A case of parotid pleomorphic adenoma with marked cystic changes is presented. A 70-year-old woman was referred to our hospital because of a painless swelling in the left parotid area. Ultrasonography demonstrated a well-demarcated apparently benign lesion in the parotid gland. MRI showed high signal intensities on Ti-, T2-, and fat-suppressed Tl-weighted images. Under a tentative diagnosis of parotid cyst, the lesion was excised with the patient under general anesthesia. The excised material was a cystic lesion with focal thickening of the wall. Pathological examination showed that a large cyst had formed in the tumor parenchyma of a pleomorphic adenoma. There has been no evidence of recurrence as of 5 years 3 months after the operation.
