With pronounced forward flexion, there is a distinct tendency for the infant’s upper cervical spine to appear dislocated or subluxed(2). This is related to generalized laxity of the ligaments in the infant and horizontal positioning of the apophyseal joints. In the older child and adult, the joints become more vertical in position, but in the infant and young child their horizontal attitude predisposes to anterior displacement of the upper vertebral bodies, one on another. Most often, this involves C2 on C3, but pseudodislocation of the cervical spine can be seen down to the C4-5 level (Fig. 8.7).

Since the spine must be flexed to produce this pseudoabnormality, the soft tissues anterior to the spine also usually are distorted, and with the airway so buckled, the problem just becomes more confusing. Nonetheless, it is important to appreciate these changes because somewhat similar displacement of C2 on C3 can be produced by a hangman’s fracture of C2. Differentiation of the two conditions can be accomplished by use of the posterior cervical line(2). This line, drawn from the cortex of the spinous tip of C1 to the same location on C3, should touch or come within 1-1.5 mm of the anterior cortex of the spinous tip of C2 (Fig. 8.8). It remains normal with pseudosubluxation, but when the hangman’s fracture is present the line misses the anterior cortex of C2 by 2 mm or more.

Wedging of C3, and sometimes C4, is another normal variation that commonly is seen in infants and young children(3). It also is associated with normal hypermobility through this area, and it is the chronic, hammering impingement of C2 on C3 that causes C3 to under grow anteriorly. As a consequence, it becomes wedged (Fig. 8.9), and the configuration should not be misinterpreted for a compression fracture(3). Anterior compression fractures of C3 are uncommon in any age group, but if there still is doubt, computed tomography (CT) should be performed because it can clearly establish whether a fracture through the vertebral body exists.

The distance between the anterior arch of C1 and the odontoid process often appears unduly wide in infants. In adults, maximum normal distance is in the neighborhood of 2 to 2.5 mm, but in young infants, it frequently is 3 mm and can range as high as 4 to 5 mm and still be normal. This latter measurement occurs in less than 5% of cases. Normally, no matter what the original configuration this space, if normal, it does not increase by more than 2 mm during flexion.

Since CT was introduced, it has become more and more apparent that normal clefts exist in the anterior and posterior
(4, 5) portions of the ring of C1. These clefts can be identified as being normal and innocuous by their smoothly corticated edges (Figs. 8.3 and 8.10). They must be differentiated from fractures that occur through the ring of C1 in the form of the Jefferson fracture. Fractures generally demonstrate thin radiolucent lines with nonsclerotic bony edges.

The normal spinal cord follows the same variations in diameter as does the spinal canal; it is wider in the cervical
region than in the thoracic area. Also recall that the spinal cord ends lower in the newborn infant, but as the infant grows older, the cord migrates towards the head, eventually ending at about L1(6,7,8). This level usually is reached in the first few months of life.

The spinal cord is readily evaluated with ultrasound and MRI in infants, and ultrasound is especially useful in the neonate. Normal findings are illustrated in Figure 8.11. On the sagittal view, the normal spinal cord produces three echogenic lines, the outer two of which represent the anterior and posterior aspects of the cord. The cord itself is hypoechoic, and within it lies the third line, the echogenic central canal. The normal conus tapers smoothly and becomes continuous with the filum terminale. Below this level are the fibers of the cauda equina that produce linear echogenicities that blend together and almost totally fill the arachnoid space. Occasionally, one encounters dilation of the distal-most portion of the central canal. The configuration is usually somewhat oval, and the dilated structure is called the “ventriculus terminalis”(9,10,11,12). It is a normal finding not to be interpreted for some pathologic problem (Fig. 8.12).

A problem often arises in terms of numbering the vertebral bodies when ultrasound is being used. It has been suggested that the angle that occurs between the lumbar and sacral portions of the spine is consistent and can be used as a marker(13). In other cases, one may match the echogenic vertebra with those seen on plain films and thereby obtain accurate numbering of the vertebral bodies.

Many of the foregoing normal findings can cause problems with diagnosis and differentiation from pathologic conditions. A more comprehensive review(14) of these problems is available.

Spondylolysis and subsequent spondylolisthesis are seldom seen on a congenital basis in infants. If, however, they should occur, severe curvature abnormalities may develop (Fig. 8.15). In older children, the problem is encountered more frequently, and primarily in the lumbar spine. There often is debate as to whether the lesion is congenital or acquired, but most likely it is acquired. However, it also may be, as I have noticed, that the pars interpeduncularis is thinner than usual in these patients. As a result, it would be more susceptible to subclinical or overt trauma. Reactive marrow changes have been demonstrated in the adjacent pedicles with MRI(1), and increased bone activity has been noted with nuclear scintigraphy using SPECT imaging(2, 3). All of this supports a traumatic, rather than a congenital origin. It is a lesion of active children(4), especially those who are athletic, and place excessive strain on the lumbar spine.

