DOI: 10.1148/rg.253045092
RadioGraphics 2005;25:603-618
© RSNA, 2005
Multidetector CT of Musculoskeletal Disease in the Pediatric Patient: Principles, Techniques, and Clinical Applications1
Laura M. Fayad, MD,
Pamela Johnson, MD and
Elliot K. Fishman, MD
1 From the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institutions, 601 N Wolfe St, JHOC 3171-C, Baltimore, MD 21287. Presented as an education exhibit at the 2003 RSNA Scientific Assembly. Received April 23, 2004; revision requested June 8; received and accepted January 24, 2005. All authors have no financial relationships to disclose.
Address correspondence to L.M.F. (e-mail: lfayad1{at}jhmi.edu).
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Abstract
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Computed tomography (CT) plays an important role in the evaluation of musculoskeletal disease in the pediatric patient. With the advent of high-performance 16-section multidetector CT, images can be produced with subsecond gantry rotation times and with submillimeter acquisition, which yields true isotropic high-resolution volume data sets; these features are not attainable with older spiral CT technology. Such capabilities are particularly helpful in the evaluation of pediatric patients by virtually eliminating the need for sedation and minimizing dependence on patient cooperation. The role of three-dimensional (3D) volume imaging in the evaluation of pediatric musculoskeletal disease continues to evolve, with this technique becoming increasingly important in detection and characterization of lesions as well as in decisions about patient care. Specific designs and protocols for multidetector CT studies can be selected to minimize radiation dose to the patient. Principal clinical applications of 3D CT in evaluation of the pediatric musculoskeletal system include developmental abnormalities, trauma, neoplasms, and postoperative imaging.
© RSNA, 2005
Abbreviations: DDH = developmental dysplasia of the hip, MPR = multiplanar reformation, SCFE = slipped capital femoral epiphysis, 3D = three-dimensional
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Introduction
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Computed tomography (CT) has always played an important role in the evaluation of complex musculoskeletal disease in the pediatric patient. The introduction of 16-section multidetector CT is especially valuable in the pediatric patient on a number of levels. First, this technique nearly eliminates the need for sedation and enables the successful completion of most studies in under 10 seconds, which helps minimize the need for patient cooperation. The tremendous speed of image acquisition with multidetector CT is particularly advantageous compared with performing magnetic resonance (MR) imaging in the pediatric patient, as MR imaging in a young child often requires sedation and the length of acquisitions necessitates significant patient cooperation. Second, with 16-section multidetector CT, isotropic volume image data are acquired and the ability to retrospectively reconstruct multiple high-resolution image sets from the original raw data is possible, thereby requiring only one acquisition for production of three-dimensional (3D) CT images in numerous planes. Finally, when used correctly, 3D CT volume imaging can help minimize the radiation dose to the pediatric patient (1–4).
In this review, key features of multidetector CT protocol design will be discussed. Many of the applications of 16-section multidetector CT in the pediatric patient will be reviewed through a series of case studies, accumulated during 20 years of CT use at a tertiary-care referral center and approximately 2 years experience with 16-section multidetector CT. The cases are chosen to highlight the advantages of this new technology and the impact of these CT studies on patient care.
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Study Protocol and Design
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Numerous articles have addressed concern over radiation dose to pediatric patients from radiologic studies, especially that due to CT (1–4). This concern has led to development of specific scan protocols tailored to patient size and weight, which have helped limit radiation dose to the pediatric patient (4). In addition, computer software and hardware on the new 16-section scanners address the issue of dose by providing more efficient detectors, as well as data acquisition schemes, like scan dose modulation or real-time dose reduction (5).
An optimal pediatric protocol will enable high-quality data sets to be generated at the lowest possible dose to the patient, while at the same time maintaining the information necessary for lesion detection and favorable patient management. The use of 16-section multidetector CT with volume visualization and postprocessing helps limit radiation exposure by offering single-plane acquisitions with isotropic data sets, which subsequently allow image display in any plane or perspective of choice (6). Anatomic areas that required acquisition of two consecutive scan data sets in perpendicular orientations in the past, such as the foot/ankle and hand/wrist, may now be imaged with a single true volume acquisition and postprocessing into the necessary planes and perspectives. Furthermore, a patient can be imaged in any position, as dictated by the patient’s comfort level, since subsequent reconstruction of the acquired data set can reformat the data into any plane of choice, including traditional axial, coronal, and sagittal planes as well as infinite oblique planes. With 16-section multidetector CT and isotropic resolution data sets, there is no longer a requirement for scanning in a particular plane.
Specific detailed scan protocols for the pediatric patient can be found in Table 1. These protocols are for a Sensation 16 scanner (Siemens Medical Solutions, Malvern, Pa), but similar guidelines apply to scanners from other manufacturers. Several important points are worth mentioning regarding protocol design: When the highest detail is needed, we suggest 0.75-mm collimation and generate 0.75-mm-thick sections at 0.5-mm intervals. When larger areas are to be scanned and when the detail needed is less critical, we use the 1.5-mm collimators and reconstruct 2-mm-thick sections at 1-mm intervals.
