Imaging Features of the Hypointense Solid Lesions in the Female Pelvis on T2-weighted MR Images

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1 Imaging Features of the Hypointense Solid Lesions in the Female Pelvis on T2-weighted MR Images Poster No.: C-0931 Congress: ECR 2014 Type: Educational Exhibit Authors: S. B. Park, J. B. Lee; Seoul/KR Keywords: Genital / Reproductive system female, Pelvis, MR physics, MR, Decision analysis, Imaging sequences, Education and training DOI: /ecr2014/C-0931 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 30

2 Learning objectives 1. List the broad spectrum of hypointense lesions in the female pelvis on T2-weighted MR images for differential diagnosis. 2. Describe the causes and imaging features of hypointensity lesions in the female pelvis on T2-weighted MR images. 3. Discuss MR strategies for identification and characterization of hypointensity lesions in the female pelvis on T2-weighted MR images. Background Malignant tissue has been shown to increase both intracellular and extracellular water, which results in increased T1 and T2 relaxation times in malignant tissue (1, 2). Therefore, most solid lesions in the female pelvis appearing hyperintense on T2-weighted images should be interpreted as malignant (1, 2). In contrast, solid lesions in the female pelvis that appear hypointense on T2-weighted images may be benign (1-3). Thus, distinguishing between hyperintense and hypointense solid lesions on T2-weighted images is important to help narrow the differential diagnosis and to avoid unnecessary radical surgery. In this presentarion, we describe the clinical and imaging features for the spectrum of hypointense solid lesions in the female pelvis on T2-weighted images. Magnetic Resonance Imaging (MRI) Strategies for Identification and Tissue Characterization Ultrasound (US) remains the first-line imaging modality in the evaluating female pelvis because it is relatively noninvasive, inexpensive, and widely available. US may the key to reliable detection and interpretation of pathologic process affecting female pelvic organs. Transabdominal US, transvaginal US, or both, should be performed (4-7). MRI plays essential roles in evaluating gynecologic disease. MRI is now widely used in the diagnosis and staging of gynecologic malignancy, in the evaluation of benign uterine and adnexal disease, or in congenital anomaly of the female genital tract. MRI can be used as a problem-solving tool when US and CT findings are equivocal or suboptimal. Many indeterminate lesions can be characterized further by MRI (2-5, 8). Recently, many studies have been published to evaluate the potential role of newer techniques in imaging of the pelvis, including functional MRI, diffusion-weighted imaging, and dynamic contrastenhanced sequences (9-14). Page 2 of 30

3 MRI is unique in its ability to explore intracellular content and recognize the presence of substances that may produce signal behavior. For many tissue parameters, such as T1, T2, magnetic susceptibility, and chemical shift, that contribute to signal intensity (SI), MRI may allow for the identification of a wider array of specific tissues (2, 3). Therefore, MRI is of great importance in clinical practice, particularly for the identification of various types of soft tissue and to differentiate between malignant and benign lesions. Malignant lesions tend to show enhancement and the presence of solid components. For the evaluation of lesions by MRI, T1- and T2-weighted images remain a basic requirement for lesion characterization (1-3). In general, owing to their high cellular water content, the majority of solid lesions in the female pelvis appear hyperintense on T2-weighted images. In contrast, frequently seen MRI pattern for solid lesions in the female pelvis is total or partial hypointensity on T2-weighted images relative to that of the outer myometrium or skeletal muscle (Table 1) (1-3, 8). Solid adnexal tissue that demonstrates low SI on T2-weighted images has been shown to be highly indicative of a benign or noninvasive lesion (13). Furthermore, solid lesions in the female pelvis appearing hypointense on T2-weighted images may be benign even though they show solid components with enhancement. We categorize T2 hypointense solid lesion in the female pelvis into two subgroups. The first subgroup includes homogeneous hypointense lesion, whereas the second subgroup includes heterogeneous hypointense or mixed signal lesion (Fig. 1) (3, 8). T2 homogeneous hypointense lesions have predominant low to similar signal (dark or darker) to that of the outer myometrium or skeletal muscle (1, 3, 8). T2 heterogeneous hypointense or mixed signal solid lesions have intermediate signal or T2 inhomogeneous signal with a mixture of T2 low and bright signal (higher than that of the outer myometrium or skeletal muscle). These may represent either benign or malignant lesions, either primary or secondary (3, 8). Images for this section: Page 3 of 30

4 Table 1: Causes and characteristics of hypointense solid lesions on T2-weighted images. Page 4 of 30

5 Fig. 1: Flowchart shows decision tree for imaging of hypointense solid lesion in the female pelvis on T2-weighted MRI. Page 5 of 30

