The value of energy spectral CT in the differential diagnosis between benign and malignant soft tissue masses of the musculoskeletal system

• Different types of tissues have different types of spectral curves.
• We find that spectral curve is useful in the differential diagnosis of benign and malignant tumor of the musculoskeletal system.
• Arc shaped curve is a specific sign for tumors containing abundant fat.

ObjectiveTo explore the value of energy spectral CT in the differential diagnosis between benign and malignant tumor of the musculoskeletal system.MethodsEnergy spectral CT scan was performed on 100 patients with soft tissue mass caused by musculoskeletal tumors found by MRI. Solid areas with homogenous density were chosen as region of interests (ROI), avoiding necrosis, hemorrhage and calcification region. Select the optimal keV on single energy images, and then the keV–CT curve was automatically generated. All 100 cases of tumors proved by histological examination were divided into four groups, 38 cases were in benign group, 10 cases in borderline group, 49 cases in malignant group, and 3 cases of lipoma (that were analyzed separately since its curve was arc shaped, significantly different from other curves). The formula used to calculate the slope of spectral curve was as follows: slope = (Hu40 keV − Hu80 keV)/40. As the slope was steep within the range of 40–80 keV based on preliminary observations, 40 keV and 80 keV were used as the reference points to calculate the slope value of the energy spectral curve. Kruskal–Wallis rank sum test was applied for statistical analysis, and P < 0.05 was considered to indicate a statistically significant difference.ResultsThe spectral curve of benign group was gradually falling type with a mean slope of 0.75 ± 0.30, that of malignant group was sharply falling type with a mean slope of 1.64 ± 1.00, and that of borderline group was a falling type between the above two groups with a mean slope of 1.34 ± 0.45. The differences of slopes between benign and malignant group, benign and borderline group were of statistical significance (P < 0.05) respectively. The spectral curves of 3 cases of lipoma showed arc shaped rising type with a mean slope of −2.00.ConclusionSpectral curve is useful in the differential diagnosis of benign and malignant tumor of the musculoskeletal system. Arc shaped curve is a specific sign for tumors containing abundant fat.