Classification of Congenital Scoliosis and Kyphosis: A New Approach to the Three-dimensional Classification for Progressive Vertebral Anomalies Requiring Operative Treatment

Noriaki Kawakami, MD; Taichi Tsuji, MD; Shiro Imagama, MD; Lawrence G. Lenke, MD; Rolando M. Puno, MD; Timothy R. Kuklo, MD

Disclosures

Spine. 2009;34(17):1756-1765. 

In This Article

Anatomic Findings of 3D Morphology in Congenital Spinal Deformities

Each type of anomalous vertebrae, such as hemivertebra, wedge vertebra, butterfly vertebra, and typical type of segmentation failure, each exhibit distinct characteristics in 3D morphology that have been not detected and have indeed been ignored for a long time.

Hemivertebra

In definition, hemivertebra is a wedged-shaped vertebra with 1 pedicle on 1 side. It can be subdivided as fully segmented, semisegmented, and unsegmented, according to the relation with the cranial and caudal adjacent vertebral bodies. There has been no description about the anomalous changes of posterior structure of hemivertebra until 2007. Nakajima et al[7] reported the types of laminae of formation failure and classified them into bilamina and hemilamina, based on the number of pedicles of the anomalous vertebra. Laminae with 1 pedicle are subclassified into fully segmented hemilamina, semisegmented hemilamina, spina bifida, and incomplete lamina, which are defined as a nearly normal bilamina with only 1 pedicle (Figure 5). Some hemivertebrae exhibit fully segmented hemibodies with semisegmented hemilaminae and others exhibit semisegmented hemibodies with fully segmented hemilaminae (Figure 4). These findings should be regarded as a discordant segmentation in hemivertebrae and may be one of the reasons why it is difficult to predict the natural history of each hemivertebra.

Figure 5.

Discordant Segmentation in Hemivertebrae.
A hemivertebra has semisegmented hemibody and fully segmented hemilamina (A). A hemivertebra has fully segmented hemibody and semisegmented hemilamina (B).

Wedge Vertebra

Wedge vertebrae are defined as wedge-shaped vertebrae with 1 pedicle on each side. Because wedge vertebrae exhibit 2 pedicles they inevitably exhibit a bilaminar posterior structure. Three-dimensional CT analysis can clearly demonstrate deformation of vertebral body and these findings may contribute to confusion as to whether it is congenital or secondary because wedge-shaped vertebral body can be quite often observed in the apical area of severe scoliosis. These changes of the apical vertebrae are secondarily caused by regression of vertebral growth on the concave side of the apical area. Forty cases of scoliosis (congenital scoliosis is not included) with the Cobb angle more than 80° treated in our hospital were evaluated and identified that the apical vertebra is severely wedged-shaped and that it never exceeded more than 50% of wedging. This study indicated that secondary wedged-deformation of the vertebrae was usually observed along a few consecutive apical vertebrae with an apical vertebra exhibiting the most severe wedged-shaped and never exhibiting a decrease more than 50% of vertebral height on the opposite side. Formation of osteophytes on the edge of the vertebral body or ridge formation on the concave side may be a result of secondary deformation of wedge-shaped vertebrae. In this context, wedge vertebra may be defined as a wedged-shaped vertebra in which the height of 1 side decrease by more than 50% of the opposite side, or whose adjacent cranial or caudal vertebra is almost normal shape, not wedged-shaped if the height on the 1 side of the wedged-shaped vertebra decreases less than 50% of the opposite side.

Butterfly Vertebra

The butterfly vertebra belongs to the anterior formation failure in the classification; it is the vertebra with 1 pedicle on each side and partial defect of the vertebral body. This type of formation failure is usually included in the congenital kyphosis because many butterfly vertebrae are clinically observed with symmetrical partial defects of the center of the vertebral body that result in anterior wedged-shaped vertebrae. Since they exhibit 2 pedicles, their posterior components are bilamina despite variations of the asymmetrical shape. An asymmetrical partial defect of the vertebral body often causes scoliosis and is sometimes is misidentified as hemivertebra on plain x-ray images (Figure 6). Many butterfly vertebrae might be diagnosed as hemivertebrae or posterior quadrant hemivertebrae before development of 3D CT reconstruction technique. To prevent this misinterpretation, we should always check the number of pedicles and the type of posterior components. If an anomalous vertebra exhibits a wedged-shaped body and a bilamina with bilateral pedicles, it is definitely an asymmetrical butterfly vertebra and we should look for a very small hemibody on the opposite side (Figure 6). In some cases, the small opposite hemibody is synostosed to the caudal or cranial adjacent vertebra. This mixture of semisegmentation will make it more difficult to make a correct diagnosis.

Figure 6.

Asymmetrical Butterfly Vertebra.
A 30-year-old man patient complained of lower back pain and numbness of the left lower extremity for more than 5 years. The plain x-ray showed 49° of scoliosis and 50° of kyphosis in the thoracolumbar area. Three-dimensional CT demonstrated an asymmetrical butterfly vertebra of T12 with posterior bilamina (arrow).

