Adult onset sinonasal rhabdomyosarcoma - a rare case report with cytohistological features.

Rhabdomyosarcoma (RMS) is a fast growing, malignant tumour arising from immature mesenchymal cells, committed to skeletal muscle differentiation. It is more often seen in the paediatric population and constitutes less than 1% of all malignancies and less than 3% of all soft tissue tumours. RMS of the paranasal sinuses constitutes 10-15% of adult head and neck RMS, ethmoidal and maxillary sinuses being the most common. We report a 56-year-oldman presenting with left nasal obstruction, epistaxis on and off and left cheek swelling. Nasal endoscopy revealed a reddish friable mass, bleeding on touch, in the left nasal cavity. CECT scan showed a heterogeneous growth in the left maxillary sinus eroding the medial orbital wall and lateral nasal wall. FNAC of the left cheek swelling yielded highly cellular smears showing predominantly singly scattered round to ovoid neoplastic cells with scanty cytoplasm and indistinct nucleoli. Few of the cells had eccentric nuclei with moderate amount of eosinophilic cytoplasm. Attempted pseudorossette formation was seen. An impression of round cell tumour was given. A diagnosis of an adult onset sinonasal rhabdomyosarcoma was made on histopathological examination of the nasal biopsy, supported by immunohistochemistry (IHC) showing strong myogenin positivity, focal positivity for PAX8 and negativity for CK, LCA, S-100 and CD99. Parameningeal RMS is rare in adults especially the elderly. However, it needs to be considered whenever a poorly-differentiated neoplasm is seen in this age and IHC is a useful aid.