Parietal Foramina

GENESIS

Parietal foramina are rare calvarial defects estimated to occur in fewer than 1 in 25,000 births. They present as symmetric oval defects situated on either side of the sagittal suture near the parietal eminences and are separated from each other by a narrow bridge of bone ( Fig. 38.1 ). They represent defects of calvarial ossification, with their size decreasing with advancing age. They manifest via autosomal dominant inheritance with variable expression with considerable intrafamilial variability. Goldsmith initially called this condition “Catlin marks” after observing the condition in 16 members of a five-generation family with the surname Catlin. This condition can present as cranium bifidum in early life and develop into parietal foramina by later childhood. Cranium bifidum means literally “cleft skull” and it presents as a wide opening between the frontal and parietal bones. In normal fetuses, the frontal, parietal, and squamous parts of the temporal bones undergo intramembranous ossification, which is a direct ossification of the vascularized membrane. These parts are usually ossified in the fifth month of gestation. When there is insufficient ossification around the parietal notch, they end up as large parietal foramina. Wilkie et al. described heterozygous MSX2 mutations in three unrelated families with enlarged parietal foramina, which suggests that loss of MSX2 activity results in calvarial defects. A second gene has been implicated in those families who do not link to 5q34-q35 (the location of MSX2 ), and mutations or deletions of ALX4 or TWIST1 can also result in parietal foramina. Absence or severe hypoplasia of the parietal bones can occur in cleidocranial dysplasia with mutations in RUNX2 . Cleidocranial dysplasia consists of large fontanels, wide sutures, clavicular hypoplasia, supernumerary teeth, and short stature. Parietal foramina occur laterally to the midline and have well-demarcated edges. Because of the availability of high-resolution antenatal sonography and magnetic resonance imaging, as well as neonatal magnetic resonance imaging, early detection of cranial and intracranial anomalies and the developmental features of this condition can be recognized.