Determining the nature of a sonographically indeterminate adnexal mass has great clinical importance. Decisions regarding the type and extent of surge

Transcription

1 Note: This copy is for your personal, non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at John A. Spencer, MA, MD, FRCP, FRCR Sunethra Ghattamaneni, MB, MRCP, FRCR MR Imaging of the Sonographically Indeterminate Adnexal Mass 1 Magnetic resonance (MR) imaging of the sonographically indeterminate adnexal mass can be used to guide patient care and reduce the costs of investigation and treatment. Most indeterminate masses result from common benign conditions, and women with such masses can avoid unnecessary or inappropriate surgery. For the minority of women in whom indeterminate masses are malignant, use of MR imaging rather than a wait and watch strategy of interval re-examination with ultrasonography offers a more timely diagnosis. There are simple diagnostic steps in the MR imaging assessment that direct a problem-solving, tailored approach based on signal characteristics and morphology. REVIEWS AND COMMENTARY n REVIEW FOR RESIDENTS RSNA, From the Department of Radiology, St James s Institute of Oncology, Beckett Street, Leeds LS9 7TF, England. Received March 5, 2009; revision requested April 21; revision received July 31; accepted September 23; fi nal version accepted November 16. Address correspondence to J.A.S. ( johnaspencer50@hotmail.com ). q RSNA, 2010 Radiology: Volume 256: Number 3 September 2010 n radiology.rsna.org 677

2 Determining the nature of a sonographically indeterminate adnexal mass has great clinical importance. Decisions regarding the type and extent of surgery necessary and who should perform this surgery depend on this judgment. Benign masses can be managed either conservatively or by simple resection of the mass, depending on the patient s symptoms and fitness for surgery. Malignant masses require radical cancer surgery performed under the care of a specialist gynecologic oncologist. It is vital that the appropriate surgical procedure occurs at the first attempt and is performed by a surgeon with the appropriate expertise. A woman with a benign adnexal mass should not undergo inappropriate cancer surgery. A woman with a primary ovarian cancer should not undergo simple removal without staging procedures and radical resection, as this commits her to a further staging procedure to provide the information to determine the need for adjuvant chemotherapy. It is for these reasons that magnetic resonance (MR) imaging has a pivotal role in the investigation of the indeterminate adnexal mass, and there is a powerful evidence base to support its use ( 1 4 ). Essentials n Most indeterminate adnexal masses result from common benign conditions. n MR imaging has been shown to be superior to US in assessment of adnexal masses and to be a cost-effective intervention. n MR imaging allows identification of blood products within hemorrhagic masses that may mimic solid tumor at US. n Fat-suppressed T1-weighted MR images may reveal small amounts of fat, which allows diagnosis of a mature teratoma. n Contrast-enhanced T1-weighted MR imaging depicts features of malignancy such as enhancing mural nodules and/or enhancing solid areas with or without necrosis. A further practical consideration is the earlier diagnosis of cancer offered by the use of MR imaging. A commonly used strategy for the indeterminate mass has been a wait and watch approach, repeating the examination after two or more menstrual cycles to allow products of hemorrhage, which can mimic solid tumor at ultrasonography (US), to resolve. By using MR imaging this delay of 2 3 months can be avoided, and this fits well within a rapid cancer diagnosis strategy ( 5 ). This review is not an encyclopedic review of the subject and does not encompass every pathologic entity that may present as a sonographically indeterminate mass. It provides a practical approach to using MR imaging to define the most frequent benign and malignant diagnoses that present as indeterminate adnexal masses in daily practice, describing their common manifestations. Examples are chosen from cases referred to a specialist gynecologic center as suspicious for ovarian cancer or from the local referral population after indeterminate US examinations of complex adnexal masses. The Evidence Base The value of MR imaging for characterization of adnexal masses was recognized within the first few years of its introduction as a clinical tool. Descriptions of the MR imaging appearances of common adnexal lesions such as endometrioma and mature cystic teratoma followed ( 6 9 ). Early workers recognized the facility to identify tissue characteristics of fat, blood, fibrous tissue, and vascularized tumor, as well as the value of direct multiplanar imaging to define the site of origin of the mass ( 10, 11 ). In the 1990s, a multicenter study was conducted by the Radiologic Diagnostic Oncology Group (RDOG), which concluded that MR imaging was superior to computed tomography (CT) and US in determining the nature of adnexal masses ( 1 ). Looking at the ovaries the accuracy of MR imaging was 0.91, higher than that of CT and significantly higher than that of Doppler US at 0.78 ( 1 ). Overall, US had similar accuracy in staging, but this finding relied on the presence of ascites, which is infrequently present with US indeterminate masses. The RDOG study looked at all-comers about to undergo surgery and therefore included a wide range of diagnoses, ranging from likely benign disease to advanced malignancy. Indeterminate adnexal masses are within the gray area between complex benign disease and early malignancy. Two key studies ( 2, 3 ) have addressed this specific patient group and produced interesting findings. Both studies showed that the majority of sonographically indeterminate masses are not rare and exotic lesions but common adnexal conditions and that malignant masses composed a minority of the diagnoses ( 2, 3 ). The common diagnoses were mature teratomas (dermoid tumors) with atypical features or only small amounts of macroscopic fat that could not be recognized at US, hemorrhagic lesions in which adherent mural blood clots may mimic mural vegetations of malignancy, and fibrous masses (ovarian fibroma/ thecoma and uterine leimyomata) whose solid nature raised concerns for malignancy ( 2 ). When MR imaging and US findings were in disagreement about the nature of the mass, MR imaging findings were correct in 19 of 20 cases. MR imaging was most valuable when the tumor marker CA-125 level was normal or only minimally elevated ( 2 ). Second, the combination of US followed by MR imaging minimized the risk of misdiagnosing a benign mass as malignant ( 2 ). In the study by Sohaib et al ( 2 ), only seven of 72 women underwent inappropriate cancer surgery. So it is clear that even with application of exemplary MR imaging technique, some masses confound our best efforts. However, the number of such women who undergo inappropriate cancer surgery Published online /radiol Radiology 2010; 256: Authors stated no fi nancial relationship to disclose. 678 radiology.rsna.org n Radiology: Volume 256: Number 3 September 2010

