This chapter should be cited as follows:
Ramkrishna J, Meagher S, Glob. libr. women's med.,
ISSN: 1756-2228; DOI 10.3843/GLOWM.419653
The Continuous Textbook of Women’s Medicine Series – Gynecology Module
Volume 10
Ultrasound in gynecology
Volume Editors:
Professor Antonia Testa, Agostino Gemelli University Hospital, Rome, Italy
Professor Simona Fragomeni, Agostino Gemelli University Hospital, Rome, Italy
Chapter
Role of Ultrasound in the Diagnosis of Benign Ovarian Masses
First published: December 2024
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INTRODUCTION
Most women who undergo screening or diagnostic ultrasound examination have normal ovaries, while a small percentage present with benign adnexal masses, which are frequently noted as an incidental finding. Only a small proportion of these carry the potential for malignant change. Recognizing patterns during ultrasound examination is crucial, and operators' experience influences diagnostic sensitivity. Studies have shown that experienced ultrasound operators can accurately diagnose benign ovarian masses with a sensitivity of around 90–95% using pattern recognition alone.1
Not all ultrasound operators have sufficient exposure in routine clinical practice to adnexal pathology. In an effort to aid clinicians in obtaining a correct diagnosis, the International Ovarian Tumor Analysis (IOTA) study group has developed diagnostic methods for the characterization adnexal pathology.
The IOTA group has published a consensus paper that established a standardized approach to describing ovarian pathology, including the terms, definitions and measurements used. This standardized approach is crucial for creating a successful ultrasound-based protocol for classifying ovarian pathology.2
In the past two decades, advancements in ultrasound technology and our knowledge of anatomy and pathology have improved significantly. For instance, in routine clinical practice, when evaluating pathology such as endometriomas, examining mobility and additional anatomical regions like the pouch of Douglas and extending the routine gynecology scan are now more widely implemented.
This chapter explores ultrasound characteristics of commonly encountered ovarian conditions and discusses the differential diagnosis of conditions that mimic ovarian masses.
ROLE OF THREE-DIMENSIONAL ULTRASOUND IN THE DIAGNOSIS OF BENIGN OVARIAN MASSES
Three-dimensional (3D) ultrasound is commonly used in gynecological ultrasound as it overcomes some of the limitations of two-dimensional (2D) ultrasound. Its ability to view, retrieve and reconstruct images provides additional valuable clinical information.
With 3D ultrasound, the internal aspect of the cyst's wall and contents can be rendered, and masses can be represented in different modes, with the use of tools such as volume contrast imaging (VCI), tomographic ultrasound imaging (TUI), and 3D rendering modes like surface, inversion and silhouette mode. The sonography-based automated volume count (SonoAVC) routinely used in infertility settings is precise in monitoring follicular number and volume. VOCAL (virtual organ computer-aided analysis) is a useful tool in 3D ultrasound imaging for the accurate and reliable measurement of ovarian volumes.
Using transvaginal power Doppler, the vascularity of a tumor is reflected by the color content which can be subjectively evaluated. This information may be used to objectively calculate the vascularization index, flow index and vascularization flow index.
Studies have found that 3D ultrasound is reproducible among different observers.3
CLASSIFICATION
The IOTA group has developed a standardized method for using specific morphological features to evaluate adnexal masses. This helps to distinguish between benign and malignant ovarian masses.
The method includes the classification of ovarian masses based on six morphological features: unilocular, unilocular cyst with solid components, multilocular cyst, multilocular with solid component, solid mass and non-classifiable/indeterminate.
In addition to these morphological features, the IOTA group also uses other sonographic features, such as the presence of acoustic shadows, color Doppler flow and the presence of papillary projections, to help differentiate between benign and malignant ovarian masses.4
ULTRASOUND EVALUATION OF AN ABNORMAL MASS IN THE OVARY
The initial evaluation of an ovarian mass should include determination of laterality of the mass (unilateral, bilateral, right, left) and measurements in three dimensions, as well as the volume of the lesion. The largest dimension of the mass should be used for risk assessment.
The "crescent sign" is a feature of an ovarian mass in which ovarian tissue is stretched around the lesion. This helps differentiate it from masses of non-ovarian origin.5
Description of any abnormality should include the presence of cystic and solid components within the cyst, measurement of the solid elements, and the presence of septations and papillary projections.
The contents of a cyst are not useful in determining the likelihood of malignancy, but can be helpful in characterizing the mass into various pathologies.
Doppler imaging should be used to examine the entire tumor, including the walls, septations, solid areas and papillary projections.
