DOI: 10.1148/rg.24si045507
RadioGraphics 2004;24:S133-S146
© RSNA, 2004
LOWER GENITOURINARY TRACT IMAGING |
Recognition of the Ovaries and Ovarian Origin of Pelvic Masses with CT1
Faysal A. Saksouk, MD and
Samuel C. Johnson, MD
1 From the Department of Radiology, Wayne State University School of Medicine, Harper University Hospital, and Hutzel Hospital, Detroit, Mich. Recipient of a Magna Cum Laude award for an education exhibit at the 2003 RSNA scientific assembly. Received February 13, 2004; revision requested March 17 and received May 5; accepted May 11. Both authors have no financial relationships to disclose. Address correspondence to F.A.S., 19 Lakeside Ct, Grosse Pointe, MI 48230-1906 (e-mail: fsaksouk@med.wayne.edu).
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Abstract
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Knowledge of the morphologic features and ligamentous attachments of the ovaries, the relationship of the ovary to the ureter, and the course of the ovarian vein and artery is necessary for confident recognition of the ovaries and differentiation between ovarian and nonovarian masses with computed tomography (CT). The suspensory ligament attaches the ovary to the pelvic sidewall and transmits the ovarian vein and artery. This ligament may be seen at CT as a linear or fan-shaped soft-tissue band leading to the ovary. The utero-ovarian ligament is occasionally visualized with CT as a soft-tissue band between the uterus and ovary. The ovaries are usually located anterior or anteromedial to the pelvic ureters, whereas iliac lymph nodes are lateral or posterolateral to the ureters. Therefore, an ovarian mass displaces the ureter posteriorly or posterolaterally, whereas a large lymph node mass displaces the ureter medially or anteromedially. An ovarian mass may be draped by ovarian parenchyma, thus revealing the origin of the mass. Tracking the ovarian vein from near the level of the renal vessels caudally to the pelvis leads to the suspensory ligament region and is often helpful in identifying the ovary and differentiating ovarian and nonovarian masses.
© RSNA, 2004
Index Terms: Ovary, 852.92 • Ovary, CT, 852.1211 • Ovary, neoplasms, 852.30
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:
- Describe the potential positions of the ovaries and the ovarian attachments.
- Discuss differentiation of enlarged lymph nodes from the ovaries near the pelvic sidewalls.
- Identify the ovarian origin of a pelvic mass.
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Introduction
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The ovaries are ovoid, almond-shaped structures that vary considerably in size depending on age, hormonal status, and the stage of the menstrual cycle (1). The adult ovary is about 2.5–5 cm long, 1.5–3 cm wide, and 1–2 cm thick (2,3). It is preferable to use the ovarian volume when assessing normalcy of size (3), and it is calculated with the formula for a prolate ellipse (0.523 x length x width x thickness). The normal mean ovarian volume measured with ultrasonography (US) in a large series was 3.0 mL (95% confidence interval, 0.2–9.1 mL) before menarche, 9.8 mL (95% confidence interval, 2.5–21.9 mL) in menstruating women, and 5.8 mL (95% confidence interval, 1.2–14.1 mL) in postmenopausal women (4).
Each ovary is suspended in the pelvic peritoneal cavity by three anchoring structures: the mesovarium, which anchors the ovary to the posterior surface of the broad ligament; the utero-ovarian ligament (ovarian ligament), which anchors the ovary to the uterus; and the suspensory ligament, which anchors the ovary to the pelvic sidewall (3,5–8).
However, the utero-ovarian ligament and the suspensory ligament of the ovary have variable degrees of laxity and behave more like mesenteries than as tightly fixating or rigid support structures (2,6). Consequently, the actual position and the orientation of the ovaries are variable in different patients and in the same patient at different times (9). Furthermore, the ovaries may assume unusual locations in the upper pelvis or lower abdomen, particularly in the presence of a large ovarian or extraovarian pelvic mass (2).
