Colloid osmotic and hydrostatic pressures in chronic subdural haematomas

Intracranial pressure (ICP) has been measured in eight patients with chronic subdural haematomas (CSH) for 24 hours prior to and for 24 hours following evacuation of the haematomas. In all patients ICP was increased prior to surgery (mean: 23 mm Hg), and it rose again to the preoperative level following evacuation of the haematomas in spite of disappearance of most symptoms and signs. In two of these patients and in another eight patients with CSH, colloid osmotic pressures were measured in samples obtained simultaneously from haematoma fluid and venous blood during surgery. The colloid osmotic pressure in haematoma fluid varied considerably between patients (lowest: 11.8 mm Hg, highest: 60 mm Hg), and thus the difference between colloid osmotic pressures in haematoma fluid and plasma also varied considerably. We suggest that the increased ICP in patients with CSH is the consequence of an increased resistance to absorption of cerebrospinal fluid due to compression of the underlying subarachnoid space. The findings with regard to colloid osmotic pressures suggest that osmotic gradients may be maintained across the boundaries of a chronic subdural haematoma.