Scoliosis and Anomalies with General Affliction of the Skeleton

Scoliosis

Regardless of its cause (Fig. 33.1), scoliosis is defined as a lateral curvature of the spine occurring in the coronal plane. This fact differentiates it from kyphosis, a posterior curvature of the spine in the sagittal plane, and lordosis, an anterior curvature of the spine also in the sagittal plane (Fig. 33.2). If the curve occurs in both coronal and sagittal planes, then the deformity is called kyphoscoliosis. Besides a lateral curvature, scoliosis may also have a rotational component in which vertebrae rotate toward the convexity of the curve.

Idiopathic Scoliosis

Idiopathic scoliosis, which constitutes almost 75% of all scoliotic abnormalities, can be classified into three groups. The infantile type, of which there are two variants, occurs in children younger than age 4 years; it is seen predominantly in boys, and the curvature usually occurs in the thoracic segment with its convexity to the left. In the resolving (benign) variant, the curve commonly does not increase beyond 30 degrees and resolves spontaneously, requiring no treatment. The progressive variant carries a poor prognosis, with the potential for severe deformity unless aggressive treatment is initiated early in the process. Juvenile idiopathic scoliosis occurs equally in boys and girls from the ages of 4 to 9 years. By far, the most common type of idiopathic scoliosis, comprising 85% of cases, is the adolescent form, seen predominantly in girls from 10 years of age to the time of skeletal maturity. The thoracic or thoracolumbar spine is most often involved, and the convexity of the curve is to the right (Fig. 33.3). Although the cause of this type is unknown, it has been postulated that a genetic factor may be at work and that idiopathic scoliosis is a familial disorder. The results of recent cytogenetic investigations point to mutations in SNTG1 gene encoding gamma-1-syntrophin located at chromosome 8q11.2, although the aberrations in the regions of chromosomes 6, 9, 16, and 17 may also be responsible for inheritance of this disorder.

Congenital Scoliosis

Congenital scoliosis is responsible for 10% of the cases of this deformity. It may generally be classified into three groups, according to MacEwen (Fig. 33.4): those resulting from a failure in vertebral formation, which may be partial or complete (Fig. 33.5); those caused by a failure in vertebral segmentation, which may be asymmetric and unilateral or symmetric and bilateral; and those resulting from a combination of the first two. The effects of congenital scoliosis on balance and support result in faulty biomechanics throughout the skeletal system.

Miscellaneous Scolioses

Several other forms of scoliosis having a specific cause may develop, including neuromuscular, traumatic, infections, metabolic, degenerative, and secondary to tumors, among others. Their discussion is beyond the scope of this text.

Radiologic Evaluation

The radiographic examination of scoliosis includes standing anteroposterior and lateral radiographs of the entire spine; a supine anteroposterior film centered over the scoliotic curve (see Figs. 33.3 and 33.5), which is used for the various measurements of spinal curvature and vertebral rotation (discussed later); and anteroposterior radiographs obtained with the patient bending laterally to each side for evaluation of the flexible and structural components of the curve. Care should be taken to include the iliac crests in at least one of these radiographs for a determination of skeletal maturity (see Figs. 33.14 and 33.15).

Ancillary techniques, such as computed tomography (CT), may be required for evaluating congenital lesions such as segmentation failures. Intravenous urography (pyelography, IVP) is essential in congenital scoliosis for evaluating the presence of associated anomalies of the genitourinary tract (Fig. 33.6). Magnetic resonance imaging (MRI) is the technique of choice to evaluate associated abnormalities of the spinal cord and the nerve roots.

An overview of the radiographic projections and radiologic techniques used in the evaluation of scoliosis is presented in Table 33.1.

Measurements

To evaluate the various types of scoliosis, certain terms (Fig. 33.7) and measurements must be introduced. Measurement of the severity of a scoliotic curve has practical application not only in the selection of patients for surgical treatment but also in monitoring the results of corrective therapy. Two widely accepted methods of measuring the curve are the Lippman-Cobb (Fig. 33.8) and Risser-Ferguson techniques (Fig. 33.9). The measurements obtained by these methods, however, are not comparable. The values yielded by the Lippman-Cobb method, which determines the angle of curvature only by the ends of the scoliotic curve, depending solely on the inclination of the end vertebrae, are usually greater than those given by the Risser-Ferguson method. This also applies to the percentages of correction as determined by the two methods; the more favorable correction percentage is obtained by the Lippman-Cobb method. The latter method,

which has been adopted and standardized by the Scoliosis Research Society, classifies the severity of scoliotic curvature into seven groups (Table 33.2).

