Page 146 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 11 · Thoracic wall anatomy and surgical approaches

costal cartilages, marking the path of the internal thoracic Neurovascular structures of the thoracic
artery along its dorsal border. Externally, several muscles wall
VetBooks.ir a multipartite muscle originating from the caudal cervical Each intercostal space contains a neurovascular bundle
create a robust thoracic wall (Figure 11.2). The scalenus is
running caudal to each rib. The intercostal nerves are
vertebrae and inserting on the lateral aspect of the more
cranial ribs. The most caudal portion inserts over the fifth
costal nerves maintain a caudal position behind each rib
rib, providing a useful anatom cal landmark. The serratus ventral branches of the thoracic spinal nerves. The inter-
i
ventralis muscle is a fan-like muscle that originates from and continue to reach the lateral aspect of the sternum,
the thoracic vertebrae and inserts on the lateral aspects sending a ventral cutaneous branch to ramify in the skin;
of the ribs; separate serrations of the muscle can be the dorsal cutaneous branch of each nerve passes cau-
dally to overlie the more caudal adjacent rib proximally. It
preserved by dissecting between them when performing
is recommended that, prior to intercostal thoracotomy,
an intercostal thoracotomy. These muscles are overlain
nerve blocks should be performed caudal and cranial to
by the robust latissimus dorsi, a triangular muscle origi-
nating from the dorsal thoracolumbar fascia and inserting the rib of the appropriate intercostal space and for both
on the aponeurosis of the triceps muscle. The dominant ribs either side. The first three or four intercostal arteries
are branches of the thoracic vertebral artery and the last
blood supply of this muscle arises from the thoracodorsal
eight or nine are direct branches from the aorta.
artery and the muscle can be transposed to achieve
The internal thoracic artery runs in a subpleural posi-
thoracic wall reconstruction. The external abdominal
tion on the inside of the ventral chest wall. It may be inad-
oblique is a large sheet-like muscle that covers the
vertently lacerated during intercostal thoracotomy, at the
ventral half of the lateral thoracic wall (costal portion)
ventral extent of the incision, or at the cranial extent of a
before extending caudally to provide the lateral portion of median sternotomy where the vessels converge towards
the composite abdominal wall (lumbar portion); the costal the midline as they arise bilaterally as branches from the
part of the external abdominal oblique originates from subclavian arteries. The left and right subclavian veins
the fourth or fifth to the 13th ribs. The ventral aspect of and external jugular veins are the major veins converging
the sternum serves as the insertion for the pec toral at the thoracic inlet, draining via the brachiocephalic veins
muscles; the superficial pectoral muscles insert only into the cranial vena cava. These large veins are separ-
on the cranial portion of the sternum, whilst the deep ated from the cranial sternum only by thin mediastinal
pectoral muscle spans more widely along the length of tissue and care must be taken to avoid laceration during
the sternum. median sternotomy.

Longissimus cervicis
Longissimus thoracis
Spinalis and semispinalis thoracis
Rhomboideus

Splenius

Serratus dorsalis cranialis

Serratus ventralis

Scalenus
Sternocephalicus
External
abdominal
Rectus oblique
thoracis
Sternothyroideus

uperficial
pectoral Rectus
abdominis
Deep pectoral

External intercostal
muscles
IV rib

11.2 Diagram showing the external muscular anatomy of the thoracic wall relevant to performing a lateral thoracotomy.

137

Ch11 HNT.indd 137 03/09/2018 15:45