DOI: 10.1148/rg.284075069
RadioGraphics 2008;28:969-983
© RSNA, 2008
Imaging Findings of Complications and Unusual Manifestations of Ovarian Teratomas1
Sung Bin Park, MD2,
Jeong Kon Kim, MD,
Kyu-Rae Kim, MD, and
Kyoung-Sik Cho, MD
1 From the Department of Radiology, Research Institute of Radiology (S.B.P., J.K.K., K.S.C.), and Department of Pathology (K.R.K.), Asan Medical Center, University of Ulsan, 388-1 Poongnap-dong, Songpa-gu, Seoul 138-736, South Korea. Presented as an education exhibit at the 2006 RSNA Annual Meeting. Received April 9, 2007; revision requested July 26 and received November 16; accepted March 20, 2008. All authors have no financial relationships to disclose.
Address correspondence to J.K.K. (e-mail: rialto{at}amc.seoul.kr).
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Abstract
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Ovarian teratomas can be associated with various complications and demonstrate a wide spectrum of clinical and imaging features. The complications include torsion (16% of ovarian teratomas), rupture (1%–4%), malignant transformation (1%–2%), infection (1%), and autoimmune hemolytic anemia (<1%). These complications require different therapeutic strategies; therefore, timely and accurate diagnosis of these complications is important for optimal patient treatment. In cases of complicated ovarian teratomas, the clinical manifestations provide only limited information and often overlap with those of other diseases. Furthermore, ovarian teratomas may have unusual clinical and imaging manifestations, thereby leading to misdiagnosis. These unusual manifestations include immature teratomas, monodermal teratomas (struma ovarii), combination tumors and collision tumors containing teratomas, and mature cystic teratomas without demonstrable fat or with pure fatty components. To provide adequate treatment and prevent misdiagnosis, it is necessary to be familiar with the imaging findings of both the complications and the unusual manifestations of ovarian teratomas.
© RSNA, 2008
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:
- Describe the clinical and imaging manifestations of complicated ovarian teratomas.
- List the imaging findings that provide important information for triage and management of ovarian teratomas.
- Discuss useful imaging findings for differentiation of complicated ovarian teratomas from other diseases.
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Introduction
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Ovarian teratoma is a common ovarian tumor, accounting for 20% of adult ovarian tumors and 50% of pediatric ovarian tumors (1). Teratomas consist of a number of histologic types of tumors containing mature or immature tissue of the three germ cell layers, including the ectoderm, mesoderm, and endoderm (2,3).
The clinical manifestations of ovarian teratomas vary from incidentally detected small masses to malignantly transformed tumors leading to high mortality (2,3). Although the imaging findings of ovarian teratomas also vary from purely cystic masses to mainly solid masses, ovarian teratomas can be readily detected and diagnosed by identifying the intratumoral fat at ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging.
Ovarian teratomas can be associated with various complications, including torsion (16% of ovarian teratomas), rupture (1%–4%), malignant transformation (1%–2%), infection (1%), and autoimmune hemolytic anemia (<1%) (2–4). These complications require different therapeutic strategies; therefore, the timely and accurate diagnosis of these complications is important for optimal patient care. In cases of complicated ovarian teratomas, the clinical manifestations provide only limited information, which often overlaps that of other diseases. Furthermore, ovarian teratomas may have unusual clinical and imaging manifestations such as immature teratomas and monodermal teratomas, thereby leading to misdiagnosis. Therefore, it is necessary to be familiar with the imaging findings of the complications as well as the unusual manifestations of ovarian teratomas.
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Common Imaging Findings of Ovarian Teratomas
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The typical imaging finding of an ovarian teratoma is a cystic mass with intratumoral fat. The most common US finding of an ovarian teratoma is a cystic mass with a densely echogenic tubercle (Rokitansky nodule) projecting into the cystic lumen. The Rokitansky nodule or dermoid plug is described as a protrusion or nipple (mammilla) arising from the inner surface of a cyst, containing hair, teeth, and fat and causing acoustic shadowing (3). Other common US manifestations include a diffusely or partially echogenic mass demonstrating sebaceous material and multiple thin echogenic bands caused by the presence of hair in the cyst cavity (Fig 1) (3,5,6).
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Figure 1a. Mature cystic teratoma of the ovary in a 28-year-old woman. (a) US scan shows a heterogeneous echogenic mass (arrows). (b) Axial unenhanced CT scan shows intratumoral fat (small arrows) and calcifications (large arrow).
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Figure 1b. Mature cystic teratoma of the ovary in a 28-year-old woman. (a) US scan shows a heterogeneous echogenic mass (arrows). (b) Axial unenhanced CT scan shows intratumoral fat (small arrows) and calcifications (large arrow).
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Diagnosis of uncomplicated teratomas at CT and MR imaging is fairly straightforward because these modalities are very sensitive for detection of intratumoral fat. At CT, intratumoral fat shows negative attenuation, which can be readily detected (7). At MR imaging, intratumoral fat can be diagnosed with the combination of T1-weighted imaging and fat-saturated T1-weighted imaging; intratumoral fat shows high signal intensity on T1-weighted images but signal drop on fat-saturated T1-weighted images (3,8–10) (Fig 2). Chemical-selective fat-saturated T1-weighted imaging is mandatory for diagnosis of teratomas because other conditions, such as hemorrhage or a high concentration of protein, can also cause T1 shortening (11–13). Chemical shift imaging consisting of in-phase and out-of-phase imaging is helpful for identifying microscopic fat in tumors that have only a tiny amount of fat (3).