FIGURE 33.1 General classification of scoliosis on the basis of cause.

FIGURE 33.2 Definitions. Scoliosis is a lateral curvature of the spine in the coronal (frontal) plane. Kyphosis is a posterior curvature of the spine, and lordosis an anterior curvature, both occurring in the sagittal (lateral) plane.

FIGURE 33.3 Idiopathic scoliosis. Anteroposterior radiograph of the spine of a 15-year-old girl shows the typical features of idiopathic scoliosis involving the thoracolumbar segment. The convexity of the curve is to the right; a compensatory curve in the lumbar segment has its convexity to the left.

FIGURE 33.4 Classification of congenital scoliosis on the basis of cause. (Modified from MacEwen GD, Conway JJ, Miller WT. Congenital scoliosis with a unilateral bar. Radiology 1968;90:711-715; Winter RB, Moe JH, Eilers VE. Congenital scoliosis. A study of 234 patients treated and untreated. J Bone Joint Surg [Am] 1968;50A:1.)

FIGURE 33.5 Congenital scoliosis. Anteroposterior radiograph of the lumbosacral spine of a 22-year-old man demonstrates scoliosis caused by hemivertebra, a complete unilateral failure of formation. Note the deformed L3 vertebra (arrow) secondary to the faulty fusion of the hemivertebra on the left side, where two pedicles are evident. The resulting scoliosis has its convex border to the left. An associated anomaly is also apparent from the presence of the so-called transitional lumbosacral vertebra (open arrow).

FIGURE 33.6 Congenital scoliosis. (A) Supine anteroposterior radiograph of the thoracolumbar spine of a 13-year-old girl shows congenital scoliosis secondary to block vertebrae consisting of a fusion of T12-L2. (B) IVP in the same patient demonstrates only the left kidney, an example of renal agenesis. Congenital scoliosis is frequently associated with urinary tract anomalies.

TABLE 33.1 Standard Radiographic Projections and Radiologic Techniques for Evaluating Scoliosis

Projection/Technique		Demonstration
Anteroposterior		Lateral deviation Angle of scoliosis (by Risser-Ferguson and Lippman-Cobb methods and scoliotic index) Vertebral rotation (by Cobb and Nash-Moe methods)
	of vertebra	Ossification of ring apophysis as determinant of skeletal maturity
	of pelvis	Ossification of iliac crest apophysis as determinant of skeletal maturity
	lateral bending	Flexibility of curve Amount of reduction of curve
Lateral		Associated kyphosis and lordosis
CT		Congenital fusion of vertebrae Hemivertebrae
Myelography		Tethering of cord
MRI		Abnormalities of nerve roots Compression and displacement of thecal sac Tethering of cord
Intravenous Urography Ultrasound		Associated anomalies of genitourinary tract (in congenital scoliosis)
CT, computed tomography; MRI, magnetic resonance imaging.

FIGURE 33.7 Terminology used in describing the scoliotic curve. The end vertebrae of the curve are defined as those that tilt maximally into the concavity of the structural curve. The apical vertebra, which shows the most severe rotation and wedging, is the one whose center is most laterally displaced from the central line. The center of the apical vertebra is determined by the intersection of two lines, one drawn from the center of the upper and lower end plates and the other from the center of the lateral margins of the vertebral body. The center should not be determined by diagonal lines through the corners of the vertebral body.

FIGURE 33.8 Lippman-Cobb method. In this method of measuring the degree of scoliotic curvature, two angles are formed by the intersection of two sets of lines. The first set of lines, one drawn tangent to the superior surface of the upper end vertebra and the other tangent to the inferior surface of the lower end vertebra, intersects to form angle (a). The intersection of the other set of lines, each drawn perpendicular to the tangential lines, forms angle (b). These angles are equal, and either may serve as the measurement of the degree of scoliosis.

FIGURE 33.9 Risser-Ferguson method. In this method, the degree of scoliotic curvature is determined by the angle formed by the intersection of two lines at the center of the apical vertebra: The first line originating at the center of the upper end vertebra, and the other at the center of the lower end vertebra.

