(Radiographics. 2000;20:923-938.)
© RSNA, 2000
US of the Spinal Cord in Newborns: Spectrum of Normal Findings, Variants, Congenital Anomalies, and Acquired Diseases1
Karin M. Unsinn, MD,
Theresa Geley, MD,
Martin C. Freund, MD and
Ingmar Gassner, MD
1 From the Departments of Pediatrics (K.M.U., T.G., I.G.) and Radiology (M.C.F.), Leopold-Franzen-University, Anichstrasse 35, A-6020 Innsbruck, Austria. Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received May 10, 1999; revision requested June 22 and received July 29; accepted August 11. Address correspondence to K.M.U. (e-mail: karin.unsinn@uibk.ac.at).
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Abstract
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Ultrasonography (US) of the spinal cord is performed in newborns with signs of spinal disease (cutaneous lesions of the back, deformities of the spinal column, neurologic disturbances, suspected spinal cord injury due to traumatic birth, and syndromes with associated spinal cord compression). The examination is performed with high-frequency linear- and curved-array transducers in the sagittal and axial planes from the craniocervical junction to the sacrum. Normal variants such as transient dilatation of the central canal and ventriculus terminalis can be demonstrated with US. US allows detection of congenital malformations, such as myelocele or myelomeningocele, spinal lipoma, dorsal dermal sinus, tight filum terminale syndrome, diastematomyelia, terminal myelocystocele, lateral meningocele, caudal regression syndrome, and hydromyelia or syringomyelia. Acquired intraspinal diseases following birth trauma and transient alterations after lumbar puncture can also be detected with US. US can demonstrate the entire spectrum of intraspinal anatomy and pathologic conditions with high geometric resolution. Therefore, US should be considered the initial imaging modality of choice for investigating the spinal cord in newborns.
Index Terms: Diastematomyelia, 30.1454 • Lipoma and lipomatosis, 30.319 • Spina bifida, 30.133 • Spinal cord, abnormalities, 30.13 • Spinal cord, developmental defect, 30.14 • Spinal cord, injuries, 30.45 • Spinal cord, US, 30.1298 • Syringomyelia, 30.1489, 30.368
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:
- Recognize the indications and anatomy of spinal sonography in newborns.
- Identify the sonographic findings of different congenital forms of spinal dysraphism.
- Recognize the sonographic findings of acquired and syndrome-associated forms of spinal abnormalities.
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Introduction
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Knowledge of the embryologic development and normal anatomy of the spinal cord and their variants is a prerequisite for diagnosis of congenital and acquired diseases of this structure. Starting on the 17th day of gestation, the neural plate thickens bilaterally to form the neural folds. During normal development, the neural folds close in toward the midline to form the neural tube. Premature disjunction of neural ectoderm from cutaneous ectoderm results in development of spinal dysraphism (1,2).
Spinal dysraphism is defined as incomplete or absent fusion of midline neural, mesenchymal, and cutaneous structures and can be classified into three categories (3):
1. Spina bifida aperta represents the most severe form of a midline fusion defect with protrusion of non–skin-covered neural tissue. Therefore, in myelocele or myelomeningocele, the contents of the spinal canal protrude through a bony spinal defect and appear as a non–skin-covered neural placode surrounded by leptomeninges.
2. The second category corresponds to a heterogeneous group of lesions designated as occult spinal dysraphism. The common feature of this group is a cleft or tethered spinal cord covered by intact skin (eg, spinal lipoma, dorsal dermal sinus, tight filum terminale syndrome, diastematomyelia). The anomaly is often associated with various cutaneous stigmata (eg, sinus tract, hemangiomatous nevi, hypertrichosis).
3. The third category comprises caudal spinal anomalies that correspond to an association of malformations of the distal spine and spinal cord and hindgut, renal, and genitourinary anomalies. Examples are the heterogeneous syndromes of terminal myelocystocele, lateral meningocele, and caudal regression.
Identification and classification of the preceding malformations has important implications for management and therapy of the lesions as well as prognosis of neurologic function.
Acquired diseases like meningeal tear or spinal cord injury due to birth trauma manifest most often as severe but nonspecific clinical symptoms (4). Therefore, early diagnosis during a bedside examination in the intensive care unit is of great importance.
Ultrasonography (US) is a well-established method of investigating the spinal canal and cord as well as the meningeal coverings in newborns and infants (5,6). In this age group, the incompletely ossified and predominantly cartilaginous spinal arches create an acoustic window that permits transmission of the ultrasound beam. Progressive ossification of the posterior elements of the vertebrae prevents a useful examination in older children.
In this article, we describe the technique of US of the spinal cord in newborns and present the normal findings, variants, congenital anomalies, and acquired diseases seen at US.
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Technique
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We perform US of the spinal cord in newborns and infants with an Ultramark 8 HDI, HDI 3000, or HDI 5000 scanner (Advanced Technology Laboratories, Bothell, Wash) equipped with a 7–12-MHz linear-array transducer and an 8–10-MHz curved-array transducer. Typically, the newborn is examined in the prone position. To examine the craniocervical junction, the neck must be flexed. Routinely, sagittal and axial scans of the spinal cord are obtained from the craniocervical junction to the conus medullaris and cauda equina. In older children with partially ossified posterior elements of the vertebrae and concomitant interference with transmission of the ultrasound beam, paramedian scans may allow sufficient examination of the spinal cord.