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Figure 2a. Mature cystic teratoma of the left ovary and endometriosis of the right ovary in a 32-year-old woman. (a) Axial T1-weighted MR image shows bilateral ovarian masses with high signal intensity. (b) Axial T2-weighted MR image shows low signal intensity of the right ovarian mass (arrow). The low signal intensity is due to blood elements, especially intracellular methemoglobin. Such "T2 shading" is typical of endometriosis. (c) Axial fat-saturated T1-weighted MR image shows a drop in the signal intensity of the left ovarian mass (arrow) compared with that in a, a finding suggestive of intratumoral fat.
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Figure 2b. Mature cystic teratoma of the left ovary and endometriosis of the right ovary in a 32-year-old woman. (a) Axial T1-weighted MR image shows bilateral ovarian masses with high signal intensity. (b) Axial T2-weighted MR image shows low signal intensity of the right ovarian mass (arrow). The low signal intensity is due to blood elements, especially intracellular methemoglobin. Such "T2 shading" is typical of endometriosis. (c) Axial fat-saturated T1-weighted MR image shows a drop in the signal intensity of the left ovarian mass (arrow) compared with that in a, a finding suggestive of intratumoral fat.
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Figure 2c. Mature cystic teratoma of the left ovary and endometriosis of the right ovary in a 32-year-old woman. (a) Axial T1-weighted MR image shows bilateral ovarian masses with high signal intensity. (b) Axial T2-weighted MR image shows low signal intensity of the right ovarian mass (arrow). The low signal intensity is due to blood elements, especially intracellular methemoglobin. Such "T2 shading" is typical of endometriosis. (c) Axial fat-saturated T1-weighted MR image shows a drop in the signal intensity of the left ovarian mass (arrow) compared with that in a, a finding suggestive of intratumoral fat.
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In addition to intratumoral fat, calcification is also commonly noted in ovarian teratomas (Fig 1) (7–9). However, as calcification can also be noted in other ovarian neoplasms, the presence of calcification does not always indicate ovarian teratoma. Therefore, it is necessary to attempt to detect intratumoral fat in order to confirm the diagnosis.
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Complications of Ovarian Teratomas
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Rupture
Rupture occurs in 1%–4% of ovarian teratomas (2). This complication causes leakage of the liquefied sebaceous contents into the peritoneum, which irritates the peritoneum and leads to acute or chronic inflammation. Acute peritonitis caused by sudden tumor rupture may result in shock or hemorrhage and is usually associated with torsion, trauma (Fig 3), infection, or labor. Chronic and recurrent leakage is more common than an acute episode of leakage and causes chronic granulomatous peritonitis, known as gliomatosis (14) (Fig 4). Although the prognosis of chronic rupture is favorable, dense peritoneal adhesions caused by chronic recurrent peritonitis may cause other secondary complications such as bowel obstruction.
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Figure 3a. Acute traumatic rupture of a mature cystic teratoma in an 83-year-old woman. (a, b) Axial contrast-enhanced CT scans show several free-floating areas of fat attenuation (arrows in a) and a mature cystic teratoma of the left ovary (arrow in b). (c) Coronal reformatted CT scan shows a free-floating area of fat attenuation (arrowhead), a pelvic bone fracture with surrounding hematomas (straight arrows), and the teratoma (curved arrow). Surgical and pathologic results indicated granulomatous peritonitis due to rupture of the teratoma.
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Figure 3b. Acute traumatic rupture of a mature cystic teratoma in an 83-year-old woman. (a, b) Axial contrast-enhanced CT scans show several free-floating areas of fat attenuation (arrows in a) and a mature cystic teratoma of the left ovary (arrow in b). (c) Coronal reformatted CT scan shows a free-floating area of fat attenuation (arrowhead), a pelvic bone fracture with surrounding hematomas (straight arrows), and the teratoma (curved arrow). Surgical and pathologic results indicated granulomatous peritonitis due to rupture of the teratoma.
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Figure 3c. Acute traumatic rupture of a mature cystic teratoma in an 83-year-old woman. (a, b) Axial contrast-enhanced CT scans show several free-floating areas of fat attenuation (arrows in a) and a mature cystic teratoma of the left ovary (arrow in b). (c) Coronal reformatted CT scan shows a free-floating area of fat attenuation (arrowhead), a pelvic bone fracture with surrounding hematomas (straight arrows), and the teratoma (curved arrow). Surgical and pathologic results indicated granulomatous peritonitis due to rupture of the teratoma.
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Figure 4a. Ruptured mature cystic teratoma in a 37-year-old woman. (a) Axial contrast-enhanced CT scan shows ascites and floating areas of fat attenuation (arrows) around the liver. (b) Axial contrast-enhanced CT scan shows a mature cystic teratoma of the left ovary. Discontinuity of the cyst wall (arrow) with surrounding infiltration is evident. Surgical and pathologic results indicated granulomatous peritonitis due to rupture of the teratoma.
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Figure 4b. Ruptured mature cystic teratoma in a 37-year-old woman. (a) Axial contrast-enhanced CT scan shows ascites and floating areas of fat attenuation (arrows) around the liver. (b) Axial contrast-enhanced CT scan shows a mature cystic teratoma of the left ovary. Discontinuity of the cyst wall (arrow) with surrounding infiltration is evident. Surgical and pathologic results indicated granulomatous peritonitis due to rupture of the teratoma.
