iniencephaly

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

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

Epidemiology

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

Pathology

The exact etiology is unknown.

Subtypes
  • iniencephaly apertus:  associated with an encephalocele
  • iniencephaly clausus: associated with spinal defect
Markers
Associations

Radiographic features

Antenatal ultrasound

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

Treatment and prognosis

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

History and etymology

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

Differential diagnosis

For an extended head position on antenatal ultrasound consider:

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