Introduction

The paired jejunal (mesenteric) lymph nodes (JLN) are located alongside the mesenteric vessels. Anatomical studies in dogs have shown they are approximately 60 mm long, 20 mm wide and 5 mm thick. Information about their normal ultrasonographic appearance and size is limited but a thickness of 5 mm has been reported. However, measurements from a range of normal dogs have not been obtained and the variable position and shape of the JLN makes consistent measurements and definition of thickness and width difficult. The purpose of this study was to describe the normal ultrasonographic appearance and dimensions of canine JLN.

Material and Method

Hospital patients (n=13) and staff owned dogs (n=13) without evidence of gastro-intestinal disease were examined with owners consent in right lateral recumbency using a 5-8 MHz sector scanner (HDI 5000 CTSono, Phillips). Scanning planes were adjusted as necessary for optimal visualisation of the JLN in their long- and short-axis, and their appearance including flow on power doppler examination recorded.

Measurements were obtained in short-axis (cross sectional image) excluding the most distal pole, where an irregular knob or lobulation may be present. Thickness was defined as the shortest distance across the cross sectional image, width as the diameter perpendicular to thickness. Minimum and maximum thickness of each JLN and the corresponding width (A and B) were identified.

Results

JLN were visualised in all 26 dogs (100%) but in 4 dogs (15.4%) only one chain was identified. Incomplete visualisation led to exclusion of 2 dogs (7.7%) from further analysis.

All nodes had an undulating rod shape, smooth margins and either no or hilar and/or central flow on power doppler examination. JLN were mildly hypoechoic (16 dogs, 66.6%) or isoechoic (8 dogs, 33.3%) to the mesentery. Echogenicity was mildly to moderately heterogenous in 5 cases (20.1%). All moderately heterogenous nodes were seen in dogs younger than 2 years.

The measurements were (range in mm, mean±SD): minimum thickness 1.5-4.2, 2.81±0.73; maximum thickness 2.3-7.5, 4.22±1.36; width A 3.0-13.10, 5.26±2.09; width B 2.8-14.7, 6.84±2.21.

Conclusions

Normal canine JLN can be routinely visualised. Young dogs may have moderately heterogenous JLN. There is a large range in width and maximal thickness, which may exceed 5 mm in normal dogs. There is less variation in the minimal thickness, which was less than 5 mm in all cases.