Page 224 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 17 · Surgery of the diaphragm

hernia, identified during evaluation of another disease, the effect of reducing the tone in the oesophageal muscle
may resolve once the underlying disease is addressed and caudal oesophageal sphincter and decreases primary
VetBooks.ir Causes of acquired hiatal herniation include: gastro-oesophageal reflux more likely and perpetuating a
and secondary oesophageal peristalsis, thus making
(Van Ham and van Bree, 1992).
chronic cycle of reflux–oesophagitis–reflux.
Competence of the gastro-oesophageal junction is
• Trauma
• Inspiratory dyspnoea, e.g. laryngeal paralysis, maintained primarily by the intrinsic muscle tone of the
laryngeal stenosis or brachycephalic airway caudal oesophageal sphincter and various extrinsic fac-
obstruction syndrome tors that act on this region (White, 1993). The extrinsic
• Lower respiratory tract disease, e.g. emphysema and factors include:
bronchogenic carcinoma
• Interference with normal muscular function of the • The pinchcock action of the right diaphragmatic crus
diaphragm, e.g. tetanus or muscular dystrophy surrounding the oesophageal hiatus
• Loss of abdominal domain following repair of acute and • The flap valve effect of the acute angle between the
chronic diaphragmatic rupture oesophagus and cardia
• Iatrogenic after cardioplasty for megaoesophagus. • The tethering effect of the phrenico-oesophageal
ligament
Rolling/para-oesophageal: This type of hernia is charac- • The mucosal choke formed by mucosal folds of the
terized by fixation of the gastro-oesophageal junction in distal oesophagus
its normal position, with protrusion of a part of the • The length of the abdominal segment of the
stomach, beginning with the fundus, through the hiatus, oesophagus
alongside the normal oesophagus (Miles et al. 1988). • The effect of abdominal pressure on the abdominal
Gastro-oesophageal reflux is less common with this type segment of the oesophagus.
of hernia. This type of hernia is usually stationary and
does not slide. The relative contribution of these factors in normal
Para-oesophageal herniation itself is uncommon and it individuals or individuals with hiatal hernia is not clear
is normally seen in conjunction with sliding hiatal hernia, (Hardie et al., 1998). However, the intrinsic tone of the
as a type III hernia (Williams, 1990). In humans, type II oesophagus is likely to be the most important factor
hernias tend to be acquired and to enlarge with time. They and primary incompetence of the caudal oesophageal
are often asymptomatic, but large hernias may allow the sphincter has not been demonstrated in dogs or cats.
herniation of other organs, such as spleen or small intes- Understanding the relevant importance of these anatom-
tine, or gastric dilatation, resulting in sudden death. ical and functional mechanisms is the key to developing a
rational surgical technique.
Pathophysiology: A simplified outline of the pathophysi-
ology is that hiatal hernia causes gastro-oesophageal Other clinical signs: Regurgitation may be caused by the
reflux, which in turn leads to oesophagitis and chronic anatomical displacement of the stomach and terminal
regurgitation. Chronic regurgitation may lead to aspira- oesophagus or by the resulting reduction in oesophageal
tion pneumonia. Herniation of other abdominal organs tone or functional length, due to spasm, following oeso-
may cause incarceration or gastric tympany. However, phagitis. However, megaoesophagus may be a primary
the exact nature of the pathophysiological changes in lesion rather than a secondary acquired lesion (Prymak
patients with the different types of hiatal hernia is not et al., 1989).
fully understood. This lack of understanding explains the Dyspnoea may be caused by either aspiration pneumo-
relatively poor success associated with both medical and nia or the space-occupying effects of herniated viscera
surgical therapy. (Waldron et al., 1990). However, hiatal hernia may also be
acquired secondary to diseases that cause dyspnoea,
Gastro-oesophageal reflux: The major consequence of because of the increased pleuroperitoneal pressure gradi-
hiatal herniation is gastro-oesophageal reflux, although ent during respiration.
herniation may occur without reflux (Ellison et al., 1987; In most instances, gastro-oesophageal reflux and res-
Bright et al., 1990; Knowles et al., 1990). However, gastro- piratory disease are mutually reinforcing diseases (Hardie
oesophageal reflux has been documented as a normal et al., 1998). The association between hiatal hernia and
physiological occurrence in dogs, without oesophagitis. lower respiratory tract disease is well known, but gastro-
The occurrence and severity of reflux oesophagitis in oesophageal reflux has been considered to be the cause
animals with hiatal hernia depends on two important of respiratory disease, primarily bronchitis and aspiration
factors: pneumonia (Ellison et al., 1987; Prymak et al., 1989; Bright
et al., 1990; Callan et al., 1993). As previously mentioned,
• The occurrence of gastro-oesophageal reflux is however, increased respiratory effort in patients with
significantly increased in young animals because of respiratory disease may predispose to hiatal herniation
developmental immaturity of the caudal oesophageal and gastro-oesophageal reflux. However, the presence
sphincter of acid reflux in the distal oesophagus may cause
• The severity of reflux oesophagitis in animals with bronchospasm, and regurgitation and aspiration may
hiatal hernia depends on the composition of the cause laryngospasm, which will worsen respiratory
refluxed material. signs (Hardie et al., 1998). Thus, a feedback loop exists
whereby res piratory disease can cause gastro-oesopha-
Whilst gastro-oesophageal reflux and hiatal hernia can geal disease and gastro-oesophageal disease can
occur independently, with or without clinical signs, when worsen respiratory disease.
both reflux and a large hernia are present, more severe Oesophageal abnormalities may be observed with
disease is likely to occur (Hardie et al., 1998). When hiatal herniation. Within a population of young (3–4-month-
gastro-oesophageal reflux causes oesophagitis, this has old) Shar-Peis, some of which showed vomiting or

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