Functional MR Sequences Can ID Recurrent Sarcoma

Recurrent sarcoma was accurately distinguished from postoperative inflammation and fibrosis when dynamic contrast material enhanced magnetic resonance (MR) imaging and quantitative diffusion-weighted imaging with apparent diffusion coefficient mapping was used in a small study.

“Although recurrent sarcoma can be detected with high sensitivity by using a conventional MR imaging protocol, the addition of functional MR sequences for postsurgical surveillance may decrease the false-positive detection rate,” wrote Filippo Del Grande, MD, MBA, MHEM, of Johns Hopkins Hospital, and colleagues in Radiology.

Del Grande and colleagues conducted this study of MR sequences in 27 patients with soft-tissue sarcoma who had been referred for postoperative surveillance after resection of their disease. The patients underwent conventional (T-1-weighted, fluid-sensitive, and contrast-enhanced T1-weighted imaging) and functional (dynamic contrast material enhanced MR imaging, and diffusion-weighted imaging with apparent diffusion coefficient mapping) imaging procedures, and the two were compared for accuracy of detecting disease recurrence.

Overall, recurrences were detected in six patients. Both conventional and functional imaging modalities achieved 100% sensitivity for the detection of sarcoma recurrence.

When using static post-contrast T1-weighted MR imaging however, “a mass-like region of enhancement was observed in almost half of the patients without recurrence, resulting in only 52% specificity for the detection of recurrence,” the researchers wrote. “Such a high false-positive rate may lead to unnecessary biopsy of a mass-like region of postoperative scar tissue.”

When dynamic contrast material enhanced MR imaging was used, the specificity increased to 97%. Sensitivity was 60% with a specificity of 97% with the addition of diffusion-weighted imaging and apparent diffusion coefficient mapping.

Based on this, the researchers said that “the use of a time-resolved dynamic contrast material enhanced MR sequence (which requires only 5 extra minutes of imaging unit time) is recommended.”

Quantitative diffusion-weighted imaging with apparent diffusion coefficient mapping is used throughout the body to characterize lesions, but its use to distinguish benign from malignant soft-tissue is debated. According to the study, low apparent diffusion coefficient values are present in cellular malignant tumors, whereas higher values are found in acellular regions or tumors of low cellularity.

This study showed that recurrences had an average apparent diffusion coefficient value of 1.08 mm² per second compared with 0.9 mm² per second for postoperative scarring and 2.34 mm² per second for hematomas (P = .03).