Another technique for measuring the degree of scoliosis, introduced by Greenspan and colleagues in 1978, uses a “scoliotic index.” Designed to give a more accurate and comprehensive representation of the scoliotic curve, this technique measures the deviation of each involved vertebra from the vertical spinal line as determined by points at the center of the vertebra immediately above the upper end vertebra of the curve and at the center of the vertebra immediately below the lower end vertebra (Fig. 33.10). Its most valuable feature is that it minimizes the influence of overcorrection of the end vertebrae in the measured angle, a frequent criticism of the Lippman-Cobb technique. Furthermore, short segments or minimal curvatures, often difficult to measure with the currently accepted methods, are easily measurable with this technique.

Recently, computerized methods for measuring and analyzing the scoliotic curve have been introduced. Although more accurate than the manual methods, they require more sophisticated equipment and are more time-consuming than the methods described earlier.

TABLE 33.2 Lippman-Cobb Classification of Scoliotic Curvature

Group	Angle of Curvature (Degrees)
I	<20
II	21-30
III	31-50
IV	51-75
V	76-100
VI	101-125
VII	>125

In addition to the measurement of scoliotic curvature, the radiographic evaluation of scoliosis also requires the determination of other factors. Measurement of the degree of rotation of the vertebrae of the involved segment can be obtained by either of two methods currently in use. The Cobb technique for grading rotation uses the position of the spinous process as a point of reference (Fig. 33.11). On the normal anteroposterior radiograph of the spine, the spinous process appears at the center of the vertebral body if there is no rotation. As the degree of rotation increases, the spinous process migrates toward the convexity of the curve. The Nash-Moe method, also based on the measurements obtained on the anteroposterior projection of the spine, uses the symmetry of the pedicles as a point of reference, with the migration of the pedicles toward the convexity of the curve determining the degree of vertebral rotation (Fig. 33.12).

The final factor in the evaluation of scoliosis is the determination of skeletal maturity. This is important for both the prognosis and treatment of scoliosis, particularly the idiopathic type, because there is a potential for significant progression of the degree of curvature as long as skeletal maturity has not been reached. Skeletal age can be determined by comparison of a radiograph of a patient’s hand with the standards for different ages available in radiographic atlases. It can also be assessed by radiographic observation of the ossification of the apophysis of the vertebral ring (Fig. 33.13) or, as is often performed, from the ossification of the iliac apophysis (Figs. 33.14 and 33.15).

FIGURE 33.10 Scoliotic index. In the measurement of scoliosis using the scoliotic index, each vertebra (a-g) is considered an integral part of the curve. A vertical spinal line (xy) is first determined whose endpoints are the centers of the vertebrae immediately above and below the upper and lower end vertebrae of the curve. Lines are then drawn from the center of each vertebral body perpendicular to the vertical spinal line (aa′, bb′, … gg′). The values yielded by these lines represent the linear deviation of each vertebra; their sum, divided by the length of the vertical line (xy) to correct for radiographic magnification, yields the scoliotic index. A value of zero denotes a straight spine; the higher the scoliotic index, the more severe the scoliosis.

FIGURE 33.11 Cobb spinous-process method. In this method for determining rotation, the vertebra is divided into six equal parts. Normally, the spinous process appears at the center. Its migration to certain points toward the convexity of the curve marks the degree of rotation.

FIGURE 33.12 Nash-Moe pedicle method. In this method for determining rotation, the vertebra is also divided into six equal parts. Normally, the pedicles appear in the outer parts. Migration of a pedicle to certain points toward the convexity of the curve determines the degree of rotation.

FIGURE 33.13 Skeletal maturity. Determination of skeletal maturity from ossification of the vertebral ring apophysis.

FIGURE 33.14 Skeletal maturity. The ossification of the iliac apophysis is helpful in determining skeletal age. Progression of the apophysis in this 14-year-old girl with idiopathic scoliosis has been completed, but the lack of fusion with the iliac crest (arrows) indicates continuing skeletal maturation.

Treatment

Various surgical procedures are available for the treatment of scoliosis. The main objective of surgery is to balance and fuse the spine to prevent the deformity from progressing; its secondary objective is to correct the scoliotic curve to the extent of its flexibility. Determining the level of fusion depends on several factors, including the cause of the scoliosis and the age of the patient as well as the pattern of the scoliotic curve and the extent of vertebral rotation as evaluated during the radiographic examination of the patient.