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Table 1. Protocols for 16-Section Multidetector CT for Evaluation of Musculoskeletal Disease in the Pediatric Patient
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Previous publications have documented the value of postprocessing CT data into multiplanar reformation (MPR) and 3D reconstruction images for the study and analysis of complex congenital or acquired skeletal diseases (7–11). After acquisition of the data set, the raw data are reconstructed as described in Table 1. The reconstructed data set is then transferred to a workstation for reformatting into 3D CT images. Two 3D rendering algorithms are used: volume rendering (VR) and shaded surface display (SSD). For general skeletal imaging, the VR technique is generally preferred over SSD to create 3D CT images because VR makes use of all the information in the acquired axial data set, whereas SSD uses only a portion of the data set to create the 3D image (6). The exception is the case of trauma, in which SSD is adequate for displaying fractures. In experienced hands, 3D manipulation of the data set may usually be performed and the results interpreted in less than 5 minutes for a routine skeletal examination.
The focus of 3D CT studies is to provide detailed display and analysis of complex cases, often for the purpose of planning surgical intervention. Key decisions as to the surgical approach, timing of surgery, selection of hardware, and sequence of repair are all based in great part on the imaging findings. Three-dimensional CT affects patient management and decision making in exstrophy repair, treatment of congenital hip disease, pectus excavatum reconstruction, and planning of osteotomies for slipped capital femoral epiphysis (SCFE). These studies are also valuable in measuring the success of a procedure, or, in cases where there is need for revision of the initial surgery, the images can be used for surgical guidance. For a patient-physician level interaction, 3D CT studies have also been shown to be valuable in patient communication by helping patients understand their disease and the planned surgical repair that may be needed. Future directions in this arena include the development of more detailed mapping information, which will be especially valuable as robotic surgery becomes mainstream.
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Clinical Applications
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Congenital and Acquired Diseases
Developmental Dysplasia of the Hip.—
Developmental dysplasia of the hip (DDH), or, as it is commonly known, congenital hip dysplasia, is a spectrum of disorders encompassing acetabular dysplasia and hip dislocation. It is due to an abnormal position of the femoral head in the acetabulum, which results in abnormal growth patterns in both the proximal femur and the acetabulum (12). In most cases, the femoral head is located superior and lateral to its normal location. DDH is up to eight times more common in girls and is said to occur in 1 in 1,000 live births (13,14).
While the diagnosis is typically made from a combination of physical examination, plain radiographic, and ultrasound findings (15), CT can be used in most difficult cases or as an imaging alternative by using low-dose scanning. At some institutions and in our experience, however, CT is more commonly used in the postoperative period to define the success of the reduction when the patient’s hip has been placed in a cast (16). MR imaging, like CT, is often reserved for more severe cases and has the advantage of also delineating acetabular hyaline cartilage and labral abnormalities.
For DDH, early diagnosis and intervention are necessary to avoid long-term complications like degenerative disease or limb shortening. In cases of late diagnosis, iliac osteotomy and/or femoral osteotomy may be necessary for successful intervention (12). In these more complicated cases, CT with 3D volume rendering is especially valuable (Figs 1–3). Reconstruction of data by using volume rendering with real-time display is ideal for defining the location of the femoral head in relationship to the acetabulum.
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Figure 1a. DDH in a 5-month-old girl with a history of hemangiomas and with widening of the left hip joint space at radiography. (a) Axial CT image does not clearly show the location of the left femoral head. (b–d) Coronal posterior (b), coronal anterior (c), and axial oblique (d) volume-rendered 3D CT images of the pelvis show superolateral displacement of the left femoral head without evidence of a space-occupying lesion. At the request of the referring physician, the lumbar spine was included in the study because the patient was experiencing hip pain. Hip pain is occasionally referred from the lumbar spine. Typically, a CT examination for DDH does not require imaging of the lumbar spine.
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Figure 1b. DDH in a 5-month-old girl with a history of hemangiomas and with widening of the left hip joint space at radiography. (a) Axial CT image does not clearly show the location of the left femoral head. (b–d) Coronal posterior (b), coronal anterior (c), and axial oblique (d) volume-rendered 3D CT images of the pelvis show superolateral displacement of the left femoral head without evidence of a space-occupying lesion. At the request of the referring physician, the lumbar spine was included in the study because the patient was experiencing hip pain. Hip pain is occasionally referred from the lumbar spine. Typically, a CT examination for DDH does not require imaging of the lumbar spine.
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Figure 1c. DDH in a 5-month-old girl with a history of hemangiomas and with widening of the left hip joint space at radiography. (a) Axial CT image does not clearly show the location of the left femoral head. (b–d) Coronal posterior (b), coronal anterior (c), and axial oblique (d) volume-rendered 3D CT images of the pelvis show superolateral displacement of the left femoral head without evidence of a space-occupying lesion. At the request of the referring physician, the lumbar spine was included in the study because the patient was experiencing hip pain. Hip pain is occasionally referred from the lumbar spine. Typically, a CT examination for DDH does not require imaging of the lumbar spine.
