Congenital Upper Cervical Disorders

An overview of head and upper neck abnormalities present at birth.

Head and upper neck conditions, also known as upper cervical disorders, craniovertebral junction (CVJ) abnormalities, or craniocervical disorders, are a large group of brain and spinal conditions that occur at the base of the skull and the top of the neck. Sometimes, an injury or illness can cause an upper cervical disorder, but you can also be born with one—this is known as a congenital disorder. Congenital means “present at birth.”

This article provides an overview of the following congenital upper cervical disorders:

  • Platybasia
  • Atlanto-axial Instability
  • Atlas Hypoplasia
  • Klippel-Feil Malformation
  • Chiari Malformation and Syringomyelia
  • Os Odontoideum
  • Achondroplasia

If you would like to learn about upper cervical disorders that develop later in life, read Acquired Upper Cervical Disorders.
Young girl with Down Syndrome smiling with her hands full of various paint colorsPlatybasia
Platybasia is a congenital disorder characterized by an abnormal flattening at the base of the skull. This condition is associated with numerous other conditions and bone abnormalities, including Basilar Invagination and atlas assimilation. Atlas assimilation occurs when the first vertebra in the neck (the atlas, or C1) fuses to the occipital bone.

While pain at the back of the head and upper neck are common symptoms, you may not experience any symptoms. In this case, you may not require any treatment. However, if platybasia is accompanied by nerve compression, you may have problems swallowing and coughing. Your doctor may recommend spine surgery, such as posterior cervical decompression and fusion, to treat nerve-related platybasia.

Atlantoaxial Instability
Atlantoaxial instability refers to excessive movement caused by either a bone or ligament abnormality between the first 2 bones of the cervical spine, which are called the atlas (or C1) and the axis (C2). These bones are unlike any others in your spine, and you can read more about them in Anatomy of the Head and Upper Neck.

When dislocation or subluxation (partial dislocation) occurs at the atlas and axis, they become misaligned. This may result in your spinal cord and other nearby nerves becoming impinged, causing pain and other neurological symptoms (like numbness). To decompress nerves and establish stability in your upper neck, your doctor may recommend a posterior spinal fusion.

However, atlantoaxial instability doesn’t always cause symptoms. If you don’t experience any symptoms, your doctor may recommend follow-up appointments involving neck x-rays and annual neurological exams to monitor your condition and ensure you can safely engage in sports and other contact activities.

Congenital atlantoaxial instability may be caused by multiple conditions, such as Down syndrome, Klippel-Feil malformation, and os odontoideum.

Atlas Hypoplasia
Atlas hypoplasia occurs when you are born with an underdeveloped or incompletely developed atlas, which is the top bone in your cervical spine (C1). This congenital condition ranges in severity, as some people may have small defects while others may have a complete lack of the back arch of their atlas.

Some cases of atlas hypoplasia don’t cause any symptoms, so your doctor may not prescribe any treatment or follow up. Your doctor may recommend preventive measures, such as avoiding contact sports. If your condition is causing nerve compression, your doctor may recommend surgery to remove the back arch of the atlas bone.

Klippel-Feil Malformation
Klippel-Feil malformation, or Klippel-Feil syndrome, occurs when the bones in your neck fail to segment properly before birth. This condition is characterized by the fusion of at least 2 of your cervical vertebrae, which reduces your range of motion in your neck.
Klippel-Feil syndromeCourtesy of WikipediaKlippel-Feil syndrome is associated with other spine and bone disorders, including scoliosis (which is present in more than half of those affected) and atlantoaxial instability.

Reduced range of motion is the most obvious sign of Klippel-Feil malformation, but other tell-tale signs include low hairline and a short neck. Some patients do not present with any symptoms, though others report pain and neurologic symptoms if the spinal cord and surrounding nerves are impacted.

Chiari Malformation and Syringomyelia
Chiari malformation occurs when the bottom part of the cerebellum moves outside of its normal location by dipping through the opening in the occipital bone and entering the top part of the spinal canal. This may compress the brain stem or spinal cord, but in some cases, no symptoms present.

There are 4 types of Chiari malformation, which have different causes and treatment options. You can learn more about the different types in Chiari Malformation: A Basic Overview.

Some people with Chiari malformation experience syringomyelia, which is a fluid-filled cyst called a syrinx that forms within the spinal cord. If the syrinx grows, it can damage your spinal cord and cause painful neurological symptoms throughout the body, including weakness and numbness.
Chiari malformationTo prevent the syrinx from expanding and harming your spinal cord, your doctor may perform surgery to remove the syrinx, though observation is a common treatment as well. You can take a deeper dive into this Chiari malformation complication in What is Syringomyelia?

Os Odontoideum
“Os” means “bone” and “odontoideum” refers to the odontoid process, or the dens, which is a part of the second bone in your spine—the axis, or C2. The dens fits into a groove in the C1 bone, or atlas, and it enables your head and neck to move properly.

In os odontoideum, a portion of the dens is removed from the rest of the axis. In some cases, this doesn’t cause any symptoms. But, other times, it results in too much motion between your atlas and axis. This can compress your spinal cord, causing neck pain, headache, balance problems, and even paralysis.

While this condition may be congenital and the cause is unknown, people with Down syndrome have a higher risk for developing os odontoideum.

If os odontoideum is not causing any symptoms, you will likely not require any treatment. However, if the joint between the C1 and C2 vertebrae is unstable, your doctor may recommend a posterior spinal fusion to stabilize the spine and reattach the dens to the C2.

Achondroplasia
Achondroplasia is the most common bone growth disorder. It causes dwarfism, which is characterized by short stature and short limbs.

The condition is caused by a problem with the FGFR3 gene, which tells your body to make a protein that’s integral to bone growth. During the early fetal stages, the majority of the skeleton is made of cartilage. Normally, that cartilage becomes bone. But in achondroplasia, the FGFR3 gene mutations interfere with healthy bone and skeletal development.

In relation to the upper cervical spine, achondroplasia has been associated with narrowing at the foramen magnum, which is the space through which your spinal cord, brain stem, and other key neural and vascular structures pass through between your head and neck. This narrowing is known as cervical medullary stenosis.

Approximately 5 to 10% of people with achondroplasia develop cervical medullary stenosis, though many more will experience some degree of compression. Cervical medullary stenosis is a serious condition, and it has been associated with infant death. Infants and toddlers with the condition may have regular imaging follow ups to determine the extent of the compression and determine appropriate treatment (observation or cervical decompression surgery). Your doctor may recommend avoiding contact sports or other high-impact activities, which may worsen compression.

Living a Healthy Life with a Congenital Upper Neck Disorder
Many head and upper neck conditions that develop before birth have excellent outcomes—and some don’t cause symptoms or impact your quality of life. Keeping regular appointments with your medical team will help ensure that any problems are detected early, giving you the best chance for treatment success.

Updated on: 10/02/17
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Upper Neck Disorders and the Cervical Spine

Overview of head and upper neck disorders your doctor may refer to as a craniovertebral junction abnormality or craniocervical disorder.
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