# Diagnosis and surgical management of intussusception in an axolotl (Ambystoma mexicanum)

Sabrina Vieu, Charlotte Coeuriot, Laetitia Dorso, Marion Fusellier

► To cite this version:

Sabrina Vieu, Charlotte Coeuriot, Laetitia Dorso, Marion Fusellier. Diagnosis and surgical management of intussusception in an axolotl (Ambystoma mexicanum). Journal of Exotic Pet Medicine, 2023, 46, pp.19-24. 10.1053/j.jepm.2023.03.006. hal-04142850

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# Diagnosis and surgical management of intussusception in an axolotl (Ambystoma mexicanum)

Sabrina Vieu, Charlotte Coeuriot, Laetitia Dorso, Marion Fusellier

<figure><img src="image_2.png" /></figure>

► To cite this version:

Sabrina Vieu, Charlotte Coeuriot, Laetitia Dorso, Marion Fusellier. Diagnosis and surgical management of intussusception in an axolotl (Ambystoma mexicanum). Journal of Exotic Pet Medicine, 2023, 46, pp.19-24. 10.1053/j.jepm.2023.03.006. hal-04142850

HAL Id: hal-04142850

https://hal.inrae.fr/hal-04142850v1

Submitted on 4 Jun 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_3.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
1 Diagnosis and surgical management of intussusception in an axolotl (Ambystoma

2 mexicanum)

3

4 Sabrina Vieu¹*, Charlotte Coeuriot²*, Laetitia Dorso³, ⁵, Marion Fusellier², ⁴

5

6 ¹ Service des Nouveaux Animaux de Compagnie, Oniris, CHUV, 44300 Nantes, France

7 ² Service d'Imagerie Médicale, Oniris, CHUV, 44300 Nantes, France

8 ³ Service Autopsie, Oniris, CHUV, 44300 Nantes, France

9 ⁴ Oniris, Nantes Université, Inserm, RMeS, F-44000 Nantes, France

10 ⁵ Oniris, INRAE, BIOEPAR, 44300 Nantes, France

11

12 * co-authors
1 Diagnosis and surgical management of intussusception in an axolotl (*Ambystoma mexicanum*)

2

3

4 Sabrina Vieu¹*, Charlotte Coeuriot²*, Laetitia Dorso³, ⁵, Marion Fusellier², ⁴

5

6 ¹ Service des Nouveaux Animaux de Compagnie, Oniris, CHUV, 44300 Nantes, France

7 ² Service d'Imagerie Médicale, Oniris, CHUV, 44300 Nantes, France

8 ³ Service Autopsie, Oniris, CHUV, 44300 Nantes, France

9 ⁴ Oniris, Nantes Université, Inserm, RMeS, F-44000 Nantes, France

10 ⁵ Oniris, INRAE, BIOEPAR, 44300 Nantes, France

11

12 * co-authors
1 Diagnosis and surgical management of intussusception in an axolotl (Ambystoma

2 *mexicanum*)

3

4 ABSTRACT

5

6 Background: Intussusception diagnosis and surgical management in axolotl (Ambystoma

7 *mexicanum*) is poorly documented.

8 Case Description: A client-owned, five-year-old, sexually intact, female axolotl was presented

9 for hyporexia of four-week duration associated with regurgitation after feedings. Clinical
10 examination showed lethargy, weight loss, and firm tissue at coelomic palpation. Coelomic
11 ultrasonography was consistent with an intestinal intussusception. An exploratory coeliotomy
12 was performed, followed by an intestinal resection and anastomosis of a thickened portion of
13 intestinal loop. Following surgical excision of the invaginated intestinal loops, anorexia was
14 not resolved, and the axolotl died four days later. A necropsy revealed a serofibrinous
15 coelomitis. Histopathology confirmed the presence of an obstructive mass in the resected
16 portion of the intestines.

17 **Conclusion and case relevance:** This report describes an intussusception diagnosis and
18 attempted treatment in an axolotl. Ultrasonography in axolotl with non-specific gastrointestinal
19 symptoms is recommended for evaluation of the coelomic organs.

20

21

22

23 **Keywords:** Axolotl, Amphibian, Enterectomy, Histopathology, Intussusception,

24 Ultrasonography
## 25 Introduction

Intussusception diagnosis and management in amphibians have been poorly documented. The following databases (PubMed and CAB) were searched with the following keywords: amphibian, axolotl, enterectomy, gastrointestinal disease, intussusception, ultrasounds, and ultrasonography on [09/17/22]; three reference textbooks were consulted.<sup>1-3</sup> No reports of intussusception were found with these searches. This case describes an intussusception diagnosis and attempted treatment in an axolotl.

## 33 Case presentation

A 5-year-old, 88 g, sexually intact, female, leucistic axolotl (*Ambystoma mexicanum*) was presented for hyporexia of four-week duration associated with regurgitation after feedings. Weight loss and poor general condition were noticed by the owner. The animal lived with another male axolotl in a glass tank (120 x 40 x 40 cm) with a water temperature between 18 °C and 21 °C (64.4 °F to 68 °F), an external filter, and small rocks as substrate. The diet consisted of axolotl pellets (NovoLotl; JBL) supplied once or twice a week. The axolotl last produced eggs two months earlier. Clinical examination revealed lethargy, reduced muscle mass over the spine and limbs, gill atrophy, and pale oral mucous membranes. Firm tissue was palpable in the mid-coelom.