Typical indications for spinal US in newborns and infants are skin-covered masses and midline cutaneous malformations of the back (eg, dimple, hemangiomatous or hairy lesion), which are suggestive of associated dysraphic anomalies of the spinal cord. US is performed in syndrome-affected newborns with known congenital spinal canal stenosis to rule out spinal cord compression. Newborns with clinically suspected birth-related spinal cord injury due to meningeal tear or traumatic cord or nerve root lesions are also examined with US. Finally, US is performed in newborns with intracranial hemorrhage to detect subarachnoid lumbar blood collections and in patients who have undergone lumbar puncture to demonstrate cerebrospinal fluid leakage or hemorrhage.
Spinal dysraphism is often associated with tethering of the spinal cord. The US appearance of tethering is a low-lying or blunt-ended conus medullaris due to abnormal fixation of the spinal cord (6). Also, movement of the spinal cord and cauda equina can be evaluated with real-time US with M-mode scanning. Typically, the tethered cord is positioned eccentrically and demonstrates reduced or absent movement.
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Normal Findings
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This section presents the normal anatomy of the spinal canal and its contents as seen on sagittal and axial US scans obtained from the craniocervical junction to the sacrum.
A suboccipital sagittal scan of the craniocervical junction shows the pons, medulla oblongata, and spinal cord as hypoechoic structures with echogenic borders, which are surrounded by the anechoic, cerebrospinal fluid–filled subarachnoid space (Fig 1). The echogenic cerebellar vermis and cerebellar tonsils, which are made visible by echogenic sulci, can be visualized on a median or paramedian sagittal scan. The cisterna magna (cisterna cerebellomedullaris) is an anechoic cerebrospinal fluid collection of varied size caudal to the cerebellum. The echogenic dorsal border of the bony foramen magnum, adjacent to the cisterna magna, may create a shadow across the medulla oblongata. The echogenic clivus can be detected ventral of the medulla oblongata (5).
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Figure 1. Normal anatomy of the spinal canal and its contents in a 10-day-old newborn. Sagittal US scan of the craniocervical junction shows the spinal cord (arrowheads) and central echo complex (arrows), medulla oblongata (2), pons (3), cerebellar vermis and tonsil (4), subarachnoid space (8), vertebral bodies (12), occipital bone (14), and cisterna magna (15).
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On a sagittal scan, the spinal cord is a hypoechoic tubular structure with an echogenic center, the so-called central echo complex (Fig 2), which represents the central canal. At histologic analysis, the central canal corresponds to the border between the myelinated ventral white commissure and the central portion of the anterior median fissure (7). In healthy newborns, the central canal is overgrown with glial fibrils and is not filled with cerebrospinal fluid.
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Figure 2. Normal anatomy of the spinal canal and its contents in a 3-day-old newborn. Sagittal US scan shows the spinal cord (arrowheads) and central echo complex (arrows), nerve roots (5), subarachnoid space (8), and vertebral bodies (12).
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The diameter of the spinal cord varies. It is largest at the cervical and lumbar levels and smallest at the thoracic level (Fig 3). The cervical enlargement gives rise to the nerve roots of the cervical plexus; the lumbar enlargement gives rise to the nerve roots of the lumbar plexus.
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Figure 3. Normal anatomy of the thoracic spinal canal and its contents in a 5-day-old newborn. Sagittal US scan of the thoracic spinal canal shows the spinal cord (arrowheads) and central echo complex (arrows), subarachnoid space (8), arachnoid and pia mater (9), dura mater (10), and vertebral bodies (12).
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The caudal end of the spinal cord corresponds to the conus medullaris (Fig 4), which continues into the filum terminale. In healthy newborns, the tip of the conus medullaris is located between L1 and L2. The tip should not be positioned below L2-3 (8). The filum terminale is a cordlike echogenic structure (Fig 5), which is surrounded by the echogenic roots of the cauda equina. Differentiation of the filum terminale from the nerve roots is sometimes difficult.
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Figure 4. Normal anatomy of the lumbar spinal canal and its contents in a 5-day-old newborn. Sagittal US scan of the lumbar spinal canal shows the spinal cord (arrowheads) and central echo complex (arrows), nerve roots (5), dura mater (10), and vertebral bodies (12).
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Figure 5. Normal anatomy of the lumbar spinal canal and its contents in a 5-day-old newborn. Axial US scan of the spinal canal at the level of L3 shows the nerve roots (5), filum terminale (7), subarachnoid space (8), vertebral body (12), vertebral arch (13), and muscle (16).
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The spinal cord is surrounded by the anechoic cerebrospinal fluid of the subarachnoid space. The arachnoid–dura mater complex of the thecal sac corresponds to the echogenic border of the spinal canal dorsal and ventral to the subarachnoid space.
