This discussion of the sonographic differential diagnosis of pelvic masses is organized according to the most frequently seen sonographic appearance of particular types of pelvic mass. If a particular pelvic mass has a spectrum of sonographic appearances, it is mentioned in more than one category. Masses that are difficult to localize relative to a particular organ or category are considered "indeterminate." These may represent lesions related to the bowel, for example.24,25
This scheme for differential diagnosis should be used only as a general approach to the sonographic characterization of a pelvic mass (Table 31-1). Sonographic findings must be correlated with the clinical ones. The sonographic depiction of morphology is helpful in determining the chance that a mass is malignant. The presence of wall or septal irregularity or papillary excrescences correlates with the chance of malignancy (Figure 31-8). Color Doppler sonography parameters can also be included in differential diagram (Table 31-2).
Table 31-1SONOGRAPHIC DIFFERENTIAL DIAGNOSES OF PELVIC MASSESa ||Download (.pdf) Table 31-1 SONOGRAPHIC DIFFERENTIAL DIAGNOSES OF PELVIC MASSESa
|Cystic ||Complex ||Solid |
Physiologic ovarian cysts
Hydatid cyst of Morgagni
Multiple follicular cysts
Germ cell tumor
Endometrial carcinoma, sarcoma
Solid ovarian tumor
Table 31-2SONOGRAPHIC FEATURES OF BENIGN AND MALIGNANT PELVIC MASSES ||Download (.pdf) Table 31-2 SONOGRAPHIC FEATURES OF BENIGN AND MALIGNANT PELVIC MASSES
| ||Benign ||Malignant |
|TVS ||CDS ||TVS ||CDS |
|Sonographic morphology ||Smooth walled, anechoic || ||Papillary excrescences, mural nodules, irregular solid areas || |
|CDS vasculature || ||Regularly spaced || ||Irregularly spaced, clus-tered |
|Impedance || ||High || ||Low |
|Velocity || ||Low || ||High |
|Change in size ||Regression or no change ||Increase or no change |
|Other findings ||No astes, no liver, masses, or lymphadenopathy ||Ascites, no liver, masses, or lymphadenopathy |
Tubal disorders depicted by transvaginal sonography. A: Transvaginal sonogram demonstrates mass (short arrow) arising from left fallopian tube, representing fallopian tube carcinoma. Adjacent to uterus (long arrow) is a pedunculated subserous fibroid (curved arrow). B: Hysterosalpingogram in the same postmenopausal woman seen in (A) with vaginal bleeding, showing intrinsic filling defect in distal left uterine tube. This was a tubal carcinoma. C: Long axis of a hydrosalpinx (arrow) .
Several types of pelvic masses can appear as cystic adnexal masses on sonography (see Figures 31-1 and 31-2). They include physiologic (follicular or luteal) ovarian cysts, hydrosalpinges, cystadenomas, parovarian cysts, and endometriomas. In general, physiologic cysts are the most common masses to appear as well-defined an-echoic, adnexal masses. Luteal cysts usually have a thicker wall than follicular cysts and tend to contain hemor-rhagic areas. Rarely, cysts that do not arise from the ovary, such as parovarian cysts or cysts of Morgagni, can mimic the sonographic features of an ovarian cyst.26,27,28 These cysts will not demonstrate a rim of ovarian tissue, however. It may be helpful to use transvaginal scanning to determine whether or not a mass is surrounded by a rim of ovarian tissue to confirm its intraovarian location.