6 Findings and procedure details Blood Products The MRI appearance of hemorrhage or hematoma is related to the presence of different blood breakdown products within the lesion. Blood shortens the T1 and T2 pulses of water. Acute hemorrhage shows an SI behavior that is consistent with intracellular deoxyhemoglobin: low SI on T1-weighted images and markedly low SI on T2-weighted images. Subacute hemorrhage (within 3-5 days) indicates the presence of intracellular methemoglobin: high SI on T1-weighted images resulting from paramagnetic effects and variable SI on T2-weighted images. The T2-weighted SI of methemoglobin depends on its located. An intracellular environment results in low SI (marked T2 shortening), while the extracellular environment causes high SI (less T2 shortening). In chronic stages, hemorrhage may have low SI on both T2- and T1-weighted images, since the intracellular forms of iron ferritin or hemosiderin provoke marked SI loss due to magnetic susceptibility effects (Table 1) (1-3). Endometriosis Endometriosis is the presence of endometrial glands and stroma outside the uterus and is a common disease in women of childbearing age. Eighty percent of all pelvic endometriosis is found in the ovary (termed "endometriotic cyst or endometrioma") (5). The most common and specific appearance of endometriosis is a relatively homogeneous, high SI on T1-weighted images with low SI on T2-weighted images (termed "T2 shading") (Fig. 2) (2, 5, 15). On the basis of these criteria, the sensitivity of MRI in the diagnosis of endometriosis varies from 68% to 90% and specificity from 83% to 98% (15). Fat-suppressed, T1-weighted images improve the sensitivity for detecting small foci of endometriosis and help with the differentiation of endometrial cyst from fatcontaining mature cystic teratoma. Multiple or bilateral adnexal lesions, cul-de-sac lesions, thicker walls, or a dilated fallopian tube with high SI on T1-weighted images favor the diagnosis of endometriosis (2). Pelvic Hematoma Pelvic hematomas tend to have loculations with different rates of clot maturation that result in a heterogeneous appearance on MRI (2). The concentric ring sign, when present, has high specificity for a subacute to chronic hematoma (2). Foci of very high SI on T1-weighted images representing methemoglobin may be present within the hematoma, although in various amounts and distribution. Subacute hematomas are commonly detected in the female pelvis in women after surgery and in women receiving anticoagulation therapy who present with pelvic pain and/or a palpable mass. Subacute hematomas have also been described in women with ectopic pregnancy (Fig. 3). Page 6 of 30

7 An ectopic pregnancy is a condition in which a fertilized ovum implants in an area other than the uterine cavity (16). The initial clinical evaluation consists of hormonal assays usually followed by pelvic US. The fallopian tube is the most common location for an ectopic pregnancy. An adenxal mass that is separate from the ovary and the tubal ring are the most common findings of a tubal pregnancy. MRI is an adjunct to US that may produce significant information and may also be helpful for locating unusual ectopic pregnancies or undetected pregnancies located in other sites, such as abdominal pregnancy, interstitial pregnancy, myometrial pregnancy, and cervical pregnancy (16). On MRI, tubal wall enhancement and the presence of tubal hematoma (Fig. 3) or a gestational sac-like structure were considered diagnostic findings (16). Smooth Muscle Both smooth and skeletal muscle have low SI on T2-weighted images, resulting from the T2 shortening effects of intramuscular actin, myosin, and collagen and decreased extracellular fluid compared with that in surrounding tissues (Table 1) (1-3). Leiomyoma Leiomyomas are benign tumors that may arise from any smooth muscle-containing structure or organ (17). Uterine leiomyomas are the most common uterine tumor and are classified as submucosal (Fig. 4), intramural (Fig. 4), or subserosal (Fig. 4); the latter may become pedunculated and simulate ovarian tumors. This classification is of clinical significance because the symptoms and treatment vary among these subtypes of leiomyomas. Although submucosal leiomyomas are the least common, representing approximately only 5% of the uterine leiomyomas, they are most commonly symptomatic; women with leiomyomas present with symptoms such as dysmenorrhea, menorrhagia, and infertility (17). Leiomyomas are usually well circumscribed and surrounded by a gray-white fibrous pseudocapsule. The cut surface bulges and exhibits a whorled pattern. On microscopic examination, the tumor is seen to consist of smooth muscle spindle cells arranged in interlacing bundles with varying admixtures of fibrous, often hyalinized, connective tissue (17). MRI is currently considered the most accurate imaging technique for detection and localization of leiomyomas. The vast majority of leiomyomas appear as wellcircumscribed, homogeneous low SI masses on T2-weighted images (Fig. 4). As leiomyomas enlarge, they may outgrow their blood supply. This results in various types of degeneration such as hyaline or myxoid degeneration, calcification, cystic degeneration, and red degeneration. There are also subtypes of leiomyomas such as cellular leiomyoma and lipoleiomyoma (17). Degenerative leiomyomas have variable appearances on T2-weighted images and contrast-enhanced images (2, 17). Cellular Page 7 of 30