An axial scan of the spinal cord shows the hypoechoic, oval or round spinal cord with the echogenic central echo complex within the anechoic subarachnoid space. The spinal cord gives rise to the paired dorsal and ventral nerve roots (Fig 6). The spinal cord is fixed by the dentate ligaments, which pass laterally from the spinal cord. The ligaments correspond to transversely oriented, echogenic arachnoid duplications and can be seen in part of the thoracic spinal canal on axial scans. The vertebral bodies of the vertebral column are seen as echogenic structures ventral to the spinal cord. The echogenic vertebral arches produce ventral shadows on axial scans. The paravertebral muscles appear as hypoechoic areas adjacent to the laminae (9) (Fig 7).
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Figure 6. Normal anatomy of the thoracic spinal canal and its contents in a 5-day-old newborn. Axial US scan of the thoracic spinal canal shows the spinal cord (arrowheads) and central echo complex (arrow), nerve roots (5), subarachnoid space (8), dentate ligament (11), vertebral body (12), vertebral arch (13), and muscle (16).
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Figure 7. Normal anatomy of the thoracic spinal canal and its contents in a 5-day-old newborn. Axial US scan of the spinal canal at the level of T12 shows the spinal cord (arrowheads), nerve roots (5), vertebral body (12), vertebral arch (13), and muscle (16).
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Variants
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A number of variations of the normal anatomy of the spinal cord can be easily detected with spinal US. Most of them are incidental findings without clinical symptoms and therefore do not represent pathologic conditions. Some challenging examples of normal variants are transient dilatation of the central canal and ventriculus terminalis.
Transient Dilatation of the Central Canal
Initially, a slight dilatation of the central canal of the spinal cord can be detected in newborns (Fig 8). This seems to be an incidental finding in healthy newborns and disappears mostly during the first weeks of postnatal life.
Ventriculus Terminalis
The ventriculus terminalis is a small, ependyma-lined, oval, cystic structure positioned at the transition from the tip of the conus medullaris to the origin of the filum terminale (Fig 9). This structure has a longitudinal diameter of 8–10 mm and a transverse diameter of 2–4 mm (10). The ventriculus terminalis develops during embryogenesis as a result of canalization and retrogressive differentiation of the caudal end of the developing spinal cord and regresses in size during the first weeks after birth (1). This variant causes no clinical symptoms.
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Figure 9. Ventriculus terminalis in a healthy 7-week-old infant. Sagittal US scan of the lumbar spinal canal shows a ventriculus terminalis (arrowheads). 1 = conus medullaris with central echo complex.
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Congenital Anomalies
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Myelocele and Myelomeningocele
Myelocele or myelomeningocele occurs in two of 1,000 live births, with a slight female predominance. Myelocele and myelomeningocele result from localized failure of fusion of the neural folds dorsally during embryogenesis. Persistence of the open spinal cord (the neural placode) causes derangement in the development of mesenchymal and ectodermal structures. The remnants of the neural ectoderm do not separate consecutively from the cutaneous ectoderm; therefore, the neural placode as well as the leptomeninges remain attached to the skin along the lateral surface of the placode. Because mesenchyme cannot migrate posterior to the neural structures, mesenchymal remnants remain anterolateral to the nervous tissue, resulting in everted pedicles and laminae.
In patients with myelocele, the placode is a flat plaque of neural tissue flush with the plane of the dorsal skin. In patients with myelomeningocele, an expansion of the ventral subarachnoid space displaces the placode dorsally, leading to protrusion of the placode (1) (Fig 10). The lesion affects mostly the lower back with the following frequency distribution: thoracic, 2%; thoracolumbar, 32%; lumbar, 22%; and lumbosacral, 44% (3). Lumbar or sacral myelocele and myelomeningocele are always associated with tethering of the spinal cord (1).
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Figure 10. Thoracolumbar myelomeningocele in an 18-day-old newborn. Sagittal US scan shows a dorsally displaced neural placode (1), dilated subarachnoid space (2), and hypoplastic thoracolumbar spinal cord (arrowheads).
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Clinical symptoms of myelocele and myelomeningocele include severe neurologic disturbances mainly of the lower extremities such as paresis or paralysis and bladder or bowel dysfunction, as well as secondary development of hydrocephalus after repair. Owing to the risk of injury or infection, preoperative imaging of the cele should be avoided. Therefore, the purpose of spinal US in patients with myelocele or myelomeningocele is recognition of associated malformations. These malformations consist of Chiari II syndrome, tethering of the spinal cord, hydromyelia or syringomyelia, diastematomyelia, and arachnoid cyst.
Chiari II syndrome occurs in 99% of patients with myelocele or myelomeningocele. In Chiari II syndrome, the pons, the medulla oblongata, and the cranial part of the cervical spinal cord are displaced downward. The cerebellar vermis herniates through the foramen magnum into the cervical spinal canal (Fig 11); the fourth ventricle is narrowed and positioned low. The cranial part of the cervical spinal cord shows kinking because of the normal fixation of the spinal cord by spinal ligaments (Fig 12).
