Normal ultrasound anatomy

1. Age-related changes

Premenopausal patient: Ovaries have homogeneous echostructure with hyperechoic stroma and peripheral follicles in the cortex.

Postmenopausal patient: Ovaries are atrophic and follicles disappear, being difficult to visualize them by ultrasound.

2. Dynamic changes during the menstrual cycle

Morphologic changes

During the proliferative phase of the menstrual cycle, several follicles begin to develop.

By day 8-12, one dominant follicle matures and the rest begin to regress.

On day 14 the follicle ruptures and the egg is extruded.

After ovulation, corpus luteum is formed, and if fertilization does not occur, the corpus luteum degenerates into a corpus albicans.

Fig. 2: 1. Immature follicles 2. Dominant follicle 3. Cumulus oophorus inside the preovulatory follicle 4. Corpus luteum: cystic echostructure and festooned contour 5. Corpus luteum: solid echostructure 6. Corpus albicans
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Cyclic variation of ovarian arterial vascularization

The ovarian artery blood shows high-resistance flow pattern indicative of an inactive state of the ovary. The flow resistance of the ovarian artery is maximum during the first 8 days of the cycle.Ovarian artery has a low-resistance flow that reaches the lowest level during the early luteal phase. At this time, the intra-ovarian vascularization is easily detectable. In late luteal phase, ovarian arterial flow is medium-resistance and gradually increases in proliferative phase.

Fig. 3: A. Spectral Doppler ultrasound shows a normal ovarian artery with a high-resistance flow pattern, low end-diastolic velocity and an early diastolic notch during proliferative phase. B. Ovarian artery with low-resistance flow during early luteal phase. C. Ovarian artery with medium-resistance flow during late luteal phase
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Ovarian pathology

Classification of ovarian pathology is summarized in table 1.

Fig. 4
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Simplified histological classification of ovarian neoplasms is shown in table 2.

Fig. 5
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Imaging modalities do not allow a specific histological diagnosis and sometimes it is difficult to distinguish benign from malignant tumors.

We review the different ovarian lesions with a practical approach to the radiologist by a didactic algorithm based on ultrasound findings, which will allow us to approach the most probable diagnosis. Four questions must be answered when we see an adnexal lesion on ultrasound examination. First: Is it an ovarian lesion? Second: Is it a cystic or a solid lesion? Third: Does it have a typical echographic pattern? Fourth: Does it have findings indicating malignancy?

Fig. 6
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Mimics of ovarian lesion

There are anatomical structures and extraovarian lesions in pelvis that can mimic the appearance of ovarian masses (table 3 of figure 7).

Fig. 7
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Occasionally, the morphology and size of unilocular cystic cystadenoma can simulate a distended bladder. We must review medical history of the patient, ask for sensation of bladder filling, and determine the location of both structures separately.

Fig. 8
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

On static images, bowel and blood vessels can mimic a normal ovarian, we must interpret images during the real-time examination for easily differentiate them. When transducer pressure is applied, bowel will compress and we will see its peristalsis. Vessels (typically pelvic varices) will also compress and will demonstrate flow with Doppler sonography.

Fig. 9
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 10
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Although the majority of adnexal pathology is originated in the ovary, there are also extraovarian adnexal lesions, for distinguish them we must see the dependence or not of ipsilateral ovarian tissue. In large masses or in postmenopausal patients with small ovaries without follicles will be very difficult to determine the origin.

Fig. 11
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 12
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 13
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 14
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 15
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 16
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 17
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 18: 80-year-old woman under treatment with Sintrom and hypogastric pain. A-C) Transabdominal US. Hematoma with thick septations and absent color Doppler flow, simulating low-grade ovarian carcinoma. D-E) CT performed 10 days later identify bilobed collection that is located in left anterolateral pelvic wall, compatible with encapsulated hematoma. B and D) Hematoma produces extrinsic compression over left wall of the bladder (V). D) Small left adnexal cyst with benign characteristics.
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 19: 50-year-old woman. A-B) Transabdominal US. C-D) Axial CT . Voluminous cystic mass with thin wall, absent color Doppler flow and presence of fluid-fluid level. Mass is located in the hypogastric with backward displacement of the uterus and ovaries (arrows). Surgeons viewed that large mass was localized in small bowel mesentery. Surgical pathology confirmed that it was a chylous mesenteric cyst.
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

CYSTIC OR CYSTIC PREDOMINANCE OVARIAN LESIONS

BENIGN CYSTIC LESIONS

Benign cystic lesions are the most common forms of ovarian pathology; we describe six typical ultrasound patterns, which are known as the “Big 6”(table 4 of figure 7).

