lead to denervation of adductor and abductor muscles gressive over months to years. Early signs may include a
of the larynx. Consequently, the vocal folds and arytenoid change in ‘voice’ (dysphonia) and gagging or coughing

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