Renal lobulation – a benign anatomical variation?

Abstract

Introduction: Renal lobulation (also known as fetal or embryonic lobulation) is a rare variation of development when renal lobules have a visible anatomical space between them. Fetal lobulation is considered to be rare in adult patients and can be seen in 0.5-4% of cases. Material and methods: The study was conducted on 54 human kidneys from patients who died due to causes unrelated to renal pathology and were fixed in a 10% formaldehyde solution. After seven days of preservation in a formaldehyde solution the kidneys were dissected manually. The data acquired during the study was analyzed statistically (Spearmans correlation, cross-tabulation analysis, Mann-Whitney test and logistic regression). Results: The group with fetal lobulation (n=16) was associated with a length M=9.89 (SD=0.6, p=0.15). By comparison the kidneys without lobulation (n=38) were associated with a numerically bigger length M=10.29 (SD=0.607, p=0.098). To test the hypothesis that lobulation is associated with a statistically significant different length a Mann-Whitney test was performed, which indicated that the length of the kidneys is smaller in case of lobulation U=198, Z= -2.04, p=0.04. cross-tabulation also demonstrated that kidney lobulation may be influenced by the presence of polar arteries with r=0.41 (p<0.02). The likelihood ratio was 7.28, df 1, p=0.003 odds ratio 6.857 (CI 95%=1.84-25.61). There was no relationship between fetal lobulation and number of major calyces or sex (p>0.05). A logistic regression was performed to ascertain the effects of polar arteries on the likelihood that kidneys have cortex lobulation (Step 1) and the effect of both polar arteries and length on the likelihood that kidneys have cortex lobulation (Step 2). In the step 1 the logistic regression model was statistically significant, χ2(1) = 8.73, p = 0.003. The model explained 21.2% (Nagelkerke R2) of the variance in kidney lobulation and correctly classified 75.9% of cases. Kidneys with lobulation were 6.85 times more likely to have polar arteries than kidneys without lobulation. Conclusions: The data from our research indicates that even though no pathological conditions are linked until now with lobulated kidneys the incidence of vascular variations (specifically polar arteries) is higher when there is persistent fetal lobulation. Therefore, this condition can be caused by hemodynamic changes inside the organ. Kidneys with fetal lobulation also tend to be smaller. The proposed model need validation and completion up to determination coefficient value 0.8.