Hiatal herniation is a relatively uncommon but increasingly recognized problem in dogs causing regurgitation of food and water, discomfort and the potential for the development of esophageal inflammation, esophageal stricture and aspiration pneumonia. In veterinary medicine there is a relatively rudimentary understanding of the function of the canine gastro-esophageal junction (GEJ), which forms the natural barrier for reflux of food, water and stomach acid back up into the esophagus. The lower esophageal sphincter (LES) is created by the muscular tone within the circular smooth muscle of the muscularis mucosa of the distal esophagus as well as the mechanical support provided by the attachments of the esophagus to the diaphragm as it passes from the chest into the abdominal cavity.

Surgical techniques for the treatment of hiatal herniation (HH) in people have been extensively studied and have received rigorous evaluation over the years in the scientific literature. The same cannot be said for HH in dogs. Of the group of gastroesophageal junction (GEJ) anomalies that are seen in the dog (which includes sliding hiatal hernia, paraesophageal hernia and gastroesophageal intussusception), sliding hiatal hernia is by far the most common. This condition can arise as a congenital anomaly and has been reported most commonly in this form in young shar-peis.^1,2 Acquired HH can be seen secondary to airway obstructive disease or neuromuscular disorders affecting the diaphragm.³ In brachycephalic breeds it is thought that increased inspiratory effort leads to a reduction in intra-esophageal and intrapleural pressures, possibly leading to the distal esophagus and stomach being pulled into the thoracic cavity during inspiration.⁴ Clinical observations have been made to substantiate this proposed pathophysiology where a population of bulldogs with HH were shown to exhibit the more severe manifestations of brachycephalic syndrome compared to bulldogs without HH.³

A multitude of treatment recommendations for HH have been made in the literature over the years. Medical management has been aimed at inhibition of normal gastric acid secretion to reduce its ulcerogenic effects on the esophagus when GERD occurs and is centered around the administration of antacids or proton pump inhibitors.

Mucosal protectants such as sucralfate have been recommended in slurry form to coat and protect the distal esophagus from the effects of reflux. Some studies have suggested that medical management is often unsuccessful in controlling clinical signs,¹ whereas others have suggested that medical management should always be attempted as it alone can be successful in over 50% of cases.⁵ These discrepant results may be partially attributable to differing case populations or to the lack of standardized reporting of outcomes for this condition. However, it is safe to say that there is an important role for surgery in the treatment of HH as treatment failures following medical management occur with some frequency. Furthermore, some authors believe that if there is a deficiency in barrier function of the GEJ that can be surgically treated this may be a better approach to management than attempts at medically alleviating the consequences of GERD. To that end several surgical therapies have been in common usage for many years for treatment of HH in dogs. The most common approach is a combination of treatments using diaphragmatic hiatal reduction (phrenoplasty or crural apposition), esophagopexy and left-sided gastropexy.^1,2,5,6 Outcome data for this combination of therapies is quite variable, and the ability to formally evaluate the procedure is adversely affected by small case numbers, combination therapies and inconsistent outcome measures.^1,2,5,6 Fundoplication procedures, often used in humans with GERD, have also been reported for use in dogs with less encouraging results and a possibly higher incidence of complications.⁵

There are currently a number of objective methods for assessment of LES function and hiatal herniation, some of which have been used for some years and others that have only recently become available. Positive contrast videofluoroscopic studies have been the gold standard for non-invasive diagnosis of hiatal hernias for many years. While clear evidence of the gastric cardia crossing the diaphragm into the thorax can be taken as reliable evidence of a hiatal hernia being present, it is likely that false negatives are common using this approach given the often intermittent nature of the condition and the possibility of missing an episode of herniation when only a short series of swallows is observed in any given study.⁷ Objective assessment of barrier function has been reported in the literature in experimental canine studies and a variety of factors have been shown to influence LES tone including, patient position, type of surgery as well as injectable and inhalant drugs.^8-10 These studies have mainly relied on either single channel manometry or pull-through pressure transducer techniques. However, currently more sophisticated modalities for assessment of esophageal tone and anatomical constraints of the GEJ have become available and are in use by the authors group. High-resolution manometry (HRM) allows accurate assessment of neuromuscular activity within the esophagus and esophageal sphincters using a probe incorporating 36 pressure sensors. The device allows the creation of spatiotemporal plots of esophageal pressure activity along the entire length of the esophagus and helps to elucidate the functional anatomy of the structures involved in HH.