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At US, CT, and MR imaging, accurate diagnosis of a ruptured ovarian teratoma can be accomplished when the discontinuity of the wall is noted. The presence of ascites and a distorted or flattened shape of the tumor suggest tumor rupture, thereby indicating surgery. Acute or chronic peritonitis can manifest as ascites, diffuse or focal omental infiltration, and inflammatory masses involving the omentum and bowel; these findings mimic peritoneal carcinomatosis and tuberculous peritonitis (15). Therefore, when these imaging findings are accompanied by an ovarian teratoma, the possibility of rupture should be kept in mind and the integrity of the tumor wall should be carefully evaluated.
Torsion
Ovarian teratoma can lead to adnexal or ovarian torsion. Adnexal torsion is the fifth most common gynecologic emergency with a prevalence of 2.7% (16,17). Adnexal torsion is caused by rotation of the ovarian pedicle, resulting in arterial, venous, or lymphatic obstruction. Torsion commonly involves the ovary and the fallopian tube rather than either alone because the broad ligament acts as a fulcrum (16–19).
Adnexal torsion is an important cause of pelvic pain in female patients, and prompt accurate diagnosis is mandatory for adequate surgical restoration of blood flow. Because its clinical symptoms and signs are similar to those of other acute diseases such as tuboovarian abscess, endometriosis, appendicitis, and ovarian cyst rupture, imaging diagnosis plays a key role in patient care (20).
Ovarian teratoma is the most common ovarian mass associated with torsion, which is reported in 3%–16% of patients with ovarian teratomas (2). Torsion of the ovarian pedicle produces circulatory stasis, which initially obstructs venous low-pressure flow. With increasing degrees of rotation, the higher-pressure arteries become constricted and finally obstructed.
The spectrum of ischemic changes associated with adnexal torsion depends on the degree of vascular compromise. In early-stage or partial torsion, blockage of the venous flow and lymphatic return occurs, along with continued arterial input to the adnexa. This process leads to massive ovarian edema. Massive ovarian edema is characterized by diffuse enlargement and edema of the ovarian parenchyma and distention of peripheral follicles (17,18,21). With further passage of time, persistent edema and increased pressure on the twisted pedicle will cause venous obstruction followed by arterial thrombosis. In this stage, ovarian necrosis or hemorrhagic infarction may develop (20). If diagnosis and reduction of ovarian torsion are delayed, hemorrhagic infarction occurs and sometimes leads to severe peritonitis and even death (22). Early diagnosis can help prevent irreversible damage to the adnexal structures and may then allow conservative, ovary-sparing treatment in young women (20).
US is the first examination for diagnosing adnexal torsion in an emergency setting. Many US findings have been introduced, including a cystic, solid, or complex mass with or without pelvic fluid, thickening of the wall, and cystic hemorrhage (20). However, these findings are nonspecific; for more accurate diagnosis, Doppler US is necessary. Identification of the twisted vascular pedicle ("whirlpool sign") at color Doppler US strongly suggests adnexal torsion; color Doppler US also allows prediction of the viability of the twisted adnexal structures by depicting arterial and venous flow within the twisted vascular pedicle (23). In addition, most ovaries with torsion demonstrate abnormal flow patterns at pulsed Doppler US, including absent venous flow and diminished or absent arterial flow with high resistance.
However, variation in the completeness of the obstruction of the vascular supply can cause a variety of flow patterns, including normal arterial and venous flow in affected ovaries (17,23–25). Furthermore, US has the inherent limitation of operator dependency. Therefore, when the US findings in patients with suspected adnexal torsion are inconclusive, CT or MR imaging may be helpful. Use of CT and MR imaging is recommended to help detect the twisted vascular pedicle or thickened tube in subacute or chronic cases and in patients with a suspected pelvic mass (20). CT and MR imaging are superior to US in demonstrating the general configuration of the twisted adnexal structures and in detecting hemorrhagic infarction of the ovary or tube (20,26).
Common CT and MR imaging features of ovarian torsion include an enlarged ovary, an ovarian mass with cortical follicles, a twisted vascular pedicle, ipsilateral fallopian tube enlargement and thickening, smooth wall thickening of the twisted adnexal cystic mass, ascites, enlarged veins, and uterine deviation to the twisted side (14,20,26). Among these features, a twisted vascular pedicle and fallopian tube thickening are the most specific for the diagnosis, as noted in 21 of 25 patients in one study (20) (Fig 5). In some instances, tubal thickening manifests as an amorphous or tubular masslike structure or a beaklike protrusion extending from the uterus (14,20). In cases of long-standing or severe adnexal torsion, hemorrhage occurs in the thickened fallopian tube, the mass, and the peritoneal space. Additional imaging findings suggestive of hemorrhagic infarction include eccentric smooth wall thickening exceeding 10 mm in a cystic ovarian mass converging on the thickened fallopian tube and lack of contrast enhancement of the internal solid component or thickened wall of the twisted ovarian mass (20).
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Figure 5a. Torsion of a mature cystic teratoma in a 28-year-old woman. (a) Axial contrast-enhanced CT scan shows a teratoma of the right ovary. Eccentric abnormal wall thickening is noted (arrowheads). Diffuse fat infiltration around the tumor is also noted. (b) Axial contrast-enhanced CT scan obtained at a more cranial level shows a thickened fallopian tube (arrow) and continuation of the tube (T) with the mass. Surgical and pathologic results demonstrated a mature cystic teratoma with torsion and hemorrhagic infarction.
