Moscow regions Research Institute of Obstetrics and Gynecology, Medical-Genetics Department, Moscow, Russia.

We were the first who described a new "octopus-like sign" for diagnosis of spina bifida and Dandy Walker malformation during the first trimester ultrasonographic examination between 11 and 14 weeks of gestation.

The principle of the method is to obtain a midsagittal scan of the fetal head to see thalamus, brainstem, midbrain, fourth ventricle and cisterna magna. Anatomical arrangement of these structures in midsagittal plane resembles a small octopus.

Image 1: Midsagittal scan of the fetal head showing following structures: 1 - thalamus (diencephalon), 2 - midbrain, 3 - brainstem, 4 - fourth ventricle, 5 - cisterna magna, 6 - nuchal translucency.

Evaluation of the octopus-like arrangement of the midsagittal brain structures is easy, quick, and provides a very sensitive way of early detection of spinal defects and posterior fossa anomalies.

Normal octopus-like appearance of the midsagittal structures is demonstrated on the images 2 and 3.

Images 2, 3: The images show midsagittal scan of the fetal head with characteristic arrangement of cranial structures. Relation of the thalamus, brainstem, midbrain, and fourth ventricle resembles an octopus (depicted in red color: head of the octopus = thalamus, first arm of the octopus = brainstem, second arm of the octopus = midbrain and fourth ventricle). Cisterna magna is depicted in yellow color, nuchal translucency is depicted in blue, and choroid plexus of the fourth ventricle is depicted in green color.

Normal appearance of the octopus-like scheme of the midsagittal cerebral structures follows following characteristic features:

1. Both arms of the octopus have the same size
2. Choroid plexus (depicted in green) has to be seen within the fourth ventricle and the second arm of the "octopus" comprising midbrain and the fourth ventricle has to be clearly separated from the first arm of the "octopus" (brainstem).
3. Cisterna magna has to be clearly separated from the second arm of the "octopus" (midbrain and the fourth ventricle).

SPINA BIFIDA

17 cases of spina bifida have been diagnosed in our center during the last 2.5 years (2011-2013). 7 of those cases were isolated, 6 of them were combined with non-chromosomal syndromes (OEIS association, Jarcho-Levin syndrome, and caudal regression), and 4 of them were associated with chromosomal defects (trisomy 13, 18, and triploidy).

In all cases the characteristic aspect of the octopus-like appearance of the midsagittal cerebral structures was changed as follows:

1. Increase size of the first arm (brainstem) of the "octopus".
2. Decreased size of the second arm of the "octopus" (only choroid plexus within very small fourth ventricle is present).
3. Cisterna magna is not visible.

Images 4-9 show examples of abnormal aspect of the octopus-like appearance of the midsagittal cerebral structures in cases of spina bifida.

Images 4, 5, and 6: Spina bifida and abnormal aspect of the octopus-like appearance of the midsagittal cerebral structures in the first trimester (11-14 weeks). The image 6 shows transverse scan of the fetal spine with spina bifida.

Images 7, 8, and 9: Spina bifida and abnormal aspect of the octopus-like appearance of the midsagittal cerebral structures in the first trimester (11-14 weeks). The image 9 shows transverse scan of the fetal spine with spina bifida (arrow).

DANDY WALKER MALFORMATION

39 cases of Dandy-Walker malformation were diagnosed in our center. 25 of them were associated with chromosomal abnormalities (triploidy - 15, monosomy X - 5, trisomy 13 - 2, trisomy 22 - 1, trisomy 21 - 1, other - 1), 10 of them were associated with non-chromosomal syndromes, and 4 of them were isolated findings.

In all cases the characteristic aspect of the octopus-like appearance of the midsagittal cerebral structures was changed as follows:

1. Aplasia of the cerebellar vermis leads enlargement of the second arm of the "octopus" due to fusion of the fourth ventricle, cisterna magna and choroid plexus.

Images 10, 11, and 12: Dandy-Walker malformation and abnormal aspect of the octopus-like appearance of the midsagittal cerebral structures in the first trimester (11-14 weeks) - aplasia of the cerebellar vermis leads enlargement of the second arm of the "octopus" (in red) due to fusion of the fourth ventricle, cisterna magna (in yellow) and choroid plexus (green). The image 12 shows transverse scan of the fetal head at the level of the dilated cisterna magna the fourth cerebral ventricle.

Images 13, 14, and 15: Dandy-Walker malformation and abnormal aspect of the octopus-like appearance of the midsagittal cerebral structures in the first trimester (11-14 weeks) - aplasia of the cerebellar vermis leads enlargement of the second arm of the "octopus" (in red) due to fusion of the fourth ventricle, cisterna magna (in yellow) and choroid plexus (green). The image 15 shows transverse scan of the fetal head at the level of the dilated cisterna magna the fourth cerebral ventricle.