The Significance of Tc-99m SPECT and MRI Findings in the Diagnosis of Skull Base Invasion in Nasopharyngeal Carcinoma

Abstract

Purpose: To evaluate the role of Tc-99m SPECT in the diagnosis of skull base invasion in nasopharyngeal carcinoma (NPC) and to compare its findings to magnetic resonance imaging (MRI). Materials and Methods: We retrospectively analyzed 179 newly diagnosed NPC patients treated between August 1, 1997 and December 31, 2000 in our institute. All patients were examined with both MRI and Tc-99m SPECT of the skull base prior to treatment. Bone involvement was suspected on MRI when there was a defect in cortical intactness or an abnormality or asymmetry in the signal intensity of the marrow. Malignancy in the skull base was suspected on SPECT when there was an abnormal focal area of increased uptake or left-to-right asymmetry in the skull bone radioactivity. Patients were staged according to the 1997 AJCC classification of NPC based on physical exam and MRI findings. Primary tumor control rates for patients stratified by T stage and MRI or SPECT results were analyzed using the Kaplan-Meier method and the log rank test. Results: Out of 179 patients, a total of 92 (51.4%) had an abnormal SPECT (positive or questionable for malignancy) in the skull base (T1: 10, T2: 14, T3: 24, and T4: 44), while 78 (43.6%) demonstrated skull base malignancy on MRI (T3: 30 and T4: 48). The 3-year primary tumor control rate of the 92 patients with an abnormal SPECT was 87.1%, versus 98.2% for the patients with a normal SPECT in the skull base (p=0.11). Twenty-three patients in stages T1-T2 had an abnormal SPECT but a normal MRI in the skull base, and their 3-year primary tumor control rate was 100%. Conclusions: An abnormal SPECT in the skull base without corresponding MRI findings is not a poor prognostic factor by itself and patients are not at an increased risk for primary tumor recurrence. However, SPECT appears to be more sensitive than MRI, although specificity is low, and it can be a helpful adjunct to MRI in the pretreatment evaluation of NPC.