Spinal fusion is now commonly accompanied by internal fixation of the spine to provide stability. One of the most popular methods for internal fixation is the Harrington-Luque technique (Wisconsin segmental instrumentation), using square-ended distraction rods and wire loops inserted through the bases of the spinous processes and connected to two contoured paravertebral rods (Fig. 33.16). The procedure involves decortication of the laminae and spinous processes, obliteration of the posterior facet joints by removal of the cartilage, and the placement of an autogenous bone graft from the iliac crest along the concave side of the curve. The hooks of the distraction rods are inserted under the laminae at the upper and lower ends of the curve. The prebent stainless-steel paravertebral rods (Luque rods or L-rods) are anchored into the spinous process or pelvis, depending on the location of the curve; wires, passed through the
base of the spinous process at each level of the spine to be fused, are then fixed to the L-rods. Variations in this technique have been used with L-rod instrumentation alone, which involves the use of sublaminar wires fixed to the rods, or a combination of Harrington distractors and wires fixed to them. Cotrel-Dubousset spinal instrumentation using knurled rods has also gained popularity. Fixation is achieved via pediculotransverse doublehook purchase at several levels. The two knurled rods are additionally stabilized by two transverse traction devices. The Dwyer technique, involving anterior fixation of the spine and obliteration of the intervertebral disks, is also used in the surgical treatment of scoliosis but more often in the paralytic types of the deformity.

FIGURE 33.15 Skeletal maturity. Determination of skeletal maturity from the status of ossification of the iliac apophysis.

FIGURE 33.16 Treatment of scoliosis. (A) Preoperative anteroposterior radiograph of the lumbar spine in a 15-year-old girl shows idiopathic dextroscoliosis. (B) Post-operative film shows the placement of the Harrington distractor and two L-rods. Note the multiple sublaminar wires fixed into the prebent L-rods.

The postoperative radiographic evaluation of internal fixation by the Harrington-Luque technique should focus on (a) whether the hooks of the Harrington rod are properly anchored with their brackets on the laminae of the superior and inferior vertebrae of the fused segment, (b) whether a hook has separated or been displaced, and (c) whether the rods and wires are intact. Moreover, evidence of pseudoarthrosis of the fused vertebrae should be sought when the postoperative loss of correction exceeds 10 degrees; a range of 6 to 10 degrees of loss of correction is ordinarily seen. The evaluation of pseudoarthrosis may require CT in addition to the conventional radiography. CT may also be needed within 6 to 9 months after surgery to demonstrate suspected nonunion of the bone engrafted on the concave side of the curve. Union of the graft with the spinal segment should appear solid; tomography may demonstrate radiolucent defects suggesting nonunion. Other complications involving the instrumentation may occur, such as fracture of a distraction rod or of a wire cable or screw, or excessive bending of the rods. Usually, these are easily demonstrated on conventional radiographs.

Anomalies with General Affliction of the Skeleton

Table 33.3 presents an overview of radiographic projections and radiologic techniques most effective for evaluating congenital and developmental anomalies with general affliction of the skeleton.

Neurofibromatosis

Originally considered a disorder of neurogenic tissue (nerve-trunk tumors), neurofibromatosis (also called von Recklinghausen disease) is now believed to be a hereditary dysplasia that may involve almost every organ system of the body. Neurofibromatosis type 1 is transmitted as an autosomal dominant trait, with more than 50% of cases reporting a family history. The condition is caused by a mutation or deletion of the NF1 gene located on the long arm of chromosome 17 (17q11.2) whose product, a protein neurofibromin (a GTPase-activating enzyme), serves as a tumor suppressor. Mutations in the NF1 gene lead to the production of a nonfunctional version of this protein that cannot regulate the cell growth and division. Sessile or pedunculated skin lesions (mollusca fibrosa) are an almost constant finding,

and café-au-lait spots, that may be present at birth or may appear over time, occur in more than 90% of patients. The latter lesions have a smooth border that has been likened to the coast of California; this distinguishes them from the café-au-lait spots seen in fibrous dysplasia, which have rugged “coast of Maine” borders. These spots increase in size and number as the person grows older. Axillary or inguinal freckles are rare at birth but appear throughout childhood and adolescence. Plexiform neurofibromatosis is a diffuse involvement of the nerves, associated with elephantoid masses of soft tissue (elephantiasis neuromatosa), and localized or generalized enlargement of a part or all of a limb (Fig. 33.17). Patients with these manifestations are particularly prone to malignant tumors (see Fig. 22.40).