3 Figure 1 Figure 1: Incidental indeterminate solid adnexal mass discovered during US for urinary tract infection in 54-year-old woman. Oblique axial T2-weighted spin-echo MR images (4830/96) along the ovarian axis, the long axis of the uterus, are planned from (a) the sagittal image. (b) In the ovarian axis there is a T2-weighted low-signal-intensity (T2-weighted dark) mass (arrow) in the right adnexal region separate from the ovaries (arrowheads). (c) At an inferior level, the mass (arrow) is also separate from the uterus, which indicates diagnosis of a broad ligament leiomyoma. can be dramatically reduced and the great majority of women may proceed to surgery in the confidence that this is appropriate to their needs. Other workers who looked at the use of MR imaging after indeterminate US findings had similar findings ( 3 ). They found that the main reason for indeterminate sonographic diagnosis was an inability to determine the origin of masses, in assessment of large masses and in characterization of purely solid and complex cystic masses. In that study, MR imaging had excellent agreement with final diagnosis, tissue content, and characteristic ( k = ) versus sonography ( k = ). The authors concluded that use of MR imaging obviated the need for surgery ( 3 ). Further, the use of MR imaging has been shown to be the most cost-effective intervention for the sonographically indeterminate adnexal mass and with the greatest shift in pre- and posttest probability in a detailed meta-analysis involving Bayesian analysis ( 4 ). In this analysis, the pretest probabilities of malignancy in pre- and postmenopausal women with indeterminate masses were 9% and 33%, respectively, but after the second test, MR imaging, these probabilities were reduced to 2% and 8% 10%, respectively ( 4 ). These data emphasize three main findings: first, the risk that a sonographically indeterminate mass is malignant is small, particularly in premenopausal women. Second, the intervention of MR imaging results in many more correct surgical diagnoses. And, finally, by removing the need for interval reassessment US, MR imaging offers the possibility of earlier diagnosis of cancer in that minority of women with malignant lesions. Teaching points. (a) Most indeterminate adnexal masses result from common benign conditions. (b) MR imaging has been shown to be superior to US in assessment of adnexal masses and to be a cost-effective intervention. Why Are Adnexal Masses Indeterminate at US? US is the first-line imaging investigation for the suspected adnexal mass and does an excellent job in helping to characterize the majority of women as having no adnexal mass, a benign mass, or a malignant mass. But there is a substantial minority of masses that are indeterminate. A sonographically indeterminate adnexal mass is defined as (a) one that has complexity but that, after thorough interrogation including Doppler assessment, cannot be confidently placed into Figure 2 Figure 2: Subserosal leiomyoma discovered during US for pelvic pain in 34-year-old woman. Oblique axial T2-weighted spin-echo MR image (5610/123) along ovarian axis clearly depicts the relationship of the mass (arrow) to both ovaries (arrowheads). The right-sided subserosal leiomyoma is abutting the right ovary but is clearly of uterine origin. Note claws of uterine tissue around the leiomyoma. At US, the mass was solid but it was unclear if it arose from the ovary or uterus. either the benign or malignant category or (b) one for which the site of origin, from the ovary, uterus, or another pelvic structure, remains to be established. Adnexal masses are increasingly discovered in the investigation of abdominal and pelvic problems, as cross-sectional imaging has supplanted radiographic Radiology: Volume 256: Number 3 September 2010 n radiology.rsna.org 679

4 Figure 3 incidentally discovered mass may be reluctant to undergo transvaginal scanning, and in the infirm and overweight patient, transabdominal scanning may be of limited value. In such cases MR imaging can help. Imaging of the indeterminate adnexal mass is now the most common gynecologic indication for MR at our institution. Not only is it helpful for problem solving in regard to the indeterminate adnexal mass but it provides an effective second confirmatory test. This is particularly the case in younger women, in whom exposure to ionizing radiation should be kept to a minimum. Figure 3: Complex appearances due to coexistent corpus luteum hemorrhage and follicular cyst in 30-year-old woman. (a) On axial T2-weighted spin-echo MR image (5000/100), left ovary contains a simple cyst (C) with a corpus luteum (arrow) anteriorly. (b) Unenhanced axial T1-weighted spin-echo MR image (470/14). (c) Contrast-enhanced axial T1-weighted spin-echo MR image (470/14) depicts high contrast enhancement in wall of corpus luteum (arrow). (d) Referral US showed bilocular left adnexal mass with differing echogenicity of contents, suspected mural nodules, and low impedance blood fl ow in the periphery. Posterior locule at US corresponds to cyst (C) and anterior, slightly more echogenic lesion represents corpus luteum, which has undergone involution (arrow) at subsequent MR examination ( a, c ). and fluoroscopic contrast material enhanced studies of the genitourinary and gastrointestinal tract ( ). Such incidental findings at specialized examinations such as CT colonography and urography, unenhanced CT for detection of urinary calculi, and general abdominopelvic CT result in further use of imaging to allay patient and physician anxiety about the nature of these findings, with substantial economic consequences. US should be the next investigation but its use may fail to clarify the nature of the mass. In some situations, the US technique may not be optimal. For example, an older woman with such an MR Imaging Technique The technique used for MR imaging of the indeterminate adnexal mass comprises two parts: a series of basic T1- and T2-weighted sequences to ascertain the site and signal characteristics of the mass; then, selected problem-solving sequences tailored to the suspected nature of the mass to refine the diagnosis. Patient preparation is minimal. There is no need for fasting. There is no need for a filled bladder; if the patient expresses a desire to void before the examination this is encouraged, as an overfull bladder may result in a restless patient and images that are degraded by motion artifact. Use of a smooth muscle relaxant is advised ( 15 ). A pelvic phased-array coil is used. The basic series of MR imaging should comprise a T2-weighted sagittal sequence of the pelvis to assess the uterus and the position of the adnexal mass (eg, repetition time msec/echo time msec, 5610/123; section thickness, 5 6 mm) and a pair of T1-weighted (eg, 473/14, section thickness of 4 5 mm) and T2-weighted (eg, 5450/96, section thickness of 4 5 mm) sequences covering the indeterminate adnexal mass in an orthogonal plane with similar section thickness to allow precise comparison of its tissue characteristics, to further detail its anatomic location, and to suggest its organ of origin. The choice of which orthogonal plane is used for this pair of sequences is left to the discretion and preference 680 radiology.rsna.org n Radiology: Volume 256: Number 3 September 2010

