The Relationship Between Splenic, Renal, Gastric And Cardiac Sonographic And Post-Mortem Measurements In Horses

The relationships between spleen size and the size of kidney, stomach, and heart were studied ultrasonographically. Kidney was studied as a non-mobile internal reference standard. Stomach has been reported to alter spleen size with changing stomach diameter. Heart would logically be hypothesized to correlate with spleen size as measure of athleticism. Standard echocardiograms, sonographic and post-mortem splenic, renal and gastric measurements were obtained from 8 donated horses. Splenic measurements were obtained at baseline and after administration of epinephrine and detomidine (separately) to mimic maximal and resting sympathetic tone and obtain minimal and maximal splenic size, respectively. No significant correlations (r<0.5, P>0.05) were observed between the sonographic or post-mortem splenic measurements and sonographic or post-mortem renal measurements. Sonographically-estimated and post-mortem spleen volume were correlated with the sonographic (r=0.89, P=0.003) and post-mortem stomach length (r=0.77, P=0.02). Sonographic and post-mortem gastric measurements were not strongly correlated. Baseline (before administration of drugs) sonographically-estimated volume of the spleen was not strongly correlated with echocardiographic or post-mortem cardiac measurements. Sonographically-estimated splenic volume after detomidine administration was correlated with left ventricular weight (r=0.82, P=0.01). The post-mortem volume of the spleen was moderately correlated with aortic root diameter (r=0.75, P=0.03) and the correlation approached significance for heart weight (r=0.7, P=0.055). The spleen-to-kidney ratio is unlikely to be useful in assessing splenomegaly in horses. Further studies are needed to assess the accuracy of the sonographic method to measure the kidneys, stomach and the effect of gastric filling on splenic size. Assessment of the interactions between cardiac size, splenic size, and athletic ability would be an interesting corollary to this experiment.