CRANIUM BIFIDUM

PARIETAL FORAMINA

Cranium bifidum

Cranium bifidum is a defect in the fusion of the cranial bone. Cranium bifidum occurs in the midline, and is most common in the occipital region. If meninges and CSF herniate through the defect, it is called a meningocele. If meninges and cerebral tissue protrude, it is called an encephalocele .

The most benign type - Persistent parietal foramina or persistent wide fontanelle:

- The parietal foramina can be transmitted as an autosomal dominant trait via a gene located on the short arm of chromosome 11. The condition is sometimes called "Caitlin marks," after the family for which it was described. Both parietal foramina and a persistent anterior fontanelle are generally asymptomatic. The intact skin and absent herniation of brain or meninges differentiates it from a cephalocele.

1. Small Foramina.
• Bilateral.
• Symmetrical.
• 90 % > 1mm (rarely as large as 5mm).
• Considered normal variants and transmit the emissary vein of Santorini.
2. Large Foramina.
• Familial tendency (AD).
• Result from faulty intramembranous ossification in the posteromedial portion of the parietal bone in the region of the obelion.
• It arises as a single ossification defect which is subsequently cleft into two foraminae by ossification in the parasagittal region.
• Several centimeters in size.
• Symmetrical round or oval defects in each parietal bone

• Overlying skin is intact.
• No herniation of membranes or brain tissue through the defect.
• Most common associated anomaly in cranial dysostosis.
• Other rare associations:
• Myelomeningoceles
• Encephaloceles
• Craniofacial anomalies
• Vertebral anomalies
• Polydactyly or syndactyly.
• May present with soft tissue swelling in the neonate and be associated with pain on palpation or bouts of nausea and vomiting

Cranium bifidum such as an encephalocele is much more serious.

- Encephaloceles are thought to occur when the anterior neuropore fails to close during days 26-28 of gestation.

- Incidence of this anomaly is 10% of the incidence of spina bifida cystica. In the United States, approximately 80% of lesions are found on the dorsal surface of the skull, with most near the occipital bone.

- In contradistinction, most encephaloceles in Asia are ventral and involve the frontal bone.

- In the Philippines and other Pacific countries, incidence of anterior encephaloceles that present as hypertelorism, obstructed nares, anterior skull masses, and cleft palate, among other presentations, is high.

In most lesions, the sac that has herniated through a midline skull defect is covered with epithelium.

REFERENCES

1. Fernandez G, Hertzberg BS. Prenatal Sonographic Detection of Giant Parietal Foramina. J Ultrasound Med 1992, 11:155-157.