Common developmental features as well as unusual normal variants can be easily mistaken for pathologic processes. The variants described below are common but not exhaustive. Ultimately, consultation with atlases of normal variants when bony defects are uniform, disproportionate to physical exam findings, or asymptomatic should prevent mischaracterization of congenital variants as disease.

The multiple primary and secondary ossification centers and their intervening synchondroses are often mistaken for fractures or avulsion fragments. Ossification in the superior and inferior ring apophysis may begin in children as young as 6 years of age and may persist well into adolescence.

During adolescence, the nucleus pulposus may herniate through the vertebral end plate, resulting in Schmorl nodes (Fig. 3.10). Additionally, notochord remnants may appear as impressions on consecutive inferior end plates, mimicking erosive or lytic lesions. Similarly, anterior intraosseous herniation of the intervertebral disc, also referred to as a limbus vertebra (Fig. 3.11), may be mistaken for a teardrop fracture. These normal variants may be differentiated from fractures by examining the edge of the lesion: physeal plates should be smooth and regular, with subchondral sclerotic lines, whereas acute fractures are irregular and non-sclerotic; fractures can occur at any location.

During the first two decades, the appearance and physiology of the cervical spine varies tremendously. Until age 15, a normal atlantoaxial interval can be as large as 5 mm and occasionally even 6 mm. More accurate assessment evaluates for change in distance between passive flexion and extension, which should not exceed 2 mm.

Physiologic displacement of C2 anteriorly on C3 is common in normal children due to ligamentous laxity (Box 3.1). Known as pseudosubluxation, this occurs because until age 10, flexion and extension are centered at the C2–3 level (Figs. 3.12 and 3.13). (In adolescence and throughout adulthood, maximum mobility is at C4–6.) In order to determine whether subluxation results from this normal variant or from a C2 arch fracture and pathologic subluxation, one can draw a curved “posterior cervical” line, connecting the anterior cortices of the C1 and C3 spinous processes (Fig. 3.12). With physiologic subluxation, this line either passes through the C2 posterior arch or passes less than 2 mm anterior to it. In the presence of an arch fracture, the distance will be greater, since the atlas and the C2 centrum slip forward at the fracture site while the spinous process remains posterior [13, 14].

Developmental pseudospread of the atlas is a normal phenomenon that occurs because the growth of the atlas is linked to the relatively rapid growth of the skull base, whereas the growth of the axis is influenced by the slower growth of the spine. With pseudospread, the lateral margins of C1 lie symmetrically lateral to the margins of C2, mimicking the bilateral lateral displacement of a Jefferson fracture of the arch of the atlas. This disparity generally resolves after age 2. The overlap is usually less than 2 mm, whereas in the case of fracture, it generally exceeds 3 mm [15].

In up to 5 % of newborns, a coronal cleft is apparent on a lateral radiograph of the thoracic or lumbar spine. This appears as a vertical lucency at the junction of the anterior two thirds and posterior third of the vertebral body [16]. The cleft is filled with hyaline cartilage, possibly a remnant of the division between dorsal and ventral ossification centers. The coronal cleft ossifies during infancy and does not persist or lead to other anomalies.

A horizontal cleft in the midportion of the vertebral body, also referred to as a Hahn cleft, may also be visible on a lateral view. It marks both the boundary of fusion between sclerotomes and the nutrient foramen (Fig. 3.14) and may persist as a sclerotic line throughout adolescence.

Bone-in-bone is another common finding during infancy (Fig. 3.15). This results from rapid growth during the first postnatal months, before remodeling of the fetal spine begins [14]. The outline of a smaller replica of the vertebral body is seen within the centrum.

Incomplete bony fusion at the neural arch of L5 or S1 is very common in children, but the incidence decreases during childhood. Cartilage usually fills this apparent gap, so it is not functionally open [17]. The S1 neural arch is incompletely fused in up to 58 % at age 8, 48 % at age 12, and 10–26 % of adults. A separation of 3 mm or less is normal and will often ossify during childhood. Occasionally, a similar narrow cleft may be encountered as an isolated finding at the T11 or T12 level. The term spina bifida occulta has been applied to this appearance (at any isolated level), but this term may be misleading as it implies pathology. Misreporting of this finding may result in confusion and unnecessary imaging.

At the T12 and L1 vertebrae, localized moderate to marked pedicle thinning occurs in 7 % of normal children and adults. The developmentally aberrant pedicle may be differentiated from a pedicle that is being deformed by mass effect because the lateral border of the aberrant pedicle is flat or concave, rather than rounded.

Spinal defects may be restricted to the vertebrae or may involve neural and non-neural structures [18]. Sixty-one percent of those with congenital spinal defects have other abnormalities as well. For example, a prenatal neural crest and sensory nerve injury may lead to a field defect that causes the constellation of upper limb, vertebral, and rib anomalies. The mnemonic VACTERL describes the clinical confluence of vertebral, anorectal, cardiac, tracheoesophageal, renal, and limb anomalies [19]. It is important to recognize that VACTERL is an association not a syndrome. Less common associated abnormalities are found in the ear, choanae, lips, palate, intestinal tract, abdominal wall (hernias), and genital system.

Scoliosis may develop if vertebrae fail to form, as with wedge vertebrae (unilateral hypoplasia) or hemivertebrae (unilateral aplasia). Less often, a hemivertebra may be supernumerary, resulting from partial duplication. Failure of segmentation may be unilateral or bilateral, resulting in an osseous bar (or bars) connecting the posterior elements, vertebral bodies, or both (Fig. 3.16). If anomalies are multiple and balanced, alignment may be normal.

Dysraphism describes the failure of midline vertebral structures to fuse. The term encompasses not only structural vertebral defects but also associated anomalies of neurologic, gastrointestinal, genitourinary, and other systems. The sequence of neural tube-notochord-yolk sac differentiation is disrupted, and thus structures that develop from the primordial layers may be affected. There may be abnormal induction of structures that develop later as well. Dysraphism is categorized as open (uncovered) or closed (covered) and the later further subdivided according to configuration (Fig. 3.29) [40]. Most open defects (meningocele (Fig. 3.30), meningomyelocele (Fig. 3.31), and myelocele) are clinically obvious, but dermal sinuses may be difficult to detect. Closed defects are completely covered with skin, which may be dysplastic and have an associated nevus, hairy patch, hemangioma, or lipoma. The spinal cord may be duplicated or split (diplomyelia and diastematomyelia), or there may be overgrowth of normal tissues (lipoma and dermoid) or herniation of one germ layer through another (neurenteric cyst).

Cross-sectional imaging provides essential information for skin-covered lesions. If cutaneous stigmata are present, US can help evaluate for tethered cord until about age 3 months (Figs. 3.32 and 3.33), with subsequent MRI if needed. CT is rarely performed to better delineate the bony abnormalities, while MRI exquisitely depicts the extent of neural and soft tissue abnormalities (see Figs. 3.30 and 3.31). MRI may occasionally be performed before surgery for open lesions, as it allows more precise diagnosis and surgical planning.