2002-05-15-11 Iniencephaly, 12 weeks © Thomas www.thefetus.net/
Iniencephaly, 12 weeks
Dominique Thomas, MD, Marc Arens, MD, Valérie Segers, MD
Dept of Obstetrics and Gynecology, Hôpital Iris Sud, sîte Ixelles, 63 rue J. Paquot 1050 Bruxelles Belgium, tel: 32 2 641 85 35 Fax: 32 2 641 85 36
A 29-year-old Caucasian woman G2P1 was referred at 12 weeks of gestation for her first ultrasound scan. A transvaginal ultrasound was performed.
The CRL was 44.7 mm. The biparietal diameter was 17.8 mm.
A large triangular cystic structure was seen in the posterior fossa (fig1).
The face looked upwards and no neck groove was seen (fig2).
Only seven vertebral structures were identified in an anterior position in the neck (fig3).
The cervical spine seemed to have a severe lordosis. No posterior vertebral structures were seen in the dorsal, lumbar, or sacral regions. Posteriorly in the neck, a small “bubble-like” structure was seen suggestive of a cervical myelomeningocele, and the nuchal translucency was estimated at 3.6 mm (fig4).
The patient was counseled on the findings and elected to terminate the pregnancy.
Termination of pregnancy was performed at 14 weeks, and the female fetus underwent histopathological examination (fig 5-6).
The cystic cervical lesion was not seen, since it had been destroyed during the expulsion. The features previously seen on ultrasound scan were confirmed, and further information was obtained. Atretic cerebellar tissue was found in the foramen magnum. The bony vertebral canal was almost entirely open. There was agenesis of the upper right lung, the liver was partly in the thorax although completely covered by the diaphragm. An anorectal atresia was present.
Chromosomal analysis of the skin revealed normal 46,XX karyotype. We point out that the triangular cystic structure located posteriorly in the posterior fossa obtained by a transverse plane of the head and obtained in a sagittal view of the fetus could be an early sonographic sign of iniencephaly as well as the fixed retroflection of the head and absence of neck groove . The vertebral column abnormality seems to be more difficult to diagnosis because of poor ossification at this gestational age.