acalvaria
Acalvaria is a rare malformation defined as 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.