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Figure 1d. DDH in a 5-month-old girl with a history of hemangiomas and with widening of the left hip joint space at radiography. (a) Axial CT image does not clearly show the location of the left femoral head. (b–d) Coronal posterior (b), coronal anterior (c), and axial oblique (d) volume-rendered 3D CT images of the pelvis show superolateral displacement of the left femoral head without evidence of a space-occupying lesion. At the request of the referring physician, the lumbar spine was included in the study because the patient was experiencing hip pain. Hip pain is occasionally referred from the lumbar spine. Typically, a CT examination for DDH does not require imaging of the lumbar spine.
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Figure 2a. DDH in a 7-year-old girl. (a, b) Coronal volume-rendered 3D CT images obtained in two slightly oblique orientations show dysplasia of the right hip with a shallow acetabulum and flattening of the right femoral head. (c) Coronal MPR CT image obtained for comparison shows identical findings.
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Figure 2b. DDH in a 7-year-old girl. (a, b) Coronal volume-rendered 3D CT images obtained in two slightly oblique orientations show dysplasia of the right hip with a shallow acetabulum and flattening of the right femoral head. (c) Coronal MPR CT image obtained for comparison shows identical findings.
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Figure 2c. DDH in a 7-year-old girl. (a, b) Coronal volume-rendered 3D CT images obtained in two slightly oblique orientations show dysplasia of the right hip with a shallow acetabulum and flattening of the right femoral head. (c) Coronal MPR CT image obtained for comparison shows identical findings.
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Figure 3a. DDH in a 16-year-old boy with Down syndrome. (a) Axial CT image shows that the femoral heads are uncovered bilaterally. (b) Coronal MPR CT image shows bilateral shallow acetabula and uncovering of the femoral heads. The abnormalities are more severe on the left side than on the right. (c) Coronal volume-rendered 3D CT image shows the deformities and displacement of the femoral heads.
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Figure 3b. DDH in a 16-year-old boy with Down syndrome. (a) Axial CT image shows that the femoral heads are uncovered bilaterally. (b) Coronal MPR CT image shows bilateral shallow acetabula and uncovering of the femoral heads. The abnormalities are more severe on the left side than on the right. (c) Coronal volume-rendered 3D CT image shows the deformities and displacement of the femoral heads.
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Figure 3c. DDH in a 16-year-old boy with Down syndrome. (a) Axial CT image shows that the femoral heads are uncovered bilaterally. (b) Coronal MPR CT image shows bilateral shallow acetabula and uncovering of the femoral heads. The abnormalities are more severe on the left side than on the right. (c) Coronal volume-rendered 3D CT image shows the deformities and displacement of the femoral heads.
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Slipped Capital Femoral Epiphysis.—
Slipped capital femoral epiphysis (SCFE) is a condition in which the femoral epiphysis typically slips posteriorly, medially, and inferiorly. The etiology of this condition includes a variety of factors such as trauma, hormonal influences, and obesity. SCFE is a bilateral condition in up to 35% of cases and is most commonly observed between the ages of 8 and 17 years. Unlike in DDH, boys are more frequently affected than girls (14,17).
While the abnormality is identifiable with radiography, CT with coronal and sagittal display may prove useful in cases where the specific diagnosis is equivocal or to exclude other causes of hip pain, including osteoid osteoma or a septic joint. CT may also help detect contralateral involvement, a useful feature since treatment is more effective in early stages. It should be noted that MR imaging has become increasingly used in the assessment of potential SCFE, as MR imaging may delineate physeal changes of both pre-SCFE and SCFE and demonstrate very early changes at a time when radiographs and CT scans may appear normal (18). In addition, MR imaging is useful for excluding other causes of hip pain, including those not easily demonstrated with CT, such as myositis.
Treatment is easier when an early diagnosis is made. Classically, repair is performed with pin placement through the epiphyseal plate to prevent further slippage (Fig 4). When repair is unsuccessful, SCFE may result in avascular necrosis (AVN) of the femoral head or premature closure of the epiphysis (14).
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Figure 4a. Evaluation of surgical screws in a 16-year-old girl with a history of hip fixation for bilateral SCFE. (a) Axial CT image shows bilateral intramedullary surgical screws. Note the streak artifacts surrounding the screws (arrows). (b) Coronal volume-rendered 3D CT image shows the bilateral intramedullary screws (arrows). Note that the streak artifacts related to the metal screws are eliminated with the rendering technique. (c) Coronal MPR CT image obtained for comparison shows the intramedullary screws (arrows). The alignment is satisfactory.
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Figure 4b. Evaluation of surgical screws in a 16-year-old girl with a history of hip fixation for bilateral SCFE. (a) Axial CT image shows bilateral intramedullary surgical screws. Note the streak artifacts surrounding the screws (arrows). (b) Coronal volume-rendered 3D CT image shows the bilateral intramedullary screws (arrows). Note that the streak artifacts related to the metal screws are eliminated with the rendering technique. (c) Coronal MPR CT image obtained for comparison shows the intramedullary screws (arrows). The alignment is satisfactory.