Lateral and dorsoventral radiographs of the whole body were unremarkable. Coelomic ultrasonography (L15-7io compact linear array transducer, PHILIPS Affiniti 70G, 7-15 MHz) revealed a mid-coelomic mass effect, with a multilayered appearance of the intestinal wall in longitudinal view, consistent with intussusception. On transverse view, multiple concentric rings were present, with the outer bowel segment (intussuscipiens) hypoechoic and thickened,
## 25 Introduction

Intussusception diagnosis and management in amphibians have been poorly documented. The following databases (PubMed and CAB) were searched with the following keywords: amphibian, axolotl, enterectomy, gastrointestinal disease, intussusception, ultrasounds, and ultrasonography on [09/17/22]; three reference textbooks were consulted.<sup>1-3</sup> No reports of intussusception were found with these searches. This case describes an intussusception diagnosis and attempted treatment in an axolotl.

## 33 Case presentation

A 5-year-old, 88 g, sexually intact, female, leucistic axolotl (*Ambystoma mexicanum*) was presented for hyporexia of four-week duration associated with regurgitation after feedings. Weight loss and poor general condition were noticed by the owner. The animal lived with another male axolotl in a glass tank (120 x 40 x 40 cm) with a water temperature between 18 °C and 21 °C (64.4 °F to 68 °F), an external filter, and small rocks as substrate. The diet consisted of axolotl pellets (NovoLotl; JBL) supplied once or twice a week. The axolotl last produced eggs two months earlier. Clinical examination revealed lethargy, reduced muscle mass over the spine and limbs, gill atrophy, and pale oral mucous membranes. Firm tissue was palpable in the mid-coelom.

Lateral and dorsoventral radiographs of the whole body were unremarkable. Coelomic ultrasonography (L15-7io compact linear array transducer, PHILIPS Affiniti 70G, 7-15 MHz) revealed a mid-coelomic mass effect, with a multilayered appearance of the intestinal wall in longitudinal view, consistent with intussusception. On transverse view, multiple concentric rings were present, with the outer bowel segment (intussuscipiens) hypoechoic and thickened,
49

and a normal inner bowel segment (intussusceptum). The mesenteric fat was hyperechogenic to the surrounding tissue (Figure 1 and Video 1).

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Surgical intervention was elected to correct the intussusception. The axolotl was sedated with butorphanol (0.2 mg/kg intramuscular [IM]; Torphasol®, Axience, Pantin, France) and alfaxalone (5 mg/kg IM; Alfaxan®, Jurox, Dublin, Ireland). Analgesia was completed with meloxicam (0.1 mg/kg IM; Metacam®, Boehringer, Lyon, France). Sedation effects were observed in less than 5 minutes after injection, and anesthesia was induced by placing the axolotl in a bath of sterile saline [0.9% NaCl] solution with alfaxalone (12.5 mg/L) oxygenated with an oxygen concentrator (100% oxygen at 0.5 L/min). The axolotl was placed in dorsal recumbency with an ultrasound Doppler probe (Parks Medical Electronics, 811-Bts Ultrasonic Doppler Flow Detector, 8.2 MHz) placed above the heart for monitoring. Branchial and transcutaneous irrigation with alfaxalone (drop-by-drop administration of 15 mg of alfaxalone diluted in saline [0.9% NaCl] solution) was performed every 3 minutes to maintain anesthesia.

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The skin was cleaned with povidone-iodine applied with gauze for 15 seconds. Local anesthesia was performed with a lidocaine drop on the skin (0.5 mg/kg; Laocaine®, MSD Santé Animale, Beaucouze, France). An exploratory coeliotomy was performed through a 4 cm craniocaudal skin incision by a paramedian approach with a #11 blade. The coelomic membrane was elevated and carefully incised. Exploration of the coelomic cavity revealed a severely congested and distended intestinal loop immediately aboral to the stomach, without an intestinal segment observed between these two structures. The small intestine after the pylorus was entirely intussuscepted in the ileocolic region (Figure 2A). Gentle manual traction on the intussusceptum and pressure on the intussuscipiens aided in reduction. Once the intussusception was resolved, enteric vessels were grossly normal. The bowel wall did not appear ischemic. The last portion reduced of the intussusception was the cranial part of the
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and a normal inner bowel segment (intussusceptum). The mesenteric fat was hyperechogenic to the surrounding tissue (Figure 1 and Video 1).