Even with the similar sonographic appearance of several types of cystic adnexal masses, the diagnostic possibilities can usually be narrowed to 1 or 2 entities based on clinical presentation and evaluation. In general, most cystic masses that arise within the pelvis are of ovarian origin. Depending on the referral population, physiologic ovarian cysts or hydrosalpinges will be the most common cystic pelvic masses encountered by the sonologist. Acute enlargement of a mass is usually the result of internal hemorrhage or venous engorgement secondary to adnexal (ovarian) torsion. The echoes that can be observed within some cystic masses arise from cellular debris, pus, organized blood, proteinaceous fluid, cholesterol crystals, or sebaceous material encountered in some der-moid cysts.29,30 Irregular thickening of a cyst wall may be the result of inflammatory or neoplastic processes involving the wall or vasculogenic edema due to torsion of the cystic mass on its pedicle. A clot ad-hered to the wall of a hemorrhagic ovarian cyst may also produce an irregular wall.31,32
Certain conditions are usually associated within a single cyst as opposed to those disorders that are associated with multiple pelvic cysts. For example, single cystic lesions are frequently physiologic ovarian cysts, whereas conditions such as endometriosis are associated with multiple pelvic cysts.33 An enlarged (over 10 to 15 mL), rounded ovary containing multiple immature follicles in the 5- to 7-mm range can be recognized in patients with polycystic ovary disease.4
Physiologic Ovarian Cysts
Several types of cystic masses can result from abnormalities that occur at different stages of folliculogenesis. In general, follicular cysts occur either due to failure of a mature follicle to rupture at the time of ovulation or to collection of blood within the follicle after ovulation occurs, resulting in a corpus luteum cyst. In most individuals, a mature follicle ranges from 15 to 20 mm in average dimension.5,34 Follicular cysts of the ovary are usually larger than a mature follicle, ranging from 3 to 8 cm in size. They may regress spontaneously or after a clinical trial of hormonal suppression. Luteal cysts may form from continued hemorrhage with a corpus luteum and usually have a thicker wall than follicular cysts. Sonography has an important role in documenting any change in size of the cyst during and after clinical observation or treatment. This is particularly important when considering hemorrhagic ovarian cysts that have a spectrum of sonographic appearances, depending on the amount and organization of internal clot. Indeed, some hemorrhagic ovarian cysts can mimic the sonographic features of solid ovarian masses, such as a teratoma. In most cases of hemorrhagic ovarian cysts, however, the degree of through transmission is greater than in truly solid masses, and the mass will regress in size over a 2- to 3-week period.35
Patients with hemorrhagic ovarian cysts may experience the abrupt onset of lower abdominal or pelvic pain.31,32 Because this history can also be elicited in cases of ruptured ectopic pregnancy, it is important to obtain an accurate pregnancy test on these patients. Other conditions, such as ovarian torsion and acute appendicitis, can mimic the clinical presentation of patients with a hemorrhagic ovarian cyst.
On sonography, the most common appearance of a hemorrhagic ovarian cyst is a complex mass with internal echoes but with enhanced through transmission. Although fibrinolyzed clot is typically hypoechoic, acute intrapar-enchymal hemorrhage frequently appears as an irregular echogenic area. The cyst wall may be irregular in contour due to a clot that is adherent to it. Occasionally, mildly echogenic interfaces can be seen within a hemorrhagic cyst, most likely representing a partially solid clot.31,32 The internal interfaces represent fibrin strands.
Hydrosalpinges occur when an inflammatory process produces adhesions of the fimbriated end of the tube, trapping intraluminal secretions. The fluid that is secreted distends the tube, resulting in a fusiform anechoic adnexal mass. The tapered fusiform shape and lack of peristalsis of a hydrosalpinx usually allows it to be differentiated from fluid-filled small bowel loops. In addition, the typical configuration of a hydrosalpinx (tapering as it enters the uterus and enlarging distally) is helpful in its sonographic recognition. Typically, a hydrosalpinx can be traced to its origin along the lateral aspects of the cornual area of the uterus. The origin of the tube can also be identified on transvaginal scanning by the pointed configuration of the endometrium in the cornu. The isthmic portion of the tube lies immediately posterior to the round ligament.
If the inflammatory process involves the ovary as a part of the wall, a tubo-ovarian abscess may be produced. It may be difficult to differentiate a simple hydrosalpinx that does not involve the ovary from a tubo-ovarian abscess on the basis of sonography. In our experience, however, the tubo-ovarian abscess has a more complex internal appearance, with low-level echoes arising from inflammatory fluid. In addition, the ovary can be identified in some patients as a border to the inflammatory mass in patients with a tubo-ovarian mass. Transvaginal sonography can also identify an incomplete septum of the tubal wall in an acute tubo-ovarian abscess. Chronic disease produces a thin wall and "beads-on-a-string" appearances representing thickened endosalpingeal folds outlined by fluid.33
In most cases, tubo-ovarian abscesses can be distinguished from other pelvic masses via sonography by determining that the abscess cavity is indeed within the confines of the ovary. This can be recognized by the abscess forming a rim of compressed tissue, or a "beak," within the ovary.
