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

Abstract

Objective: 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 region of interest at the center of the lesion by two radiologists independently. Receiver operatingcharacteristic analysis to determine the sensitivity and specificity, area under the curve 95% confidence intervals and cutoff values of CT density to differentiate metastases from enostoses. Results: Patients were 28 ± 7 years old (72% males). 41 (89%) patients had 124 enostoses (2–15 mm) with an average density of 1007 ± 122 Hounsfiled unit (HU, observer1) and 1052 ± 107 (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%). 13 patients had 1 bone island, 8 patients had 2, 9 cases had 3 and 11 cases had more than 3 enostoses. Overall, 114 UOM were evaluated, their average density was 728 ± 163 HU (observer1) and 712 ± 178 HU (observer2). The area under the curve value of mean density to distinguish enostoses from UOM was 0,982. Using a cut-off 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.

Atypical Enostoses—Series of Ten Cases and Literature Review

“…Among the ten patients, five showed associated pain, seven demonstrated interval enlargement, two had an atypical imaging appearance including one with cortical erosion ( Figure 1 A,B) and five showed increased activity on BS including one with concurrent enlargement ( Figure 2 A–C). Mean CT attenuation values ranged from 528 to 1375 Hounsfield Units (HU) with only one BI falling below the proposed 885 HU cutoff [ 2 , 3 ]. Most bone islands were found in the pelvis (7) followed by the femur (3) and vertebrae (1).…”

“…There are rare reports of abnormal features ( Table 1 ). However, most published studies describe only the radiologic features [ 2 , 3 , 4 , 10 , 11 , 12 , 13 ].…”

“…Enostosis, also known as bone island (BI), is a common benign osseous lesion that consists of a focus of compact (cortical) bone within cancellous (spongy) bone [ 1 , 2 ]. Characteristically, enostoses are asymptomatic, “cold” on bone scintigraphy and stable metabolically with scarce evidence of documented growth [ 2 , 3 , 4 , 5 , 6 ]. However, when enostoses display atypical features of pain, increased radiotracer uptake, and/or enlargement, they can be difficult to differentiate from more sinister bony lesions such as osteoblastic metastasis, low-grade central osteosarcoma, osteoid osteoma and osteoblastoma.…”

“…Each tissue has unique CT attenuation values, although the values vary by tissue components [ 7 ]. Recently, mean CT attenuation thresholds have been proposed to differentiate BI from untreated osteoblastic metastasis with a mean of 885 HU serving as the cutoff above which BI is favored and below which a metastatic lesion is the favored diagnosis [ 2 , 3 ].…”

Advanced Quantitative Spine Imaging

“…50,52 Bone islands are much more common than sclerotic metastases and tend to have higher bone density. 53,54 This density difference can be used to distinguish bone island and sclerotic metastasis with a high level of certainty. This is done by drawing a region of interest (ROI) as large as possible on the lesion without extending beyond the lesion's margins, irrespective of whether intravenous contrast was administered or not.…”