Seroma (pocket of clear serous liquid) after an excision of a pleomorphic adenoma in a 47 year old female patient. Pleomorphic ademoma is a type of benign (harmless) tumour and the most common type of salivary gland tumour (here, the parotid gland). In a small number of patients, after surgery, the wound can slowly swell due to an accumulation of body fluid or saliva.