Parietal foramina are a type of congenital calvarial defect. They result from delayed/incomplete ossification of the parietal bone.
They can occur as an isolated autosomal dominant trait or as part of a syndrome. Ossification along a midline bar may separate confluent parietal defects into paired parasagittal defects during the first few months of life, which can persist into adult life.
Underlying genetic anomalies have been identified in chromosome 11p deletions with mutation of the ALX4 (60%) and MSX2 (40%) genes in those with enlarged parietal foramina.
Increased incidence of venous and cortical anomalies 4.
Second trimester ultrasound (or MRI) may identify the calvarial deficits.
Seen as paired, rounded deficits in the parietal bone located near the intersection of the sagittal and lambdoid sutures. The deficits may be large and unified across the midline.
Superior to CT for detecting any associated cortical, venous or meningeal anomalies.
Treatment and prognosis
They are generally considered benign. Small foramina are sometimes even considered being part of the spectrum of normal variation. Some authors however suggest imaging of underlying brain parenchyma and vasculature in those with enlarged parietal foramina (>5 mm) due to high associations with cortical and venous anomalies 4.
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