Lipoma, Pedunculated - Horse
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A pedunculated lipoma is a benign, fatty mass originating from the mesentery of the horse. Lipomas are a common cause of small intestinal strangulation or obstruction in horses older than fifteen years of age. Less commonly they may affect the small colon. Lipomas are seen in all types of horses but mostly in ponies and cob-type horses. Geldings appear to be at 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 the most-common intra-abdominal tumour of geriatric horses. They 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). The pain may intially 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. At this stage there may be reduced borborygmi and cessation of defecation. If vascular compromise has occured, signs of endotoxaemia may be present including congested mucous membranes, 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 may be palpable on rectal examination or visible on ultrasonographic examination. 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. The surgeon will evaluate the colour of the mesentery, the mucosa, intestinal motility and whether a pulse remains in the mesenteric vessels when deciding whether to resect and the portion of intestine to be removed. Endotoxaemia and post-operative ileus are significant potential complications of surgery. Additional risks include infection, adhesions and stenosis of the surgical 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