The error is that the clot was NOT in his brain.

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Background: An acute subdural hematoma (SDH) is a rapidly clotting blood collection below the inner layer of the dura but external to the brain [emphasis added] and arachnoid membrane. Two further stages, subacute and chronic, may develop with untreated acute SDH. Each type has distinctly different clinical, pathological, and imaging characteristics.

Generally, the subacute phase begins 3-7 days after acute injury. (Surgical literature favors 3 days; radiological, 7).

The chronic phase begins about 2-3 weeks after acute injury.

Pathophysiology: Typically, low-pressure venous bleeding of bridging veins (between the cortex and venous sinuses) dissects the arachnoid away from the dura and layers out along the cerebral convexity. Cerebral injury results from direct pressure, increased intracranial pressure (ICP), or associated intraparenchymal insults.

In the subacute phase, the clotted blood liquifies. Occasionally, in the prone patient, the cellular elements layer, which can appear on CT imaging as a hematocritlike effect.

In the chronic phase, cellular elements have disintegrated, and a collection of serous fluid remains in the subdural space. In rare cases, calcification develops.

Frequency:

In the US: Frequency is related directly to the incidence of blunt head trauma. An SDH is the most common type of intracranial mass lesion, occurring in about a third of those with severe head injuries (Glasgow Coma Scale [GCS] score <9).
Mortality/Morbidity: Acute SDH is associated with high mortality and morbidity rates.

Simple SDH accounts for about half of all cases and implies that no parenchymal injury is present. Simple SDH is associated with a mortality rate of about 20%.

Complicated SDH accounts for the remaining cases and implies that parenchymal injury (eg, contusion or laceration of a cerebral hemisphere) is present. Complicated SDH is associated with a mortality rate of about 50%.

Age: The majority of SDHs are associated with age factors related to the risk of blunt head trauma. Certain age factors are related to more unusual variants of this disease.

SDH is more common in people older than 60 years. The elderly are predisposed to cerebral atrophy because they have less resilient bridging veins. Moreover, these veins can be damaged more easily in the elderly.

Since the adhesions existing in the subdural space are absent at birth and develop with aging, bilateral SDHs are more common in infants.

Interhemispheric SDHs often are associated with child abuse.