Alveolar Soft Part Sarcoma as a Great Masquerader of Unilateral Sinonasal Tumour in Child: A Case Report Alveolar soft part sarcoma (ASPS) is a rare mesenchymal neoplasm that accounts for less than 1% of all sarcoma and the most common site of tumour is found in the soft tissue of the extremity. The incidence of ASPS in paediatric age group is rare. It is extremely uncommon for the tumour arising from the sinonasal within the head and neck region. Most of the reported cases were in the orbit and tongue. Localised ASPS carries a good prognosis after complete total resection. Diagnosing ASPS can be challenging as it can be a masquerader to other sinonasal soft tissue malignancy which required the laborious process of histopathological examination, immunohistochemistry, and ultrastructural examination to solve the complexity. We encountered an 11-year-old girl who presented with sudden onset of left nasal obstruction and on examination noted a unilateral vascular mass in the left nasal cavity turned out to be ASPS. She underwent left nasal tumour debulking via endoscopic approach under general anaesthesia. Post-operative, she recovered well with regular endoscopic surveillance and was referred to the oncology team for post-operative radiotherapy.