Understanding Hydranencephaly: Causes, Symptoms, and Palliative Care
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: What Is Hydranencephaly?
Hydranencephaly is a severe congenital brain abnormality in which the cerebral hemispheres fail to develop or are destroyed before birth and are replaced by sacs of cerebrospinal fluid. [1] [2] Unlike hydrocephalus, it involves a lack of brain structure rather than pressure on an existing brain. [1] [2] It occurs in roughly 1 in 10,000 to 1 in 5,000 pregnancies. [1] [2]
What the research says
A brain scan separates hydranencephaly from look-alike conditions. A clinical review describes the cerebral hemispheres as absent and replaced by a fluid-filled sac, with the midbrain usually spared, and names severe hydrocephalus, porencephalic cyst, and alobar holoprosencephaly as the main conditions to rule out; its case patient was still alive at 36 months (Pavone et al., Ital J Pediatr, 2014 [3]).
Hormone problems can accompany the condition. In a systematic review of nine hydranencephaly cases complicated by central diabetes insipidus, the most common features were macrocephaly, developmental delay, and seizures; 44% had a ventriculoperitoneal shunt, and 22% each had hypothyroidism, low cortisol, or panhypopituitarism (Omar and Khu, Childs Nerv Syst, 2019 [4]).
Key Takeaways
Feature | Details |
Medical Definition | |
Primary Cause | Uncertain; likely vascular, genetic, or linked to in-utero toxin exposure (e.g., smoking, cocaine). [2] |
Incidence Rate | |
Key Symptoms | Enlarged head, failure to thrive, muscle twitching, and respiratory issues. [1] |
Diagnosis | |
Treatment Goal | Palliative care, symptom management, and family support. [1] |
What is hydranencephaly, and how does it develop?
Hydranencephaly is a condition that affects the central nervous system during fetal development. While the baby's brainstem (which controls involuntary functions like heart rate and breathing) is usually present, the cerebrum, which is responsible for thought, movement, and sensory processing, is absent. [2]
Hydranencephaly vs. Related Conditions
It is often confused with other brain malformations, but the differences are critical for prognosis:
Hydrocephalus: Fluid buildup that creates pressure on the brain. The brain is present but potentially compressed. [2]
Holoprosencephaly: The forebrain fails to divide into two hemispheres. In hydranencephaly, the hemispheres are missing entirely.
What causes hydranencephaly, and what are the risk factors?
The exact cause of hydranencephaly remains unknown, though medical researchers believe it may involve a combination of genetic and environmental factors. [1] [2]
Genetic inheritance: Some evidence suggests the condition may be inherited, though the specific mechanisms are not yet understood. [1]
Vascular disruption: The most commonly proposed theory is that a blockage or injury to the carotid arteries during pregnancy prevents blood flow to the developing cerebrum. [2]
Infection: Certain infections during pregnancy have also been implicated as a possible cause. [2]
Toxin exposure: Cases have been linked to maternal exposure to toxins, including smoking, cocaine use, and certain antiseizure medications like sodium valproate. [1] [2]
What are the symptoms of hydranencephaly?
Infants born with hydranencephaly may appear healthy at birth because the brainstem allows for basic reflexes like sucking and swallowing. [2] However, symptoms typically emerge within weeks or months. [1] [2]
Macrocephaly: A larger-than-normal head due to fluid accumulation. [1] [2]
Failure to thrive: Difficulty growing and meeting developmental milestones. [1]
Muscle abnormalities: Increased or decreased muscle tone, twitching, or rigid limbs. [1]
Sensory deficits: Significant problems with vision and hearing. [1]
Respiratory distress: Chronic trouble breathing or respiratory failure. [1] [2]
How is hydranencephaly diagnosed?
Early diagnosis allows families to make informed decisions about care and management.
Prenatal ultrasound: The first line of detection, showing fluid-filled sacs instead of brain tissue. [1] [2]
Fetal MRI: Provides high-resolution images to confirm the extent of the malformation. [1]
Transillumination: A postnatal test where a light is shone through the infant's skull; in hydranencephaly, the light passes through the fluid-filled cavity easily. [1] [2]
Angiography: Used to examine blood vessels and check for vascular blockages. [1] [2]
How is hydranencephaly managed with palliative care?
Because there is no cure for hydranencephaly, the focus of medical intervention is palliative, aiming to improve comfort and manage complications. [1] [2]
Intervention | Purpose |
Shunt Surgery | |
Endoscopic Choroid Plexus Coagulation (ECPC) | |
Antiseizure Medication | |
Nutritional Support | Feeding tubes or specialized support for failure to thrive. |
Respiratory Support | |
Physical Therapy |
What is the outlook and prognosis for hydranencephaly?
