Gastric Dilatation-Volvulus in a Guinea Pig (Cavia porcellus)

Introduction

Guinea pigs are frequently presented to small animal practitioners for gastrointestinal (GI) stasis, a condition characterized by nonobstructive ileus and gaseous distention of the stomach, cecum, and/or intestines. Clinical signs of GI stasis include anorexia, decreased or absent fecal production, evidence of a painful abdomen, and abdominal distention. Diagnosis of GI stasis is based on history, physical examination, and radiographic findings. Investigating the systemic health of the guinea pig is important to detect an underlying cause of the GI stasis. Medical management of nonobstructed GI stasis consists primarily of supportive care including aggressive fluid therapy, pain management, and assisted feeding.

Less commonly, guinea pigs are presented with similar clinical signs as nonobstructed GI stasis, yet they are ultimately diagnosed with gastric dilatation-volvulus (GDV). Very few cases of GDV in guinea pigs have been reported, and, to date, each of these reports have been in laboratory animals.^1–3 The clinical signs and physical examination findings of GDV reported in guinea pigs are similar to those of functional ileus; therefore, radiographs are required to distinguish between the two conditions. In contrast to GI stasis, which is treated with medical management, GDV is a surgical emergency. The prognosis for guinea pigs with GDV is likely guarded to poor; however, no information is available regarding surgical management of GDV in guinea pigs, because all of the published GDV cases reported to date have been diagnosed at necropsy.^1–3 In these prior reports, GDV in guinea pigs has been associated with breeding sows, frequent repositioning during anesthesia, and the use of xylazine for anesthesia.^1,2

The purpose of this report is to describe the antemortem radiographic diagnosis and necropsy findings of GDV in a pet guinea pig. This condition is contrasted with diagnostic findings and management of GI stasis in guinea pigs.

Case Report

A 3-year-old, intact female guinea pig was presented for anorexia and lethargy of 24 hours’ duration. The owner reported having not observed urination or defecation for at least 12 hours. The sow had been treated by the owner with 33 mL/kg of lactated Ringer’s solution subcutaneously 12 hours prior to presentation, but no improvement was seen in her condition. The guinea pig was housed individually on a wood pulp fiber bedding,^a which she had not been observed to eat. Normal diet included timothy hay, an alfalfa-based pelleted guinea pig diet,^b and fresh vegetables offered daily. Water was provided ad libitum via sipper bottle. No other supplements were administered, and no recent changes in environment or diet were reported.

On physical examination, the guinea pig was obtunded. Body weight was 900 g, and the sow was subjectively determined to be mildly obese. Rectal temperature was 95.3°F (normal 99° to 103.1°F⁴); heart rate was 220 beats per minute (BPM) (normal 240 to 310 BPM⁴) with no murmurs or arrhythmias noted; and respiratory rate was 60 breaths per minute (normal 40 to 100 breaths per minute⁵) with clear lung sounds but an increased respiratory effort. The mucous membranes were pale pink and slightly dry, and capillary refill time was approximately 2 seconds. No gross evidence of dental malocclusion was seen. Abdominal palpation revealed a firm, markedly gas-distended GI tract, which appeared nonpainful on palpation. Borborygmi were absent on auscultation of all quadrants of the abdomen.

The guinea pig was placed on a gel heating pad to gradually increase the body temperature, and oxygen was administered (fraction of inspired oxygen was 100%) via facemask while diagnostics were performed. Butorphanol (0.5 mg/kg intramuscularly [IM]) was administered one time for analgesia, and midazolam (0.5 mg/kg IM) was administered one time to reduce anxiety and provide sedation. Abdominal radiographs revealed severe gas distention of two separate viscous structures in the abdomen. On the right lateral projection was a centrally positioned, large, round viscous structure flanked by two gas-distended bowel segments both cranially and caudally [Figure 1A]. The central structure was of intermediate opacity, indicating a dependent fluid component. On the ventrodorsal projection, the larger dilated structure appeared to the left and more caudal than on the lateral projection, and a right-sided, caudal gas-filled bulge was superimposed on a well-defined, gas-distended tubular segment [Figure 1B]. Additionally, a separate gas-dilated, viscous structure in the right cranial abdomen contained granular ingesta. Small, tubular, gas-filled structures were observed cranial to the left-sided dilated structure. Smoothly marginated, mineralized opacities were identified cranial to the coxofemoral joints bilaterally on the ventrodorsal projection and within one of the stifle joints on the lateral projection. Skull radiographs to assess dental health were not obtained.