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Figure 5b. Torsion of a mature cystic teratoma in a 28-year-old woman. (a) Axial contrast-enhanced CT scan shows a teratoma of the right ovary. Eccentric abnormal wall thickening is noted (arrowheads). Diffuse fat infiltration around the tumor is also noted. (b) Axial contrast-enhanced CT scan obtained at a more cranial level shows a thickened fallopian tube (arrow) and continuation of the tube (T) with the mass. Surgical and pathologic results demonstrated a mature cystic teratoma with torsion and hemorrhagic infarction.
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Malignant Transformation
Malignant transformation occurs in 1%–2% of ovarian teratomas and accounts for 1% of all ovarian malignancies (2,27). Malignant transformation may occur in any of the three germ cell layers including the ectoderm, mesoderm, and endoderm. Squamous cell carcinoma arising from the squamous lining of the cyst is the most common type of malignant transformation, accounting for 80% of the reported cases (2,3). According to the gynecologic oncology reports with analysis of clinical and laboratory data (28–30), findings associated with malignant transformation include patient age greater than 45 years, tumor diameter greater than 9.9 cm, and serum squamous carcinoma antigen level greater than 2 ng/mL (our institutional criteria, in most laboratories). Squamous cell carcinoma antigen is a tumor antigen that was originally purified from squamous cell carcinoma of the uterine cervix. It is a glycoprotein secreted by various cancers and has been used as a guide for the management of squamous carcinoma (31).
It is common to see a soft-tissue protuberance in a mature cystic teratoma; this is known as a Rokitansky nodule or dermoid plug. Although this protuberance may be partly solid and consist of diverse tissues, benign teratomas never show transmural growth of the protuberance. Because a Rokitansky nodule is a common site of malignant transformation, it should be sectioned appropriately during pathologic analysis (7,32). Contrast enhancement of a Rokitansky nodule raises the possibility of malignant transformation (4), although this finding does not always necessarily indicate malignancy (33,34).
Making a differential diagnosis is very important for patients with ovarian tumors because the surgery performed is quite different for benign and malignant tumors. Specifically, laparoscopic surgery is now often performed in the management of mature cystic teratoma, but this procedure is quite risky when malignant transformation is suspected.
CT and MR imaging findings of malignant transformation of ovarian teratoma include invasive growth of large, irregularly marginated soft-tissue components through the tumor wall or irregular soft-tissue components within the tumor (35) (Fig 6). According to Park et al (36), who compared the imaging findings of malignant teratomas with those of size- and age-matched nonmalignant teratomas, the presence of an enhancing soft-tissue component and an obtuse angle between the soft tissue and the inner wall of the cyst are common CT or MR imaging findings of malignant transformation of ovarian teratomas (Fig 7). They also observed an elevated CA-125 level beyond 35 U/mL in 67% of their study patients and an elevated CA 19-9 level beyond 37 U/mL in 75% of these patients.
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Figure 6a. Squamous cell carcinoma arising from a mature cystic teratoma of the left ovary in a 31-year-old woman. The CA-125 level (157 U/mL; normal, <35 U/mL) and CA 19-9 level (68.3 U/mL; normal, <37 U/mL) were elevated. However, the carcinoembryonic antigen level was in the normal range. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a multilocular teratoma in the pelvis with a nodule-forming soft-tissue component (arrow). An obtuse angle (arrowhead in a) between the soft-tissue component and the inner wall of the cyst is evident. Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. A normal-appearing right ovary (arrowhead in b) is also noted. (c) Axial fat-saturated T1-weighted MR image shows a drop in the high-signal-intensity fat component (arrowheads). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. (d) Sagittal contrast-enhanced T1-weighted MR image shows transmural extension with invasion of the uterus (arrow). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. Left paraaortic lymphadenopathy was also evident. (e) Photograph of the gross specimen shows a Rokitansky nodule (arrow), which appears as a soft-tissue component on the corresponding MR images. Transmural invasion is also evident. (f, g) Photomicrographs (original magnification, x10 [f] and x40 [g]; hematoxylin-eosin stain) show metaplasia and malignant transformation arising from the squamous lining (arrow in f) of the cyst. Squamous cell carcinoma with keratin pearls is also evident. (Reprinted, with permission, from reference 36.)
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Figure 6b. Squamous cell carcinoma arising from a mature cystic teratoma of the left ovary in a 31-year-old woman. The CA-125 level (157 U/mL; normal, <35 U/mL) and CA 19-9 level (68.3 U/mL; normal, <37 U/mL) were elevated. However, the carcinoembryonic antigen level was in the normal range. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a multilocular teratoma in the pelvis with a nodule-forming soft-tissue component (arrow). An obtuse angle (arrowhead in a) between the soft-tissue component and the inner wall of the cyst is evident. Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. A normal-appearing right ovary (arrowhead in b) is also noted. (c) Axial fat-saturated T1-weighted MR image shows a drop in the high-signal-intensity fat component (arrowheads). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. (d) Sagittal contrast-enhanced T1-weighted MR image shows transmural extension with invasion of the uterus (arrow). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. Left paraaortic lymphadenopathy was also evident. (e) Photograph of the gross specimen shows a Rokitansky nodule (arrow), which appears as a soft-tissue component on the corresponding MR images. Transmural invasion is also evident. (f, g) Photomicrographs (original magnification, x10 [f] and x40 [g]; hematoxylin-eosin stain) show metaplasia and malignant transformation arising from the squamous lining (arrow in f) of the cyst. Squamous cell carcinoma with keratin pearls is also evident. (Reprinted, with permission, from reference 36.)