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Surgical intervention was elected to correct the intussusception. The axolotl was sedated with butorphanol (0.2 mg/kg intramuscular [IM]; Torphasol®, Axience, Pantin, France) and alfaxalone (5 mg/kg IM; Alfaxan®, Jurox, Dublin, Ireland). Analgesia was completed with meloxicam (0.1 mg/kg IM; Metacam®, Boehringer, Lyon, France). Sedation effects were observed in less than 5 minutes after injection, and anesthesia was induced by placing the axolotl in a bath of sterile saline [0.9% NaCl] solution with alfaxalone (12.5 mg/L) oxygenated with an oxygen concentrator (100% oxygen at 0.5 L/min). The axolotl was placed in dorsal recumbency with an ultrasound Doppler probe (Parks Medical Electronics, 811-Bts Ultrasonic Doppler Flow Detector, 8.2 MHz) placed above the heart for monitoring. Branchial and transcutaneous irrigation with alfaxalone (drop-by-drop administration of 15 mg of alfaxalone diluted in saline [0.9% NaCl] solution) was performed every 3 minutes to maintain anesthesia.

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The skin was cleaned with povidone-iodine applied with gauze for 15 seconds. Local anesthesia was performed with a lidocaine drop on the skin (0.5 mg/kg; Laocaine®, MSD Santé Animale, Beaucouze, France). An exploratory coeliotomy was performed through a 4 cm craniocaudal skin incision by a paramedian approach with a #11 blade. The coelomic membrane was elevated and carefully incised. Exploration of the coelomic cavity revealed a severely congested and distended intestinal loop immediately aboral to the stomach, without an intestinal segment observed between these two structures. The small intestine after the pylorus was entirely intussuscepted in the ileocolic region (Figure 2A). Gentle manual traction on the intussusceptum and pressure on the intussuscipiens aided in reduction. Once the intussusception was resolved, enteric vessels were grossly normal. The bowel wall did not appear ischemic. The last portion reduced of the intussusception was the cranial part of the
intestinal tract located directly aboral to the pylorus, with a major thickening over 0.75 mm in length. Firm pink nodules of 1 mm were observed on the duodenal serosa (Figure 2D) with yellow mesenteric nodules. The rest of the intestinal tract appeared normal. Intestinal resection and anastomosis (IRA) of the thickened portion was initiated in a similar manner as in mammals. The thickened portion was raised with cotton-tipped applicators and clamped with hemostats, separating it from the remaining viscera. The blood vessels supplying the isolated segment were ligated with a 5-0 poliglecaprone monofilament absorbable suture (Monocryl 5/0®, Ethicon, Issy-les-Moulineaux, France). The mesentery was incised near the ligated vessels. After vessel ligation, the intestinal portion was removed, and a single-layer closure was used for end-to-end anastomosis (5-0 poliglecaprone). The resected loop portion was fixed in 10% buffered formalin. The coelomic cavity was rinsed with a sterile saline [0.9% NaCl] solution. The coelomic membrane was closed with a continuous suture pattern (5-0 poliglecaprone), and the skin in a horizontal mattress pattern with a 4-0 nylon monofilament non-absorbable suture (Filapeau 4/0®, Peters Surgical, Boulogne-Billancourt, France). After surgery, the axolotl was placed in a water bath with oxygen delivered by an oxygen concentrator (100% oxygen at 0.5 L/min) for recovery and was fully awake in 60 minutes.

One day after the surgery, the axolotl was discharged with metronidazole (10 mg/kg per os q24 h; Flagyl® 125 mg/mL, Sanofi Aventis, Gentilly, France) for 7 days. However, two days later, the axolotl became more lethargic, developed an abnormal position in the water column, and died four days after the surgery. No signs of appetite were observed.

At necropsy, no signs of skin or coelomic membrane dehiscence were noted. A serofibrinous coelomitis characterized by the presence of a light brown serofibrinous effusion of 2 ml and brown coloration of the entire thickness of the intestinal tract and of the parietal coelom
intestinal tract located directly aboral to the pylorus, with a major thickening over 0.75 mm in length. Firm pink nodules of 1 mm were observed on the duodenal serosa (Figure 2D) with yellow mesenteric nodules. The rest of the intestinal tract appeared normal. Intestinal resection and anastomosis (IRA) of the thickened portion was initiated in a similar manner as in mammals. The thickened portion was raised with cotton-tipped applicators and clamped with hemostats, separating it from the remaining viscera. The blood vessels supplying the isolated segment were ligated with a 5-0 poliglecaprone monofilament absorbable suture (Monocryl 5/0®, Ethicon, Issy-les-Moulineaux, France). The mesentery was incised near the ligated vessels. After vessel ligation, the intestinal portion was removed, and a single-layer closure was used for end-to-end anastomosis (5-0 poliglecaprone). The resected loop portion was fixed in 10% buffered formalin. The coelomic cavity was rinsed with a sterile saline [0.9% NaCl] solution. The coelomic membrane was closed with a continuous suture pattern (5-0 poliglecaprone), and the skin in a horizontal mattress pattern with a 4-0 nylon monofilament non-absorbable suture (Filapeau 4/0®, Peters Surgical, Boulogne-Billancourt, France). After surgery, the axolotl was placed in a water bath with oxygen delivered by an oxygen concentrator (100% oxygen at 0.5 L/min) for recovery and was fully awake in 60 minutes.

One day after the surgery, the axolotl was discharged with metronidazole (10 mg/kg per os q24 h; Flagyl® 125 mg/mL, Sanofi Aventis, Gentilly, France) for 7 days. However, two days later, the axolotl became more lethargic, developed an abnormal position in the water column, and died four days after the surgery. No signs of appetite were observed.

