Microscopic intraosseous extension of osteosarcoma: assessment on dynamic contrast-enhanced MRI.

OBJECTIVE: This study investigated whether dynamic MRI could determine microscopic intraosseous invasion in osteosarcoma.

PATIENTS: Six patients with osteosarcoma who underwent total resection of the tumor after chemotherapy were studied.

DESIGN: The steepest slope value of the time-intensity curve was calculated on the basis of the first-pass method on dynamic MRI performed after chemotherapy. Slope value modified log = [100.(SIb - SIa)/(Tb - Ta)/SIa], where SIa and SIb represent the signal intensity at time points Ta and Tb when the steepest slope started and ended, respectively. The slope value was correlated with the histological findings of the surgical specimens. The findings on conventional MRI were also reviewed.

RESULTS AND CONCLUSIONS: In five of six patients microscopic tumor invasion ranging from 1 to 3.5 cm in depth was pathologically proven. The slope value within the microscopic invasion (-0.052 +/- 0.267) was significantly greater than that of tumour-free marrow (-0.609 +/- 0.220) and less than that in areas showing macroscopic tumor invasion (0.595 +/- 0.483) (P < 0.001). Histological examination disclosed the dilatation of small vessels within the macroscopic and microscopic invasion. Findings on conventional MRI varied among patients; microscopic invasion was not detected in one, underestimated in two, and overestimated in two. It is concluded that calculation of the slope value on dynamic MRI can discriminate regions of microscopic invasion from tumor-free marrow in patients with osteosarcoma after chemotherapy.