Tenosynovial giant cell tumour of the nasal dorsum: a novel presentation.

Tenosynovial giant cell tumour (TSGCT) of the head and neck is exceedingly rare. We report a case of a TSGCT at a novel anatomical site, the nasal dorsum. This case also contributes to the expanding genetic landscape of TSGCT through the identification of a gene fusion that has not previously been described in the literature, to the best of our knowledge. A 20-year-old male presented with progressive changes in the shape of his nasal dorsum, without prior history of trauma or surgery. Clinical examination revealed a firm, mobile, non-tender swelling over the middle third of the nose. Imaging identified a well-defined soft tissue mass, closely related to the nasal cartilage. The mass was completely excised via an external septorhinoplasty approach, enabling removal with reconstruction of the nasal contour. Histopathological analysis demonstrated a giant cell-rich neoplasm with mononuclear cells, foamy histiocytes, and haemosiderin deposition. The unusual location of the mass prompted molecular analysis by next-generation sequencing, RNA analysis of which identified a novel CSF1::AKNAD1 gene fusion. A localised TSGCT was diagnosed. Whilst TSGCT typically arises at sites where synovium is present, its presence at the nasal dorsum introduced uncertainty regarding the tumour's pathogenesis. This case demonstrates the importance of integrating clinical, radiological, histopathological, and molecular findings in diagnosing rare presentations of soft tissue tumours and expands the anatomical locations at which TSGCT may arise.