The degree of subsequent slippage of the upper vertebral body varies, and while usually the condition is painful(2, 5), it is surprising how often it is discovered as an incidental finding. It is a relatively common cause of low back pain in children, and associated spinal nerve root entrapment has been demonstrated(6). If only a defect exists, the term “spondylolysis” is used, but if there is associated anterior displacement of the upper vertebral body, the condition is called “spondylolisthesis.” The defect usually is visible on lateral view but is more exquisitely demonstrated on oblique view (Fig. 8.17). The findings also are vividly demonstrable with CT (Fig. 8.18).

The next most common place for spondylolysis to occur is at the C2 level(7, 8). It is questionable in many cases, however, whether the finding is completely congenital or actually the result of trauma and representative of a missed hangman’s fracture(9). One useful rule in differentiating the two is that, with congenital defects, the margins of the defect are smooth and sclerotic (Fig. 8.19), and the neural arch usually is deformed(10). It is not deformed when the defect is due to a hangman fracture. Congenital defects usually are stable on flexion-extension views, because the defect is replaced by fibrous or cartilaginous tissue. Familial cases have been reported(11).

When a posterior neural arch defect is due to a hangman fracture, the defect is narrow, sharp, and shows no sclerosis of the defect edges. The fracture is unstable and will require surgical intervention. In my experience, hangman fractures of C2 are more common than congenital defects, but they frequently go unnoticed (Fig. 8.20). Because they often are asymptomatic(12), they often are not initially detected, and also for this reason, others(13), as do I, believe that most of these defects are posttraumatic.

Coronal cleft vertebra frequently is found as an incidental finding and usually involves the lumbar vertebrae. Coronal cleft vertebrae can be seen singly or multiply and can occasionally extend into the thoracic region (Fig. 8.21). The defect probably results from tardy union of the anterior and posterior ossification centers.

Coronal cleft vertebrae have been documented with conditions such as imperforate anus, VATER syndrome, spinal meningocele, and chondrodystrophia calcificans, but they are probably just as frequently encountered in the absence of these conditions and in normal infants. Consequently, one must be cautious in assigning any special significance to this anomaly. The clefts usually disappear as the infant grows older, and it is unusual to encounter them after 6 to 12 months of age. Coronal cleft vertebra is more common in males than in females and is common in a number of syndromes(1).

Occipitalization of C1, with or without associated basilar invagination and platybasia, is not usually a problem in the newborn infant. Problems related to these anomalies usually arise later in childhood. Extensive fusion-segmentation anomalies are seen with the Klippel-Feil syndrome and are seen in the neonate. This problem is very heterogenous(1), but most infants show marked shortening of the neck, with or without torticollis. Radiographs demonstrate extensive fusion-segmentation and curvature anomalies of the cervical, and at times, the upper thoracic spine (Fig. 8.22A). In some cases, associated upward rotation of the scapula also occurs and results in the so-called Sprengel’s deformity (Fig. 8.22B). Rib anomalies also are occasionally encountered, and the Klippel-Feil syndrome can be associated with congenital deafness, renal agenesis, and other anomalies.

Another relatively constant feature of this complex of anomalies is the omovertebral bone. This structure can be seen in the ligament extending from the spine to the abnormally positioned scapula in those patients with associated Sprengel’s deformity (Fig. 8.22C). Usually, the cervical spinal cord is normal even though the spinal anomalies may appear alarming. However cord abnormalities can occur(2). In mild cases, only minimal deformity of the cervical vertebral bodies may be seen and no clinical abnormality is detectable. However, neurologic deficits can develop in adulthood(3, 4).

Congenital absence of the odontoid is rare, and absence of the laminal arches and other anomalies were discussed previously. A bifid odontoid is the result of lack of fusion of the two ossification centers of the odontoid(5). Hypoplasia of the odontoid is associated with ligament underdevelopment and laxity and formation of the os odontoideum(6). The os odontoideum is an overgrown normal os terminale which overgrows when the dens is hypoplastic(6). It also can be acquired after trauma(7, 8). This occurs in infancy but is rare. In infancy in these cases blood supply to the dens is disrupted with severe upper spinal injuries and the dens fails to grow to normal proportions. It then becomes hypoplastic and as such induces the os terminale, on a compensatory basis, to overgrow and form an acquired os odontoideum. In these cases, as apposed to when the os odontoideum is congenital there are no other anomalies of the upper cervical spine. With a congenital os odontoideum, anomalies are numerous and often very bizarre (Fig. 8.23). The os odontoideum can fuse with the anterior arch of C1, and the entire complex of findings is more common in syndromes such as trisomy 21, spondyloepiphyseal dysplasia, and a variety of chondrodystrophies(6). When the posterior arch of C1 is severely hypoplastic or absent, hypermobility is profound (Fig. 8.24). In terms of deficiencies the posterior arch of C1 it should be noted that isolated defects are most common at this level (Fig. 8.25). Furthermore, even though they may appear bizarre and alarming, they are stable unless they are associated with a hypoplastic dens.

