Imaging of Congenital Spine and Spinal Cord Malformations




This article reviews normal embryologic development of the spine and spinal cord and the imaging features of congenital abnormalities of the spine and spinal cord, with particular focus on magnetic resonance imaging. The authors discuss spinal dysraphisms, a heterogeneous group of congenital abnormalities of the spine and spinal cord, and provide information to expand understanding of these complex entities.


Spinal cord development


There are 3 basic embryologic stages to spinal development. The first stage occurs during the second or third week of embryonic development and is referred to as gastrulation. During gastrulation, the embryonic disk converts from a bilaminar disk to a trilaminar disk composed of ectoderm, mesoderm, and endoderm. Primary neurulation is the second stage in spinal development and occurs during weeks 3 to 4. During primary neurulation, the notochord and overlying ectoderm interact to form the neural plate, which then bends and folds to form the neural tube. The neural tube then closes bidirectionally in a zipperlike manner ( Fig. 1 ). Secondary neurulation is the final stage of spinal development and occurs during weeks 5 and 6. During secondary neurulation, the secondary neural tube is formed by the caudal cell mass. The secondary neural tube is initially solid, subsequently cavitates, and eventually forms the tip of conus medullaris and filum terminale via a process called retrogressive differentiation. Abnormalities in any of these developmental stages can lead to spine or spinal cord malformations.




Fig. 1


Primary neurulation. ( A D ) Stages of primary neurulation. Interaction of the notochord ( circle ) and overlying ectoderm results in formation of the neural plate ( dark green ), which then bends to form the neural tube and ultimately closes in a zipperlike fashion.

( Reprinted from Rufener SL, Ibrahim M, Raybaud CA, et al. Congenital spine and spinal cord malformations–pictorial review. Am J Roentgenol 2010;194:S26–37; with permission.)




Categorization of spinal dysraphisms


Spinal dysraphisms can be broadly divided into open and closed types. Open spinal dysraphisms describe entities that have an overlying skin defect with neural tissue exposed to the environment. Closed spinal dysraphisms describe entities in which the overlying skin remains intact. Closed spinal dysraphisms can be further subcategorized based on whether a subcutaneous mass is present or absent. The key features of open and closed spinal dysraphisms are summarized in Table 1 .



Table 1

Summary of spinal dysraphisms




































































Open Spinal Dysraphisms -Not covered by intact skin
Myelocele Neural placode flush with skin surface
Myelomeningocele Neural placode protrudes above skin surface
Hemimyelocelee Myelocele associated with diastematomyelia
Hemimyelomeningocele Myelomeningocele associated with diastematomyelia
Closed Spinal Dysraphisms -Covered by intact skin
With a Subcutaneous Mass:
Lipomyelocele Placode-lipoma interface within the spinal canal
Lipomyelomeningocele Placode-lipoma interface outside of the spinal canal
Meningocele Herniation of CSF filled sac lined by dura
Terminal myelocystocele Terminal syrinx herniating into posterior meningocele
Myelocystocele Dilated central canal herniating through posterior spina bifida
Without a Subcutaneous Mass:
Simple Dysraphic States
Intradural lipoma Lipoma within the dural sac
Filar lipoma Fibrolipomatous thickening of filum
Tight filum terminale Hypertrophy and shortening of filum
Persistent terminal ventricle Persistent cavity within conus medullaris
Dermal sinus Epithelial lined fistula between neural tissue and skin surface
Complex Dysraphic States
Dorsal enteric fistula Connection between bowel and skin surface
Neurenteric cyst More localized form of dorsal enteric fistula
Diastematomyelia Separation of cord into two hemicords
Caudal agenesis Total or partial agenesis of spinal column
Segmental spinal dysgenesis Various segmentation anomalies




Categorization of spinal dysraphisms


Spinal dysraphisms can be broadly divided into open and closed types. Open spinal dysraphisms describe entities that have an overlying skin defect with neural tissue exposed to the environment. Closed spinal dysraphisms describe entities in which the overlying skin remains intact. Closed spinal dysraphisms can be further subcategorized based on whether a subcutaneous mass is present or absent. The key features of open and closed spinal dysraphisms are summarized in Table 1 .



