The Zurich magnetic resonance imaging protocol for standardized staging and restaging of sinonasal tumours

161 To the Editor: In combination with paranasal sinus computed tomography (CT), cross-sectional imaging with magnetic resonance imaging (MRI) is mandatory for staging and restaging of primary sinonasal malignancies . In the initial staging, MRI defines tumour size, provides information on extension into adjacent compartments of the sinonasal tract (in particular orbit, anterior or middle cranial fossa, leptomeningeal and brain parenchyma) and consecutively helps to determine the clinical T category. Furthermore, MRI delineates tumour from surrounding tissue (e. g. retention of mucus, reactive polyps) and may even identify perineural spread and bone marrow infiltration . The signal intensity of tumours varies depending on their cellularity, mucin content and presence of hemorrhage. However, even state-ofthe-art cross-sectional imaging may fail to correctly identify orbital or skull base infiltration. Thus, both, false-positive and false-negative findings must be considered. Common pitfalls particularly include 1) the discrimination of bony pressure erosion and bony infiltration of the anterior skull base or the medial orbital wall and 2) the discrimination of reactive dural enhancement and dural infiltration by tumour . Based on these difficulties and in analogy to upper aero-digestive tract squamous cell carcinomas, we recently suggested an obligatory exploration of all sinonasal tumours under general anesthesia and targeted biopsy, if necessary . Besides its role in the initial staging (Figure 1), MRI is also important in the restaging setting, where tumour persistence or recurrence and treatment-associated alterations may be challenging