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Figure 6c. Squamous cell carcinoma arising from a mature cystic teratoma of the left ovary in a 31-year-old woman. The CA-125 level (157 U/mL; normal, <35 U/mL) and CA 19-9 level (68.3 U/mL; normal, <37 U/mL) were elevated. However, the carcinoembryonic antigen level was in the normal range. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a multilocular teratoma in the pelvis with a nodule-forming soft-tissue component (arrow). An obtuse angle (arrowhead in a) between the soft-tissue component and the inner wall of the cyst is evident. Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. A normal-appearing right ovary (arrowhead in b) is also noted. (c) Axial fat-saturated T1-weighted MR image shows a drop in the high-signal-intensity fat component (arrowheads). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. (d) Sagittal contrast-enhanced T1-weighted MR image shows transmural extension with invasion of the uterus (arrow). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. Left paraaortic lymphadenopathy was also evident. (e) Photograph of the gross specimen shows a Rokitansky nodule (arrow), which appears as a soft-tissue component on the corresponding MR images. Transmural invasion is also evident. (f, g) Photomicrographs (original magnification, x10 [f] and x40 [g]; hematoxylin-eosin stain) show metaplasia and malignant transformation arising from the squamous lining (arrow in f) of the cyst. Squamous cell carcinoma with keratin pearls is also evident. (Reprinted, with permission, from reference 36.)
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Figure 6d. Squamous cell carcinoma arising from a mature cystic teratoma of the left ovary in a 31-year-old woman. The CA-125 level (157 U/mL; normal, <35 U/mL) and CA 19-9 level (68.3 U/mL; normal, <37 U/mL) were elevated. However, the carcinoembryonic antigen level was in the normal range. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a multilocular teratoma in the pelvis with a nodule-forming soft-tissue component (arrow). An obtuse angle (arrowhead in a) between the soft-tissue component and the inner wall of the cyst is evident. Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. A normal-appearing right ovary (arrowhead in b) is also noted. (c) Axial fat-saturated T1-weighted MR image shows a drop in the high-signal-intensity fat component (arrowheads). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. (d) Sagittal contrast-enhanced T1-weighted MR image shows transmural extension with invasion of the uterus (arrow). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. Left paraaortic lymphadenopathy was also evident. (e) Photograph of the gross specimen shows a Rokitansky nodule (arrow), which appears as a soft-tissue component on the corresponding MR images. Transmural invasion is also evident. (f, g) Photomicrographs (original magnification, x10 [f] and x40 [g]; hematoxylin-eosin stain) show metaplasia and malignant transformation arising from the squamous lining (arrow in f) of the cyst. Squamous cell carcinoma with keratin pearls is also evident. (Reprinted, with permission, from reference 36.)
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Figure 6e. Squamous cell carcinoma arising from a mature cystic teratoma of the left ovary in a 31-year-old woman. The CA-125 level (157 U/mL; normal, <35 U/mL) and CA 19-9 level (68.3 U/mL; normal, <37 U/mL) were elevated. However, the carcinoembryonic antigen level was in the normal range. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a multilocular teratoma in the pelvis with a nodule-forming soft-tissue component (arrow). An obtuse angle (arrowhead in a) between the soft-tissue component and the inner wall of the cyst is evident. Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. A normal-appearing right ovary (arrowhead in b) is also noted. (c) Axial fat-saturated T1-weighted MR image shows a drop in the high-signal-intensity fat component (arrowheads). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. (d) Sagittal contrast-enhanced T1-weighted MR image shows transmural extension with invasion of the uterus (arrow). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. Left paraaortic lymphadenopathy was also evident. (e) Photograph of the gross specimen shows a Rokitansky nodule (arrow), which appears as a soft-tissue component on the corresponding MR images. Transmural invasion is also evident. (f, g) Photomicrographs (original magnification, x10 [f] and x40 [g]; hematoxylin-eosin stain) show metaplasia and malignant transformation arising from the squamous lining (arrow in f) of the cyst. Squamous cell carcinoma with keratin pearls is also evident. (Reprinted, with permission, from reference 36.)
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Figure 6f. Squamous cell carcinoma arising from a mature cystic teratoma of the left ovary in a 31-year-old woman. The CA-125 level (157 U/mL; normal, <35 U/mL) and CA 19-9 level (68.3 U/mL; normal, <37 U/mL) were elevated. However, the carcinoembryonic antigen level was in the normal range. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a multilocular teratoma in the pelvis with a nodule-forming soft-tissue component (arrow). An obtuse angle (arrowhead in a) between the soft-tissue component and the inner wall of the cyst is evident. Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. A normal-appearing right ovary (arrowhead in b) is also noted. (c) Axial fat-saturated T1-weighted MR image shows a drop in the high-signal-intensity fat component (arrowheads). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. (d) Sagittal contrast-enhanced T1-weighted MR image shows transmural extension with invasion of the uterus (arrow). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. Left paraaortic lymphadenopathy was also evident. (e) Photograph of the gross specimen shows a Rokitansky nodule (arrow), which appears as a soft-tissue component on the corresponding MR images. Transmural invasion is also evident. (f, g) Photomicrographs (original magnification, x10 [f] and x40 [g]; hematoxylin-eosin stain) show metaplasia and malignant transformation arising from the squamous lining (arrow in f) of the cyst. Squamous cell carcinoma with keratin pearls is also evident. (Reprinted, with permission, from reference 36.)