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Figure 4c. Evaluation of surgical screws in a 16-year-old girl with a history of hip fixation for bilateral SCFE. (a) Axial CT image shows bilateral intramedullary surgical screws. Note the streak artifacts surrounding the screws (arrows). (b) Coronal volume-rendered 3D CT image shows the bilateral intramedullary screws (arrows). Note that the streak artifacts related to the metal screws are eliminated with the rendering technique. (c) Coronal MPR CT image obtained for comparison shows the intramedullary screws (arrows). The alignment is satisfactory.
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Legg-Calvé-Perthes Disease. —
Legg-Calvé-Perthes disease is also known as idiopathic avascular necrosis of the hip. It occurs at a younger age than SCFE (4–8 years); but, as with SCFE, Legg-Calvé-Perthes disease is more common in boys (19). Although the diagnosis is usually accomplished with plain radiography or, more recently, MR imaging (19), multidetector CT is commonly being used with low-dose protocols and a study time of under 5 seconds (20,21), which is critical in these younger patients. The findings of asymmetric femoral epiphysis, joint effusion, and/or the crescent sign can all be defined on coronal MPR or volume-rendered images. Later-stage disease with fragmentation of the epiphysis or irregularity of the epiphysis, as well as deformities of the femoral neck, are well documented on 3D CT views (21) (Fig 5).
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Figure 5a. Legg-Calvé-Perthes disease in a 9-year-old boy with left hip pain. (a) Axial CT image shows remodeling of the left femoral neck. The epiphysis is difficult to evaluate on axial source images. (b) Coronal volume-rendered 3D CT image shows fragmentation of the left femoral epiphysis (thin arrow), a finding compatible with Legg-Calvé-Perthes disease. The patient has already undergone left acetabuloplasty (thick arrow). (c) Coronal MPR CT image shows fragmentation of the epiphysis (thin arrow) and remodeling of the femoral neck (thick arrow).
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Figure 5b. Legg-Calvé-Perthes disease in a 9-year-old boy with left hip pain. (a) Axial CT image shows remodeling of the left femoral neck. The epiphysis is difficult to evaluate on axial source images. (b) Coronal volume-rendered 3D CT image shows fragmentation of the left femoral epiphysis (thin arrow), a finding compatible with Legg-Calvé-Perthes disease. The patient has already undergone left acetabuloplasty (thick arrow). (c) Coronal MPR CT image shows fragmentation of the epiphysis (thin arrow) and remodeling of the femoral neck (thick arrow).
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Figure 5c. Legg-Calvé-Perthes disease in a 9-year-old boy with left hip pain. (a) Axial CT image shows remodeling of the left femoral neck. The epiphysis is difficult to evaluate on axial source images. (b) Coronal volume-rendered 3D CT image shows fragmentation of the left femoral epiphysis (thin arrow), a finding compatible with Legg-Calvé-Perthes disease. The patient has already undergone left acetabuloplasty (thick arrow). (c) Coronal MPR CT image shows fragmentation of the epiphysis (thin arrow) and remodeling of the femoral neck (thick arrow).
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These images are used for both defining the extent of disease as well as for surgical planning in cases where surgery is contemplated. In general, outcome is related to the age of the patient at presentation and the severity of disease (22). Surgery is usually considered for advanced cases and older children and often consists of acetabular reconstruction with femoral osteotomy (14). Multidetector CT may be useful in the postoperative period to define results or for evaluation of patients with new or persisting symptoms. In this setting, 3D CT is helpful in limiting artifacts from metal pins or screws (6).
Pectus Deformities.—
In most patients with pectus deformities, CT is not necessary to determine the extent of disease or for surgical planning, as chest radiography may be sufficient. However, in patients with more severe deformities or in cases where initial repair was unsuccessful, CT with 3D mapping of the chest wall may be critical in planning the type of surgical approach as well as the timing of surgery (23). In these cases, a single breath-hold or shallow breathing acquisition at a lower milliampere-seconds value can be performed, with the key information needed by the pediatric thoracic surgeon provided through a combination of sagittal MPR views and volume-rendered 3D mapping (Figs 6, 7).
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Figure 6a. Pectus excavatum in a 7-year-old boy. (a) Sagittal volume-rendered 3D CT image shows pectus excavatum and narrowing of the anteroposterior diameter of the chest. Arrow = sternum. (b) Sagittal 3D CT image, produced by modifying the volume-rendering parameters to selectively display the skeletal anatomy, shows the deformed sternum (arrowheads).
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Figure 6b. Pectus excavatum in a 7-year-old boy. (a) Sagittal volume-rendered 3D CT image shows pectus excavatum and narrowing of the anteroposterior diameter of the chest. Arrow = sternum. (b) Sagittal 3D CT image, produced by modifying the volume-rendering parameters to selectively display the skeletal anatomy, shows the deformed sternum (arrowheads).