The variable position of the ovaries hinders their identification with computed tomography (CT). When the ovaries are located at or near the pelvic sidewalls, they are difficult to distinguish from enlarged lymph nodes. Determining the site of origin of a pelvic mass is often a challenging task, since ovarian and extraovarian masses may have similar morphologic appearances and large masses distort the pelvic anatomy. In particular, pedunculated subserosal uterine leiomyomas projecting into the adnexal region, iliac fossa, or lower abdomen can simulate solid or complex ovarian lesions (10) and some cystic leiomyomas closely resemble malignant cystic ovarian tumors (11). Differentiation between the ovarian and uterine origin of a pelvic malignancy with CT is reported to be indeterminate in 23% of patients (10). A thorough understanding of the pertinent pelvic anatomy, including the anatomic relationship between the ovaries and other pelvic structures, is essential for the confident recognition of the ovaries at CT and may facilitate identifying the ovarian origin of such pelvic masses.
In this article, we describe identification of the ovaries and ovarian masses with CT. Specific topics discussed are the pertinent anatomy, recognition of normal ovaries with CT, identifying surgically transposed ovaries, distinguishing the ovaries from enlarged lymph nodes, and identifying the ovarian origin of pelvic masses.
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Review of the Pertinent Anatomy
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Position of the Ovary
In nulliparous women, the ovary is typically located close to the lateral pelvic sidewall in a shallow peritoneal depression called the ovarian fossa (5,8,9, 12,13) and also known as the fossa of Waldeyer (14). The ovarian fossa is bounded posteriorly by the ureter and internal iliac artery, superiorly by the external iliac vein, and anteriorly by the obliterated umbilical artery (1,5,12,13) (Fig 1). During the first pregnancy, the ovaries are pulled up into the abdomen by the enlarging uterus and the stretched or widened broad ligament. After delivery, the ovaries often do not return to their original position in the pelvis and the broad ligament may remain enlarged or elongated and redundant, thus allowing more ovarian mobility (8).
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Figure 1. Illustration shows the ovarian fossa at the posterolateral pelvic sidewall. The fossa is bounded posteriorly by the ureter and superiorly by the external iliac vein. The ovary is draped by the fallopian tube, which arches over much of the ovarian surface.
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In general, the ovarian position is influenced by uterine size, ovarian size, degree of filling of the urinary bladder, degree of distention of the rectosigmoid colon, and the presence of a pelvic mass (3). However, because the mesovarium anchors the ovary to the posterior layer of the broad ligament, the normal ovary is generally located in the posterior pelvic compartment or above the uterine fundus but not between the urinary bladder and the uterus or in the anterior cul-de-sac (3). The potential ovarian locations include the adnexal regions lateral to the uterus, the posterior cul-de-sac, and superior or posterior to the uterine fundus. When the uterus is retroverted, either or both ovaries can be ventral and lateral to the uterus (2).
Broad Ligament and Ovarian Attachments
The broad ligament is a double fold of the peritoneum that extends from the lateral uterine margins to the pelvic sidewalls bilaterally and incompletely divides the true pelvis into anterior and posterior compartments (Fig 2). It is formed by the two peritoneal layers covering the anterior and posterior surfaces of the uterus. The two layers of the broad ligament are continuous with each other cephalad at the free edge, where they enclose the fallopian tube (Fig 3). The extreme lateral part of the tube (the ampulla and the fimbriated infundibulum) is not enclosed (5,8,13).
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Figure 2. Posterior view shows the broad ligament and ovarian attachments with the fallopian tube separated from the ovary. The suspensory ligament extends from the superolateral part of the broad ligament to the pelvic sidewall. The medially located utero-ovarian ligament is enclosed between the two peritoneal layers of the broad ligament.
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Figure 3. Sagittal view shows the mesovarium anchoring the ovary to the posterosuperior aspect of the broad ligament. The mesovarium is the primary route of transit for blood vessels entering and exiting the ovarian hilum.