Endometriosis is a condition resulting from ectopic location of endometrial tissue within the peritoneal cavity and on the surface of abdominal and pelvic organs and pelvic ligaments. Endometriotic implants typically locate on the uterosacral ligaments and serosal surfaces of the bowel and peritoneum. These implants are difficult to depict with sonography because they are typically very small (5 mm) and in a position that is difficult to image sonographically (posterior to the uterine surface).34 Occasionally, they can be recognized as echo-genic areas within the cul-de-sac on TVS. The ectopic endometrial tissue undergoes cyclical changes and bleeds during the menstrual cycle. Diffuse, low-level echoes can be observed within these masses arising from the clotted blood.
Endometriosis can also cause obstructive uropathy by implanting near the ureters and, rarely, can cause bowel obstruction secondary to implantation on the serosal surfaces of the bowel. The periodic bleeding that occurs within the mass causes pain, and extravasated blood can result in fibrosis around the region of the endo-metriotic implant. Rupture of an intraperitoneal endometrioma that contains clotted blood may result in acute peri-tonitis.
In up to 40% of patients with endometriosis, endometrial implants that are present within the peritoneum are associated with endometrial implants within the myometrium. This condition is termed adenomyosis. Al-though the involved uterus may not be noticeably enlarged, there usually is an irregularly thickened and echogenic or hypoechoic texture of the inner portion of the myometrium.
There is a spectrum of sonographic findings in endometriosis, depending on the size and number of endo-metriomas present and their internal contents.34 In some patients with endometriosis, no recognizable sonographic findings will be observed because the endometriosis results in fibrosis and thickening of the adnexal ligaments without production of definite masses. When the endometriomas themselves become larger than 1 to 2 cm, they can be identified as multiple cystic masses by sonography. Low-level echoes may be observed in some endometriomas arising from clotted blood contained within these masses, giving them a "ground glass" appearance. Intraovarian endometriomas have a similar sonographic appearance to hemorrhagic corpus luteum cysts, and occasionally cannot be confidently distinguished from them. Rupture of endometriomas that contain clotted blood can result in diffuse peritoneal inflammatory response. Endometriosis can be encountered in patients who are febrile and thought to have a tubo-ovarian abscess because masses can become secondarily infected. Sonography is a useful means to monitor the effectiveness of medical therapy of the more extensive cases. It can also guide aspiration in selected cases.
Cystadenomas are the most common type of cystic ovarian tumors. Although they are most frequently encountered in postmenopausal women, they can occasionally be encountered in women of child-bearing age. These tumors arise from cells of the coelomic peritoneum that covers the ovary. The cells that line these tumors can secrete either a mucinous or a serous substance. Papillary tumors tend to have irregular solid areas and projections of solid tissue internally. In general, the more solid and irregular the internal morphology of an epithelial tumor, the more likely it is malignant. Whereas unilocular ovarian cysts smaller than 10 cm in asymptomatic postmenopausal women are associated with minimal risk of ovarian cancer, ones that contain solid areas are associated with a significant risk of malig-nancy.35,36
In the early stages of development, cystadenomas may have a similar appearance to other cystic adnexal masses. When they enlarge, they frequently contain characteristic internal components, such as septations or papillary excrescences, which allow their sonographic recognition. These tumors metastasize by extending through the capsule of the tumor and spreading to peritoneal, serosal, omental, and diaphragmatic surfaces. As-citic fluid may be cytologically negative, but its presence raises concern that spread beyond the tumor capsule has occurred. Because ascitic fluid is usually produced in response to peritoneal implantation and obstruction of transdiaphragmatic lymph drainage, the lack of ascites does not ensure that the mass is benign. Sonography is not accurate in depicting tumor invasion into the bladder or rectum, or the presence or absence of associated lymphadenopathy.
Other Less Common Cystic Masses
A variety of masses that do not arise directly from the uterus or ovaries can appear as adnexal cystic masses. The most common one is the paraovarian cyst, which arises from wolffian duct remnants in the mesovarium. This type of mass usually measures from 3 to 5 cm but can be as large as a pelvoabdominal cystadenoma. Occasion-ally, these cysts contain hemorrhage; rarely they contain internal septations.27,28 Like other adnexal cysts, these masses may potentiate torsion of the adnexa. By applying gentle pressure between the mass and the ovary, paraovarian cysts can be shown to separate from the ovary.