Color scoring, in which scores from 1 to 4 are given based on the amount of flow observed, is the most used method for assessing Doppler flow. A score of 1 indicates no flow and increases the likelihood of the mass being benign. A score of 3 or 4 increases the likelihood of malignancy but, of note, can also be seen in some benign masses.
Flow indices, including peak systolic velocity (PSV), pulsatility index (PI), and resistance index (RI), can also be measured to assess blood flow in the ovarian mass. A low RI or PI may suggest a malignant mass, and malignant masses often exhibit increased blood flow with a low-resistance pattern and central vascularity. Peripheral vascularity is more common in benign masses.4
FUNCTIONAL AND SIMPLE CYSTS
Functional ovarian cysts are the most common type of ovarian cyst, and they develop because of normal ovarian function. They are usually benign and resolve within a few menstrual cycles.
On ultrasound, functional cysts are anechoic with smooth thin walls, lack the presence of papillae and demonstrate posterior acoustic enhancement. On color Doppler imaging, functional ovarian cysts typically have no or minimal blood flow within the cyst.
Follicular cysts typically resolved with time, but persistent cysts greater than 3 cm or those increasing in size are likely to represent other ovarian pathologies such as cystadenomas.6
Cysts smaller than 3 cm in premenopausal women are unlikely to be of clinical significance. Follow-up imaging is recommended if the cysts are greater than 5–7 cm.
In postmenopausal women, simple cysts greater than 3 cm should be followed up.7
A woman with an asymptomatic, isolated, simple adnexal cyst that has been well visualized has no difference in cancer risk compared with a woman without such a cyst irrespective of menopausal status or cyst size. The incidence of ovarian cancer developing in an unilocular cyst under 10 cm in women over 50 is less than 1% (Figures 1 and 2).8,9
1
The varied appearances of a corpus luteum, which may range from simple cyst to a unilocular solid cyst. A corpus luteum presents a characteristic peripheral vascularity pattern known as the ‘ring of fire’, a finding that is important in distinguishing the varied appearances of ovulation from pelvic pathology. Images of a corpus luteum are shown with 2D color Doppler (a,e,f), 3D tomographic imaging (b) and 3D volume contrast imaging with color (c,d).
2
Simple ovarian cysts in reproductive-age women, showing unilocular avascular cyst (a), bilocular avascular cyst (b) and trilocular avascular cyst (c). All spontaneously resolved within 3 months following the initial examination. 3D images show VCI and render (a), 3D render and VOCAL (virtual organ computer-aided analysis) (b) and VCI and VOCAL (c).
HEMORRHAGIC CYSTS
Hemorrhagic ovarian cysts typically occur due to bleeding into a corpus luteum. These types of cyst are commonly found in women of reproductive age. Symptoms can vary depending on the size of the cyst and the presence or absence of associated complications. Smaller cysts are usually asymptomatic and tend to resolve spontaneously within 6–8 weeks. However, larger cysts may cause incremental pain due to complications such as rupture or torsion. There are other types of complex ovarian cysts that can mimic the appearance of hemorrhagic ovarian cysts on ultrasound, so further evaluation may be necessary to confirm resolution.
On ultrasound, hemorrhagic cysts typically have internal echoes or solid components, as well as a fluid-filled layered appearance (Figure 3). They are usually unilateral and have an irregular or uneven border. Reticular cobwebs or lace patterns may be visible in resolving hemorrhagic cysts, and the appearance may change over time as the bleeding subsides. A clot within the cyst may retract from the wall and be confused with a solid component, but a lack of color flow is in support a clot formation.
3
Hemorrhagic ovarian cysts may present with varying ultrasound appearances. Lace-like clot (a,c,f) and clot adhered to the cyst wall (b–e), shown with 2D grayscale (a,b), 3D render (c–e) and silhouette modes (f).
POLYCYSTIC OVARY SYNDROME
Polycystic ovary syndrome (PCOS) is a common hormonal disorder affecting women of reproductive age, which can lead to irregular menstrual cycles and infertility due to a lack of ovulation. Women with PCOS may also have an increased risk of developing psychological disorders and type 2 diabetes. Additionally, the presence of obesity and insulin resistance in these women may contribute to the development of non-alcoholic fatty liver disease. While the symptoms of PCOS may vary, the impact of this condition on the individual's health and wellbeing is significant.10,11
Criteria for diagnosis of PCOS
The diagnosis of PCOS, according to the Rotterdam criteria of 2003,12 requires two of three criteria to be met: clinical or biochemical hyperandrogenism, irregular menstrual cycle, and polycystic ovary morphology. Previous research has shown that identifying polycystic ovaries using a count of 10 or more follicles arranged around a dense core stroma is a more accurate method.
