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Bone islands incidentally detected on computed tomography: frequency of enostosis and differentiation from untreated osteoblastic metastases based on CT attenuation value.

OBJECTIVES
The frequency of enostosis incidentally found on CT and CT attenuation value to distinguish them from untreated osteoblastic metastases (UOM).


METHODS
Enostosis group: 46 polytrauma patients underwent thoracoabdominal CT. Inclusion criteria: age range 14-35 years. Exclusion criteria: cancer, previous fractures. UOM group: 20 patients with radiological diagnosis of UOM. Analyzed data: number, size, location and density of enostoses and metastases. The density was measured with the broadest possible ROI at the center of the lesion by two radiologists independently. ROC analysis to determine the sensitivity and specificity, AUC 95% CIs and cutoff values of CT density to differentiate metastases from enostoses.


RESULTS
Patients were 28 ± 7 years old (72% males). Fourty one (89%) patients had 124 enostoses (2-15 mm) with an average density of 1007 ± 122 HU (observer1) and 1052 ± 107 HU (observer2). The most common sites of occurrence were the proximal femur (34%), the pelvis (22%), the acetabulum (20%), the proximal humerus (11%), the vertebrae (11%) and the rib (2%). Thirteen patients had one bone island (BI), eight patients had 2, nine cases had three and eleven cases had more than three enostoses. Overall 114 UOM were evaluated, their average density was 728 ± 163 HU (observer1) and 712 ± 178 HU (observer2). The AUC value of mean density to distinguish enostoses from UOM was 0,982. Using a cutoff of 881 HU for mean density, sensitivity was 98% and specificity 95%.


CONCLUSION
The frequency of enostosis in this study is 89%. The average density identified can help to distinguish enostoses from UOM.


ADVANCES IN KNOWLEDGE
we report the exact frequency of enostosis.