Examination of pattern of RI accumulation in thyroid cartilage on bone scintigraphy

In bone scintigraphy, abnormal RI accumulation in ossified thyroid cartilage is often noted. However, because similar accumulation is also seen in tumor-involved cartilage, distinction between these two lesions is sometimes difficult. We examined the differences in RI accumulation by ossification of the thyroid cartilage and cartilage invasion with anterior, posterior, and oblique views of bone scintigraphy in this study.

This study included 120 patients (104 men, 16 women; mean age 67.8 +/- 9.6 years; range 48-90 years) with laryngeal or lower pharyngeal carcinoma. The patients had exhibited abnormal accumulation of RI on thyroid cartilage on bone scintigraphy between February 1999 and March 2007. We evaluated accumulation of thyroid cartilage in the anterior, posterior, and oblique views on bone scintigraphy. The presence/absence of tumor invasion of the thyroid cartilage was checked by comparing the findings of enhanced computed tomography and magnetic resonance imaging (MRI) as well as evaluating operative records. RI accumulation in thyroid cartilage was divided into four types (diffuse accumulation, intense diffuse accumulation, slight inhomogeneous accumulation, and intense inhomogeneous accumulation).

Tumor invasion of thyroid cartilage was noted in 2 of the 42 patients with diffuse accumulation, 1 of the 18 patients with intense diffuse accumulation, 1 of the 38 patients with slight inhomogeneous accumulation, and 17 of 22 patients with intense inhomogeneous accumulation. Because the degree of tumor invasion was highest in cases in which bone scintigraphy revealed intense inhomogeneous accumulation of RI in the thyroid cartilage, we judged this pattern of RI accumulation to be an indicator of tumor invasion. When diagnosis was based on this criterion, positive predictive value, negative predictive value, and accuracy were 77%, 96%, and 93%, respectively (P < 0.0001, Chi-square test).

The findings of this study suggest that ossification of thyroid cartilage can be distinguished from tumor-involved thyroid cartilage on the basis of the pattern of abnormal RI accumulation in the thyroid cartilage in patients with head/neck cancer.