Hydranencephaly

What is Hydranencephaly?

Hydranencephaly is a rare birth defect that happens during the second trimester of pregnancy, where the baby’s brain does not properly form. Instead, the brain’s two hemispheres, commonly referred to as the right and left sides of the brain, are replaced with a sac filled with a fluid called cerebrospinal fluid (CSF). Sometimes, small amounts of brain tissue and cells might be present along the line dividing the right and left sides of the brain.

The areas of the brain that house and protect it, like the skull and the outer layers of brain tissue (meninges), remain intact. This condition often occurs due to some sort of disruption to the blood supply to the brain early in development. However, other parts of the brain, including the brainstem, are usually present.

Babies with this condition may appear normal at birth, displaying natural instinctive responses (primitive reflexes). Over time, they might develop a larger-than-normal head due to increased pressure from the CSF. Rarely, they might have a smaller head. It is possible to diagnose this condition before birth with an ultrasound.

While there is no definitive cure, the treatment primarily involves supportive measures to manage the child’s symptoms. However, if the child develops a condition called hydrocephalus, where there’s excess fluid in the brain, a procedure may be considered to drain the fluid.

What Causes Hydranencephaly?

The exact cause of hydranencephaly, a severe brain condition, isn’t always known, but researchers have proposed several different reasons.

For example, a common assumption is that it’s caused by an “ischemic stroke,” which occurs when the blood supply to the brain is restricted or reduced. This type of stroke could be caused by the blockage of important blood vessels in the brain between the 8th and 12th weeks of a baby’s development. This blockage results in the lack of development of certain parts of the brain which should have been supplied by these blood vessels.

Another reason could be an infection transferred to the baby in the womb. These infections include conditions like toxoplasmosis or various viral infections, such as enteroviruses or the herpes virus. These infections may cause inflammation and damage to the baby’s blood vessels, leading to hydranencephaly.

Another cause could be lack of oxygen or “hypoxia” to the baby’s brain, particularly if the mother has been exposed to high levels of carbon monoxide.

Hydranencephaly can also be due to certain genetic factors, such as mutations in the COL4A1 or LAMB1 genes, or issues with the PI3K-Akt3-mTOR pathway, which is a group of genes that influence the growth and development of cells.

Extreme cases of a condition called “leukomalacia,” where multiple cysts form and eventually merge within the baby’s skull, could also lead to hydranencephaly.

Exposure to certain harmful substances such as cocaine, tobacco smoke, estrogens, or a medication called sodium valproate, during pregnancy may also contribute to the condition.

In some cases, it has been observed during a twin pregnancy. If one twin dies in the womb, material from the deceased twin can lead to the development of hydranencephaly.

Lastly, some rare syndromes, such as Fowler syndrome, deficiency of a blood-clotting component known as “factor XIII,” or sudden bleeding in the brain, may also cause the condition.

Risk Factors and Frequency for Hydranencephaly

Hydranencephaly is a rare condition that is not often encountered these days, generally due to therapeutic abortions. This condition varies in occurrence, but tends to occur in between 0.01% to 0.02% of pregnancies. There’s no difference in incidence between boys and girls.

A study conducted in Texas recorded that Hydranencephaly occurs in between 1.4 to 2.8 out of every 100,000 live births. A similar study in Japan found the incidence to be 2.1 out of every 100,000 live births. Yet another study found that 1% of patients diagnosed with hydrocephalus also had hydranencephaly.

There’s no established pattern of how the condition is passed from mother to baby. However, there are a few cases where the condition has been linked to autosomal recessive inheritance. Autosomal recessive inheritance is relevant in patients with a rare genetic syndrome and/or related conditions.

• Fowler syndrome: This condition is also known as proliferative vasculopathy and hydranencephaly-hydrocephaly syndrome. It has an autosomal recessive inheritance resulting from a mutation in the FLVCR2 gene in chromosome 14q24.3. This leads to proliferative glomeruloid vasculopathy which damages areas of the brain and spinal cord.
• Trisomy 13
• Renal aplastic dysplasia
• Polyhydramnios
• Arthrogryposis

Poly-valvular heart disease

Signs and Symptoms of Hydranencephaly

Hydranencephaly is a condition that severely impacts a baby’s brain. Although most babies with this condition sadly don’t survive past birth, some do. A mother carrying a baby with hydranencephaly might not notice any unusual signs during pregnancy – she would feel her baby moving as expected and her belly would grow normally.

