the term iniencephaly implies that the brain and the neck (inion) demonstrate the principal anomalies. severely deformed iniencephalic fetuses show, in addition to retroflexion of the head, severe spinal defects including an exaggerated cervico-thoracic lordosis in all cases, and often anterior or posterior spina bifida. the head is large in relation to the shortened body, the face looks upwards, and the neck is absent. the skin of the face is continuous with the skin of the chest, and the scalp, if present, is directly connected with the skin of the back. the defective and retroflexed occiput may be joined to the vertebrae of the lower spine. rachischisis exists in most cases, but the defective spinal cord and column are usually covered dorsally by brain, cerebellum, and skin, so that the opened neural plate and vertebral trough are not seen on the surface (iniencephaly clausus). marked retroflexion of the head may also occur in anencephalics or fetuses with open rachischisis (iniencephaly apertus). thus in closed iniencephaly the cranial contents remain within the cranial cavity and in the open form they protrude into an encephalocele or are present as exencephaly or anencephaly. the cervical spine is always severely deformed and shortened by formation of block vertebrae or by vertebral deficiencies.


the observation of a deformed head overriding the shoulder should alert the ultrasonographer to iniencephaly. the presence of the fetal thorax and head in the same scanning plane at the level of the chest indicates severe retroflexion and cervico-thoracic lordosis. if difficulties are experienced trying to locate the fetal spine in a sagittal plane, iniencephaly should also be considered. the principal ultrasound findings in iniencephaly will include: – absence of the normal parietal bones and a deficit of occipital bones resulting in a large foramen magnum – absence of brain tissue – partial or total absence of cervical and thoracic vertebrae with irregular fusion of those present with incomplete closure of the vertebral arches and/or bodies – overriding of the head on the shoulders in fixed retroflexion – craniorachischisis – polyhydramnios is also frequently present associated defects are noted in 80% of cases. other cranial anomalies include cephalocele and hydrocephalus. craniofacial abnormalities such as cyclopia and micrognathia may be observed. related systemic disorders include omphalocele, diaphragmatic hernia, agenesis of the diaphragm, pulmonary hypoplasia or hyperplasia, congenital heart defects, renal malformations (polycystic disease), clubfoot, and gastrointestinal atresia. iniencephaly is a lethal condition, and like other neural tube defects is most probably of multifactoral aetiology. there is a recurrency risk of approximately 5% in each successive pregnancy.

differential diagnosis

the combination of rachischisis and vertebral anomalies require differentiation from the following: in anencephaly, there is complete absence of the calvarium, as opposed to a partial deficit, which may be noted even in the presence of a large cephalocele; there is no pronounced retroflexion in anencephalics. both are lethal conditions with risks of recurrence. in klippel-feil syndrome, there is a spectrum of fusion and malformation of the cervical vertebrae. fixed retroflexion and defective neurulation, however, are not characteristic. a cervical myelomeningocele may coexist with iniencephaly, but may also occur in isolation; in the latter case, the bony defects are likely to be restricted to marked splaying of the posterior ossification centres rather than the more severe disorganisation usually associated with iniencephaly.

sonographic features

head maintained in fixed retroflexion.

fetal thorax and head may be seen in the same plane at chest level.

absence of brain tissue.

absence or partial absence of cervical and thoracic vertebrae with varying degrees of craniorachischisis.

associated syndromes


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