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Tarsal Coalition.—
Tarsal coalition is one of the causes of hindfoot rigidity and foot or ankle pain. Talocalcaneal and calcaneonavicular are the most common forms of tarsal coalition, with other coalitions including calcaneocuboid and cuboid-navicular being uncommon. Tarsal coalitions may be osseous or nonosseous (fibrous or cartilaginous) in nature, and multiple coalitions often exist in the same patient (24). The diagnosis can be overlooked by radiography, and CT has been the study of choice for evaluation of these patients.
In the past, it typically required two separate acquisitions to fully view all the subtalar articulations. With 16-section multidetector CT and isotropic data sets, acquisition in only one plane is required and subsequent reconstruction to other desired planes can be performed. In general, for detection of a coalition between two bones, a plane perpendicular to the articulation will demonstrate the coalition (Fig 8). For example, for a talocalcaneal coalition of the middle facet, the coronal plane is favored (Fig 9). The benefit of 3D CT is that imaging is not limited to a single plane; rather, multiple imaging planes can be reconstructed in real time to search for the different types of coalitions.
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Figure 8. Albright hereditary osteodystrophy in an 11-year-old girl. Sagittal oblique volume-rendered 3D CT image of the ankle shows proximity of the anterior process of the calcaneus to the navicular bone with surrounding sclerosis (arrow), findings indicative of a nonosseous calcaneonavicular coalition. Note the shortened third and fourth metatarsals associated with the syndrome.
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Figure 9a. Bilateral talocalcaneal coalitions in a 7-year-old patient with foot pain. Coronal MPR CT images of the right (a) and left (b) ankles show nonosseous talocalcaneal coalitions. The patient was treated with surgery and resection of the coalitions.
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Figure 9b. Bilateral talocalcaneal coalitions in a 7-year-old patient with foot pain. Coronal MPR CT images of the right (a) and left (b) ankles show nonosseous talocalcaneal coalitions. The patient was treated with surgery and resection of the coalitions.
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The diagnosis of a tarsal coalition may be made with MR imaging, but CT is a more cost-effective modality for determining the presence of a coalition, since an MR imaging examination of the foot is typically several hundred dollars more expensive than a CT study of the foot (25).
Trauma
Although most patients with fractures need little more than radiographic evaluation, in more complex cases, CT can be invaluable for defining the extent and severity of injury, thereby ensuring timely and proper therapeutic intervention (26). In Salter fractures or fractures involving the epiphyseal plate, CT is useful in defining the extent of displacement of the physeal component, especially in Salter 2–4 injuries (Fig 10). The information provided by CT is especially useful for selecting which patients will need internal fixation, which is usually determined by the extent of physeal displacement. These decisions are critical as Salter injuries, particularly Salter 3–5 injuries, are associated with growth arrest. For example, in distal tibial physeal fractures, premature closure of the physis occurs in 27% of Salter injuries and, specifically, 38% of Salter 3 and 4 injuries (27). In addition to the information provided by multidetector CT at the initial diagnosis of a Salter injury, multidetector CT can also be used at follow-up for the assessment of developing deformities and premature physeal closure. Other complaints following fractures include compartment syndrome and ligamentous laxity, which can occasionally be suggested by multidetector CT.
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Figure 10a. Tibial fracture in a 13-year-old boy who experienced a fall. (a) Axial CT image shows a fracture of the distal tibia. However, the relationship of the fracture to the physis is not clearly demonstrated. (b) Coronal volume-rendered 3D CT image of the ankle shows that the fracture is a Salter type IV injury. (c, d) Coronal MPR CT images (c obtained posterior to d) show the Salter type IV fracture extending into the joint space.
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Figure 10b. Tibial fracture in a 13-year-old boy who experienced a fall. (a) Axial CT image shows a fracture of the distal tibia. However, the relationship of the fracture to the physis is not clearly demonstrated. (b) Coronal volume-rendered 3D CT image of the ankle shows that the fracture is a Salter type IV injury. (c, d) Coronal MPR CT images (c obtained posterior to d) show the Salter type IV fracture extending into the joint space.
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Figure 10c. Tibial fracture in a 13-year-old boy who experienced a fall. (a) Axial CT image shows a fracture of the distal tibia. However, the relationship of the fracture to the physis is not clearly demonstrated. (b) Coronal volume-rendered 3D CT image of the ankle shows that the fracture is a Salter type IV injury. (c, d) Coronal MPR CT images (c obtained posterior to d) show the Salter type IV fracture extending into the joint space.
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Figure 10d. Tibial fracture in a 13-year-old boy who experienced a fall. (a) Axial CT image shows a fracture of the distal tibia. However, the relationship of the fracture to the physis is not clearly demonstrated. (b) Coronal volume-rendered 3D CT image of the ankle shows that the fracture is a Salter type IV injury. (c, d) Coronal MPR CT images (c obtained posterior to d) show the Salter type IV fracture extending into the joint space.
