US Appearances of Ovarian Cystic Teratoma: Revisited with CT/MRI Comparison

Although it is known that US diagnosis of mature cystic teratoma (MCT) is easy and straightforward because of characteristic hyperechogenicity of the mass. Not infrequently, however, we experience difficulty in making a diagnosis at US and in understanding correlation of US findings with CT or MRI findings. The most characteristic finding of MCT is a cystic mass with echogenic mural nodule representing dermoid plug which may accompany strong posterior sonic attenuation when they contain calcifications, large amount of fat, or tuft of hair. However, most MCTs show mixed echotexture and the proportion of echogenic or solid-looking component is various depending on the composition of the tumor. Less commonly, entirely cystic appearance is found. The cystic content of a MCT is usually greasy sebaceous material, which is liquid at body temperature, mixed with skin squames and matted hairs. Multiple, streaky and mottled echoes may be found in the cyst and are usually due to hair mixed with cyst fluid (dermoid mesh). Fluid-fluid levels may be present in the cyst with bright fluid interfaces. A floating echogenic sphere may be seen at the fluid-fluid level. Multiple spherical structures may float in a large cyst (intracystic floating globules). These spherical structures are thought to be formed by the aggregation of sebum around hair core, and composed of keratin, sebum, fibrin and hemosiderin. MCTs may appear as solid or completely echogenic masses. This finding is thought to be due to a large sphere that occupies most portion of the tumor. In these cases, the differentiation from solid malignancies of the ovary may be difficult. Peripheral curvilinear hypoechogencity, which is suggestive of the fluid portions of the tumor, is helpful in differentiation. The lesions that may mimic MCTs on US are hemorrhagic ovarian cysts, endometriomas, air-containing bowel loops, ovarian neoplasms with echogenic mural nodules, and exophytic lipomatous uterine masses such as lipoleiomyoma. Preoperative diagnosis of MCT is important because rupture and spill of its cystic content during laparoscopic surgery may cause peritoneal granulomatosis. Therefore familiarity with typical and atypical US findings of MCT is important. Careful comparison with CT or MRI findings, if available, will be valuable in understanding their US findings.