In 2003, the number of follicles measuring 2–9 mm in diameter needed to diagnose polycystic ovaries was increased to >12 follicles based on a consensus opinion.13 With advancements in ultrasound technology and improved transducer frequency, a threshold of 12 or more follicles per ovary led to a significant increase in polycystic ovarian morphology, especially in women under 30 years old.
A 2014 review article suggested renaming polycystic ovaries or PCOS to hyperandrogenic anovulation and using a revised threshold of at least 25 follicles per ovary.12,14 Currently, effective international guidelines that are evidence-based for assessing and managing PCOS have been in existence since 2018.13
Ultrasound examination is not necessary to diagnose PCOS in patients with irregular menstrual cycles and hyperandrogenism, but it can assist in identifying the complete PCOS phenotype.
Ultrasound should not be used to diagnose PCOS in adolescent females due to the high prevalence of multifollicular ovaries. However, transvaginal ultrasound transducers with an 8-MHz bandwidth can be used to diagnose polycystic ovary morphology (PCOM) with a threshold of 20 follicles per ovary or 10 ml of ovarian volume while excluding cysts, corpora lutea and follicle dominance.
To determine the number of follicles during transabdominal ultrasound, the most accurate method is to measure ovarian volume with a 10-ml threshold.
Reporting requirements include the last menstrual period, frequency and bandwidth of the transducer, approach/route examined, total number of follicles per ovary measuring 2–9 mm, specific volume of each ovary, endometrial thickness, and appearance (preferably), and any other ovarian and uterine pathology (including ovarian cysts, corpus luteum, and dominant follicles measuring 10 mm).
Hyperechoic stroma in the central region, proximity of follicles to the periphery (string-of-beads sign), and follicles measuring 2–9 mm in size are other morphological characteristics that have been described but do not contribute to the formal diagnostic criteria.13
The most reliable method for counting antral follicles is the grid system, developed by Lujan and colleagues in 2010, which has a sensitivity of 85% and specificity of 94%. Using 3D ultrasound and automatic volume calculations of antral follicles (such as VOCAL and SonoAVC) can further improve accuracy and reduce interobserver variation compared to manual 2D measurements (Figure 4).15,16
4
Polycystic ovaries in two patients shown with 2D (a,d), 3D inversion mode (b) and VOCAL (c,e,f) imaging.
ENDOMETRIOMA
Endometriosis is considered a common disorder. A study conducted in Australia with 13,508 women found that 1 in 9 women received a diagnosis of endometriosis by the age of 44.17 Studies report a prevalence of endometriosis of 5–10% in the general population, and a prevalence of 35–50% in infertile women, women who undergo surgery for a benign condition, and women who suffer from pelvic pain. Approximately 17–44% of women with endometriosis suffer from ovarian endometriosis. An analysis of surgically removed ovarian lesions revealed that endometrioma constituted 21–33% of the benign masses removed.18
In up to 23% of cases, an ovarian endometrioma is associated with deep endometriosis (DE).19 There is a correlation between left endometriomas and rectal deep infiltrating endometriosis and left uterosacral ligament involvement, as well as bilateral endometriomas and adhesions and pouch of Douglas obliteration. However, there was found to be no correlation between endometrioma size and deep infiltrating endometriosis.20
On ultrasound, endometriomas are most often seen as a cystic lesion with "ground-glass" echogenicity, homogeneous low-level echoes, and no papillary projections or solid areas (Figure 5). This type of cystic lesion is commonly referred to as a "chocolate cyst" due to the appearance of the cyst fluid. Color Doppler shows no internal vascularity. The presence of the "ovarian crescent sign" suggests the presence of normal, compressed ovarian tissue, which is frequently seen in benign tumors. Additional features of ovarian endometriomas include fluid–fluid level, the presence of papillary projections or solid areas, multilocularity and a cyst wall containing small hyperechoic foci (Figure 6). While acoustic streaming is a recognized feature of ovarian cystadenomas, it is not a specific feature of endometriomas with several studies reporting that streaming is seldom observed.21,22
5
Two endometriomas. (a,b) Typical endometrioma with ground-glass echogenicity on 2D and 3D render mode. Color Doppler examination revealed no vascularity. (c–e) Subtle differences shown on 2D (c), 3D static (d) and VCI (e). Note with 3D static and VCI, the borders and cyst wall of the endometrioma are more clearly defined.