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Figure 11. Chiari II syndrome in a 3-week-old newborn with myelomeningocele. Sagittal US scan of the craniocervical junction shows an abnormal caudally positioned cerebellar vermis (arrowheads). 1 = cerebellar hemisphere, arrows = occipital bone.
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Figure 12. Chiari II syndrome in a 1-month-old infant with myelomeningocele. Sagittal US scan of the craniocervical junction shows kinking (arrowheads) of the cervical spinal cord (1).
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Tethering of the spinal cord occurs in 70%–90% of patients. In tethering of the spinal cord, abnormal dorsal fixation of the spinal cord adjacent to the arches of the vertebrae is seen when the patient is in the prone position (Fig 13) (6). In addition, failure of pulsatile movement of the spinal cord and nerve roots can be demonstrated with M-mode scanning.
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Figure 13. Tethering of the spinal cord in a 2-day-old newborn with lumbosacral myelomeningocele. Sagittal US scan shows a dorsally displaced thoracolumbar spinal cord (arrowheads) due to tethering.
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Hydromyelia or syringomyelia occurs in 40%–80% of patients. These conditions result from disturbance of cerebrospinal fluid circulation. Hydromyelia and syringomyelia always occur cranial to the placode (Fig 14) and may be focal or involve the entire spinal cord. If untreated, these conditions may cause rapid development of scoliosis.
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Figure 14. Hydromyelia in a 1-month-old infant in whom lumbar myelomeningocele and thoracic hydromyelia were noted on the 1st day of life. Sagittal US scan shows a dilated central canal (arrows).
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Diastematomyelia occurs in 20%–40% of patients. This condition represents duplication of the spinal cord cranial or caudal to the cele.
Arachnoid cysts occur in 2% of patients. Typically, arachnoid cysts result from a developmental deficiency during formation of the arachnoid or dura mater with a subdural location. Larger cysts may displace and compress the spinal cord (Fig 15).
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Figure 15. Arachnoid cyst in a 17-day-old newborn with lumbar meningocele. Sagittal US scan shows the thoracic spinal cord (arrowheads) displaced ventrally and compressed by a cyst (1).
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In addition, cranial US can show associated malformations of the brain: hydrocephalus and hypoplasia or aplasia of the corpus callosum.
A common complication after repair of a myelocele or myelomeningocele is tethering of the spinal cord due to postoperative scarring or a constricting dura mater. Symptoms of tethering are deterioration of neurologic function and development of scoliosis. Spinal US shows a deformed, dorsally attached neural placode (Fig 16) with reduced pulsatile movement of the placode and the attached nerve roots. Neurologic deterioration may also be caused by spinal cord compression due to associated lipomas, dermoid cysts, or spinal cord ischemia.
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Figure 16. Tethering of the spinal cord in a 4-month-old infant who underwent surgical correction of a lumbosacral myelomeningocele on the 2nd day of life. Axial US scan shows a deformed and displaced neural placode (1) and nerve roots (2) and a dilated subarachnoid space (3).
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Spinal Lipoma
A spinal lipoma is an intraspinal mass of fat and fibrous tissue that occurs in continuity with the adjacent spinal cord. Spinal lipomas are the most common type of occult spinal dysraphism and are classified as follows (1): lipomyelocele or lipomyelomeningocele (84%), fibrolipoma of the filum terminale (12%), and intradural lipoma (4%). Spinal lipoma manifests as a skin-coated subcutaneous back mass, which is sometimes associated with hemangiomatous or hairy lesions and occurs mainly in the lumbosacral region. Neurologic symptoms are sensory deficiencies, paresis, and neurogenic bladder dysfunction.
Premature separation of the superficial ectoderm from the neural ectoderm induces the development of lipomyelocele or lipomyelomeningocele. The not-yet-closed neural tube will be filled with mesenchyme, which further differentiates into fat (11). In lipomyelocele and lipomyelomeningocele, the lipoma lies adjacent to the cleft spinal cord and extends into the central canal of the spinal cord and into the spinal canal, causing tethering of the neural tissue. Dorsally, the lipoma is continuous with the subcutaneous fat (3) and covered by intact skin. Lipomyelocele is always associated with spina bifida and often associated with segmentation anomalies of the vertebrae.
Spinal US shows an echogenic intraspinal mass adjacent to the deformed spinal cord (Fig 17). Dorsally, the mass is contiguous with slightly hypoechoic subcutaneous fat. The spinal cord is cleft dorsally, has an undulating deformed contour, and is tethered. Owing to failure of dorsal fusion of the spinal cord, the ventral and dorsal nerve roots leave the neural placode ventrally. In patients with lipomyelomeningocele, a dilated subarachnoid space can be demonstrated. Associated malformations like hydromyelia or syringomyelia can be detected easily with spinal US.
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Figure 17. Lumbosacral lipomyelocele with associated cutaneous hemangioma in a 6-week-old infant. Sagittal US scan of the lumbosacral region shows an echogenic lipoma (1) adjacent to the dorsal surface of a deformed lumbar spinal cord (2). The lipoma is contiguous with and more echogenic than the subcutaneous fat (3).