Fig. 7
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Follicular cyst

Follicular cyst develops when the mature follicle does not release the ovule or does not involute.

US features: rounded morphology, thin wall with posterior acoustic shadowing /enhancement  and anechoic content.

Most of them are asymtomatic.

Solved in 8-12 weeks.

Fig. 20
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Corpus luteum cyst

Corpus luteum cyst occurs when there isn´t reabsorption of the corpus luteum after ovulation.

US aspect: Variable appearance, from thick-walled cyst with festooned contours to a more collapsed cyst, giving it a relatively solid appearance. Color Doppler ultrasound demonstrates peripheral flow that has been called a “ring-of-fire”, with a low-resistance waveform.

Clinic: It can cause pain because they tend to bleed and rupture.

Solved in 8-12 weeks.

Fig. 21
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Polycystic ovaries

Diagnostic criteria for polycystic ovary syndrome:

Clinical criterion: Oligo-ovulation and/ or anovulation

Analytical criterion: Hyperandrogenism

US criteria:

• >12 folliclesand measure 2-9 mm in diameter

• Increased ovarian volume (> 10 cm3)

• Typical peripheral distribution of follicles and hyperechogenic stroma; but it´s not considered diagnostic criterion, because this ovarian morphology is common, especially in adolescents without menstrual dysfunction

Fig. 22
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Hemorrhagic cyst

Hemorrhagic cyst is caused by internal bleeding in functional cyst (more common in corpus luteum cyst).

US appearance is variable:

• Acute phase: hyperechoic avascular cyst of heterogeneous or homogeneous echostructure

• Subacute phase: A reticular pattern of thin internal echoes due to fibrin strands and absence of detectable flow at Doppler US

• Phase of clot retraction: solid avascular mass with concave outer margin

• The presence of free fluid echogenic indicates leaking or rupture of cyst

Clinic: Acute pelvic pain.

Solved in 8 weeks.

Fig. 23
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 24
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 25
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 26
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Endometrioma

Endometrioma corresponds to functional endometrial tissue located in the ovary.

US features:

• Avascular, well defined, uni or multilocular cyst that contains diffuse, homogeneous and low- to medium-level internal echoes, which have a “ground-glass” appearance

• Additional features reported include echogenic foci in the wall and small solid areas along the wall. This may be confused with a solid neoplasm

• A small percentage of endometriomas have less typical US features such as anechoic fluid or a fluid-fluid level

Clinic: Pelvic pain during menstrual periods.

No solved.

Fig. 27
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 28
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 29
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Mature cystic teratoma (dermoid cyst)

Mature cystic teratomas contain tissues derived from the three primary cell layers, with predominance of ectodermal components.

US: variable appearance from anechoic to hyperechoic cysts. Most dermoids have a variety of typical sonographic features, which, in most cases, may be used to make an accurate diagnosis.

• Dermoid plug or Rokitansky nodule: a hyperechoic nodule +/- posterior sonic attenuation. This feature is believed to be caused by a mixture of hair and sebum

• “Tip of the iceberg” sign: The hyperechoic area of the cyst causes posterior attenuation of sound, so the deeper part of the mass is not seen. Attenuation of sound is probably caused by hair and sebum. It mimics intestinal gas.

• “Dermoid mesh”: Multiple thin, echogenic lines caused by floating hair in the cyst cavity.

• Presence of calcifications or dental (tooth) components

• Presence of fluid-fluid levels

Risk of ovarian torsion; the rupture and malignant transformation are rare.

