Lipoma, Pedunculated - Horse
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A pedunculated lipoma is a benign fatty mass originating from the mesentery and is the most-common intra-abdominal tumour of the geriatric horse. A lipoma may lead to obstruction or strangulation of the small intestine, occasionally affecting the small colon. The tumours are seen in all types of horses but mostly in ponies and cob-types. Geldings appear to be at a higher risk compared to mares and stallions, suggesting a possible endocrine aetiology. It is unclear whether the risk of lipoma formation is associated with body condition.
Lipomas are often multiple in number and attach to the mesentery of the intestine via a stalk or pedicle of varying length. The stalk becomes wrapped around a segment of small intestine, causing compression of the intestinal lumen and corresponding mesenteric vessels. Longer stalks are associated with more severe and complete intestinal strangulation. More rarely, broad-based tumours arising close to the intestine can occur causing periodic restriction of ingesta without intestinal compromise. Lipomas may also be incidental findings at post mortem or exploratory laparotomy.
Clinical signs may very depending on the extent of intestine involved and the degree of strangulation that has occurred. Initial signs may be restricted to those indicative of acute onset abdominal pain (for example flank-watching, rolling, kicking and pawing). Occasionally the owner may report a history of exercise immediately prior to the onset of abdominal pain. This is hypothesised to be due to the lipoma wrapping around the gut in the abdomen of the rapidly moving horse.
Initially, the abdominal pain may respond well to analgesia. In the early stage of the disease, gut sounds may be present and faeces may be passed. It may take up to eight to twelve hours before additional clinical signs including tachycardia and tachypnoea occur. If strangulation has occurred, borborygmi are absent and defecation ceases. Vascular compromise is associated with signs of endotoxaemia including congested oral mucous membranes with 'toxic rings', weak peripheral pulses and a prolonged capillary refill time.
The disease is characterised by the production of large volumes of gastric reflux following nasogastric intubation, although this may be absent in the early stages of disease. Multiple distended loops of small intestine ('bicycle tyres') may be palpable on rectal examination. Transabdominal ultrasonography using a 5MHz linear scanner allows assesment of intestinal motility and distension. Occasionally the lipoma may be felt per rectum. Fluid obtained by peritoneal tap may be normal early in the course of the obstruction; however, most horses with strangulating lipomas have an increased peritoneal fluid total protein and WBC count.
The only treatment available for the disease is surgical resection of the tumour and any strangulated bowel. At surgery, an assessment will be made of the colour of the mesentery, intestinal motility and the presence or absence of a pulse in the mesenteric vessels. Devitalised intestine may be resected and a surgical anastamosis performed.
Endotoxaemia and post-operative ileus are significant potential complications of surgery. Additional risks include infection, adhesions and stenosis of the anastamosis. Various post-operative regimes have been reported to reduce the risk of complication including faecal softeners, anti-inflammatories and pro-kinetics.
Studies have shown that around 75% of horses that have undergone surgery will be discharged, but the long term survival following surgery varies from 38% to 50%. The prognosis is more favourable if surgery is performed before signs of cardiovascular compromise have occurred.
- Bertone, J. (2006) Equine Geriatric Medicine and Surgery Elsevier Health Sciences
- Orsini, J. A., Divers, T. (2007) Equine Emergencies: Treatment and Procedures Elsevier Health Sciences
- Mair, T. S., and Edwards, G. B. (2003) Strangulating Obstructions of the Small Intestine Equine Veterinary Education 15(4): 192-199
- Merck and Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial