Horseshoe kidney and polycystic horseshoe kidney: a forensic autopsy-based study in Portugal.

Horseshoe kidney (HSK) is the most common congenital renal fusion anomaly, while autosomal dominant polycystic kidney disease (ADPKD) is the most prevalent inherited renal disorder. Their coexistence-polycystic horseshoe kidney (P-HSK)-is exceedingly rare. This retrospective forensic study assessed the prevalence of HSK and P-HSK in a consecutive autopsy series from the three regional delegations of the Portuguese National Institute of Legal Medicine and Forensic Sciences between 2017 and 2022. A total of 31,325 autopsy reports (22,854 males and 8,471 females) were reviewed. HSK was identified in 17 cases (0.054%; 95% CI: 0.032%-0.087%), including 3 cases (17.7%) of P-HSK (0.0096%; 95% CI: 0.0020%-0.0280%). None had been diagnosed in life, nor were other developmental anomalies present. The mean age of HSK cases was 55.3 ± 12.8 years. Causes of death did not significantly differ between individuals with or without HSK, and no deaths were attributable to HSK. Prevalence did not vary significantly by sex (p = 0.75) or nationality (p = 0.36). Among native Portuguese, HSK and P-HSK prevalence were 0.048% and 0.010%, respectively. The observed prevalence of P-HSK was significantly higher than expected under the assumption of independent occurrence. Regionally, HSK prevalence was higher in the North than in the Centre and South, although differences did not reach statistical significance (p = 0.083); notably, the North is also the region with the highest prevalence of ADPKD. This study provides population-specific data on asymptomatic HSK in Portugal and suggests a possible epidemiological association between HSK and ADPKD, warranting further investigation.