51

CT Anatomy ofthe Female Pelvis:A Second Look1Mary C. Foshager, MD

James W. Walsh, MD

Computed tomography (CT) remains a valuable technique in the as-

sessment of the female pelvis. The CT appearance of the normal liga-mentous, vascular, and visceral anatomy of the female pelvis can be

confusing. Newer high-resolution CT scanners combined with me-

chanical intravenous contrast medium injectors and thinner sectionshave substantially improved the imaging of female genital tract anat-omy. In addition to the cardinal, uterosacral, and round ligaments,

the ovaries and their ligamentous attachments, as well as the blood

supply to the female internal organs, can now be visualized. Inferior-

to-superior image acquisition following bolus administration of intra-venous contrast material with an angiographic injector facilitates pre-

cise identification of the uterine artery and its relationship to thepelvic ureter and the vascular plexus supplying the vagina, ovaries,

and uterine body. Ideally, familiarity with variations in the CT appear-ance of normal female pelvic anatomy will enable more accurate evalu-ation of pelvic abnormalities.

. INTRODUCTION

The computed tomographic (CT) appearance of the normal ligamentous, vascular,

and visceral anatomy of the female pelvis can be confusing unless one is familiarwith the basic anatomy of these structures and normal variations in their appear-

ance. High-resolution CT scanners and techniques tailored to examination of the

pelvis now permit detailed visualization of the ovaries, uterus, and cervix, as well asprecise identification of their ligamentous attachments and vascular supply. In this

article, we review the normal anatomy and CT appearance of the female internal

genitalia and discuss techniques that facilitate visualization of these structures.

Index terms: Computed tomography (CT), thin-section, 85. 12 1 18 #{149}Pelvic organs. 85. 12 1 18, 85.92 #{149}Pelvic organs,

neoplasms. 85.32

RadioGraphics 1994; 14:51-66

� From the Department ofDiagnostic Radiology, University ofMinncsota Hospital. Box 292 UMIIC, 420 Delaware St SE.

Minneapolis. MN 55455. Recipient ofa Cum Laude award for a scientific exhibit at the 1992 RSNA scientific assembly.

Received February 12, 1993; revision requested March 26 and received July 14; accepted July 15. Address reprint re-

quests to M.C.F.

‘ RSNA, 1994

See the commentary by flattery et al following this article.

52 U Scientific Exhibit Volume 14 Number 1

Figure 1. Posteriorview of the femaleligaments and vis-cera. Drawing illus-trates the broad,round, cardinal,uterosacral, and

ovarian ligamentsand their relation-ships to the uterus,

ovaries, and pelvicureters.

U PATIENT POPULATION AND

IMAGING TECHNIQUESCT images were selected from a review of 135pelvic CT examinations performed on 125women ranging in age from 22 to 83 years. Agroup of 80 patients (1 5 with normal findings

and 65 with abnormal findings) and another

group of 45 patients (10 with normal findings

and 35 with abnormal findings) underwentimaging performed with two different scan-

ners. Diagnoses in the patients with abnormal

findings were cancer of the ovary, endome-

trium, cervix, vagina, and vulva.

All images were acquired with a Somatom

Plus CT scanner with an Impress detector sys-

tem (Siemens, Iselin, NJ) or a GE 9800 Quick

CT scanner (Milwaukee, Wis). All studies uti-

lized a tailored pelvis protocol consisting of

(a) a bolus intravenous injection of 100-150mL of 60% iodinated contrast material admin-istered with an angiographic injector at 2 mL/

sec; (b) inferior-to-superior image acquisition

with an 8-10-mm section thickness from the

pubis to the iliac crest, a 1-second scan time,

and a 5.0-6.5-second interscan delay; (C) de-layed 2-5-mm sections through the pelvic ab-normality or region of interest; and (d) oraladministration of 750 mL of 2% barium dur-

ing the 2 hours before the examination to op-

timize colonic opacification at image acquisi-

tion.

