Orbital inflammatory diseases are a heterogenic group of conditions that often entail a difficult diagnostic process and many patients are treatment resistant. Inflammatory diseases can be visualized by Zirconium-89-labelled rituximab PET-CT (89Zr-rituximab PET/CT). In this study, we describe our experience and possible potential of the 89Zr-rituximab PET/CT for diagnostic and therapeutic management of refractory orbital inflammation. Retrospectively, 89Zr-rituximab uptake was assessed and related to clinical data. The main outcome measures were the characteristics of the scan and the clinical relation of uptake with the diagnostic process and treatment effectivity. Twelve patients with thyroid eye disease (TED) and suspected idiopathic orbital inflammation (IOI) were scanned. Six patients had a strong 89Zr-rituximab uptake and showed a focal distribution within the lesion. Four patients (one TED, three IOI) responded well to rituximab treatment after a positive scan. 89Zr-rituximab PET/CT was essential to the diagnosis of optic nerve meningioma in one patient. 89Zr-rituximab PET/CT has the potential to be a powerful tool for the detection of B cell-mediated disease within the orbit and ocular adnexa. This technique can be a valuable addition for diagnosing diseases around the eye and can potentially predict rituximab treatment response in patients with refractory inflammation.

The following case potentially provides insight into the mechanisms of lymphogenic metastasis in sinonasal cancer. A 63‐year‐old patient who presented with progressive diplopia and left‐sided periocular pain was diagnosed with a cT4bN0M0 mucosal melanoma of the ethmoid sinus. She underwent a combined endonasal and transcranial tumor resection, and an orbital exenteration. Upon histopathological examination, besides the primary tumor, two separate localizations of melanoma surrounded by lymphoid tissues and lymph follicles were identified. The tumor was upstaged to pT4bN1, and the patient received a combination of adjuvant immunotherapy and radiotherapy. At present, the patient displays no evidence of disease. The presence of orbital lymph nodes has previously never been confirmed. These findings indicate the potential involvement of lymphatic drainage through the retrobulbar fat in the regional spread of sinonasal tumors closely associated with the orbit.