The prognosis for hydranencephaly is unfortunately poor. Most affected infants die before birth or within the first year of life. In rare cases, with intensive medical and supportive care, children have survived for several years, though they face profound developmental and physical challenges. [1] [2]
Conclusion
A diagnosis of hydranencephaly is a devastating event for any family. While the medical outlook is severe, healthcare providers focus on providing compassionate care for the infant and comprehensive counseling for the parents. Understanding the condition is the first step toward navigating the difficult journey of palliative care and finding support within the medical community.
Frequently Asked Questions
Is hydranencephaly the same as "water on the brain"?
"Water on the brain" usually refers to hydrocephalus. While both involve fluid, hydranencephaly means the brain tissue itself never formed or was destroyed, whereas in hydrocephalus, the brain is present but under pressure. [1] [2]
Can a baby with hydranencephaly survive?
Most babies do not survive past their first birthday. [2] Rarely, a child can survive for years with intensive supportive care, and isolated reports describe survival into adulthood. [1] [2]
Does the baby feel pain?
Because the brainstem is intact, the baby may have basic sensory responses. Palliative care focuses heavily on ensuring the infant remains comfortable and pain-free.
Can hydranencephaly be prevented?
Since the exact cause is unknown, there is no guaranteed prevention. Avoiding toxins like tobacco, cocaine, and certain medications during pregnancy is highly recommended. [1]
Is it a genetic condition?
Scientists believe there may be a genetic component, but it has not been fully mapped. Genetic testing is often recommended for families after a diagnosis.
Can a baby with hydranencephaly see or hear?
Vision is often severely affected because the parts of the brain that process sight are missing. [2] Hearing is more often preserved but can also be affected. [2]
Why do some babies look normal at birth?
The brainstem controls basic survival reflexes like breathing and heart rate, which can make the baby appear healthy until the lack of higher brain function becomes evident.
What is transillumination?
Transillumination is a simple test where a bright light is held against the baby's head in a dark room. If the head is filled with fluid instead of brain tissue, the light glows through the skull. [1] [2]
What is a shunt?
A shunt is a small tube surgically placed to drain excess cerebrospinal fluid from the skull to another part of the body, like the abdomen, to be reabsorbed.
Does a shunt cure hydranencephaly?
No. It only manages the symptom of fluid buildup and head enlargement; it cannot regrow missing brain tissue.
Can hydranencephaly be detected in the first trimester?
Hydranencephaly is usually detected during the second-trimester anatomy scan (around 20 to 23 weeks), though earlier detection is sometimes possible with high-resolution ultrasound.
What is the difference between hydranencephaly and anencephaly?
In anencephaly, the skull itself does not close, and the brain is exposed. In hydranencephaly, the skull is intact and filled with fluid. [2]
Can a mother have a healthy baby after one with hydranencephaly?
In many cases, yes, but genetic counseling is advised to understand any potential risks.
What are the most common complications?
Seizures, respiratory infections, and severe feeding difficulties are the most frequent challenges.
Is there any research into a cure?
Currently, there is no way to regrow cerebral hemispheres. Research focuses on early detection and improving palliative care.
How rare is this condition?
Hydranencephaly is estimated to occur in 1 in 10,000 to 1 in 5,000 pregnancies. [1] [2] Population studies have reported about 1.4 to 2.8 cases per 100,000 live births in Texas and 2.1 per 100,000 in Japan. [2]
Does hydranencephaly affect the heart?
Usually, the heart is structurally normal (though heart valve disease is a reported association), as its function is controlled by the brainstem, which is typically preserved. [2]
What is failure to thrive?
Failure to thrive is a medical term for an infant who does not gain weight or grow at the expected rate for their age.
Can physical therapy help?
Yes. It can help manage muscle stiffness (spasticity) and make the infant easier to hold and care for.
What is "therapeutic abortion"?
Therapeutic abortion is a medical procedure to end a pregnancy before birth. Some families consider it when a severe, life-limiting condition like hydranencephaly is confirmed during pregnancy. [2] It is a personal decision made together with the care team.
Are there support groups for parents?
Yes. Rare disease organizations such as the National Organization for Rare Disorders (NORD) provide resources and connect families with others facing similar conditions.
Can hydranencephaly cause seizures?
Yes. Abnormal electrical activity in the remaining brain structures can lead to seizures, which are managed with medication. [2]
What is the cerebrum?
