Chapter 25 - Ultrasound of the Female Pelvis

188

Jeffrey Scott Friedenberg, MD, and

Susan E. Rowling, MD

UltrasoUnd of the female Pelvis

1. What are the main indications to perform an ultrasound (US) examination of the

female pelvis?

US is useful in the evaluation of pelvic masses, pelvic pain, and abnormal bleeding. A pelvic US can also be performed

to evaluate for uterine anomalies or to monitor for the development of ovarian follicles in infertility patients.

2. How is a pelvic US performed?

The typical scanning techniques are transabdominal and endovaginal. We typically begin with a transabdominal scan,

which is performed with the patient’s bladder full. If we are satisfied with the images and have answered the clinical

question, the study is complete. If additional information can be obtained with an endovaginal examination, the patient

is asked to empty her bladder before the examination is performed. Transperineal US is seldom performed, but can be

useful in the evaluation of the urethra, vagina, and cervix.

3. What is the normal US appearance of the uterus?

The uterus has a homogeneous myometrium of moderate echogenicity with a central echogenic band representing the

endometrial stripe complex. Peripheral arcuate vessels may also be identified. A thin hypoechoic layer may surround the

endometrium, particularly in postmenopausal women, and represents the innermost layer of myometrium. During the

late proliferative (periovulatory) phase of the menstrual cycle, the endometrial stripe may have a trilaminar appearance,

with an echogenic outer layer surrounding two hypoechoic layers separated by a thin echogenic line that represents

apposition of the two endometrial layers.

4. How is the endometrial stripe routinely measured?

The endometrial stripe complex is measured in the sagittal plane at its widest point, including both layers, from the most

anterior to the most posterior echogenic portions of the stripe. If there is fluid within the endometrial cavity, the fluid is

not included in the measurement. Endovaginal US is the most accurate way to measure the endometrium.

5. What is the normal thickness of the endometrium?

Endometrial stripe thickness varies depending on the timing of the patient’s menstrual cycle. During the menstrual

phase, the endometrium typically measures 1 to 4 mm. In the proliferative phase, the endometrial stripe may measure

4 to 8 mm, and in the secretory phase, the endometrial stripe may measure 8 to 16 mm. These numbers do not apply

for a postmenopausal woman, in whom a thickness of 8 mm is considered normal if she is asymptomatic. Abnormal

thickening of the endometrium can be a sign of endometrial cancer.

6. What is the name of the simple cysts identified within the cervix? What is their

clinical significance?

Cysts within the cervix are called nabothian cysts. They represent dilated or obstructed endocervical glands. They are

very common in women of reproductive age and are usually of no clinical significance. Occasionally, the cysts appear

complicated, secondary to hemorrhage or infection. Nabothian cysts can be a cause of benign cervical enlargement if

they are large or multiple.

7. What is the most common tumor of the uterus?

The most common uterine tumors are fibroids (leiomyomas), which are seen in approximately 25% of women. Fibroids

are benign tumors of smooth muscle origin that can enlarge under hormonal influence. They are typically heterogeneous

masses with posterior shadowing and may contain coarse calcifications or, rarely, central fluid secondary to necrosis.

Fibroids can be subserosal, intramural, or submucosal in location. Large subserosal or intramural fibroids may cause

symptoms by exerting pressure on adjacent organs. Submucosal leiomyomas are common causes of abnormal uterine

bleeding and may become pedunculated within the endometrial cavity.

8. What are the most common causes of vaginal bleeding in a postmenopausal woman?

Postmenopausal bleeding can occur for numerous reasons, the most ominous of which is endometrial carcinoma.

Other causes include endometrial hyperplasia, endometrial atrophy, submucosal fibroids, and endometrial polyps

189

genitourinary tract

(

Fig. 25-1

). Although US may not definitively

diagnose endometrial carcinoma, the purpose

of the study is to determine which women need

more invasive testing, such as an endometrial

biopsy or hysteroscopy.

9. What are the US findings related to

endometrial carcinoma?

The main finding of endometrial carcinoma

is an abnormally thickened endometrium.

Other findings include increased vascularity

with multiple feeding vessels and an indistinct

interface between the endometrium and the

myometrium. These findings are not specific for

endometrial carcinoma, however, and further

imaging or tissue sampling, or both, is necessary.