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Figure 6g. Squamous cell carcinoma arising from a mature cystic teratoma of the left ovary in a 31-year-old woman. The CA-125 level (157 U/mL; normal, <35 U/mL) and CA 19-9 level (68.3 U/mL; normal, <37 U/mL) were elevated. However, the carcinoembryonic antigen level was in the normal range. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a multilocular teratoma in the pelvis with a nodule-forming soft-tissue component (arrow). An obtuse angle (arrowhead in a) between the soft-tissue component and the inner wall of the cyst is evident. Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. A normal-appearing right ovary (arrowhead in b) is also noted. (c) Axial fat-saturated T1-weighted MR image shows a drop in the high-signal-intensity fat component (arrowheads). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. (d) Sagittal contrast-enhanced T1-weighted MR image shows transmural extension with invasion of the uterus (arrow). Surrounding chemical shift artifact is pathognomic for a mature cystic teratoma. Left paraaortic lymphadenopathy was also evident. (e) Photograph of the gross specimen shows a Rokitansky nodule (arrow), which appears as a soft-tissue component on the corresponding MR images. Transmural invasion is also evident. (f, g) Photomicrographs (original magnification, x10 [f] and x40 [g]; hematoxylin-eosin stain) show metaplasia and malignant transformation arising from the squamous lining (arrow in f) of the cyst. Squamous cell carcinoma with keratin pearls is also evident. (Reprinted, with permission, from reference 36.)
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Figure 7a. Adenocarcinoma arising from a mature cystic teratoma of the left ovary in a 63-year-old woman. The carcinoembryonic antigen level (33.5 ng/mL; normal, <6 ng/mL) and CA 19-9 level (129 U/mL; normal, <37 U/mL) were elevated. However, the CA-125 level was in the normal range. (a, b) Axial unenhanced (a) and contrast-enhanced (b) CT scans show a nodule-forming and enhancing soft-tissue component (arrow). The soft-tissue component has an attenuation of 10 HU on the unenhanced scan and 45 HU on the contrast-enhanced scan. (c) CT scan (bone window) shows an osteolytic lesion in the right acetabulum (arrows). The lesion is a bone metastasis. (d) Positron emission tomographic scan shows hypermetabolic increased uptake in the soft-tissue component of the mature cystic teratoma (arrow) and in the acetabular metastasis (arrowhead). (Reprinted, with permission, from reference 36.)
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Figure 7b. Adenocarcinoma arising from a mature cystic teratoma of the left ovary in a 63-year-old woman. The carcinoembryonic antigen level (33.5 ng/mL; normal, <6 ng/mL) and CA 19-9 level (129 U/mL; normal, <37 U/mL) were elevated. However, the CA-125 level was in the normal range. (a, b) Axial unenhanced (a) and contrast-enhanced (b) CT scans show a nodule-forming and enhancing soft-tissue component (arrow). The soft-tissue component has an attenuation of 10 HU on the unenhanced scan and 45 HU on the contrast-enhanced scan. (c) CT scan (bone window) shows an osteolytic lesion in the right acetabulum (arrows). The lesion is a bone metastasis. (d) Positron emission tomographic scan shows hypermetabolic increased uptake in the soft-tissue component of the mature cystic teratoma (arrow) and in the acetabular metastasis (arrowhead). (Reprinted, with permission, from reference 36.)
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Figure 7c. Adenocarcinoma arising from a mature cystic teratoma of the left ovary in a 63-year-old woman. The carcinoembryonic antigen level (33.5 ng/mL; normal, <6 ng/mL) and CA 19-9 level (129 U/mL; normal, <37 U/mL) were elevated. However, the CA-125 level was in the normal range. (a, b) Axial unenhanced (a) and contrast-enhanced (b) CT scans show a nodule-forming and enhancing soft-tissue component (arrow). The soft-tissue component has an attenuation of 10 HU on the unenhanced scan and 45 HU on the contrast-enhanced scan. (c) CT scan (bone window) shows an osteolytic lesion in the right acetabulum (arrows). The lesion is a bone metastasis. (d) Positron emission tomographic scan shows hypermetabolic increased uptake in the soft-tissue component of the mature cystic teratoma (arrow) and in the acetabular metastasis (arrowhead). (Reprinted, with permission, from reference 36.)
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Figure 7d. Adenocarcinoma arising from a mature cystic teratoma of the left ovary in a 63-year-old woman. The carcinoembryonic antigen level (33.5 ng/mL; normal, <6 ng/mL) and CA 19-9 level (129 U/mL; normal, <37 U/mL) were elevated. However, the CA-125 level was in the normal range. (a, b) Axial unenhanced (a) and contrast-enhanced (b) CT scans show a nodule-forming and enhancing soft-tissue component (arrow). The soft-tissue component has an attenuation of 10 HU on the unenhanced scan and 45 HU on the contrast-enhanced scan. (c) CT scan (bone window) shows an osteolytic lesion in the right acetabulum (arrows). The lesion is a bone metastasis. (d) Positron emission tomographic scan shows hypermetabolic increased uptake in the soft-tissue component of the mature cystic teratoma (arrow) and in the acetabular metastasis (arrowhead). (Reprinted, with permission, from reference 36.)
