The present retrospective study confirms some findings of other studies and offers some new insights into this disorder for the small animal practitioner. Specifically, investigating those factors that influence the outcome for endoscopic foreign body retrieval has practical implications regarding estimated anaesthetic time and likelihood of surgical intervention.
The type of dogs presented (middle-aged, small breeds), and their clinical signs were similar to previous reports [10, 13, 6, 16]. In addition, they did not differ between the two groups presented in the study and signalment or clinical features provided no insight into success or otherwise of endoscopic foreign body retrieval. Several other studies have suggested terrier breeds as being over-represented [10, 6, 16], although in one study poodles were overrepresented [13], suggesting that breed predisposition may be more representative of the general dog population. However, in the present study there was a definite breed predisposition for terrier breeds and WHWT compared to the general hospital population interrogated over the same time period. As a consequence, while other disorders may give rise to similar clinical signs of acute regurgitation and retching, oesophageal foreign bodies should be given greater priority in terriers and WHWT in particular.
In dogs, bones or bone fragments are the most common cause of oesophageal obstruction ranging from 47% to 100% in reported studies [13, 6, 9, 12]. Similarly, the majority of foreign bodies were bones in the present study. Foreign bodies typically lodge in the oesophagus where there is physiologic narrowing including the pharynx, thoracic inlet, heart base and distal oesophagus. All regions except for the pharynx were represented in the present study and overall the most commonly affected area was the distal oesophagus caudal to the heart base. Interestingly, while location did not affect outcome, it was different between the terriers and non-terriers being significantly more commonly found caudal to the heart base in the former group. It is unclear why terriers are over-represented or why the location varies. Behavioural differences have been speculated with little scientific foundation [9]. A second possible explanation is that the sites of reduced oesophageal diameter may be different between breeds and this concept may be supported by the different locations found in the present study. However, another possibility is that terriers are predisposed to oesophageal motility disorders and gastro-oesophageal reflux (GER), as reported previously [1]. A motility disorder increases the risk of oesophageal foreign bodies normally conducted to the stomach in other breeds. In addition, GER could predispose them to slight stricture formation of the distal oesophagus accounting for the different location as reported here. However this is largely speculative and motility disorders previously reported in terriers have only been demonstrated in young dogs, younger than the cases presented in the current study.
Radiographs were available for retrospective study in the majority of cases. Not surprisingly given that most foreign bodies were bones, most were visible radiographically. In order to account for differences in breed size, the dimensions of the foreign bodies were normalised to the individual animal. However, the size of the foreign bodydid not influence outcome or the incidence of long-term complications and should not be used as a reason to avoid endoscopic retrieval. Despite this, radiographic assessment is still valuable as it provides important information on location and on changes that can occur secondary to the foreign body (perforation, aspiration pneumonia).
The overall success rate of just over 65% for endoscopic retrieval or dislodgement was lower in this study compared to rates of between 73% and 87% reported elsewhere [16, 12]. This may reflect the fact that duration of clinical signs prior to presentation was longer than in most previous reports combined with a different emphasis in this study as an attempt was being made to better define factors that could predict outcome. Specifically animals in which endoscopic retrieval was not attempted because of known complications (e.g. oesophageal rupture) were also included. If such animals were excluded, the overall success rate was approximately 73% and therefore more comparable to the previous studies. The recovery rate and incidence and type of short-term complications is also similar in this and other studies [16, 4, 12]. Overall there was a relatively low rate of short-term complications together with a low mortality rate of just over 10% in accordance with previous studies [16, 9, 12], while other studies have reported mortality rates of 15.2-26% [13, 10, 8]. However, dogs in which surgical intervention was required took significantly longer before spontaneously feeding resulting in more prolonged hospitalisation and increased costs.
In this study the degree of oesophagitis did not influence the success or otherwise of endoscopic retrieval or dislodgement. However, clinical signs were present for longer in those dogs in which endoscopic removal was not successful. By contrast in another study, the duration of clinical signs prior to presentation was significantly shorter for dogs with mild oesophagitis compared to those with moderate-to-severe oesphagitis [12]. This difference may be explained by the way in which oesophageal damage was assessed in the latter paper using the Savary-Miller classification which puts more emphasis on the confluence of erosions rather than the more subjective classification used here. Nevertheless it is reasonable to suggest that the longer the foreign body is present the more likely an alternative to endoscopy is required for removal. As a consequence, such cases should be managed early in the day with appropriate preparation for possible surgical intervention.
Of the 28 survivors for which long-term outcome was known, approximately one quarter were suspected to have oesophageal stricture, based on the owners reports of regurgitation of any food not mashed beforehand. Few studies have clearly reported the rate of stricture formation but it seems that in older reports stricture formation was rare [9, 16] while in more recent studies a rather high incidence of complications was identified on long-term follow-up. In a recent retrospective study of oesophageal obstruction caused by a dental chew treat, oesophageal stricture developed in 6 of 25 dogs (24.0%) that survived initial hospitalisation [8]. In another retrospective study of 60 cases, mild stricture formation was reported 9-21 days post-removal in 5 of 17 (29.4%) dogs for which outcome was available and this only occurred in dogs previously classified as having moderate-to-severe oesophagitis [12]. While intuitively, stricture formation would be considered more likely associated with more severe damage to the oesophagus, this was not the case in the present study. Again, the subjective way the oesophageal damage was classified may be responsible for the difference in the studies. Due to the retrospective nature of this study, a classification based on circumference damage was not possible but may correlate better to the rate of stricture formation. However, the fact that the rate of stricture formation was high in a previous report on dental chews [8] and developed in cases presented here with soft foreign bodies and in cases where damage to the oesophageal mucosa was judged mild, suggests that stricture formation is a possible consequence of any oesophageal foreign body and may relate more to the extent of contact rather than its oesophageal penetration. To prevent stricture formation, the use of topical and/or systemic antacids is standard [17, 15]. Administration of antibiotics along with dietary restriction is also traditionally recommended. Withholding food and water, providing parenteral or gastric nutrition and hydration, is thought to minimize trauma to the mucosa and reduce fibroblastic reaction responsible for stricture formation [17]. All of these measures are routinely implemented in the UVH but obviously do not decrease the risk completely and other preventive measures should be investigated. Although withholding food per os post-removal is usually recommended for preventing oesophageal strictures, it potentially could favour stricture formation by preventing natural stretch with larger food particles. Studies directly comparing dogs fed a normal diet and those fed liquid food post-foreign body removal have not yet been published. In humans, the use of mitomycin-C an anthracycline, after oesophageal dilatation has been shown to be effective in reducing the rate of stricture reformation [7]. Research in rats, after standardised trauma to the oesophagus, show promising results with the antimetabolic agent halofuginone when topically applied [5]. Similar research is lacking in dogs and cats.