Differential diagnoses for the caudal left-sided, gas-filled structure included gastric dilatation, GDV, foreign body obstruction, or cecal torsion. The shape and size of the more opaque gas-distended structure located on the left side of the abdomen in the ventrodorsal view was most compatible with a pathologically distended stomach. The more lucent gas-distended structures overlying one another on the right side of the abdomen in the ventrodorsal view were thought to be segments of cecum and large intestine, based on the solid character of the ingesta and size of the dilated region of the GI tract. The gas-filled structures visualized in the ventrodorsal view cranial to the stomach were compatible with cranially displaced intestinal loops. On a right lateral projection of a normal guinea pig, the most cranial bowel segment is the stomach. In this case, on the right lateral view the stomach was distended and caudally displaced, and the cranial structure was most compatible with a cranially displaced, distended cecum. The periarticular mineralizations were consistent with incidental, mild, secondary joint disease of the coxofemoral joints and one of the stifles.

Abdominal ultrasonography was attempted but was hindered by the large amount of gas contained in the abdominal contents; however, the stomach could not be identified in the normal location on ultrasound. The urinary bladder was small without any evidence of cystic calculi.

Based on the radiographic findings, a tentative diagnosis of GDV was made. This was determined to be a surgical emergency, and exploratory surgery was recommended to the owner. The owner was advised of potential complications of abdominal surgery, which included anesthetic death, peritonitis, ileus, and the formation of adhesions in the abdomen that could lead to long-term complications. Without surgery, the guinea pig was at risk of death from hypovolemic shock, ischemia of the stomach, and respiratory compromise due to the massive dilatation of the stomach. The owner was informed that because of a lack of available information regarding this condition in guinea pigs, the prognosis was unknown but thought to be guarded. The owner declined further treatment and elected euthanasia.

A complete necropsy of the guinea pig was performed. On gross examination, the stomach, mesentery, and associated small intestines were rotated 360° clockwise around the long (ventrodorsal) axis of the stomach, and the stomach was markedly distended with gas. Portions of the small and large intestines and mesentery filled the right cranial abdomen, abutting the visceral surface of the liver and displacing the stomach caudally and to the left. The stomach occupied the entire left side of the abdomen, from the diaphragm to the pelvis, and the greater curvature of the stomach paralleled the spine [Figure 2A]. No significant findings on necropsy could explain the development of GDV in this guinea pig. The cecum was markedly distended with gas but was not malpositioned.

Histological examination of the GI tract did not reveal evidence of gastritis or necrosis. Moderate, diffuse, hepatocellular lipidosis was present and may have been a consequence of anorexia. Additional histological findings were considered incidental and included mild, lymphoplasmacytic, perivascular nodules in the lungs; moderate, lymphofollicular hyperplasia of the spleen; mild, multifocal glomerulosclerosis; renal tubular ectasia; and mild, multifocal, renal tubular mineralization. The final diagnosis was GDV and severe cecal distention.

Discussion

Gastric dilatation-volvulus has been reported only infrequently in laboratory guinea pigs.^1–3 In addition, a case of gastric dilatation with possible volvulus was reported in a pet guinea pig; however, no necropsy findings were reported.⁶ Clinical signs reported to be associated with GDV in the guinea pig include tachypnea with shallow breathing, cyanosis of the mucous membranes, tachycardia, abdominal distention, and absence of normal borborygmi.¹ In several cases, affected animals were found dead with no prior clinical signs of disease.

