Minimum fascia-tumor distance of parotid tumors: a comparison of ultrasound and computed tomography.

OBJECTIVES

The minimum fascia-tumor distance (MFTD) measured by ultrasound (US) has been proposed for detecting deep lobe parotid tumors, but probe compression may cause measurement bias. Computed tomography (CT), free from such distortion, may provide more reliable measurements. This study compared MFTD values from CT and US in the same cohort.

METHODS

We retrospectively analyzed 128 parotid tumor patients who underwent both CT and US before surgery. MFTD values were compared, correlation and agreement were assessed with Spearman coefficients and Bland-Altman plots, and diagnostic accuracy was evaluated using ROC curves.

RESULTS

CT-based MFTD values were significantly larger than US-based values (2.00 ± 2.64 mm vs. 1.49 ± 1.86 mm, P < 0.001), with a mean difference of 0.51 mm. This discrepancy increased with tumor depth. A strong correlation was observed between CT and US (r = 0.936, P < 0.001), but agreement was not optimal. ROC analysis showed comparable performance of CT and US in differentiating deep from superficial lobe tumors (AUC = 0.723 vs. 0.712, P = 0.910), with optimal cutoffs of 4.00 mm for CT and 3.40 mm for US.

CONCLUSION

CT-based MFTD values were consistently larger than those from US, supporting the presence of probe compression-related bias. Nevertheless, both modalities demonstrated similar accuracy for tumor localization. With appropriate cutoff adjustments, CT and US can both serve as effective tools for preoperative identification of deep lobe parotid tumors.