Subdural Hematoma is a collection of blood that pools under the dura. The dura is a relatively tough connective tissue (collagenous) membrane, about the thickness of parchment paper. It is firmly attached to the under surface of the skull and in the spinal canal it is separated from the bony structure by a layer of fatty tissue. The inner underside of the dura is applied to a much thinner, transparent membrane, the arachnoid, that overlies the brain and subarachnoid space. This interface is easily separated, forming the subdural space. The subdural space and is referred to as a "potential space" because a space is not generally created unless a subdural hematoma or another space occupying mass is formed.

 

When a subdural hematoma forms, it is generally an indicator of a broken vein on the underlying surface of the brain. Veins draining the surface of the brain pass through the subarachnoid space and then the dura on their way into the sagittal sinus and other intradural venous sinuses that carry the venous blood eventually to the jugular system. If one or more of these veins that "bridge" the dura are injured, bleeding occurs into the subdural "space" causing a subdural hematoma (clot). For whatever reason, most subdural hematomas in "Shaken Baby" cases, as well as non-accidental trauma cases in infants, are bilateral. An early study by Gulthkelch found that subdural hematomas were bilateral in children 78% of the time. This differes from the rates found in adults. A study by Nashelsky found bilateral subdural hematomas in only 50% of adult cases.

Contra Coup Injuries- Contra Coup injuries occur when there is an injury to the opposite side of the head from the impact site. Contra coup injuries are generally thought to be an indicator of a moving head hitting a stationary, unyielding force or object (Spitz and Fisher III ed.).

 

When the dura is cut and removed a subdural hematoma may be seen. This blood will appear bright red if it is "acute" and the color of port wine or "crank case oil" if it is older. The pathologist should note be if the blood is red/black, brownish, yellowish-orange, "machine oil" or straw colored (or combinations of all of these). The pathologist should weigh (volume), sample and photgraph this blood.

Acute Subdural Hematoma

 

Chronic Subdural Hematoma

 

"Chronic" or old subdurals will be darker in color and may leave an iron stain on the dura the color of port wine, brown or yellow.

If the blood is adherent to the skull cap, dura or elsewhere (and if so, to what degree). If so, care should be taken to properly fix the specimen before attempting to make a tissue section, since the clot and valuable information may be carried away in the process. Even apparently acute clots may have chronic elements within them that only histological study can reveal.

 

Neuropathology/ Histology
Timing and Dating of Injuries

 

Histology Slide of Subacute Subdural Hematoma

 

7-8 day old or so subdural hematoma membrane...beneath the membranous cellular reaction is a recent hemorrhage, the age of which is 2 days old or less

 

The pathologist should retain a sample of the dura for examination by a forensic neuropathologist. Dating of a Subdural Hematoma by visual inspection is unreliable, but histologically, using the Munro and Merritt chart, greater accuracy is possible. Although the Munro and Merrit dating concept was done from limited adult data, it is the most comprehensive study to date. Differences in aging and dating between adults and infants has never been shown and should not invalidate the use of the Munro and Merritt schema of dating hemorrhages in infants and children.

The arachnoid is the thin web like membrane beneath the dura and covering the surface of the brain.

Diffuse Axonal Injury: This condition has a number of other names (traumatic axonal injury--TAI, inner cerebral trauma, etc.). Classically persons suffering from DAI are in deep coma after suffering major closed head trauma such as major falls, automobile accidents and the like. They may or may not have subdural hematomas or skull fractures or any major bleeding in the brain yet they are unconscious and may or may not survive. When autopsy is done within a few days of trauma the brain is edematous, there are numerous scattered deep brain hemorrhages classically in the corpus callosum, deep white matter around the ventricles and in the cerebral peduncle and upper brain stem-diencephalon. Microscopically there are swollen axons with various reactions about them.

DAI is often alleged in so-called shaken babies and is said to occur from the rotational forces that accompany shaking. The issue here is that there is no biomechanical evidence that the forces involved in pure shaking can attain the tissue injury threshold needed for production of DAI in experimental animals. Furthermore, it has been shown that regardless of what might have occurred prior to death, once the individual has been on a respirator, with significant hypoxia/ischemia to the brain with or without edema or any other pathology the findings of axonal injury by any staining method are unreliable in predicting what form of injury might have preceeded death. Put another way Beta-APP staining or any other method has no forensic significance when there have been 3 hours or more of hypoxia/ischemi and/or edema from any cause before death (Oehmichen; Geddes).

 

Beta APP stain showing beaded axon to the left and accumulation in other axons and nerve cells.