January 1994 Foshager and Walsh #{149}RadioGraphics #{149}53

Figure 2. Axial view of the female pelvic

viscera and ligaments at the level of the uter-

me body. Drawing illustrates the uterine

body and the ovaries and their relationshipsto the round, broad, and ovarian ligaments.

The purpose of the tailored pelvis protocol

was fivefold: (a) to help differentiate pelvic

blood vessels from lymph nodes and parame-trial tumor extension; (b) to enhance uterine

myometrium and epithelium and delineate

the endometrial cavity; (c) to enhance the

cervical stroma and epithelium; (d) to demar-

cate tumor from normal uterine and cervical

parenchyma; and (e) to opacify the bladder

and pelvic ureters, further delineate abnor-

malities, and eliminate partial volume averag-

ing on delayed thin sections.

U PELVIC LIGAMENTS

The broad ligament is formed by two layers of

peritoneum, which drape over the uterus and

extend laterally from the uterus to the pelvic

sidewall (Figs 1 , 2) (1-5). The superior free

edge is formed by the fallopian tube medially

and the suspensory ligament of the ovary lat-

erally (2,4-6). The lower margin of the broad

ligament ends at the cardinal ligament (Fig 1).

Between the two leaves of the broad ligament

is loose extraperitoneal connective tissue,

smooth muscle, and fat known as the para-

metrium, which contains the fallopian tube,

round ligament, ovarian ligament, uterine and

ovarian blood vessels, nerves, lymphatic yes-

sets, mesonephric remnants, and a portion of

the ureter (1,2,7,8). Although the broad liga-ment is rarely seen unless ascites is present,

its position can be determined by structures

that it abuts or contains.

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54 U Scientific Exhibit Volume 14 Number 1

Figure 3. Normal round ligaments. (a) CT scanthrough the uterus (U) and a right ovarian cyst (0)

shows normal round ligaments bilaterally (black ar-rows). The left ligament tapers distally (small whitearrow), where it crosses the left external iliac artery

and vein anteriorly (large white arrows). (b) CT scanthrough an enlarged uterus (U) shows fine round liga-ments (small white arrows) that cross anteriorly to-ward the inferior epigastric vessels (large white ar-row), where the ligaments enter the internal inguinalring. The necrotic cavity (N) and metastatic right ob-turator lymph node (L ) are due to recurrent cervicalcarcinoma. (c) CT scan through the uterus (U), nor-mal pelvic ureters (white arrows), and right ovary (o)shows a normal asymmetric left round ligament (blackarrows) resulting from a variation in uterine position.Note the triangular shape of this round ligament, withgradual distal tapering.

Figure 4. Axial view of the cardinal and uterosacral

ligaments. Drawing illustrates the relationship of thecardinal and uterosacral ligaments to the cervix.

a. b.

C.

January 1994 Foshager and Walsh U RadioGraphics #{149}55

The round ligament is a band of fibromus-

cular tissue that attaches to the anterolateral

uterine fundus just below and anterior to the

fallopian tube and anterior to the ovarian liga-

ment (Figs 1, 2) (1,2,4,6,7). It is positioned

anterolaterally in a curved course within the

broad ligament to enter the internal inguinal

ring and terminates in the labia majora (Fig 2)

(1-3,5,7). The round ligament is frequently

seen on CT scans as a thin soft-tissue band

that extends laterally from the fundus and

gradually tapers from its relatively broad baseat the uterus (9). Its appearance is variable

(Fig 3).

Figure 5. Normal cardinal ligaments. (a) CT scan

through a small, normal cervix (C) in a postmenopausal

woman shows normal, bilateral, thin, tapering cardinalligaments (arrows). An additional finding is a largeright inguinal lymph node metastasis (m) from knowncarcinoma of the vulva. (b) CT scan through a normalcervix (C) shows marked asymmetry of the cardinal hg-

aments, with the triangular left ligament (white arrow)tapering laterally toward the pelvic sidewall and theright cardinal ligament (black arrows) ending abruptlywith a wedgelike appearance. (C) CT scan through ananteflexed normal uterus and cervix (c) shows an un-common variation of the cardinal ligaments (arrows),which do not taper and have a squared appearancewhere they end in the paracervical fat.