TABLE 33.3 Most Effective Radiographic Projections and Radiologic Techniques for Evaluating Common Anomalies with General Affliction of the Skeleton

Projection/Technique		Crucial Abnormalities
*Arthrogryposis*
Anteroposterior, lateral, and oblique of affected joints		Multiple subluxations and dislocations Fat-like lucency of soft tissues Cubital and popliteal webbing
*Down Syndrome*
Anteroposterior
	of pelvis and hips	Hip dysplasia
	of ribs	11 pairs of ribs
Dorsovolar of both hands		Clinodactyly and hypoplasia of fifth fingers
Lateral of cervical spine		Atlantoaxial subluxation
Tomography (lateral) of cervical spine (C1, C2)		Hypoplastic odontoid
*Neurofibromatosis*
Anteroposterior, lateral, and oblique		Pit-like erosions
	of long bones	Pseudoarthrosis of distal tibia and fibula
Anteroposterior		Rib notching
	of ribs
	of lower cervical/upper thoracic spine	Scoliosis Kyphoscoliosis
Oblique of cervical spine		Enlarged neural foramina
Lateral of thoracic/lumbar spine		Posterior vertebral scalloping
Myelography		Intraspinal neurofibromas Increased volume of enlarged sub-arachnoid space Localized dural ectasia
CT MRI		Complications (e.g., sarcomatous degeneration) Neurofibromas
*Osteogenesis Imperfecta*
Anteroposterior, lateral, and oblique of affected bones		Osteoporosis Bowing deformities Trumpet-like metaphysis Fractures
Lateral of skull		Wormian bones
Anteroposterior and lateral of thoracic/lumbar spine		Kyphoscoliosis
*Achondroplasia*
Anteroposterior		Shortening of tubular bones, particularly humeri and femora
	of upper and lower extremities
	of pelvis	Rounded iliac bones Horizontal orientation of acetabular roofs Small sciatic notches
	of spine	Narrowing of interpedicular distance
Lateral of spine		Short pedicles Posterior scalloping of vertebral bodies
Dorsovolar of hands		Short, stubby fingers Separation of middle finger (trident appearance)
CT		Spinal stenosis
*Morquio-Brailsford Disease*
Anteroposterior and lateral of spine		Oval- or hook-shaped vertebrae with central beak
Anteroposterior		Overconstriction of iliac bodies
	of pelvis	Wide iliac flaring
	of hips	Dysplasia of proximal femora
*Hurler Syndrome*
Anteroposterior and lateral		Rounding and lower beaking of vertebral bodies
	of spine	Recessed hooked vertebra at apex of kyphoscoliotic curve
	of skull	Frontal bossing Synostosis of sagittal and lambdoidal sutures Thickening of calvarium J-shaped sella turcica
Anteroposterior of pelvis		Flaring of iliac wings Constriction of inferior portion of iliac body Shallow, obliquely oriented acetabula
*Osteopetrosis*
Anteroposterior and lateral		Increased density (osteosclerosis)
	of long bones	Bone-in-bone appearance
	of spine	“Rugger-jersey” vertebral bodies
Anteroposterior of pelvis		Ring-like pattern of normal and abnormal bone in ilium
*Pyknodysostosis*
Anteroposterior and lateral of long bones		Increased density (osteosclerosis)
Dorsovolar of hands		Resorption of terminal tufts (acroosteolysis)
Lateral of skull		Wormian bones Persistence of anterior and posterior fontanelles Obtuse (fetal) angle of mandible
*Osteopoikilosis*
Anteroposterior of affected bones		Dense spots at the articular ends of long bones
*Osteopathia Striata*
Anteroposterior of affected bones		Dense striations, particularly in metaphysis
*Progressive Diaphyseal Dysplasia*
Anteroposterior of long bones (particularly lower limbs)		Symmetric fusiform thickening of cortex Sparing of epiphyses
*Melorheostosis*
Anteroposterior and lateral of affected bones		Asymmetric, wavy hyperostosis (like dripping candle wax) Ossifications of periarticular soft tissues
CT, computed tomography; MRI, magnetic resonance imaging.

