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The fetal brain.


The brain is the only fetal organ with a constantly changing appearance during gestation. Basic evaluation of the fetal brain is done in three axial planes:

* Transventricular: skull, midline, falx, cavus septi pellucidi, lateral ventricles, head circumference, ventricular atrium

* Transventricular: + thalami, hippocampal gyrus

* Transcerebellar: + cerebellar hemispheres and vermis, TCD, cisterna magna.

A more detailed neurosonographic evaluation is done in additional coronal and sagittal planes, visualised ideally with transvaginal ultrasound through the anterior fontanelle.

Stage               (Gest.) age   Development

Dorsal induction    5-6 wks       Closure of neural tube

Ventral induction   7-12 wks      Formation of brain segments and

Migration and       12-24 wks     Migration of neurons from
histiogenesis                     periventricular germinal matrix to
                                  cortex; cortical organisation

Myelination         24 wks-3      Myelination

Stage               Anomalies

Dorsal induction    Anencephaly, encephalocoele, Chiari
                    malformation, spina bifida

Ventral induction   Holoprosencephaly, corpus callosum agenesis,
                    vermian agenesis, facial abnormalities

Migration and       Gray matter heterotopias (e.g. schizencephaly,
histiogenesis       lissencephaly, polymicrogyria); phacomatosis
                    (e.g. neurofibromatosis, tuberous sclerosis)

Myelination         Dysmyelination


* Transfrontal: interhemispheric fissure, frontal cortex in front of lateral ventricles, orbita, sphenoid

* Transcaudate: genu corpus callosum, cavum septi pellucidi, frontal horn of lateral ventricles, caudate nucleus, Sylvian sulcus

* Transthalamic: thalami, third ventricle, atrium lateral ventricle with choroid plexus

* Transcerebellar (via posterior fontanelle): posterior horn of lateral ventricles, tentorium, cerebellar hemispheres and vermis.


* Midsagittal: corpus callosum, cavum septi pellucidi, brainstem and pons, 4th ventricle, vermis

* Parasagittal: lateral ventricle, choroid plexus, periventricular area, cortex.

To understand developmental abnormalities, it is useful to understand the different embryological stages of brain development (see table below).

Acquired problems include:

* Hypoxia (porencephaly, hemi-atrophy, hydranencephaly)

* Ischaemia (periventricular leucomalatia)

* Metabolic destructive

* Toxic

* Infection/inflammation (e.g. TORCH, Parvo B19)

* Germinal matrix bleeding.


Malinger G, Monteagudo A, Pilu G, Timor-Tritsch IE, Toi A. Sonographic examination of the fetal central nervous system: guidelines for performing the 'basic examination' and the 'fetal neurosonogram'. Ultrasound Obstet Gynecol 2007; 29(1): 109-116.

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Title Annotation:SASUOG Congress 2010: 7-9 May 2010, Ilanga Estate, Bloemfontein
Author:Pistorius, L.
Publication:South African Journal of Obstetrics and Gynaecology
Article Type:Report
Geographic Code:6SOUT
Date:Apr 1, 2010
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