Talbert DG: Institute of Reproductive and Developmental Biology, Imperial College School of Medicine, Queen Charlotte's Hospital, Du Cane Road, London W 12 ONN, UK. email@example.com
It is known that retinal haemorrhages can result in adults when elevated intrathoracic pressures due to coughing, cardiopulmonary resuscitation, etc., force blood into the head. In infants under one year of age retinal and intracranial haemorrhage commonly occur together, but the same is not true for the older child and adult. The role of the elasticity of the infant skull (resulting from suture and fontanelle stretching) compared to the rigid mature skull, was investigated in a computer aided method. This showed that although in the event of Valsalva-like situations very high lumen pressures may be present in both groups, in the rigid adult skull an immediate corresponding increase in intracranial pressure is produced which surrounds and supports vascular walls leaving transmural pressures little changed. No such support is provided in the eye, and retinal vessels may rupture. Within the skull there may be drastic effects on brain circulation, but since changes in vascular transmural pressure are minimal vessel distension is not induced. In the infant skull the sutures stretch as pressure rises. Since vascular volume is only about 5% of intracranial volume each 1% increase in skull volume permits a 20% increase in vascular volume. Quite small skull expansions will allow dangerous vascular distension and risk of wall damage. Until skull bones fuse, intra-cranial bleeding will be expected in the soft infant skull in any situation where retinal haemorrhage alone is known to occur in the adult or child.