CT anatomy of the female pelvis: a second look.
Transcription
CT anatomy of the female pelvis: a second look.
CT Anatomy of the Female Pelvis: A Second Look1 Mary C. Foshager, James W. Walsh, MD MD Computed tomography (CT) remains a valuable technique in the assessment of the female pelvis. The CT appearance of the normal ligamentous, vascular, and visceral anatomy of the female pelvis can be confusing. Newer high-resolution CT scanners combined with mechanical intravenous contrast medium injectors and thinner sections have substantially improved the imaging of female genital tract anatomy. 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. Inferiorto-superior image acquisition following bolus administration of intravenous contrast material with an angiographic injector facilitates precise identification of the uterine artery and its relationship to the pelvic ureter and the vascular plexus supplying the vagina, ovaries, and uterine body. Ideally, familiarity with variations in the CT appearance of normal female pelvic anatomy will enable more accurate evaluation 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 familiar with the basic anatomy of these structures and normal variations in their appearance. High-resolution CT scanners and techniques tailored to examination of the pelvis now permit detailed visualization of the ovaries, uterus, and cervix, as well as precise identification of their ligamentous attachments and vascular supply. In this article, genitalia Index we review the normal and discuss techniques terms: Computed neoplasms. 1994; the Received ‘ 85. 12 1 18 #{149} Pelvic organs. 85. 12 1 18, 85.92 #{149} Pelvic organs, ofDiagnostic MN Recipient February 55455. 12, 1993; Radiology, ofa revision Cum requested University Laude ofMinncsota award March for a scientific 26 and received Hospital. exhibit July Box at the 14; accepted 292 UMIIC, 420 1992 RSNA scientific July 15. Address Delaware St SE. assembly. reprint re- to M.C.F. RSNA, See thin-section, of the female internal of these structures. 14:51-66 Department Minneapolis. quests (CT), and CT appearance facilitate visualization 85.32 RadioGraphics From tomography anatomy that 1994 the commentary by flattery et al following this article. 51 Figure 1. Posterior view of the female ligaments and viscera. Drawing illustrates the broad, round, cardinal, uterosacral, and ovarian ligaments and their relationships to the ovaries, and uterus, pelvic ureters. U PATIENT POPULATION AND IMAGING TECHNIQUES CT images were selected from a review of 135 pelvic CT examinations performed on 125 women ranging in age from 22 to 83 years. A group 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) underwent imaging performed with two different scanners. Diagnoses in the patients with abnormal findings were cancer of the ovary, endometrium, 52 U Scientific Exhibit cervix, vagina, and vulva. All images were acquired with a Somatom Plus CT scanner with an Impress detector system (Siemens, Iselin, NJ) or a GE 9800 Quick CT scanner (Milwaukee, Wis). All studies utilized a tailored pelvis protocol consisting of (a) a bolus intravenous injection of 100-150 mL of 60% iodinated contrast material administered 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) delayed 2-5-mm sections through the pelvic abnormality or region of interest; and (d) oral administration of 750 mL of 2% barium during the 2 hours before the examination to optimize colonic opacification at image acquisition. Volume 14 Number 1 Figure 2. Axial view of the female pelvic viscera and ligaments at the level of the uterme body. Drawing illustrates the uterine body and the ovaries to the round, broad, and their relationships and ovarian ligaments. The purpose of the tailored pelvis protocol fivefold: (a) to help differentiate pelvic blood vessels from lymph nodes and parametrial tumor extension; (b) to enhance uterine myometrium and epithelium and delineate the endometrial cavity; (c) to enhance the cervical stroma and epithelium; (d) to demarcate tumor from normal uterine and cervical parenchyma; and (e) to opacify the bladder and pelvic ureters, further