Purpose: Little information is known about the natural history of closure of the processus vaginalis. The authors studied children who had ventriculoperitoneal shunts to determine the natural history of closure of the processus vaginalis and to better understand the role of intraabdominal pressure in the etiology of congenital inguinal hernia.
Materials and methods: A retrospective review of all children undergoing insertion of ventriculoperitoneal shunts between 1985 and 1995 at the Royal Children's Hospital was undertaken. In each case, the sex, the cause of hydrocephalus, the age at insertion of the shunt, and the subsequent development of an inguinal hernia or hydrocele was recorded.
Results: There were 430 children in the study. An inguinal hernia developed in 15% of children after insertion of a ventriculoperitoneal shunt, and a hydrocele developed in an additional 6% of boys. Inguinal hernias were bilateral in 47% of boys and 27% of girls. The incidence of subsequent development of an inguinal hernia or hydrocele was closely related to the age of insertion of the ventriculoperitoneal shunt, being 30% during the last 8 weeks of gestation and the first few months of life, then falling quite sharply to reach about 10% at 1 year.
Conclusions: The high occurrence of inguinal hernias and hydroceles after ventriculoperitoneal shunt insertion supports the role of raised intraabdominal pressure in the etiology of these conditions. It appears that raised intraabdominal pressure is associated with an increased incidence of clinical hernias, but not with increased incidence of patency of the processus vaginalis. The development of an inguinal hernia or hydrocele after insertion of a ventriculoperitoneal shunt can be used as an indirect marker of patency of the processus vaginalis at the time of insertion of the shunt. From this, we propose that the processus vaginalis remains patent in at least 30% of children in the first few months of life, after which time the patency rate appears to fall off quite sharply.