At necropsy, no signs of skin or coelomic membrane dehiscence were noted. A serofibrinous coelomitis characterized by the presence of a light brown serofibrinous effusion of 2 ml and brown coloration of the entire thickness of the intestinal tract and of the parietal coelom
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caudally to the IRA site was observed (Figure 3). The remainder of the examined tissues were unremarkable. The IRA and intestinal mesentery closure were in place.

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Histological examination of the surgically resected loop revealed a multilobulated, non-encapsulated mass, protruding widely into the lumen and resulting in partial obstruction, seemingly coming from the duodenal muscularis mucosa. The digestive epithelium exhibited superficial necrosis, and only some duodenal glands remained. This mass exhibited coagulation necrosis affecting approximately 75% of the tissue, characterized by hyperacidophilic tissue where cellular silhouettes persisted. Within this mass, acellular, refractive, constant diameter, well-delineated spaces were observed, suggestive of the histological appearance of sutures (Figure 4A). This observation is consistent with surgery during which a suture was used for hemostasis. Vascular structures, collagenous matrix, and spindle cells were identifiable, although the cell boundaries were blurred, and some nuclei were not visible (Figure 4B). The spindle cell nuclei were hyperchromatic without cytonuclear abnormalities (Figure 4C). The surgically resected tissue consisted exclusively of the duodenal portion.

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Post-mortem histological sections of the duodenum did not reveal any lesions in the epithelium, chorion, submucosa, or duodenal muscularis, which were well preserved. There were five exophytic, pedunculated, serous lesions, 300 and 900 µm in diameter on the duodenal muscularis mucosa, consisting of adipocytes and blood capillaries, lined with activated mesothelial cells, within a moderately abundant collagenous connective tissue, with a focally myxoid appearance (Figure 4D). These lesions suggested mesothelial activation due to serous inflammation, and they were observed during surgery (Figure 2D). The pancreas exhibited an acute inflammatory lesion, characterized by the disappearance of part of the pancreatic acini, which were replaced by a marked fibrinous exudation, associated with numerous extravasated erythrocytes and inflammatory cells. This was indicative of acute, marked necrotic-
caudally to the IRA site was observed (Figure 3). The remainder of the examined tissues were unremarkable. The IRA and intestinal mesentery closure were in place.

Histological examination of the surgically resected loop revealed a multilobulated, non-encapsulated mass, protruding widely into the lumen and resulting in partial obstruction, seemingly coming from the duodenal muscularis mucosa. The digestive epithelium exhibited superficial necrosis, and only some duodenal glands remained. This mass exhibited coagulation necrosis affecting approximately 75% of the tissue, characterized by hyperacidophilic tissue where cellular silhouettes persisted. Within this mass, acellular, refractive, constant diameter, well-delineated spaces were observed, suggestive of the histological appearance of sutures (Figure 4A). This observation is consistent with surgery during which a suture was used for hemostasis. Vascular structures, collagenous matrix, and spindle cells were identifiable, although the cell boundaries were blurred, and some nuclei were not visible (Figure 4B). The spindle cell nuclei were hyperchromatic without cytonuclear abnormalities (Figure 4C). The surgically resected tissue consisted exclusively of the duodenal portion.

Post-mortem histological sections of the duodenum did not reveal any lesions in the epithelium, chorion, submucosa, or duodenal muscularis, which were well preserved. There were five exophytic, pedunculated, serous lesions, 300 and 900 µm in diameter on the duodenal muscularis mucosa, consisting of adipocytes and blood capillaries, lined with activated mesothelial cells, within a moderately abundant collagenous connective tissue, with a focally myxoid appearance (Figure 4D). These lesions suggested mesothelial activation due to serous inflammation, and they were observed during surgery (Figure 2D). The pancreas exhibited an acute inflammatory lesion, characterized by the disappearance of part of the pancreatic acini, which were replaced by a marked fibrinous exudation, associated with numerous extravasated erythrocytes and inflammatory cells. This was indicative of acute, marked necrotic-
hemorrhagic pancreatitis, which may be related to the signs of coelomitis seen on gross
examination. Immunohistochemistry (IHC) was performed with the detection system
OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700) optimized for automated IHC
(Benchmark XT stainer, Ventana Medical Systems, Roche Diagnostics) using antibodies
directed against SMA (Smooth Muscle Actin), Desmin, and CD117 (Table 1). No positive
cells were observed.
hemorrhagic pancreatitis, which may be related to the signs of coelomitis seen on gross
examination. Immunohistochemistry (IHC) was performed with the detection system
OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700) optimized for automated IHC
(Benchmark XT stainer, Ventana Medical Systems, Roche Diagnostics) using antibodies
directed against SMA (Smooth Muscle Actin), Desmin, and CD117 (Table 1). No positive
cells were observed.
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Discussion

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The axolotl's clinical diagnosis was an intussusception. The underlying cause of the intussusception remained unclear, and the intraluminal mass could be necrotic intussuscepted intestine or neoplasm (spindle-cell tumor was suspected based on histopathology).