Another cystic mass that can be encountered in the patient with previous surgery is a peritoneal inclusion cyst. The cysts result from serous fluid collections that become entrapped by adhesions or overlaps of pelvic peritoneum related to previous pelvic surgery. So-called ovarian remnants may appear as cystic masses. These arise from ovarian tissue that remains after oophorectomy and can be associated with pain. Rarely they can enlarge to cause extrinsic compression of the distal ureter. Paraovarian cysts and tumors can usually be distinguished from ovarian ones by their location. As in ovarian tumors, paraovarian ones that contain solid areas or septation should be considered as potentially malignant.37,43 Cysts arising from the fimbriated end of the tube (cysts of Morgagni) may appear as cystic adnexal masses and are best seen if there is fluid surrounding the tube. Inclusion cysts of the cervix (nabothian cysts) can usually be distinguished from other adnexal cysts in that they can be delineated to be within the confines of the uterine cervix and endocervical canal. Nabothian cysts are typically a few millimeters in size and can be distinguished from Gartner duct cysts, which appear as tubular cystic structures in the upper vagina and (less frequently) within the uterine wall. Distended arcuate veins that course along the outer third of the myometrium can also appear as punctate cystic structures within the confines of the uterus. Calcifications within the arcuate arteries can be observed, particularly in postmenopausal women.
Complex masses are defined as those that contain both fluid and solid areas (see Figures 31-3 and 31-4). These masses can be further subdivided into those that are predominantly cystic and those that are predominantly solid. As stated previously, some cystic masses that have pus, cellular debris, sebum, suspended proteinaceous mate-rial, or organized clot may appear as echogenic material within a complex mass. In some cases, these internal echoes within masses can be identified as being dependent by changing orientation on the layer of echogenic material as imaged when the patient is scanned in the right- and left-anterior oblique positions. Ovarian tumors that contain solid components or irregular septations may also be classified into this complex mass category. In addition, those masses that usually contain areas of internal hemorrhagic degeneration, such as granulosa cell tumors, are categorized as complex pelvic masses.
Neoplasms that arise from the germinal tissue within and around the ovary are generally described as germ cell tumors of the ovary. The most common type of germ cell tumor is the benign cystic teratoma or dermoid cyst. Malignant varieties of germ cell tumors include the teratocarcinoma, malignant dysgerminoma, and endodermal sinus tumor.
Dermoid cysts are the most common type of germ cell tumor encountered in patients of child-bearing age.38 These masses contain a variety of internal components consisting of fat, skin, teeth, and hair. Because the internal components of a dermoid cyst vary, their sonographic appearance differs depending on their internal consistency. In general, the most common sonographic appearance of a dermoid cyst is a complex, predominantly solid mass with echogenic internal components arising from fat and calcified portions of the mass. Less common appearances of dermoid cysts range from the totally cystic dermoid cyst, encountered in those der-moid cysts lined by neuroectoderm, to the almost completely solid dermoid cysts that have a large amount of soft tissue component within. Similarly, other germ cell tumors have a variety of appearances. The granulosa cell tu-mor, which may be associated with precocious puberty in the child and a variety of disorders related to hyperestro-genism in the adult, usually has a complex, predominantly cystic appearance with multiple cystic areas within the mass corresponding to hemorrhagic areas.
Be aware that dermoid cysts can mimic the findings of gas- or feces-containing bowel loops within the pelvis. Because the majority of dermoid cysts form pedunculated ovarian masses, and because they have a high fat con-tent, they typically are located superior to the uterine fundus. This location may contribute to an initial failure to recognize the presence of a dermoid cyst because of confusing a highly echogenic focus (arising from fat within the dermoid cyst) with gas-filled bowel loops. Real-time scanning, however, will demonstrate peristaltic activity in an echogenic area within bowel loops as opposed to the relatively stationary configuration of fat within a dermoid cyst. Occasionally, the sebum with a dermoid cyst will be layered within the mass, producing an internal interface between more serous components of the cyst and the sebaceous fluid. Changes in orientation in this interface that are gravity dependent can also be documented with real-time scanning. The presence of distal acoustical shadowing, associated with some dermoid cysts that contain a large amount of fat, may also be a helpful indicator of the presence of a dermoid cyst. A pelvic radiograph, CT, or fat-suppressed MRI may be helpful in confirming the sonographic impression of a dermoid cyst, because calcification, radiolucency, or a characteristic MR signal associated with the fat of a dermoid cyst may be apparent.