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The other group of patients that benefits from CT is the group with potential multiorgan injury associated with skeletal trauma. For example, the child who has been involved in a motor vehicle accident will be evaluated for abdominal organ injury and potential bladder injury as well as fractures. In these cases, a single CT examination can answer all questions without requiring additional CT or radiographic examinations, thereby limiting the patient’s overall radiation exposure dose. For example, a planned CT examination of the pelvis can eliminate the need for pelvic radiographs and cystography. This is accomplished by one of the main advantages of multidetector CT, its ability to enable retrospective reconstruction of the acquired data set with different algorithms, specifically at thinner sections and at closer scan intervals for evaluation of the skeleton in addition to other organ systems.
On our current 16-section multidetector CT system, the 0.75-mm detectors can reconstruct data at any section thickness from 0.75 to 10 mm (with the exception of 9 mm). Similarly, with the 1.5-mm detectors, any section thickness from 2 to 10 mm (with the exception of 9 mm) can be obtained. Of course, any interscan interval can be used and is typically selected in the 0.5–1-mm range. Therefore, the same data set acquired in a CT study performed for evaluation of thoracic and abdominal organ injury (3–5-mm section thickness) can be reconstructed at a thin section thickness (0.75 mm) to evaluate the thoracic and lumbar spine for the presence of fractures.
With trauma being the leading cause of morbidity and mortality in the pediatric patient (28), more aggressive use of CT may improve both diagnosis and outcome (Figs 10–13).
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Figure 11a. Elbow fracture in a 7-year-old girl. Multidetector CT was performed for surgical planning and complete evaluation of the fracture, which was diagnosed with radiography. At clinical evaluation, intraarticular displacement of a fracture fragment was suspected. (a) Axial CT image shows a fracture of the right proximal radius. There is posterolateral displacement of a fracture fragment (arrow). (b) Coronal oblique volume-rendered 3D CT image of the elbow shows a fracture dislocation of the radial head. Note the fracture fragment (arrow). (c) Sagittal volume-rendered 3D CT image of the elbow shows posterior displacement of the fracture fragment (thin arrow). Note the remaining preserved epiphysis (thick arrow).
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Figure 11b. Elbow fracture in a 7-year-old girl. Multidetector CT was performed for surgical planning and complete evaluation of the fracture, which was diagnosed with radiography. At clinical evaluation, intraarticular displacement of a fracture fragment was suspected. (a) Axial CT image shows a fracture of the right proximal radius. There is posterolateral displacement of a fracture fragment (arrow). (b) Coronal oblique volume-rendered 3D CT image of the elbow shows a fracture dislocation of the radial head. Note the fracture fragment (arrow). (c) Sagittal volume-rendered 3D CT image of the elbow shows posterior displacement of the fracture fragment (thin arrow). Note the remaining preserved epiphysis (thick arrow).
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Figure 11c. Elbow fracture in a 7-year-old girl. Multidetector CT was performed for surgical planning and complete evaluation of the fracture, which was diagnosed with radiography. At clinical evaluation, intraarticular displacement of a fracture fragment was suspected. (a) Axial CT image shows a fracture of the right proximal radius. There is posterolateral displacement of a fracture fragment (arrow). (b) Coronal oblique volume-rendered 3D CT image of the elbow shows a fracture dislocation of the radial head. Note the fracture fragment (arrow). (c) Sagittal volume-rendered 3D CT image of the elbow shows posterior displacement of the fracture fragment (thin arrow). Note the remaining preserved epiphysis (thick arrow).
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Figure 12a. Acetabular fracture after a motor vehicle accident in a 17-year-old patient. (a) Coronal volume-rendered 3D CT image (anterior projection) shows asymmetry of the acetabula with a possible fracture on the right (arrow). (b) Sagittal volume-rendered 3D CT image clearly shows the fracture of the posterior acetabular wall (arrow).
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Figure 12b. Acetabular fracture after a motor vehicle accident in a 17-year-old patient. (a) Coronal volume-rendered 3D CT image (anterior projection) shows asymmetry of the acetabula with a possible fracture on the right (arrow). (b) Sagittal volume-rendered 3D CT image clearly shows the fracture of the posterior acetabular wall (arrow).
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Figure 13a. Slipped humeral epiphysis in a 13-year-old boy who was injured while playing football. He presented with right shoulder pain. (a) Axial CT image of the right shoulder does not clearly show a slipped humeral epiphysis. (b, c) Coronal MPR (b) and volume-rendered 3D (c) CT images show the slipped epiphysis.
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Figure 13b. Slipped humeral epiphysis in a 13-year-old boy who was injured while playing football. He presented with right shoulder pain. (a) Axial CT image of the right shoulder does not clearly show a slipped humeral epiphysis. (b, c) Coronal MPR (b) and volume-rendered 3D (c) CT images show the slipped epiphysis.
