Thoracic Spine X-Ray

Thoracic spine radiography images the 12 thoracic vertebrae, the intervertebral discs, the costovertebral and costotransverse joints and the paravertebral soft tissues, with an anteroposterior (AP) view and a lateral view. The lateral view of the upper thoracic spine (T1 to T4) is limited by overlapping shoulders, and a swimmer's view or CT is used to show this region.

A coned view of the cervicothoracic junction can be required. The effective dose is about 1 mSv for an AP and lateral pair. Thoracic kyphosis normally measures 20 to 40 degrees by the Cobb method between T4 and T12, and the AP view shows the pedicles, interpedicular distances, paraspinal lines, and any lateral curvature.

Plain films remain a first investigation for thoracic back pain with red flags, vertebral fractures, deformity (kyphosis and scoliosis), suspected infection and metabolic bone disease, but their sensitivity is limited; MRI is the test for neurological symptoms, infection, and tumour, and CT for trauma and fracture planning.

Osteoporotic compression fractures (commonest at T7 to T8 and T12 to L1) are often incidentally detected on chest radiographs and lateral spine films. Most thoracic pain in adults is mechanical or musculoskeletal and does not need imaging.

Indications. Thoracic back pain with red flags (age over 50 with new pain, cancer history, fever, weight loss, unexplained nocturnal pain, neurological signs, trauma, immunosuppression). Suspected vertebral fracture (osteoporotic or traumatic) where CT is not available. Kyphosis or scoliosis assessment. Suspected spinal tuberculosis or other infection.

Known malignancy with spinal metastasis surveillance in settings without MRI. Ankylosing spondylitis and diffuse idiopathic skeletal hyperostosis. Follow up after fixation or vertebroplasty. Not for non-specific thoracic back pain without red flags.

Contraindications and precautions. No absolute contraindication. Pregnancy: avoid unless essential, because the dose to the uterus is small but nonzero; MRI is preferred. In trauma, the spine is immobilised and the patient is log rolled; the lateral view is a cross-table film. Remove clothing with metal and ECG leads.

Preparation and technique. Standing or supine AP view with full inspiration for the AP film (to blur lung markings on the lateral), and lateral view with the arms raised and the breath held in inspiration or expiration, depending on the vertebral level.

Normal appearances. Gentle thoracic kyphosis of 20 to 40 degrees. Vertebral bodies increase slightly in height from T1 to T12, with straight sides, uniform endplates and posterior wall height similar to the anterior. Disc spaces are similar and slightly wedged anteriorly in the mid-thoracic region.

Pedicles are oval and symmetrical, the interpedicular distance is smooth and increases gradually, and the paravertebral lines are thin (the left is visible beside the aorta, and widening over 10 mm suggests a mass).

Interpretation.

• Osteoporotic compression fracture: loss of anterior vertebral height (mild 20 to 25%, moderate 25 to 40%, severe over 40%) as a wedge, biconcave or crush deformity, with preserved posterior wall and cortical breaks, typically in older patients with osteopenia. Multiple fractures increase the kyphosis.
• Traumatic fractures: anterior wedge compression (stable), burst fracture (loss of posterior wall height, retropulsion of fragments into the canal, widened interpedicular distance on AP), Chance fracture (horizontal fracture through the vertebral body and posterior elements, from flexion distraction injuries with lap seat belts), and fracture dislocation (displacement and rib fractures).
• Malignancy: lytic or sclerotic vertebral lesions, collapse of the vertebral body with loss of a pedicle on the AP view ("winking owl" sign), a paravertebral soft tissue mass, and sparing of the disc space. Vertebral collapse with a pedicle lesion favours malignancy over osteoporosis. Plain films show metastases only after 30 to 50% of bone density has been lost.
• Spinal infection: disc space narrowing with endplate erosion and paravertebral soft tissue swelling (pyogenic discitis); tuberculosis (Pott disease) shows anterior vertebral body destruction, multilevel involvement, preserved disc space early on, paravertebral abscess, calcification and gibbus deformity.
• Kyphosis: Scheuermann disease (three or more consecutive vertebrae with anterior wedging of 5 degrees or more, endplate irregularity, Schmorl nodes, and thoracic kyphosis over 45 degrees); postural kyphosis without wedging; senile kyphosis; and congenital kyphosis.
• Scoliosis: lateral curvature on the AP view, measured by the Cobb angle (over 10 degrees defines scoliosis), with rotation, and vertebral anomalies (hemivertebra, block vertebra).
• Spondyloarthropathy: squaring of vertebrae, syndesmophytes and fusion (bamboo spine); diffuse idiopathic skeletal hyperostosis shows flowing ossification along the anterior spine over at least four contiguous levels with preserved disc spaces.
• Degenerative disease: osteophytes, disc space narrowing, endplate sclerosis, and Schmorl nodes.
• Paget disease: enlarged vertebra with coarse trabeculae and a picture frame outline.