6
Varying ultrasound appearance of endometriomas. (a) Endometrioma with avascular hyperechoic nodule; (b) endometrioma ‘cyst within a cyst’; (c) clot indicating recent hemorrhage within endometrioma; (d) fluid–fluid level; (e) multilocular endometrioma mimicking a mucinous cystadenoma; (f) chronic endometriotic fluid of varying echogenicity; and (g) endometrioma mimicking a hemorrhagic cyst.
In the presence of an endometrioma, additional signs to assess include site-specific tenderness when moving the ultrasound probe against the affected ovary and lack of mobility of the ovary/cyst against the uterus and lateral pelvic wall, and juxtaposition of the ovaries across the midline, typically referred to as "kissing ovaries".
The main differential diagnoses to consider are simple or serous cystadenomas, hemorrhagic cysts and unilocular mucinous cystadenomas.
Decidualized endometriomas are typically large and unilocular solid or multilocular solid (Figure 7). Papillary projections with vascularity are also frequently demonstrated with the use of power Doppler. A decidualized endometrioma and ovarian cancer arising from an endometrioma deserve special consideration. Under the influence of progesterone during pregnancy, endometriomas take on the appearances of ovarian cancer. Cysts often develop solid papillary projections on their internal surfaces. In contrast to malignancy, decidualized endometriomas have smooth papillary projections.23,24
A malignant transformation of an ovarian endometrioma (Figure 8) is estimated to occur in 0.6–0.8% of cases.25 Malignant endometriotic cysts are more common in older women, with the risk rising in the postmenopausal years.
7
Decidualized endometriomas. (a,b) 2D with color Doppler and 3D render of cyst seen at 10 weeks' gestation; (c,d) a decidualized endometrioma on 2D grayscale and color Doppler at 8 weeks' gestation; (e,f) unilocular cysts with ground-glass echoes but multiple internal projections on 2D grayscale and 3D; (g,h) a 7-week pregnancy and adjacent 4-cm decidualized right ovarian endometrioma on 2D grayscale and 3D.
8
Malignant change with endometriosis in two cases. (a–c) Serous borderline carcinoma within an endometrioma. There is a 6-cm cystic mass with ground-glass echogenicity and a 25 × 21-mm solid area with internal vascularity. (d–f) 2D, color and 3D render of an endometrioid carcinoma.
FIBROMA
Fibromas and thecomas are types of sex cord stromal tumor that can have overlapping histology, resulting in solid ovarian tumors called fibrothecomas. These tumors are typically benign and asymptomatic and occur more frequently in middle-aged women. Unlike other sex cord stromal tumors, fibromas do not typically produce estrogen. Because fibromas and fibrothecomas contain a high level of collagen and fibroblasts, they have a similar appearance to fibroids on imaging studies.26
A fibroma or fibrothecoma is a solid tumor on ultrasound that typically appears round, oval or lobulated and demonstrates posterior acoustic shadowing (Figures 9–11). It may be associated with fluid in the pouch of Douglas and typically shows minimal to moderate vascularization on color Doppler.
According to a study by Chen and colleagues, 70.49% of ovarian fibrothecomas identified on ultrasound appear as a hypoechoic mass with a smooth and clear margin, ranging in size from 1 to 25 cm with a mean of 5.86 cm. The preoperative ultrasound diagnosis was correct in 72.13% of cases, but misdiagnosed in 19.67% as subserous myoma, in 1.64% as ovarian malignancy, in 3.28% as endometrioma, in 1.64% as complex cyst and in 1.64% as cystadenoma.27
In asymptomatic postmenopausal women, the risk of malignancy in purely solid benign-appearing adnexal masses is 2%. It may be possible therefore to treat most of these lesions conservatively.28
Ovarian fibromas have also been described in association with Gorlin, Meigs and Sotos syndromes.29
In bilateral cases, the presence of ovarian fibromas may be indicative of Gorlin-Goltz syndrome (GGS), a rare autosomal dominant disorder characterized by a predisposition to basal cell carcinomas (BCCs) and other benign or malignant tumors.30
Ovarian fibromas constitute most benign tumors observed in patients with Meigs syndrome. Meigs syndrome is characterized by the complete disappearance of exudate following surgical removal of the ovarian tumor.31
Sotos syndrome, like other overgrowth syndromes, can increase the risk of tumors. Management of fibromas is determined by the lesion's benignity and consists of surgical excision.32
9
Ovarian fibromas may vary in size and have a variable appearance on ultrasound ranging from small densely calcified lesions to large uniformly homogeneous masses. They may arise centrally from within the ovary or be exophytic. (a) A 1–2-cm densely calcified ovarian fibroma with posterior shadowing. (b) A heterogeneous mass with shadowing. (c–e) Homogeneous avascular masses without shadowing.