Babies born with hydranencephaly may seem completely healthy when they’re first born, with the usual reflexes like sucking, swallowing, crying, and moving their arms and legs. However, these babies could have some deformities in their skull and upper face if the pressure in their skull was too high. Babies who are more severely affected by the condition may have noticeable symptoms like seizures, muscle twitching, and trouble breathing.

Though they may seem normal at birth, babies with hydranencephaly start showing more concerning signs a few weeks later, like being overly irritable, having changes to their muscle tone, an increase in the size of their head, and their soft spot on their head (anterior fontanelles) bulging. These signs tend to become more noticeable after several more weeks. Further down the line, these babies could develop conditions like seizures and hydrocephalus, which is a buildup of fluid in the brain.

Despite the many challenges these babies face, their hearing is usually unaffected. In some rare cases though, they may have some hearing loss. Vision problems are more common – even though their eyes may be normal, they often have problems with their vision because they’re missing the part of their brain that processes what we see (visual cortex).

Other symptoms that may develop as the baby grows include:

• Not growing as expected
• Unusual stiffness or floppiness in both legs (spastic diplegia)
• Delay in cognitive development
• Eyes that are further apart than usual (hypertelorism)
• Underdeveloped optic nerves (optic nerve hypoplasia)
• Widespread damage to the retina (diffuse chorioretinal atrophy)
• Changes to the pigments in the eyes (pigment clumping)
• Abnormal retina (dysplastic retina)
• Blindness

Testing for Hydranencephaly

Most patients with hydranencephaly are diagnosed during pregnancy with multiple techniques. Initially, a regular ultrasound might be used to suspect hydranencephaly. This is a fairly simple and non-invasive procedure, just like the one used to monitor the baby’s development during pregnancy. However, to be sure about the diagnosis, a more advanced ultrasound, known as a level 2 ultrasound, is typically used.

Another technique that can help diagnose hydranencephaly is magnetic resonance imaging (MRI), an advanced imaging technique that provides detailed images of the brain. Despite being highly accurate, the use of MRI during pregnancy is less common.

If hydranencephaly is not diagnosed during pregnancy, the diagnosis may be delayed for several weeks or months after birth, as newborns may initially seem and function like healthy babies. The most reliable form of diagnosis is a brain MRI, as it can accurately differentiate hydranencephaly from conditions with similar symptoms, such as severe hydrocephalus and holoprosencephaly.

More specific details about what certain tests show when diagnosing hydranencephaly include:

– Ultrasounds performed between the 21st to 23rd weeks of pregnancy can show the absence of cerebral hemispheres, which are replaced with a material that produces a consistent echo. Presence of structures like the thalamus, brainstem, and cerebellum are retained. The same technique can also be used in the postbirth period to confirm diagnosis.

– Brain MRI (the most reliable method) shows the absence of a part of the brain called the “supratentorial brain parenchyma,” replaced with a fluid called cerebrospinal fluid (CSF). Brain structures like the cerebellum and brainstem, however, remain visible.

– A Head CT scan yields results similar to an MRI, although an MRI is generally more precise.

– Transillumination involves placing a flashlight at the base of the head. If hydranencephaly is present, the light will be visible throughout the scalp/head as it gets reflected and dispersed, indicating that the head is filled with CSF fluid. This technique can be used if advanced imaging tools are not available and hydranencephaly is highly suspected from a physical examination.

Additional tests include:

– An electroencephalogram, which is used to monitor the electrical activity of the brain.
– A brainstem auditory evoked response test, which tests the functioning of the brainstem using sounds.
– Auditory and ocular tests, which confirm the loss of cortical activity (upper-level brain functions) with the preservation of brainstem functions. In some cases, a total absence of visual evoked potential may be present.
– Digital subtraction angiography or brain magnetic resonance angiography, both used in some cases to visualize the blood vessels in the brain.

Treatment Options for Hydranencephaly

Hydranencephaly is a serious condition where a baby’s brain does not fully develop. Unfortunately, this condition often results in the baby not surviving pregnancy, or passing away within the first year of life. For this reason, if hydranencephaly is diagnosed during pregnancy, doctors may discuss the option of ending the pregnancy to prevent further physical and emotional strain on the mother. If the condition is diagnosed after birth, treatments focus on managing symptoms and related health problems as best as possible.

Some of the treatments may include:

* Treating hydrocephalus: This is a common condition in babies with hydranencephaly where fluid builds up in the brain, increasing pressure. Doctors might place a special tube called a shunt, either in the stomach (ventriculoperitoneal) or heart (ventriculoatrial) to help drain excess fluid and reduce pressure.
* Using anti-seizure medication: Seizures are common in babies with hydranencephaly, and medication can help manage this.
* A tracheostomy or mechanical ventilation: These techniques aid in breathing for babies with respiratory failures.
* Physical therapy: This therapy helps improve physical abilities as most children with this condition have poor movement skills.
* Nutritional intervention: Proper nutrition can help promote overall health.

