Do we miss half of the injuries sustained during rape because we cannot see them? An overview of the use of toluidine blue tissue stain in the medical assessment of rape cases

Abstract

The prosecution of rape cases is difficult due to the absence of eyewitnesses. McCauley found that the detection of vaginal lacerations increased from one in 24 to 14 in 24 in reported adult rape cases when toluidine blue was used. Proof of injuries consistent with sexual penetration adds significantly to the evidentiary value of the medico-legal testimony. Although rape is not a clinical diagnosis and there are no diagnostic criteria to confirm rape, the possibility of genital injury during rape far exceeds the possibility of injury with consensual intercourse. If a complete examination, including the use of toluidine blue, is not used a rapist may walk away to rape again, while the victims remain with the stigma that they may have made a false allegation. Toluidine blue is a basic thiazine metachromatic dye. It has a high affinity for acidic tissue components, thereby staining tissues rich in DNA and RNA. The epithelium of the external genitalia does not have nucleated cells and prevents contact of stain with nuclei. Where the epithelium is damaged and the underlying nucleated cells are exposed, the nuclei stain blue. Injuries sustained during genital penetration show a distinctive distribution.Toluidine blue stain is easy and safe to use, available, inexpensive and does not interfere with other medico-legal evidence, therefore it is recommended to be used in the examination of all cases of alleged rape.

Sexual Assault: Forensic Examination in the Living and Deceased

“…Detecting sex-related genital injuries, which are usually small and superficial, on the female genitalia, with its many creases and rugae, can be difficult, but examination enhancement techniques such as magnification (colposcopy), staining with toluidine blue (22), or the use of ultraviolet light (23) will increase the likelihood of detection. Toluidine blue is said not to compromise biological evidence but false negatives may occur if any barrier overlies the lesions and false positives may occur in some genital skin conditions (e.g., vulvitis, herpes) (Image 3).…”

“…Less information is available with respect to injuries resulting from anal penetration and published research focuses almost exclusively on nonconsensual study groups; in a recent study, 27% of 174 women reporting nonconsensual completed anal penetration sustained injury, most commonly perianal lacerations (7). Perianal lacerations due to anal penetration are commonly radial, not limited to the midline, and frequently extend into the anus (Image 4) (22).…”