Summary

Both cranium bifidum and foramina parietalia permagna are defects in intramembranous ossification of the cranium. Parietal foramina are symmetrical, oval defects in the parietal bone situated on each side of the sagittal suture and separated from each other by a narrow bridge of bone. The size of the openings, normally obliterated during the fifth fetal month, decrease with age and considerable intrafamilial variability is observed. Although small parietal foramina are common variants in up to 60% to 70% of normal skulls, large parietal foramina ranging from 5 mm to multiple centimeters are less common, with a prevalence of 1:15,000 to 1:25,000. Parietal foramina are usually asymptomatic, but may be associated with headache, scalp defects and structural or vascular malformations of the brain. Cranium bifidum is characterized by wide openings in the calvaria present at birth, bilaterally or in the midline of the skull, that persist into childhood. Several cases were reported of progression from cranium bifidum in infancy to symmetric parietal foramina during childhood and adulthood in the same patient. This led to the conclusion that the 2 manifestations are the same entity expressed in an age-dependent manner. Both anomalies may be associated with circumscribed aplasia of the scalp, seizures, or clefts of the lip and/or palate, as well as spina bifida occulta. A spontaneous decrease in the size of these defects with growth of the infant normally occurs, but this closure is usually incomplete. Surgical intervention of persistent large foramina protects the child against potential injury to the underlying brain. Cranioplasty for active young children and those at risk for injury (i.e., seizure disorder) decrease the risk for potential intracranial injury. Inheritance is autosomal dominant, and isolated cases of parietal foramina were found to be the result of mutations in the homeobox gene MSX2, which maps to 5q34-q35. These mutations were either entire-gene deletions or loss-of-function mutations, which supports the hypothesis of haploinsufficiency of the corresponding protein. Parietal foramina may occur also as part of the contiguous gene deletion syndrome (CGDS). This syndrome called Potocki-Shaffer syndrome, includes also mental retardation and multiple exostoses, and is caused by monosomy of 11p11.2 with haploinsufficiency of the ALX4 gene. Parietal foramina due to mutations in the MSX2 gene are referred to as parietal foramina-1, those due to mutations in the ALX4 gene are referred to as parietal foramina-2.

Expert reviewer(s)

• Dr Martine LE MERRER