Journal of Small Animal Practice © 2012 British Small Animal Veterinary Association 1
Journal of Small Animal Practice (2012)
Accepted: 27 June 2012
Radiographic kidney measurements in North American pet ferrets (Mustela furo)
D. Eshar, J. A. Briscoe and W. Mai
Department of Clinical Studies, University of Pennsylvania School of Veterinary Medicine, 3900 Delancey Street, Philadelphia, PA 19104-6010, USA
D. Eshar’s current address is Avian and Exotics Service, Veterinary Teaching Hospital, Ontario Veterinary College, University of
Guelph, Guelph, Ontario, Canada N1G2W1
J. A. Briscoe’s current address is US Department of Agriculture, Animal Plant Health Inspection Service, Animal Care Program, 4700
River Road, Unit 84, 6D-03.7, Riverdale, MD 20737-1234, USA
W. Mai’s current address is Section of Radiology, School of Veterinary Medicine, University of Pennsylvania, 3900 Delancey Street,
Philadelphia, PA 19104-6010, USA
OBJECTIVES: The purpose of the current study was to determine normal radiographic kidney measurements in pet ferrets.
METHODS: Kidney length and width dimensions and the length of the second lumbar vertebra (L2) were determined from survey ventrodorsal radiographs in 53 neutered ferrets of various ages, weight and sex, with no evidence of urogenital disease. Kidney dimensions were expressed as a ratio to the body length of L2.
RESULTS: All ferrets in this study had six lumbar vertebrae. The median length of L2 was 13·3 mm, and was longer in males than females (P=0·0001). The 95% confidence interval for kidney-length-to-L2 ratios was 2·21 to 2·31 for the right and 2·15 to 2·25 for the left. For the kidney-width-to-L2 ratios these intervals were 1·09 to 1·14 for the right and 1·07 to 1·12 for the left kidney. There was a significant association between kidney size and weight or sex but not with age.
CLINICAL SIGNIFICANCE: The results of this radiographic study may allow practitioners to have a more objective clinical radiographic evaluation of kidney size of pet ferrets based on individual traits.
According to the 2006 AVMA survey, ferrets are among the most popular pets kept in households in the United States (Shepherd 2008). As with dogs and cats, survey radiographs are recommended in the evaluation of ferrets with symptoms of urinary tract disorders (Orcutt 2003, Fisher 2006). Radiographic abnormalities in renal number, position, size, shape, opacity or contour can all indicate renal pathology (Ackerman 1983, Feeney and Johnston 2007). In dogs and cats it has been suggested that changes in radiographic kidney size can differentiate between chronic and acute renal diseases, as kidneys may appear smaller or larger, respectively (Ackerman 1983). Similar statements have been made with regard to ferrets, although renomegaly can also be caused by renal cysts or pseudocysts, abnormal cellular infiltration (inflammation, infection and neoplasia), urinary tract obstruction and acute tubular necrosis or can also be normal in middle-aged to older ferrets (Oglesbee 2011). However, to the best of the authors’ knowledge, what constitutes normal kidney size on survey radiographs in ferrets has not been defined, as it has for dogs and cats (Silverman and Tell 2005, Capello and
The size of the kidneys can be impacted by other factors aside from pathology, such as age, sex and reproductive status (Korenchevsky and Dennison 1934, Freudenberger and Howard h t t p :/ / w w w .b s a v a .c o m /
D. Eshar and others 2 Journal of Small Animal Practice © 2012 British Small Animal Veterinary Association the readers considered one or both kidneys to be insufficiently visible to obtain accurate measurement, the case was discarded.
For each ferret, data were averaged across all three reviewers and these individual average values were used to generate mean and 95% confidence intervals (CIs) for the entire study group.
The data were assessed for normal distribution using normal quantile plots. For normally distributed data, the descriptive statistics used were mean and 95% CI and statistical analysis was performed using tests that assume a normal distribution. In case of a non-normal distribution, data were described as median and range, and non-parametric statistical tests were used for comparisons between groups. Agreement in the measurements between the three readers was determined using analysis of variance (ANOVA) for repeated measurements for the normally distributed kidney length and width parameters, and Friedman test for
L2 length, patients’ weight and age. If an overall significant difference was noted between the three readers in the radiographic measurements (right kidney length/width, left kidney length/ width) during this analysis, the absolute differences between measurements for all three possible pairs of readers was calculated for each patient. The maximum absolute difference observed was recorded for each measurement in each patient and, for each of the radiographic measurements, the 95% CI of the absolute maximum inter-observer difference was calculated for the right renal length, right renal width, left renal length and left renal width.
The difference in weight between males and females was assessed using a Wilcoxon rank-sum test. Differences in length and width between the left and right kidneys were tested using a paired t-test. Regression analysis was used to assess association between kidney measurements and age or weight. Association between 1937, Kochakian 1959, Broulik 1983, Shukla and others 1992,
Shiroma and others 1999, Lane 2008). For example, kidneys have been shown to be larger in males than females in humans, rats, mice, hamsters and dogs (Lane 2008). Age may also have an influence on kidney size, as kidneys in males have been shown to grow more rapidly during sexual maturation (Costantino-Ceccarini and Morell 1973, Shukla and others 1992).
In dogs and cats, the ratio of kidney length to the length of the body of the second lumbar vertebra (L2) on a ventrodorsal (VD) radiograph is used to evaluate kidney size (Feeney and Johnston 2007). The purpose of the current study was to determine the ratio of kidney length to L2 length in neutered ferrets without evidence of urinary tract disease, as well as to determine possible association with age and sex. Findings of this study could be used to help practitioners evaluate radiographic renal size in ferrets and serve as a basis for further study of the radiographic evaluation of ferrets with renal disease.