WHAT IS A SUB-DURAL HEMATOMA? Between the inside of the skull and the brain itself is a membrane, the dura. It's firmly attached to the skull and, along with the fluid in which the brain is bathed, it helps protect the delicate brain from the relatively rigid bone of the skull. If, for any reason, there is bleeding between the brain and the dura you get a sub-dural hematoma (SDH). Almost any blow to the head is capable of causing a sub-dural hematoma, although the more severe the blow the more likely it is. The danger is that this causes pressure on the brain as the build up of fluid can't cause the skull to push out, so it causes the brain itself to "herniate", that is, be shoved out of position. In extreme cases, the pressure depresses the brain stem, which controls breathing, and leads to coma, respiratory failure and death. Even should death not occur, varying degrees of long-term brain damage are common.

ARE ALL SUB-DURALS THE SAME? There are different types of SDH. These are, in order of increasing age from the time of the incident that causes the SDH:

• HYPER-ACUTE - follows almost immediately on the incident that causes the bleeding. Very rapid build up of pressure in the brain (Inter-Cranial Pressure, or ICP).
• ACUTE - within a few hours to days of the incident.
• SUB-ACUTE - Measured in days.
• CHRONIC - Weeks to months. The most common form of SDH it usually, but not always, heals with no problem and most people will be unaware that they have even had one.

However, different doctors will use different time-bands to describe a SDH as, e.g. "sub-acute" or "chronic".

WHICH IS MOST DANGEROUS? Obviously the hyper-acute, but there really is no such thing as a "benign" type of SDH, all are potentially dangerous to the child. Whether from the direct bleeding and pressure of a hyper-acute, or the more insidious phenomenon of a "re-bleed" of the chronic or sub-acute form.

WHAT IS A RE-BLEED? In the case of a chronic (or sub-acute) SDH there is some sort of head trauma which causes bleeding between the brain and the dura. This bleeding stops and doesn't cause immediate problems (although the person will probably have a bad headache). This is the difference between this and the other forms of SDH in which the bleeding is either so severe, or doesn't stop, that immediate and severe problems are caused. Mostly the body copes with a chronic SDH and heals, however, it's not a totally stable situation, almost anything can, if the sufferer is unlucky enough, cause bleeding to start again. It's rather like having a cut in a very awkward position, such that the scab can be easily knocked off, and fresh bleeding start. Any abrupt movement of the head, even a sneeze, could cause fresh bleeding and an escalating situation leading to severe problems.

WHAT ARE THE SYMPTOMS? In the crisis situation, however caused and whatever the type, the child suffer seizure, failure to breathe and will be in an obviously severe condition in which skilled and prompt medical attention is the only hope. In a re-bleed the onset is typically insidious, hard to define and frequently the early signs are missed as being among the usual childhood ailments. But may include irritability, lethargy, loss of appetite.

HOW CAN WE TELL THESE DIFFERENT TYPES APART? With great difficulty, an experienced eye will be able to tell you something from looking at the CT scan, since there are well recognised changes over time in the density of the SDH (which is what the CT scan measures). An example being the presence of a band of serum, if of a certain shape, being a strong indicator of a chronic form. However, that is very much a matter of opinion, and honest differences are quite possible. In fatal cases, changes in and on the dura (such as the presence of a "neo-membrane") can be seen in post-mortem pathology, and observation of the brain tissue itself may identify how the sub-dural occurred and when. The critical specialities are neuroradiology and neuropathology.

WHICH FORM DO YOU GET WITH SHAKING/IMPACT? There's some dispute over this, but generally you'd expect an acute or hyper-acute form with a "pure" shaking/impact. However, the issue of the repeatedly abused child, in which the final assault is the culmination of increasingly severe abuse, means that you might find evidence of all types present. Indeed, the presence of SDHs at differing stages of healing is taken as a strong indicator of abuse.

WHICH TYPE MEANS ABUSE? All of them, or none of them. All types can occur through accident or abuse. There is huge controversy about how severe an accident has to be to cause an SDH, or indeed, if head trauma is the only (even if most common) cause of an SDH. Despite public claims of some, there is no absolute medical consensus about many of the most critical issues.

ISN'T IT TRUE THAT A CHRONIC SDH IS VERY RARE IN INFANTS? No. It's very puzzling how this idea has grown up, the following is a quote from Aicardi's "Diseases of the Nervous System in Childhood":
"Chronic SDH occurs mainly in infants 2-9 months in age."

WELL, AREN'T RE-BLEEDS UNKNOWN IN INFANTS? Again the answer is no, in this case the quote is from The Oxford Textbook of Medicine, referring to re-bleeds it says:
"Importantly, the prognosis is not related to age and therefore this condition should be sought for and treated actively in all age groups."
There appears to be no reason to assume such a thing cannot happen, and plenty of evidence that it can.

YOU SAID THAT THERE HAD TO BE SOME HEAD TRAUMA TO CAUSE EVEN A CHRONIC SDH DIDN'T YOU? Yes. That's a generalisation, and there are certain genetic conditions that render infants more vulnerable to lesser trauma, but in general yes.

WELL, WOULDN'T ANY PARENT KNOW? There's no reason to assume they would have to. In a study of adults who had chronic SDH (with and without re-bleeds), over half could not recall any injury that had happened to them. If this is true of adults, who can both tell you about such an incident and have thicker skulls than infants, how much more true must it be for a baby who cannot talk? This may be an unusual condition, but it's by no means unknown, it's well documented in all the standard textbooks. Children do bang their heads, to assume they cannot develop the same conditions from this as other age-groups is an assertion made without any good evidence, in other words a dogma.