delineate abnor- edge is formed by the fallopian tube medially and the suspensory ligament of the ovary laterally (2,4-6). The lower margin of the broad ligament ends at the cardinal ligament (Fig 1). malities, sets, mesonephric remnants, and a portion of the ureter (1,2,7,8). Although the broad ligament is rarely seen unless ascites is present, was and ing on delayed U PELVIC extend January thin partial volume averag- sections. LIGAMENTS The broad peritoneum, sidewall eliminate ligament is formed by two layers of which drape over the uterus and laterally from the uterus to the pelvic (Figs 1 , 2) (1-5). The superior free 1994 Between is loose the two leaves of the extraperitoneal broad connective ligament tissue, smooth muscle, and fat known as the parametrium, which contains the fallopian tube, round ligament, ovarian ligament, uterine and ovarian blood vessels, nerves, lymphatic yes- its position that it abuts can or be determined by structures contains. Foshager and Walsh #{149} RadioGraphics #{149} 53 i; a. Figure 3. Normal round ligaments. (a) CT scan the uterus (U) and a right ovarian cyst (0) shows normal round ligaments bilaterally (black arrows). The left ligament tapers distally (small white arrow), where it crosses the left external iliac artery and vein anteriorly (large white arrows). (b) CT scan through an enlarged uterus (U) shows fine round ligaments (small white arrows) that cross anteriorly toward the inferior epigastric vessels (large white arrow), where the ligaments enter the internal inguinal ring. The necrotic cavity (N) and metastatic right obturator lymph node (L ) are due to recurrent cervical carcinoma. (c) CT scan through the uterus (U), normal pelvic ureters (white arrows), and right ovary (o) shows a normal asymmetric left round ligament (black arrows) resulting from a variation in uterine position. Note the triangular shape of this round ligament, with gradual distal tapering. through .,.,. .. :. . . .,. ‘I , I .c .\ Figure 4. Axial view of the cardinal and uterosacral ligaments. Drawing illustrates the relationship of the cardinal and uterosacral ligaments to the cervix. 54 U Scientific Exhibit Volume 14 Number 1 a. b. Figure through woman 5. Normal cardinal ligaments. (a) CT scan a small, normal cervix (C) in a postmenopausal shows normal, bilateral, thin, tapering cardinal ligaments (arrows). An additional finding is a large right inguinal lymph node metastasis (m) from known carcinoma of the vulva. (b) CT scan through a normal cervix (C) shows marked asymmetry of the cardinal hgaments, with the triangular left ligament (white arrow) tapering laterally toward the pelvic sidewall and the right cardinal ligament (black arrows) ending abruptly with a wedgelike appearance. (C) CT scan through an anteflexed normal uterus and cervix (c) shows an uncommon variation of the cardinal ligaments (arrows), which do not taper and have a squared appearance where they end in the paracervical fat. C. The round ligament is a band of fibromuscular tissue that attaches to the anterolateral uterine fundus just below and anterior to the fallopian tube and anterior to the ovarian ligament (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 base at the uterus (9). Its appearance is variable (Fig 3). January 1994 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 merge with a fascia overlying the obturator internus muscle (Figs 1, 4) (2,7). The uterine artery runs along its superior aspect (1). The cardinat 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). Foshager and Walsh U RadioGraphics #{149} 55 6. Normal and abnormal uterosacral ligaments. (a) CT scan through a normal cervix (C) shows the typical appearance of uterosacral ligaments (arrows) tapering posteriorly from the posterolateral margin of the cervix toward the sacrum (s). (b) CT Figure scan (C) of a thin 4-mm shows very fine section uterosacral through a normal cervix ligaments (arrows). These ligaments were not identified on the standard, 8-mm pelvic CT sections. s = sacrum. (C) CT scan through the cervix (C) in a patient who underwent radiation cervix therapy shows adjacent ally. These for female for squamous thickening to the uterosacral cell of the tissue ligaments changes are typical genital tract cancer. after carcinoma of the planes of and (arrows) pelvic bilater- irradiation C. Figure 7. Normal ovarian ligament. CT scan through the uterus (U) shows both ovaries (o) and the left ovarian ligament (arrow), which lies between the ovary and the body of the uterus. Note also the normal anterior location of the left round ligament (arrowhead). 