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Gastrointestinal disorders are common in axolotls, and surgery such as gastrotomy and enterotomy have been described.⁴⁻⁵ As no description of intussusception in axolotl was available, it was assumed that the ultrasound images would be similar to those of dogs and cats.

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Indeed, the abnormalities in this case correlated with the appearance of intussusception described in companion animals, highlighted by the superimposed wall layers of the intussusceptum (inner bowel segment) and the intussuscipiens (outer bowel segment).⁶⁻⁷

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In dogs and cats, intussusception has been associated with intestinal parasitic infestation, bacterial or viral enteritis, foreign bodies, mesenteric cysts, cecal inversion, previous abdominal surgery, nonspecific gastroenteritis, or neoplasia, and it has been documented in postparturient dogs.⁸⁻¹¹ Due to the diffuse nature of the lesion in the intestinal wall, the mass effect was not detected on ultrasound.

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Recurrence is a common complication following surgical correction of intussusception in dogs at a location proximal to the original intussusception.¹⁰ After correction of the intussusception, enteroplication or IRA must be performed. IRA is required in nonreducible intussusception associated with adhesions, devitalized intestine, or detection of a mass.¹⁰,¹² In the present case, IRA was chosen to remove the abnormal portion and to prevent recurrence.

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The rapid deterioration of the axolotl's general condition was attributed to the coelomitis following surgery. In small animals, postoperative septic peritonitis can be associated with dehiscence of anastomotic or enterotomy sites, which has been reported to occur in 7% to 16%

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Discussion

128

The axolotl's clinical diagnosis was an intussusception. The underlying cause of the intussusception remained unclear, and the intraluminal mass could be necrotic intussuscepted intestine or neoplasm (spindle-cell tumor was suspected based on histopathology).

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Indeed, the abnormalities in this case correlated with the appearance of intussusception described in companion animals, highlighted by the superimposed wall layers of the intussusceptum (inner bowel segment) and the intussuscipiens (outer bowel segment).⁶⁻⁷

In dogs and cats, intussusception has been associated with intestinal parasitic infestation, bacterial or viral enteritis, foreign bodies, mesenteric cysts, cecal inversion, previous abdominal surgery, nonspecific gastroenteritis, or neoplasia, and it has been documented in postparturient dogs.⁸⁻¹¹ Due to the diffuse nature of the lesion in the intestinal wall, the mass effect was not detected on ultrasound.

Recurrence is a common complication following surgical correction of intussusception in dogs at a location proximal to the original intussusception.¹⁰ After correction of the intussusception, enteroplication or IRA must be performed. IRA is required in nonreducible intussusception associated with adhesions, devitalized intestine, or detection of a mass.¹⁰,¹² In the present case, IRA was chosen to remove the abnormal portion and to prevent recurrence.

The rapid deterioration of the axolotl's general condition was attributed to the coelomitis following surgery. In small animals, postoperative septic peritonitis can be associated with dehiscence of anastomotic or enterotomy sites, which has been reported to occur in 7% to 16%
152 of patients.¹¹ Anastomotic leakage was not ruled out. Coelomitis could be either primary or
153 secondary to acute pancreatitis. In dogs and cats, acute pancreatitis has several origins that can
154 be considered for amphibians such as toxins, hyperlipidemia, duct obstruction by complications
155 of gastrointestinal surgery or localized peritonitis, pancreatic trauma, ischemia/reperfusion, or
156 idiopathic.¹³,¹⁴,¹⁵ Given the location of the pancreas close to the surgical site, duct obstruction
157 or primary coelomitis may be the cause of pancreatitis. However, as both pancreatitis and
158 coelomitis were concomitant and in the acute phase of the inflammation, the primary cause
159 remained uncertain.

160

161 Previous case reports of neoplasia in axolotls have included cutaneous (chromatophoroma,
162 mastocytoma, and teratoma), oral, and coelomic tumors with splenic involvement.¹⁶⁻²⁰ In our
163 case, the observed mass originating from the duodenum muscularis mucosae presented spindle
164 cells mixed with collagen fibers, compatible with spindle-cell tumor.²¹ Differential diagnoses
165 of intestinal tumors are leiomyoma, fibroma, neurofibroma, and gastrointestinal stromal tumor
166 (thought to be of Cajal cell origin).²² However, extensive necrosis prevented reaching a
167 definitive diagnosis of neoplasia in this case. As recommended, immunohistochemistry (anti-
168 SMA, Desmin, and CD117) was performed to refine the differential diagnosis.²¹ Failure of the
169 IHC could be related to the extensive sample necrosis or because the antibodies used were not
170 compatible with axolotl tissue.²¹

171 This case describes an intussusception diagnosis and attempted treatment in an axolotl.

172 Intussusception should be considered in amphibian patients with dysorexia and regurgitation.

173 Ultrasonography may be a safe, useful, noninvasive diagnostic tool in axolotls to further
174 characterize disease of the gastrointestinal tract. However, more cases are needed to draw
175 definitive conclusions on the management of intussusception in this species.
152 of patients.¹¹ Anastomotic leakage was not ruled out. Coelomitis could be either primary or
153 secondary to acute pancreatitis. In dogs and cats, acute pancreatitis has several origins that can
154 be considered for amphibians such as toxins, hyperlipidemia, duct obstruction by complications
155 of gastrointestinal surgery or localized peritonitis, pancreatic trauma, ischemia/reperfusion, or
156 idiopathic.¹³,¹⁴,¹⁵ Given the location of the pancreas close to the surgical site, duct obstruction
157 or primary coelomitis may be the cause of pancreatitis. However, as both pancreatitis and
158 coelomitis were concomitant and in the acute phase of the inflammation, the primary cause
159 remained uncertain.

