Pretherapeutic evaluation of cancer of the external auditory canal using FDG-PET/CT.

Objectives To evaluate the clinical usefulness of FDG-PET/CT for staging of cancer of the external auditory canal.

Methods Eighteen patients with cancer of the external auditory canal were included in this retrospective study (5 men, 13 women, 60.9±13.0 years old). Local spread of the primary tumor was judged on high-resolution CT (HRCT) by two radiologists. Two nuclear medicine physicians evaluated the FDG-PET/CT for the assessment of cervical nodal or distant metastases. The Pittsburgh tumor staging system was applied for the TNM staging. Maximum standardized uptake values (SUVmax) were measured in the primary tumor and metastatic lesions. Because all patients had undergone FDG-PET/CT by the dual-time-point protocol, which includes spot images of the head and neck area at 60 min and 120 min and whole-body scan at 75 min after the FDG injection, we used the spot images for evaluating the head and neck area. All the imaging findings were compared with the histopathologic reports or correlated with the findings of clinical follow-up.

Results The T stage was judged as T1 in 7 patients, T2 in 4 patients, T3 in 3 patients, and T4 in 4 patients on HRCT. Except for one case (adenoid cystic carcinoma, T2), all the primary tumors showed FDG uptake which could be confirmed by visual interpretation (SUVmax = 6.52±2.48 and 7.53±3.14, in the early and delayed phases, respectively). Although FDG-PET/CT detected small preauricular lymph node metastases in two patients, there were three false-positive cases and two false-negative cases. The patient-based sensitivity, specificity and accuracy of FDG-PET/CT for the N staging were 60%, 77% and 72%, respectively. There were no distant metastases in our subjects.

Conclusions Although most primary cancers of the external auditory canal are FDG-avid, the usefulness of FDG-PET/CT for N staging is limited.