FIGURE 33.17 Neurofibromatosis. A 19-year-old man presented with a history of slow but progressive enlargement of his left thigh. Clinical examination also revealed several café-au-lait spots. (A) Sagittal inversion recovery (IR) and (B) axial T2-weighted fat-suppressed MR images of the upper left thigh show numerous of large, lobulated bright masses representing neurofibromas, the largest involving the sciatic nerve, consistent with plexiform type of neurofibromatosis. (C) An 18-year-old woman with known NF1 presented with sensory deficits in both thighs. Postcontrast coronal T1-weighted fat-saturated MRI of the right thigh and (D) coronal postcontrast MRI of both thighs demonstrate bilateral plexiform neurofibromas involving the lateral and anterior femorocutaneous nerves, more prominent on the left. Note the characteristic “bull’s eye” enhancement of the neurofibromas of the left thigh, with peripheral pattern of enhancement.

FIGURE 33.18 Neurofibromatosis. Anteroposterior radiograph of the lower legs of an 11-year-old girl shows pit-like erosions in the proximal tibiae and fibulae (arrows), a common finding in this condition.

Skeletal abnormalities are often encountered in neurofibromatosis; at least 50% of patients demonstrate some osseous changes, most commonly extrinsic, pit-like cortical erosions resulting from direct pressure by adjacent neurofibromas. This is commonly seen in the long bones (Fig. 33.18) and ribs. The long bones often exhibit bowing deformities, and pseudoarthroses, seen in approximately 10% of cases, most commonly occur in the lower tibia and fibula (Fig. 33.19). This type of false joint formation must be differentiated from congenital pseudoarthrosis. Moreover, the long bones are the site of lesions that were once considered to represent intraosseous neurofibromas; these cyst-like radiolucencies are now regarded as lesions representing fibrous cortical defects and nonossifying fibromas, associated with neurofibromatosis (see Fig. 19.6). Whittling of the bones is also a typical feature of neurofibromatosis (Fig. 33.20).

The spine is the second most common site of skeletal abnormalities in neurofibromatosis. Scoliosis or kyphoscoliosis, which characteristically involves a short segment of the vertebral column with acute angulation, commonly occurs in the lower cervical or upper thoracic spine. Widening of the intervertebral foramina in the cervical segment may also occur, resulting from dumbbell-shaped neurofibromas arising in spinal nerve roots (Fig. 33.21). In the thoracic and lumbar segments, scalloping of the posterior border of vertebral bodies is another characteristic feature (Fig. 33.22). Although most of these abnormalities can easily be diagnosed with conventional radiography, some ancillary techniques may be useful. Myelography is particularly valuable for demonstrating the increased volume of the enlarged subarachnoid space and the localized dural ectasia extending into the scalloped defects in the vertebral bodies; with the introduction of MRI, this modality became more prevalent in investigation of the aforementioned abnormalities.

FIGURE 33.19 Neurofibromatosis. Lateral radiograph of the right lower leg of an 11-year-old boy with generalized disease demonstrates anterior bowing of the distal tibia and fibula, associated with pseudoarthrosis. Note the pressure erosions in the middle third of the tibial diaphysis.

FIGURE 33.20 Neurofibromatosis. Lateral radiograph of the lower leg and foot of a 37-year-old woman shows whittling of the calcaneus and marked hypertrophy of the soft tissues (elephantiasis), typical for plexiform type of this condition.

FIGURE 33.21 Neurofibromatosis. Oblique radiograph of the cervical spine of a 26-year-old man demonstrates widening of the upper neural foramina (arrows) secondary to “dumbbell” neurofibromas arising in the spinal nerve roots.

FIGURE 33.22 Neurofibromatosis. Lateral spot film of the lower thoracic spine in a 29-year-old woman shows scalloping of the posterior border of the T12 vertebra, a common manifestation of this condition.

Neurofibromatosis type 2 is autosomal dominant disorder with a high penetrance caused by mutation of an NF2 gene located on the chromosome 22 (22q12.2), which regulates the production of a tumor-suppressor protein merlin (for moezin-ezrin-radixin-like protein), also referred to as schwannomin. Type 2 of neurofibromatosis is characterized by multiple schwannomas, meningiomas, and ependymomas.

Osteogenesis Imperfecta

Osteogenesis imperfecta (OI), also known as fragilitas ossium, is a congenital, non-sex-linked, hereditary disorder that manifests in the skeleton as a primary defect in the bone matrix. It is characterized by bone fragility resulting from abnormal quality and/or quantity of type I collagen. Depending on the type of OI, the inheritance of the disorder can be autosomal dominant, autosomal dominant with new mutation, or autosomal recessive. Recently, it has been suggested that this disease results from mutations in the genes COL1A1, COL1A2, CRTAP, and LEPRE1. Looser, in 1906, divided this condition into two forms, “congenita” and “tarda,” and suggested that they are expressions of the same disease. OI congenita (Vrolik disease) has been classified as the more severe form, which is evident at birth and marked by bowing of the upper and lower extremities in an infant who is either stillborn or does not survive the neonatal period. The more benign OI tarda (Ekman-Lobstein disease), in which there is a normal life expectancy, may show fractures present at birth, but these more often appear later in infancy. This condition is also associated with other manifestations, such as deformities of the extremities, blue sclerae, laxity of ligaments, and dental abnormalities.