10
Images taken from a routine baseline scan for the investigation of infertility. Both ovaries are multifollicular (a,b). The right ovary also contains an exophytic fibroma (a,c,d). (b) Using VOCAL, the antral follicle count is more accurately assessed (SonoAVC).
11
Solid pelvic masses which may mimic ovarian lesions. (a,b) A 5–6-cm solid left adnexal mass with grade-III vascularity. The mass was of limited mobility and was seen quite separate from the ovary. Histopathology confirmed a benign Schwannoma. (c,d) A broad ligament fibroid, separate from the ovary. Neither a bridging vessel nor pedicle between the uterus and mass could be demonstrated.
CYSTADENOMA
Ovarian epithelial tumors, specifically serous or mucinous types, are prevalent and account for approximately 75% of all ovarian tumors and 90–95% of ovarian malignancies. These tumors can develop in women of various age groups, with average ages reported between 20 and 60 years.
Mucinous cystadenoma
Mucinous cystadenomas are a type of ovarian tumor that make up 15–20% of all ovarian tumors. They are most common in women aged 20–40 but have been known to occur in younger and older patients.
Mucinous tumors can be made up of gastrointestinal or endocervical-type mucinous epithelium. Gastrointestinal-type mucinous cystadenomas are variable in size, unilocular or multilocular, and contain gelatinous material. Endocervical-type mucinous cystadenomas are usually unilocular with a smooth surface and occasionally have a solid component with a white homogeneous cut surface.
Some sonographic features that are commonly seen in mucinous cystadenomas include a multilocular cystic mass with thick walls and internal septations (Figure 12). The walls may appear irregular and thick, and the cysts may contain thick, gelatinous fluid that can appear echogenic. Internal echoes or septations may also be present (Figure 13), which are typically thicker than those seen in serous cystadenomas. On color Doppler imaging, low-level peripheral vascularity is often observed, which is generally less than that seen in malignant ovarian masses.33
12
Typical appearances of multilocular ovarian mucinous cystadenomas. 2D and 3D rendered images of a 7-cm ovoid multilocular mucinous cystadenoma (a,b) and a 9-cm multilocular mucinous cystadenoma (c,d).
13
Varied appearances of mucinous cystadenomas. (a,b) A unilocular mucinous cystadenoma in 2D and 3D. The cyst contains mucin which appears as fluid with low-level echogenicity. Acoustic streaming was also noted at the time of the examination. (c,d) A mucinous cystadenoma which was incidentally seen in the first instance on prior CT scan; the cyst was 70 mm in maximum diameter and the septal thickness was <3 mm. No vascularity was seen along the cyst wall or internal septa. (e,f) 2D and 3D of a large multilocular 20-cm mucinous cystadenoma.
Serous cystadenoma
Serous cystadenomas (Figure 14) are a common type of benign ovarian tumor, accounting for 20–30% of all ovarian neoplasms. There are four subtypes of ovarian serous neoplasia, including benign, borderline, low-grade serous carcinoma, and high-grade serous carcinoma, and they may contain both fibrous and stromal elements.
These tumors are usually bilateral and generally smaller than mucinous cystadenomas.
On ultrasound, they typically appear as well-defined, unilocular or multilocular cystic masses with thin, smooth walls. The cysts are usually anechoic or hypoechoic, with internal septations that may contain echoes. Small papillary projections may occasionally be seen within the cysts. Color Doppler imaging may show low-level peripheral vascularity, which is generally less than that observed in malignant ovarian masses.
The differential diagnosis of benign cystic ovarian tumors includes hemorrhagic corpus luteum, multilocular endometrioma, tubo-ovarian masses and hydrosalpinx.26
14
Two serous cystadenomas. (a,b) Images from a 57-year-old with a persistent 6–7-cm avascular anechoic cyst, and (c,d) images from a 83-year-old with a persistent septated thin-walled cyst. Histopathology in both confirmed serous cystadenomas.
CYSTADENOFIBROMA
Cystadenofibromas are benign epithelial neoplasms that occur in the ovary and are commonly seen in women aged between 40 and 60 years.
They are rare and are distinguished by a dense fibrous tissue and cysts formed by epithelial cells.
Despite sharing certain imaging features with ovarian malignancies, cystadenofibromas are benign and can be distinguished by their large, solid areas that contain scattered glands or thick papillary projections. It is important to differentiate these from other ovarian tumors such as fibromas, Brenner tumors, struma ovarii, endometriosis and metastatic ovarian tumors from the gastrointestinal tract, which have a high fibrous content.34
On ultrasound, cystadenofibromas are typically seen as having a mixture of solid and cystic areas, often with papillary projections (if they belong to the serous subtype). They are typically avascular and do not show any color Doppler signals. The solid parts of the cystadenofibroma may also produce posterior acoustic shadowing due to the dense fibrous tissue present (Figure 15).