5 Figure 5 Predominant MR Imaging Signal Intensity Characteristic and Morphology of Adnexal Masses Signal Intensity Characteristic Morphology T1-weighted bright mass Complex cystic or cystic-solid mass T2-weighted solid mass Figure 4 of the supervising radiographer/technologist or radiologist. If the mass is noted to lie lateral to the uterus on the initial sagittal T2-weighted images its relationship to the uterus may be better shown on coronal or coronal oblique images, and if it lies above or behind the uterus on axial or axial oblique images. Mature cystic teratoma (dermoid) Hemorrhagic cyst and endometrioma/hematosalpinx Mucinous cyst Melanoma metastasis Hydrosalpinx Tubo-ovarian abscess Cystadenoma Cystadenofi broma Borderline and invasive primary malignancy Metastasis Leiomyoma Solid mature teratoma (eg, struma ovarii) Fibroma/thecoma Primary malignancy Metastasis Lymphoma Figure 4: Decision tree for the T1-weighted high-signal intensity (bright) mass. CET1W = contrast-enhanced T1-weighted, FST1W = fat-suppressed T1-weighted. MR Appearances and Identification of the Normal Ovary To determine the site of origin of the indeterminate adnexal mass it is important to identify both ovaries, presuming there has not been prior resection. Definition of two normal ovaries Figure 5: Decision tree for complex cystic or cystic-solid masses. CET1W = contrast-enhanced T1-weighted. separate from the mass indicates that the mass is either uterine or arising within one of its suspensory ligaments, is tubal, or is even nongynecologic. Identification of the ovaries may be aided by performing an oblique T2- weighted sequence angled along the long axis of the uterine body, parallel to the endometrial stripe. This obliquity is planned from the sagittal T2- weighted sequence ( Fig 1a ). On this oblique sequence along the ovarian axis the ovaries typically lie lateral to the uterine cornua below the iliac bifurcation on the pelvic sidewall, though there is variation in their location. We have found that this sequence assists particularly in determining the site of origin of T2 solid indeterminate masses ( Figs 1, 2 ). The appearances of the normal ovary on T2-weighted MR images are similar to those on US studies, with a central stroma with low signal intensity and peripheral follicles that have high signal intensity. Immature follicles are usually less than 1 cm in size but normal ovaries may contain a dominant follicle larger than this. A follicle that exceeds 3 cm in size is termed a follicular cyst. An excess of stroma and an increased number of enlarged peripheral follicles or cysts is the hallmark of polycystic ovaries ( 6 ). In a normal premenopausal ovary there may also be a more complex structure that represents a corpus luteum. Radiology: Volume 256: Number 3 September 2010 n radiology.rsna.org 681

6 Its appearance varies with development and regression. There may be hemorrhage within the central fluid portion of the corpus luteum. This has high signal intensity on T1-weighted images. Otherwise normal ovaries are of intermediate signal intensity similar to the uterus on T1-weighted images. The wall of the corpus luteum may show marked enhancement on contrast-enhanced T1-weighted images ( Fig 3 ). Postmenopausal ovaries are now commonly identified by using modern high-resolution cross-sectional imaging. The old adage that if identified at crosssectional imaging, postmenopausal ovaries are probably enlarged and thus abnormal no longer holds true. They are now often seen with high-resolution US and thin-section CT. At MR imaging postmenopausal ovaries are predominantly solid with a relative increase in stromal tissue, which has low signal intensity on T2-weighted images and which may contain small senescent follicles. The solid stroma does not enhance. Some postmenopausal ovaries are represented by tiny nodules of tissue attached to the proximal ends of the round ligament. Others may contain dysfunctional cysts that may measure several centimeters in size ( 16 ). Figure 6 Figure 7 Figure 6: Decision tree for the T2-weighted (T2W) low-signal-intensity mass: homogeneous T2-weighted dark masses and inhomogeneous mixed-signalintensity masses. CET1W = contrastenhanced T1- weighted. MR Appearances of the Indeterminate Adnexal Mass After performing the basic T1- and T2- weighted sequences described above, the likely site and origin of the mass and its characteristics are established. Problem-solving sequences are then chosen to refine the diagnosis based on the predominant signal intensity characteristic and morphology. Masses are divided into three broad categories ( Table ) for which specific problem-solving sequences are applied ( Figs 4 6 ): For each of these three broad categories of mass, there is a focused problemsolving approach that further refines the diagnosis. Decision Trees The process of assessment of the sonographically indeterminate adnexal mass Figure 7: MR images in 36-year-old woman with pelvic discomfort and complex left adnexal mass at US, shown at MR to be a mature cystic teratoma. (a) Axial T2-weighted spin-echo image (5600/120) shows complex cystic mass containing a fl uid fl uid level posterior to uterus and a small amount of free pelvic fl uid that is within physiologic range. (b) Axial T1-weighted spinecho image (470/14) shows high signal intensity within top fl uid layer of the mass and further highsignal-intensity areas posterolaterally (arrowheads). (c) Fat-suppressed T1-weighted spin-echo image shows complete loss of high signal intensity in components that represented oil and fat. 682 radiology.rsna.org n Radiology: Volume 256: Number 3 September 2010

7 Figure 8 Figure 8: MR images of tubo-ovarian endometriosis in 34-year-old woman with chronic low back pain and complex right-sided pelvic mass at US. (a) Sagittal T2- weighted spin-echo MR image (5000/100) shows a convoluted tubular structure with predominant low signal intensity and some layered high signal intensity, classic shading in an endometrioma. (b) Axial T2-weighted spin-echo MR image (5000/100) better depicts the shading phenomenon and a classic tubal morphology of the mass. (c) Fat-suppressed T1-weighted spin-echo image (553/14) shows persisting high T1 signal intensity consistent with products of hemorrhage. Figure 9 Figure 9: Images in 45-year-old woman with sudden severe loin pain found to have a mature cystic teratoma with only a small amount of macroscopic fat at MR. (a) Complex cystic solid left adnexal mass at US raises concerns for thickened internal septations and nodules. (b) Axial T2- weighted spin-echo MR image (5000/100) shows left-sided cystic mass with high- and low-signalintensity locules. (c) T1-weighted spin-echo MR image (473/14) at a higher level than b shows a solitary tiny focus of high signal intensity (arrow). (d) The hyperintense focus loses signal intensity (arrow) on the fat suppressed T1-weighted image (553/14). The preoperative diagnosis of a mature cystic teratoma with minimal fat was histologically confi rmed. Note the troublesome zipper artifact from the iliac vessels, which extends across the mass on some of the images along the phase encoding axis, notably c and d, where the signal from the arms is also aliased over the buttock musculature. Radiology: Volume 256: Number 3 September 2010 n radiology.rsna.org 683

