Spinal Dysraphism - Causes, Types, Radiological Evaluation, and Diagnosis

Introduction

Spinal dysraphism is also called spina bifida, in which the spine and spinal cord do not form properly during pregnancy. Therefore, the spine and spinal cords get exposed to the surrounding environment, either inside or outside the body. Spinal dysraphism usually occurs due to incomplete midline closure of the bony and neural spinal tissues. Magnetic resonance imaging is considered to be the best imaging modality to diagnose these conditions.

What Does Spinal Dysraphism Mean?

Spinal dysraphism is a term that includes both visible and invisible incomplete formations of the spine, spinal cord, or nerve roots.

• Spine is the bony structure of individual vertebrae (bones) that protects the spinal cord.

• Spinal cord is the bundle of nerves and other tissues that connects the brain to the body. The spinal cord is also protected by layers of membranes. The spinal cord is responsible for sending sensory information from the different parts of the body to the brain and from the body to the brain.

• Nerve roots start from the spinal cord and reach the rest of the body.

What Is the Epidemiology of Spinal Dysraphism?

This condition usually develops in the embryonic stage and is more commonly seen in females as compared to males. The estimated incidence of spinal dysraphism is found to be 1 to 3 per 1000 live births. However, the prevalence of spinal dysraphism has been declining over the last few decades as women are getting sufficient nutrition and improved prenatal care during pregnancy with the help of high-resolution imaging tests such as MRI.

What Are the Causes of Spinal Dysraphism?

Spinal dysraphism has multifactorial causation factors, including both genetic and environmental ones. There are still investigations going on regarding the etiological factors of spinal dysraphism, and it has been found that it can occur randomly and is hereditary, that it can pass down through families.

What Are the Types of Spinal Dysraphism?

There are multiple types of spinal dysraphism types which include -

• Spina Bifida - This is the most common and mild form of spinal dysraphism. It is usually found in 10 to 20 percent of children. In this type, one or more bones in the spine or vertebrae do not unite properly.

• Closed Neural Tube Defect - In this type, various malformations are present in fat, spine bone spinal cord, nerves, and membranes on the spinal cord.

• Open Neural Tube Defect - In this neural structures get exposed to CSF (cerebrospinal fluid) leak and do not have any covering either of skin or sac. Patients with this type of spinal dysraphism have a less favorable prognosis than closed neural tube defects.

• Meningocele - Membranes covering the brain and spinal cord bulge through the opening in the spinal column and forms a swelling in the back.

• Myelomeningocele - This is the severe form of spina bifida and it occurs when the spinal bones or vertebrae fail to close which leads to the spinal cord and nerves protruding through the defect in the spinal column appearing as a swelling in the back. Patients with this type are usually partially or completely paralyzed and may have difficulty with bowel and bladder control and may have orthopedic problems and cerebrospinal fluid leakage.

• Tethered Cord - In this condition the movement of the spinal cord is restricted, and cannot move freely in the spinal column. This leads to the stretching of the spinal cord causing damage to the cord leading to neurological problems such as weakness, and sensory loss, and urological and orthopedic problems such as leg or ankle deformities.

• Spinal Lipoma (Lipomyelomeningocele) - In this condition, an abnormal growth of fat can be seen on the spinal cord and its membranes.

• Diastematomyelia - A complex type of spinal structural abnormality in which the spinal cord splits into two different cords.

What Is the Role of Radiological Investigations for Spinal Dysraphism?

• Simple radiographs (X-rays) are also a screening modality for finding bony spinal anomalies.

• During the prenatal stage, ultrasound is considered a good modality for evaluating various spinal anomalies but in the case of infants, it can only be used as a screening modality as it is sensitive to detect dysraphism.

• Computed Tomography (CT) scan with multi-slice detectors is an excellent option to diagnose vertebral anomalies and bony septum in diastematomyelia. But it has less soft tissue contrast and may need to inject a non-ionic contrast medium to evaluate the thecal sac and its content.

• Ultrasound and CT scans are not able to show small abnormalities of the spinal cord and nerves and also do not have good soft tissue contrast as compared to MRI (magnetic resonance imaging). Therefore MRI is considered the best choice for evaluating spinal anomalies.

• Magnetic Resonance Imaging (MRI) scan is the best modality to diagnose spinal dysraphism. The MRI is considered the only diagnostic modality required for evaluating and formulating a pre-surgical plan for spinal dysraphism and associated syndrome.

In case of an MRI scan, some of the following precautions have to be taken which include -

• It is a time-consuming procedure and requires the patient to remain still for about 30 to 40 minutes in the machine.

• Many pediatric patients may require sedation (anesthesia) to perform this imaging test to get a good-quality scan without any artifacts.

• A long time of MRI scan may cause complications as more general anesthesia has to be administered to keep the patient still.

What Is the Diagnosis for Spinal Dysraphism and Its Types?

• The severe form of spinal dysraphism can be diagnosed early in life such as myelomeningocele can be diagnosed before birth with the help of ultrasound and is visible with the naked eye and can be diagnosed easily in newborns.

• A dermal sinus tract which is a pit or dimple on the skin over the spine requires imaging tests such as MRI as with the naked eye it is not possible to determine whether the tract reaches the spinal cord.

• Lipomyelomeningocele can be diagnosed before birth with the help of ultrasound.

• Conditions like spina bifida occulta, diastematomyelia, and dermoid and epidermoid cysts are not visible to the naked eye but they can cause skin changes such as the growth of extra skin or hair growth or change in skin pigmentation. Therefore these conditions can be diagnosed by a physical examination in childhood.

Spinal ultrasound is a common screening test done in the case of newborns. MRI (magnetic resonance imaging) is one of the essential diagnostic tools for spinal dysraphism, which provides detailed images of soft tissues using radio waves.

How Can Neural Tube Defects Be Diagnosed During Pregnancy?

Some of the neural tube defects can be diagnosed in the fetus stage which include -

• Ultrasound - Some defects can be detected through this test.

• Serum AFP - A blood test can be done to detect AFP (alpha-fetoprotein) levels in the 16th to 18th week of pregnancy. The higher levels of AFP mean the presence of neural tube defects in the baby.

• Fetal MRI (Magnetic Resonance Imaging) - This provides more detailed images than ultrasound.

Conclusion

Imaging of spinal dysraphism may be considered a complicated procedure, as this is a group of diverse conditions that have variable imaging appearances. Therefore, MRI is one of the best tools among ultrasound and CT scans which help in the detection of spinal dysraphism conditions. It is a non-invasive method that provides detailed images of soft tissues. This can be done at any stage and helps in distinguishing between the multiple types of spinal dysraphism.