In a retrospective analysis of 201 serous cystadenofibromas using pattern recognition to examine their ultrasound appearances, the most common pattern observed was a unilocular solid cyst with one or more papillary projections, but no other solid components. The second most common pattern was a multilocular solid mass with small solid component(s), but no papillary projections.35
15
Cystadenofibroma in four different cases. (a,b) Two cases with unilocular solid ovarian cysts with a single irregular avascular wall projection, with shadowing of the protrusion seen in (b), which is a typical feature of cystadenofibroma. (c–f) Two cases with multiple internal wall protrusions seen on both 2D and 3D. Histopathology in all cases confirmed cystadenofibromas.
MATURE CYSTIC TERATOMA OR DERMOID CYSTS
A dermoid cyst, also known as a mature cystic teratoma, is a benign ovarian neoplasm. It can arise from at least two of the three germ-cell layers. The ectoderm component is usually dominant.
Dermoid cysts account for up to 25% of all benign ovarian neoplasms in premenopausal women and can grow up to 40 cm in size.
They can be uni- or multilocular and, given they are often asymptomatic, they are frequently detected by ultrasound during pregnancy. However, they can cause pain and may be associated with torsion.
Dermoid cysts can be mistaken for endometriosis, mucinous cystadenomas or solid tumors.
Complications can include torsion, rupture, and infection, as well as rare associations such as autoimmune hemolytic anemia and paraneoplastic anti-N-methyl-D aspartate receptor encephalitis.36,37
Malignant transformation occurs in less than 2% of dermoid cysts, most commonly squamous cell carcinoma, and is more likely to occur in larger masses and older women.38
Ultrasound features of dermoid cysts include mixed echogenic content, acoustic shadowing and little or no vascularization.
Typical ultrasound features include "dots and/or lines" corresponding to hair in the cystic fluid, an "echogenic white ball" corresponding to aggregation and compaction of hair and oily fluids in the cyst, and a "fat-fluid level" indicated by a straight, sharp demarcation between hyperechogenic and less echogenic cystic fluid (Figure 16).
Other features include cotton wool tufts, the mushroom cap sign, a completely echogenic lesion, and the starry sky sign (Figure 17). Vascularized solid components and vascularized septa may also be present.39
Shadowing can make it difficult to measure accurately the size of dermoid cysts. Some teratomas may be difficult to detect due to their echogenicity being similar to that of the surrounding bowel. Moving the mass with transducer pressure may help delineate its margins.40,41
16
This series of images show three typical dermoid cysts. (a,b) A dermoid cyst with fat, hair and sebum. (c,d) A dermoid cyst containing predominantly hair. (e,f) A large dermoid cyst in which the solid component is predominant.
17
This series of images show the varied appearances of dermoid cysts. (a,b) ‘Cotton ball’ appearance of multiple fatty deposits, and (c,d) ‘starry sky’ appearance of sebum sometimes seen as the predominant tissue element in dermoid cysts.
ADNEXAL TORSION
Adnexal torsion refers to the twisting of an organ around its axis. Typically, both the Fallopian tubes and the ovaries are affected. If diagnosed and treated promptly, it may be possible to save both organs. Adnexal torsion is one of the most common gynecological emergencies in premenopausal women, and the most reported symptoms are acute or subacute pelvic pain and nausea.
The most removed lesions through surgery for torsion are dermoid cysts and cystadenomas.42
In most cases, a benign solid mass is present. The affected ovary is often larger than normal (Figure 18), with small follicles located near its periphery and increased echogenicity (edema) in the center. Free fluid can be seen in the pelvis (Figure 19a). A whirlpool sign may also be present in the affected adnexa, which is characterized by a circular coiling structure with or without Doppler flow (Figure 19b). The follicle sign may also be present, which is characterized by a peripherally located antral follicle surrounded by a hyperechoic ring.43
However, it is important to note that the absence or abnormality of venous blood flow is highly indicative of adnexal torsion, but the presence of normal blood flow does not completely rule it out, since arterial flow may be preserved in the first instance.44
Based on five ultrasound criteria, 358 torsion cases were analyzed in a recent retrospective study and from these criteria a scoring scale was established. The criteria included atypical adnexal position, the presence of a mass or cyst, unilateral ovarian enlargement, vascular pedicle twisting, and ovarian edema with peripheral hypervascularity of the corpus luteum. In patients with torsion scores of 3, 4 and 5, the predicted diagnosis rates were 84.16%, 93.52% and 98.27%, respectively.45
A recent systematic review found that ovarian edema, the whirlpool sign, and ovarian Doppler findings were of value, but were not sensitive.46
Differential diagnoses in the setting of suspected torsion include ruptured hemorrhagic cyst, ovarian hyperstimulation syndrome, massive ovarian edema (as with intermittent torsion) and degenerating fibroid.47
18
Varied appearances of ovarian torsion. (a,b) Ovarian enlargement related to diffuse parenchymal edema in two cases of ovarian torsion. In the third case (c–e), 2D, 3D and surgical findings are presented. In this case, ovarian necrosis is evident. The ovary was not salvageable and oophorectomy was necessary at the time of laparoscopy.
