Page 219 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

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

Right Ventral Left Left Ventral Right
VetBooks.ir Sternal part

Costal part
Caval foramen Central tendon Sternal part
Caudal mediastinum
Oesophageal hiatus Central tendon
Lumbar part Caudal vena cava
Oesophagus Costal part
Aorta
Aortic hiatus Lumbar part
13th rib
Left crus
Lumbar vertebra
Right crus
Lumbar vertebra
Dorsal Dorsal
(a) (b)
17.1 Anatomy of the diaphragm. (a) Abdominal surface. (b) Thoracic surface.

The space between the pleural and peritoneal cavities
Embryology is partially occluded by the enlargement of the meso-
A complex structure such as the diaphragm has a simi- nephric organs. As these organs later atrophy, the retro-
larly complex embryology. A thorough understanding peritoneal flaps they occupied, known as pleuroperitoneal
of the embryological development of the diaphragm folds, continue to enlarge. These folds fuse with the mes-
entery of the oesophagus and dorsal portion of the septum
allows the congenital abnormalities of the diaphragm to
transversum.
be explained.
The diaphragm is derived from four main structures: The remaining communication between these two
cavities, the pleuroperitoneal canals or foramina of Boch-
dalek, is then closed by the developing posthepatic mes-
• The septum transversum, ventrally
enchymal plate, under the influence of the adjacent
• The dorsal aspect of the mediastinum (dorsal
developing lung bud.
mesentery of the oesophagus), dorsomedially
Once these component parts have fused and the
• The pleuroperitoneal folds, dorsolaterally
pleural cavity enlarges, myoblasts from the posthepatic
• The posthepatic mesenchymal plate. mesenchymal plate and abdominal wall invade the peri-
pheral border of the diaphragm to form the costal and
In the developing embryo, the initial partition between sternal parts.
the thoracic and abdominal cavities is provided by
the septum transversum. This structure originates in the Clinical anatomy
neck, but migrates to the level of the first lumbar vertebra,
where it forms the central tendon. The cervical origin of The radiographic appearance of the diaphragm in health
the septum transversum explains the cervical origin of the (Grandage, 1974) and in disease (Park, 1994) is well
phrenic nerves (Figure 17.2). documented.
The dorsal mesentery of the oesophagus develops Patient factors such as breed, age, size, body condi-
dorsal to the septum transversum and forms the diaphrag- tion, temperament and visceral distension, other clinically
matic crura, oesophageal hiatus and aortic hiatus. induced variables such as sedation or anaesthesia and
phase of respiration, and geometric factors associated
with the radiographic view, such as positioning, direction
of the primary beam, and centring of the primary beam all
influence the radiographic appearance of the diaphragm
(Grandage, 1974). Although these factors produce an
almost limitless number of variations in the appearance,
the clinician should be aware of the radiographic appear-
Aorta ance of the diaphragm in the standard views and should
Meso-oesophagus aim to keep the other variables as constant as possible.
Oesophagus
Muscular ingrowth Only a small part of the diaphragm is apparent on any
Caudal vena from body wall
cava Pleuroperitoneal single radiograph. Visualization of the diaphragm is
membrane dependent on the adjacent structures being of different
radiopacity. Thus, the thoracic surface is easily visualized
Septum because of the adjacent air-filled lungs. However, the
transversum abdominal surface is less well demarcated because adja-
cent structures such as the liver and stomach have a
soft tissue opacity, although the falciform fat outlines the
17.2 Embryological development of the diaphragm.
ventral aspect of the diaphragm on the lateral view.

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