The cerebrum is the largest part of the brain, divided into two hemispheres, responsible for voluntary movement, speech, and thought.
What is the brainstem?
The lower part of the brain that connects to the spinal cord; it controls basic life functions like breathing and swallowing.
Can toxins cause this?
Exposure to certain drugs or environmental toxins during early pregnancy has been linked to the condition. [1] [2]
Is the condition painful for the mother?
The condition itself does not cause the mother pain during pregnancy, though the emotional toll is significant.
How is an MRI different from an ultrasound?
An MRI uses magnets to create much more detailed images of the brain's internal structures than an ultrasound can provide.
What is cerebrospinal fluid (CSF)?
A clear fluid that normally surrounds and cushions the brain and spinal cord.
Can an infection cause hydranencephaly?
Some researchers believe certain infections during pregnancy, such as toxoplasmosis or viral infections, could damage the developing brain and lead to the condition. [2]
Why does the head get large?
Without brain tissue to occupy the space, the fluid can accumulate and put outward pressure on the growing skull.
Is there a specific gene for hydranencephaly?
No single gene explains every case. Changes in genes such as COL4A1, LAMB1, and FLVCR2 (Fowler syndrome) have been reported in some affected children, and research is ongoing. [2]
Can a baby with hydranencephaly cry?
Yes. Crying is a reflex controlled by the brainstem, so infants can cry, though it may sound different.
Does the baby have reflexes?
Yes. Basic reflexes like the "startle" reflex or grasping are often present at birth.
What is a tracheostomy?
A surgical opening in the neck to the windpipe to help a baby breathe if their airway is blocked or their lungs are weak.
Can hydranencephaly be caused by a stroke in the womb?
Yes. A fetal stroke that cuts off blood to the cerebrum is one of the leading theories for the cause. [2]
What is macrocephaly?
The medical term for an abnormally large head.
Can a baby with hydranencephaly swallow?
Most can swallow initially, but this ability often declines as the condition progresses.
How do doctors confirm the diagnosis after birth?
Is hydranencephaly more common in boys or girls?
Hydranencephaly appears to affect both sexes equally. [2]
What is "palliative care"?
Medical care focused on providing relief from symptoms and stress, rather than trying to cure the disease.
Can hydranencephaly be misdiagnosed?
In early pregnancy, it can sometimes be mistaken for severe hydrocephalus, [3] which is why follow-up MRIs are important.
What is ECPC surgery?
Endoscopic choroid plexus coagulation is a procedure to reduce the production of cerebrospinal fluid. [1] [2]
Does hydranencephaly affect the spinal cord?
Usually, the spinal cord is formed correctly, but the signals from the brain to the body are missing.
Can hydranencephaly cause rigid limbs?
Yes. The lack of brain control leads to increased muscle tone, making the arms and legs stiff.
What is the carotid artery?
The main artery in the neck that supplies blood to the brain; blockages here are a suspected cause of hydranencephaly. [2]
Is there a test for hydranencephaly before pregnancy?
No, because the specific genetic markers are not yet known.
How do families cope?
Through specialized counseling, hospice services, and support from rare disease communities.
Can hydranencephaly cause twitching?
Yes. Involuntary muscle twitching (myoclonus) is common in affected infants.
What is the "forebrain"?
The anterior part of the brain, including the cerebral hemispheres, which is missing in hydranencephaly.
Where can I find clinical trials?
Information on rare disease research can be found through the NIH and the National Organization for Rare Disorders (NORD).
Medical disclaimer: The information provided in this article is for educational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional for diagnosis and treatment of any health condition.
References
Cleveland Clinic. Hydranencephaly: Causes, Symptoms, Diagnosis & Treatment. Cleveland Clinic. Last updated April 18, 2022. https://my.clevelandclinic.org/health/diseases/22799-hydranencephaly
Sandoval JI, De Jesus O. Hydranencephaly. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated August 23, 2023. PMID: 32644417. https://www.ncbi.nlm.nih.gov/books/NBK558991/
Pavone P, Praticò AD, Vitaliti G, et al. Hydranencephaly: cerebral spinal fluid instead of cerebral mantles. Ital J Pediatr. 2014;40:79. PMID 25326191. https://doi.org/10.1186/s13052-014-0079-1
Omar AT, Khu KJO. Hydranencephaly complicated by central diabetes insipidus: report of two cases and systematic review of literature. Childs Nerv Syst. 2019;35(7):1165-1171. PMID 30929071. https://doi.org/10.1007/s00381-019-04137-9
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