Page 218 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 17
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Surgery of the diaphragm

Stephen Baines

Anatomy psoas minor muscle. Each crus may be differentiated into
lateral, intermediate and medial portions.
General structure The costal part is formed by fibres radiating from the
costal wall to the tendinous centre. It arises peripherally
The diaphragm is a musculotendinous sheet that sepa- from the proximal 13th rib, distal 12th rib, costochondral
rates the thoracic and abdominal viscera. It projects crani- junction of the 11th rib, whole length of the 10th and ninth
ally into the thoracic cavity like a dome, giving it a convex ribs, and the curved portion of the eighth costal cartilage.
thoracic surface and a concave abdominal surface. The These fibres run centrally into the lateral borders and
mesothelial linings of these two cavities, the pleura and columns of the central tendon.
peritoneum, are separated from the diaphragmatic surface The sternal part of the diaphragm is an unpaired
by the endothoracic and transversalis fascia, respectively. medial muscle, continuous with the costal part. It arises
from the base of the xiphoid cartilage, the adjacent trans-
Anatomical relationships versalis fascia and the eight costal cartilages. These fibres
run dorsally to the apex of the body of the central tendon
The mediastinum attaches to the diaphragm in the midline, (Figure 17.1).
dorsal to the oesophagus, but, ventral to the oesophagus, The aortic hiatus is bordered ventrally by the
the mediastinum deviates to the left in a wide arc, across diaphragmatic crura and dorsally by the ventral aspects
the surface of the costal muscles, returning to the midline of the lumbar vertebrae. The aorta, azygos and hemia-
just dorsal to the sternum. On the right side, a reflection of
zygos veins and the lumbar cistern of the thoracic duct
the mediastinum, the plica venae cavae, is attached to the pass through this hiatus. The oesophageal hiatus is
diaphragm. This plica and the mediastinum form a recess
bordered by the thick medial edges of the medial part of
between the heart cranially and the diaphragm caudally, the crura. The oesophagus, associated vessels and the
which invests the accessory lung lobe. The oesophagus is
vagal trunks pass through this hiatus. The caval hiatus
attached to the diaphragm by a reflection of the diaphrag-
matic and endothoracic fascia that attaches around is located entirely within the central tendon of the dia-
phragm, although muscle fibres from the costal portion
the entire circumference of the thoracic oesophagus. The
stronger diaphragmatic fascial reflection is referred to as may radiate into the dorsal border of the hiatus. The
splanchnic nerves and sympathetic trunk pass dorsal
the phrenico-oesophageal ligament. On the abdominal
surface, the diaphragm is attached to the liver by the trian- to the dorsal aspect of the lateral part of the crura, in the
lumbocostal arch.
gular ligaments, and the coronary ligaments surround the
caudal vena cava at the caval hiatus.
Nerves and vessels
Detailed structure The main blood supply to the diaphragm is derived from
The diaphragm is composed of a central tendon and a the caudal phrenic arteries. These arise from the paired
peripheral muscular part. The muscle fibres arise from phrenicoabdominal arteries, which branch from the lateral
the axial skeleton peripherally and radiate towards the surface of the abdominal aorta between the cranial
central tendon. mesenteric and renal arteries. These vessels pass along
The central tendon is relatively small and Y-shaped, the medial border of the dorsal extension of the central
formed by a ventral triangular body with narrow dorsal tendon and ramify over the ventrocaudolateral surface of
extensions on either side. The muscular part is formed by the diaphragm. These vessels follow the course of the
lumbar, costal and sternal muscles. muscle fibres peripherally and anastomose with phrenic
The lumbar part is formed by the two diaphragmatic branches of the 10th, 11th and 12th intercostal arches.
crura. The right crus is larger than the left. Each crus Motor innervation to the diaphragm is provided by the
arises from a long bifurcate tendon, which comprises a phrenic nerves, which arise from the ventral branches of
long, strong portion arising from the cranial edge of the the fifth, sixth and seventh cervical nerves in the dog and
body of the fourth lumbar vertebra and a shorter, weaker the fourth, fifth and sixth cervical nerves in the cat. A small
portion arising from the body of the third lumbar vertebra. contribution to the phrenic nerves from the fourth cervical
These tendons unite close to the midline, medial to the nerve is present in some dogs.

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, second edition. Edited by Daniel J. Brockman, David E. Holt and Gert ter Haar. ©BSAVA 2018 209

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