Introduction:
Spinal dysraphism, or spina bifida, is a frequently occurring congenital anomaly that encompasses a diverse range of neural tube defects. It is typically categorized into two main types: spina bifida aperta and spina bifida occulta. Advances in prenatal screening techniques have led to a decrease in the occurrence of spina bifida aperta, while the detection of spina bifida occulta has risen, primarily due to the utilization of magnetic resonance imaging (MRI).
What Is Spinal Dysraphism?
Spina bifida, literally translating to ‘spine in two parts’ or ‘open spine,’ refers to a group of congenital anomalies collectively known as spinal dysraphism. These anomalies involve the presence of a defective neural arch, which can result in the herniation of meninges or neural elements, leading to a range of clinical manifestations. The condition is typically classified into two categories: ‘aperta’, which denotes visible lesions, and ‘occulta,’ where no external lesions are evident. These anomalies can manifest in different forms, each with its own set of pathological findings and names. Spina bifida aperta is typically characterized by a visible skin defect and carries a risk of cerebrospinal fluid (CSF) leakage, classifying it as an ‘open defect.’ In contrast, the occult forms do not exhibit any abnormalities in skin cover. The management approaches for these two forms differ significantly due to their distinct characteristics.
What Are the Conventional Imaging Techniques Used for Detecting Spinal Dysraphism?
Conventional imaging techniques used for detecting spinal dysraphism are listed below:
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X-rays: X-ray imaging provides two-dimensional views of the spine. While X-rays are less effective in visualizing soft tissues and neural elements, they are often the initial step in assessing spinal issues.
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Ultrasound: Ultrasound is commonly used during pregnancy as a prenatal screening tool. It can detect certain spinal abnormalities, particularly open spina bifida, by visualizing the spinal cord and its surrounding structures in the developing fetus. It is non-invasive and safe for both the mother and the unborn child.
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Computed Tomography (CT) Scans: CT scans use X-rays to create detailed cross-sectional images of the spine. These scans are especially effective in assessing bony abnormalities and can provide information about the extent of vertebral defects.
What Are the Innovations in Imaging for Diagnosing Spinal Dysraphism?
The field of medical imaging for spinal dysraphism has seen significant advancements in recent years. These innovations have improved the accuracy of diagnosis and treatment planning, leading to better outcomes for individuals affected by this condition. Following are some of the innovations in imaging for spinal dysraphism:
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3D MRI Imaging - Traditional MRI (magnetic resonance imaging) scans provide two-dimensional images of the spine and spinal cord. However, the latest innovations have enabled the acquisition of high-resolution 3D (three-dimensional) images. These three-dimensional images offer greater anatomical detail, allowing healthcare professionals to assess the extent of spinal dysraphism more accurately and plan surgical interventions with precision. This innovation has been particularly valuable in complex cases.
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Fetal MRI - Early diagnosis of spinal dysraphism during pregnancy is crucial for planning postnatal interventions and improving outcomes. Fetal MRI is a groundbreaking innovation that allows healthcare providers to visualize the developing fetus's spine and spinal cord in utero. This technology has significantly improved the early detection of spinal dysraphism, enabling parents and healthcare teams to make informed decisions and prepare for the child's medical needs before birth.
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Diffusion Magnetic Resonance Imaging (dMRI) - Over the past three decades, diffusion magnetic resonance imaging (dMRI), encompassing diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI), has proven to be a valuable tool for characterizing tissue microstructure and white matter anatomy. This imaging method capitalizes on its sensitivity to microscopic-scale diffusion-driven molecular motion. A potential application of prenatal dMRI is the characterization of white matter development and the assessment of potential upstream neuronal damage in cases of spinal dysraphism. The neurodevelopmental consequences associated with spinal dysraphism may, in part, be attributed to in-utero injury affecting the developing white matter, resulting in measurable changes in cerebral tissue diffusion properties.
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Fractional Anisotropy: Studies have indicated that fractional anisotropy, a DTI-derived metric reflecting axonal density and myelin integrity, is elevated in the midbrain of fetuses with spina bifida. This elevation may be linked to the commonly accompanying Chiari-II malformation, which can disrupt cerebrospinal fluid (CSF) drainage, leading to microstructural and tissue diffusivity alterations.
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Postnatal MRI scans: Postnatal MRIs have revealed that individuals who underwent fetal repair exhibit white matter abnormalities compared to those who did not. Postnatal studies in spina bifida suggest that there are additional white matter abnormalities beyond those caused by changes in fluid dynamics. These extra abnormalities may result from damage to the nerves and brain pathways. Diffusion MRI (dMRI) studies show that both deep gray matter structures and most major white matter pathways are affected in spina bifida. These unusual findings in the brain's white matter and deep gray matter could provide a basis for understanding cognitive and behavioral challenges seen in many individuals with spina bifida. This also suggests that dMRI might be used to predict cognitive development in individuals with spina bifida as they grow up.
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Tractography: This image processing technique extends the utility of dMRI and enables the reconstruction of major white matter pathways. Moreover, dMRI and tractography have the potential to characterize the microstructural properties of spinal abnormalities, including the spinal cord and its distal peripheral nerves. Some reported pediatric cases involve spina bifida patients with sacral nerve root agenesis. Tractographic reconstructions of the sacral plexus have successfully revealed that in patients with spinal dysraphism, the plexus appears asymmetrical and disorganized when compared to healthy controls.
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Diffusion Tensor Imaging (DTI) - DTI is an advanced MRI technique that focuses on the measurement of water diffusion in multiple directions within the brain and spinal cord. It is particularly useful for assessing white matter tracts and neural connectivity. In the context of spinal dysraphism, DTI can provide valuable insights into the integrity of neural pathways and identify abnormalities in neural connectivity.
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H-MRS (Proton Magnetic Resonance Spectroscopy) -
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MR spectroscopy is a technique that provides information about the chemical composition of tissues. It can be used to detect metabolic changes in the spinal cord and surrounding structures. This imaging is a widely utilized technique for examining the concentrations of metabolites in living tissues. During the progression of spinal dysraphism, various factors such as ischemia, anaerobic metabolism, and disruptions in neuronal membranes can bring about changes in the chemical makeup of both cerebrospinal fluid (CSF) and amniotic fluid.
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In cases of open spina bifida, the analysis of degradation products and other compounds in the CSF and amniotic fluid holds promise as a means of identifying potential markers for neurological dysfunction using MRS. MRS investigations have revealed elevated concentrations of succinic acid and glutamine in the amniotic fluid of fetuses with spinal dysraphism compared to control groups. Studies involving adult patients with spinal dysraphism have shown increased levels of lactate, choline, glycerophosphocholine, acetate, and alanine in the CSF compared to control subjects.
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Functional Imaging - In addition to anatomical imaging, functional imaging techniques like functional MRI (fMRI) and magnetoencephalography (MEG) have played a significant role in understanding the neurological aspects of spinal dysraphism. fMRI can assess brain function and connectivity, while MEG measures magnetic fields produced by neural activity. These techniques help healthcare professionals map neural pathways and better understand the functional implications of spinal dysraphism, guiding treatment decisions and rehabilitation strategies.
Conclusion:
New and improved ways of taking pictures inside the body have made a big difference in how to understand and treat spinal dysraphism. These innovative imaging techniques and technologies that assist doctors in interpreting the images are changing the lives of people with spinal dysraphism. They help identify problems earlier, plan treatment more accurately, and perform surgery more successfully. Scientists are still working on even better ways to capture images, so there is hope for even more progress in managing this condition in the future.