8 leiomyomas, which are composed of compact smooth muscle cells with little or no collagen, can have relatively higher SI on T2-weighted images (Fig. 4) (17). Adenomyosis Adenomyosis is characterized by the presence of heterotopic endometrial glands and stroma in the myometrium with adjacent smooth muscle hyperplasia (2, 18). Adenomyosis is most commonly a diffuse abnormality but may also occur as a focal mass known as an adenomyoma or focal adenomyosis. The histopathologic features of adenomyosis are varied and contribute to its imaging appearance. The accompanying smooth muscle hyperplasia produces the typical gross appearance and corresponds to thickening of the junctional zone and areas of decreased SI on MRI (Fig. 5) (18). More specific findings include a junctional zone of at least 12 mm, focal thickening of the junctional zone, ill-defined spiculated low SI masses, and subcentimeter foci of high SI representing imbedded endometrial glands on T2weighted images (Fig. 5). Some of these ectopic foci of the endometrium also have high SI on T1-weighted images, a finding that corresponds to hemorrhage (2, 18). In its focal form, adenomyosis appears as an ill-defined, poorly marginated area of low SI within the myometrium on T2-weighted images, whereas leiomyomas often appear as wellcircumscribed masses (18). Focal Myometrial Contraction Focal myometrial contractions cause more compact smooth muscle with compressed venous structures and thus can mimic either leiomyoma or focal adenomyosis on MRI (2). Situations in which contractions are seen are during pregnancy and less typically during any phase of the menstrual cycle. Documenting the transient nature of the pseudomass will establish the diagnosis. Fibrosis Paucicellular regions of fibrous tissue (with a large proportion of collagen and few cells and vessels) will have low SI on T2-weighted images because of T2 shortening (Table 1) (1-3). Fibrothecoma The fibrous tissue that comprises the majority of most of these tumors is responsible for the low SI on both T1- and T2-weighted images. Minimal enhancement and hypointense solid lesions on T2-weighted images are MRI features that help to further characterize fibrothecomas (Fig. 6) (2). However, larger tumors show varied MRI findings because of degenerative changes, such as cystic degeneration, edematous change, hemorrhagic infarction, or necrosis caused by torsion, and myxomatous change. As a result, many fibrothecomas are not uniformly hypointense on T2-weighted images (Fig. 7). Page 8 of 30

9 Fibromatosis Ovarian fibromatosis is a rare benign non-neoplastic process associated with ovarian enlargement and characterized by diffuse fibrosis and collagen-producing spindle cell proliferation (15). One or both ovaries in young women (13-39 years old) are affected. Clinically patients may present with menstrual abnormality, abnormal pain, or less commonly hirsuitism or virilization. On MRI thick low T2 signal fibrous tissue surrounding ovarian parenchyma has been reported with a characteristic appearance of 'black garland' around the ovary. The presence of entrapped follicle between the fibrous tissues may be an important differentiating feature of this condition from ovarian fibromas (15). Brenner Tumor Ovarian Brenner tumors compose approximately 1#2% of all ovarian tumors, and most are benign. Brenner tumors are often discovered incidentally at surgery or pathologic examination because they are small and asymptomatic (Fig. 8) (2, 19). Brenner tumors are composed of ovarian epithelial cells that undergo metaplasia to transitional cells and are surrounded by dense fibrous tissue. In 30% of cases, Brenner tumors are associated with epithelial ovarian neoplasms of either the ipsilateral or contralateral ovary (Fig. 9) (2). In imaging studies, these tumors manifest as a well-defined, multiloculated, cystic mass with solid components or, less commonly, as a mainly solid mass (Figs. 8, 9). Brenner tumors contain abundant fibrous stroma, which account for the low SI on T2-weighted images (Figs. 8, 9). Extensive amorphous calcification within the solid component is the characteristic feature of these tumors (2, 19). Brenner tumors demonstrate at least moderate enhancement after contrast material administration (Fig. 8), whereas fibrothecomas demonstrate minimal enhancement (3). Primary or Metastatic Adenocarcinoma Various amounts of fibrous tissue are commonly present in tumors. Malignant tumors with a large amount of fibrous noncalcificed matrix (especially due to adenocarcinoma) can also show low SI on T2-weighted images (1). In the case of primary ovarian adenocarcinoma, the most common MRI appearance is that of a solid mass with cystic components (19). Mural nodules, papillary projections, and septations can be visualized on MRI. Papillary projections enhance and may have regions of high SI on T2-weighted images that histopathologically correlate to edema within the papillae (19). Malignant hypointense solid lesions may be multiple or appear heterogeneous mixed SI (Fig. 10). Krukenberg tumors are metastatic tumors of the ovary that contain mucin-secreting "signet ring" cells that invade abundant hypercellular stroma. The offending neoplasm is usually gastric in origin, but breast, colon, pancreas, and gallbladder carcinomas can all give rise to this type of ovarian metastasis. Imaging features of metastatic ovarian Page 9 of 30