In an asymptomatic postmenopausal woman not

undergoing hormone replacement therapy, the

endometrial stripe should not exceed 8 mm. In a

woman with postmenopausal bleeding, a biopsy

should be considered if the endometrium measures greater than 5 mm. When the endometrium measures 4 mm or less,

endometrial atrophy is the most likely diagnosis, and no further work-up is necessary.

10. How can US help differentiate an endometrial polyp from other causes of

endometrial thickening?

The most reliable technique to distinguish between these entities is sonohysterography, in which a catheter is

introduced into the endometrial canal, and approximately 5 mL of saline is infused into the endometrial cavity during

endovaginal US. An endometrial polyp is a focal endocavitary mass that most commonly appears homogeneous

and echogenic in texture, but may contain internal cysts, and has either a narrow or broad-based attachment to the

endometrium. On color or power Doppler interrogation, the most specific finding of an endometrial polyp is a single

central feeding vessel entering from the endometrium.

11. What is the US appearance of endometrial hyperplasia?

Endometrial hyperplasia is commonly a diffuse process with diffuse thickening of the endometrium, but it

may occasionally be asymmetric or focal. The thickening is homogeneous or contains small cysts. On color

Doppler, hyperplasia is relatively hypovascular, in contrast to cancer, which is typically markedly hypervascular.

Sonohysterography helps confirm the diffuse nature of the thickening, which can be adequately sampled with blind

biopsy or dilation and curettage. Alternatively, if a focal abnormality is identified at sonohysterography, hysteroscopy

is necessary for biopsy or resection because focal lesions may be missed at the time of blind endometrial biopsy or

dilation and curettage.

12. Describe the major congenital uterine anomalies.

The uterus, cervix, and upper portion of the vagina

develop from the fused ends of the müllerian ducts.

Multiple uterine anomalies result from various

degrees of arrested development of the müllerian

ducts (agenesis, hypoplasia, or unicornuate uterus),

failure of fusion of the müllerian ducts (bicornuate or

didelphys uterus) (

Fig. 25-2

), or failure of resorption of

the median septum (septate uterus). When a uterine

anomaly is identified, it is important to evaluate the

kidneys because associated anomalies, such as renal

agenesis or renal ectopia, are common.

13. What is the role of US in the diagnosis

of uterine anomalies?

Some uterine anomalies can be accurately diagnosed

with US, such as absent uterus or didelphys uterus, in

which there are two widely separated uterine horns

and two cervices. Two-dimensional US may not be

accurate, however, in the diagnosis of other uterine

Figure 25-1.

Endometrial polyp. Sagittal view of the uterus

shows focal echogenic thickening of the endometrial stripe. Doppler

interrogation showed a single feeding vessel in this lesion, which turned

out to be an endometrial polyp.

Figure 25-2.

Uterine didelphys. Transabdominal transverse view of

the pelvis shows two distinct, widely separate uterine horns (arrows).

190

ultrasound of the female Pelvis

anomalies. It is difficult to distinguish a bicornuate

uterus from a septate uterus because it may be

impossible to assess the external fundal contour of the

uterus. A bicornuate uterus should have a deep fundal

indentation of 1 cm or greater, whereas a septate

uterus has a normal outer fundal contour. Magnetic

resonance imaging (MRI) or three-dimensional US is

more accurate in making the appropriate diagnosis

and guiding treatment planning.

14. What are the findings associated with

adenomyosis on US?

Adenomyosis occurs when there are ectopic

endometrial glands within the myometrium. It is

a common cause of pelvic pain, menorrhagia, or

uterine enlargement (

Fig. 25-3

). Although MRI is more

accurate in the diagnosis of adenomyosis, some US

findings are suggestive, such as globular uterine

enlargement with asymmetric thickening of the

myometrium, heterogeneous myometrium with streaky

shadowing, and small myometrial cysts. Compared

with fibroids, adenomyosis is more ill-defined, is

noncalcified, and is tender to palpation with the

vaginal probe.

15. What is the normal US appearance of the ovary in a premenopausal woman?

The ovaries appear as ovoid soft tissue structures in the adnexa with a volume of approximately 10 mL. During the

follicular phase of the cycle, the ovaries contain a varying number of anechoic follicles, which can vary in size depending

on the phase of the cycle. During the periovulatory phase, there is commonly a dominant follicle that may measure 2.5

to 3 cm. After ovulation, in the luteal phase, there is commonly a hemorrhagic corpus luteum with internal echoes and a

characteristic rim of increased peripheral blood flow.