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Figure 13c. Slipped humeral epiphysis in a 13-year-old boy who was injured while playing football. He presented with right shoulder pain. (a) Axial CT image of the right shoulder does not clearly show a slipped humeral epiphysis. (b, c) Coronal MPR (b) and volume-rendered 3D (c) CT images show the slipped epiphysis.
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Skeletal Tumors
Multidetector CT supplemented by multiplanar reformation (MPR) and 3D imaging provides certain unique capabilities in the evaluation of known or suspected musculoskeletal tumors in the pediatric patient. The importance of the ability for scan times under 10 seconds cannot be overemphasized in a scared and fragile pediatric patient. CT is more sensitive to the presence of a pediatric tumor and has been shown to demonstrate information not attainable with bone scintigraphy or plain radiography; in up to 77% of cases, CT has been shown to be of significant diagnostic value, providing better information regarding tumor extent, location, and relationships compared with other modalities (29,30).
Use of multidetector CT has specific advantages that include but are not limited to the following capacities: (a) The ability to detect lesions in difficult to evaluate areas, including the sacrum and bony pelvis (Fig 14). (b) The ability to combine volume acquisitions with CT angiography for better definition of tumor vascularity and to define involvement of adjacent structures, including blood vessels and muscle. (c) The ability to define the extent of tumor involvement, including extension across the epiphysis or joint space. (d) The ability to detect and define the presence of tumor matrix (such as osteoid or chondroid) as well as the presence of fat or calcification within tumors. (e) The ability to define the presence and extent of periosteal or endosteal reaction. (f) The ability to distinguish true neoplasms from processes that mimic tumors, such as osteomyelitis, myositis ossificans, and fractures (Fig 15). Such entities may demonstrate increased fluorine 18 fluorodeoxyglucose (FDG) uptake at positron emission tomography (PET) (31,32).
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Figure 14a. Sacral osteosarcoma in an 11-year-old girl with a history of pelvic osteosarcoma. (a) Axial CT image of the pelvis shows a left-sided sacral lesion (arrow) that contains osteoid matrix and is associated with a soft-tissue mass. The relationship to the posterior sacroiliac joint is not clearly demonstrated. (b) Coronal volume-rendered 3D CT image shows that the sacral lesion abuts the sacroiliac joint and involves the lower sacral foramina. (c) Coronal volume-rendered 3D CT image (posterior perspective) shows the sacral lesion.
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Figure 14b. Sacral osteosarcoma in an 11-year-old girl with a history of pelvic osteosarcoma. (a) Axial CT image of the pelvis shows a left-sided sacral lesion (arrow) that contains osteoid matrix and is associated with a soft-tissue mass. The relationship to the posterior sacroiliac joint is not clearly demonstrated. (b) Coronal volume-rendered 3D CT image shows that the sacral lesion abuts the sacroiliac joint and involves the lower sacral foramina. (c) Coronal volume-rendered 3D CT image (posterior perspective) shows the sacral lesion.
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Figure 14c. Sacral osteosarcoma in an 11-year-old girl with a history of pelvic osteosarcoma. (a) Axial CT image of the pelvis shows a left-sided sacral lesion (arrow) that contains osteoid matrix and is associated with a soft-tissue mass. The relationship to the posterior sacroiliac joint is not clearly demonstrated. (b) Coronal volume-rendered 3D CT image shows that the sacral lesion abuts the sacroiliac joint and involves the lower sacral foramina. (c) Coronal volume-rendered 3D CT image (posterior perspective) shows the sacral lesion.
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Figure 15a. Fibrous cortical defects and nonossifying fibromas in a 13-year-old boy with right knee pain. Multiple lesions were seen at plain radiography. (a) Axial CT image obtained through one of the lesions shows an eccentric lytic lesion involving the cortex with a probable very thin rim of overlying periosteum, findings indicative of a fibrous cortical defect. (b) Coronal MPR CT image shows multiple eccentric, well-defined, lobulated, low-attenuation lesions with sclerotic borders, findings compatible with nonossifying fibromas and fibrous cortical defects.
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Figure 15b. Fibrous cortical defects and nonossifying fibromas in a 13-year-old boy with right knee pain. Multiple lesions were seen at plain radiography. (a) Axial CT image obtained through one of the lesions shows an eccentric lytic lesion involving the cortex with a probable very thin rim of overlying periosteum, findings indicative of a fibrous cortical defect. (b) Coronal MPR CT image shows multiple eccentric, well-defined, lobulated, low-attenuation lesions with sclerotic borders, findings compatible with nonossifying fibromas and fibrous cortical defects.
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Certain tumors in the pediatric age group are not only more frequent but have signatures, detectable with CT, that may allow a very specific diagnosis (33). These are shown in Table 2. Compared with MR imaging, which is more often useful for defining the extent of a marrow or soft-tissue abnormality, CT can be more helpful in characterizing a lesion.
The use of CT angiography as part of a comprehensive CT examination may also prove valuable, especially in cases with muscle or soft-tissue involvement. Neovascularity is well seen with either the volume rendering technique or maximum intensity projection (MIP) imaging (34). Multidetector CT can also be used to select a biopsy site in cases of suspected tumors. Of course, biopsies can be performed under CT guidance, especially in systems with CT fluoroscopy.
