Hydranencephaly: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 23, 2026.
What kind of doctor treats Hydranencephaly?
A pediatric neurologist (a doctor who treats brain and nerve conditions in children) usually leads care after birth. When it is found during pregnancy, a maternal-fetal medicine doctor (a specialist in high-risk pregnancies) is often involved. A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What is hydranencephaly?
Hydranencephaly is a rare condition that is present from birth. The cerebral hemispheres, the two large halves of the brain, are destroyed and replaced with a sac filled with cerebrospinal fluid (CSF). The skull and the layers that cover the brain are intact. The brainstem and other deep parts of the brain are present.
The National Institute of Neurological Disorders and Stroke calls it an extreme form of porencephaly. Porencephaly is an extremely rare disorder in which a cyst or cavity filled with cerebrospinal fluid develops in the brain. It affects males and females equally.
Symptoms
A baby with hydranencephaly can look completely normal at birth. Reflexes such as sucking, swallowing, and crying may be normal at first. Signs can show up a few weeks later and become stronger over time.
- Being very irritable and feeding poorly.
- Muscle tone that is too high or too low.
- A growing head. Some babies have an enlarged head at birth.
- Hydrocephalus, a buildup of fluid in the brain that raises pressure inside the skull.
- Seizures, which can start months after birth.
- Vision problems. Most children have normal eyes, but the part of the brain that handles sight is missing.
- Slow growth.
- Delays in thinking skills.
- Poor control of body temperature.
Hearing is usually preserved. Babies with more severe disease can have seizures or sudden muscle jerks from birth.
Causes and who gets it
The cause is usually unknown. The most commonly proposed cause is a blockage of the large arteries that bring blood to the brain, called the internal carotid arteries. This blockage is thought to happen mostly between the 8th and 12th weeks of pregnancy. Infections in the womb, such as toxoplasmosis and cytomegalovirus, may be responsible. Low oxygen for the baby, especially from severe carbon monoxide exposure of the mother, is another possible cause. Changes in genes such as COL4A1 and LAMB1, or rare syndromes such as Fowler syndrome, can play a part. Exposure of the mother to toxins, such as cocaine or smoking, may cause hydranencephaly.
There is no established pattern of passing it from mother to baby, but a few cases have been linked to autosomal recessive inheritance. In this pattern, a child must get the same changed gene from each parent.
How doctors diagnose it
Most cases are found during pregnancy. A regular ultrasound can give a first answer. A more detailed ultrasound (level 2 or higher) is needed to confirm it. If it is not found before birth, the diagnosis can be delayed by weeks to months because babies may seem to function normally at first.
A brain MRI is the gold standard, which means the best test. It can tell hydranencephaly apart from similar conditions, such as severe hydrocephalus. A head computed tomographic (CT) scan shows very similar findings, but MRI is more accurate.
Treatment
Treatment is supportive. This means doctors treat symptoms and complications.
- A shunt, a thin tube that drains extra fluid from the brain, to lower pressure inside the skull.
- Anti-seizure medicines for seizures.
- Breathing support, such as a tracheostomy or a breathing machine, if breathing fails.
- Physical and occupational therapy.
- Nutrition support.
Shunts often need to be redone because they stop working, and infections are common. The outlook is poor. Most babies die before birth, and those who survive usually die within the first year of life. There are reports of people who survived as long as 32 years. If it is found during pregnancy, the care team talks through the options with the whole family.
When to see a doctor
A baby who looks healthy can still have this condition, so signs that show up later need a doctor's visit. These signs include irritability, poor feeding, muscle changes, a growing head, and seizures. Call 911 or go to the emergency room if a child has trouble or abnormal breathing, bluish or grey skin, cannot be woken, has a seizure that lasts more than 5 minutes, or has a fever with a stiff neck or unusual sleepiness.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor usually charges more and often works alongside insurance. Such a doctor can help with early evaluation and referrals to specialists such as a pediatric neurologist. They can also offer steady follow-up and help the family keep track of many specialist visits.
Common questions
Is hydranencephaly the same as hydrocephalus?
No, they are different conditions. Hydrocephalus is a buildup of fluid in the brain. In hydranencephaly, the cerebral hemispheres are destroyed and replaced by a fluid-filled sac. Hydrocephalus is common in people with hydranencephaly.
Can hydranencephaly be found before birth?
Yes, most cases are found during pregnancy. A detailed ultrasound is used to confirm it.
Can a baby with hydranencephaly look healthy at birth?
Yes, a baby can look completely normal at birth. Signs such as irritability and muscle changes can start a few weeks later.
Does hydranencephaly affect vision and hearing?
Most children have vision problems. Hearing is usually preserved. The part of the brain that handles sight is missing, even though the eyes are normal.
Sources
- StatPearls - Hydranencephaly
- National Organization for Rare Disorders - Hydranencephaly
- National Institute of Neurological Disorders and Stroke - Birth Disorders of the Brain and Spinal Cord
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