Classification

In general, four major clinical features characterize OI: (a) osteoporosis with abnormal bone fragility, (b) blue sclera, (c) defective dentition (dentinogenesis imperfecta), and (d) presenile onset of hearing impairment. Other clinical features also may be seen, among them are ligamentous laxity and hypermobility of joints, short stature, easy bruising, hyperplastic scars, and abnormal temperature regulation. The earlier classification of OI into two types, congenita and tarda, failed to reflect the complexity and heterogenous nature of this disorder. The classification proposed by Sillence and colleagues in 1979, and later revised, is based on phenotypic features and the mode of inheritance. Currently, four major types of OI and their subtypes are recognized:

Type I: This most common type of the disorder is a relatively mild form, with autosomal dominant inheritance. Bone fragility is mild to moderate, and osteoporosis is invariably present. Sclerae are distinctly blue, and hearing loss or impairment is a common feature. Stature is normal or near normal. Wormian bones are present. The two subtypes are distinguished by the presence of normal teeth (subtype IA) or dentinogenesis imperfecta (subtype IB).

Type II: This is the fetal or perinatal lethal form of the disorder. This form demonstrates an autosomal dominant inheritance with new mutation. The very severe nature of generalized osteoporosis, bone fragility, and severe intrauterine growth retardation results in death in the fetal or early perinatal period. Of those infants who survive, 80% to 90% die by 4 weeks of age. All patients in this group have radiologic features typical of OI. In addition, the sclerae are blue and the face has a triangle shape caused by soft craniofacial bones and a beaked nose. The calvarium is large relative to the face, and the skull shows a marked lack of mineralization as well as wormian bones. Limbs are short, broad, and angulated. Three subtypes, A, B, and C, are marked by differences in the appearance of the ribs and the long bones. In subtype A, the long bones are broad and crumpled and the ribs are broad, with continuous beading. In subtype B, the long bones also are broad and crumpled, but the ribs show either discontinuous beading or no beading. Subtype C is characterized by thin fractured long bones and ribs that are thin and beaded.

Type III: This is a severe progressive form and represents a rare autosomal dominant inheritance with new mutations. Bone fragility and osteopenia are considerable, leading with age to multiple fractures and severe progressive deformity of the long bones and spine. Bone abnormalities are generally less severe than in type II and more severe than in types I or IV. Sclerae are normal, although pale blue or gray at birth, but the color changes through infancy and early childhood until it is normal by adolescence or adulthood. The calvarium is large, thin, and poorly ossified; wormian bones are present.

Type IV: This is also a rare type of OI and is inherited as an autosomal dominant trait. Characteristically, osteoporosis, bone fragility, and deformity are present, but they are very mild. Sclerae are usually normal. The incidence of hearing impairment is low and is even lower than in type I.

Recently, Glorieux and colleagues added two more types, V and VI, and Ward and associates described in details the rarest form of OI, type VII. Type V includes the patients who originally have been classified as type IV but had a discrete phenotype including hyperplastic callus formation without evidence of mutations in type I collagen. These patients also exhibit calcification of the radioulnar interosseous membrane and radiodense metaphyseal bands adjacent to the growth plates. Histologically, this type is characterized by a mesh-like pattern of lamellation under polarized light microscopy. Type VI includes the patients who sustained more frequent fractures (particularly of the vertebrae) than those with type IV, first documented between 4 and 18 months of age. Sclerae of these patients were white or faintly blue, and dentinogenesis imperfecta was uniformly absent. Serum alkaline phosphatase levels were elevated compared with age-matched patients with OI type IV. The type VII is an autosomal recessive form, with moderate to severe phenotype, characterized by fractures at birth, blue sclerae, early deformity of the lower extremities, coxa vara, and osteopenia. Rhizomelia is a prominent clinical feature. This form of OI has been localized to chromosome 3p22-24.1, which is outside the loci for type I collagen genes.