Segmentation Failure

The circumferentially unsegmented vertebrae (block vertebrae Figure 7) and the unilateral unsegmented bar (Figure 8) typifies segmentation failure in congenital spinal deformity. This latter is considered as one of progressive congenital vertebral abnormalities. According to the location of segmentation, segmentation failure has been reported to be subclassified into anterior, anterolateral, posterolateral, posterior, and circumferential.[1]

Figure 7.

Block Vertebra.
A 12-year-old girl existing 62° of scoliosis. Front and back images of 3D CT demonstrate no segmentation between T10 and T11 (block vertebra, arrows).

Figure 8.

Unilateral Unsegmented Bar.
A 7-year-old girl existing 128° of scoliosis. Three-dimensional CT image of thoracic spine (A) shows a severe scoliotic curvature with severely lateral wedged vertebrae. The long bar can be easily recognized on the coronal reconstructed image (B) and plain radiograph image (C) (arrows).

Although 3D analysis can be used to demonstrate the presence or absence of segmentation in detail, it is very hard to differentiate segmentation from no segmentation in some patients. In particular, the upper and midthoracic spine is the location where it is almost impossible to judge about the presence or absence of segmentation because of the coverage of the disc space and pedicles with rib heads. Disc space may be only the clue to differentiate segmentation from no segmentation. However, there is also difficulty in evaluation of segmentation for the anomalous vertebrae with disc space narrowing. This may be incomplete segmentation or secondary change influenced by posterior no segmentation observed in the mixed complex type.

Segmentation Abnormalities in Formation Failure

As reported by McMaster et al[12] the most progressive type is unilateral unsegmented bar with contralateral hemivertebrae. This type is associated with hemivertebrae on the opposite site, and should belong to the mixed-type. However, if it is hypothesized that it is a combination of some asymmetrical butterfly vertebrae and that 1 side of their smaller hemibodies become synostosized with cranial and caudal adjacent vertebrae, this unilateral unsegmented bar with contralateral hemivertebrae can be regarded as 1 type of segmentation failure in formation failure. In fact, there are so many hemivertebrae and butterfly vertebrae that have synostosis to the adjacent vertebrae. Considering this, it is confusing which type should be named as failure of formation or failure of segmentation.

Three-dimensional CT analysis can demonstrate many different types of failure of segmentation. We need to clarify the location of segmentation failure and formation failure. Imagama et al[6] analyzed the location of synostosis in 40 patients with formation failure in congenital spinal deformities and reported the existence of difference of synostosis of the anterior and posterior structure even in the same type of abnormal vertebrae. We should differentiate these complicated vertebral anomalies from a pure segmentation failure that exhibit no formation failure.

Relationship of the Anterior Structure with the Posterior Structure

Both anterior and posterior structures of anomalous vertebrae correspond with each other in some patients (unison type). The unison type can be also called a simple type from the viewpoint of complexity of the vertebral anomalies. It is not difficult to evaluate these anomalies even using plain x-ray image because malformed vertebrae in the simple type could be explained by formation failure of certain vertebral components one by one. However, other patients exhibit differences between the anterior and posterior structures (discordant type, Figure 9).[7] Congenital vertebral malformation that shows discordant relationship between the anterior and posterior structures can be called a complex type. It also demonstrates abnormal continuity between the posterior components of the malformed vertebrae and those of the neighboring vertebrae. It is very difficult to correlate the anterior structure with the posterior structure of each segment of anomalous vertebrae. Furthermore, it is virtually impossible to judge which vertebrae are normal or abnormal. These characteristics makes independent evaluation of the malformation in each vertebra as one segment impossible, and evaluation of complex malformations, involving multiple vertebrae is necessary. The discordant anomaly can be divided into 2 types, the mismatched complex type and mixed complex type, according to the mode of false fusion between each structure of the abnormal vertebrae (Figure 10). The former is one in which either side of the primordia of vertebral body may couple with an adjacent opposite side of the posterior component. Usually several vertebral segments are involved in this mismatching phenomena and we need to evaluate this type of anomaly as an abnormal vertebral complex despite the inclusion of some normal-shaped vertebrae in this complex. The mixed complex type is a group of vertebral anomalies that exhibit differences of the failure type between the anterior and posterior structure.

Figure 9.

Discordant Anomaly in Formation Failure.
The patient was a 6-year-old boy with hemivertebrae at L2 and L3. The front image by 3D CT (B) coincided with the radiographic observation (A). The vertebral arch components connected to the hemivertebra united with the adjacent vertebral arch components of the vertebra in the direction of the head. The circles show the positions of the pedicles of the vertebral arch, and the arrows show the same pedicles of the vertebral arch imaged by 3D CT from the front and back (B, C, D). A vertebral arch was formed by pairing of the vertebral arch components connected to the right pedicle of the vertebral arch at L1 and the vertebral arch components at L2. The area shown by the thick arrow was surgically proved to be isolated hemilamina.

Figure 10.

Drawings of the 2 Types of Complex Type.
Mismatched complex type: The vertebral arch components of the hemivertebra are united with the opposing vertebral arch components of the adjacent caudal or cranial vertebra. Mixed complex type: The anterior structure of malformed vertebral bodies belonging to formation failure and the posterior structure consists of complex fused vertebral arches (Drawn by A. Nakajima).

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