The most common type of malignant transformation is squamous cell carcinoma, seen in 80% of reported cases. Increased risk of transformation is seen in patients older than 45 years of age, tumors larger than about 10 cm, and serum squamous carcinoma antigen level greater than 2 ng/mL.
Imaging findings can be nonspecific. Invasion of adjacent structures and lymph node and distant metastases are obviously signs of malignancy. Other findings can suggest malignancy: A complex, predominantly solid tumor, significant areas of necrosis, and poor definition of adjacent soft-tissue planes all suggest malignancy.
The Rokitansky nodule or dermoid plug of ovarian teratomas is a frequent site of malignant transformation and imaging findings suggestive of malignant transformation have been proposed. Transmural growth of the Rokitansky nodule should raise concern for malignant transformation. Softer signs of malignant transformation include contrast enhancement of the Rokitansky nodule and an obtuse angle between the nodule and the inner wall of the cyst.
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- Park SB, Kim JK, Kim KR, Cho KS. Preoperative diagnosis of mature cystic teratoma with malignant transformation: analysis of imaging findings and clinical and laboratory data. Arch Gynecol Obstet. 2007 Jan;275(1):25-31.