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Dorsal Dermal Sinus
A dorsal dermal sinus is an epithelium-lined tract from the skin to the spinal cord, cauda equina, or arachnoid. Such sinuses are predominantly located in the lumbosacral region and less often in the occipital region (12). Dorsal dermal sinus is caused by incomplete separation of the superficial ectoderm from the neural ectoderm at a circumscribed point only, resulting in a focal segmental adhesion. Later during embryogenesis, the spinal cord ascends relative to the spinal canal and stretches the adhesion into a long, tubular tract. There is no genetic predominance.
Dorsal dermal sinus manifests as a small dimple or pinpoint ostium, which is often associated with an area of hyperpigmented, angiomatous skin or hypertrichosis and occurs in a midline location or rarely in a paramedian location (13). Soft-tissue asymmetry and bone anomalies are common findings. Typical complications are infections such as recurrent meningitis, epidural or subdural abscess, and intramedullary spinal cord abscess. In particular, dorsal dermal sinus occurring in a paramedian location is often associated with an intraspinal dermoid or epidermoid cyst, which causes compression of neural structures with neurologic symptoms. For these reasons, dorsal dermal sinus has to be differentiated from simple sacral dimple or pilonidal sinus: The latter two anomalies do not extend to neural structures.
Scrupulously performed spinal US shows the entire length of the tract from the skin to the spinal cord (14). Within the subcutaneous fat, the tract appears slightly hypoechoic and is sometimes hardly detectable with US. Conversely, the tract is clearly demonstrated in the anechoic, cerebrospinal fluid–filled subarachnoid space as an echogenic structure (Fig 18).
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Figure 18. Dorsal dermal sinus in a 4-day-old newborn. Sagittal US scan of the lumbar spinal canal shows an epithelium-lined tract (arrowheads) from the skin to the spinal cord (1). The tract is detectable as an echogenic band within the anechoic subarachnoid space. In the hypoechoic subcutaneous fat, the tract is hardly visible.
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Tight Filum Terminale Syndrome
Tight filum terminale syndrome is caused by incomplete involution of the distal spinal cord during embryogenesis. The incomplete involution leads to development of an abnormally thickened filum terminale, which may be associated with lipomas or cysts within the filum (1,3). Tight filum terminale syndrome is always associated with tethering of the spinal cord and an abnormally positioned conus medullaris below L2-3 (normal range, L1-L2) (15).
Clinical symptoms are due to stretching of the spinal cord with resulting vascular insufficiency at the level of the conus medullaris. These symptoms can occur at any age, may be unspecific, and consist of neurologic deficiencies, pain or dysesthesia, and bladder or bowel dysfunction. Associated vertebral body deformities and spina bifida are common findings.
Spinal US shows an abnormally thickened filum terminale (Fig 19), sometimes in combination with a centrally located small cyst or lipoma. By definition, the diameter of the filum terminale exceeds 2 mm (normal range, 0.5–2 mm) at the level of L5-S1. Owing to the presence of tethering, the tip of the conus medullaris is located below L2-3, and reduced or absent spinal cord movements are demonstrated (14).
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Figure 19. Tight filum terminale syndrome in a 1-month-old infant. Lumbosacral sagittal US scan shows the tip of the conus medullaris positioned normally between L1 and L2, but the filum terminale is thickened (arrowheads).
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Diastematomyelia
Diastematomyelia is characterized by a sagittal cleft in the spinal cord, which is divided into two asymmetric hemicords in most cases. Each hemicord has an eccentric central canal and gives rise to the ipsilateral dorsal and ventral nerve roots. In patients with a fibrous, cartilaginous, or osseous septum, each hemicord has a separate arachnoidal and dural sheath, whereas a single sheath surrounds both hemicords when no septum is present (1,3). In most cases, the hemicords reunite caudal to the cleft. Occasionally, the cleft extends unusually low and the hemicords remain distinct, with two separate coni medullaris. The conus medullaris has an abnormally low position, and thickening of the filum terminale may be present.
Diastematomyelia develops very early during embryogenesis and may be caused by an adhesion between the ectoderm and endoderm with splitting of the early notochord. The lumbar spinal cord is predominantly affected, and most cases occur in females. Patients with diastematomyelia present with cutaneous malformations on the back (eg, nevi, hairy patches, or hemangiomas). There is a high prevalence of associated congenital anomalies of the legs (eg, clubfoot), severe scoliosis due to segmentation anomalies of the spine, and spina bifida with ensuing neurologic symptoms.
US performed in the axial plane typically shows both hemicords in cross section, each with a central canal and ipsilateral nerve roots (Fig 20). In patients with an osseous septum between the hemicords, examination of the spinal cord is nearly impossible at the level of the septum because of the shadow it produces at US. Spinal US may also demonstrate associated malformations like hydromyelia or syringomyelia and thickened filum terminale (16).
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Figure 20. Diastematomyelia in a 2-day-old newborn. Axial US scan of the lumbar spinal canal shows left (1) and right (2) hemicords within a dilated spinal canal (arrows). Each hemicord has an eccentric central canal. The dentate ligament can also be seen (arrowhead).