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Infection and Autoimmune Hemolytic Anemia
Infection occurs in only 1% of patients with ovarian teratoma. Coliform bacteria are the organisms most commonly implicated (14,37). Autoimmune hemolytic anemia has been associated with mature cystic teratomas in rare cases (38–40). In these cases, removal of the tumor resulted in complete symptom resolution. The mechanism of the hemolysis has not yet been defined, although several hypotheses have been proposed, such as cross-reactivity of tumor and red blood cell antigens, production of red blood cell autoantibodies by the tumor, and alteration of the red blood cell molecules by the tumor, which renders them antigenic to the host (40,41).
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Unusual Imaging Findings of Ovarian Teratomas
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Immature Teratomas
Like mature teratomas, immature teratomas consist of tissue derived from three germ cell layers. However, immature teratomas can be differentiated from mature cystic teratomas by the presence of immature or embryonic tissue. Furthermore, immature teratomas typically affect a younger age group (usually during the first two decades of life) and have a worse prognosis (3).
Because mature cystic teratomas are the most common ovarian tumors in younger patients, preoperative recognition of possibly immature lesions will be of help in determining treatment options and performing tumor sampling.
On CT and MR images, immature teratomas demonstrate a prominent solid component with cystic areas and intratumoral fat (Figs 8, 9). The presence of a prominent solid component is helpful in differentiating immature from mature cystic teratomas. Tumor diameter may also be useful for this differentiation because immature teratomas tend to be larger (mean diameter, 12–25 cm) than mature cystic teratomas (approximately 7 cm) at the time of diagnosis (42).
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Figure 8. Immature teratoma in a 12-year-old girl. Axial contrast-enhanced CT scan shows a heterogeneously enhancing solid mass in the right lower abdomen. Intratumoral calcifications and fat (arrows) are seen.
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Figure 9a. Immature teratoma in a 17-year-old girl. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a mass with heterogeneous signal intensity. (c) Axial fat-saturated gadolinium-enhanced T1-weighted MR image shows decreased signal intensity (arrows) compared with that on the T1-weighted image. The decreased signal intensity represents the fat component.
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Figure 9b. Immature teratoma in a 17-year-old girl. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a mass with heterogeneous signal intensity. (c) Axial fat-saturated gadolinium-enhanced T1-weighted MR image shows decreased signal intensity (arrows) compared with that on the T1-weighted image. The decreased signal intensity represents the fat component.
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Figure 9c. Immature teratoma in a 17-year-old girl. (a, b) Axial T1-weighted (a) and T2-weighted (b) MR images show a mass with heterogeneous signal intensity. (c) Axial fat-saturated gadolinium-enhanced T1-weighted MR image shows decreased signal intensity (arrows) compared with that on the T1-weighted image. The decreased signal intensity represents the fat component.
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Struma Ovarii
Struma ovarii, an ovarian mature cystic teratoma composed entirely or predominantly of thyroid tissue and containing variable-sized follicles with colloid material, accounts for 0.3%–1% of all ovarian tumors and for approximately 3% of all mature cystic teratomas (43). About 5% of cases show symptoms or signs of thyrotoxicosis.
The gross pathologic appearance of struma ovarii differs from that of mature cystic teratomas because struma ovarii consists of amber-colored thyroid tissue, hemorrhage, necrosis, and fibrosis. Although malignant struma ovarii is uncommon, the clinical behavior is benign. Because 95% of strumae ovarii are benign and usually occur in premenopausal women, preoperative diagnosis is very important to avoid unnecessary surgery such as hysterectomy and dissection of pelvic lymph nodes (44).
There are overlaps between the imaging findings and the clinical features of struma ovarii. Although findings are nonspecific, US and CT demonstrate its complex appearance with multiple cystic and solid areas, reflecting the gross pathologic appearance of the tumor (Fig 10). MR imaging findings may be more helpful for diagnosis because the cystic spaces demonstrate both high and low signal intensity on T1- and T2-weighted images (45,46). Some cystic spaces may show low signal intensity on both T1- and T2-weighted images owing to the thick, gelatinous colloid of the struma (45,47,48). When struma ovarii is not associated with hyperthyroidism, the differential diagnosis should include mature cystic teratoma without fatty tissue, cystadenoma or cystadenocarcinoma, endometriosis, tuboovarian abscess, and metastatic tumor because the imaging features of these tumors may resemble those of struma ovarii (45,47).
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Figure 10a. Monodermal teratoma (struma ovarii) in a 46-year-old woman. (a, b) Axial unenhanced (a) and contrast-enhanced (b) CT scans show a fat-containing mass with calcifications. A nodule-forming soft-tissue component with enhancement is noted in the tumor. (c) Photomicrograph (original magnification, x40; hematoxylin- eosin stain) shows thyroid follicles containing thick colloid.
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Figure 10b. Monodermal teratoma (struma ovarii) in a 46-year-old woman. (a, b) Axial unenhanced (a) and contrast-enhanced (b) CT scans show a fat-containing mass with calcifications. A nodule-forming soft-tissue component with enhancement is noted in the tumor. (c) Photomicrograph (original magnification, x40; hematoxylin- eosin stain) shows thyroid follicles containing thick colloid.
