Page 71 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery

connected by fibrous tissue, permitting more movement surface of the canal to the pinna. Damage to this vessel
and flexibility of the ear. The junctions of these tubes may can result in necrosis and sloughing of the caudal half of
VetBooks.ir auricular abscesses and fistulae form. before splitting into superficial temporal and maxillary
the ear flap. The external carotid artery continues rostrally
be the sites of canal rupture and drainage when para-
branches. The superficial temporal artery provides blood
The air-filled middle ear is separated from the external
ear canal by the tympanic membrane; the middle ear is
connected to the nasopharynx by the auditory, or supply to the front half of the pinna. It is helpful to palpate
for the external carotid artery and its branches during total
Eustachian, tube. Within a small dorsal recess are the tiny ear canal ablation, since damage to this artery during
auditory bones (ossicles) – the malleus, incus and stapes – dissection causes significant blood loss.
that transmit sound vibrations. In the cat, a bony septum
separates the dorsolateral portion of the tympanic bulla
and the ossicles from the larger ventromedial tympanic
cavity. A partial septum may also be seen in canine bullae Surgery of the pinna
(Figure 5.2). Across from the opening of the external
ear canal are the cochlear (round) and vestibular (oval) Because of its exposed position, the pinna is easily trau-
windows, the openings to the inner ear, where the organs matized by animals and objects in the environment.
of hearing (cochlea) and balance (utriculus, sacculus Additionally, many dogs have the habit of vigorously
and semicircular canals) reside. In the cat, the cochlear shaking their heads and whipping their ears about, which
window is found in a gap within the septum between the can cause pinnal damage. Blood supply to the pinna is
two bulla compartments. quite extensive, and blood loss can be dramatic and
frightening to owners, although it is usually easily con-
trolled with pressure. To prevent excessive bleeding and
Innervation to improve visualization of the pinna, some veterinary
The facial nerve exits the skull through the stylomastoid surgeons (veterinarians) use lasers or cautery during dis-
foramen, an opening just caudal to the external acoustic section or resection.
meatus. It splits into several branches after exiting the skull,
but the major portion of the nerve continues rostrally to the Lacerations and defects
face, travelling under and around the horizontal ear canal.
Midway up the rostral surface of the ear canal, it splits into Treatment depends on the extent of the laceration and
branches to the lower and upper lips, eyelids and front half whether it is partial or full thickness.
of the pinna. From a lateral view the ear canal is almost
completely surrounded by the nerve and its branches, • Linear lacerations of the skin usually heal by second
making dissection without nerve damage very challenging. intention, as long as the skin is still firmly attached to
the underlying cartilage. If the skin becomes elevated
Vasculature from the cartilage, as in an L-shaped tear, it should be
closed with simple interrupted skin sutures. Dead
The external carotid artery lies just ventral to the horizontal space, if present, can be closed with a continuous
ear canal. Its caudal auricular branch travels up the caudal suction drain or mattress sutures placed through the

Anatomy of the canine
5.2 bulla.

Horizontal Temporalis
canal muscle

Auditory
Auricular ossicles
cartilage
Cochlea
Auditory
tube

Annular Osseous Tympanic Tympanic Tympanic
cartilage ear canal membrane ear cavity bulla

62

Ch05 HNT.indd 62 03/09/2018 14:30