* Department of Gynecology, Félix Guyon Hospital, 97400Saint-Denis, Ile de la Réunion, France;
** Sonographer, Moufia"s street, 97400 Saint-Denis, Ile de la Réunion, France;
*** Department of Neonatology, Hôpital Félix Guyon, 97400Saint-Denis, Ile de la Réunion, France.

Case report

A secundigravida, primipara presented to our department at 23rd week of pregnancy. Her first ultrasonography at 13th week and biochemical triple test at 16th week were normal. Our ultrasound investigation revealed:

• Bilateral cerebral ventriculomegaly (colpocephaly);

• Absence of the cavum septi pellucidi;

• Agenesis of the corpus callosum;

• Upward displacement of dilated third cerebral ventricle (interhemispheric cyst).

The karyotype was normal (46 XX). The serological test (Toxoplasmosis, Rubeola, CMV, Herpes, Chikungunya) were also normal. MRI was done at 28th week and confirmed our diagnosis. The parents opted for termination of the pregnancy but refused autopsy.

Images 1 and 2: 23rd week, 2D ultrasonography; Image 1 - transverse plane showing dilated lateral cerebral ventricles and interhemispheric cyst (dilated third ventricle); Image 2 - the same image with drawings and descriptions of structures.

Images 3 and 4: 23rd week, 2D ultrasonography; Image 3 - more cranial transverse plane through the fetal skull showing dominant interhemispheric cyst (dilated third ventricle) and displacement of both medial and lateral walls of the lateral ventricles from the midline; Image 4 - the same image with drawings and descriptions of structures.

Images 5 and 6: 23rd week, 2D ultrasonography; Image 5 - coronal anterior plane through the fetal skull showing dominant interhemispheric cyst (dilated third ventricle) and lateral ventricles which have at this level a "steer horn" appearance; Image 6 - the same image with drawings and descriptions of structures.

Images 7 and 8: 23rd week, 2D ultrasonography; Image 7 - transverse oblique plane showing interhemispheric cyst anteriorly and normal posterior fossa and cerebellum; Image 8 - transverse plane showing dilated lateral cerebral ventricles and interhemispheric cyst (dilated third ventricle).

Images 9 and 10: 23rd week; Image 9 - coronal anterior plane through the fetal skull showing dominant interhemispheric cyst (upward displacement of the dilated third ventricle) and lateral ventricles which have at this level a "steer horn" appearance; Image 10 - Coronal anterior color Doppler image showing anterior cerebral arteries next the interhemispheric cyst.

Images 11 and 12: Sagittal planes through the fetal skull - gray scale (image 11) and color Doppler (image 12) images showing interhemispheric cyst located anteriorly.

Images 13 and 14: 28th week; Image 11 - coronal 2D gray scale scan of the skull showing dilated lateral ventricles (dorsal parts of lateral ventricles); Image 14 - 28th week; MRI axial image showing dilated lateral cerebral ventricles and interhemispheric cyst (dilated upward displaced third ventricle).

Images 15 and 16: 28th week of pregnancy; MRI - sagittal (image 15) and anterior coronal (image 16) planes through the fetal skull showing interhemispheric cyst.