A study on evaluation of skull base bone involvement of nasopharyngeal cancer with 99Tcm-MDP SPECT combined localizable CT

Objective: Whole body planar bone imaging (WBI) could not accurately evaluate skull base bone involvement (SBBI) due to complex structure of the nasopharynx. The purpose of this study was to preliminarily evaluate the role of SPECT combined localizable CT for diagnosing SBBI of nasopharyngeal cancer (NPC). Methods: Forty-four patients with NPC underwent the skull 99Tcm-methylene diphosphonate (MDP) SPECT combined localizable CT, WBI and MRI within a week. Ten patients with non NPC were controls. The region of interest (ROI) of the suspected SBBI (L) was drawn and the same ROI was copied to the upper cervical vertebrae C1 to C3 (S) on the 99Tcm-MBP sagittal SPECT imaging. The uptake ratio of L and S (L/S) was calculated and the L/S > I indicated SBBI. Statistical analysis was performed using nonparametric test (Chi-Square test) or Fisher test. Results: (1)There was no increased tracer uptake at the SBB in all controls with L/S =0.66 ± 0.13. (2) Using MRI as the 'gold standard', the sensitivity, specificity and accuracy of SPECT combined localizable CT in diagnosing SBBI were 83.3% (20/24), 80.0% (16/20) and 81.8% (36/44) respectively, which were higher than those of WBI and SPECT alone, whose sensitivity, specificity and accuracy were 70.8% (17/24), 70.0% (14/20), 70.4% (31/44) and 77.3% (17/22), 72.7% (16/22), 75.0% (33/44), respectively, but the difference was not significant (χ2=2.00, P=0.37). SPECT combined localizable CT correlated well with MRI [χ2=17.65, coefficient of contingency (CC)=0.535, P<0.05]. (3)There was close correlation between the SBBI and headache since the occurrence rates of the SBBI in headache and non headache groups were 92.9% (13/14) and 36.7% (11/30), respectively, χ2=12.16, P <0.05. However, the differentiation of squamous cell carcinoma (SCC) did not correlate with SBBI since the occurrence rates of the SBBI in differentiated and non differentiated SCC were 50.0% (19/38) and 83.3% (5/6), respectively, χ2=2.69, P=0.19. (4) SPECT combined localizable CT could provide anatomical information, and detect bone destruction in some cases. Conclusion: SPECT combined localizable CT bone imaging was an effective method for detecting SBBI of NPC. (authors)