Characterising equine abdominal lipomata: Can histological features improve the understanding of pathogenesis and risk?

Background: Strangulating lipomata are the most common cause of small intestinal strangulating obstruction. Evaluation of histological features of pathological and non-pathological lipomata, and the histological properties of omental and retroperitoneal fat have not been described.

Objectives: To characterise histological features of equine abdominal lipomata, omental and retroperitoneal adipose tissue, and associations between them.

Study design: Prospective observational anatomic (gross and histological).

Methods: Horses undergoing emergency laparotomy for management of abdominal pain in a single hospital were recruited. Signalment was recorded. Gross features of lipomata that were a cause of strangulating obstruction (pathological lipomata [PAL]), and lipomata that were currently not causing an intestinal obstruction (pedunculated [PEL] or non-pedunculated [NPL]) were recorded. Lipomata that were removed intra-operatively, or following owner-requested euthanasia, as well as omentum or retroperitoneal adipose tissue, where excised routinely as part of routine management (or post-euthanasia) were fixed in 10% neutral-buffered formalin prior to staining (haematoxylin and eosin, picrosirius red). Descriptive statistical analyses were performed. Pearson's chi-square, Fisher's exact or Kruskal-Wallis tests, as appropriate, were used to assess associations. Significance was p < 0.05.

Results: Seventy-four horses were enrolled; 71 lipomata, 48 retroperitoneal adipose samples, and 26 omental samples underwent evaluation. Increasing age was predictive of lipomata presence and PAL/PEL. Neither omental nor retroperitoneal adipose tissue histological features were correlated with lipomata presence or type. PAL were more likely to exhibit capsule formation (PAL: 70%, NPL: 42%, p = 0.03), and had a higher vascular density (median 10.6; IQR: 8.8-16.8; p = 0.05), compared with NPL. PEL were more likely to exhibit steatonecrosis (PEL: 92%, NPL: 33%, p = 0.01) and had increased mineralisation (PEL: 67%, NPL: 17%, p = 0.05) compared with NPL.

Main limitations: Small sample size.

Conclusions: Histological features of omental and retroperitoneal fat do not predict presence of lipomata or type. However, there are histological features of PAL and PEL which may be related to pathological potential.