Holoprosencephaly

Holoprosencephaly is a brain malformation that is caused by a primary defect in patterning and induction of the basal forebrain during embryo-genesis, causing the brain to develop improperly and resulting in incomplete division of the cerebral hemispheres. H oloprosencephaly can be caused by either a single gene mutation or as part of a syndrome with multiple genetic anomalies. This defect can occur spontaneously or it can be inherited from the parents. Individuals with very mild manifestations of this defect will often have facial changes including hypotolerism, hypertolerism, flat nose, or cleft lip. From most severe to least, the types of Holoprosencephaly include alobar, semilobar, and lobar.
 * Holoprosencephaly **

**[|Alobar Holoprosencephaly] **  In alobar holoprosencephaly, there is a single, small ventricular cerebrum without division into hemispheres, a single ventricle, and absent olfactory bulbs and optic tracts. Alobar holoprosencephaly, the most serious form in which the brain fails to separate, is usually associated with severe facial anomalies and occurs before six weeks of gestation.



** The "alobar" form of holoprosencephaly is shown here in which there a single large ventricle **

**[|Semilobar Holoprosencephaly]** In semilobar holoprosencephaly, the intermediate form of holoprosencephaly, there are rudimentary cerebral lobes with partially separated hemispheres. Olfactory bulbs and tracts are either absent or hypoplastic, and a rudimentary corpus callosum is present. Facial anomalies are milder and include a cleft lip and palate and hypotelorism. Semilobar holoprosencephaly occurs when the brain has partially divided.



Shows closed eyes, absent nose and abnormal mouth
 * Face of an infant with semilobar holoprosencephaly

Though two hemispheres exist, a midline fissure persists between them. The olfactory tracts, bulbs, thalamu, and corpora striata may of may not be complete. Facial anomalies are absent or mild, similar to the semilobar form. In some cases of lobar holoprosencephaly, the patient's brain may be nearly normal. Unlike semilobar holoprosencephaly, the falx is present, the interhemispheric fissure is fully formed and the thalami are not fused.
 * [|Lobar Holoprosencephaly] **



Lobar Holoprosencephaly Brain

 What is visible on all modalities is the lobar holoprosencephaly and can be best characterised by the MRI. It can also be identified on the antenatal ultrasound. If the ultrasound is performed. Gaillard, Frank. "Lobar holoprosencephaly." Radiopaedia.org. Dr Frank Gaillard (FRANZCR), 18 August 2010. Web. 9 Feb 2012. < http://radiopaedia.org/articles/lobar-holoprosencephaly >. [|Lobar Holoprosencephaly]  