Fig. 30
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 31
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 32
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 33
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 34: 51-year-old woman. Cystic lesion in right ovary is hyperintense on T2 with a fluid-fluid level and an unenhanced thin wall; findings compatible with hemorrhagic cyst. Heterogeneous cystic lesion in left ovary with high signal on T1, less intensity on T2 by "shading effect“ and absence of enhancement, compatible with endometriotic cyst.
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 35: 20-year-old woman. Transabdominal US: hyperechogenic mass in Douglas space, with probable right adnexal origin. The lesion doesn´t present flow on color Doppler US and for its echogenicity is suggestive of ovarian teratoma. MRI: On the T1-weighted image with saturation fat, there is suppression of the signal that confirms the fatty content and it is diagnostic of teratoma.
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Other typical sonographic patterns:

Fig. 7
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Unilocularcystic cystadenoma

Ovarian cystadenoma is a benign epithelial tumor.

Variable size (4-20cm).

US: Cystic lesion with avascular thin wall and presence of anechoic content (serous) or low-level echoes (mucin).

Fig. 36
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Ovarian hyperstimulation syndrome

The ovarian hyperstimulation syndrome is a complication of ovarian stimulation treatment for in vitro fertilisation. Rarely, it may also occur as a spontaneous event in normal pregnancy and in gestational trophoblastic disease.

US:Bilateral symmetric enlargement of ovaries (often > 12 cm in size) with multiple theca lutein cysts of varying sizes and thin wall, which they can replace most of the ovary.

Ovarian torsion

Torsion occurs in normal ovaries or associated with adnexal lesion.

US features:

• Enlarged ovarian
• Multiple cortical follicles
• Absence or decreaseflow on Doppler ultrasound compared to contralateral ovarian. Presence of flow does not eliminate the possibility of torsion
• Free liquid in Douglas space

Fig. 37
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Tubo-ovarian abscess

Tubo-ovarian abscess is a late complication of pelvic inflammatory disease.

US: Multi-locular complex cyst with internal echoes, septations, and irregular thick walls.

Clinical features of infection is a key to distinguish of other pathologies with similar. appearances

There may be echogenic liquid (pus) in Douglas space.

Fig. 38
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 39
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

INDETERMINATE CYSTIC LESIONS

Occasionally, cystic lesions have some atypical sonographic features, in which case they should be classified as indeterminate lesions (table 4 of figure 7).

Fig. 7
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

In these cases the main differential diagnosis is considered between cystadenoma and cystadenocarcinoma.

Fig. 40
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Benign lesions, such as hemorrhagic cysts, endometriomas and teratomas, will be included in the differential diagnosis, because they can also have atypical features. For example a hemorrhagic cyst that contain retracting clot inside can mimic an ovarian tumor.

Fig. 41: 32-year-old woman US shows ovarian cystic lesion with indeterminate characteristics. Pathological diagnosis: Mature cystic teratoma
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

MALIGNANT CYSTIC LESIONS

Sonographic criteria of malignancy

Radiographic findings that orient malignancy are shown in table 4 of figure 7.

Fig. 7
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

The features suggesting malignancy on color and spectral Doppler ultrasound are:

• High-velocity arterial flow (peak systolic velocity > 15 cm / s)
• Low-resistance arterial flow  (resistance index<0.4)
• Tortuous vessels, with multiple inter-vessel connections and dilatations with changing calibers. Presence of central vascularization in the complex or solid component

Tumors of the epithelial cells

Epithelial cells tumors account for 70% of all ovarian tumors and 90% of malignant ones.

Imaging cannot differentiate histological types of epithelial neoplasms.

Ovarian serous cystadenocarcinoma

Serous cystadenocarcinomas are the most common tumors.

Typical Feature:Papillary projections arising from the walls and septations.

Ovarian mucinous cystadenocarcinoma

Typical characteristics:

• Tumor can be seen as a large cystic mass occupying the entire pelvis and abdomen
• Tumor contains low-level echoes due to mucinous content

Borderline ovarian tumor

Tumor has histological features of malignancy, but without evidence of stromal invasion, so they have a good prognosis.

Endometrioid ovarian carcinoma

Endometrioid carcinoma is the second most frequent malignant epithelial neoplasm.

It has a similar appearance to other malignant epithelial tumors.

Clear-cell ovarian carcinoma

Clear cell tumors are arising from the embryonic mesonephros.

US: complex predominantly cystic mass, without distinguishing characteristics of other epithelial tumors.