56 #{149} Scientific Exhibit Volume 14 Number 1 a. b#{149} 8. Normal suspensory ligament of the ovary. Serial inferior-to-superior sections through a large central endometrial tumor (7). (a) Scan shows the base ofthe left round ligament (arrow). (b) Scan shows a portion of the left suspensory ligament of the ovary (white arrow) posterior to the round ligament (black arrow). (C) Scan shows the normal left ovary Figure (a-c) (o) with the The uterosacral from the ligament lateral extends cervix and posteri- 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 dinah ligament with (Figs posterior the uterosacral ligament ters thick, it is frequently lution CT scanners (Fig January 1994 fibers 1, 4) (2,4,1 of the ligament (arrow). The ovarian ligament (round ligament of 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 (infundibulopelvic ligament) occupies the lateral aspect of the free upper edge of the broad ligament (Fig 1) (3,4). It extends from the ovary anterolaterally over the external iliac C. orly its suspensory vessels to fuse with connective tissue over psoas muscle (1). The suspensory ligament transmits the ovarian artery and vein and rarely seen on CT scans (Fig 8) (1,3,6). the is car- 1). Although is only a few millimeseen with high-reso6). Foshager and Walsh U RadioGraphics #{149} 57 Fo1 1 Figure 9. Posterior view of the pelvic vascular supply. Drawing illustrates o=Vk( the course of the uterine and ovarian blood vessels and their relationships pelvic 1!’ \ u. uw*. Aflsry k w wd to the viscera F and ligaments. Figure ternal course their Note 10. Detailed organ vascular of the uterine branches, particularly anterior view of the pelvic insupply. Drawing illustrates the and ovarian arteries and veins, and their rich anastomotic the relationship of the to the pelvic ureter uterine artery. as the ureter passes networks. uterine artery below the U VASCULAR SUPPLY TO THE PELVIC ORGANS The paired uterine arteries provide the primary blood supply to the uterus (Figs 9, 10) (1,7). These large arteries are branches from the anterior (visceral) trunk of the internal iliac (hypogastric) arteries (2,3,7). The uterine artery courses medially above the cardinal ligament 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 cerncovaginal branch inferior to the vagina and lower cervix and a larger uterine branch supenor to the uterus (Figs 9, 10) (3,7,15). Each of these branches is tortuous and forms extensive and vascular uterus, artery ultimately trifurcates at the upper with branches to the fallopian tube, uterine fundus, and the ovary (1,2,5). uterus the 58 #{149} Scientific Exhibit networks respectively lateral (4,7, to the vagina 14). The uterine The ies that vagina arise is also directly supplied from by vaginal the internal arteriliac arteries (1). The uterine arteries, their branches and rich anastomotic networks, and their anatomic relation to the pelvic ureters can often be precisely identified with high-resolution CT scanning techniques tailored to the pelvis. The arteries, which demonstrate the most intense opacification when the arterial bolus of contrast material reaches the pelvis, enhance along with the internal and external iliac arteries. The CT appearance of the uterine arteries is variable (Figs 1 1, 12). Volume 14 Number 1 Figure 1 1 . Normal uterine arteries. (a) CT scan at the level of the left uterine artery (arrow) Note the concurrent opacification of the (b) CT scan obtained at a slightly higher level than a shows that the the lateral aspect of the uterus (U) and lower uterine segment. (C) a beaded appearance of the opacified right uterine artery (arrow). . cervix (C) shows a prominent enhanced external iliac arteries (arrowheads). artery (arrows) courses superiorly along CT scan through a normal cervix (C) shows (d) CT scan through an anteverted uterus shows 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). i;” ‘, - . .. . ..:--‘#{149}-. a. c&!