Histochemical detection of gunshot residues on brain and dura mater sections using a sodium rhodizonate staining technique

Introduction: by a medico-legal point of view it is important to identify a gunshot injury when the characteristics of a penetrating wounds are not obvious to the naked eye. In these cases can be very useful a histological study of both the wounded skin and the injured organs [1, 2, 3]. Sodium rhodizonate has been used as a specific histochemical marker for the detection of gunshot residues on skin, due to its property to form a coloured complex in presence of lead, antimony and barium [4, 5], but it has never been tested on organs. This study proposes a histochemical staining technique with sodium rhodizonate and light green SF yellowish for the detection of gunshot residues in injured brain and dura mater, in order to determine if sodium rhodizonate can be consider a useful histological marker even when it is applied on organs. Methods: the study has been performed on subjects who died of close range gunshot head injury; samples of brain and dura mater were taken, in proximity of the injury, both near the entrance and the exit wound, fixed in 10% neutral buffered formalin and later underwent histological routine procedures; 5-μm-thick sections were obtained. All sections were first stained with sodium rhodizonate, then contrasted with light green SF yellowish, in order to detect gunshot residues and define their characteristics. Samples of integral brain and dura mater have been used as control sections. Results: a brown-blackish particulate has been detected in injured brain and dura mater sections stained with sodium rhodizonate and light green SF yellowish, mostly located in the areas of greater hemorrhage infiltration near the entrance wound, on a well-contrasted connective tissue. The intensity of staining appeared to be proportional to the concentration of gunshot residues, being brighter in the areas where the tissue was most affected by disruptive processes and where, most likely, particles had deposited in greater amounts. However, greater particulate dispersion could be observed also near the exit wound. Control samples were completely free from any brown-blackish particulate. Conclusions: sodium rhodizonate has proven extremely useful in detecting gunshot residues on brain and dura mater sections. The presence of a brown-blackish particulate within the injured tissues demonstrates that in close range gunshot injuries there is a carriage of gunshot residues and/or substances from the bullet for the entire length of the internal lesion, and these substances can be easily detectable with a histochemical exam. The negativity of control sections (brain and dura mater) confirms the histological specificity of sodium rhodizonate as a marker for lead, antimony and barium, even when it is tested on organs. The histological study of injured organs can be consider as a useful and specific medico-legal instrument applicable to difficult cases, also due to its cheapness and simplicity