Fig. 42: Voluminous mass that is predominantly cystic, with thin septations (some calcified) and solid areas that present enhancement after contrast injection. Pathological diagnosis: ovarian mucinous cystadenocarcinoma
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 43: Bilateral papillary serous cystadenocarcinoma. Tumor presents general features of advanced malignancy such as ascites, peritoneal implants some of them calcified, denominated “psammomatous bodies” (arrow) and metastatic lymph nodes. Pathological confirmation.
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 44: Ultrasound reveals left cystic adnexal mass with internal septations and vascularized solid component that presents a low-resistance flow pattern. Pthological diagnosis: Papillary seromucinous cystadenocarcinoma with foci of seromucinous borderline tumor.
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

OVARIAN SOLID LESIONS

Tumors of the epithelial cells

Transitional cell tumor or Brenner tumor

Solid tumor composed of fibrous stromal. Cysts areas are unusual and when they are present usually due to a coexisting cystadenoma. These tumors are very similar to ovarian thecomas and uterine leiomyomas.

Fig. 45
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Tumors of the germ cells

Germ tumors account for 15-20% of all ovarian neoplasms and 95% corresponds to mature cystic teratoma (benign neoplasm already seen in the section on typical ovarian lesions).

Immature ovarian teratoma, ovarian dysgerminoma and endodermal sinus tumor are the most common malignant neoplasm in girls and young women.

Predominantly solid ovarian mass identified on a girl or young woman should consider the diagnosis of malignant germ cell tumor.

Sex cord/stromal ovarian tumors

Sex cord/stromal ovarian tumors account for 8-10% of all ovarian tumors.

Ovarian Fibroma / Ovarian Thecoma / Ovarian fibrothecoma

Benign tumors of sex cord - stromal origin (theca cells and fibrous tissue).

Thecomas are associated with estrogen production.

US Features: Hypoechoic mass with marked acoustic shadowing (not present if cystic degeneration or edema of the tumor exist).

Differential diagnosis: uterine leiomyoma and Brenner tumor.

Fig. 46: Well-circumscribed solid mass in the left ovary with marked acoustic shadowing and low-flow on color Doppler US. Hypointensity on both T1 and T2 weighted sequences with delayed weak enhancement. Pathological diagnosis: Ovarian fibrothecoma.
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Granulosa cell tumor of ovary

It is the most common estrogen-producing ovarian tumor.

Variable appearance: Mass with predominant solid or cystic component.

Fig. 47: 75-year-old woman with pelvic mass. US and CT show a voluminous solid-cystic lesion. Pathological diagnosis:granulosa cells tumor.
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Ovarian Sertoli-Leydig cell tumor

Rare tumor.

Virilizing symptoms in 30% of the cases.

Tumor has a solid aspect similar to granulose cell tumors.

Ovarian metastasis

Metastases represent 5-10% of all ovarian neoplasms.

Breast and gastrointestinal tumors are the most common primary tumors to result in ovarian metastasis. Krukenberg tumor is referred to ovarian metastases that contain mucin-secreting “signet ring” cells and usually originate in gastric or colonic tumors.

US features:

• Bilateral solid masses
• Presence of necrosis in metastasis can give a predominantly cystic aspect that simulates a primary cystadenocarcinoma

Fig. 48: Heterogeneous solid masses compatible with bilateral ovarian metastases from breast cancer.
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 49: Enlarged ovaries with vascularized solid masses that present low-resistance arterial flow. Findings are in relation with ovarian metastases of a patient with advanced gastric carcinoma.
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

MANAGEMENT OF OVARIAN LESIONS

Management of ovarian lesions will depend on imaging findings and the presence of risk factors (postmenopausal women, elevated tumor markers, family or personal history of breast or ovarian cancer).

Type of guideline for an ovarian lesion diagnosed by ultrasound:

• Nothing: lesion doesn´t need periodic control or written report of ultrasound finding
• Ultrasound report: Lesion is indicated in the report, but it does´t require monitoring
• Ultrasound monitoring: Lesion requires periodic ultrasound control
• Evaluation by MRI
• Evaluation by CT
• Surgery

Management of ovarian pathology is summarized in tables 5-6.

Fig. 50
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain

Fig. 51
References: Department of Radiology, University Hospital Miguel Servet; Zaragoza, Spain