*1 . b. e. January 1994 Foshager and Walsh U RadioGraphics #{149} 59 a. 12. Figure tomic Uterine relationship arteries and their to the pelvic ureters. through a normal, anteflexed lateral uterine arteries (large orly over ureters artery arc sign’ ‘ is the of the uterine artery scan through a cervix tumor (7) shows rows) completely arrow), nal the arrows) classic (c) uterine segment carcinoma shows shows biarcing anteri- (U) . This anatomic ‘ ‘uterine I. relationship to the pelvic ureter. (b) CT replaced with endometrial an arc of blood surrounding representing branches. (small uterus arrows) normal ana(a) CT scan vessels the the uterine CT scan obtained (white ar- left ureter (black artery and its vagiat the lower in a patient with stage IIIB cervical bilateral prominent uterine arter- ies (white arrows) arising teries (arrowheads), with arcing over an obstructed ‘V from the internal iliac arthe right uterine artery ureter (black arrow). Venous drainage of the upper vagina, ceruterus, and ovaries is via an extensive plexus of thin-walled, valveless veins that lie between the layers of the broad ligament within the parametrium (1,3,5,12). This vix, plexus eventually forms veins that largely parallel the arterial blood supply (1,4,5,7). The left ovarian vein, however, drains into the left renal vein instead of the inferior vena cava (4,5). The veins and their companion arteries can be seen on CT scans as enhancing vascular networks or a plexus in the pelvic fat. Their appearance varies from prominent yessets to very delicate strands (Fig 13). The paired ovarian arteries (gonadal arteries) arise the the origin ovarian directly from the aorta just below of the renal arteries (2,3,7). Once artery descends to the pelvis, it enters the broad ligament through the suspensory ligament of the ovary (Figs 9, 10) and sends multiple branches to the ovary via the mesovarium (1,2,5,7). The artery continues medially 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 techniques (Fig 14). U PELVIC Improved bihities, VISCERA high-resolution combined with CT scanning dynamic capa- inferior-to- superior image acquisition, utilize the rich vascular supply to the uterus, cervix, and vagina to better define normal and disease processes not previously visualized on CT scans. Endometrium and myometrium cannot yet be differentiated from one another on CT scans. However, endometrial and myometrial 60 #{149} Scientific Exhibit Volume 14 Number 1 a. b. 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 hatera! paracervical cervical tumor (7) fat. (b) CT scan through surrounded by normal cervical stroma shows a prominent fled cervicovaginal vascular plexus scan obtained at the level of the that the bilateral paravaginal rows) is prominent lateral jacent to the pelvic a central peripheral bilateral, (arrows) vagina (V) . opaci(c) CT shows vascular plexus (arto the rectum (r) and ad- sidewall. C. a. Figure b. 14. Ovarian vascular supply. (a) CT scan through the uterus (U) and both ovaries (o) shows an enhancing curvilinear vessel (arrow) along the posterior aspect of the right ovary. (b) CT scan of the same patient, obtained at a slightly higher level through the right ovary (o), shows the contrast-enhanced right ovarian blood vessels (arrow) in the right ovarian ligament. January 1994 Foshager and Walsh #{149} RadioGraphics S 61 a. b. C. Figure 15. Normal and abnormal uterus. (a) CT scan through an anteflexed uterus and a large central cervical 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 delineate a portion of the nonenhanced obstructing cervical tumor (7). (c) Dynamic CT scan through an adenosquamous carcinoma of the myometrium shows a round hypoattenuating tumor (7) invading the myometrium (m) and a dilated almost complete washout the mass (arrow) is seen. enhancement metrial cavity helps from identification