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Terminal Myelocystocele
Terminal myelocystocele corresponds to an association of posterior spina bifida, meningocele, tethered spinal cord with hydromyelia, and cystic dilatation of the distal central canal. A bifid spinal cord is surrounded by the dilated subarachnoid space of the meningocele, which protrudes through a spina bifida in the subcutaneous fat. The central canal of the spinal cord demonstrates hydromyelia, terminates in a large cyst distal to the meningocele, and is coated with fat. The subarachnoid space of the meningocele communicates with the subarachnoid space of the spinal canal but not with the terminal cyst (1,3,14).
Terminal myelocystocele develops early during embryogenesis as a result of disturbance of cerebrospinal fluid circulation with resulting dilatation of the ventriculus terminalis and disruption of the dorsal mesenchyme. Patients with terminal myelocystocele present with a skin-covered mass in the lumbosacral region. Associated anomalies of the anorectal system, genitourinary tract, and vertebrae such as anal atresia, cloacal exstrophy, scoliosis, and sacral agenesis are common.
At spinal US, sagittal scans show the spinal cord surrounded dorsally and ventrally by a dilated subarachnoid space; the nerve roots leave the spinal cord ventrally (Fig 21a, 21b). Axial scans show a bifid dorsal spinal cord and the dilated subarachnoid space (Fig 21c) as well as associated hydromyelia.
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Figure 21a. Terminal myelocystocele in a 2-month-old infant. (a) Sagittal US scan obtained with a curved-array transducer shows the whole extent of a terminal myelocystocele, with a deformed and displaced spinal cord (1) surrounded dorsally and ventrally by a dilated subarachnoid space (2). 3 = nerve roots. (b) Oblique US scan obtained more caudally with a linear-array transducer shows the nerve roots (3) leaving the deformed spinal cord (1) ventrally. 2 = subarachnoid space. (c) Axial US scan shows posterior spina bifida (1) and the dilated subarachnoid space (2).
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Figure 21b. Terminal myelocystocele in a 2-month-old infant. (a) Sagittal US scan obtained with a curved-array transducer shows the whole extent of a terminal myelocystocele, with a deformed and displaced spinal cord (1) surrounded dorsally and ventrally by a dilated subarachnoid space (2). 3 = nerve roots. (b) Oblique US scan obtained more caudally with a linear-array transducer shows the nerve roots (3) leaving the deformed spinal cord (1) ventrally. 2 = subarachnoid space. (c) Axial US scan shows posterior spina bifida (1) and the dilated subarachnoid space (2).
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Figure 21c. Terminal myelocystocele in a 2-month-old infant. (a) Sagittal US scan obtained with a curved-array transducer shows the whole extent of a terminal myelocystocele, with a deformed and displaced spinal cord (1) surrounded dorsally and ventrally by a dilated subarachnoid space (2). 3 = nerve roots. (b) Oblique US scan obtained more caudally with a linear-array transducer shows the nerve roots (3) leaving the deformed spinal cord (1) ventrally. 2 = subarachnoid space. (c) Axial US scan shows posterior spina bifida (1) and the dilated subarachnoid space (2).
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Lateral Meningocele
A lateral meningocele is a cerebrospinal fluid–filled protrusion of dura mater and arachnoid that extends laterally through an enlarged intervertebral foramen into the paraspinal, intrathoracic, or retroperitoneal region. Lateral meningoceles occur unilaterally or bilaterally and as solitary or multiple lesions, mainly in the thoracic or lumbar spine. Patients may be asymptomatic or have slight sensory or motor deficiencies and sometimes develop severe scoliosis. Lateral meningocele may be associated with mesenchymal disorders such as Marfan or Ehlers-Danlos syndrome or neurofibromatosis (1,2).
Spinal US shows a cystic mass in an expanded spinal canal (Fig 22). The adjacent spinal cord is displaced and may be compressed by the meningocele. Secondary bone abnormalities such as erosion of vertebral bodies, thinning of vertebral arches, and enlarged intervertebral foramina due to mass effect can be demonstrated with spinal radiography, computed tomography, or magnetic resonance imaging.
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Figure 22. Thoracic lateral meningocele in a 1-day-old newborn with severe cerebral malformations and scoliosis. Sagittal US scan shows a cystic dilated subarachnoid space (1) with protrusion of the meninges through the intervertebral foramen. The spinal canal (arrows) is enlarged, and the spinal cord (2) is displaced.
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Caudal Regression Syndrome
Caudal regression syndrome corresponds to a spectrum of anomalies of the caudal end of the trunk. Malformations vary from isolated partial agenesis of the sacrococcygeal spine to more severe deformities like sirenomelia (17,18). Associated malformations are imperforate anus, genitourinary anomalies, and renal dysplasia. The frequency of caudal regression syndrome is 1:7,500 births with no gender predominance but with an association with a diabetic mother. Caudal regression syndrome is due to abnormal retrogressive differentiation of the developing spine and spinal cord as well as disturbance of the caudal mesoderm, with failed development of the lumbar and sacral spine probably caused by hyperglycemia or teratogenic agents (3).
