A sinus print is a bony feature in the skull that can be used to make an identification of skeletal remains. To use a sinus print in this way, it is necessary that a skull be found among the remains and that ante-mortem skull x rays are available.
The sinuses are four pairs of air-filled cavities, surrounded by bone, at the side and top of the nose. They make the voice resonate and also lighten the bones of the skull. The frontal sinuses are found above the eyebrows and are bounded, at the top, by a scalloped ridge. Research has shown that the detailed shape of this bony ridge is an individualizing characteristic. The pattern is known as a sinus print and, like a fingerprint, it is unique to each individual. Identifications using sinus prints have been carried out since approximately 1921.
When skeletal remains are discovered, the forensic anthropologist, having first confirmed that they are human, will try to date them. Police will usually have a list of persons reported missing around that period of time. Should any of these have had a skull x ray for medical reasons, this will be part of their medical records and can be made available to the investigating team. An x ray is made of the skull and superimposed on the antemortem x ray. Should the sinus prints of antemortem and postmortem x rays match, this is powerful evidence of identity. If they do not match up, the missing person can be eliminated from the enquiry.
Identification from a sinus print may be confirmed by looking for other points of comparison in the antemortem and postmortem skull x rays. For instance, the side profiles of the skulls should also be compared. If there are teeth available with the discovered skull, then dental records can also help confirm identity. If there is no antemortem x ray, the skull may still be useful if there is a photograph of the missing person. In photo superimposition, the forensic anthropologist overlays a photographic transparency of the skull, scaled to match the angle of the head in the portrait. They will look for matches at points such as the chin, teeth, and eyebrow ridge. Lack of fit is usually very obvious. This technique is especially useful for disproving identity. However, it is not as powerful as the sinus print for establishing identity and can only be seen as a guide.
see also Anthropology; Osteology and skeletal radiology.