Necropsy findings in guinea pigs with GDV included a markedly distended stomach comprising >50% of the abdominal cavity.^1,2 The stomach rotates on its mesenteric axis and has been reported to rotate 90°, 180°, or 360°.^1–3 Other necropsy findings that have been associated with GDV in guinea pigs include splenic torsion and congestion, pancreatic infarction, gastric infarction, hepatic necrosis, and concurrent biliary hyperplasia with chronic extrahepatic bile duct obstruction.^1,3 Often, no lesions of inflammation or necrosis are identified either in the stomach wall or intestines.¹ The cause of death in guinea pigs with GDV appears to be respiratory compromise due to compression of the diaphragm by the gas-distended stomach.² Circulatory collapse caused by compression of the caudal vena cava could also be involved.²

Reports of GDV in laboratory guinea pigs have identified breeding animals as being more commonly affected.¹ In addition, frequent repositioning during anesthesia and the use of xylazine for anesthesia may have contributed to the development of GDV in one case.² The guinea pig described in the current report had no history of breeding, recent anesthesia, or drug administration. A complete necropsy was performed in an attempt to determine the underlying cause for the development of GDV in this guinea pig; however, no underlying disease was identified. The guinea pig in the current report did not exhibit evidence of splenic torsion and congestion, gastric infarction, or pancreatic infarction, as have been reported on necropsy of other guinea pigs with GDV.

As in other reports of guinea pigs, this case lacks confirmatory histopathological findings for GDV that are described in other species. Typical findings in other species include gastric mucosal or transmural congestion and/or acute infarction with or without hemorrhagic gastric contents and hemoabdomen. Edema and circulatory shock due to reduced venous return may also be seen. One possible explanation for the lack of histological lesions in this case (and other guinea pig cases of GDV) is that the initial clinical signs were caused by gastric dilatation and displacement only, while the volvulus was peracute or terminal. More specifically, histological lesions had no time to develop. Another possibility is that the volvulus occluded the lumen of the stomach but did not occlude the associated blood vessels; therefore, no infarction or impedance of venous return occurred. Alternatively, the volvulus could have been intermittent, allowing periodic blood flow.

In dogs, GDV occurs much more commonly, yet its cause is unclear. However, certain risk factors have been identified, including increased gastrin levels, decreased motility of the stomach, and delayed gastric emptying.⁷ Other factors that may contribute to the development of GDV in dogs include diet, feeding behavior, exercise, and stress.⁷ Large-breed, deep-chested, and older dogs are considered to be at the highest risk for the development of GDV, while dogs that are described by their owners as having a “happy personality” are considered to be at decreased risk.^7–9

It is difficult to determine whether any of the risk factors predisposing dogs to GDV could play a part in guinea pigs developing GDV, especially given the differences between the canine and guinea pig GI tracts. Guinea pigs are herbivorous rodents and hindgut fermenters. Compared to the carnivore GI tract, which is relatively simple and has a short hindgut, the guinea pig GI tract is more complex and relies on a large cecum for microbial fermentation.¹⁰ Guinea pigs practice coprophagy and have a GI transit time of approximately 20 hours (66 hours if coprophagy is taken into account).⁴ The guinea pig stomach is glandular and does not contain a keratinized portion, as is found in some other rodents.¹¹ Guinea pigs, like other herbivorous rodents and rabbits, are unable to vomit.¹² Because of these differences in anatomy and physiology, unknown factors may predispose guinea pigs to the formation of GDV.

