Ex vivo comparison of ultrasonographic intestinal wall layering with histology in horses: A feasibilty study

Abstract

Ultrasonography is increasingly being used as a clinical and research method for evaluating the gastrointestinal tract in horses, however published studies comparing ultrasonographic and histologic characteristics of equine intestinal wall layers are currently lacking. Objectives of this prospective, observational, methods comparison, case series study were to compare the layering pattern and thickness of the intestinal wall layers determined using ex vivo and in vivo ultrasonography with those determined using histology. For the ex vivo study, twelve horses were euthanized for reasons unrelated to gastrointestinal disease, and samples of the duodenum, jejunum, ileum, cecum, right dorsal colon, and small colon were collected and imaged sonographically ex vivo in an isotonic bath within 1 hour of euthanasia. For the in vivo study, ultrasonography was performed in four clinical cases, and findings were compared with histopathology.A 5-layer pattern of alternating echogenicity was observed in 70 of 72 ex vivo samples.Agreement between histologic and sonographic measurements was deemed good for all segments except the ileum. Formalin fixation did not alter the sonographic appearance or wall measurements. Findings from the four clinical cases illustrated the feasibility of also obtaining ultrasonographic images with sufficient sonographic detail in vivo to recognize wall layering and obtain comparable results to pathologic lesions. Findings from the current study can serve as background for future studies comparing ultrasonographic characteristics of the intestinal wall in horses with different gastrointestinal diseases.

Ex vivoultrasonographic and histological morphometry of small intestinal wall layers in horses

“…Transabdominal and transrectal US in horses encounter many anatomical and technical limitations to intestinal walls’ imaging quality (e.g., size of the abdomen, distance of the viscera from the contact surface, low‐frequency probes). A thinner small intestinal wall compared to the present findings has been reported scanning ex vivo intestine using a 7.5 MHz probe, 9 and also a high frequency (10–18 MHz) probe 8 . Noteworthy, in the present study, the thicker US measurement was in line with a thicker histological measurement of the wall, compared to the findings previously reported by Freeman et al.…”

“…In particular, a further thin hyperechoic line within the muscular layer, representing the interface between the inner and outer parts of the tunica muscularis , was observed along all the equine small intestine as also described in humans 13–15 and dogs 5 . Worth 10 already described this line by ex vivo US in the wall of the ileum, while more recently it was found also in the other small and large intestinal tracts, albeit not consistently, by means of a high‐frequency transducer 8 . Histologically, such additional ultrasonographic line was consistent with connective and nerve tissues of the myenteric plexus and intrinsic and extrinsic nerve fibers, interposed between the LML and CML of the tunica muscularis 16–18 .…”

“…(i.e., small intestinal total wall thickness 2.43 ± 0.25 mm) 9 and Bevenino et al. (total wall thickness 2.08 ± 0.71 mm, 1.61 ± 90.99 mm, and 3.94 ± 1.7 mm for duodenum, jejunum, and ileum, respectively) 8 …”

“…The US focus was set at the level of the intestinal lumen and the same ultrasonographic parameters were used for all samples. Altered small intestinal US appearance was judged based on abnormal echogenicity of each wall layer as previously reported 2–3,6,8 . An indelible marker (Marker pen, Phoenix Contact, Cusano Milanino, Italy) was used to mark the site where the transverse images were obtained as a guide for the histological transverse sections.…”

“…The normal US appearance and reference ranges of the overall intestinal wall thickness in the different GI tracts have been widely reported in horses 1,5 . Based on previous publications in small animals, 6,7 the equine ultrasonographic intestinal layers were assumed to correlate well with the histological layers (mucosa, submucosa, muscularis, and serosa), but few research have been performed on ex vivo equine intestine 8–10 . More recently, only one study describes the ultrasonographic thickness of each small intestinal wall layer of the equine and its good correlation with histological measurements of any segment, except for the ileum 8 .…”