of lesions wall (Fig vical and determined. enhancing correlates central endometrial of the initial myometrial to distinguish the uterus and within the endoaids in the uterine 1 5). The CT spectrum of normal cervaginal enhancement is still being It is likely that the moderately peripheral portion of the cervix with the fibrous stroma described in MR imaging and pathologic (16,17). The highly enhancing believed 16) (16). the cavity (e). (d) enhancement to represent The intense cervical central inner zone is epithelium (Fig vaginal enhance- its ovarian ships, patient focal shows enhancement superiorly posteriorly vessels; (Figs as well of by the by the external ureter and in- and medially by the ovar1, 2) (1 ,3). These relation- as the are well Ovarian (3,7,10,1 Exhibit of the same residual vessels; ternal iliac ian ligament 17). #{149} Scientffic Some vessels; ovaries, 62 CT scan (m). ment likely corresponds to vaginal mucosa that can be differentiated from the poorly enhancing 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 iliac correlations Delayed internal delineated position anatomy of the on CT scans is extremely (Fig variable 1). Volume 14 Number 1 a. b. Figure 16. Cervix and vagina. (a) Dynamic CT scan through a normal cervix shows presumed normal central enhancement ofthe cervical epithelium (arrow). The peripheral cervical stroma enhances to a lesser degree (arrowhead) . (b) CT scan through the vagina at the suprapubic level shows central intense contrast enhancement of the vaginal mucosa (black arrows) and the poorly enhancing vagina! wall (white arrows). b. a. 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) Dynamic CT scan through a central small cervical tu- mor (7) shows an anatomic variation sition of the ovaries (o) bilaterally. with a low p0- C. January 1994 Foshager and Walsh #{149} RadioGrapbics U 63 . CONCLUSION Advances in CT technology and protocols taibred to examination of the female pelvis make possible precise identification of structures previously not well delineated with CT. The utility of this knowledge in the evaluation of female pelvic abnormalities when compared with ultrasound and magnetic resonance imaging has not yet been definitively studied. Transvaginal ultrasound is ideally suited to the evaluation of the ovaries and characterization of pelvic Knowledge and We also thank ration, and We thank RT (R) for her Helen Elizabeth Rhonda assistance Durgin Dempsey Dragan Elizabeth in image Ander- 5. 7. 8. 10. 11. . 13. 14. prepa- illustrations, for photography. REFERENCES 1. Gardner E, Gray DJ, O’Rahilly R. Philadelphia, Pa: Saunders, 1960; 609. 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It is hoped that familiarity with variations in the CT appearance of normal female pelvic anatomy will facilitate more accurate assessment of pelvic abnormalities. son, Jones masses. of ligamentous Acknowledgments: 4. 17. il- 18. Mass: 83-104. Pa: Lippincott, 1992; 447-448, 591-592. Meschen I. An atlas ofanatomy basic to radiology. Philadelphia, Pa: Saunders, 1975; 10831095. Carrington B, Hricak HM. The uterus and vagina. In: Hricak H, ed. Mifi of the pelvis. Norwalk, Conn: Appleton & Lange, 1991; 93-127. LeeJKT, Gersell DJ, Balfe DM, WorthingtonJL, Picus D, Gapp G. The uterus: in vitro MR-anatomic correlation of normal and abnormal specimens. Radiology 1985; 157:175-179. Walsh JW. Computed tomography of the pelvis. In: Haaga JR, ed. CT and MIII of the whole body. 3rd ed. St Louis, Mo: Mosby-Year Book (in press). Commentary From: Robert R. Hattery, Cahill, PhD, MD, Department The preceding article principles applicable Carl C. Reading, MD, Department ofAnatomy, Mayo Clinic and contains three basic to CT of the pelvis: CT technique, image quality, and knowledge female pelvic anatomy. Accurate diagnoses, 64 #{149} Scientific Exhibit of of Diagnostic Mayo Foundation, Radiology, Rochester, Donald R. Minnesota staging of neoplasm, assessment of postoperative changes or follow-up of a disease process for example, are dependent on impeccable technique, the highest quality of images, and recognition of normal anatomy. Volume 14 Number 1