Postoperative Imaging
Sixteen-section multidetector CT with postprocessing of the data set by using MPR and 3D volume rendering is valuable in the postoperative patient with orthopedic hardware in place, as it is capable of potentially eradicating streak artifact associated with metal devices (6,35). CT of orthopedic hardware results in severe x-ray attenuation, which can lead to "missing" data on reconstructed axial images. With 3D imaging, data reformation from the axial plane into other planes will weight the true signal over the randomly distributed artifact when integrating two adjacent axial images. In this way, the true signal will be enhanced and artifact related to metal will be reduced on volume-rendered 3D CT images.
Multidetector CT can be used to evaluate the success of intervention as well as determine the etiology of any new symptoms or complaints (Figs 16–20).
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Figure 16a. Orthopedic hardware in a 6-year-old girl with McCune-Albright syndrome (polyostotic fibrous dysplasia). She underwent osteotomy with placement of a dynamic hip screw and a lateral plate. (a) Coronal volume-rendered 3D CT image shows varus deformity of the right hip. Note the orthopedic hardware. (b) Coronal volume-rendered 3D CT image obtained more obliquely shows the metallic hardware. (c) Coronal MPR CT image shows extensive streak artifacts related to the orthopedic hardware. Volume rendering nearly eliminates these artifacts.
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Figure 16b. Orthopedic hardware in a 6-year-old girl with McCune-Albright syndrome (polyostotic fibrous dysplasia). She underwent osteotomy with placement of a dynamic hip screw and a lateral plate. (a) Coronal volume-rendered 3D CT image shows varus deformity of the right hip. Note the orthopedic hardware. (b) Coronal volume-rendered 3D CT image obtained more obliquely shows the metallic hardware. (c) Coronal MPR CT image shows extensive streak artifacts related to the orthopedic hardware. Volume rendering nearly eliminates these artifacts.
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Figure 16c. Orthopedic hardware in a 6-year-old girl with McCune-Albright syndrome (polyostotic fibrous dysplasia). She underwent osteotomy with placement of a dynamic hip screw and a lateral plate. (a) Coronal volume-rendered 3D CT image shows varus deformity of the right hip. Note the orthopedic hardware. (b) Coronal volume-rendered 3D CT image obtained more obliquely shows the metallic hardware. (c) Coronal MPR CT image shows extensive streak artifacts related to the orthopedic hardware. Volume rendering nearly eliminates these artifacts.
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Figure 17. Orthopedic hardware in a 12-year-old girl with Kniest syndrome (a skeletal dysplasia). She was treated with bilateral valgus osteotomy. Coronal volume-rendered 3D CT image of the lower extremities shows orthopedic hardware. Note the dysplastic acetabula and enlarged distal femoral epiphyses.
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Figure 18. Orthopedic hardware in a 17-year-old girl with cerebral palsy and scoliosis who underwent corrective surgery. Coronal volume-rendered 3D CT image of the pelvis shows transpedicle screws and vertical rods in the spine. She also underwent a right Chiari osteotomy with internal fixation for a right hip subluxation. Note the absence of metal artifact.
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Figure 19a. Orthopedic hardware in a 14-year-old boy with Legg-Calvé-Perthes disease. A left hip osteotomy was performed to increase coverage of the femoral head and reduce subluxation. (a) Coronal volume-rendered 3D CT image of the pelvis shows surgical screws at the osteotomy site. Note the deformed femoral head. (b) Coronal MPR CT image shows streak artifacts related to one of the surgical screws. Note the deformed femoral head and remodeled femoral neck.
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Figure 19b. Orthopedic hardware in a 14-year-old boy with Legg-Calvé-Perthes disease. A left hip osteotomy was performed to increase coverage of the femoral head and reduce subluxation. (a) Coronal volume-rendered 3D CT image of the pelvis shows surgical screws at the osteotomy site. Note the deformed femoral head. (b) Coronal MPR CT image shows streak artifacts related to one of the surgical screws. Note the deformed femoral head and remodeled femoral neck.
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Figure 20. Orthopedic hardware in a 14-year-old girl who was struck by a bicycle and sustained multiple fractures. Coronal oblique volume-rendered 3D CT image of the pelvis shows a surgical screw traversing a fracture of the anterior column of the acetabulum.
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Conclusions
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Sixteen-section multidetector CT has unique imaging capabilities that are advantageous in the pediatric population. This article has reviewed some of the principles of imaging as well as detailed some of the common and uncommon applications in pediatric musculoskeletal imaging.
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References
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- Suess C, Chen X. Dose optimization in pediatric CT: current technology and future innovations. Pediatr Radiol
2002; 32:729–734.[CrossRef][Medline]
- Linton OW, Mettler FA Jr; National Council on Radiation Protection and Measurements. National conference on dose reduction in CT, with an emphasis on pediatric patients
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Abstract
Introduction
