Initial Imaging for Scoliosis in a 12-Year-Old Girl
Upright PA (posteroanterior) and lateral radiographs of the complete spine are the most appropriate initial imaging studies for this 12-year-old girl with a scoliometer reading of 18 degrees. 1
Rationale for Plain Radiography First
Radiography is the primary diagnostic modality for adolescent idiopathic scoliosis, which represents 75-80% of all scoliosis cases and is the most likely diagnosis in this patient. 1
The upright PA and lateral views serve multiple critical functions: they confirm the diagnosis, exclude congenital vertebral anomalies, measure the Cobb angle to quantify curve severity, and establish a baseline for monitoring progression. 1, 2
A scoliometer reading of 18 degrees suggests significant curvature that warrants radiographic confirmation, as this level of trunk rotation typically correlates with a Cobb angle requiring active monitoring or treatment. 2
Why Not MRI Initially?
While MRI has important roles in scoliosis evaluation, it is not the first-line imaging study for typical adolescent idiopathic scoliosis:
MRI is selectively indicated only when specific risk factors for neural axis abnormalities are present, as only 2-4% of adolescents with idiopathic scoliosis have intraspinal abnormalities. 1, 3
Risk factors that would prompt MRI include: left thoracic curve pattern, short segment curve (4-6 levels), absence of apical segment lordosis (hyperkyphosis), rapid curve progression (>1° per month), functionally disruptive pain, focal neurologic findings, male sex, or pes cavus. 1, 2
The American College of Radiology recommends radiographs as usually appropriate for initial imaging in adolescent idiopathic scoliosis when no risk factors are present. 4
Critical Next Steps After Initial Radiographs
Once radiographs are obtained, management depends on the measured Cobb angle:
If Cobb angle >20 degrees in this skeletally immature patient, the likelihood of curve progression exceeds 70%, warranting close monitoring or bracing consideration. 1, 2
Serial PA radiographs become integral for follow-up, limited to once every 12 months for patients at Risser stages 0-3 to minimize radiation exposure. 1, 4
Consider MRI evaluation if radiographs reveal any atypical features (left thoracic curve, short segment involvement, absence of normal apical lordosis) or if the patient has neurologic symptoms, even if subtle. 2, 3
Common Pitfalls to Avoid
Do not assume a normal neurologic examination excludes intraspinal pathology - studies show physical examination has only 62% accuracy for detecting intraspinal anomalies in congenital scoliosis, and similar limitations exist in idiopathic cases. 1
Use PA projection rather than AP to reduce breast radiation exposure in this adolescent female, as repeated imaging will likely be necessary for monitoring. 2
Do not delay radiographic confirmation - the scoliometer reading of 18 degrees is significant enough to warrant definitive measurement via Cobb angle, which can only be obtained from radiographs. 5