This subject is mentioned to emphasize that an ectopic pregnancy can present as a complex and sometimes solid adnexal mass in women of child-bearing age. The topic of ectopic pregnancy is extensively covered in Chapter 4.
The discussion of cystadenoma is repeated in this section because some of these ovarian tumors demonstrate a complex sonographic appearance. As mentioned previously, the greater the amount of internal solid area or irregular septation, the more likely that these types of tumors are malignant.13 The presence of ascites usually indicates that the tumor has extended beyond its capsule and implanted on the peritoneal, dia-phragmatic, or omental surfaces. Rarely, ascites is associated with a benign tumor, such as the ovarian fibroma (Meigs syndrome). Very rarely, ascites may be associated with uterine fibroids, which are probably the result of a transserosal exudate.
An enlarged ovary has the potential for attenuating its pedicle and torsing along its axis (see Figures 31-5 and 31-6). Masses within the ovary, such as those resulting from hemorrhagic corpus luteum, can potentiate tor-sion. There are no specific sonographic findings in ovarian torsion.3,14 Usually, the ovary is enlarged and contains a single hypoechoic area representing a hemorrhagic area. If the torsion is intermittent and incomplete, massive stromal edema of the ovary can result. In these cases, the ovary is diffusely enlarged and contains multiple hypoechoic and echogenic areas resulting from hemorrhagic infarcts. Intraperitoneal fluid may be present, related to obstruction of venous and lymphatic return, resulting in a transudate from the capsule of the ovary. Duplex Doppler examination of the ovarian blood supply along the ovarian and infundibu-lopelvic ligaments may facilitate the specific diagnosis of ovarian torsion by demonstrating absent or high-impedance arterial flow and absent venous flow. The full spectrum of findings on TV-CDS is presented in detail in Chapter 36.
One relatively rare cause of a complex mass in a patient presenting with pain is an ovarian remnant. This ovarian tissue left behind after difficult oophorectomy may contain hemorrhagic corpus luteum appearing as a hypoechoic area with internal interfaces. These masses may obstruct the distal ureter. Peritoneal cysts, which also form after pelvic surgery, tend to envelope the ovary rather than arise from within it. Therefore, it is important to delineate the presence or absence of a parenchymal rim around the mass.39
In general, most solid pelvic masses are of uterine, rather than of ovarian, origin. Therefore, distinction of the internal consistency of a pelvic mass is indirectly helpful in establishing a uterine or ovarian origin.
Uterine leiomyomata is the most common mass to appear as a solid mass on sonography. These tumors typically have a hypoechoic texture and can usually be traced to be within the borders of the uterus.40 A subserosal fibroid, however, may be pedunculated or even parasitize to the broad ligament bowel or omentum, creating the impression of an extrauterine mass. Uterine masses are discussed in detail in Chapter 33.
Compared with the frequency of solid masses representing uterine leiomyomata, ovarian solid masses are less common. Solid ovarian tumors include adenocarcinoma, fibromas, and thecomas. Some rapidly growing epithelial tumors of the ovary, such as cystadenofibromas, may also appear as solid. Fibromas and thecomas may be associated with benign ascitic fluid.
Ovaries that undergo partial or intermittent torsion, or both, may appear as a solid mass. These ovaries are usually extremely edematous related to the obstruction in venous return. Fibromas typically appear as solid masses that demonstrate marked attenuation due to the fibrous tissue elements.41 Cystadenofi-bromas may appear as solid masses with areas of calcification, similar to the sonographic findings of an extrau-terine fibroid. Other less common solid ovarian tumors can arise from metastasis from the gastrointestinal tract, lymphomas, and other primary neoplasms.
