Perfusion MR imaging at 3-Tesla: Can it predict tumor grade and histologic necrosis rate of musculoskeletal sarcoma?

To identify quantitative perfusion parameters that are best associated with tumor grade and tumor necrosis at magnetic resonance (MR) imaging at 3-Tesla.

MR perfusion studies of 31 patients with a musculoskeletal sarcoma were retrospectively evaluated by two readers. There were 18 men and 13 women with a mean age of 34.9±24.4 (standard deviation [SD] years) (range: 6-87 years). All patients underwent carcinologic tumor resection less than 3 months after MR imaging. For all patients six perfusion parameters (three semi-quantitative and three permeability parameters) were analyzed. The percentage of tumor necrosis was estimated using MR imaging. Perfusion data were compared between groups of tumors with different grades and necrosis ratios. Interobserver variability was calculated using intraclass correlation coefficient (ICC).

Interobserver variability among the perfusion parameters was good to excellent (ICC: 0.72-0.9). The area under the curve and maximum slope values showed a significant association with the degree of tumor necrosis (P=0.02-0.04). When tumors with low necrosis ratios were compared to those with high ratios the former parameter was 80% lower. In the same groups, the imaging necrosis index was 56.9-59.8% higher in patients with grade 2 necrosis (P=0.01). Extracellular space volume (V_e) was 31.4% to 55.8% lower in tumors with high grade while the backflow constant (K_ep) was 33.6% to 40.1%% higher in tumors with high grade.

Semi-quantitative MR perfusion parameters have an excellent reproducibility and are associated with the degree of histologic tumor necrosis in musculoskeletal sarcomas. The utility of permeability parameters for determining tumor grade needs further investigations.