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The mesovarium is a short, double-layered peritoneal fold that extends backward from the posterior layer of the broad ligament and attaches to the anterior border of the ovary (the mesovarian border) (Fig 3). The hilum of the ovary is located at this anterior border and is enclosed by the attachment of the mesovarium. The ovarian blood vessels and lymphatic vessels pass in between the two layers of the mesovarium and enter or exit the ovary through the hilum. In particular, the anastomotic branches of the ovarian and uterine arteries and the plexus of veins draining the ovary are located in the mesovarium (1,3,5,9,12).
The suspensory ligament of the ovary is a peritoneal fold that suspends the ovary from the posterolateral pelvic wall (15), near the brim of the true pelvis, and is derived from the superior lateral part of the broad ligament (8,16) (Figs 2, 4). It is formed by a fan-shaped band of intertwined fibromuscular fibers and the overlying peritoneum, which is thickened in this region and is elevated by the band into a triangular fold (3,7). The suspensory ligament can be 4–5 cm long (16), is attached to the tubal end of the ovary, and extends cephalad over the external or common iliac vessels to blend with the connective tissue and the peritoneum covering the psoas major muscle (1,5,7). The tubal end of the ovary usually faces the external iliac vein, and to it is also attached the ovarian fimbria of the fallopian tube (5,12). The ovarian blood vessels and lymphatic vessels pass through the suspensory ligament to reach the mesovarium and subsequently the ovarian hilum. The arterial system involutes with age to a greater extent than the venous system, and eventually the veins constitute the main component of the suspensory ligament (16).
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Figure 4. Illustration shows the suspensory ligament anchoring the ovary to the posterolateral wall of the pelvis. The typically fan-shaped ligament widens as it approaches the ovary. The ovarian blood vessels passing through it are somewhat obscured by the overlying peritoneal fold.
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The suspensory ligament has also been referred to by many authors and clinicians as the infundibulopelvic ligament (1–3,6–9,14,16). However, Netter (13) describes them as two contiguous distinct ligaments extending from the superior lateral aspect of the broad ligament; the infundibulopelvic ligament attaches the extreme lateral part of the fallopian tube (the infundibulum and ampulla) to the pelvic sidewall (13,14), whereas the suspensory ligament attaches the ovary to the pelvic sidewall and transmits the ovarian blood vessels to and from the mesovarium (13).
The utero-ovarian ligament or ligament of the ovary is a rounded fibromuscular band that extends from the uterine end of the ovary to the uterine cornu, immediately posterior and inferior to the fallopian tube, and is enclosed between the two layers of the broad ligament (3,5,7,13) (Figs 2, 5). The uterine end of the ovary usually faces the pelvic floor (5). The ovarian branches of the uterine artery and vein pass through the utero-ovarian ligament and anastomose in the mesovarium with the branches of the ovarian blood vessels (2).
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Figure 5. View from above shows the left ovary and its attachments within the true pelvis. (This view simulates the appearance of the right hemipelvis at cross-sectional imaging.) The utero-ovarian ligament extends between the ovary and uterine cornu. The suspensory ligament transmits the ovarian vein and artery near the pelvic brim.
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Ovarian Blood Vessels
The ovarian artery originates from the abdominal aorta slightly below the renal artery, courses caudally and laterally ventral to the psoas major muscle, and crosses over the external or common iliac vessels (Fig 6). It then passes through the suspensory ligament of the ovary near the pelvic brim, courses inferiorly and medially between the two layers of the broad ligament near the mesovarian border, and sends multiple branches that reach the ovarian hilum via the mesovarium (1,5,6). The artery usually has a tortuous course that is maximal near the level of the ovary (16).
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Figure 6. Illustration shows the ovarian artery and vein without the overlying peritoneum and suspensory ligament. The vessels are medial to the ureter in the upper abdomen, cross obliquely anterior to the ureter in the middle to lower lumbar region, and are lateral to the ureter in the lower abdomen and pelvis.
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The veins draining the ovary form the pampiniform plexus of veins in the mesovarium and suspensory ligament. The plexus of veins merge to usually form a single ovarian vein that leaves the pelvis along the side of the ovarian artery. In some individuals, the plexus of veins may merge to form two or more veins, but they commonly become a single vein by the time they reach the abdomen (1). The left ovarian vein drains into the left renal vein. The right ovarian vein drains into the inferior vena cava below the level of the renal vessels (1,6,8).
