Iniencephaly

Iniencephaly
Classification and external resources
ICD-10	Q00.2
ICD-9-CM	740.2
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Iniencephaly, a term derived from the Greek word "inion" for nape of the neck, is a rare type of cephalic disorder that was first described by Étienne Geoffroy Saint-Hilaire in 1836. Those afflicted with the disorder all share 3 common characteristics: a defect to the occipital bone, spina bifida of the cervical vertebrae and retroflexion (backward bending) of the head on the cervical spine.Stillbirth is the most common outcome, with a few rare examples of live birth, after which death almost invariably occurs within a short time.

There are two types of iniencephaly. The more severe group is iniencephaly apertus, involving the development of an encephalocele. In the other group, iniencephaly clausus, the encephalocele is absent.

The affected infant tends to be short, with a disproportionately large head. The fetal head of Infants born with iniencephaly are hyperextended while the foramen magnum is enlarged and opens through the widened pedicles. The defective neural arches directly into the upper cervical reach of the spinal canal, causing the formation of a common cavity between most of the spinal cord and the brain. The skin of the anterior chest is connected directly to the face, bypassing the formation of a neck, while the scalp is directly connected to the skin of the back. Because of this, those born with this anomaly either have a highly shortened neck or no neck at all. This causes extreme retroflexion, or backward bending, of the head in a "star-gazing" fashion. The spine is severely distorted as well along with significant shortening due to marked lordosis. The vertebrae, especially cervical, are fused together in abnormal shapes and their numbers are reduced. The spinal cord is almost always defective while the ventricular system is often dilated and the cortex is thinned. Sometimes, in the case of iniencephaly apertus, an encephalocele (sac-like protrusions of the brain through an opening in the cranium) forms.

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