27 Eric Monnet and Boel A. Fransson The diaphragm is a musculotendinous plate separating the thoracic from the abdominal cavity. The triangular central tendon occupies approximately 21% of the diaphragm and is surrounded completely by the muscular parts on all sides (Figure 27.1). Through it, the caval foramen transmits the caudal vena cava. Figure 27.1 Diaphragm, abdominal surface. a, medial; b, intermediate; c, lateral portions of pars lumbalis. (Source: Hermanson [4]. Reproduced with permission from Elsevier.) The muscular diaphragm consists of the lumbar and the costal parts. The costal part has a 40% greater cross-sectional area and exerts 60% more force than the crural parts.1 Both show a mixed population of slow- and fast-twitch fibers allowing for continuous cycles of activity and an ability to respond to intermittent high ventilatory loads. The crura close to the esophageal hiatus show high density of slow-twitch fibers, which are associated with a sphincter function.2 In cats, the lower esophageal sphincter and the crural diaphragm are anatomically superimposed.3 The lumbar part of the diaphragm is formed by the right and left crura (Figure 27.2) between which the aortic hiatus is enclosing the aorta, the azygos and hemiazygos veins, and the thoracic duct. In dogs, the right crus is larger than the left. The thick (5–6 mm) medial aspect of the right lumbar crus is surrounding the esophageal hiatus, which transmits the two vagal nerve trunks together with esophagus and its vessels. Figure 27.2 Diaphragm, thoracic surface. (Source: Hermanson [4]. Reproduced with permission from Elsevier.) The costal part consists of muscle fibers radiating from the costal wall to the central tendon. The muscle arises from the medial proximal part of the 13th rib, the distal 12th rib, and the costochondral junction of the 11th rib, as well as from the entire length of the 9th and 10th ribs. The diaphragm is innervated by the phrenic nerves, arising from the fifth through seventh cervical nerves. The right branch reaches the muscle within the plica vena cava. The left phrenic nerve lies in its own fold in the ventral mediastinum. The phrenico-pericardial ligament attaches to the diaphragm near the midline.4 This arrangement contrasts to humans, in whom the pericardial sac itself attaches to the diaphragm, enabling traumatically acquired peritoneopericardial hernias, which are not seen in small animals. The diaphragm protrudes as a cupola into the chest cavity. The active muscle contraction flattens the cupola, leading to inspiration of lungs. It is considered the prime mover of tidal air,3 and both muscular parts contract during respiration. However, the diaphragm also has important functions associated with swallowing and emesis. In swallowing, the esophageal distension leads to reflex relaxation of crural diaphragm, allowing the bolus to pass. In vomiting, the diaphragm first contracts strongly as a single muscle during retching. During expulsion, the crura relaxes by central nonvagal mechanisms while the costal diaphragm remains contracted.3 It has been suggested that the crural contraction during inspiration may be due less to respiration but more to increase the pressure on the esophagus, thus minimizing reflux.3 Peritoneal-pericardial diaphragmatic hernia (PPDH) is a common congenital anomaly in dogs and cats. Cats are more often affected than dogs, with prevalences in one study of 0.062% and 0.015% in cats and dogs, respectively.5 Of small animal diaphragmatic hernias (DHs), PPDH constitutes around 15%.6 Weimaraners and domestic long hair cats have been overrepresented.5,7 The direct underlying developmental abnormality has not been determined. Surgical herniorrhaphy of PPDH has mainly consisted in primary closure of the defect.5,7 In one dog with partial agenesis of the diaphragm, reconstruction using the pericardium was performed.5 Adhesions between herniated organs to the pericardium and heart have been noted in 19 of 83 (23%) of cats,5,7,8 but in none of 27 dogs in two studies.5,7 However, adhesions may occur in dogs as well. When present, dissection of adhesions may add significantly to surgical morbidity.7 Chest tubes may not be routinely indicated after PPD herniorrhaphy, but if the pleural cavity has been entered because of adhesion dissection, their use has been recommended.5,7 The perioperative mortality rate has ranged between 5.1% and 14%,5,7,8 with lower fractions in more recent studies. In conservative management of primarily nonclinical disease, 16 of 24 (67%) died during the study period,5 all from reasons supposedly unrelated to PPDH. Two animals with clinical signs of PPDH, in which the owners declined surgery, survived the study period with no clinical signs at the end of the study.5 Minimally invasive herniorrhaphy has not yet been reported in PPDH but is likely to be in the future, similar to that in traumatic DH. If adhesions or diaphragmatic agenesis is encountered, conversion to open surgery may be indicated. The vast majority of DHs in dogs and cats, between 77% and 85%, are of traumatic origin.6 Vehicular trauma has been noted as the most common underlying reason.6,9 Dyspnea was seen in a majority of cats (72%) at time of admission, but in dogs, only 41% showed dyspnea, and gastrointestinal signs were often seen.9 Importantly, 30% to 40% of animals also sustained other soft tissue traumatic injury,9 and surgical treatment needs to include careful assessment in order to not overlook concurrent trauma. Radiographic evaluation is commonly diagnostic for DH (Figures 27.3 and 27.4), and pleural effusion may be indicative of a more extensive rupture.10 Ultrasonography was accurate in diagnosing DH in 93% of cases.11 The most commonly herniated organs include the liver, stomach, and small intestines.6,10 The large intestine and spleen were shown to be herniated less frequently, in 12% to 38% of cases.6,10 Assessment of a patient before minimally invasive herniorrhaphy may benefit from computed tomography (CT) to better outline the extent of the DH and concurrent soft tissue trauma before surgery (Figure 27.5). Animals with extensive traumatic injury may be less ideal candidates for minimally invasive surgery (MIS). Figure 27.3 Thoracic radiograph of a 4 year-old German shepherd hit by a car 5 hours earlier. Right lateral recumbency. The chest cavity did not show obvious signs of trauma. Figure 27.4 Thoracic radiograph in right lateral recumbency of the same dog in Figure 27.3 48 hours later. A large soft tissue opacity, containing a marginated structure, is present in the left caudal thorax. A 7-cm left ventral radial diaphragmatic tear was found during surgery, and the hernia was containing spleen and omentum. Figure 27.5 Sagittal plane of contrast-enhanced computed tomography image of a 3-year-old German shorthair pointer with a 4-week history of pleural effusion. The gallbladder and right liver lobe are herniated into the thoracic cavity through a 4-cm right ventral diaphragmatic defect. Diaphragmatic hernias frequently occur in the costal muscles and less often in the central tendon; the crural muscles are seldom ruptured.6 Orientation of tears of the pars costalis in surgery are 40% radial, 40% circumferential, and 20% a combination of the two.12 Adhesions are rare and have not been seen in acute acquired DH.12 The mean survival rate for dogs and cats undergoing open surgical repair has varied between 79% to 89% in the past 2 decades.9,13 Historically, survival rates were reported as low as 56%.12 Older studies considered survival rates being dependent on the timing of surgical intervention after trauma, with early surgery (within 24 hours) leading to a poor outcome.14,15 However, with improvements in critical care, the timing of surgery is no longer a critical factor.9 Chronic DH, defined as DH lasting longer than 2 weeks, was historically considered more challenging than acute DH, but more recent studies showed a 79% resolution rate with surgical treatment.13
Diaphragmatic and Inguinal Herniorrhaphy
Preoperative Considerations
Anatomy and Physiology of the Diaphragm
Congenital Diaphragmatic Hernia
Acquired Diaphragmatic Hernia
Indication and Case Selection for Minimally Invasive Herniorrhaphy
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