19
Images from a 31-year-old who presented with acute right iliac fossa pain. (a) Free fluid is seen surrounding the edematous right ovary (arrows). (b) Color Doppler interrogation of the right pelvic side wall showed the typical ‘whirlpool sign’ which is a strong indicator of ovarian or adnexal torsion. Torsion of the pelvic side wall pedicle may occur as clockwise or counterclockwise wrapping of vessels around the central axis.
PELVIC ADHESIONS
Inclusion cysts or pseudocysts are benign fluid-filled masses that are lined with mesothelial cells and can vary in size. Pseudocysts do not have an actual cyst wall, and instead, the fluid is trapped between adhesions of the peritoneum (Figure 20).
On ultrasound, they may be challenging to distinguish from ovarian tumors, since the ovary is visualized separately but close to the cyst. The pseudocyst may appear irregular in shape, as it is influenced by the adhesions and surrounding structures. A history of pelvic surgery, infections or endometriosis is often present.48
20
Pseudocysts in two patients with a history of pelvic surgery. (a,b) Patient with recurrent endometriosis. Multiple locules of peritoneal fluid are seen. (c) Multiple violin string adhesions in another patient.
OVARIAN HYPERSTIMULATION SYNDROME
Ovarian hyperstimulation syndrome (OHSS) is an iatrogenic, potentially fatal complication of assisted reproductive technology (ART). It can occur after any type of controlled ovarian hyperstimulation (COH) using oral or injectable medications.
It is characterized by ovarian enlargement, ascites, hemoconcentration, hypercoagulability, and electrolyte abnormalities. Grading or staging of OHSS include mild, moderate, severe and critical.
Symptoms can manifest as early as 3–7 days after exogenous hCG trigger administration and as late as 9 days after endogenous hCG trigger from an ongoing pregnancy.
Age under 35 years, low body mass index, high antral follicle count, high basal anti-mullerian hormone levels, rapid rise in serum estradiol levels, hypothyroidism, PCOS and previous OHSS history are all risk factors.
OHSS is caused by increased vascular permeability and subsequent loss of protein-rich fluid to the extravascular space because of increased vascular permeability. This is thought to be triggered by hyperstimulated ovaries being exposed to hCG, resulting in increased vascular permeability through release of interleukin-1, tumor necrosis factor, endothelin-1, and vascular endothelial growth factor.
Ultrasound features include bilateral symmetrical enlargement of the ovaries (usually over 12 cm in diameter) and multiple cysts of various sizes may give the appearance of ‘spoke wheels' (Figure 21). Ascites, pleural, and/or pericardial effusions may also be present.
Additionally, ultrasound can detect intra-abdominal hemorrhage, ovarian torsion, pelvic abscess formation and ectopic pregnancy.
There is an estimated 16% incidence of adnexal torsion among pregnant women with OHSS.
The differential diagnosis of hyperstimulated ovaries includes ovarian tumors like multiloculated mucinous cystadenoma.49,50
21
Images from a patient with ovarian hyperstimulation syndrome. Bilateral multilocular enlarged ovaries (a,b), and ascites (c) can be seen. (d) 3D render of the hyperstimulated ovary. Other signs, including pleural effusion, were also present in this patient.
PARATUBAL CYST
Paratubal cysts, also known as para-ovarian cysts, originate from remnants of the broad ligament, mesonephric, or paramesonephric structures. Although they are typically benign, these cysts can cause acute pelvic pain due to adnexal torsion.
Unlike ovarian cysts, paratubal cysts do not have their own pedicle and instead twist along with the ovary, Fallopian tube or both. Complications that can arise from paratubal cysts include cyst enlargement, torsion, rupture, hemorrhage, and neoplasms such as serous cystadenoma, papillary serous cystadenoma, serous cystadenofibroma, mucinous cystadenoma and endometrioid cystadenoma.
