Page 220 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 17 · Surgery of the diaphragm

Radiography may demonstrate the right and left crura, These combinations are thought to be sporadic or due
intercrural cleft and the central dome (cupula). to teratogenic events rather than being inherited (Eyster
VetBooks.ir view: which defects were present in the cranial abdominal wall,
The radiographic appearance alters according to the
et al., 1977; Bellah et al., 1989).
A variant of the usual PPDH has been described in
• Dorsoventral (DV): a single dome-shaped structure
• Ventrodorsal (VD): three separate domed structures caudal sternum and ventral diaphragm, but abdominal
organs which had herniated through the diaphragm were
• Right lateral: crura parallel, with the dependent right restricted to the caudal mediastinum, and did not enter the
crus more cranial pericardial sac (Bellah et al., 1989).
• Left lateral: the crura form a Y-shape, with the
dependent left crus more cranial. Aetiology: These defects may be caused by the following
events:
Function
• Failure of the lateral pleuroperitoneal folds and sternal
Contraction of the diaphragmatic muscles causes flatten-
part of the diaphragm to unite during separation of the
ing of the dome of the diaphragm, resulting in caudal dis- thoracic and abdominal cavities
placement of the abdominal viscera and outward
• Faulty development of the dorsolateral septum
displacement of the body wall. Contraction of the costal transversum
part also causes expansion of the caudal rib cage. These
• Rupture of a thin tissue membrane in the region of the
actions cause enlargement of the thoracic cavity and a developing septum transversum
reduction in pleural space pressure, resulting in inspira-
• Prenatal injury to the septum transversum or site of
tion. Expansion of the chest wall is also provided by con- fusion of the septum transversum and pleuroperitoneal
traction of the internal intercostal muscles, which explains
folds.
why breathing movements may still be made in animals
with paralysis of the diaphragm.
These aetiologies are suggested in view of the consis-
tent location of these defects in the ventral or ventrolateral
portions of the diaphragm, that is, the parts contributed by
Diseases of the diaphragm the septum transversum and pleuroperitoneal folds (Evans
and Biery, 1980).
Diseases affecting the diaphragm are primarily alterations In one report, two successive litters from the same two
in its anatomical structure, such as congenital hernias parents had a 1:3 ratio of puppies with PPDH to puppies
and acquired ruptures, and alterations in its function, without PPDH, suggesting an autosomal recessive genetic
such as diaphragmatic paralysis. A hernia is the pro- predisposition (Feldman et al., 1968).
trusion of viscera through a normal anatomical opening, Although trauma has been suggested as a potential
which may be pathologically enlarged, and is generally cause of acquired peritoneopericardial diaphragmatic
congenital in origin, whereas a rupture is protrusion of hernia, no such cases have been described in small
viscera through an opening that has been acquired, animals. Postnatally, there is no direct contact between
usually as a result of trauma. the pericardial sac and peritoneal cavity, although they are
connected by the caudal mediastinal pleura, and traumatic
Congenital diseases disruption of these two mesothelial sacs, with subsequent
re-establishment of continuity between them, would seem
Peritoneopericardial diaphragmatic hernia to be a rare, if not impossible, event. However, trauma may
worsen a pre-existing hernia.
Anatomy and incidence: Peritoneopericardial diaphrag-
In the embryo, cardiac septation and sternal fusion
matic hernia (PPDH) consists of herniation of abdominal
organs through a direct communication between the perito- take place at the same time as the development of the
neal cavity and the pericardial sac. It is the most common septum transversum and fusion to the other components
congenital diaphragmatic and pericardial defect in dogs of the diaphragm. Hence, any environmental insult during
(Eyster et al., 1977; Evans and Biery, 1980; Bellah et al., this period might be expected to result in defects in the
diaphragm and in the cardiac septa and sternum.
1989a,b) and cats (Frye and Taylor, 1968; Hay et al., 1989).
The Weimaraner and Miniature Schnauzer dogs and Persian Alternatively, abnormal blood flow within the chambers of
cat may be predisposed to this anomaly (Evans and Biery, an abnormally positioned heart may lead directly to septal
1980; Hay et al., 1989). defects through mechanical teratogenesis.
PPDH is often accompanied by other defects (Eyster
et al., 1977; Evans and Biery, 1980; Bellah et al., 1989). Pathophysiology: Abdominal organs that herniate into
These include: the pericardial sac include the liver, gallbladder, falciform
ligament, omentum, spleen, small intestine and, rarely,
• Sternal defects, e.g. reduced number of sternebrae, the stomach.
defects in the sternum, fusion of sternebrae and sternal The pathophysiological changes are similar to those
dysraphism occurring during diaphragmatic rupture, but the organs are
• Cranial midline abdominal wall hernia constrained by the pericardial sac and are generally
• Umbilical hernia located caudal and lateral to the heart. Hence, gross com-
• Abnormal swirling of the hair in the cranial ventral promise of pulmonary function from direct pressure does
midline not generally occur, but indirect pressure from the
• Intracardiac defects, e.g. pulmonic stenosis, ventricular enlarged pericardial sac may still cause respiratory com-
septal defects, atrial septal defects, tricuspid dysplasia promise. Cardiovascular signs result from pressure on the
and tetralogy of Fallot heart or great vessels. Cardiac tamponade may be caused
• Pulmonary vascular disease by compression from the abdominal viscera, bloating of a
• Portosystemic shunts. herniated stomach, or an effusion from an incarcerated

211

Ch17 HNT.indd 211 31/08/2018 13:45