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Figure 10c. Monodermal teratoma (struma ovarii) in a 46-year-old woman. (a, b) Axial unenhanced (a) and contrast-enhanced (b) CT scans show a fat-containing mass with calcifications. A nodule-forming soft-tissue component with enhancement is noted in the tumor. (c) Photomicrograph (original magnification, x40; hematoxylin- eosin stain) shows thyroid follicles containing thick colloid.
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Combination Tumors and Collision Tumors Containing Teratomas
A combination tumor contains intermixed varying histologic components originating from a common stem cell. Mixed germ cell tumor is a typical example and contains more than one germ cell component (1,14). Although the imaging findings of mixed germ cell tumors are variable, the possibility of mixed germ cell tumor should be considered when a predominantly solid and heterogeneous ovarian tumor contains fatty areas or when a mature cystic teratoma contains an enhancing solid portion (14) (Fig 11). In some instances, imaging findings of mixed germ cell tumor may be similar to those of malignantly transformed teratomas. Elevation of 
-fetoprotein and human chorionic gonodotropin levels and a younger patient age can help establish the diagnosis of mixed germ cell tumor (14).
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Figure 11a. Mixed germ cell tumor (mature cystic teratoma and yolk sac tumor) in an 18-year-old woman. Axial unenhanced (a) and contrast-enhanced (b) CT scans show a cystic mass with prominent solid nodules (arrows in b) and calcifications (arrowheads in a).
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Figure 11b. Mixed germ cell tumor (mature cystic teratoma and yolk sac tumor) in an 18-year-old woman. Axial unenhanced (a) and contrast-enhanced (b) CT scans show a cystic mass with prominent solid nodules (arrows in b) and calcifications (arrowheads in a).
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A collision tumor is defined as consisting of two adjacent but histologically distinct tumors without histologic admixture at the interface. It is different from a composition tumor or a combination tumor (49). A composition tumor shows an intimate admixture of two different cell types without a definite interface and may arise from simultaneous development of malignancies in different tissues or from sarcomatous change in the stroma of a carcinoma. Composition tumor is a true mixed tumor, and the typical example is a carcinosarcoma (50).
The most common composition of ovarian collision tumor is a mixture of mature cystic teratoma and mucinous cystadenoma or cystadenocarcinoma (51). The most typical imaging finding of collision tumors is that of two adjacent septated cystic masses, either of which contains intratumoral fat (Fig 12).
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Figure 12a. Collision tumor (mature cystic teratoma and mucinous cystadenoma) in a 34-year-old woman. (a) Axial contrast-enhanced CT scan shows a lesion consisting of a mass with fat and calcifications (arrow) on the left side and a cystic mass on the right side. (b) CT scan obtained at a more caudal level shows the multiloculated cystic mass on the right side and the fat-containing mass on the left side. Surgery revealed a collision tumor consisting of mature cystic teratoma and mucinous cystadenoma.
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Figure 12b. Collision tumor (mature cystic teratoma and mucinous cystadenoma) in a 34-year-old woman. (a) Axial contrast-enhanced CT scan shows a lesion consisting of a mass with fat and calcifications (arrow) on the left side and a cystic mass on the right side. (b) CT scan obtained at a more caudal level shows the multiloculated cystic mass on the right side and the fat-containing mass on the left side. Surgery revealed a collision tumor consisting of mature cystic teratoma and mucinous cystadenoma.
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Preoperative diagnosis of a collision tumor is important because it may affect patient treatment. Preoperative suggestion of a collision tumor may lead the pathologist to perform a thorough examination of the mass and prevent missing the diagnosis of the second part of the mass, which may be critical to the further treatment and prognosis of the patient (51).
Mature Cystic Teratomas without Demonstrable Fat
Some mature cystic teratomas may have only scanty intratumoral fat that cannot be demonstrated at imaging. According to Yamashita et al (52), 15% of mature cystic teratomas may not show a fat component and appear only as cystic masses at imaging (Fig 13). In these cases, differentiation from other epithelial ovarian neoplasms is difficult; identifying fat in the cyst wall, especially with chemical shift imaging with in-phase and out-of-phase imaging, suggests the proper diagnosis.
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Figure 13. Mature cystic teratoma without a fat component in a 57-year-old woman. Axial contrast-enhanced CT scan shows a homogeneous cystic mass. A fat or calcification component is not noted in the mass.
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Teratomas with Pure Fatty Components
Rarely, mature cystic teratomas may be composed only of pure fat, as can be seen at imaging (Fig 14). These tumors may mimic other uncommon lipid-containing pelvic tumors such as peduculated lipomatous uterine tumor, benign pelvic lipoma, and liposarcoma (14,53).
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Figure 14. Mature cystic teratoma composed of a pure fat component in a 74-year-old woman. Axial contrast-enhanced CT scan shows a well-defined lobulated fatty mass (M). Note the absence of a solid component or calcification in the mass.
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Conclusions
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Ovarian teratomas may cause various complications and show a wide spectrum of clinical and imaging features. To achieve adequate treatment and prevent misdiagnosis, a good understanding of the imaging findings of the complications of ovarian teratomas as well as the unusual manifestations is necessary.
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Footnotes
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2 Current address: Department of Radiology, Ulsan University Hospital, University of Ulsan, Ulsan, South Korea. 
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Abstract
LEARNING OBJECTIVES