The cardinal ligament (transverse cervical

ligament, Mackenrodt ligament) forms the

base of the broad ligament and provides the

primary ligamentous support for the uterus

and upper vagina (2,7). It extends laterally

from the cervix and upper vagina to mergewith a fascia overlying the obturator internus

muscle (Figs 1, 4) (2,7). The uterine artery

runs along its superior aspect (1). The cardi-

nat ligament is usually seen on CT scans as a

triangular soft-tissue structure with the base

of the triangle abutting the cervix and the

apex tapering toward the pelvic sidewall(10, 1 1). There is a wide variation in thickness,

shape, and contour of the normal cardinal

ligament (Fig 5).

56 #{149}Scientific Exhibit Volume 14 Number 1

Figure 6. Normal and abnormal uterosacral liga-ments. (a) CT scan through a normal cervix (C) showsthe typical appearance of uterosacral ligaments (ar-rows) tapering posteriorly from the posterolateralmargin of the cervix toward the sacrum (s). (b) CTscan of a thin 4-mm section through a normal cervix

(C) shows very fine uterosacral ligaments (arrows).

These ligaments were not identified on the standard,8-mm pelvic CT sections. s = sacrum. (C) CT scanthrough the cervix (C) in a patient who underwent

radiation therapy for squamous cell carcinoma of the

cervix shows thickening of the tissue planes of andadjacent to the uterosacral ligaments (arrows) bilater-

ally. These changes are typical after pelvic irradiationfor female genital tract cancer.

C.

Figure 7. Normal ovarian ligament. CT scan throughthe uterus (U) shows both ovaries (o) and the leftovarian ligament (arrow), which lies between theovary and the body of the uterus. Note also the nor-mal anterior location of the left round ligament (ar-rowhead).

a. b#{149}

C.

January 1994 Foshager and Walsh U RadioGraphics #{149}57

The uterosacral ligament extends posteri-

orly from the lateral cervix and vagina at the

level of the internal cervical os and forms a

curved arc toward the anterior body of the

sacrum at S-2 orS-3 (4,5,7,10,11). Its fibers

fuse medially with posterior fibers of the car-

dinah ligament (Figs 1, 4) (2,4,1 1). Although

the uterosacral ligament is only a few millime-

ters thick, it is frequently seen with high-reso-

lution CT scanners (Fig 6).

Figure 8. Normal suspensory ligament of the ovary.(a-c) Serial inferior-to-superior sections through a

large central endometrial tumor (7). (a) Scan showsthe base ofthe left round ligament (arrow). (b) Scanshows a portion of the left suspensory ligament of theovary (white arrow) posterior to the round ligament(black arrow). (C) Scan shows the normal left ovary(o) with its suspensory ligament (arrow).

The ovarian ligament (round ligament of

the ovary) extends medially from the ovary to

the uterus, just inferior and posterior to the

fallopian tubes and round ligaments (Figs 1,

2) (3,4,9). Its position varies with the ovaries.This structure is usually not identified on CT

scans (Fig 7).The suspensory ligament of the ovary (in-

fundibulopelvic ligament) occupies the lateral

aspect of the free upper edge of the broad

ligament (Fig 1) (3,4). It extends from theovary anterolaterally over the external iliac

vessels to fuse with connective tissue over the

psoas muscle (1). The suspensory ligament

transmits the ovarian artery and vein and is

rarely seen on CT scans (Fig 8) (1,3,6).

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58 #{149}Scientific Exhibit Volume 14 Number 1

Figure 9. Posteriorview of the pelvicvascular supply. Draw-

ing illustrates the

course of the uterineand ovarian bloodvessels and their re-lationships to the

pelvic viscera andligaments.