Feeding behavior is unlikely to be related to the development of GDV in guinea pigs. As opposed to dogs, which tend to eat food quickly as individual meals, guinea pigs generally consume food frequently throughout the day. Conformation is also an unlikely factor in the guinea pig, since its body shape is roughly tubular and does not vary greatly among breeds, as it does in dogs. Age may play a factor in guinea pigs developing GDV, but in the few reports of GDV in guinea pigs to date, the condition appears to be more common in young animals rather than in older animals, unlike what is seen in dogs. In one report, all of the guinea pigs with GDV were <26 months of age.¹ The guinea pig in the current report was approximately 36 months old and therefore slightly older than guinea pigs with GDV previously reported in the literature. The average life span of pet guinea pigs is 5 to 6 years.⁴

Factors that could contribute to the formation of GDV in a guinea pig include stress, delayed gastric emptying, and, possibly, abnormal movements of the animal. Gastrointestinal stasis is a common condition in guinea pigs that potentially could lead to delayed gastric emptying and distention of the stomach with food, fluid, or air.⁵ Once the stomach becomes dilated, it could rotate subsequent to certain movements of the animal (e.g., frequent repositioning during anesthesia for placement of a jugular venous cannula).² Clinicians should be aware of this possibility and avoid excessive repositioning of guinea pigs with gastric dilatation when performing radiographs. Finally, guinea pigs are shy animals and are predisposed to stress. The catecholamine response to a stressful event may be strong enough to lead to the death of the animal.¹³ In dogs, physiological factors involved in the stress response have been suggested to affect GI tract motility and function.⁹ A similar mechanism may also play a role in the development of GDV in guinea pigs. No stressors were reported in this guinea pig’s environment, such as changes in food or water, addition of new animals to the household, or sudden temperature changes.

Some of the more common systemic diseases of guinea pigs that could contribute to stress or lead to secondary GI stasis and possibly predispose to GDV include dental disease, cystic calculi, respiratory disease, and hypovitaminosis C. No underlying disease processes such as these were identified on either the physical examination or necropsy of the guinea pig in this report.

The guinea pig in this report was diagnosed with GDV based on a combination of clinical signs and radiographic findings. Gastrointestinal stasis, however, is a much more common condition in guinea pigs. The clinical signs of anorexia, lack of fecal production, absence of borborygmi, dehydration, obtundation, increased respiratory effort, hypothermia, and gas distention of the abdomen—all of which were observed in this case—could be observed in guinea pigs with either GI stasis or GDV. Other signs consistent with either condition include tachycardia, tachypnea, pain on palpation of the abdomen, bruxism, hyperthermia, and injected mucous membranes.^1–3,5,6 The bradycardia and lack of pain response upon abdominal palpation in the guinea pig of this report were unusual findings and possibly results of hypovolemic shock and the obtunded mentation of the animal. Gastrointestinal stasis can cause massive dilatation of the stomach (“bloat”), leading to compression of the vena cava with associated poor perfusion, as well as compression of the diaphragm and respiratory compromise. Therefore, clinical signs associated with gastric dilatation can be similar to signs of GDV. Radiographs are necessary to determine whether GDV or other obstructive diseases requiring surgical intervention are present.

Only one previous report of a guinea pig with GDV included radiographic findings.⁶ In that report, as well as the current report, the stomach was massively dilated and displaced from its normal orientation. Previous reports of necropsy findings have identified a stomach filling >50% of the abdominal cavity in guinea pigs with GDV.^1,2 Severe gastric dilatation in the absence of volvulus can also occur. In cases of gastric dilatation without volvulus, the intestines may be distended with gas, but they typically remain in their normal location caudal to the stomach [Figure 3A]. In addition, the stomach is markedly distended with gas but remains in the normal orientation in the left cranial abdomen, and the degree of dilatation of the stomach is generally <50% of the abdominal cavity [Figure 3B]. In contrast, displacement of the stomach from its normal position by intestines or cecum supports a diagnosis of GDV, as was observed in this case [Figure 1A].

Compartmentalization of the stomach observed in the right lateral radiograph, leading to the classic appearance that is found in dogs,¹⁴ can be found in guinea pigs; however, in the current case, no obvious evidence of compartmentalization of the stomach was seen. This radiographic finding may depend on the degree of rotation of the stomach. Abdominal ultrasound may help distinguish between GDV and GI stasis, although the presence of gas in the viscera can hinder the ability to distinguish among abdominal organs, as occurred in this case.

