This type of congenital malformation appears when parts of the brain are not well divided.
When we imagine a brain, be it human or not, the image that comes to mind is generally composed of an organ whose outer layer is full of folds, among which we can see some cracks that allow us to appreciate the presence of two halves or brain hemispheres.
This separation is something that most human beings have, forming during our fetal development. But not all: there are boys and girls whose brains are not divided or whose hemispheres are fused: we are talking about children with holoprosencephaly.
Holoprosencephaly: what is it?
Holoprosencephaly is a type of malformation throughout fetal development in which there is no division between the different structures of the forebrain: there is a fusion between the cerebral hemispheres, as well as between some subcortical structures and the cerebral ventricles. This fusion or rather non-separation can occur at a complete or partial level (the hemispheres being completely fused or only in some parts).
Generally, the division of the brain into different lobes and hemispheres occurs around the fourth week of gestation. In holoprosencephaly, this division does not occur or it cannot be completed, which has severe repercussions both before and after birth. This condition usually comes together with the presence of cranial and facial malformations, with alterations such as hypertelorism or eyes together, cyclopia or one eye, alterations of the nose, cleft lip, cleft palate or hydrocephalus. Likewise, it is frequent that problems appear in feeding and in the maintenance of heat, cardiac and respiratory disorders and seizures. It is also associated with different degrees of intellectual disability, in cases mild enough to allow life.
In general, holoprosencephaly has a very poor prognosis, especially in the alobar type: boys and girls usually die either before birth or before reaching six months of life. In the other types, survival is possible up to one or two years of life. Depending on whether there are other complications and the severity of the disorder. In milder cases, survival is possible, although in general they will suffer from cognitive deficits to a greater or lesser extent.
Some of its main main variants
Holoprosencephaly is a medical condition that can present in different ways, depending on the possible degree of separation of the cerebral hemispheres. The first three variants stand out, the most common, although it must be taken into account that there are others. These types of holoprosencephaly are as follows.
1. Lobar holoprosencephaly
Lobar holoprosencephaly is the mildest form of this type of disorder. In this case, the presence of almost perfectly separated lobes can be observed , although this separation has not been carried out in the frontal lobes and they do not usually have septum pellucidum.
2. Semilobar holoprosencephaly
In this variant of holoprosencephaly there is a division between the hemispheres in part of the brain, but the frontal and parietal lobes are fused. The interhemispheric fissure is only seen in the temporal and occipital.
Hypotelorism is frequent, that is, the baby’s eyes are much less separated than would be usual, that they are small or that they do not exist directly. Cleft lip or palate can also be observed, as well as absence or malformations at the nasal level.
3. Alobar holoprosencephaly
It is the most serious form of holoprosencephaly, in which the hemispheres do not separate to any degree, being completely fused. There is often a single ventricle and / or a single thalamus.
Many of these children are also born with only one eye, in which case cyclopia is considered. In fact, probably the emergence of the mythical figure of the Cyclops was based on the observation of some case of this type of holoprosencephaly. The nose usually has malformations, being able to have a proboscis-shaped formation or even no nostril (something that can cause suffocation of the child) or only one of them.
4. Interhemispheric holoprosencephaly
This variant, less common than the previous three, occurs when the division of the brain does not occur in the middle part: the posterior parts of the frontal and parietal lobes. There is no corpus callosum (with the possible exception of genu and splenium), although generally at the level of subcortical structures there is no overlap or fusion. Also called synthelencephaly.
Although technically it would no longer be holoprosencephaly, aprosencephaly is also sometimes considered a variant of this disorder, in which the forebrain does not directly form.
Causes of this problem
Holoprosencephaly is an alteration that occurs during fetal development, with a wide variety of possible factors that can lead to its appearance. The existence of a large number of cases in which there are genetic alterations in numerous genes (one in four has alterations in the ZIC2, SIC3, SHH or TGIF genes), as well as different syndromes and chromosomal disorders (the syndrome of Patau or Edwards syndrome among them).
An association with environmental factors has also been observed, such as uncontrolled diabetes in the mother or the abuse of alcohol and other drugs, as well as the consumption of some medications.
This condition, generally of a genetic type, does not have a curative treatment. The treatments to be applied will generally be of a palliative nature, aimed at maintaining your vital signs, correcting difficulties and improving your well-being and quality.
In mild cases that achieve survival, the use of occupational therapy and cognitive stimulation is recommended. The need to apply a multidisciplinary treatment involving professionals from different disciplines, both medicine and occupational therapy, clinical psychology, physiotherapy and speech therapy, should be assessed. And this without neglecting the treatment of the parents and environment (which will require psychoeducation and counseling, as well as possibly a psychological intervention).
- Monteagudo, A. & Timor-Tritsch, IE, (2012). Prenatal diagnosis of CNS anomalies other than neural tube defects and ventriculomegaly (online). Available at: http://cursoenarm.net/UPTODATE/contents/mobipreview.htm?9/28/9665/abstract/4-12
- Cohen, MM & Sulik, KK (1992). Perspectives on holoprosencephaly: Part II. Central nervous system, craniofacial anatomy, syndrome commentary, diagnostic approach, and experimental studies. J. Craniofac. Genet. Dev. Biol., 12: 196.