8 Figure 10 Figure 10: MR images of an endometrioma in 38-year-old woman with long-standing history of pelvic pain and heavy periods shown to have a complex solid left adnexal mass at US. (a) Axial T2-weighted spin-echo MR image (5000/100) of a left ovarian mass of uniform low signal intensity ( ). (b) Axial T1-weighted spinecho image (460/14) shows uniform high signal intensity within the mass. (c) Axial fat-suppressed T1-weighted image (587/14) shows persistent T1 hyperintensity in keeping with blood products. Figure 11 Figure 11: MR images in 17-year-old patient with complex mature cystic teratoma (dermoid tumor) with incomplete fat suppression. (a) Sagittal T2-weighted spinecho image (5000/100) shows chemical shift artifact (arrowheads) and complex internal signal intensity including T2 dark areas (arrow) (b) The mass is predominantly of high signal intensity on the axial T1-weighted image (554/14). (c) Fat-suppressed T1-weighted image (698/14) shows fat suppression in some but not all of the mass. At surgery, the mass was a mature teratoma with both osseous and cartilaginous tissues corresponding to the T2 dark areas. is thus divided into two parts: evaluation of the predominant signal characteristic and morphology of the mass and application of focused problemsolving sequences. Usually only one additional sequence, tailored to the individual mass, is required. Simple decision trees for the T1-weighted high-signalintensity mass, the complex cystic or cystic-solid mass, and the T2-weighted low-signal-intensity mass lead the observer to clinically relevant end points in the distinction of benign from malig- nant masses and of uterine from ovarian masses ( Figs 4 6 ). T1-weighted High-Signal-Intensity Masses T1-weighted high-signal-intensity (or bright ) masses ( Fig 4 ) contain regions of high signal intensity and require additional T1-weighted sequences with fat suppression using chemical presaturation. Fat or oil within a mature cystic teratoma will show signal intensity loss becoming hypointense or dark on the fatsuppressed T1-weighted images ( Fig 7 ). Other causes of high-signal-intensity masses on T1-weighted images include blood products within hemorrhagic masses, including endometriomas ( Fig 8 ) or masses that have undergone torsion; mucin and other proteinaceous material within some cystic neoplasms; malignant neoplasms with hemorrhagic change; and, rarely, melanin within melanoma metastases. All these remain bright on the fat-suppressed T1-weighted 684 radiology.rsna.org n Radiology: Volume 256: Number 3 September 2010

9 Figure 12 Figure 13 Figure 12: Malignant change in an endometrioma in 41-year-old woman with prior endometriosis and persistent complex adnexal mass on serial US. (a) Transvaginal US image of right ovary shows a cyst containing a suspicious subcentimeter nodule. (b) On axial T2-weighted spin-echo image (4830/98) the nodule is an area of higher signal intensity (arrow) within the shaded signal intensity loss. (c) Axial T1-weighted (473/14). (d) Axial contrast-enhanced T1-weighted image (473/14). The nodule (arrow) showed contrast enhancement and at surgical pathologic evaluation was a stage IA endometrioid ovarian cancer developing within an endometrioma. images ( Fig 8 ). It is essential that the fat-suppressed T1-weighted sequence employs chemical presaturation. Use of short-tau inversion recovery (STIR) is not recommended. This is because fat suppression with STIR is not specific for fat and thus signal from tissues with T1 values similar to that of fat, such as mucinous or proteinaceous material, hemorrhage, and melanin, may also be suppressed. Conversely, fat in tumors may vary in composition and may have a dif ferent T1 value to normal white fat. Thus, signal from these areas might not be suppressed. The fat-suppressed T1-weighted sequence should be performed in the same plane as the T1-weighted sequence and with similar parameters to allow direct comparison ( Figs 7, 8 ). Some foci of fat in teratomas are very small, but these still show distinct signal loss on images from the fat-suppressed T1-weighted sequence ( Fig 9 ). There are other signature appearances of fat and blood on the standard T1- and T2-weighted sequence images ( Fig 8 ). Products of hemorrhage result in T2* effects: diffuse darkening or dependent graded shading of fluid contents, bright-dark fluid-fluid levels, and T2 darkening in the walls of endometriomas ( 7 ). This loss of signal is caused by accumulation of protein and iron owing to recurrent hemorrhage and can be uniform or layered due to sedimentation of blood products. Thus, a hemorrhagic mass with uniform Figure 13: Hydrosalpinx with a small amount of adjacent loculated peritoneal fl uid in 36-year-old woman with chronic pelvic pain. (a) Sagittal T2- weighted spin-echo MR image (5000/100) of a cystic mass shows typical morphology of a hydrosalpinx with incomplete folds or plicae (arrows) and tubular shape. (b) Axial T2-weighted spin-echo MR image (5000/100) shows a defi ned waist and the dark postmenopausal right ovary (arrow head) along the right wall of the mass. At US, both the folds and the senescent ovary mimicked solid tissue. low signal intensity on T2-weighted images can mimic a fibrous lesion. However, such hemorrhagic masses still retain their bright appearance on T1-weighted images, which avoids confusion ( Fig 10 ). T2-weighted low signal intensity in the walls is also due to hemosiderin deposition. Blood products of differing ages, sedimentation, deposition of blood products within cyst Radiology: Volume 256: Number 3 September 2010 n radiology.rsna.org 685

10 Figure 14 Figure 14: Mucinous cystadenoma of ovary in a 35-year-old woman with menorrhagia who declined to undergo transvaginal US. (a) Transabdominal US image shows large, multiloculated, cystic mass with thickened septa and focal echogenic areas suspicious for malignancy. (b) Axial T2-weighted spin-echo MR image (6220/120) shows typical stained-glass appearance, with differing signal intensities within the locules refl ecting mucins of varying degrees of hydration. The wall of the lesion and septa are uniformly thin and there are no vegetations demonstrated, which places this lesion in the benign category. (c) Axial T1- weighted spin-echo MR image (567/14). (d) Axial fat-suppressed T1-weighted MR image (700/14) shows persistent high signal intensity within some of the locules shown to be mucin at surgical pathologic evaluation. walls, and multiplicity suggest endometriosis. Teratomas can have widely varying appearances. The presence of even very small amounts of visible fat signal intensity indicates a mature teratoma ( Fig 9 ) but there may also be blood products from prior torsion of the mass or proteinaceous fluid from glandular components, for example, with secretions from respiratory or enteric type epithelium. One should not to be dissuaded of the diagnosis when there is demonstrable fat suppression if one encounters these persistently bright areas on the fat-suppressed T1-weighted images ( Fig 11 ). It is also important to look for chemical shift artifact, which may identify very small fatty elements ( Fig 11 ). Some teratomas contain focal T2-weighted dark elements reflecting calcifications, ossifications, or well-developed dental structures ( Fig 11 ). The contralateral ovary should be carefully assessed for features of a small teratoma, as these tumors may be bilateral in about 10% of cases ( 17 ). It is unusual to require further sequences to diagnose a mature teratoma. It is unnecessary to routinely perform contrast-enhanced T1-weighted sequences. Indeed if these are obtained there may be marked enhancement of some mature elements such as skin appendages that may cause undue concern. Malignant change in a mature teratoma is rare but should be suspected with a dominant solid component showing wall thickening, irregularity, or breach. In the older woman with a mature teratoma, malignant change is rare but, if present, is usually a squamous carcinoma arising from skin elements ( 18 ). With hemorrhagic lesions problems may arise in the sonographic distinction of a blood clot from a vegetation, notably when this is adherent to the cyst wall. One helpful hint is that by the time MR imaging takes place the clot may have become smaller as further retraction occurs. This is just one reason why comparison with the initial US study is necessary. When there is concern for a solid malignant nodule or vegetation in a T1-weighted bright mass, it must be regarded as a cystic-solid mass and thus requires intravenous administration of a gadolinium-based contrast agent for clarification. A vascularized tumor nodule shows contrast enhancement ( Fig 12 ) and an old fibrotic postinflammatory or endometriotic nodule does not. Another clue to the development of malignancy within an endometrioma is diffuse loss of the T2* shading effect ( 19 ) over serial examinations. This is thought to be due to the dilutional effect of the secretions from malignant epithelium. Teaching points. (a) MR imaging allows identification of blood products within hemorrhagic masses, which may mimic solid tumor on US. (b) Fatsuppressed T1-weighted images reveal small amounts of fat, which allow diagnosis of a mature teratoma. Complex Cystic or Cystic-Solid Masses Complex cystic or cystic-solid masses ( Fig 5 ) include a wide spectrum of neoplastic and inflammatory conditions, ranging from cystadenoma through borderline 686 radiology.rsna.org n Radiology: Volume 256: Number 3 September 2010

