Digital Quantification of Nuclei in Porcine Experimental and Forensic Wounds: Effects of Wound Age and Body Location on Nuclei Density

Age assessment of wounds is a challenge in both human and veterinary forensic pathology. This study aimed to evaluate the density, dimensions, and circularity of nuclei in experimental and forensic porcine wounds over time by application of software for nucleus detection and characterization. Moreover, to evaluate whether the nuclei density is affected by the location of the wound on the body. HE-stained tissue sections of granulation tissue from 181 porcine wounds (n = 47 pigs) from a porcine excisional wound model were included, together with 30 porcine skin wounds (n = 22 pigs) received for forensic examination. In addition, tissue sections of intact skin from 13 experimental pigs were included as controls. The experimental wounds had healed by second intention and were divided into seven groups based on wound age (5, 10, 15, 20, 25, 30, and 35 days). Forensic wounds were divided into three age groups based on the age assessment stated in the forensic reports (days, > 1 week, or several weeks). Moreover, the forensic wounds, several weeks old, were divided into three groups based on body location (umbilical outpouching, limbs, and ear/tail). All tissue sections were digitized, and nuclei were quantified and measured (area, diameter, and circularity) by application of the InstanSeg extension in QuPath. The density of nuclei in granulation tissue from the experimental wounds showed a significant decrease over time (P < 0.05, η2P ≥ 0.88). In granulation tissue from forensic wounds, the nuclei density also showed a tendency of a time-dependent pattern, but this was not statistically significant (P > 0.05). Nuclei density was significantly lower in wounds located on umbilical outpouchings compared to wounds located on ears/tails (P < 0.05). Nucleus area, diameter, and circularity did show significant differences between age groups (P < 0.05, η2H ≤ 0.03). However, effect sizes were too low and differences too small to be suitable for age assessment of wounds. Digital quantification of nuclei density is promising as a supportive tool for assessing wound age in veterinary forensic pathology. However, nuclei density can be affected by the body location of the wound and should not be used as a standalone method for age assessment.