Meningeal-cutaneous relationships in anencephaly: evidence for a primary mesenchymal abnormality.

The pathogenesis of cranial and spinal dysraphia has been controversial. Studies of spinal dysraphia have shown that the relationships of the pia and dura to the cutaneous layers were best understood as the result of a primary abnormality of mesenchymal structures, with the nervous system lesions occurring as a result of exposure of the bare spinal cord on the body surface. This study was undertaken to determine if the relationship of the cutaneous layers in anencephaly were similar to those found in spinal dysraphia. We reviewed serial histologic sections of the cranial structures of 10 anencephalic fetuses autopsied at The Johns Hopkins Hospital. We found the dura to be continuous with the deep dermis and the pia continuous with the superficial dermis and epidermis, the same arrangement observed in myelomeningocele. The development of eyes and cranial nerves, the absence of a bony calvarium, and the meningeal-cutaneous relationships found in this study support the idea that anencephaly can originate as an abnormality of mesenchymal structures and that the brain is secondarily lost to injury in utero because of its exposed position.