The clinical presentation demonstrates a wide spectrum of abnormalities. Sacral agenesis is always associated with narrowing of the hips, hypoplastic gluteal muscles, and a flat intergluteal cleft. Orthopedic problems range from isolated deformities of the feet (eg, clubfoot) to complex deformities of the lower extremities (Fig 23). In patients with sirenomelia, complete lumbosacral agenesis and fused lower extremities are present (Fig 24a, 24b). Genitourinary deformities include kidney malformations (agenesis or hydronephrosis) and various forms of duplication of the müllerian ducts. Neurologic deficiencies such as sensorimotor paresis or urinary bladder dysfunction can occur.
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Figure 23a. Caudal regression syndrome in a 2-month-old infant. (a) Radiograph shows amelia of the right lower extremity. (b) Axial US scan shows the lumbar spinal cord (1) in cross section. The left-sided nerve roots are present (arrows), but the right-sided nerve roots are absent.
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Figure 23b. Caudal regression syndrome in a 2-month-old infant. (a) Radiograph shows amelia of the right lower extremity. (b) Axial US scan shows the lumbar spinal cord (1) in cross section. The left-sided nerve roots are present (arrows), but the right-sided nerve roots are absent.
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Figure 24a. Caudal regression syndrome in a 1-day-old newborn with sirenomelia. (a) Radiograph shows aplasia of the lumbar spine and sacrum. (b) Radiograph shows fusion and severe deformation of the lower extremities. (c) Sagittal US scan of the thoracolumbar region shows a blunt-ending thoracic spinal cord (1) at the level of T11.
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Figure 24b. Caudal regression syndrome in a 1-day-old newborn with sirenomelia. (a) Radiograph shows aplasia of the lumbar spine and sacrum. (b) Radiograph shows fusion and severe deformation of the lower extremities. (c) Sagittal US scan of the thoracolumbar region shows a blunt-ending thoracic spinal cord (1) at the level of T11.
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Figure 24c. Caudal regression syndrome in a 1-day-old newborn with sirenomelia. (a) Radiograph shows aplasia of the lumbar spine and sacrum. (b) Radiograph shows fusion and severe deformation of the lower extremities. (c) Sagittal US scan of the thoracolumbar region shows a blunt-ending thoracic spinal cord (1) at the level of T11.
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Various imaging methods allow differentiation of two groups of patients with caudal regression syndrome according to the configuration and level of the conus medullaris (3). In group 1, spinal US demonstrates a blunt, deformed conus medullaris that terminates above the normal level of L1 (Fig 24c) and is sometimes associated with a dilated central canal or a cerebrospinal fluid–filled cyst at the lower end of the conus. In group 2, the conus medullaris is elongated and tethered by a thickened filum terminale or intraspinal lipoma and ends below L1. Patients in group 1 have major sacral deformities, whereas neurologic disturbances are more severe in group 2 (3).
Hydromyelia and Syringomyelia
Hydromyelia consists of localized or generalized dilatation of the central canal of the spinal cord. Syringomyelia corresponds to paracentral cavities lined by gliotic parenchyma due to laceration of the ependyma covering the central canal with ensuing permeation of cerebrospinal fluid into the circumferential spinal cord parenchyma. Congenital hydromyelia or syringomyelia may be the result of dysregulation of cerebrospinal fluid circulation or a variant of dysraphic malformations (1).
Clinical symptoms of hydromyelia and syringomyelia include sensory disturbances, muscular weakness, spastic paraparesis, and scoliosis. Typically, symptoms occur late in adolescence or in early adulthood. Spinal US shows dilatation of the central canal of the spinal cord (Fig 25). In newborns with hydromyelia or syringomyelia, associated malformations such as myelomeningocele, Chiari II syndrome, and diastematomyelia may be present and are easily detectable with US.
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Figure 25. Syringomyelia in a 2-day-old newborn. Sagittal US scan of the thoracolumbar spinal canal shows a syrinx (1) at the level of T11-T12 and a dilated central canal (arrowheads).
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Acquired Diseases
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Spinal Cord Injury and Intraspinal Hematoma
Birth trauma to the spinal cord is a serious complication of delivery. Common predisposing factors are intrauterine malposition of the fetus, mainly breech presentation, or use of forceps (4). The mechanism of injury is excessive longitudinal traction of the spinal cord combined with hyperextension, hyperflexion, or torsion. Towbin (19) described three main pathologic patterns of spinal cord injury in newborns: (a) meningeal damage with epidural hemorrhage, (b) laceration or avulsion of spinal nerve roots, and (c) laceration and distortion of the cord to complete cord transection.
Clinical symptoms are nonspecific; newborns may have severe peripartal asphyxia, generalized hypotonia, absent tendon reflexes, or paradoxical breathing. Sometimes only a history of a difficult extraction suggests the diagnosis.
