Hypostasis is also known as Postmortem Lividity, livor mortis, vibices, suggillation, postmortem staining. It is the purplish-blue or reddish-blue discoloration due to the settling of blood by the gravitational force within the dependent dilated and toneless small veins and capillaries of rete mucosum.
It is an intravascular phenomenon and occurs in the dependent part of the body. The areas that remain in direct contact with the ground will not show staining. This is known as Contact Pallor. Lividity can occur in internal organs as well and hence can be confused with contusion of the organs or congestion. Post mortem lividity does not appear over scars or scarred areas as these areas are devoid of blood vessels.
A bruise is the extravasation or collection of blood due to the rupture of blood vessels caused by the application of mechanical force of blunt nature without loss of continuity of tissues. It is also known as a contusion. It is caused by a blunt force impact causing crushing or tearing of subcutaneous tissue or dermis without breaking the overlying skin. As the blood vessels rupture, the blood gets collected underneath the tissue. This causes swelling and pain.
The contusion stain appears to be reddish or purplish which is very much similar to postmortem lividity and hence a differential diagnosis may happen.
Difference Between Hypostasis and Bruise
| Hypostasis | Bruise |
|---|---|
| It is a change that occurs after death. | It happens due to an antemortem event that may or may not be fatal. |
| It happens due to the distension of vessels with blood in the dermis | It occurs due to ruptured vessels. |
| It occurs over an extensive area of the most dependent parts. | It occurs at the site and the surrounding areas of the injury and it can appear anywhere on the body. |
| Swelling or elevation is not seen. | Mostly it is swollen because of extravasated blood and edema. |
| The epidermis is not abraded. | It may be abraded. |
| The margins will be clearly defined. | The margins are not much clear and they merge with the surrounding area |
| It will be mostly in a uniformed bluish-purple color | Fresh bruises appear to be reddish or purplish. But it changes color during the process of healing. |
| On incision, blood is seen in blood vessels, which can be easily washed away. The subcutaneous tissues will be pale. | On incision, it shows extravasation of blood into the surrounding tissues, which is firmly clotted and can not be washed by a gentle stream of water. The subcutaneous tissues are deep reddish-black |
| It cannot be seen in areas of the body which is even under slight pressure. | It appears to be a little lighter over the area of pressure or support. |
| It is superficial | It can be near the surface or deep inside the skin. |
| Blanched by pressure | Not blanched by pressure |
| Not accompanied by abrasions | Mostly accompanied by abrasion |
| Can be washed out | Cannot be washed out unless healed completely. |
| No signs of inflammation | May show signs of inflammation |
Conclusion
In decomposed bodies, especially in the scalp, hemolysis of red cells produces a diffuse discoloration of the soft tissues, due to which it becomes impossible to differentiate between an antemortem contusion and an area of postmortem hypostasis.
In hypostatic areas, blood vessels break down with leakage of red cells into the soft tissue which haemolyse due to decomposition, in a contusion also, erythrocytes in soft tissue hemolysis and is very much similar in appearance to a hypostasis.
Hence it is very important to clearly understand the features that can be used while examining to differentiate hypostasis and bruise thus preventing a differential diagnosis.
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