Table 1

Summary of spinal dysraphisms




































































Open Spinal Dysraphisms -Not covered by intact skin
Myelocele Neural placode flush with skin surface
Myelomeningocele Neural placode protrudes above skin surface
Hemimyelocelee Myelocele associated with diastematomyelia
Hemimyelomeningocele Myelomeningocele associated with diastematomyelia
Closed Spinal Dysraphisms -Covered by intact skin
With a Subcutaneous Mass:
Lipomyelocele Placode-lipoma interface within the spinal canal
Lipomyelomeningocele Placode-lipoma interface outside of the spinal canal
Meningocele Herniation of CSF filled sac lined by dura
Terminal myelocystocele Terminal syrinx herniating into posterior meningocele
Myelocystocele Dilated central canal herniating through posterior spina bifida
Without a Subcutaneous Mass:
Simple Dysraphic States
Intradural lipoma Lipoma within the dural sac
Filar lipoma Fibrolipomatous thickening of filum
Tight filum terminale Hypertrophy and shortening of filum
Persistent terminal ventricle Persistent cavity within conus medullaris
Dermal sinus Epithelial lined fistula between neural tissue and skin surface
Complex Dysraphic States
Dorsal enteric fistula Connection between bowel and skin surface
Neurenteric cyst More localized form of dorsal enteric fistula
Diastematomyelia Separation of cord into two hemicords
Caudal agenesis Total or partial agenesis of spinal column
Segmental spinal dysgenesis Various segmentation anomalies




Open spinal dysraphisms


Myelomeningocele and Myelocele


Myelomeningocele and myelocele result from defective closure of the primary neural tube and are characterized clinically by neural placode exposure through a midline skin defect on the back. Myelomeningoceles account for greater than 98% of open spinal dysraphisms. Myeloceles are rare. Because open spinal dysraphisms are often diagnosed clinically (often antenatally), imaging of these entities is not always performed. When imaging is performed, the main differentiating feature between a myelomeningocele and myelocele is neural placode position relative to the skin surface. With a myelomeningocele, the neural placode protrudes above the skin surface ( Fig. 2 ). With a myelocele, the neural placode is flush with the skin surface ( Fig. 3 ).




Fig. 2


Myelomeningocele. ( A ) Axial diagram. Expansion of underlying subarachnoid space ( arrow ) results in protrusion of the neural placode ( star ) above the skin surface. ( B ) Sagittal and ( C ) axial T2-weighted magnetic resonance (MR) images in a newborn with Chiari II malformation show large open defect in the lower lumbar spine ( small arrows ). There is extension of the neural placode ( arrowhead ) to the skin surface caused by expansion of the underlying subarachnoid space, which is characteristic of a myelomeningocele.

(Part [ A ] Reprinted from Rufener SL, Ibrahim M, Raybaud CA, et al. Congenital spine and spinal cord malformations–pictorial review. Am J Roentgenol 2010;194:S26–37; with permission.)



Fig. 3


Myelocele. ( A ) Axial diagram. The exposed neural placode ( arrow ) is flush with the skin surface. ( B ) Axial T2-weighted MR image shows an exposed neural placode ( arrow ) that does not protrude above the skin surface, consistent with a myelocele. There is no expansion of the underlying subarachnoid space.

( Reprinted from Rufener SL, Ibrahim M, Raybaud CA, et al. Congenital spine and spinal cord malformations–pictorial review. Am J Roentgenol 2010;194:S26–37; with permission.)


Hemimyelomeningocele and Hemimyelocele


Hemimyelomeningocele and hemimyelocele have been described but are rare. These entities occur when a myelomeningocele or myelocele is associated with diastematomyelia (cord splitting) and one hemicord fails to neurulate.




Closed spinal dysraphisms with a subcutaneous mass


Lipomas with a Dural Defect


Lipomas with a dural defect can be characterized as lipomyelocele or lipomyelomeningocele and occur as a result of defective primary neurulation whereby mesenchymal tissue enters the neural tube and forms lipomatous tissue. Clinically, lipomyeloceles and lipomyelomeningoceles are characterized by the presence of a subcutaneous fatty mass above the intergluteal crease. The position of the placode-lipoma interface is the main differentiating feature between a lipomyelocele and lipomyelomeningocele. If the placode-lipoma interface lies within the spinal canal, it is characterized as a lipomyelocele ( Fig. 4 ). If the placode-lipoma interface lies outside of the spinal canal because of expansion of the subarachnoid space, it is characterized as a lipomyelomeningocele, ( Fig. 5 ).




Fig. 4


Lipomyelocele. ( A ) Axial diagram. Placode-lipoma interface ( arrow ) is located within the spinal canal. ( B ) Axial T2-weighted MR image shows the placode-lipoma interface ( arrow ) within the spinal canal, characteristic for a lipomyelocele. ( C ) Sagittal T1-weighted MR image shows a subcutaneous fatty mass ( arrow ) and placode-lipoma interface ( arrowhead ) that is located within the spinal canal.

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Mar 21, 2017 | Posted by in NEUROLOGICAL IMAGING | Comments Off on Imaging of Congenital Spine and Spinal Cord Malformations
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