MR mimics of recurrent nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is highly sensitive to radiotherapy, however, the local tumour recurrence rate still is around 30% in those patients who present with advanced T stage disease [Wolden SL, Zelefsky MJ, Hunt MA, Rosenzweig KE, Chong LM, Kraus DH, Pfister DG, et al. Failure of a 3D conformal boost to improve radiotherapy for nasopharyngeal carcinoma. Int. J Radiat Oncol Biol Phys 2001;49:1229-34]. Local tumour recurrence is particularly difficult to treat. Further radiotherapy causes significant acute and late complications, while surgery is only suitable for early stage recurrence and the role of chemotherapy is mainly palliative. The identification of recurrent nasopharyngeal carcinoma can be a challenge for both the clinician and the radiologist. The main diagnostic difficulty for MR imaging is the differentiation of recurrent tumour from post treatment scarring and fibrosis. However, we have encountered several other pathological processes that also may mimic local tumor recurrence. We present three such pathologies, radiation induced infection/inflammation, radiation induced granulation tissue, and radiation induced sarcoma (RIS). In all cases the patients underwent MR imaging for the evaluation of suspected tumor recurrence. Each case is presented, the pathology discussed, and the MR features that were useful in distinguishing these entities from malignancy are highlighted.