11 to invasive malignancy and from hydrosalpinx to tubo-ovarian abscess. All complex cystic or cystic-solid masses require contrast-enhanced T1-weighted imaging to determine the presence of neoplastic tissue. This applies not only to classic cystic-solid masses but also to other masses with worrying solid components, such as endometriomas or teratomas containing complex mural or internal solid elements. The most common benign masses within this category are multilocular benign cysts, complex tubal disease, and cystadenofibromata ( 2, 3 ). The most worrying diagnosis is ovarian malignancy, either borderline or frankly invasive primary cancer or metastatic disease, though as these studies emphasize, such masses are the minority. Purely cystic lesions are benign and rarely cause diagnostic problems for US (likewise for chronic hydrosalpinx). However, the dilated fallopian tube can occasionally cause problems in US assessment. Its convoluted shape and apposed folds may cause US findings that mimic thickened septa ( Fig 13 ). It may contain mural nodules that represent condensations of pus, inflammation, or fibrotic mucosal plical folds. Key signs of the dilated tube, which differ from those of ovarian cysts, include incomplete folds (plica) that do not cross the width of the tube (unlike complete and interconnecting septations within ovarian cysts), an oval or elongated shape, and wall deformities such as waists or beaks depending on the type of convolution ( 20 ). Acute tubo-ovarian masses may produce very complex masses with wall thickening and pseudosolid areas. These enhance brilliantly and can mimic malignancy. The clinical features of acute pelvic infection and malignancy usually differ, though some chronic infections such as tuberculosis and actinomycosis may exactly mimic malignancy ( 21 ). Multilocular mucinous cystadenomas may appear more complex at US than at MR imaging. These lesions may be large, and interrogation of all areas can prove difficult ( 3 ), especially with transabdominal imaging ( Fig 14 ). Dense mucin can mimic solid areas and there Figure 15 Figure 15: MR images of a small stage IA clear-cell ovarian carcinoma in 47-year-old woman with strong family history of ovarian cancer. (a) Transvaginal US image shows a worrying change in a known rightsided ovarian cyst. (b) Axial T2-weighted spin-echo MR image (5000/100) shows a mural nodule (arrow). (c) Corresponding axial T1-weighted spin-echo MR image (460/14). (d) Axial contrast-enhanced T1-weighted MR image (460/14) demonstrates an enhancing tumor nodule within the right ovary (arrow). may be pseudothickening of septa. MR images show complex multiseptate/multilocular appearances and differing signal intensities within the locules. Such mucinous tumors are called stained glass lesions ( Fig 14 ) ( 22 ). The variation in signal intensity between the locules arises because of the differing viscosity of the mucin in varying states of hydration. Their differing shades resemble stained glass. This appearance is most frequently encountered in mucinous ovarian neoplasms, although some of the other ovarian tumors have been described to produce this sign ( 22 ). The principal features of malignancy on MR images ( 23, 24 ) are familiar from US. These are wall thickening and irregularity, septal thickening and irregularity, or frankly solid components with or without necrosis ( Figs 15, 16 ). In terms of thickening, a measurement of 3 mm has translated from the US morphologic scoring systems into the MR imaging literature ( 23 ). Assessment of contrast enhancement has not been clearly quantified. A five-point subjective assessment scale was used, ranging from extremely conspicuous to barely perceptible ( 23 ). Nonetheless this judgment proved highly effective in distinguishing between benign and malignant masses. Standard contrast-enhanced T1-weighted imaging was used. Others workers have recommended use of fat-suppressed contrast-enhanced T1-weighted imaging ( Fig 16 ) ( 24 ). This must be regarded as a matter of preference, but it requires an additional unenhanced fat-suppressed T1-weighted sequence to be performed with which to compare signal intensity. Within a streamlined algorithmic approach, the Radiology: Volume 256: Number 3 September 2010 n radiology.rsna.org 687