The author’s research group has been studying two populations of dogs with hiatal hernias using one or more of these modalities as well as a clinical dysphagia assessment tool (CDAT) to evaluate the owner’s perceptions of clinical signs pre- and post-operatively. Dogs that have not responded or responded insufficiently to medical management have undergone surgical management using the technique described by Prymak⁶ and subsequently reported by others.⁵ These dogs have been prospectively enrolled in a study evaluating pre- and post-operative clinical evaluation questionnaires (CDAT), positive contrast video-fluoroscopy and intraoperative geometric analysis of the LES using impedance planimetry. The results of this study were recently published and showed that in 80% of dogs with pre- and post-operative clinical assessments, completed postprandial regurgitation improved. Hiatal hernia severity scores from videofluoroscopic swallow studies improved significantly, although the frequency score did not reach statistical significance.¹¹ However, it is important to note that although improvement was seen in a majority of dog’s clinic signs, many of them did not have complete resolution of clinical signs.

Minimally invasive surgery is the standard of care for treatment of hiatal hernia and GERD in humans, and development of these techniques for dogs with these conditions should be advanced. The author's group have now performed laparoscopic hiatal hernia repair on 16 dogs at UC–Davis with generally good but also variable results.¹² The outcomes in these dogs are being carefully evaluated as was done in the study of the traditional open surgical approach. This will allow some degree of comparison to be made between open and laparoscopic approaches to ensure that a minimally invasive approach is at least as good as the traditional approach. These data will be published in the future.

References

1.  Callan MB, Washabau RJ, Saunders HM, et al. Congenital esophageal hiatal hernia in the Chinese Shar-Pei dog. J Vet Intern Med. 1993;7:210–215.

2.  Guiot LP, Lansdowne JL, Rouppert P, et al. Hiatal hernia in the dog: a clinical report of four Chinese Shar-Peis. J Am Anim Hosp Assoc. 2008;44:335–341.

3.  Hardie EM, Ramirez O, Clary EM, et al. Abnormalities of the thoracic bellows: stress fractures of the ribs and hiatal hernia.  J Vet Intern Med. 1998;12:279–287.

4.  Stalcup SA, Mellins RB. Mechanical forces producing pulmonary edema in acute asthma. N Eng J Med. 1997;297:592–596.

5.  Lorinson D, Bright RM. Long-term outcome of medical and surgical treatment of hiatal hernias in dogs and cats: 27 cases (1978–1996). J Am Vet Med Assoc. 1998;213:381–384.

6.  Prymak C, Saunders HM, Washabau RJ. Hiatal hernia repair by restoration and stabilization of normal anatomy. An evaluation in four dogs and one cat. Vet Surg. 1989;18:386–391.

7.  Pollard RE. Imaging evaluation of dogs and cats with dysphagia. ISRN Vet Sci. 2012;238–505.

8.  Hashim MA, Waterman AE, Pearson H. A comparison of the effects of halothane and isoflurane in combination with nitrous oxide on lower esophageal sphincter pressure and barrier pressure in anesthetised dogs. Vet Rec. 1995;137:658–661.

9.  Waterman AE, Hashim MA, Pearson H. Effect of body position on oesophageal and gastric pressures in the anaesthetised dog. J Small Anim Pract. 1995;36:196–200.

10.  Strombeck DR, Harrold D. Effects of atropine, acepromazine, meperidine and xylazine on gastresophageal sphincter pressure in the dog. Am J Vet Res. 1985;46:963–965.

11.  Mayhew PD, Marks SL, Pollard R, et al. Prospective evaluation of surgical management of sliding hiatal hernia and gastroesophageal reflux in dogs. Vet Surg. 2017;46:1098–1109.

12.  Mayhew PD, Marks SL, Pollard R. Prospective evaluation of laparoscopic treatment of type 1 sliding hiatal hernia and gastroesophageal reflux in four dogs. Vet Surg. 2016;45:O124–125.