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Chủ Nhật, 14 tháng 10, 2012


Figure 4d.  Mature cystic teratoma of the right ovary in a 19-year-old pregnant woman. (d) Photograph of the gross specimen shows yellowish, pasty sebaceous material (black arrowhead) and hair (white arrowheads) within the cyst cavity, findings that account for the fat echogenicity and signal intensity seen at US and MR imaging. Two molar teeth are also evident (arrows).
Figure 4(a) Sagittal transabdominal US image shows an echogenic mass with sound attenuation (arrows). 
Ovarian teratomas include mature cystic teratomas (dermoid cysts), immature teratomas, and monodermal teratomas (eg, struma ovarii, carcinoid tumors, neural tumors). Most mature cystic teratomas can be diagnosed at ultrasonography (US) but may have a variety of appearances, characterized by echogenic sebaceous material and calcification.

At computed tomography (CT), fat attenuation within a cyst is diagnostic. At magnetic resonance (MR) imaging, the sebaceous component is specifically identified with fat-saturation techniques. The US appearances of immature teratoma are nonspecific, although the tumors are typically heterogeneous, partially solid lesions, usually with scattered calcifications.

At CT and MR imaging, immature teratomas characteristically have a large, irregular solid component containing coarse calcifications. Small foci of fat help identify these tumors. The US features of struma ovarii are also nonspecific, but a heterogeneous, predominantly solid mass may be seen. On T1- and T2-weighted images, the cystic spaces demonstrate both high and low signal intensity. Familiarity with the US, CT, and MR imaging features of ovarian teratomas can aid in differentiation and diagnosis.
Most mature cystic teratomas can be diagnosed at US. However, the US diagnosis is complicated by the fact that these tumors may have a variety of appearances. Three manifestations occur most commonly. The most common manifestation is a cystic lesion with a densely echogenic tubercle (Rokitansky nodule) projecting into the cyst lumen (16). The second manifestation is a diffusely or partially echogenic mass with the echogenic area usually demonstrating sound attenuation owing to sebaceous material and hair within the cyst cavity (Fig 4) (17),(18). The third manifestation consists of multiple thin, echogenic bands caused by hair in the cyst cavity (Fig 3). Pure sebum within the cyst may be hypoechoic or anechoic (19). Fluid-fluid levels result from sebum floating above aqueous fluid, which appears more echogenic than the sebum layer (18). The dermoid plug is echogenic, with shadowing due to adipose tissue or calcifications within the plug or to hair arising from it. Diffuse echogenicity in these tumors is caused by hair mixed with the cyst fluid (Fig 4).
In a prospective US study that made use of these criteria, Mais et al (20) found a sensitivity of 58% and a specificity of 99% in the diagnosis of mature cystic teratoma. Numerous pitfalls have been described in the US diagnosis of mature cystic teratoma (21). Blood clot within a hemorrhagic cyst can appear echogenic, although a mature cystic teratoma usually demonstrates sound attenuation rather than increased through-transmission. Hemorrhagic cysts or blood clots typically demonstrate increased through-transmission. Echogenic bowel can frequently be mistaken for diffusely echogenic mature cystic teratoma and vice versa (21). Perforated appendix with appendicolith and fibrous lesions such as cystadenofibromas have also been described as false-positive findings (21),(22).
 © RSNA, 2001

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