12 Figure 16 study, including an evaluation of microvessel density and other markers of angiogenic status. There was a correlation between angiogenic status and the maximum upslope of the enhancement profile of the tumor at dynamic contrastenhanced MR, with malignant tumors showing steeper enhancement than the other two groups of tumors ( 25 ). A search should be performed for secondary signs of malignancy including peritoneal spread and lymphadenopathy. Gadolinium enhancement is also useful for identifying small foci of peritoneal carcinomatosis that may support a diagnosis of ovarian malignancy ( Fig 17 ) ( 26 ). Teaching points. (a) Contrastenhanced T1-weighted imaging can be used to identify features of malignancy as enhancing mural nodules and/or enhancing solid areas with or without necrosis. (b) Gadolinium enhancement is also useful for identifying small foci of peritoneal carcinomatosis that may support a diagnosis of ovarian malignancy and indicate a more advanced stage of disease. Figure 16: MR images in 56-year-old woman with a borderline ovarian carcinoma. (a) Coronal T2- weighted spin-echo MR image (5190/123) of complex cystic right adnexal mass with irregular thickening of the septa. (b) Coronal T1-weighted spin-echo MR image (460/14) does not show high signal intensity within the mass. (c) Coronal T1-weighted MR image (460/14) after intravenous administration of gadolinium-based contrast agent shows avidly enhancing irregular soft tissue along the septa. (d) Corresponding coronal contrastenhanced T1-weighted MR image with fat suppression (553/14). fat-suppressed T1-weighted sequence is best reserved for problem-solving of T1-weighted bright masses ( Fig 4 ). Some contrast enhancement may be seen in benign lesions in the adenofibroma/cystadenofibroma spectrum but these usually show distinct low signal intensity on T2-weighted images ( 24 ). Stromal lesions like these are one of the commonest benign masses misdiagnosed as malignant at MR imaging ( 24 ). Dynamic contrast-enhanced MR imaging can be performed in the interval between the unenhanced and contrastenhanced T1-weighted sequences. Recent data suggest that enhancement profiles within solid vegetations can help in identifying lesions that require cancer surgery by distinction of benign from borderline and malignant disease ( 25 ). In that study, 48 epithelial ovarian tumors underwent detailed histologic T2-weighted Imaging of Low-Signal- Intensity Masses Some sonographically indeterminate masses are solid and the differential diagnosis is wide ( Table ) ( Fig 6 ). Two patterns of T2-weighted signal intensity are seen with sonographically solid masses. Some have T2-weighted signal intensity that is homogeneously low T2-weighted dark masses with signal intensity similar to that of skeletal muscle. These T2-weighted dark solid masses are almost always benign tumors. Other sonographically solid masses have intermediate signal intensity higher than that of muscle on T2-weighted images and may be inhomogeneous. These masses have a differential diagnosis ranging from benign masses that may have undergone torsion or degeneration through to frank malignancy. T2-weighted dark masses are a common finding after indeterminate US examinations ( 2 ) and usually represent either uterine leiomyomata or ovarian fibromata ( 3 ). Further assessment should 688 radiology.rsna.org n Radiology: Volume 256: Number 3 September 2010

13 Figure 17 Figure 18 Figure 17: MR images in 73-year-old woman with a newly diagnosed endometrial cancer with malignant peritoneal involvement and an unexpected coincident left ovarian cancer. (a) Sagittal T2-weighted spin-echo MR image (5100/123) of a predominantly solid left ovarian mass (arrow) with a small amount of free fl uid present in the dependent pelvis. (b) Axial T2-weighted spin-echo MR image (4800/96) shows pelvic ascites and mild diffuse thickening of the pelvic peritoneum on the left (arrows). (c) Fat-suppressed contrastenhanced gradient-echo T1-weighted axial MR image (3.64/1.71) obtained for endometrial cancer staging at the level of the left ovary shows mild heterogeneous contrast enhancement (arrow). (d) Fat-suppressed contrast-enhanced gradient-echo T1-weighted axial MR image (3.64/1.71) inferior to the ovary better depicts the diffuse contrast enhancement of the thickened pelvic peritoneum (arrowheads) indicating peritoneal involvement. Surgical pathologic fi ndings revealed synchronous primary tumors with peritoneal metastases. thus help determine if the mass arises from the ovary or uterus. Application of oblique ovarian axis may provide the diagnosis by revealing the organ of origin ( Figs 1, 2 ). Further confirmation can be obtained from an additional T2-weighted oblique imaging sequence (section thickness, 3 4mm) perpendicular to the long axis of the uterus or along the plane of suspected connection between the mass and the uterus or ovary. A pedunculated uterine leiomyoma is attached to the uterus by a stalk or vascular bridge which may contain the bridging vessels that supply it ( Fig 18 ) Figure 18: T2-weighted spin-echo MR images in 39-year-old woman being considered for uterine artery embolization who was found to have a large pedunculated uterine leiomyoma. (a) Sagittal image (5610/123) of a pedunculated leiomyoma attached to the uterus but within the pouch of Douglas. (b) Oblique axial image (4830/96) through the uterus. Both a and b show the bridging vessels supplying the fi broid across the connection with the uterus (arrow). ( 27, 28 ). Conversely adnexal masses are usually supplied from the gonadal pedicle. These signs of vascular supply may be valuable in further confirming the origin of the indeterminate mass but are not always present. The obliquity of the T2-weighted sequence used to demonstrate the relationship or connection to the uterus should aim to be perpendicular to the maximal point of contact with the uterus ( Fig 18 ). Radiology: Volume 256: Number 3 September 2010 n radiology.rsna.org 689

14 Figure 19 Figure 19: Features of a subserosal leiomyoma in 56-year-old woman. Sagittal T2-weighted spin-echo MR image (4000/120) shows a T2 dark anterior wall leiomyoma with myometrium stretched along and grasping its posterior aspect like a claw (arrows). With a subserosal uterine leiomyoma there is normal myometrium grasping around its margins (the claw sign) ( Figs 2, 19 ). A leiomyoma within the broad ligament is separate from the uterus and the ovary on that side ( Fig 1 ). With an ovarian fibroma there may be a small amount of normal remnant ovary draped around and clawing the solid mass or the solid mass may be exophytic from the ovarian tissue ( 29 ). When there is a homogeneous T2- weighted dark solid mass that has one of these characteristics, diagnosis is further clarified by use of oblique T2- weighted sequences which define the connection or otherwise with the uterus or ovary. T2-weighted intermediate solid ovarian masses with inhomogeneous low or intermediate signal intensity on T2- weighted images may be either benign stromal masses with edema or degeneration following torsion ( 30 ) or solid malignant masses. Distinction between these two groups requires further assessment with contrast-enhanced T1- weighted images. Benign solid stromal masses such as ovarian fibromas usually show no contrast enhancement ( Fig 20 ) or minimal contrast enhancement ( Fig 21 ) ( 31, 32 ). Masses with substantial contrast enhancement should be regarded as likely malignant primary or secondary tumors Figure 20 Figure 20: Classic T2 dark ovarian fi broma discovered incidentally in 62-year-old woman with a sonographically indeterminate solid mass during investigation of postmenopausal bleeding. (a) Sagittal T2-weighted spin-echo MR image (4650/98) of a T2 dark solid mass separate from and posterior to the uterine fundus with a small amount of free pelvic fl uid. (b) Fat-suppressed contrast-enhanced gradient-echo T1-weighted axial MR image (3.64/1.71) obtained for endometrial cancer staging shows no enhancement within the mass. At surgery the mass was a simple ovarian fi broma and the peritoneal fl uid cytology was negative for malignant cells. of the ovary. The latter are of greater concern in a woman with a history of a cancer recognized to metastasize to the ovary, such as gastric, colorectal, or breast cancer ( Fig 22 ). Metastatic tumors to the ovary from gastrointestinal or breast primary are classically referred to as Krukenberg tumors. Friedrich Krukenberg in 1896 first described what he presumed to be new type of ovarian tumor while he was still a medical student. The metastatic nature of these lesions was established a few years later. These metastases were solid, bilateral, fibrocellular tumors ( 33 ). A prominent MR imaging sign of a Krukenberg tumor is the presence of large intralesional radiating flow voids ( Fig 22 ). Such tumors are not always bilateral as described originally by Krukenberg and are not always metastatic from the stomach. Similar histologic findings have been described with metastases from carcinomas of the gallbladder, biliary tract, pancreas, small intestine, ampulla of Vater, cervix, and urinary bladder/urachus ( 34 ). Other considerations for the indeterminate solid mass include solid mature teratoma, for example struma ovarii and endocrine-active tumors such as thecoma, Leydig cell tumor, sclerosing stromal tumor, or granulosa cell tumor ( 35, 36 ). Endocrine tumors with functioning stroma are rare indeterminate masses, as these more commonly present clinically with hormonal effects such as hirsutism or uterine estrogenization with endometrial thickening or uterine dysfunction with abnormal bleeding. Hence these are discovered in a search for the cause of the hormonal problem rather than as an indeterminate mass. These tumors have a variety of morphologic features but usually show substantial enhancement ( 35, 36 ). Rarely, low-signal-intensity masses on T2-weighted images show areas of high signal intensity on T1-weighted images. This may reflect hemorrhage within a primary cancer such as an endometrioid carcinoma or granulosa cell tumor ( 36 ) or reflect the presence of melanin in metastases to the ovary from malignant melanoma ( 37 ). Teaching points. (a) Indeterminate solid adnexal masses are usually uterine leiomyomata or ovarian fibromata whose nature and site of origin can be shown by using oblique T2-weighted imaging. (b) T2-weighted inhomogeneous or intermediate signal intensity solid masses require contrast-enhanced T1-weighted imaging, with contrast enhancement suggesting malignancy. 690 radiology.rsna.org n Radiology: Volume 256: Number 3 September 2010

