Which are the causes of Hydranencephaly?

TL;DR: Hydranencephaly is a rare condition characterized by the replacement of the cerebral hemispheres with fluid-filled sacs, typically caused by a destructive vascular event rather than a primary genetic disorder. While the exact cause often remains unknown, it is most frequently associated with the interruption of blood supply to the developing fetal brain during the second trimester of pregnancy.

What exactly causes Hydranencephaly?

In the vast majority of cases, Hydranencephaly is not a hereditary condition, but rather the result of a "vascular accident." Think of the developing fetal brain as a complex landscape that requires a steady, high-volume flow of water (blood) to thrive. If the main "pipes"—the internal carotid arteries—become blocked or damaged, the brain tissue that relies on that blood supply cannot survive and is essentially reabsorbed by the body, leaving behind cerebrospinal fluid in its place.

Are genetic factors involved in Hydranencephaly?

While Hydranencephaly is usually sporadic, meaning it occurs by chance in a pregnancy without a family history, researchers have identified rare instances where genetic factors may play a role. In some complex cases, specific genetic mutations (such as those in the SMARCE1 gene) have been linked to severe brain malformations that overlap with the clinical presentation of Hydranencephaly. However, geneticists emphasize that because the condition is most often a destructive event occurring in utero, the recurrence risk for future pregnancies is generally considered very low, often cited at less than 1%.

What environmental or external triggers are linked to Hydranencephaly?

Research indicates that several environmental and physiological factors can disrupt the blood flow necessary for brain development, leading to Hydranencephaly. These events often occur between the 12th and 24th weeks of gestation. Potential triggers include:

• Infections: Maternal infections such as toxoplasmosis, cytomegalovirus (CMV), or herpes simplex virus can cause severe inflammation that damages fetal blood vessels.


• Vascular Occlusions: Blood clots (thrombi) or emboli that travel to the fetal brain and block major arteries.


• Maternal Trauma: Severe abdominal trauma or significant placental complications that restrict blood flow to the fetus.


• Toxic Exposures: Certain chemical exposures during critical windows of neurological development.

Is the cause of Hydranencephaly fully understood?

Despite significant advancements in prenatal imaging and fetal medicine, the precise etiology of Hydranencephaly remains elusive in many cases. Because the destruction of the brain tissue often occurs months before birth, the original insult—whether it was a viral infection, a clotting event, or a vascular malformation—has often resolved by the time the child is born. This makes identifying a definitive "cause" in clinical practice very challenging. Our 37 community members at DiseaseMaps.org reflect this journey, as many families report receiving a diagnosis only after ultrasound or MRI evidence of the condition is already present.

How is current research improving our understanding?

Current clinical research is focused on distinguishing Hydranencephaly from other conditions like severe hydrocephalus or porencephaly. Scientists are using advanced neuroimaging and retrospective analysis of pregnancy history to better categorize the timing of the vascular event. Furthermore, improved genomic sequencing is helping clinicians rule out rare genetic syndromes, providing families with more accurate information regarding the likelihood of recurrence in future pregnancies.

Next steps

• Consult with a pediatric neurologist or a clinical geneticist to review prenatal records and discuss the possibility of genetic testing if indicated.


• Connect with the DiseaseMaps.org community to share experiences and find support from other families navigating Hydranencephaly.


• Work with a multidisciplinary care team, including palliative care specialists and therapists, to focus on the child’s comfort and quality of life.

Medical disclaimer: This information is for educational purposes only and does not constitute medical advice, diagnosis, or treatment; always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

References

• National Institute of Neurological Disorders and Stroke (NINDS) - Hydranencephaly Information Page.


• NIH Genetic and Rare Diseases (GARD) Information Center.


• Orphanet: Portal for rare diseases and orphan drugs (ORPHA:415).


• OMIM (Online Mendelian Inheritance in Man) - Entry #236600.