What is caudal regression syndrome?

Caudal regression syndrome is a rare congenital disorder. It’s estimated that 1 to 2.5 in every 100,000 newborns is born with this condition.

It occurs when the lower spine doesn’t fully form before birth. The lower spine is a part of the “caudal” half. This area contains the parts of the spine and bones that form the hips, legs, tailbone, and several important organs in the lower body.

This condition is sometimes called sacral agenesis because the sacrum, a triangle-shaped bone that connects the backbone to the pelvis, only partially develops or doesn’t develop at all.

Keep reading to learn more about why this may happen, what treatment options are available, and what to expect in the short and long terms.

The exact cause of caudal regression syndrome isn’t always clear. Some research suggests that having diabetes or not getting enough folic acid in your diet during pregnancy can increase the chance of your child’s caudal region not fully developing. The incidence of this syndrome is much higher in infants born to mothers with diabetes, particularly if the diabetes is poorly controlled. But since it also occurs in infants whose mothers don’t have diabetes, there may be other genetic and environmental factors involved.

The first signs of caudal regression syndrome usually appear between your fourth and seventh weeks of pregnancy. In most cases, the condition can be diagnosed by the end of your first trimester.

If you have diabetes — or if you’ve developed gestational diabetes during pregnancy — your doctor may perform an ultrasound specifically to look for signs of this condition. Otherwise, routine ultrasound tests will look for any fetal abnormalities.

If your doctor suspects caudal regression syndrome, they may perform an MRI after 22 weeks of pregnancy. This will allow them to see even more detailed images of your child’s lower body. An MRI may also be used after your child is born to confirm the diagnosis.

After a diagnosis is made, your doctor will use ultrasound or MRI testing to determine how severe the condition is.

They will go on to diagnose one of the following types:

  • Type I: Only one side of the sacrum has any abnormalities or hasn’t developed. It’s usually referred to as being partial, or unilateral.
  • Type II: Both sides of the sacrum have abnormalities or didn’t develop. This is referred to as being uniform, or bilateral.
  • Type III: The sacrum hasn’t developed at all, and some of the lower vertebrae just above the sacrum in the lower back have fused together.
  • Type IV: The leg tissues have completely fused together.
  • Type V: One set of leg tissue is missing.

Types I and II are the most commonly reported. They usually involve missing bones around the sacrum. Types III and IV are more severe and can involve abnormalities in the brain and other bodily functions.

In rare cases, your child may be diagnosed with Type V caudal regression syndrome. This means that your child has only grown one set of the tibia and femur bones, two of the main bones that make up your leg. Type V is sometimes called sirenomelia, or “mermaid syndrome,” because of the presence of only one leg.

Your child’s symptoms will depend on the type of caudal regression syndrome that’s diagnosed.

Mild cases may not cause any noticeable changes in your child’s appearance. But in severe cases, your child may have visible differences in the leg and hip area. For example, their legs may be permanently bent in a “frog-like” stance.

Other visible characteristics may include:

  • spine curving (scoliosis)
  • flat buttocks that are noticeably dimpled
  • feet bent upward at a sharp angle (calcaneovalgus)
  • clubfoot
  • imperforate anus
  • opening of the penis on the underside instead of the tip (hypospadias)
  • testicles not descending
  • not having any genitals (genital agenesis)

Your child may also experience the following internal complications:

  • abnormally developed or missing kidneys (renal agenesis)
  • kidneys that have grown together (horseshoe kidney)
  • nerve damage to the bladder (neurogenic bladder)
  • bladder that sits outside of the abdomen (bladder exstrophy)
  • misshapen large intestine or large intestine that sits abnormally in the gut
  • intestine that pushes through weak areas of your groin (inguinal hernia)
  • vagina and rectum that are connected

These characteristics can lead to symptoms such as:

Treatment depends on how severe your child’s symptoms are.

In some cases, you child may only need special shoes, leg braces, or crutches to help them walk and move around. Physical therapy may also help your child build strength in their lower body and gain control of their movements.

If your child’s legs didn’t develop, they may be able to walk using artificial, or prosthetic, legs.

If your child has trouble controlling their bladder, they may need a catheter to drain their urine. If your child has an imperforate anus, they may need surgery to open a hole in their intestine and pass stools outside of their body into a bag.

Surgery can also be done to treat certain symptoms, such as bladder exstrophy and inguinal hernia. Surgery performed to treat these symptoms usually resolves them completely.

Your child’s outlook will depend on the severity of their symptoms. Your doctor is your best resource for information about your child’s individual diagnosis and any anticipated complications.

In mild cases, your child may go on to live an active and healthy life. Over time, they may be able to use special shoes, braces, or prosthetics to support their body weight and help them move around.

In severe cases, complications in the heart, digestive system, or renal system may affect your child’s life expectancy. Your doctor can provide you with more information about what to expect after childbirth and discuss your options moving forward.