Distinguishing between GI stasis and GDV is important, because the recommended treatments for the two conditions are different. Although treatment for GDV in guinea pigs has not been reported, the assumption is that the treatment of choice would be the same as in dogs: surgery. Not performing surgery increases the risk of ischemia of the stomach, hypovolemic shock, and respiratory compromise from compression of the diaphragm by the dilated GI organs.⁷ In dogs, the recommendation is to proceed with surgery as soon as the animal is stable enough—no later than 2 to 3 hours after presentation.⁷ Surgical management of GDV in a guinea pig is anticipated to be similar to that in dogs.

Despite the small size of guinea pigs, it is possible to place intravenous or intraosseous catheters to provide fluid therapy using a combination of crystalloids and colloids. Decompression of the stomach can be attempted prior to surgery either by placement of a gastrostomy tube or by percutaneous decompression;⁵ however, each of these procedures carries risk. For example, passage of a gastrostomy tube can be very stressful to the guinea pig, and percutaneous decompression has a risk of perforation of the stomach with leakage of GI contents.⁵ Percutaneous decompression of the stomach was not attempted in the guinea pig in the current report, because it was considered to carry too high a risk of rupture of the stomach and leakage of gastric contents into the abdomen. If the owner had elected surgery, placement of an orogastric tube once the guinea pig was anesthetized could have been attempted.

Intubation in guinea pigs for maintenance of general anesthesia is particularly challenging because of the presence of a palatal ostium.¹⁵ Techniques for intubating guinea pigs have been described, including the use of endoscopy; however, these approaches can be difficult, especially in an emergency situation. Therefore, anesthesia of the guinea pig would possibly require maintenance via facemask during surgery, leading to increased anesthetic risks.¹⁶ Alternatively, temporary tracheostomy could be considered.¹³

Surgical techniques for abdominal exploratory and derotation of the stomach could follow recommendations for dogs, but the biology and anatomy of the guinea pig must be considered. Gentle handling of the GI tract is important during surgery to reduce the risk of postoperative ileus.¹³ While gastropexy is indicated to reduce the risk of GDV recurrence in dogs, it is unknown whether guinea pigs are likely to develop a recurrence of such a rare condition and whether gastropexy would be of benefit in the guinea pig.

In contrast to GDV, most cases of GI stasis without gastric volvulus are nonobstructive and require aggressive medical therapy. The standards of medical treatment for GI stasis in small herbivorous mammals are pain control; hydration using intravenous, intraosseous, or subcutaneous fluids; and assisted feeding to promote GI motility.^5,17 If diarrhea is present or enterotoxemia is suspected, antibiotics may be considered. Other medications such as gastric motility agents or antifoaming agents to reduce gas in the stomach are sometimes utilized, but their efficacy is unproven in guinea pigs.^5,17 Gastric motility agents should not be used in cases where obstruction is possible, such as with severe gastric dilatation or abdominal pain.¹⁷ In some cases of GI stasis, decompression of gas-filled viscera may be required either by passage of an orogastric tube or by percutaneous trocarization.⁵

Treatment of GDV in guinea pigs has not been reported; therefore, the prognosis is unknown. Since the prognosis for severe gastric dilatation is generally considered to be grave in guinea pigs, and because the mortality rate for dogs with GDV is 15% to 33% even with appropriate treatment, the prognosis for guinea pigs with GDV is also expected to be poor.^6,18

Conclusion

Gastric dilatation-volvulus was diagnosed in this 3-year-old, female guinea pig with no evidence of concurrent health problems. While GDV is an uncommon presentation in guinea pigs, it should be considered as a differential diagnosis for severe abdominal distention and/or abdominal pain. Every attempt should be made to distinguish between GDV and GI stasis because of the increased risk of morbidity and mortality associated with abdominal surgery in guinea pigs. A stomach that is dilated and occupying >50% of the abdominal cavity in addition to being caudally displaced by intestines on radiographs is suggestive of GDV. Abdominal ultrasonography may be beneficial in confirming the diagnosis of GDV. The prognosis for guinea pigs with GDV, while unknown, is likely guarded to poor.