Although the use of shunts is common, they do have drawbacks. They frequently need to be replaced due to malfunctions, can get infected easily, especially in children, and can be quite expensive. Due to these issues, other procedures have been proposed as alternatives to shunts. One such alternative is Endoscopic Choroid Plexus Coagulation (ECPC), a procedure that has shown success in treating rapidly enlarging heads due to hydrocephalus in children with hydranencephaly.

Studies have revealed that children treated with ECPC have shown better outcomes compared to those treated with shunts. With a success rate of 50-80%, some believe ECPC should be the standard treatment for hydranencephaly-related hydrocephalus. However, due to the specific physical characteristics of hydranencephaly-affected children, ECPC is limited to only these children and not applicable for other forms of hydrocephalus. A possible complication of ECPC is the collapse of a part of the brain called the arachnoid space, which can prevent doctors from being able to coagulate, or control bleeding in, the choroid plexuses, parts of the brain responsible for the production of the fluid.

What else can Hydranencephaly be?

Hydranencephaly is a medical condition that has certain unique features seen on images and tests. These help doctors tell it apart from other similar conditions like severe or extreme hydrocephalus, holoprosencephaly (particularly the type called alobar holoprosencephaly), severe open schizencephaly, and anencephaly.

Here’s how these other conditions generally manifest:

• Severe-Extreme Hydrocephalus: This can happen due to various reasons. The outer layer of the brain is intact. There is a presence of a third cavity or ventricle in the brain, abnormal head size at birth, full and bulging soft spots on the skull of a baby, and a normal blood vessel study. There are notable improvements in clinical and X-ray findings after a procedure called shunt placement, which can lead to a better outcome.
• Alobar Holoprosencephaly: This is the most extreme form of a condition called holoprosencephaly. This arises due to a birth defect in the brain resulting from missing or incomplete division of the front part of the brain. Patients with this condition have a partial fusion of the inner parts of the brain, absence of a certain membrane in the brain, facial irregularities, and a small head circumference.
• Severe Open Schizencephaly: This situation happens as a result of abnormal development of neurons, creating gaps surrounded by abnormal brain matter. The outer layer of the brain is thin but preserved, a feature that distinguishes it from Hydranencephaly.
• Anencephaly: This condition is caused by an obstruction to the neural tube. The classic sign will be a defect in the skull and the parenchyma, or functional part of the brain.

What to expect with Hydranencephaly

Hydranencephaly is a condition that sadly doesn’t have any known cure. Patients with this diagnosis generally receive treatment meant to alleviate symptoms and provide comfort and support. Most patients with hydranencephaly tragically do not survive before birth and if they do, their life expectancy is short – often, they do not live beyond their first year. There are, however, exceptions where patients have survived up to 32 years of age.

If a patient with hydranencephaly does survive, it’s largely due to the well-functioning parts of their brain – particularly the brainstem. The brainstem is an incredibly crucial area of the brain that controls vital functions like heart and lung function and body temperature regulation. In some rare cases, patients live past their first year, even without seeing improvements from treatments like shunt placement which helps to drain excess fluid from the brain. The abilities of these patients remain limited throughout their life – they may have only minimal use of their hands and limited communication skills, though some can use a few words.

Possible Complications When Diagnosed with Hydranencephaly

Hydranencephaly often comes with various complications, which typically result in the patient’s death if they survive the initial condition.

• Slow development
• Seizures that don’t respond to medication
• Stiff muscles, mainly in the legs
• Significant lack of growth
• Infections, particularly in the respiratory system
• Cerebral palsy
• Moodiness or grouchiness
• Difficulty breathing
• Long-term dependence on a ventilator to breathe
• Acid reflux
• Emotional, mental, and financial stress for the parents

Preventing Hydranencephaly

Having a child with a condition called hydranencephaly can have a deep emotional impact. There’s no way to fully prevent this condition except in cases where it’s known to be caused by exposure to certain harmful substances like cocaine, tobacco, and a drug called sodium valproate. It’s important to avoid these substances. Parents should have access to guidance and support, particularly to help them understand what their child’s diagnosis means and what to expect in the future. It may also be helpful for parents to have meetings with a psychologist or psychiatrist to support their emotional well-being.