Assessment with magnetic resonance imaging of response to radiotherapy for tongue and mouth floor tumors

Abstract To investigate the role of Magnetic Resonance Imaging (MRI) in assessing the effects of radiation therapy and in differentiating postirradiation scar tissue from residual tumor, we examined 22 patients with primary squamous cell carcinoma of the tongue and floor of the mouth treated with definitive radiation therapy; all patients were examined before and after treatment. Pretreatment MRI showed mass effect and obliteration of the fascial planes, with hyperintense signal on T2 and T1 post-Gd-DTPA injection sequences in all patients. Follow-up exams were performed 4 months after radiation therapy completion to wait for postirradiation phlogistic changes to become less apparent. The role of posttreatment exams was determined on the basis of clinical and bioptic follow-up. Radiation therapy yielded complete remission in 16/22 patients and partial remission in 6/22. MR follow-up showed, in complete remission patients, persistently obliterated fascial planes in 12/16 patients (75%) and a residual mass, hypointense on T2-weighted sequences and without enhancement in 9/16 patients (56%). In all partial remission patients, MRI showed some residual tissue hyperintense on T2-weighted sequences, with persistent enhancement. Persistent alterations in primary tumor sites, such as residual tissue and fascial plane obliteration, are frequent findings after irradiation. Hyperintense signal and enhancement can persist for months after radiation therapy as signs of postirradiation changes. To conclude, MRI performed 4 months after radiation therapy appears as a reliable tool to refer a residual mass to scar tissue when MR signal is hypointense on T2-weighted and enhanced sequences and to residual tumor when MR signal is hyperintense on T2-weighted and post-Gd-DTPA sequences.