Figure 10. Detailed anterior view of the pelvic in-ternal organ vascular supply. Drawing illustrates thecourse of the uterine and ovarian arteries and veins,their branches, and their rich anastomotic networks.

Note particularly the relationship of the uterine artery

to the pelvic ureter as the ureter passes below theuterine artery.

U VASCULAR SUPPLY TO THE PELVIC

ORGANSThe paired uterine arteries provide the pri-

mary blood supply to the uterus (Figs 9, 10)

(1,7). These large arteries are branches from

the anterior (visceral) trunk of the internaliliac (hypogastric) arteries (2,3,7). The uterine

artery courses medially above the cardinalligament in the base of the broad ligament

and crosses anterior to the pelvic ureter en

route to the cervix (Fig 10) (1,3-6,12-14).

The artery divides and sends a smaller cern-

covaginal branch inferior to the vagina and

lower cervix and a larger uterine branch supe-

nor to the uterus (Figs 9, 10) (3,7,15). Each of

these branches is tortuous and forms exten-

sive vascular networks lateral to the vaginaand uterus, respectively (4,7, 14). The uterine

artery ultimately trifurcates at the upperuterus with branches to the fallopian tube,the uterine fundus, and the ovary (1,2,5).

The vagina is also supplied by vaginal arter-

ies that arise directly from the internal iliac

arteries (1). The uterine arteries, their branchesand rich anastomotic networks, and their ana-

tomic relation to the pelvic ureters can oftenbe precisely identified with high-resolutionCT scanning techniques tailored to the pelvis.The arteries, which demonstrate the most in-

tense opacification when the arterial bolus of

contrast material reaches the pelvis, enhance

along with the internal and external iliac ar-teries. The CT appearance of the uterine ar-

teries is variable (Figs 1 1, 12).

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January 1994 Foshager and Walsh U RadioGraphics #{149}59

Figure 1 1 . Normal uterine arteries. (a) CT scan at the level of the cervix (C) shows a prominent enhanced

left uterine artery (arrow) . Note the concurrent opacification of the external iliac arteries (arrowheads).

(b) CT scan obtained at a slightly higher level than a shows that the artery (arrows) courses superiorly along

the lateral aspect of the uterus (U) and lower uterine segment. (C) CT scan through a normal cervix (C) shows

a beaded appearance of the opacified right uterine artery (arrow). (d) CT scan through an anteverted uterusshows prominent enhancing uterine vessels (arrows) ascending along the lateral aspect of the uterus, where

they will eventually anastomose with branches of the ovarian vessels. These vessels most likely represent

uterine arteries, given the concurrent enhancement of the external iliac arteries (arrowheads). (Reprinted,

with permission, from reference 18.) (e) CT scan through the cervix (c) in an elderly diabetic woman shows

characteristic calcification in both uterine arteries (arrows).

a.

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60 #{149}Scientific Exhibit Volume 14 Number 1

Figure 12. Uterine arteries and their normal ana-

tomic relationship to the pelvic ureters. (a) CT scan

through a normal, anteflexed uterus (U) shows bi-lateral uterine arteries (large arrows) arcing anteri-orly over the ureters (small arrows) . This ‘ ‘uterine

artery arc sign’ ‘ is the classic anatomic relationshipof the uterine artery to the pelvic ureter. (b) CT

scan through a cervix replaced with endometrial

tumor (7) shows an arc of blood vessels (white ar-rows) completely surrounding the left ureter (black

arrow), representing the uterine artery and its vagi-nal branches. (c) CT scan obtained at the lower

uterine segment in a patient with stage IIIB cervicalcarcinoma shows bilateral prominent uterine arter-ies (white arrows) arising from the internal iliac ar-

teries (arrowheads), with the right uterine arteryarcing over an obstructed ureter (black arrow).