US allows detection of epidural or subdural (subarachnoid) hemorrhage (Fig 26) as well as complete spinal cord transection (4,20). Direct signs such as edema, venous congestion, or hemorrhage increase the echogenicity of the spinal cord; indirect signs such as displacement of the spinal cord due to hemorrhage also enable better detection with US. Follow-up examinations reveal resorption of intraspinal blood collections, changes in cord caliber, and persistent increased echogenicity due to early glial proliferation in patients with myelomalacia (21).
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Figure 26a. Erb paresis of the left upper extremity and the left hemidiaphragm in a 3-day-old newborn after traumatic birth. (a) Radiograph shows an elevated hemidiaphragm on the left side. (b) Sagittal US scan of the thoracic spinal cord shows ventral displacement of the dura mater (arrowheads) by an epidural fluid collection (blood) (1), which was due to a meningeal tear.
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Figure 26b. Erb paresis of the left upper extremity and the left hemidiaphragm in a 3-day-old newborn after traumatic birth. (a) Radiograph shows an elevated hemidiaphragm on the left side. (b) Sagittal US scan of the thoracic spinal cord shows ventral displacement of the dura mater (arrowheads) by an epidural fluid collection (blood) (1), which was due to a meningeal tear.
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Syndrome-associated Spinal Cord Compression
US can also be used as the initial imaging method during the first days of life in syndrome-affected newborns with known congenital spinal canal stenosis to rule out spinal cord compression. In syndrome-affected newborns, spinal cord compression due to congenital narrowing of the spinal canal may cause unspecific neurologic symptoms ranging from muscular deficiencies to respiratory insufficiency. In the literature, several syndromes with malformation of the cervical vertebrae resulting in respiratory distress and death have been reported. In particular, patients with Larsen syndrome or diastrophic dysplasia have spinal canal narrowing due to kyphosis, slightly displaced vertebral bodies, and hypoplasia or dysraphism of posterior elements (22).
Cervical vertebral body deformities, odontoid hypoplasia, and subluxation of C1 and C2 are characteristic findings in patients with spondyloepiphyseal dysplasia, Morquio syndrome, or metatropic dysplasia (23). In patients with achondroplasia, narrowing of the foramen magnum results in compression of the craniocervical junction (24). Flexion of the neck leads to severe compression of the spinal cord and spinal arteries; such compression may result in respiratory insufficiency and death (25).
In our clinical experience, spinal US of one patient with metatropic dysplasia showed severe osseous narrowing of the spinal canal. Secondarily, the subarachnoid spaces were obliterated at the level of C1–C2 and the spinal cord was moderately compressed (Fig 27). In one patient with osseous dysplasia, a markedly narrowed subarachnoid space at the craniocervical junction was detectable with US.
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Figure 27a. Spinal cord compression in a 6-day-old newborn with metatropic dysplasia. Sagittal (a) and axial (b) US scans of the craniocervical junction show spinal cord compression due to severe narrowing of the cervical spinal canal (arrows).
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Figure 27b. Spinal cord compression in a 6-day-old newborn with metatropic dysplasia. Sagittal (a) and axial (b) US scans of the craniocervical junction show spinal cord compression due to severe narrowing of the cervical spinal canal (arrows).
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Iatrogenic Lesion
Laceration of the dura mater and leptomeninges during lumbar puncture may lead to development of a cerebrospinal fluid leak. The ensuing circumferential epidural or subdural cerebrospinal fluid collection can compress the nerve roots of the cauda equina. Patients are often asymptomatic, and the cerebrospinal fluid collection disappears within a few days. Spinal US can demonstrate the narrowed nerve roots due to the surrounding space-occupying cerebrospinal fluid collection (Fig 28).
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Figure 28a. Cerebrospinal fluid leak in a 5-week-old infant after lumbar puncture. Sagittal (a) and axial (b) US scans of the lumbosacral spinal canal show a circumferential epidural cerebrospinal fluid collection (1), which was due to laceration of the dura mater and leptomeninges. The dura (arrowheads) lies close to the narrowed cauda equina (2).
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Figure 28b. Cerebrospinal fluid leak in a 5-week-old infant after lumbar puncture. Sagittal (a) and axial (b) US scans of the lumbosacral spinal canal show a circumferential epidural cerebrospinal fluid collection (1), which was due to laceration of the dura mater and leptomeninges. The dura (arrowheads) lies close to the narrowed cauda equina (2).
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Conclusions
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US of the spinal cord and spinal canal is a reliable method of examining newborns and young infants. Indications for early US examination during the newborn period are the following clinical findings: cutaneous lesions of the back (eg, hypertrichosis, sacral sinus, subcutaneous lipoma); deformities of the spinal column (eg, scoliosis, malformations of the sacrum); neurologic disturbances (eg, paresis, neurogenic bladder or bowel dysfunction); suspected spinal cord injury due to traumatic birth; and syndromes with associated spinal cord compression.
Early performed US allows an exact examination of the spinal canal and its contents and enables one to rule out significant pathologic conditions. In patients with normal findings, no further imaging examinations are necessary. In patients with spinal malformations at US, a further examination can be performed at the time of the elective surgical intervention. In addition, in complex spinal malformations, the role of US is to allow detection of associated anomalies.
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Abstract
LEARNING OBJECTIVES