10 lesions are nonspecific, which underscores the need for obtaining a clinical history when evaluating adnexal masses. Bilateral oval solid masses with sharp margins are observed on MRI (5). An unusual feature on T2-weighted images was peripheral or randomly distributed low SI (Fig. 11), which corresponded histopathologically to dense collagenous stroma. This imaging finding is rare in primary ovarian tumors and, when present, should suggest the diagnosis of Krukenberg tumors. Fibrotic Masses after Radiation Therapy or Surgery Patients with pelvic cancer who have been treated with surgery and/or radiation therapy may have scarring that is mass-like, mimicking recurrent tumors (Fig. 12) (2). However, recurrent malignancies with a desmoplastic reaction can have relatively low SI on T2weighted images. Both treatments related to scarring and tumors have low SI that correlates with the amount of fibrosis present. Analysis of lesion morphology can help distinguish between the two; post-treatment fibrosis or scarring often has angular margins (Fig. 12), whereas recurrent malignancy is usually round (2). Deep Nodular (Solid) Endometriosis Deep nodular endometriosis is typically found in the rectovaginal septum and in other fibromuscular pelvic structures such as the uterine ligaments and the muscular wall of pelvic organs. The endometrial glands and stroma infiltrate the adjacent fibromuscular tissue and elicit smooth muscle proliferation and fibrous reaction, resulting in solid nodule formation (2). MRI characteristics of these solid masses have been described as low to intermediate in SI with punctate regions of high SI on T1-weighted images, uniform low SI on T2weighted images (Fig. 2), and enhancement corresponding to the abundant fibrous tissue seen in these lesions at histopathologic examination. Inflammatory Pseudotumor (Inflammatory Myoblastic Tumor) Inflammatory pseudotumor is a rare benign condition of unknown cause. Inflammatory pseudotumor is characterized histologically by the presence of acute and chronic inflammatory cells with a variable fibrous response. Inflammatory pseudotumor most commonly involves the lung and orbit, but it has been described in almost any location, in both sexes, at all ages. Although the radiologic findings of inflammatory pseudotumor are nonspecific, particular findings are observed. MRI shows a hypointense lesion on T1- and T2-weighted images (possibly reflecting the fibrotic change), and shows marked gadolinium enhancement. In these inflammatory pseudotumors, delayed enhancement has frequently been observed, probably because of the accumulation of extravascular contrast media in the fibrotic component within the mass. Inflammatory pseudotumor of the pelvis shows a large soft tissue mass on imaging studies (Fig. 13) and may often mimic malignancy such as rhabdomyosarcoma. Page 10 of 30

11 Solitary Fibrous Tumor Solitary fibrous tumors are rare neoplasms of submesothelial mesenchymal origin that most commonly arise in the pleura. Extrapleural solitary fibrous tumors have been reported with increasing frequency and have been found in nearly almost every location of the body. Solitary fibrous tumors of the pelvis are a solitary localized mass that is attached by a richly vascular pedicle or a broad base. The low SI of solitary fibrous tumors on T2weighted images may be characteristic. Intense enhancement after intravenous contrast injection has been reported to be due to the high vascularities of solitary fibrous tumors. Persistent, prolonged enhancement on delayed imaging was occasionally noted. Melanin Melanin typically has high SI on T1-weighted images because of paramagnetic effects and low SI on T2-weighted images because of T2 shortening (Table 1) (1-3). Melanoma Melanoma is the second commonest vulval malignancy and the next to carcinoma, accounting for 5% of malignant vulval neoplasms. It is much more common in the vulva than in the vagina. The melanotic variety classically demonstrates intermediate-to-high SI on T1-weighted images and low-to-intermediate SI on T2-weighted images. Calcification Calcification typically has low SI on both T1- and T2-weighted images (Table 1); however, faint and tiny calcifications may not be detectable on MRI (1-3). Leiomyoma Secondary calcification occurs in hyalinized tissue in about 4% of uterine leiomyomas. The calcification is usually dense and amorphous. This pattern of calcification on plain radiography almost exclusively indicates the diagnosis of leiomyoma. A rarely observed pattern is peripheral ring-like calcification at the margins of a leiomyoma (Fig. 14). This type of calcification appears to represent thrombosed veins from previous red degeneration. Mature Cystic Teratoma Mature cystic teratomas are the most common benign ovarian tumors in women less than 45 years old (5, 20). Page 11 of 30