Venous drainage of the upper vagina, cer-

vix, uterus, and ovaries is via an extensive

plexus of thin-walled, valveless veins that lie

between the layers of the broad ligamentwithin the parametrium (1,3,5,12). This

plexus eventually forms veins that largely par-

allel the arterial blood supply (1,4,5,7). The

left ovarian vein, however, drains into the leftrenal vein instead of the inferior vena cava

(4,5). The veins and their companion arteries

can be seen on CT scans as enhancing vascu-lar networks or a plexus in the pelvic fat.

Their appearance varies from prominent yes-

sets to very delicate strands (Fig 13).

The paired ovarian arteries (gonadal arter-

ies) arise directly from the aorta just below

the origin of the renal arteries (2,3,7). Once

the ovarian artery descends to the pelvis, it

enters the broad ligament through the sus-

pensory ligament of the ovary (Figs 9, 10) and

sends multiple branches to the ovary via themesovarium (1,2,5,7). The artery continuesmedially to anastomose with the ovarian

branch ofthe uterine artery (Figs 9, 10) (1,3,5,7).This vessel is infrequently visualized, even

with high-resolution dynamic scanning tech-

niques (Fig 14).

U PELVIC VISCERA

Improved high-resolution CT scanning capa-

bihities, combined with dynamic inferior-to-

superior image acquisition, utilize the rich

vascular supply to the uterus, cervix, and va-gina to better define normal and disease pro-

cesses not previously visualized on CT scans.Endometrium and myometrium cannot yet be

differentiated from one another on CT scans.However, endometrial and myometrial

a. b.

C.

a. b.

January 1994 Foshager and Walsh #{149}RadioGraphics S 61

Figure 13. Cervical and vaginal vascular plexus.(a) CT scan through a normal cervix (c) shows a

very delicate, enhancing vascular network (arrows)along the lateral aspects of the cervix and in the hat-era! paracervical fat. (b) CT scan through a central

cervical tumor (7) surrounded by normal peripheral

cervical stroma shows a prominent bilateral, opaci-fled cervicovaginal vascular plexus (arrows) . (c) CT

scan obtained at the level of the vagina (V) shows

that the bilateral paravaginal vascular plexus (ar-rows) is prominent lateral to the rectum (r) and ad-jacent to the pelvic sidewall.

Figure 14. Ovarian vascular supply. (a) CT scan through the uterus (U) and both ovaries (o) shows an en-

hancing curvilinear vessel (arrow) along the posterior aspect of the right ovary. (b) CT scan of the same pa-

tient, obtained at a slightly higher level through the right ovary (o), shows the contrast-enhanced right ovar-ian blood vessels (arrow) in the right ovarian ligament.

a. b.

C.

Figure 15. Normal and abnormal uterus. (a) CT scan through an anteflexed uterus and a large central cer-

vical tumor (7) shows a normal contrast-enhanced uterine myometrium (m) and central endometnal cavity(e). (b) CT scan through a uterine fluid collection (f) that contains a Copper-7 intrauterine device (arrow)

(Searle Laboratories, Chicago, Ill) shows contrast enhancement ofthe myometrium (m), which helps to de-lineate a portion of the nonenhanced obstructing cervical tumor (7). (c) Dynamic CT scan through an ad-

enosquamous carcinoma of the myometrium shows a round hypoattenuating tumor (7) invading the myo-

metrium (m) and a dilated central endometrial cavity (e). (d) Delayed CT scan of the same patient showsalmost complete washout of the initial myometrial enhancement (m). Some residual focal enhancement of

62 #{149}Scientffic Exhibit Volume 14 Number 1

the mass (arrow) is seen.

enhancement helps to distinguish the endo-

metrial cavity from the uterus and aids in theidentification of lesions within the uterine

wall (Fig 1 5). The CT spectrum of normal cer-

vical and vaginal enhancement is still being

determined. It is likely that the moderatelyenhancing peripheral portion of the cervix

correlates with the fibrous stroma described

in MR imaging and pathologic correlations

(16,17). The highly enhancing inner zone is

believed to represent cervical epithelium (Fig16) (16). The intense central vaginal enhance-

ment likely corresponds to vaginal mucosa

that can be differentiated from the poorly en-

hancing vaginal wall (Fig 16) (16).