16. Describe the management of simple ovarian cysts in premenopausal women.

Simple cysts within the ovary that are anechoic, thin-walled, and without septations or solid components are

managed based on their size. Because the normal dominant follicles can range up to 3 cm (or sometimes greater),

simple ovarian cysts smaller than 3 cm in premenopausal women need no follow-up and typically resolve

spontaneously. Cysts greater than 3 cm generally require a 6-week follow-up, which places the patient at a

different phase in her cycle. If the cyst is large or shows interval growth or lack or regression, further evaluation

with laparoscopy may be warranted because many of these lesions represent cystic ovarian neoplasms, such as a

benign serous cystadenomas.

17. What are the US findings associated with a hemorrhagic cyst?

A hemorrhagic cyst is a common finding in a premenopausal woman, particularly in the luteal phase of the menstrual

cycle, and is often associated with acute onset of pelvic pain. The appearance of the internal blood products varies with

the age of the hemorrhage. Acute hemorrhage may mimic an echogenic mass, but can be distinguished from a soft

tissue mass by increased through-transmission and lack of internal blood flow. As the clot lyses and retracts, there may

be an internal reticular pattern of lacelike septations, an internal fluid-fluid level, or a retracting avascular clot adherent

to the wall (

Fig. 25-4

Figure 25-3.

Adenomyosis. There is marked thickening and

heterogeneity of the posterior wall of the uterus. No discrete mass is

identified to suggest fibroids.

Key Points: Ultrasound of the Female Pelvis

1. US is useful in evaluating women with pelvic pain, pelvic masses, and dysfunctional uterine bleeding. US can also

help in the diagnosis of congenital uterine anomalies and the evaluation of ovarian follicles in infertility patients.

2. Thickening of the endometrial stripe may be a sign of endometrial carcinoma, and further evaluation with

hysteroscopy or endometrial biopsy should be performed.

3. Ovarian cysts are very common in premenopausal women, and follow-up of these lesions should be based on their

size and morphology.

4. Features that can suggest a benign versus malignant etiology of an ovarian mass depend on the age of the patient,

morphology of the lesion, size of the mass, and resistive index.

ultrasound of the female Pelvis

191

genitourinary tract

18. What features of an ovarian mass

suggest a benign versus malignant

etiology?

Patient age is important because benign lesions

predominate in premenopausal women. The

size of mass is important, too, because masses

smaller than 6 cm are typically benign, whereas

malignant masses may be very large, often

greater than 10 cm. Lesion morphology may be

assessed on US. Benign lesions tend to be simple

cystic masses with thin, smooth walls. Solid

masses or complex cystic masses with thick,

irregular septations or mural nodules are typically

malignant. Finally, Doppler US findings should

be assessed. Malignant masses commonly have

increased blood flow to their septations and mural

nodules, and they display relatively high diastolic

flow, with low resistive indices (<0.4) on pulsed

Doppler.

19. If a woman presents with a

palpable mass in the pelvis, but

no abnormality is identified on US,

which lesion should be considered?

(Hint: This is the most common

ovarian neoplasm to occur in

women younger than 50 years old.)

The palpable mass may represent a dermoid

cyst, also known as a mature teratoma (

Fig.

25-5

). Dermoids may be bilateral in 10% to 15%

of patients. They have a variety of appearances

on US, owing to components arising from any

of the three germ layers. They range from

completely cystic to completely echogenic with

shadowing. The most specific finding is a cystic

mass with an echogenic mural nodule, termed

the dermoid plug, which often contains bone

or teeth. Other dermoids have fat/fluid levels

or a mesh of floating linear echoes owing to

hair. Dermoid cysts with prominent posterior

shadowing can be difficult to detect with US

because they mimic the appearance of bowel

gas, or they may be much larger than what is

visible on US, which is known as the “tip-of-

the-iceberg” sign.

20. What findings are associated with

pelvic inflammatory disease on US?

The findings related to pelvic inflammatory

disease depend on the severity of the infection.