The ovarian artery and vein are medial to the ureter near the level of the lower renal poles, cross obliquely anterior to the ureter at about the middle to lower lumbar region, and are lateral to the ureter in the lower abdomen and pelvis. The vein is larger than the usually small-caliber artery and is typically readily identifiable lateral to it along the anterior surface of the psoas major muscle. Tracking the ovarian vein, from near the level of the renal vessels caudally to the pelvis, leads to the region of the suspensory ligament in the immediate vicinity of the ovary and can thus be most helpful in identifying the ovary and in differentiating between ovarian and nonovarian masses.
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Recognition of Normal Ovaries with CT
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The CT recognition of the ovaries is facilitated by knowledge of the morphologic features and of the relationship of the ovary to the ureter, the course of the ovarian vein and artery, and the ligamentous attachments of the ovaries.
Morphologic Features
The ovaries are ovoid parenchymatous structures that are frequently present at either side of the uterus. Their morphologic features vary with age and the hormonal status of the patient. In women of childbearing age, the majority of normal ovaries can be identified (17) and usually contain visible cystic follicles or physiologic cysts, which can be distinctly depicted as fluid-attenuation areas and are characteristic of the ovaries (Fig 7d). The ovarian parenchyma devoid of cysts, or surrounding the cystic areas, has uniform soft-tissue attenuation. When there are many minute cystic follicles, too small to be resolved, the ovary may have a low-attenuation appearance.
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Figure 7a. CT features of normal ovaries. (a) CT scan shows the ovarian blood vessels (OBV) coursing in the upper pelvis lateral to the ureters. (b) CT scan shows that the ovarian blood vessels are continuous with the suspensory ligaments (SL), which are visualized near the external iliac vessels. The left suspensory ligament is seen as a narrow soft-tissue band that demonstrates subtle widening as it approaches the ovary. U = ureter. (c) CT scan shows that the suspensory ligaments lead to the ovaries (Ov), which are typically located in the ovarian fossa and bounded by the ureters (U) and external iliac veins. SLA = ovarian attachment of the left suspensory ligament. (d) CT scan shows that the ovaries (Ov) have a characteristic morphologic appearance, with distinct cystic follicles seen in the right ovary. U = ureter.
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Figure 7b. CT features of normal ovaries. (a) CT scan shows the ovarian blood vessels (OBV) coursing in the upper pelvis lateral to the ureters. (b) CT scan shows that the ovarian blood vessels are continuous with the suspensory ligaments (SL), which are visualized near the external iliac vessels. The left suspensory ligament is seen as a narrow soft-tissue band that demonstrates subtle widening as it approaches the ovary. U = ureter. (c) CT scan shows that the suspensory ligaments lead to the ovaries (Ov), which are typically located in the ovarian fossa and bounded by the ureters (U) and external iliac veins. SLA = ovarian attachment of the left suspensory ligament. (d) CT scan shows that the ovaries (Ov) have a characteristic morphologic appearance, with distinct cystic follicles seen in the right ovary. U = ureter.
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Figure 7c. CT features of normal ovaries. (a) CT scan shows the ovarian blood vessels (OBV) coursing in the upper pelvis lateral to the ureters. (b) CT scan shows that the ovarian blood vessels are continuous with the suspensory ligaments (SL), which are visualized near the external iliac vessels. The left suspensory ligament is seen as a narrow soft-tissue band that demonstrates subtle widening as it approaches the ovary. U = ureter. (c) CT scan shows that the suspensory ligaments lead to the ovaries (Ov), which are typically located in the ovarian fossa and bounded by the ureters (U) and external iliac veins. SLA = ovarian attachment of the left suspensory ligament. (d) CT scan shows that the ovaries (Ov) have a characteristic morphologic appearance, with distinct cystic follicles seen in the right ovary. U = ureter.
