Dexter is a 7 year old, neutered male Staffordshire Bull Terrier. He came to the practice with a subcutaneous mass on the hind leg. The mass was surgically removed and diagnosed as a mast cell tumour. Dexter was referred to us for a CT scan to monitor for metastasis and local reaction. Mast cell tumours can cause local swelling and skin reaction. The CT images showed skin swelling was evident in the surgical sight. No local lymph nodes where reactive however, despite presenting with no clinical signs, there was a nodule in the spleen indicating the importance of full body scan.