The US findings may be normal in mild infections

or show fluid within the cul-de-sac, mild uterine enlargement, or endometrial fluid. More severe ascending infections

result in salpingitis with pyosalpinx (dilated fallopian tube with internal debris and thickened hyperemic fallopian tube

wall). The diagnosis of tubo-ovarian abscess is made when the dilated, inflamed tube is inseparable from the ovary,

forming a complex hypervascular cystic mass.

21. What is the imaging modality of choice in a patient with suspected endometriosis?

MRI is the best modality to evaluate for endometriosis. US provides little information in cases with disseminated

endometriosis. In the focal form of the disease, US can detect endometriomas, which often appear as complex cystic

adnexal masses with diffuse, homogeneous, low-level echoes; increased through-transmission; and calcification in the

wall (

Fig. 25-6

Figure 25-4.

Hemorrhagic cyst. Endovaginal examination of the ovary

shows a complex cystic mass with increased through-transmission, a

lacelike pattern, and a retractile clot adherent to the wall. Color Doppler

showed the lesion to be avascular.

Figure 25-5.

Ovarian dermoid—a complex adnexal mass containing

cystic and solid components. Anteriorly, there is a solid nodule

(arrowhead ) within the cystic portion of the lesion; this represents

the dermoid plug. Posterior is an echogenic structure with shadowing

(arrow) that represents a tooth.

192

ultrasound of the female Pelvis

22. If a woman presents with infertility,

hirsutism, and oligomenorrhea, and

pelvic US displays large ovaries with

multiple, peripherally based follicles,

what is the diagnosis?

The diagnosis is Stein-Leventhal syndrome

(polycystic ovarian disease) (

Fig. 25-7

). Although

this diagnosis is made clinically, the US finding

of enlarged ovaries (e.g., with a volume >18 mL)

supports the diagnosis. The ovaries are often

rounded in shape, with increased central stroma

and multiple, small, peripheral follicles of uniform

size, owing to the lack of maturation of a dominant

follicle and anovulation. Normal ovaries also

often have numerous follicles, but the follicles are

typically of varying sizes.

23. What are the US findings associated

with ovarian torsion?

Although suspected ovarian torsion is a common

indication given by emergency department

clinicians for emergent pelvic US, the incidence is rare, and the diagnosis often must be made clinically. Certain US

findings suggest ovarian torsion, however. In the absence of an underlying cyst or mass, the torsed ovary appears

enlarged, edematous, and echogenic with small cortical cysts and absent or diminished blood flow, particularly venous.

There may be preserved arterial flow because of the dual blood supply or incomplete occlusion of the artery. Severe pain

and free fluid are common.

iBliography

[1] K.G. Davidson, T.J. Dubinsky, Ultrasound evaluation of the endometrium in postmenopausal vaginal bleeding, Radiol. Clin. North Am.

41 (2003) 769–780.

[2] D. Levine, Female pelvis, in: J.P. McGahan, B.B. Goldberg (Eds.), Diagnostic Ultrasound: A Logical Approach, Lippincott-Raven,

Philadelphia, 1998, pp. 935–964.

[3] D. Levine, Postmenopausal pelvis, in: J.P. McGahan, B.B. Goldberg (Eds.), Diagnostic Ultrasound: A Logical Approach, Lippincott-Raven,

Philadelphia, 1998, pp. 965–985.

[4] K.T. Nguyen, The ovaries and adnexae, in: E.E. Sauerbrei, K.T. Nguyen, R.L. Nolan (Eds.), A Practical Guide to Ultrasound in Obstetrics and

Gynecology, Lippincott-Raven, Philadelphia, 1998, pp. 71–103.

[5] M.J. O’Neill, Sonohysterography, Radiol. Clin. North Am. 41 (2003) 781–797.

[6] E.E. Sauerbrei, The non-gravid uterus, vagina, and urethra, in: E.E. Sauerbrei, K.T. Nguyen, R.L. Nolan (Eds.), A Practical Guide to

Ultrasound in Obstetrics and Gynecology, Lippincott-Raven, Philadelphia, 1998, pp. 33–70.

Figure 25-7.

Polycystic ovarian disease. US shows an enlarged ovary

with multiple peripheral follicles and echogenic central stroma.

Figure 25-6.

Endometrioma. Sagittal view of the ovary shows a mass

with diffuse, low-level echoes and increased through-transmission.

Document Outline