How many millimeters–how big–must a chronic subdural hematoma be before it begins producing symptoms?

After all, if a brain bleed beneath the dura mater is small enough, it won’t cause any symptoms.

I posed this question to Charles Park, MD, neurological surgeon, Director of The Minimally Invasive Brain and Spine Center at Mercy Medical Center in Baltimore.

Dr. Park explains, “Usual rule of thumb is 10 mm.”

My mother had a chronic subdural hematoma after falling and hitting her head.

The symptoms started up, suddenly, six weeks after the accident. The CT scan revealed two bleeds: One was 15 mm and one was four mm.

Only the 15 mm collection was drained. The neurosurgeon said that the tiny collection would be reabsorbed by her body.

After the surgery, my mother’s symptoms were gone (headache and bilateral leg weakness).

Dr. Park continues, “Also, what is important is whether the [chronic] subdural hematoma will produce a ‘midline’ shift, which means that the brain is shifted to the opposite side. 

“This will be a more reliable indicator for the seriousness of the SDH and a determining factor in deciding on surgery.”

On my mother’s CT scan, I clearly saw the midline shift.

Because chronic subdural hematomas that are less than 10 mm, and certainly smaller than five mm, will typically not cause symptoms, we can say that there are people who develop a chronic subdural hematoma and never know it.

These are small collections under 10 mm — and more likely under five mm—that don’t produce any symptoms and are simply reabsorbed into the body.

How are these tiny subdural hematomas even discovered in the first place?

These small collections may be discovered incidentally when the patient undergoes a head CT for another reason that coincides with the timeline of the chronic subdural hematoma.

Or, they may be detected when the CT scan is performed because the patient is exhibiting symptoms from a larger cSDH that accompanies the tiny one.

Dr. Park specializes in minimally invasive surgical techniques for treatment of conditions affecting the brain and spine. He’s skilled in advanced procedures and techniques that utilize innovative computer technology and image-guided surgery systems.
Lorra Garrick has been covering medical, fitness and cybersecurity topics for many years, having written thousands of articles for print magazines and websites, including as a ghostwriter. She’s also a former ACE-certified personal trainer.  


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