Ultrasound imaging can detect paratubal cysts as a well-defined, oval or round cyst close to but separate from the ovary, with the absence of surrounding follicles, and the ability to slide away from the ovary under pressure (Figure 22). However, the presence of papillary projections may suggest malignancy, even though these projections can also be seen in benign paratubal neoplasms. Other potential diagnoses for paratubal cysts include ovarian cysts, hydrosalpinx and peritoneal pseudocysts.51
22
Two types of para-ovarian cyst. (a,b) Typical appearances of a unilocular cyst positioned immediately adjacent to the ovary. On manual palpation, the cysts were seen to slide off the surface of the ovary. (c,d) Unilocular solid cyst. The internal wall projections were avascular on color Doppler examination. Histopathology confirmed cystadenofibroma within a paraovarian cyst.
HYDROSALPINX
A hydrosalpinx refers to a Fallopian tube that is distended and blocked at its distal end. The causes of hydrosalpinx can vary greatly, but are mainly attributed to endometriosis and pelvic inflammatory disease (PID). Other causes include non-gynecological pelvic pathology such as inflammatory bowel disease or previous abdominal/pelvic surgery.
Ultrasound imaging of hydrosalpinx will reveal a tubular, elongated, and cystic mass with incomplete septations or indentations along its walls (Figure 23), giving rise to a "cogwheel" like appearance on ultrasound. In the chronic stage, small nodules may also be visible along the tubal wall, resembling "beads on a string." These findings are strongly indicative of a hydrosalpinx diagnosis.52
Hydrosalpinx has been associated with decreased pregnancy rates, increased rates of ectopic pregnancy, and miscarriage. However, regardless of the type of treatment received, hydrosalpinx management can increase the chances of subsequent pregnancy.53
23
Images from patient with chronic hydrosalpinx. A tubular, avascular structure with incomplete septa is seen on 2D grayscale imaging (a) and mucosal ridges along the internal hydrosalpinx wall are seen on 3D rendering (b).
TUBO-OVARIAN ABSCESS
Tubo-ovarian abscess (TOA) can result from severe PID and can be diagnosed by ultrasound (Figure 24). The sensitivity and specificity of ultrasound for TOA diagnosis have been reported to be as high as 93% and 98%, respectively.54
The ultrasound appearance of TOAs can be variable, depending on the duration of the infection, and can appear as a complex cyst with thick walls and solid areas, with some cases being amenable to percutaneous drainage. Other TOA findings on ultrasound can include loss of tissue boundaries between pelvic organs and thick and dilated Fallopian tubes, which can overlap with other entities such as endometriosis, hemorrhagic cysts, dermoid cysts, or other cystic ovarian masses.55 It is important to note, however, that clinical presentation is key in the correct diagnosis of TOA.
24
Images from patient with tubo-ovarian abscess, showing a 7-cm tubular cystic mass on grayscale (a) and color Doppler (b) imaging, with low-level echoes and negative vascularity in the left adnexal region. The mass was tightly adhered to the left ovary and it was focally tender on palpation. Surgical exploration confirmed the diagnosis of tubo-ovarian abscess.
CONCLUSION
Benign ovarian masses are frequently encountered in clinical practice, whether they present with symptoms or are incidentally discovered during routine imaging.
While ultrasound is a cost-effective and widely available imaging modality, interpretation can be subjective and dependent on the operator's experience.
Recently developed standardized pattern-based analyses, such as that of the IOTA group, have proven useful in predicting malignancy, identifying complications, and recommending appropriate management and follow-up. Following these guidelines can also help maintain consistent communication between the sonographer and treating physician.
Accurate diagnosis and treatment of benign ovarian masses are crucial to reduce patient anxiety and minimize unnecessary surgical interventions.
PRACTICE RECOMMENDATIONS
- Ultrasound is a cost-effective and widely available imaging modality, but interpretation is subjective and depends on the operator.
- A standardized method has been developed by the International Ovarian Tumor Analysis (IOTA) group for evaluating adnexal masses based on specific morphological features. As a result, benign and malignant ovarian masses can be distinguished.
- The "crescent sign" is a feature of an ovarian mass in which ovarian tissue is stretched around the lesion. This helps differentiate it from masses of non-ovarian origin.
- A mass that is vascular is more likely to be malignant, but it is also important to note that some benign masses are vascularized.
CONFLICTS OF INTEREST
The author(s) of this chapter declare that they have no interests that conflict with the contents of the chapter.
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