Metastatic Sinonasal Undifferentiated Carcinoma to the Temporal Bone: A Case Report and Literature Review.

Introduction: Sinonasal undifferentiated carcinoma (SNUC) is a rare malignancy of the nasal cavity and paranasal sinuses, with highly aggressive behaviour. Although a multimodal strategy is considered the standard treatment approach, recurrence remains common both locally and at distant metastatic sites. Temporal bone metastases represent a rare entity, with patients primarily manifesting otologic symptoms. Breast, lung, and prostate cancers are the most common primary malignancies associated with temporal bone metastases, whereas no cases originating from the nasal cavity or paranasal sinuses have previously been reported. Herein, we report a unique case of metastatic SNUC to the temporal bone, presented with facial nerve paralysis. A brief descriptive review of all cases of distant metastases in SNUC is also reported. Case Report: We report the case of a patient with SNUC who developed temporal bone recurrence three years after trimodal treatment (induction chemotherapy, surgery and adjuvant radiotherapy) performed with good oncological outcome. Moreover, we retrospectively reviewed our case series of patients surgically treated for sinonasal undifferentiated carcinoma from 2006 to 2023 and we also performed a search of the literature from January 1, 1980, to December 31, 2024. Conclusion: The incidence of recurrent metastasis from SNUC disease in patients treated surgically is variable. This case report represents the first case of SNUC metastasis on the temporal bone, highlighting the rare occurrence of a middle ear recurrence after multimodal treatment. Despite its rarity, temporal bone metastasis should be considered in oncological patients presenting with facial palsy or other persistent otologic symptoms.