Radiologic Evaluation

The radiologic features of OI are easily identified on conventional radiographs. Severe osteoporosis, deformities of the bones, and thinning of the cortices are consistently observed features. The bones are also attenuated and gracile, with a trumpet-shaped appearance to the metaphysis (Fig. 33.23). The fractures are commonly observed (Fig 33.24). Other typical skeletal abnormalities are seen in the skull, where wormian bones are a recognizable feature (Fig. 33.25), and in the spine, where severe kyphoscoliosis may develop from a combination of osteoporosis, ligamentous laxity, and posttraumatic deformities (Fig. 33.26). In children with a severe degree of disorder, the metaphyses and epiphyses of the long bones may exhibit numerous scalloped radiolucent areas with sclerotic margins (Fig. 33.27). This appearance is referred to as popcorn calcifications, and it may be the result of traumatic fragmentation of the growth plate. The pelvis is invariably deformed, and acetabular protrusio is a common finding (Fig. 33.28).

Differential Diagnosis

Occasionally, OI may be misdiagnosed as child abuse and vice versa. Patient and family history, physical examination, diagnostic imaging, and the clinical course of the abnormalities all contribute to the distinction of this condition from child abuse. The keys to distinguishing OI from a battered

child syndrome (“shaken baby syndrome,” parent-infant trauma syndrome) are (a) the presence of blue sclera or abnormal teeth in OI, (b) investigation of clinical and family history (invariably positive in OI), (c) physical examination, and (d) radiologic examination for the detection of wormian bones and osteoporosis in OI; and metaphyseal corner fractures and “buckethandle” fractures that are highly specific and virtually pathognomonic features of child abuse. Several other features are also specific for child abuse, including multiple rib fractures, especially posterior rib fractures near or at the costovertebral junction; multiple fractures and/or multiple fractures showing different stages of healing; and sternal or scapular fractures, especially of the acromion. Transverse, oblique, or spiral fractures of a long bone with normal mineralization in the absence of any previous history, especially in a nonambulatory infant, are also highly suggestive of child abuse. The key to diagnosis of either condition is the correlation of clinical history, physical examination, family history, and imaging findings.

FIGURE 33.23 Osteogenesis imperfecta. Lateral radiograph of the leg of a 12-year-old boy with type III disease demonstrates thinning of the cortices and anterior bowing of the tibia and fibula. Note the trumpet-shaped appearance of the tibial metaphysis (arrow).

FIGURE 33.24 Osteogenesis imperfecta. (A) Anteroposterior and (B) lateral radiographs of the elbow of a 27-year-old man show typical appearance of bones in this condition. Note comminuted supracondylar fracture of the humerus.

FIGURE 33.25 CT of osteogenesis imperfecta. Axial CT sections of the skull (A) through the frontal and parietal bones and (B) through the vertex show sutural (wormian) bones.

FIGURE 33.26 MRI of osteogenesis imperfecta. (A) Sagittal T2-weighted MR image of the thoracic spine of a 13-year-old boy shows compression fractures of several vertebral bodies associated with kyphosis and compression of the spinal cord. (B) Sagittal T2-weighted MRI of the lumbar spine demonstrates multiple vertebral fractures and dural ectasia.

FIGURE 33.27 Osteogenesis imperfecta. Anteroposterior radiograph of the left leg of a 12-year-old boy with a type III disease shows “popcorn calcifications” at the articular ends of the long bones. A Rush pin has been placed in the tibia because of a pathologic fracture.

FIGURE 33.28 Osteogenesis imperfecta. Marked deformity of the pelvis, seen here in a 27-year-old woman, is a consistent finding in OI tarda. Note the bilateral acetabular protrusio and the pathologic fracture of the right femur (arrow).

Treatment

There is no specific treatment for OI other than correction of the deformities it produces and the prevention of fractures. The condition, however, tends to improve spontaneously at puberty, with cessation or a decrease in the number of fractures. Recent reports suggest a gradual increase in bone density after treatment with intravenous infusion of sodium pamidronate. The limb deformities are corrected by various types of osteotomies, with the popular method being the Sofield (“shish kabob”) technique, in which the deformed bones are osteotomized in a fragmentation procedure, cut into short segments, and then realigned by threading them onto a rigid or expandable rod (Fig. 33.29). The most common complications of this treatment are rod breakage, refracture of the bone at the end of the metallic device, and pseudoarthrosis.

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