12 Although the imaging findings of mature cystic teratomas vary from purely cystic masses to mainly solid masses, they can be readily detected and diagnosed by identifying the intratumoral fat and calcification (20). On MRI, intratumoral fat can be diagnosed with the combination of T1-weighted images and fat-suppressed, T1-weighted images; intratumoral fat shows high SI on T1-weighted images, but the signal decreases on fatsuppressed, T1-weighted images (5, 20). Dense calcification typically has low SI on both T1-weighted and T2-weighted images. This appearance of entirely calcified lesion is not common and is shown as focal hypointense portion within the cystic mass. Struma ovariis are ovarian mature cystic teratomas composed entirely or predominantly of thyroid tissue and containing variable-sized follicles with colloid materials (20). MRI findings may be more helpful for diagnosis because some cystic spaces may show low SI on both T1- and T2-weighted images owing to the thick, gelatinous colloid of the struma (Fig. 15) (20). This lesion is frequently associated with a focal teratomatous component containing fat tissue, providing a clue for the specific diagnosis of struma ovarii (15). Struma ovarii typically demonstrates strong enhancement of the solid components on postcontrast T1-weighted images (Fig. 15) (3). Images for this section: Table 1: Causes and characteristics of hypointense solid lesions on T2-weighted images. Page 12 of 30

13 Fig. 2: A 37-year-old woman with left ovarian and deep pelvic nodular endometriosis. Page 13 of 30

14 Fig. 3: A 32-year-old woman with heterotrophic pregnancy. A 42-year-old woman with chronic ectopic pregnancy. Page 14 of 30

15 Fig. 4: A 33-year-old woman with uterine leiomyoma. A 38-year-old woman with cellular uterine leiomyoma. Page 15 of 30

16 Fig. 5: A 40-year-old woman with adenomyosis. Page 16 of 30

17 Fig. 6: A 33-year-old woman with right ovarian fibrothecoma. A 27-year-old woman with right ovarian fibrothecoma. Page 17 of 30

18 Fig. 7: A 51-year-old woman with left ovarian fibrothecoma, manifesting as a heterogeneous mass with hemorrhage. Page 18 of 30

19 Fig. 8: A 69-year-old woman with left ovarian Brenner tumor. This lesion is detected incidentally. Page 19 of 30

20 Fig. 9: A 74-year-old woman with right ovarian Brenner tumor and mucinous borderline tumor. Page 20 of 30

21 Fig. 10: A 32-year-old woman with right ovarian endometrioid adenocarcinoma and endometrial cancer. Page 21 of 30

22 Fig. 11: A 46-year-old woman with bilateral ovarian metastases from gastric signet ring cell carcinoma. Page 22 of 30

23 Fig. 12: A 47-year-old woman with bilateral masses at the vaginal stump after hysterectomy and radiation therapy for uterine cervix cancer. Page 23 of 30

24 Fig. 13: A 47-year-old woman with inflammatory pseudotumor of the retroperitoneum. Page 24 of 30

25 Fig. 14: A 47-year-old woman with a calcified uterine leiomyoma. Page 25 of 30

26 Fig. 15: A 49-year-old woman with a left struma ovarii. Page 26 of 30

27 Conclusion There are several causes and imaging characteristics of hypointense solid lesions in the female pelvis on T2-weighted images. In general, solid lesions in the female pelvis appearing hypointense on T2-weighted images may be benign; however, they are important from an imaging standpoint because they may have solid portions and so mimic malignant tumors (Fig. 16). The primary affected sites in the female pelvis of hypointense solid lesions are also crucial for correct interpretation (Fig. 17). We suggest that familiarity with the clinical setting and imaging features of hypointense solid lesions in the female pelvis on T2-weighted images will facilitate prompt, accurate diagnosis and treatment. Images for this section: Fig. 16: Varous lesions of T2 low SI solid lesions Page 27 of 30

28 Fig. 17: Hypointense solid lesions in the female pelvis on T2-weighted images Page 28 of 30

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