160

161 Previous case reports of neoplasia in axolotls have included cutaneous (chromatophoroma,
162 mastocytoma, and teratoma), oral, and coelomic tumors with splenic involvement.¹⁶⁻²⁰ In our
163 case, the observed mass originating from the duodenum muscularis mucosae presented spindle
164 cells mixed with collagen fibers, compatible with spindle-cell tumor.²¹ Differential diagnoses
165 of intestinal tumors are leiomyoma, fibroma, neurofibroma, and gastrointestinal stromal tumor
166 (thought to be of Cajal cell origin).²² However, extensive necrosis prevented reaching a
167 definitive diagnosis of neoplasia in this case. As recommended, immunohistochemistry (anti-
168 SMA, Desmin, and CD117) was performed to refine the differential diagnosis.²¹ Failure of the
169 IHC could be related to the extensive sample necrosis or because the antibodies used were not
170 compatible with axolotl tissue.²¹

171 This case describes an intussusception diagnosis and attempted treatment in an axolotl.

172 Intussusception should be considered in amphibian patients with dysorexia and regurgitation.

173 Ultrasonography may be a safe, useful, noninvasive diagnostic tool in axolotls to further
174 characterize disease of the gastrointestinal tract. However, more cases are needed to draw
175 definitive conclusions on the management of intussusception in this species.
176 **Funding**

177 The authors did not receive financial support for the research, authorship, and/or publication
178 of this article.

179 **Acknowledgments**

180 The authors wish to thank Sophie Domingues for her assistance and language review.

181 **REFERENCES**

182 1) Divers SJ, Stahl SJ. Mader's reptile and amphibian medicine and surgery. 3rd ed. St. Louis (MO): Elsevier Inc.; 2019. doi: https://doi.org/10.1016/C2014-0-03734-3

183 2) Miller ER, Fowler ME. Fowler's Zoo and Wild Animal Medicine. Volume 8. St. Louis (MO): Elsevier Inc.; 2015. doi: https://doi.org/10.1016/C2012-0-01362-2

186 3) Miller ER, Lamberski N, Calle PP. Fowler's Zoo and Wild Animal Medicine. Volume 9. St. Louis (MO): Elsevier Inc.; 2019. doi: https://doi.org/10.1016/C2016-0-01845-4

188 4) Takami Y, Une Y. A retrospective study of diseases in Ambystoma mexicanum: a report of 97 cases. *J Vet Med Sci.* 2017;79(6):1068-1071. doi:10.1292/jvms.17-0066

190 5) Chai N. Surgery in Amphibians. *Vet Clin North Am Exot Anim Pract.* 2016;19(1):77-95. doi:10.1016/j.cvex.2015.08.004.

192 6) Penninck D, D'Anjou M-A. Gastrointestinal tract. In: Penninck D and D'Anjou M-A, eds: Atlas of small animal ultrasonography (2nd ed). Oxford: John Wiley & Sons; 2015, p. 259-308.

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176 **Funding**

177 The authors did not receive financial support for the research, authorship, and/or publication
178 of this article.

179 **Acknowledgments**

180 The authors wish to thank Sophie Domingues for her assistance and language review.

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202

203

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C, Thomson CB, Mayhew PD, Bernstein R, Dominic C, Mankin KT, Regier P, Case

205

JB, Arai S, Gatineau M, Liptak JM, Bruce C. Clinical findings and outcomes of 153

206

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207

doi:10.1111/vsu.13442

208

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209

Small Animal Expert. 2nd ed St Louis, Missouri: Elsevier; 2017, p. 1513-41.

210

12) Patsikas MN, Papazoglou LG, Paraskevas GK. Current views in the diagnosis and

211

treatment of intestinal intussusception. *Top Companion Anim Med*. 2019;37:100360.

212

doi:10.1016/j.tcam.2019.100360

213

13) Mansfield C. Acute pancreatitis in dogs: advances in understanding, diagnostics, and

214

treatment. *Top Companion Anim Med.* 2012;27(3):123-132.

215

doi:10.1053/j.tcam.2012.04.003

216

14) Ellison GW. Complications of gastrointestinal surgery in companion animals. *Vet*

217

*Clin North Am Small Anim Pract.* 2011;41(5):915-34. doi:

218

10.1016/j.cvsm.2011.05.006.