There is a wide gamut of lower lumbar and sacral spine abnormalities ranging from absence to mild hypoplasia. Hypoplasia may involve the entire sacrum or be more pronounced on one side. In the more severe cases of sacral agenesis, the lower lumbar spine is also usually absent. Absence of the spine above T11 or T12 is usually incompatible with life, and in these more severe cases the lower extremities are often fused in the so-called mermaid deformity. Extensive genitourinary and gastrointestinal anomalies (ectopic anus) are commonly present in such cases. Both of the lower extremities may be absent or underdeveloped, and the entire complex has been referred to as the caudal regression syndrome. These abnormalities are more frequently seen in infants delivered of diabetic mothers.

Generalized sacral hypoplasia, especially if mild, may go unnoticed but in later life may lead to various degrees of bowel, bladder, or motor impairment. In sacral agenesis, on the other hand, neurologic deficit is more profound, and associated clubfoot deformity, wasting of the muscles of the lower extremities, and incontinence of the urinary and anal sphincters are seen. Neurologic deficit in these cases results from underdevelopment of the corresponding nerve roots and distal spinal cord. Innervation usually is intact to the L5-S1 level and, as a result, development of the thigh muscles
is relatively normal. This leads to a tapered or coneshaped appearance of the lower extremities.

Roentgenographically, the sacral anomalies are readily appreciated (Fig. 8.26). The pelvic bones are more closely apposed than normal, and the pelvis often becomes somewhat contracted. Intraspinal lipomas can co-exist, and these infants frequently show cutaneous abnormalities such as tufts of hair, dimples, and subcutaneous lipomas.

Meningocele and meningomyelocele are common abnormalities of the spinal cord and meninges. Meningocele denotes herniation of the meninges only; in meningomyelocele, the sac also contains the spinal cord and nerve roots. Both abnormalities are commonly associated with lacunar skull and the Arnold-Chiari malformation. Most commonly, meningocele and meningomyelocele are encountered in the lumbosacral region, and next most commonly they occur in the lower thoracic spine. Least frequent are cervical defects, and in rare instances, these lesions may be contiguous with a midline posterior occipital encephalocele. Multiple defects also can occur.

There is no difficulty in clinically recognizing this abnormality, because the widened spinal canal and numerous vertebral defects and deformities are readily apparent roentgenographically (Fig. 8.27). In some cases, the neural arches are so defective that only vague vestiges remain. Some of these rudimentary bony structures are so misplaced that one might misinterpret them as representing the bony spicule of diastematomyelia. In other, less common instances there may be a soft tissue bulge only and little in the way of vertebral body or neural arch abnormality. In more advanced cases, the anterior aspect of the vertebral bodies becomes rounded (Fig. 8.27B). These patients can demonstrate a severe lumbar kyphosis that now is corrected surgically in early infancy(1). This is performed to avoid later severe scoliotic and kyphotic curvature problems.

It is not possible to determine the precise level of communication from plain roentgenograms because it does not necessarily correspond to the area of most severe deformity. The communication may be small but, in any case, if one is interested in obtaining further information regarding these lesions and, more specifically, in outlining the spinal cord and nerve roots, it is best to employ MRI(2,3,4). This modality most clearly delineates the abnormal underlying anatomy. In the neonate, however, ultrasonography can be useful in delineating the sac of the meningocele, the echogenic neural elements inside, and the presence of associated lesions such as lipomas.

Not uncommonly, the spinal cord in patients with meningomyelocele or meningocele shows widening secondary to hydromelia(3). Lipomas frequently co-exist(1) and on CT studies are of low signal intensity (i.e., radiolucent). On MRI, they produce high T1 signal intensity, and they are highly echogenic on ultrasonographic studies. Rib anomalies and deformities also commonly co-exist, and with more severe dysraphism, intraabdominal structures such as the aorta and kidneys can be displaced posteriorly and centrally. For this reason, it is often difficult to examine these kidneys with ultrasound. Meningoceles and meningomyeloceles also can be detected in utero with ultrasound.

Although most meningoceles are midline and dorsal in location, one can occasionally encounter a lateral or anterior meningocele. The latter abnormalities most commonly occur in the thoracic or sacral regions. Such meningoceles
are frequently associated with neurofibromatosis, and the roentgenographic findings include the presence of a mass (meningocele), a variety of vertebral abnormalities, and in the thorax, thinning of the adjacent ribs.

Anterior sacral meningoceles enter into the differential diagnosis of presacral pelvic masses in newborn and young infants. Primarily, one must differentiate them from presacral teratoma, hydrometrocolpos, ovarian cysts, and pelvic neuroblastoma. Intrasacral or so-called occult sacral meningoceles are not usually detected in the newborn and young infant.

In rare instances, one may come upon a complete midline defect of the spinal column, including the neural arches posteriorly and the vertebral bodies anteriorly (Fig. 8.28). This abnormality has been called “double spine,” total rachischisis, split notochord, or combined anterior and posterior meningomyelocele(6, 7). In some instances, dorsal herniation of the gastrointestinal tract through this defect can occur(6). In other instances, associated neurenteric cysts or neurenteric fistulas can be encountered, and yet in other cases the defects may be associated with hamartomas or actual deformed, accessory extremities(8, 9) (Fig. 8.28). Although originally the split notochord syndrome was considered an entity unto itself, more and more it is included in the spectrum of meningocele, diastematomyelia, diplomyelia, and neurenteric cyst(7).