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Figure 7d. CT features of normal ovaries. (a) CT scan shows the ovarian blood vessels (OBV) coursing in the upper pelvis lateral to the ureters. (b) CT scan shows that the ovarian blood vessels are continuous with the suspensory ligaments (SL), which are visualized near the external iliac vessels. The left suspensory ligament is seen as a narrow soft-tissue band that demonstrates subtle widening as it approaches the ovary. U = ureter. (c) CT scan shows that the suspensory ligaments lead to the ovaries (Ov), which are typically located in the ovarian fossa and bounded by the ureters (U) and external iliac veins. SLA = ovarian attachment of the left suspensory ligament. (d) CT scan shows that the ovaries (Ov) have a characteristic morphologic appearance, with distinct cystic follicles seen in the right ovary. U = ureter.
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Postmenopausal ovaries are small, difficult to recognize, and often not identified (17). Although small ovarian cysts can normally be seen after menopause, the ovaries in most postmenopausal women typically have featureless soft-tissue attenuation. It is unusual to find follicular activity 4–5 years after menopause, even at histologic examination (2). The ovaries in premenarchal girls are less frequently identified than in menstruating women (17). When premenarchal ovaries are visualized with CT, small cysts (<9 mm in diameter) are a common normal finding at all ages, with macrocysts (>9 mm) being evident in older girls (18).
Relationship to the Ureter
The ovary in its typical location at the ovarian fossa (Figs 1, 5, 7c) is usually anterior or anteromedial to the pelvic ureter.
Tracking the Ovarian Vein to the Ovarian Region
The ovarian vein can be readily identified with CT and followed, along the anterior surface of the psoas major muscle, to the true pelvis and often may be visualized to the level of the suspensory ligament in the immediate vicinity of the ovary (Figs 7, 8). The ovarian artery is smaller and less confidently or consistently identifiable with CT than the vein.
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Figure 8a. CT scans of normal ovaries located relatively high in the pelvis. (a) The ovarian blood vessels (OBV) are lateral to the ureters (U) in the lower abdomen. (b) The ovarian blood vessels are continuous with the suspensory ligaments (SL), which appear thicker than the vessels. (c) The suspensory ligaments lead to the ovaries (Ov), which are located near the level of the iliac fossa. The right ovary demonstrates a typical relationship to the ureter, being just anterior to it. The left ovary is not close to the ureter.
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Figure 8b. CT scans of normal ovaries located relatively high in the pelvis. (a) The ovarian blood vessels (OBV) are lateral to the ureters (U) in the lower abdomen. (b) The ovarian blood vessels are continuous with the suspensory ligaments (SL), which appear thicker than the vessels. (c) The suspensory ligaments lead to the ovaries (Ov), which are located near the level of the iliac fossa. The right ovary demonstrates a typical relationship to the ureter, being just anterior to it. The left ovary is not close to the ureter.
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Figure 8c. CT scans of normal ovaries located relatively high in the pelvis. (a) The ovarian blood vessels (OBV) are lateral to the ureters (U) in the lower abdomen. (b) The ovarian blood vessels are continuous with the suspensory ligaments (SL), which appear thicker than the vessels. (c) The suspensory ligaments lead to the ovaries (Ov), which are located near the level of the iliac fossa. The right ovary demonstrates a typical relationship to the ureter, being just anterior to it. The left ovary is not close to the ureter.
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Suspensory Ligament Leading to the Ovary
The suspensory ligament leads to the ovary (Figs 4, 5), to which it is attached, and is a good anatomic landmark for localizing the ovary (16). The suspensory ligament transmits the ovarian artery and vein and may be depicted with CT (Figs 7b, 8b), in continuity with the ovarian vessels, as a short and narrow fan-shaped soft-tissue band that widens as it approaches the ovary and is slightly thick at its ovarian attachment or as a linear band slightly thicker than the ovarian vein leading into it. This depicted ligamentous band is actually a summation of the peritoneal fold and the enclosed ovarian vessels, nerves, and fibromuscular fibers. In our experience, the suspensory ligament is more commonly identifiable with CT than the other ovarian ligamentous attachments, and recognizing it is facilitated by tracking the ovarian blood vessels caudally to the adnexa. When visualized on axial CT scans, the suspensory ligament usually extends from the ovary along the direction of the external or common iliac vessels.