15 Figure 21 Alternatives to MR Imaging Historically the two most commonly used strategies for the sonographically indeterminate mass have been to repeat the US examination after two or more menstrual cycles or to proceed to diagnostic laparoscopy or surgical excision of the mass. Strategies for dealing with uncertainty with any indeterminate mass include the following: discussion, further investigation, intervention (ideally image-guided biopsy or minimally invasive surgery), or procrastination, in this case interval repeat US examination ( 38 ). Figure 21: MR images show T2-weighted heterogeneous-signal-intensity ovarian fi broma in 46-year-old woman found to have a fi broid uterus at US during investigation of pelvic discomfort. (a) Coronal T2-weighted spin-echo MR image (5876/112) shows a T2 heterogeneous mass squashing the uterus but without either feeding vessels or a claw attaching the two. (b) Coronal T1-weighted spin-echo MR image (564/14) shows a subtle lower signal intensity within the mass. (c) Contrast-enhanced coronal T1-weighted spin-echo MR image (564/14) shows minimal contrast enhancement of the mass and clearly different signal intensity from the uterus. At simple resection the mass was an ovarian fi broma. Certainly it is valuable to discuss indeterminate masses with clinical colleagues. They may have knowledge of prior imaging studies with which to compare. There may be a history of chronic pelvic inflammatory disease or endometriosis. When these are the leading clinical diagnoses and there is a low clinical index of suspicion for malignancy it is reasonable to adopt a watch and wait policy, procrastination, with interval re-examination at US to look for stability or resolution of the indeterminate features. However, with any concern for malignancy further investigation with MR imaging is preferred to procrastination. MR imaging offers the opportunity for earlier diagnosis as it does not require the delay imposed by interval re-examination with US, although the benefits of this strategy for patient outcomes have not been tested. One situation in which a delay in diagnosis is best avoided is in pregnancy, and here also interventional options are limited or even prejudicial to the gestation. A number of studies have now demonstrated the value of MR imaging in pregnancy where defining the nature of a mass in the emergent setting substantially effects management of the pregnancy ( 39, 40 ). What other specialist investigations are available? Multidetector CT has been assessed recently in two studies ( 41, 42 ). Multidetector CT performed extremely well, indeed almost as well as MR imaging. However, the case mix in these studies was different to that seen with US indeterminate masses. In one study malignant masses were predominant ( 41 ), reflecting practice in a leading cancer hospital, and in both studies features of peritoneal dissemination were used as significant discriminators of benign from malignant disease ( 41, 42 ). Such biases are inevitable in studies that aim to correlate imaging with surgical pathologic evaluation. Most women with indeterminate adnexal masses do not require surgery. Many such masses occur in women of childbearing age who should be spared unnecessary irradiation. These two factors argue strongly for the use of MR imaging over multidetector CT for characterization of the indeterminate adnexal mass, particularly given the low pretest probabilities of cancer ( 2, 4 ). Multidetector CT is, however, the mainstay of preoperative staging of suspected ovarian cancer ( 43, 44 ). Limitations of MR Imaging Some masses may continue to confound the radiologist applying meticulous technique and interpretation, and this reflects the current limitation of MR imaging. Fat-poor teratomas including struma ovarii and benign enhancing masses such as stromal tumors ( Fig 23 ), Radiology: Volume 256: Number 3 September 2010 n radiology.rsna.org 691

