Iniencephalie

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

• maternal serum alpha fetoprotein (MSAFP) may be elevated

Associations

• other intracranial associations, e.g. anencephaly
• myelomeningocele(s)

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

Siehe auch:

• Klippel-Feil-Syndrom
• Anomalien des kraniozervikalen Übergangs
• retro-flexion of the fetal head
• fetale Zwerchfellhernie

und weiter:

• Neuralrohrdefekt
• rachischisis
• iniencephaly with diaphragmatic hernia