Relationship to the Broad Ligament
The broad ligament and the mesovarium (Figs 2, 3) are usually not obvious at CT unless surrounded by a large amount of ascites (19) (Fig 9). In this setting, the ovaries can be seen suspended from the posterior surface of the broad ligament.
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Figure 9a. Visualization of the broad ligament with CT. (a) CT scan shows a large amount of ascites outlining the right cephalic free edge of the broad ligament (BL), where the fallopian tube is enclosed. The subtle soft-tissue structure (white arrow) extending from the posterolateral aspect of the broad ligament toward the right ovary is most consistent with the mesovarium. Ut = uterine fundus. (b) CT scan obtained just superior to a shows that the suspensory ligament attachment at the anterolateral margin of the right ovary (Ov) is contiguous to the mesovarium (white arrow in a). BL = broad ligament, M = complex mass in the left ovary.
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Figure 9b. Visualization of the broad ligament with CT. (a) CT scan shows a large amount of ascites outlining the right cephalic free edge of the broad ligament (BL), where the fallopian tube is enclosed. The subtle soft-tissue structure (white arrow) extending from the posterolateral aspect of the broad ligament toward the right ovary is most consistent with the mesovarium. Ut = uterine fundus. (b) CT scan obtained just superior to a shows that the suspensory ligament attachment at the anterolateral margin of the right ovary (Ov) is contiguous to the mesovarium (white arrow in a). BL = broad ligament, M = complex mass in the left ovary.
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Utero-ovarian Ligament
The utero-ovarian ligament (Figs 2, 5) may occasionally be visualized with CT (19) and is depicted as a short and narrow soft-tissue band extending between the uterus and ovary (Fig 10).
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Figure 10. Postmenopausal ovaries identified by means of their ligamentous attachments. CT scan shows that the ovaries (Ov) appear featureless and in an unusual position, anterolateral to the ureter (U) and next to the iliac bone. The ovaries were identified by means of the ligamentous attachment to the uterus, which is known as the utero-ovarian ligament (UOL). The left utero-ovarian ligament is visualized more clearly than the right. The uterus contains leiomyomatous calcifications.
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Identifying Surgically Transposed Ovaries
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Young patients anticipated to undergo therapeutic irradiation of the pelvis may have the ovaries surgically transposed out of the radiation field in order to preserve their function. The procedure involves mobilizing the ovary together with the suspensory ligament and the contained ovarian blood vessels (20–22). The ovaries are most commonly repositioned laterally either to the lower paracolic gutters, close to the lateral aspect of the colon near the iliac fossa level, or to the posterior intraperitoneal space in the upper pelvis, lateral or anterolateral to the psoas muscle (20). One or two large metallic surgical clips are typically affixed to each ovary to mark its location. Lateral transposition is performed in patients with cervical cancer, vaginal cancer, pelvic sarcoma, and Hodgkin disease. Midline transposition can be performed in patients with Hodgkin disease, in which case the ovaries are placed in the midline of the true pelvis and sutured to the surface of the uterus (21).
The CT identification of the surgically transposed ovaries is aided by recognizing the characteristic morphologic features of ovaries containing physiologic cysts, identifying the surgical clips marking the ovarian locations (21), and tracking the ovarian blood vessels toward the ovaries (20) (Figs 11, 12). The ovarian vessels in lateral transposition typically deviate laterally near the iliac fossa rather than coursing inferiorly into the pelvis. Familiarity with the CT features of ovarian transposition is essential in preventing diagnostic errors resulting from mistaking a featureless ovary placed close to the colon for a colonic or peritoneal mass, as well as from mistaking cystic or complex ovarian masses for peritoneal cystic lesions, abscess, hematoma, or even appendiceal mucocele (20).