16 Figure 22 means for early diagnosis of ovarian cancer in women believed to be at high risk. With transvaginal color Doppler US, then in its infancy, the odds ratio was reversed, with nine of 10 positive tests results proving false, and thus 10 women were required to undergo surgery per cancer detected ( 45 ). Caution has to be exercised in overdue reliance on the use of color Doppler US, particularly in pre- and perimenopausal women ( 46 ). Blood flow from normal physiologic structures can mimic that of neoplastic tissue ( Fig 3 ) and a variety of inflammatory and hemorrhagic conditions can do likewise. Physiologic changes in pregnancy can also confound US ( 47 ). Figure 22: Images in 63-year-old woman with weight loss who was found to have a complex solid mass at US that was eventually shown to be a Krukenberg tumor metastatic from an occult cecal signet ring carcinoma. (a) Color Doppler image shows prominent internal vascularity. (b) Sagittal T2-weighted spin-echo MR image (5000/100) shows heterogeneous signal intensity and an engorged vascular pedicle supplying the mass posteriorly (arrow) and small volume ascites (*). (c) Axial T2-weighted spin-echo MR image (5000/100) demonstrates radiating internal vascular voids, characteristic of Krukenberg tumor. (d) Sagittal contrast-enhanced T1-weighted MR image (484/14) shows diffuse contrast enhancement of the mass. particularly adenofibromas and cystadenofibromas ( 24 ), are among the benign diagnoses misdiagnosed as malignancy. Stromal masses in the fibroma spectrum may also be associated with ascites ( Fig 20 ), further raising concerns for malignancy. However, in the series reported so far these false-positive diagnoses of cancer represented less than one case in 10 of US indeterminate masses evaluated at MR imaging ( 2 ). It is salutary to compare these figures with those from 2 decades ago when US was used as Future Developments in MR Imaging Developments in MR imaging that may further enhance the ability to characterize adnexal masses include diffusionweighted imaging and high-field-strength MR imaging at 3 T and above. Diffusionweighted imaging can be used to assess both cyst contents and solid tissues. However, diffusion-weighted imaging has not yet been shown to be sufficiently robust or reliable to justify its use in routine assessment. In one study, when endometriotic cysts and mature cystic teratomas (masses well characterized by using standard MR imaging) were excluded, investigators using diffusionweighted imaging were unable to distinguish benign from malignant lesions in the remainder ( 48 ). In another study there were technical problems in assessment of larger cysts ( 49 ). More recent data indicate that diffusion-weighted imaging is unreliable in the assessment of solid components and should not be used for distinguishing benign from malignant masses ( 50 ). To our knowledge, there are no data yet published comparing 1.5- and 3-T MR imaging of indeterminate adnexal masses. Most US indeterminate masses evaluated at MR imaging result from complex but benign conditions. MR imaging can help reduce the number of women undergoing unnecessary cancer surgery as it allows identification of benign features that obviate this. Conversely, an indeterminate adnexal mass with abnormal solid enhancing (contrastenhanced T1-weighted) soft-tissue elements should be viewed as a cancer, referred to a specialist surgeon, and undergo staging and further assessment within a cancer center. MR imaging has maximal diagnostic and therapeutic impact for the sonographically indeterminate adnexal mass when CA-125 levels are normal or only slightly raised ( 2 ). MR imaging is a valuable adjunct to US, not only as a problem-solving tool but as a second confirmatory test, particularly 692 radiology.rsna.org n Radiology: Volume 256: Number 3 September 2010

17 Figure 23 Figure 23: Ovarian adenofi broma in 67-year-old woman that was preoperatively regarded as malignant. (a) Sagittal T2-weighted spin-echo MR image (5000/100) demonstrates a large solid mass with a central cystic area and heterogeneous signal intensity anteriorly. The mass is separate from the uterus. (b) Coronal T2-weighted spin-echo MR image (4800/96) of the mass. (c) Coronal T1-weighted MR image (420/14) does not demonstrate any high signal intensity within the mass. (d) Coronal T1-weighted MR image (420/14) obtained after administration of intravenous gadolinium-based contrast material with substantial contrast enhancement in the peripheral solid portion. Surgical histologic fi ndings revealed an ovarian adenofi broma. when clinical and laboratory findings are at variance with the sonographic diagnosis. Acknowledgments: We are grateful to Fiona Lang for help with production of the illustrations and to Sheila Boyes for help with preparation of the manuscript. References 1. Kurtz AB, Tsimikas JV, Tempany CM, et al. Diagnosis and staging of ovarian cancer: comparative values of Doppler and conventional US, CT, and MR imaging correlated with surgery and histopathologic analysis report of the Radiology Diagnostic Oncology Group. Radiology 1999 ; 212 ( 1 ): Sohaib SA, Mills TD, Sahdev A, et al. The role of magnetic resonance imaging and ultrasound in patients with adnexal masses. Clin Radiol 2005 ; 60 ( 3 ): Adusumilli S, Hussain HK, Caoili EM, et al. MRI of sonographically indeterminate adnexal masses. AJR Am J Roentgenol 2006 ; 187 ( 3 ): Kinkel K, Lu Y, Mehdizade A, Pelte MF, Hricak H. Indeterminate ovarian mass at US: incremental value of second imaging test for characterization meta-analysis and Bayesian analysis. Radiology 2005 ; 236 ( 1 ): Department of Health. Referral guidelines for suspected cancer. London, England : Stationery Office, Mitchell DG, Gefter WB, Spritzer CE, et al. Polycystic ovaries: MR imaging. Radiology 1986 ; 160 ( 2 ): Nishimura K, Togashi K, Itoh K, et al. Endometrial cysts of the ovary: MR imaging. Radiology 1987 ; 162 ( 2 ): Togashi K, Nishimura K, Itoh K, et al. Ovarian cystic teratomas: MR imaging. Radiology 1987 ; 162 ( 3 ): Mitchell DG, Mintz MC, Spritzer CE, et al. Adnexal masses: MR imaging observations at 1.5 T, with US and CT correlation. Radiology 1987 ; 162 ( 2 ): Outwater EK, Dunton CJ. Imaging of the ovary and adnexa: clinical issues and applications of MR imaging. Radiology 1995 ; 194 ( 1 ): Siegelman ES, Outwater EK. Tissue characterization in the female pelvis by means of MR imaging. Radiology 1999 ; 212 ( 1 ): Xiong T, Richardson M, Woodroffe R, Halligan S, Morton D, Lilford RJ. Incidental lesions found on CT colonography: their nature and frequency. Br J Radiol 2005 ; 78 ( 925 ): Pickhardt PJ, Hanson ME, Vanness DJ, et al. Unsuspected extracolonic findings at screening CT colonography: clinical and economic impact. Radiology 2008 ; 249 ( 1 ): Katz DS, Scheer M, Lumerman JH, Mellinger BC, Stillman CA, Lane MJ. Alternative or additional diagnoses on unenhanced helical computed tomography for suspected renal colic: experience with 1000 consecutive examinations. Urology 2000 ; 56 ( 1 ): Johnson W, Taylor MB, Carrington BM, Bonington SC, Swindell R. The value of hyoscine butylbromide in pelvic MRI. Clin Radiol 2007 ; 62 ( 11 ): Outwater EK, Talerman A, Dunton C. Normal adnexa uteri specimens: anatomic basis of MR imaging features. Radiology 1996 ; 201 ( 3 ): Doss N Jr, Forney JP, Vellios F, Nalick RH. Covert bilaterality of mature ovarian teratomas. Obstet Gynecol 1977 ; 50 ( 6 ): Kido A, Togashi K, Konishi I, et al. Dermoid cysts of the ovary with malignant transformation: Radiology: Volume 256: Number 3 September 2010 n radiology.rsna.org 693