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Articles » Aneuploidy » Trisomy 18
 2007-01-02-14 Trisomy 18, diencephalo-rhombencephalic dysplasia © Cuillier

Trisomy 18, diencephalo-rhombencephalic dysplasia

Fabrice Cuillier, MD, K. Comalli Dillon, BA, RDMS, A. Ranjatoelina-Randrianaivo, MD, A. L. Delezoide, MD.


Department of Gynecology, Félix Guyon Hospital, 97400 Saint-Denis, Ile de la Réunion, France. Tel : 0262 90 55 22, Fax : 0262 90 77 30 ;


Sonographer, Translator, Editor, Novato, California;


Pathophysiologist, Groupe Hospitalier Sud Reunion, 97400 Saint-Pierre, Ile de la Réunion,  France ;


Fetopathology Department, 48th, Blvd Serrurier, 75935, Paris, Codex 19.

Case report

We present the case of a 40-year-old woman scanned at 14 weeks GA. Her medical and family history were unremarkable. She had no toxic exposure.

A single live fetus was seen on sonography. The fetus had a normal nuchal translucency but abnormal brain structures. Clear sonographic indications for trisomy 18 were visualized and the parents decided to interrupt the pregnancy. Amniotic fluid was sampled at that time, confirming trisomy 18.

Figures 1, 2. Pregnancy at 14 weeks GA showing the fetus (length = 65 mm). Note the flat face. 


Figures 3, 4. 3 - Coronal view of the brain; 4 - Transverse view of the brain.


Figures 5, 6. Transverse views of the brain.


Figures 7, 8. Transverse views of the brain.


Figures 9, 10. 9 - Frontal view of face and eyes; 10 -Transverse view of the brain.


Figures 11, 12. 11 - Frontal view of face and eyes; 12 -  Transverse view of the bladder with single umbilical artery.


Figures 13, 14. 3D views of the right hand. 


Figures 15, 16. 2D views of the right hand. 


Figures 17, 18. 3D view of the left hand.


Figures 19, 20. 19 - 2D view of the right hand; 20 - 2D view of the feet. 


Figures 21, 22. 21 - 2D view of the feet; 22 - Postmortem view of fetus.


Clinical examination

Choroid plexus dilatation was observed at 14 weeks GA. A trilobed interhemispheric fissure and anomalies of the posterior fossa were seen.  
Macroscopic examination

The weight of the brain was below the 5th percentile for 16 weeks GA based on biometric measurements taken at 14-15 weeks GA.  The occipitofrontal diameters corresponded to biometric measurements for 13-14 weeks GA. The weight and diameter of the cerebellum were much lower than expected. On external examination, the cerebellum was small and globular. A very long mesencephalon was noted; it formed a posterior beak above the vermis. 

In frontal section, the lateral ventricles appeared enlarged such that the third ventricle was effaced. The rest of the visualized anatomy was unremarkable.

Histologic examination

The encephalon was studied in semiserial sections. A major dilatation of the lateral ventricles was present; the third ventricle was effaced, replaced by ependymal rosettes found in the thalami and, in a very disorganized fashion, in the anterior wall of the diencephalon and at the level of the hypothalamus. In more posterior sections, a continuity between the lateral ventricles was observed, as well as a dilated third ventricle which occupied the interhemispheric space, preventing development of the corpus callosum.

Sequential sections of the mesencephalon showed a very pocked appearance of the aqueduct of Sylvius and a completely dysplastic, hamartomatous dorsal mesencephalon surrounding the ependymal rosettes, remnants of the aqueduct. Serial sections of subtentorial structures demonstrated a completely dysplastic rhombencephalon: the pontine structures were undeveloped. The fourth ventricle was abnormally shaped and had multiple ependymal rosettes throughout the parenchyma. The cerebellar vermis was absent, replaced by entirely dysplastic structures in the median and dorsal regions. There appeared what was most likely an outline of cerebellar hemispheres, but these were altogether abnormal. In the area of the olivary bodies, an abnormal bulbous floor was seen.


The brain was small for gestational age. The diencephalon and rhombencephalon were completely dysplastic, with absence of the third ventricle, replaced by an interhemispheric cyst tangential to the lateral ventricles. Agenesis of the corpus callosum was seen as was stenosis of the aqueduct of Sylvius. Cerebellar and pontine dysplasia were observed.

Cerebral dysmorphia of this degree is uncommon in the context of trisomy 18.


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