Classification
| Entity | Imaging Features | Notes / Associations |
|---|---|---|
| Cranium bifidum (encephalocele) | Midline calvarial defect with herniation of meninges ± brain tissue (meningocele / meningoencephalocele). | Common sites: occipital > frontoethmoidal > parietal. |
| Aplasia cutis congenita | Localized absence of skin and bone, most often at vertex; smooth margins. | Usually isolated; may be seen in trisomy 13 or fetal exposure syndromes. |
| Parietal foramina | Bilateral, symmetric, oval defects in posterior parietal bones near sagittal suture. | Normal emissary vein openings if <1 cm; large = developmental variant. |
| Cleidocranial dysostosis | Persistent wide fontanelles, wormian bones, thin calvarium, absent clavicles. | Delayed suture closure, frontal bossing. |
| Achondroplasia | Small skull base, depressed nasal bridge; no true bone “defect” but cranial dysmorphism. | |
| Neural tube defect (acrania / exencephaly / anencephaly) | Absence of cranial vault bones with exposed or absent brain tissue. | Diagnosed antenatally by US/MRI. |