Bone SPECT to Assess Mandibular Invasion by Intraoral Squamous-Cell Carcinomas

It is important for head and neck surgeons planning their operative approach to assess tumor infiltration to the mandible by intraoral squamous-cell carcinomas. Two- to 3-hr planar bone scintigraphy is sensitive but not specific in detecting mandibular invasion by tumor. We evaluated 3-hr SPECT bone scintigraphy, which provides better anatomical detail, to determine if it more accurately assesses tumor invasion. Thirty consecutive patients with proven intraoral squamous-cell carcinomas were studied. Semiquantitative assessment of the mandible was performed with a three-level graded scoring system, based on comparisons of tracer uptake in the mandible to that in the upper cervical vertebrae and in an unaffected part of mandible. Lesion-to-cervical spine (L/S) count ratios and lesion-to-nonlesion (L/N) count ratios in the mandible on the 3-hr SPECT images were calculated. All patients with proven tumor invasion showed higher tracer uptake than those with normal mandible or other dental diseases. The L/S and L/N count ratios on the SPECT images were significantly higher in patients with tumor invasion than in those without (L/S, p < 0.001; L/N, p < 0.01). L/S ratios provided better differentiation than L/N ratios. Bone SPECT provides a reliable means of assessing tumor invasion to the mandible by intraoral squamous-cell carcinomas.