219

15) Piegols HJ, Hayes GM, Lin S, Singh A, Langlois DK, Duffy DJ. Association between

220

biliary tree manipulation and outcome in dogs undergoing cholecystectomy for

221

gallbladder mucocele: A multi-institutional retrospective study. *Vet Surg.*

222

2021:50(4):767-774. doi: 10.1111/vsu.13542.
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241

242

243
223

16) Menger B, Vogt PM, Jacobsen ID, Allmeling C, Kuhbier JW, Mutschmann F, Reimers

224

K. Resection of a large intra-abdominal tumor in the Mexican axolotl: a case report. *Vet*

225

Surg. 2010;39(2):232-233. doi:10.1111/j.1532-950X.2009.00609.x

226

17) Brunst VV, Augustine LR. A spontaneous teratoma in an axolotl (*Siredon mexicanum*).

227

*Cancer Res* 1969;29(1):223-9.

228

18) Khudoley VV, Eliseiv VV. Multiple melanomas in the axolotl *Ambystoma mexicanum*.

229

*J Natl Cancer Inst* 1979;63(1):101-3.

230

19) Harshbarger JC, Chang SC, DeLanney LE, Rose FL, Green DE. Cutaneous

231

mastocytomas in the neotenic caudate amphibians *Ambystoma mexicanum* (axolotl) and

232

*Ambystoma tigrinum* (tiger salamander). *J Cancer Res Clin Oncol*. 1999;125(3-4):187-

233

192. doi:10.1007/s004320050262

234

20) Modesto F, Nicolier A, Hurtrel C, Benoît J. Excisional biopsy and radiotherapy for

235

management of an olfactory neuroblastoma in an axolotl (*Ambystoma mexicanum*). *J*

236

Am Vet Med Assoc. 2021;260(4):436-441. doi:10.2460/javma.20.09.0498

237

21) Pellegrino V, Muscatello LV, Sarli G, Avallone G. Canine gastrointestinal spindle cell

238

tumors efficiently diagnosed by tissue microarray-based immunohistochemistry. *Vet*

239

*Pathol* 2018;55(5):678-81. doi:10.1177/0300985818777793

240

22) Hayes S, Yuzbasiyan-Gurkan V, Gregory-Bryson E, Kiupel M. Classification of canine

241

nonangiogenic, nonlymphogenic, gastrointestinal sarcomas based on microscopic,

242

immunohistochemical, and molecular characteristics. *Vet Pathol.* 2013;50(5):779-88.

243

doi:10.1177/0300985813478211
244 FIGURES

245 **Figure 1.** Identification and illustration of long-axis and transverse intussusception. The inner
246 small intestinal loop (red circle = intussusceptum) is readily identified within the outer bowel
247 loop (white circle = intussuscipiens)

248 A. Long-axis view of the intussusception

249 B. Transverse image of the intussusception

250 C. Proximal view of the intussusception site

251

252 **Figure 2.** Surgery of the intussusception. (Cr.: Cranial; Ca.: Caudal)

253 A. Mass effect of intestinal loops at the beginning of the coeliotomy

254 B and C. Visualization of intussuscipiens (white arrow) and intussusceptum (red arrow)

255 D. Portion of the intestinal loops resected (between white dotted lines) with pink serosal
256 nodules (black arrow).

257

258 **Figure 3.** Necropsy of the axolotl five days after the surgery. Serofibrinous coelomitis is
259 observed.

260 1: Intestinal loops proximal to the IRA site

261 2: Site of IRA

262 3: Intestinal loops distal to the IRA site

263 4: Mesentery

264 5: Mesentery suture site

265

266 **Figure 4.** A: Histological section of the duodenum shows a multilobulated necrotic mass,
267 protruding widely into the lumen and contributing to its obstruction (black line). Acellular,
244 **FIGURES**

245 **Figure 1.** Identification and illustration of long-axis and transverse intussusception. The inner
246 small intestinal loop (red circle = intussusceptum) is readily identified within the outer bowel
247 loop (white circle = intussuscipiens)

248 A. Long-axis view of the intussusception

249 B. Transverse image of the intussusception

250 C. Proximal view of the intussusception site

251

252 **Figure 2.** Surgery of the intussusception. (Cr.: Cranial; Ca.: Caudal)

253 A. Mass effect of intestinal loops at the beginning of the coeliotomy

254 B and C. Visualization of intussuscipiens (white arrow) and intussusceptum (red arrow)

255 D. Portion of the intestinal loops resected (between white dotted lines) with pink serosal
256 nodules (black arrow).

257

258 **Figure 3.** Necropsy of the axolotl five days after the surgery. Serofibrinous coelomitis is
259 observed.

260 1: Intestinal loops proximal to the IRA site

261 2: Site of IRA

262 3: Intestinal loops distal to the IRA site

263 4: Mesentery

264 5: Mesentery suture site

265

266 **Figure 4.** A: Histological section of the duodenum shows a multilobulated necrotic mass,
267 protruding widely into the lumen and contributing to its obstruction (black line). Acellular,
268

refractive, constant diameter, well-delineated spaces are observed, suggestive of the
histological appearance of sutures (arrows). (HES x4)

269

270

**B:** Histological examination of the duodenum showing spindle-shaped cells with blurred cell boundaries (black arrow). (HES x10)

271

272

**C:** Histological examination of the duodenum with details of spindle cells with hyperchromatic nuclei without cytonuclear abnormalities. (HES x40)