The ovaries lie tucked in the ovarian fossa

on the posterior floor of the true pelvis (1,5).

They are bordered anteriorly by the broad

ligament, mesovarium, and hilus of ovary with

its ovarian vessels; superiorly by the external

iliac vessels; posteriorly by the ureter and in-

ternal iliac vessels; and medially by the ovar-

ian ligament (Figs 1, 2) (1 ,3). These relation-

ships, as well as the internal anatomy of the

ovaries, are well delineated on CT scans (Fig17). Ovarian position is extremely variable

(3,7,10,1 1).

a. b.

a. b.

C.

January 1994 Foshager and Walsh #{149}RadioGrapbics U 63

Figure 16. Cervix and vagina. (a) Dynamic CT scan through a normal cervix shows presumed normal cen-

tral enhancement ofthe cervical epithelium (arrow). The peripheral cervical stroma enhances to a lesser de-gree (arrowhead) . (b) CT scan through the vagina at the suprapubic level shows central intense contrast en-hancement of the vaginal mucosa (black arrows) and the poorly enhancing vagina! wall (white arrows).

Figure 17. Normal ovaries. (a) CT scan through a

normal uterus (U) and a small left ovarian cyst (o)

shows the normal relationship of the pelvic ureter

(white arrow) posteriorly and the round ligament

(black arrow) anteriorly. (b) CT scan through an

anteverted uterine body (U) shows a normal right

ovary with multiple large follicles (arrows). (c) Dy-

namic CT scan through a central small cervical tu-

mor (7) shows an anatomic variation with a low p0-sition of the ovaries (o) bilaterally.

64 #{149}Scientific Exhibit Volume 14 Number 1

. CONCLUSION

Advances in CT technology and protocols tai-

bred to examination of the female pelvis

make possible precise identification of struc-

tures previously not well delineated with CT.

The utility of this knowledge in the evaluationof female pelvic abnormalities when com-

pared with ultrasound and magnetic reso-

nance imaging has not yet been definitively

studied. Transvaginal ultrasound is ideally

suited to the evaluation of the ovaries and

characterization of pelvic masses.

Knowledge of ligamentous and visceral

anatomy is currently helpful in identifying

pelvic structures and distinguishing gyneco-

logic from nongynecologic abnormalities on

CT scans. Further investigation is necessary tofully define the usefulness of the precise vas-

cular definition now available with CT and to

determine its potential usefulness in tumor

staging. It is hoped that familiarity with varia-

tions in the CT appearance of normal female

pelvic anatomy will facilitate more accurate

assessment of pelvic abnormalities.

Acknowledgments: We thank Elizabeth Ander-son, RT (R) for her assistance in image acquisition.

We also thank Helen Durgin for manuscript prepa-ration, Elizabeth Dempsey for medical illustrations,

and Rhonda Dragan for photography.

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Invited Commentary

4. Jones HW, Jones GS. Novak’s textbook of gyne-cology. 10th ed. Baltimore, Md: Williams &Wilkins, 1981; 8-15.

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14. Hoskins WJ, Perez CA, Young RC. Principles

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16. Carrington B, Hricak HM. The uterus and va-gina. In: Hricak H, ed. Mifi of the pelvis. Nor-walk, Conn: Appleton & Lange, 1991; 93-127.

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From:Robert R. Hattery, MD, Carl C. Reading, MD, Department of Diagnostic Radiology, Donald R.

Cahill, PhD, Department ofAnatomy, Mayo Clinic and Mayo Foundation, Rochester, Minnesota

The preceding article contains three basic

principles applicable to CT of the pelvis: CT

technique, image quality, and knowledge offemale pelvic anatomy. Accurate diagnoses,

staging of neoplasm, assessment of postopera-

tive changes or follow-up of a disease process

for example, are dependent on impeccabletechnique, the highest quality of images, and

recognition of normal anatomy.