Abstract

Mechanical ileus has been reported in numerous marine mammal species.^1–10 Antemortem diagnostic imaging associated with small bowel obstruction in dolphins has not been described, at least in part due to the typically peracute clinical progression. This report retrospectively describes the temporal radiographic and ultrasonographic findings in two adult dolphins with mechanical ileus in 2021, a male Pacific white-sided dolphin (Lagenorhynchus obliquidens, Lo) and a female bottlenose dolphin (Tursiops truncatus, Tt).

Both animals presented with acute onset inappetence and lethargy ± decreased fecal output. Preoperative ultrasonographic findings included severe small intestinal fluid distension (Lo x̄=3.6 cm max diam [3.4–3.9 cm], Tt x̄=3.9 cm max diam [3.0–4.4 cm] [normal diam ≤1.8 cm, unpubl data]), segmental intestinal wall thickening (Lo x̄=9.3 mm max thickness [8.9–9.6 mm], Tt x̄= 4.8 mm max thickness [3.5–5.5 mm] [normal 1.3–3.5 mm, unpubl data]), and hypoechoic peritoneal effusion (scant to mild [≤1.5 cm depth] in Lo, moderate to severe [10–17 cm depth] in Tt). Ultrasonographic small intestinal motility was significantly increased in both animals until day 7–8, but notably poor on day 9 in the Tt. Echogenicity of peritoneal effusion and of the mesentery surrounding the most abnormal intestinal segments subjectively increased over time. Tricavitary effusion developed in the Tt on day 9. Preoperative radiographic findings included severe small intestinal gas and fluid distension (Lo x̄=4.4 cm max diam [4.0–5.0 cm], Tt x̄=5.5 cm max diam) and the presence of horizontal fluid lines on lateral horizontal beam abdominal radiographs.

Mechanical ileus was suspected preoperatively in both cases based on clinical findings and radiographic and in-person ultrasonographic evaluation (small intestinal intussusception in Lo, cause of obstruction not identified pre-operatively in Tt). The Lo underwent emergency exploratory laparotomy. A jejunal intussusception was confirmed and resected. Additional surgical findings included severe orad bowel dilation and evidence of peritonitis. The Lo died during anesthetic recovery. The Tt died in the immediate preoperative period. On post-mortem, the Tt had a mesenteric volvulus involving the most distal/aborad small intestine and marked orad bowel dilation.

Time from clinical onset of disease to death was 8–10 days. Time from clinical onset of disease to surgery (performed in one animal and imminent in other) was 8–9 days. Post-operative survival was <1 h (Lo with intussusception). On necropsy, both animals had a septic abdomen and intestinal wall infarction and ulceration.

Rapid initiation of diagnostics, including serial radiographic and detailed ultrasonographic abdominal imaging by experienced personnel, is essential to promptly diagnose small bowel mechanical ileus in dolphins, minimizing time between onset of clinical signs and exploratory laparotomy and maximizing likelihood of successful clinical outcome. Additional extensive research into best practices for post-operative management of cetaceans is needed.

Acknowledgements

The authors thank the veterinary and animal care staff as well as the leadership of Clearwater Marine Aquarium and Shedd Aquarium. The tireless efforts of the individuals at these institutions in caring for these animals and dealing with massive, urgent, complicated logistics are beyond commendable. A special thank you to extraordinary aquatic animal clinicians Drs. Lauren Kane, Carolina Le-Bert, Mike Walsh, William Van Bonn, and Mike McEntire, veterinary surgeons Dean Hendrickson and Mitch Robbins, anesthesiologists Katie Bennett and James Bailey, pathologist Nancy Stedman, University of Illinois Zoo Pathology Program, and clinical pathologist Nicole Stacy.

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