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A rare malformation characterized by missing scalp and flat bones over an area of the cranial vault. The size of the affected area is variable. In rare cases, acalvaria involves the whole of the dome-like superior portion of the cranium comprising the frontal, parietal, and occipital bones. Dura mater and associated muscles are absent in the affected area but the central nervous system is usually unaffected, although some neuropathological abnormality is often present (e.g. holoprosencephaly or gyration anomalies). Skull base and facial bones are normal.
ORPHA:945Classification level: Disorder
- Primary acalvaria
- Prevalence: Unknown
- Inheritance: Not applicable
- Age of onset: Neonatal, Antenatal
- ICD-10: Q00.0
- OMIM: -
- UMLS: C0702169 C2930936
- MeSH: C535570 D009436
- GARD: 361
- MedDRA: -
The prevalence is less than 1 per 100,000 births.
Acalvaria is regarded as a postneurulation defect. The presumed pathogenesis of acalvaria is faulty migration of the membranous neurocranium with normal placement of the embryonic ectoderm, resulting in absence of the calvaria but an intact layer of skin over the brain parenchyma.
Prenatal diagnosis is made by ultrasonography and usually confirmed by magnetic resonance imaging because the condition may be confused with anencephaly or encephalocele.
The malformation is most often lethal at birth, but a few surviving infants have been reported.