Rarely, tubal disorders, such as carcinomas, produce solid adnexal masses. These are best depicted using TVS (see Figure 31-8). Some nongynecologic masses that can appear solid include lymphadenopathy, masses related to the bowel, or both. Lymphadenopathy can be recognized by its typical location in the iliac or para-aortic regions, or both. Only massively enlarged groups of lymph nodes can be detected on sonography, and they usually appear as a lobulated, hypoechoic mass in the expected region of a major lymph node chain. Solid masses resulting from bowel tumors can be diagnos ed by the typical echogenic center arising from the bowel lumen.38 Ectopic pelvic kidneys may be located superior to the bladder dome and have a reniform shape with an echogenic central interface arising from the collecting system. Loculated fluid collection can mimic the sonographic features of some pelvic masses; however, their irregular shape and unusual location can be depicted by TVS or TAS (Figure 31-9).
Miscellaneous conditions. A: Transvaginal sonogram (TVS) of loculated fluid with peritoneal adhesions that mimic the appearance of a cystadenoma. B, C: Transvaginal sonogram (B) and transabdominal sono-gram (C) of a patient presenting with right lower quadrant pain. The TVS shows a normal uterus. Compression TAS demonstrated a thick-walled appendix. This patient had appendicitis at surgery. D: Transvaginal sonogram of a patient status post bowel surgery showing a peritoneal "pseudocyst" or loculated fluid in the right lower quadrant. E, F: Transabdominal sonograms through area of cul-de-sac showing intraperitoneal fluid (E) and a hemorrhagic corpus luteum (between cur-sors) (F). G, H: Long (G) and short (H) axes of fusiform mass in the right lower quadrant is consistent with a thickened appendix. Appendicitis was confirmed at surgery. I: Transvaginal sonogram of a walled-off appendiceal abscess adjacent to adhesed small bowel loops. J: Transvaginal sonogram of solid mass containing ringlike interfaces. This was found to be a mucocoele. (Courtesy of Paul Grappell, MD.)
Benign versus Malignant Determination Based on Sonographic Morphology
Scoring systems have been developed that quantitate the probability of benignancy or malignancy based on sonographic morphology.35 In one system, inner wall structure, wall thickness, septae, and echo-genicity were the major categories with grades from 1 to 5 depending on the sonographic feature. Malignancies had scores over 9, with dermoid cyst showing the greatest propensity for overlap (Figure 31-10).
Morphologic scoring by TVS. Each of 4 parameters as assessed, including inner wall structure, wall thickness (mm), septa (mm), and echogenicity. Malignancies tended to have high scores (over 9). (Reproduced with permission from I. Timor, MD.)
This type of system is helpful for standardizing sonographic assessment of pelvic masses by their morphol-ogy. It should also serve as a reminder to the sonologist and sonographer of which parameters need to be as-sessed.
Persistent Versus Regressing Masses
In pre- or perimenopausal women, follow-up in 6 to 8 weeks may be indicated in those masses thought to be be-nign, even though some may persist up to 2 to 3 months (Figure 31-11). About 70% of cysts in premenopausal women will demonstrate regression in 2 to 3 months.42 If a mass does not regress, one should consider other etiologies. Acute enlargement can result from intraluminal hemorrhage and/or torsion.
Graph showing the interval from diagnosis to involution of cystic masses. The vertical axis represents the percentage of cystic masses that regressed within a particular time after initial presentation. (Data from Pinatti J. Int J Gynecol Ob-stet 1988;26:109.)
In postmenopausal women, the presence of a pelvic mass is more ominous, because there is an increased risk of malignancy (Figure 31-12). However, one study showed that up to 15% of asymptomatic postmenopausal women have cystic masses up to 3 cm in size.43 If followed for 6 months, over half regress and approximately one-fourth enlarge and one-fourth stay the same in size.44 Clinical judgment in these cases is needed to determine which patients may benefit from surgery, aspiration and cytology, or observa-tion. CA-125 has only a limited role because of its poor sensitivity and specificity. Enlargement, development of irregular solid areas, or ascites are signs indicating the possibility of malignancy.
TA/TV 3D of pelvic mass. A: Multiplanar reconstruction (MPR) 3D of ovarian cyst. B: Cyst with fibrin stands. C: Hemorrhagic cyst. D: Ovarian cancer with papillary excrescences.