Critical values and findings needing immediate action.

• Unstable fracture (burst fracture with retropulsion, Chance fracture, fracture dislocation) or neurological deficit after trauma: immobilise, protect the cord, CT and MRI, and urgent spinal surgical review.
• Back pain with new weakness, sensory level, or bladder or bowel disturbance with any vertebral lesion: suspected spinal cord compression, urgent MRI of the whole spine and, for malignant compression, high dose dexamethasone and oncology and surgical decisions within hours.
• Vertebral destruction with paravertebral abscess or gibbus: MRI, blood cultures, biopsy, and anti-tuberculous or antibiotic treatment as the microbiology directs.
• Pathological fracture with a pedicle lesion in a patient with no known cancer: whole body staging.
• Scoliosis with rapid progression, pain or neurological signs in a child: MRI to exclude intraspinal disease.

Limitations and artefacts.

• Plain films are insensitive to early infection, small metastases, spinal cord compression, disc herniation and acute osteoporotic fractures without height loss. A normal film does not exclude serious disease when red flags are present.
• The upper thoracic vertebrae are obscured on the lateral view by shoulders and ribs, and bowel gas and the lungs overlie the lower vertebrae. Mild osteopenia reduces the contrast.
• Distinguishing osteoporotic from malignant collapse needs the pedicles, soft tissue mass and other lesions to be examined; MRI is superior.
• Radiographic degenerative changes are common and not related to the level of pain.
• Scoliosis measurements vary by 3 to 5 degrees between observers and with posture; use the same method and end vertebrae each time.
• Radiation dose is higher than the chest film, and repeated films for scoliosis follow up increase cumulative breast and thyroid exposure in children; use slot scan or low dose techniques.
• Old healed fractures and developmental variants (butterfly vertebra, limbus vertebra) may be misread.

Special groups.

• Older adults, postmenopausal women and patients on long term corticosteroids: look for vertebral fractures, which predict future fractures and need bone density assessment and treatment.
• Children and adolescents: Scheuermann disease and scoliosis; use low dose techniques, and MRI for atypical curves.
• Patients with cancer or immunosuppression: low threshold for MRI.
• Patients with HIV or tuberculosis contacts: spinal tuberculosis can present with minimal pain.
• Pregnancy: avoid unless essential.
• Regions: spinal tuberculosis is a common cause of kyphosis and paraplegia in parts of Africa and Asia, and plain films with high clinical suspicion direct early treatment where MRI is scarce.

Follow up tests. MRI of the whole spine for cord compression, infection or tumour, CT for fracture detail and surgical planning, bone scintigraphy or whole body imaging for metastases, dual energy X-ray absorptiometry for osteoporosis, serum calcium, alkaline phosphatase, vitamin D and parathyroid hormone, serum protein electrophoresis, inflammatory markers, blood cultures,

tuberculosis tests (sputum, tuberculin or interferon gamma release assay, and biopsy), HLA-B27 for suspected spondyloarthropathy, and spinal surgical review.