Basal vacuolization of renal tubules in hypothermia: A comprehensive pathological study based on 79 forensic autopsy cases.

This study investigated the usefulness of histopathological examination in diagnosing ketoacidosis in hypothermia cases. Out of 79 cases (38 females), 30 showed basal vacuolization (BV), a representative histopathological finding of ketoacidosis, in their hematoxylin and eosin (H&E)-stained specimens. Through the use of both lipid staining with osmium tetroxide postfixation and immunohistochemistry for adipophilin (ADFP-IHC), BV pattern pathology was identified in 43 cases. Serum was available in 75 cases, with 37 having serum β-hydroxybutyrate levels exceeding 1000 μmol/L. Serum β-hydroxybutyrate concentrations showed a significantly negative correlation with age and tended to be lower in outdoor hypothermia cases than in indoor cases. When comparing serum β-hydroxybutyrate levels with histopathological findings, all but one of the BV-positive cases on H&E staining were serologically diagnosed as ketoacidosis. However, when combining multiple staining methods, six cases were histologically positive but serologically negative. Using multiple staining methods increases BV detection sensitivity, but it may also detect findings of unknown pathological significance. Therefore, identifying a distinct BV pattern in H&E-stained specimens is crucial for suspecting ketoacidosis in the usual practice of forensic pathology, and ADFP-IHC is useful for confirming lipid droplet presence. Our results suggest that BV positivity rates are strongly influenced by the case characteristics of the study cohort, particularly the proportion of older adults. Thus, the extent to which BV is complicated by hypothermia should be examined and understood on a country-by-country or region-by-region basis.