Introduction

Neural tube defects (NTDs) are a group of genetic abnormalities that arise during the early stages of embryonic development when the neural tube, the precursor to the brain and spinal cord, fails to form or close properly.¹ Open neural tube defects like spina bifida and anencephaly are more widely recognised; however, closed neural tube defects, though less common, can still lead to significant neurological impairments and disabilities if left undetected and untreated.

Anatomy of the neural tube

To fully comprehend closed neural tube defects, it is essential to understand the normal development and formation of the neural tube. During the third and fourth weeks of embryonic development, a flat sheet of cells called the neural plate undergoes neurulation.² In this process, the neural plate folds inward, creating the neural groove, forming a closed, cylindrical neural tube. This neural tube eventually develops into the brain and spinal cord. Disruptions or abnormalities during this delicate process can result in a range of neural tube defects, including closed defects where the neural tube fails to close completely or forms abnormally.

Types of closed neural tube defects

Spina bifida occulta

A mild form of spina bifida, characterised by a small gap or incomplete fusion of one or more vertebral arches, typically in the lower back region. The spinal cord and meninges may protrude through this gap, but there is no visible external opening or sac on the back.

Many individuals with spina bifida occulta remain asymptomatic, as the spinal cord and nerves are often not significantly compressed or damaged.³ Diagnosis is frequently incidental during imaging studies for other reasons or subtle signs like a dimple or hairy patch on the lower back may prompt further investigation.

Tethered cord syndrome

A condition in which the spinal cord is abnormally anchored or tethered, limiting its normal movement and ascent within the spinal canal during growth and development. This tethering can occur due to various underlying causes, such as spina bifida occulta, lipomas (fatty masses), or diastematomyelia (split spinal cord).

As the child grows, the tethered spinal cord becomes increasingly stretched, leading to progressive neurological symptoms like lower back pain, leg weakness or numbness, gait abnormalities, and bladder/bowel dysfunction. MRI scans are crucial for diagnosis, as they can visualise the site of tethering and any associated malformations or lesions contributing to the tethering.⁴

Diastematomyelia

A rare congenital anomaly characterised by a split or duplicated spinal cord, resulting in two separate hemicords (half cords) within a single dural sac. A bony or fibrous septum separates the two hemicords, often associated with other spinal malformations like hemivertebrae or vertebral body fusion.

This can lead to varying degrees of neurological impairment, depending on the level and extent of the split cord. Diagnosed primarily through MRI scans, which can visualise the split cord and the presence of the bony or fibrous septum.

Symptoms and complications

While closed neural tube defects may not be immediately visible at birth, they can present with a range of symptoms and potential complications, including:

• Musculoskeletal deformities: Scoliosis (curvature of the spine), clubfoot, limb weakness or paralysis due to malformation or compression of the spinal cord and nerves
• Bladder and bowel dysfunction: Incontinence, urinary retention, constipation, or loss of bowel control due to damage or compression of the nerves responsible for bladder and bowel function
• Sensory disturbances: Numbness, tingling, or loss of sensation in the legs or lower body, depending on the level of spinal cord involvement
• Skin changes include dimples, hairy patches, or discolouration in the lower back region, which can indicate an underlying spinal cord malformation

Potential serious complications include motor and sensory deficits, orthopaedic issues like scoliosis or kyphosis (outward curvature of the spine), and autonomic dysfunctions affecting bladder, bowel, and other autonomic functions.

Diagnosis and screening

Early detection and accurate diagnosis are crucial for timely intervention and optimal patient outcomes. Various diagnostic approaches are employed:

Prenatal screening techniques

Ultrasound examinations to detect signs of spinal abnormalities or defects.

Maternal serum alpha-fetoprotein (MSAFP) screening measures levels of a protein produced by the foetus. Elevated levels can indicate the presence of neural tube defects, including some closed defects.

Postnatal diagnosis

1. Physical examination: Assessing for skin markings, musculoskeletal deformities, and neurological function can aid in identifying potential closed NTDs
2. Imaging studies:
   • X-rays can reveal vertebral anomalies or spinal cord malformations
   • Ultrasound can evaluate the spinal cord and surrounding structures in infants and young children
   • CT scans provide detailed images of bony structures and can identify spinal cord anomalies or associated malformations
   • MRI is considered the gold standard, offering superior soft tissue contrast to visualise the spinal cord, nerve roots, and associated malformations or lesions⁵ 

Treatment and management

Effectively treating and managing closed neural tube defects often requires a multidisciplinary team approach, involving various medical specialists and healthcare professionals working together to address each patient's unique needs.

