When we imagine a brain, whether human or not, the image that comes to our mind is usually composed of an organ whose outer layer is full of folds, between which we can see cracks that allow us to see the presence of two halves or hemispheres. cerebral.
This separation is something that most of us humans have, forming during our fetal development. But not all: there are boys and girls whose brains are not divided or the hemispheres are fused: we are talking children with holoprosencephaly.
Holoprosencephaly: what is it?
It is called holoprosencephaly a a type of malformation throughout fetal development in which there is no division between the different structures of the forebrain: there is fusion between the cerebral hemispheres, as well as between certain subcortical structures and the cerebral ventricles. This fusion or rather the non-separation can occur at the total or partial level (the hemispheres being fused completely or only in certain parts).
usually the division of the brain into different lobes and hemispheres it occurs around the fourth week of gestation. In holoprosencephaly, this division does not occur or it fails to complete itself, which has serious repercussions before and after birth. This condition is usually accompanied by the presence of head and facial malformations, with alterations such as hypertelorism or eyes together, cyclopia or one eye, alterations in the nose, cleft lip, palate, or hydrocephalus. It is also common for food and thermal maintenance problems, heart and respiratory problems and seizures. It is also associated with varying degrees of intellectual disability, in cases mild enough to support life.
In general, holoprosencephaly has a very poor prognosis, especially in the alobar type: boys and girls they usually die before birth or before the age of six months. In other types, it is possible to survive for 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 they usually suffer from cognitive deficits to a greater or lesser extent.
Some of its main variations
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 should be borne in mind 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, they can observe the presence of almost perfectly separated lobesAlthough this separation did not take place in the frontal lobes and they generally do not have a septum pellucidum.
2. Semi-barbaric holoprosencephaly
In this variant of holoprosencephaly, there is a division between the hemispheres of one part of the brain, but the frontal and parietal lobes are fused. Interhemispheric fissure is observed only in the temporal and occipital areas.
It is common for hypotelorism to occur, that is, the child’s eyes are much less separated than usual, small, or directly non-existent. A cleft lip or palate may also be observed, as well as an absence or malformations in the nasal area.
3. Alobar holoprosencephaly
It is the most severe form of holoprosencephaly, in which the hemispheres do not separate to any degree, being completely fused. It is common to have only one ventricle and / or a single thalamus.
Many of these children are no longer born with one eye, and in this case, the existence of a Cyclops is considered. In fact, probably the emergence of the mythical figure of the Cyclops was based on the observation of a case of this type of holoprosencephaly. The nose usually has deformities and may have a proboscis-shaped formation or even no nasal orifice (which can cause the child to suffocate) or just 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 the genus and splenium), although usually at the level of subcortical structures, there is no overlap or fusion. Also called synthelencephaly.
Although technically it is no longer holoprosencephaly, sometimes a variant of this disorder is also considered aprosencephaly, in which the forebrain does not form directly.
Causes of this problem
Holoprosencephaly is a disorder that occurs during the developing fetus, with a variety of possible factors that can lead to its occurrence. It has been observed that a large number of cases exist in which has genetic alterations in many genes (One in four have alterations in the ZIC2, SIC3, SHH or TGIF genes), as well as different syndromes and chromosomal disorders (Patau syndrome or Edwards syndrome among them).
A link has also been observed with environmental factors, such as uncontrolled diabetes in the mother or alcohol and other drug abuse, as well as the use of certain medications.
This condition, usually of a genetic type, has no cure. The treatments to be applied will generally be of a palliative nature., Aiming to maintain their vital signs, correct difficulties and improve their well-being and quality.
In mild cases that allow survival, the use of occupational therapy and cognitive stimulation is recommended. The need for 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 parents and the environment (who will need psychoeducation and counseling, as well as possibly psychological intervention).
- Monteagudo, A. and Timor-Tritsch, IE, (2012). Prenatal diagnosis of CNS abnormalities 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 and Sulik, KK (1992). Perspectives on holoprosencephaly: part II. Central nervous system, craniofacial anatomy, syndrome commentary, diagnostic approach and experimental studies. J. Craniofac. Broom. Dev. Biol., 12: 196.