273

274

**D:** Histological examination of duodenum serosa showing exophytic, pedunculated, serous lesions of 300 and 900 µm in diameter, consisting of adipocytes and blood capillaries, lined with activated mesothelial cells, within a moderately abundant collagenous connective tissue, with a focally myxoid appearance. (HES x10)

275

276

277

278

279

**Video 1:** Movement of intestinal loops at the site of intussusception
268

refractive, constant diameter, well-delineated spaces are observed, suggestive of the
histological appearance of sutures (arrows). (HES x4)

269

270

**B:** Histological examination of the duodenum showing spindle-shaped cells with blurred cell boundaries (black arrow). (HES x10)

271

272

**C:** Histological examination of the duodenum with details of spindle cells with hyperchromatic nuclei without cytonuclear abnormalities. (HES x40)

273

274

**D:** Histological examination of duodenum serosa showing exophytic, pedunculated, serous lesions of 300 and 900 µm in diameter, consisting of adipocytes and blood capillaries, lined with activated mesothelial cells, within a moderately abundant collagenous connective tissue, with a focally myxoid appearance. (HES x10)

275

276

277

278

279

**Video 1:** Movement of intestinal loops at the site of intussusception
<table><caption>**Table 1.** Immunohistochemistry performed on an intraluminal mass of the duodenum in an axolotl (Ambystoma mexicanum).</caption><thead><tr><th></th><th>Antigen retrieval/ enzyme</th><th>Primary antibody/ clone</th><th>Immunogen</th><th>Manufacture primary Antibody</th><th>Dilution primary antibody</th><th>Secondary antibody detection system</th><th>Chromogen/ counterstaining</th><th>Controls</th></tr></thead><tbody><tr><td>SMA</td><td>CC1 cell conditioning medium, Roche Diagnostics 950-124</td><td>Monoclonal mouse anti-human muscle actin clone HHF35</td><td>SDS-extracted protein fraction of human myocardium</td><td>Dako</td><td>1/100</td><td>Mouse secondary antibody OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700)</td><td>3,3'-diaminobenzidine (OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700))</td><td>Axolotl mass: negative<br>Healthy dog duodenum: positive</td></tr><tr><td>Desmin</td><td>32 min: CC1 cell conditioning medium, Roche Diagnostics 950-124</td><td>Monoclonal mouse anti-human desmin clone D33</td><td>Desmin purified from human muscle</td><td>Dako</td><td>1/400</td><td>Mouse secondary antibody OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700)</td><td>3,3'-diaminobenzidine (OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700))</td><td>Axolotl mass: negative<br>Healthy dog duodenum: positive</td></tr><tr><td>CD117</td><td>32 min: CC1 cell conditioning medium, Roche Diagnostics 950-124<br>4 min: glutaraldehyde 2.5 µL/mL</td><td>Anti-KIT rabbit monoclonal antibody clone YR145</td><td>v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog</td><td>Roche Diagnostics</td><td>1/100</td><td>Rabbit secondary antibody OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700)</td><td>3,3'-diaminobenzidine (OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700))</td><td>Axolotl mass: negative<br>Healthy dog duodenum: positive</td></tr></tbody></table>
<table><caption>**Table 1.** Immunohistochemistry performed on an intraluminal mass of the duodenum in an axolotl (Ambystoma mexicanum).</caption><thead><tr><th></th><th>Antigen retrieval/ enzyme</th><th>Primary antibody/ clone</th><th>Immunogen</th><th>Manufacture primary Antibody</th><th>Dilution primary antibody</th><th>Secondary antibody detection system</th><th>Chromogen/ counterstaining</th><th>Controls</th></tr></thead><tbody><tr><td>SMA</td><td>CC1 cell conditioning medium, Roche Diagnostics 950-124</td><td>Monoclonal mouse anti-human muscle actin clone HHF35</td><td>SDS-extracted protein fraction of human myocardium</td><td>Dako</td><td>1/100</td><td>Mouse secondary antibody OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700)</td><td>3,3'-diaminobenzidine (OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700))</td><td>Axolotl mass: negative<br>Healthy dog duodenum: positive</td></tr><tr><td>Desmin</td><td>32 min: CC1 cell conditioning medium, Roche Diagnostics 950-124</td><td>Monoclonal mouse anti-human desmin clone D33</td><td>Desmin purified from human muscle</td><td>Dako</td><td>1/400</td><td>Mouse secondary antibody OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700)</td><td>3,3'-diaminobenzidine (OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700))</td><td>Axolotl mass: negative<br>Healthy dog duodenum: positive</td></tr><tr><td>CD117</td><td>32 min: CC1 cell conditioning medium, Roche Diagnostics 950-124<br>4 min: glutaraldehyde 2.5 µL/mL</td><td>Anti-KIT rabbit monoclonal antibody clone YR145</td><td>v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog</td><td>Roche Diagnostics</td><td>1/100</td><td>Rabbit secondary antibody OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700)</td><td>3,3'-diaminobenzidine (OptiView DAB IHC Detection Kit (Roche Diagnostics, 760-700))</td><td>Axolotl mass: negative<br>Healthy dog duodenum: positive</td></tr></tbody></table>
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