Congenital hydrocephalus and clasped thumbs: two cases of brothers in a family.

Two cases of brothers with congenital hydrocephalus and clasped thumbs are reported. In consideration of the rare incidence of sporadic congenital hydrocephalus, hereditary origin of these cases based on X-linked recessive inheritance was suspected. Serial sectioning of the brain stem revealed stenosis and abnormal dorso-ventral elongation of the aqueduct. These findings support the postulation of Landrieu et al that the primary defect in X-linked hereditary hydrocephalus is a communicating hydrocephalus leading usually to aqueductal stenosis in consequence of lateral compression of the brain stem.