Role of the Apparent Diffusion Coefficient as a Predictor of Tumor Progression in Patients with Chordoma

BACKGROUND AND PURPOSE: Diffusion-weighted imaging may aid in distinguishing aggressive chordoma from nonaggressive chordoma. This study explores the prognostic role of the apparent diffusion coefficient in chordomas.

MATERIALS AND METHODS: Sixteen patients with residual or recurrent chordoma were divided postoperatively into those with an aggressive tumor, defined as a growing tumor having a doubling time of <1 year, and those with a nonaggressive tumor on follow-up MR images. The ability of the ADC to predict an aggressive tumor phenotype was investigated by receiver operating characteristic analysis. The prognostic role of ADC was assessed using a Kaplan-Meier curve with a log-rank test.

RESULTS: Seven patients died during a median follow-up of 48 months (range, 4–126 months). Five of these 7 patients were in the aggressive tumor group, and 2 were in the nonaggressive tumor group. The mean ADC was significantly lower in the aggressive tumor group than in the nonaggressive tumor group (P = .002). Receiver operating characteristic analysis showed that a cutoff ADC value of 1.494 × 10⁻³ × mm²/s could be used to diagnose aggressive tumors with an area under the curve of 0.983 (95% CI, 0.911–1.000), a sensitivity of 1.000 (95% CI, 0.541–1.000), and a specificity of 0.900 (95% CI, 0.555–0.998). Furthermore, a cutoff ADC of ≤1.494 × 10⁻³ × mm²/s was associated with a significantly worse prognosis (P = .006).

CONCLUSIONS: Lower ADC values could predict tumor progression in postoperative chordomas.