Iniencephaly is a rare neural tube defect resulting in the following features 1,2:

  • occipital bone defect
  • partial or total absence (rachischisis)  of cervicothoracic vertebrae 
  • fixed fetal head retroflexion

The estimated incidence is at ~0.1-10 per 10,000 live births 5. There is a recognized female predilection 5.

The exact etiology is unknown. 

The fetus is described to have a fixed " stargazer" type extended posture. Other features include:

  • exaggerated cervicothoracic lordosis
  • deficient (short) or fused cervical vertebrae
  • variable deficit in the occipital bone
  • due to the head position, the fetal crown-rump length may be lower than expected for gestational age
  • may have concurrent polyhydramnios

Iniencephaly is almost always lethal. However, usually there is no increased risk of recurrence in a future pregnancy.

Derived from the Greek words inion = back of head and encephalos = brain.

For an extended head position on antenatal ultrasound consider:

  • physiological cervical hyperextension: transient, no occipital body defects and/or vertebral anomalies
  • Klippel Feil syndrome

Article information

rID: 10294
Synonyms or Alternate Spellings:

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Cases and figures

  • Case 1: with concurrent diaphragmatic hernia
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  • Case 2: ultrasound
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