Radiology: DE CT may play a role in evaluation of traumatic bone marrow lesions in the ankle

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Noncalcium images reconstructed from dual-energy (DE) CT exams may rule out distinct bone marrow lesions of the ankle joint, according to a study published online in Radiology May 8. Although the protocol provided high sensitivity and excellent negative predictive value, it was hampered by poor specificity and positive predictive value.

Early diagnosis of traumatic bone marrow lesions of the ankle joint, which are histologically heterogeneous, can guide appropriate therapy. Although MR serves as the standard for detection of these lesions, it is not routinely performed in patients presenting with ankle trauma. Single-energy CT does not allow for bone marrow evaluation.

DE CT allows subtraction of calcium from images. Roman Guggenberger, MD, of the department of radiology at University Hospital Zurich in Switzerland, and colleagues hypothesized that reconstruction of the noncalcium images might enable detection of traumatic bone marrow lesions in the ankle joint.

Thirty patients with acute ankle trauma were enrolled in the study and underwent dual-source DE CT and MR imaging within one day of the injury.

Two independent readers used a four-point scale to evaluate CT images for the presence of traumatic bone marrow lesions. Grade 1 referred to distinct signs of abnormal bone marrow attenuation; grade 2 with less pronounced changes; grade 3 with equivocal findings and grade 4 with normal bone marrow. A third reader reviewed MR images for the presence of traumatic bone marrow lesions, and a fourth reader completed quantitative image analysis.

Guggenberger et al reported substantial (k = 0.66) interreader agreement for qualitative grading of CT images. When grades 1 and 2 lesions were considered positive according to MR images, there were 16 false-negative and 38 false-positive findings with DE CT. When only grade 1 lesions were considered positive according to MR images, sensitivity of DE CT reached 90 percent for both readers, while positive predictive value decreased to 26.5 percent and 25.4 percent for reader 1 and 2, respectively.

The findings suggest that DE CT with reconstruction of noncalcium images allows for diagnosis of traumatic bone marrow lesions with high sensitivity and excellent negative predictive value when strict image interpretation criteria are followed, according to Guggenberger and colleagues. However, sensitivity and negative predictive value dropped when subtle lesions were included in the analysis; and specificity and positive predictive value of DE CT were poor, regardless of interpretation criteria, they offered.

The researchers shared several potential indications for the use of noncalcium DE CT: early detection of traumatic bone marrow lesions, exclusion of such lesions and obviation of MR, an alternative for patients with contraindications to MR and improved detection of occult fractures. However, all of these potential indications must be proven in future studies, they wrote.