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Significance of a Subdural Hematoma in a Child with External Hydrocephalus

Most physicians take the presence of a subdural hema-toma in a child without a history of trauma as presump-tive evidence of abuse. This assumption rests on our understanding of the pathophysiology of subdural hemorrhage ; subdural hematomas are caused by tearing intra-cranial bridging veins and it requires substantial force to rupture the veins and cause bleeding. The force required is thought to be more than can be generated in a short fall or by typical household accidents. Moreover, subdural hematomas most frequently occur in conjunction with other injuries, such as retinal hemorrhages and long bone fractures, which are indicative of severe trauma. There are some conditions, however, that are recognized to pre-dispose a child to develop a subdural hematoma after even minor injury: among them are coagulopathies, glu-taric aciduria, large arachnoid cysts and osteogenesis im-perfecta [1–5]. There have been suggestions that the presence of external hydrocephalus (i.e. familial macrocepha-ly, benign subdural effusions of infancy) also puts a child at risk [6–8]. Both theoretical and clinical evidence supports this position. Theoretical evidence comes from Papasian and Frim [9], who have created a mathematical model specifically to examine the forces required to cause a subdural hema-toma in a child with external hydrocephalus. They used two concentric hollow spheres to represent the brain and skull. Bridging veins were modeled to run orthogonally between the two spheres. Using currently accepted information about venous length and tensile strength, the authors calculated the strain on the veins caused by various forces and then defined the likelihood that the veins would fail in a given situation. They found that the same force caused veins to stretch proportionately more in children with extra axial collections than in those without. They calculated that the forces associated with low impact injuries were sufficient to cause venous rupture in children with external hydrocephalus. This finding held true for simulations with a variety of vessel lengths and diameters. Other groups have come to similar conclusions [10]. As a practical issue, it does appear that a disproportionate number of children with external hydrocephalus develop subdural hemorrhages. Several groups have commented on the relationship. Laubscher et al. [11] described 22 children with megalencephaly and enlarged subarachnoid spaces. Three of the 22 had subdural hema-tomas: all apparently did well and none had recognized trauma. Similar results were reported by Mori et al. [12], Azais and Echenne [13] and, later, by Piatt [14]. The clinical association …