Multidisciplinary team

• Neurosurgeons for surgical interventions and spinal cord/nervous system management
• Orthopaedic surgeons for treating musculoskeletal deformities and orthopaedic complications
• Urologists for managing bladder and bowel dysfunction and urinary tract complications
• Physical and occupational therapists for rehabilitation services to improve functional abilities and independence
• Psychologists and counsellors for emotional and psychological support

Surgical interventions

• Spinal cord detethering procedures for conditions like tethered cord syndrome release the tethering and prevent further neurological deterioration
• Repair of associated malformations, such as lipoma resection, closure of spina bifida defects, or removal of bony/fibrous septa in diastematomyelia

Rehabilitation and supportive care

• Physical therapy improves strength, flexibility, coordination, and functional abilities through exercises, gait training, and assistive devices
• Occupational therapy for developing daily living skills, utilising adaptive equipment and home modifications
• Psychological support for coping strategies, body image concerns, and emotional challenges

Prognosis and outlook

The prognosis and long-term outlook for individuals with closed neural tube defects can vary significantly, depending on factors such as the severity of the defect, the extent of neurological involvement, timely intervention, and the presence of associated complications. While many achieve functional independence with proper management, disabilities and limitations are still common. Ongoing rehabilitation, supportive care, and access to comprehensive multidisciplinary teams are vital for optimising outcomes and quality of life.

Prevention strategies

Although the precise causes are not fully understood, certain preventive measures can help reduce the risk of neural tube defects, including closed defects:

• Folic acid supplementation: Adequate intake of folic acid (vitamin B9) before and during early pregnancy has decreased the risk significantly¹
• Prenatal screening and genetic counselling: Regular prenatal care, screening tests, and genetic counselling for those at increased risk can aid in early detection and informed decision-making.
• Managing medical conditions and avoiding teratogens: Maintaining a healthy lifestyle, managing pre-existing conditions like diabetes, and avoiding potential teratogens (agents that can cause birth defects) during early pregnancy may also reduce risk

Current research and future directions 

Ongoing research efforts aim to improve our understanding, diagnostic capabilities, and treatment options for closed neural tube defects:

• Advancements in minimally invasive surgical techniques, such as endoscopic or robotic-assisted procedures, for correcting malformations and untethering operations with reduced surgical trauma and recovery times
• Emerging therapies and technologies, including stem cell-based treatments, gene therapy approaches, and regenerative medicine strategies for spinal cord repair or regeneration
• Improved prenatal screening and diagnostic methods for more accurate and early detection of closed neural tube defects
• Refining surgical techniques, rehabilitation protocols, and supportive care approaches to maximise functional outcomes and quality of life
•  Furthering our understanding of the genetic and environmental factors contributing to the development of these conditions, informing more effective prevention strategies²

Summary

Closed neural tube defects, though less common than their open counterparts, represent a diverse group of conditions with the potential for significant neurological impairments and disabilities. Early detection through prenatal screening and thorough postnatal examinations, coupled with advanced imaging techniques like MRI, is crucial for identifying these defects and initiating timely interventions.

A multidisciplinary team approach involving neurosurgeons, orthopaedists, urologists, therapists, and counsellors is essential for providing comprehensive care tailored to each patient's unique needs. Surgical interventions, such as spinal cord untethering and repair of associated malformations, offer opportunities for preserving neurological function. At the same time, rehabilitation services play a vital role in maximising functional abilities and promoting independence.

Prevention strategies, including folic acid supplementation, prenatal care, and genetic counselling, remain paramount in reducing the incidence of neural tube defects and promoting better outcomes for families at risk. Ongoing research continues to shed light on the underlying causes, refine diagnostic methods, and develop innovative therapeutic approaches, offering hope for improved treatments and better quality of life for those affected.

While closed neural tube defects present significant challenges, a comprehensive and multifaceted approach to care, coupled with ongoing advancements in medical technology and research, can significantly improve outcomes for individuals affected by these conditions. By prioritising early intervention, comprehensive rehabilitation, and support, we can promote functional independence, enhance quality of life, and prevent these complex and challenging conditions.