CT findings of mature cystic teratoma with malignant transformation: comparison with mature cystic teratoma

Purpose

To evaluate the imaging findings of mature cystic teratoma with malignant transformation (malignant teratoma) compared with the corresponding mature cystic teratoma (benign teratoma).

Materials and methods

This study enrolled 1325 patients with 12 malignant teratomas and 1313 benign teratomas. We compared the computed tomographic (CT) findings of eight malignant teratomas and 15 benign teratomas; both groups were matched in terms of tumor size (>9.9 cm) and patient age (>45 years). The CT images were retrospectively evaluated with focus on soft tissue components; size, border (regular or irregular), the presence or absence of nodular formation, enhancement, the angle formed between the soft tissue components and the inner wall of the cyst (acute or obtuse), and transmural growth as well as metastasis including lymphadenopathy and disseminated disease. Using the Fischer's Exact test, each evaluating parameter was compared between the two groups.

Results

Soft tissue components were observed in 75% (six of eight) of malignant teratomas and in 33% (five of fifteen) of benign teratomas; 100% (six of six) of soft component in malignant teratomas had a nodular formation and none of soft component in benign teratomas showed nodular formation; 83% (five of six) of soft component in malignant teratomas had enhancement as well as an obtuse angle between the soft tissue components and the inner wall of the cyst. None of soft component in benign teratomas showed enhancement and 20% (one of five) of soft component in benign teratomas had an obtuse angle; 33% (two of six) of soft component in malignant teratomas showed transmural growth, 13% (one of eight) of malignant teratoma showed lymphadenopathy, and 38% (three of eight) showed disseminated disease. None of benign teratomas showed transmural growth, lymphadenopathy, or disseminated disease. A statistically significant difference between patients with and without malignant transformation was seen in terms of nodular formation, obtuse angle, and enhancement of the soft tissue components (P<.05).

Conclusion

Malignant teratoma is characterized by the following imaging findings: the presence of a nodular forming and enhancing soft tissue component, an obtuse angle between the soft tissue and the inner wall of the cyst, as well as extracapsular tumor growth with extension into adjacent structures or metastasis. Therefore, we can differentiate malignant teratoma from benign teratoma using CT findings.