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Figure 11. Surgically transposed ovary in a young patient with cervical cancer. CT scan shows the right ovary (Ov) positioned close to the colon at the level of the iliac fossa; the ovary is characterized by its multiple physiologic cysts. The laterally placed surgical clip (SC) is a marker for the ovary. In cases of lateral transposition, the ovarian blood vessels typically course laterally near the iliac fossa and lead to the suspensory ligament (SL), which is seen joining the ovary.
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Figure 12. Cysts replacing a surgically transposed ovary in a young patient with cervical cancer (same patient as in Fig 11). CT scan shows multiple cystic loculi (OC) posterior to the ascending colon. The ovarian origin of the loculi is indicated by the laterally placed surgical clip (SC), which is a marker for the surgically transposed right ovary. The ovarian vein (OBV) leading to the cystic ovary is not well visualized.
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Distinguishing the Ovaries from Enlarged Lymph Nodes
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The ovaries are intraperitoneal structures and are therefore always located internal to the parietal peritoneum (which may be seen near the pelvic sidewalls, especially when there is abundant intrapelvic fat). The lymph nodes at the pelvic sidewalls are extraperitoneal, lateral or posterolateral to the ureter (Fig 13), and closely related to the iliac vessels and sidewall musculature. A large lymph node mass at the pelvic sidewall may displace the ureter medially or anteromedially and can efface or encase the iliac vessels (Figs 14, 15) or efface the sidewall musculature (24). A large ovarian mass may displace the ureter posteriorly or posterolaterally (24). A lymph nodal metastatic mass may have a necrotic or cystic appearance (23) (Fig 15) and can be differentiated from a complex adnexal mass by recognizing the extraperitoneal location of the nodal mass, as reflected by its relationship to the ureter and pelvic sidewall structures.
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Figure 13. Differentiation of the ovaries from enlarged lymph nodes in a patient with metastatic cervical cancer. CT scan shows that the intraperitoneal ovaries (Ov) are medial to the ureters (U) and contain cystic follicles. The enlarged iliac lymph nodes (LN) are lateral to the ureters and closely related to the iliac vessels and pelvic sidewalls. SLA = ovarian attachment of the left suspensory ligament.
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Figure 14. Normal ovary and an enlarged lymph node at the pelvic sidewall in a patient with metastatic cervical cancer. CT scan shows two structures at the left pelvic sidewall. The anterior structure is identified as the ovary (Ov) because of its ovoid shape and the multiple minute cystic follicles. The posterior structure is an enlarged lymph node (LN), which slightly impresses and obscures the margin of the external iliac vein.
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Figure 15a. Cystic lymph node mass simulating an adnexal mass. CT scans show a large cystic mass between the uterus and the left pelvic sidewall. The mass was determined to be a lymph node mass (LN) because of its effacement and obscuration of the external iliac vein (EIV) and its location lateral to the ureter, which was visualized on images obtained at higher levels. These findings indicate an extraperitoneal nodal location of the mass. This impression is confirmed by identification of the cystic left ovary (Ov) just anterior to the uterine fundus. The patient was known to have cervical cancer, which is partly visualized as an area of low attenuation in b. The cystic consistency of the nodal mass is not unusual for metastatic cervical carcinoma (23).
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Figure 15b. Cystic lymph node mass simulating an adnexal mass. CT scans show a large cystic mass between the uterus and the left pelvic sidewall. The mass was determined to be a lymph node mass (LN) because of its effacement and obscuration of the external iliac vein (EIV) and its location lateral to the ureter, which was visualized on images obtained at higher levels. These findings indicate an extraperitoneal nodal location of the mass. This impression is confirmed by identification of the cystic left ovary (Ov) just anterior to the uterine fundus. The patient was known to have cervical cancer, which is partly visualized as an area of low attenuation in b. The cystic consistency of the nodal mass is not unusual for metastatic cervical carcinoma (23).
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Identifying the Ovarian Origin of Pelvic Masses
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Distinguishing ovarian from nonovarian intraperitoneal pelvic masses is aided by determining the relationship of the mass to the anatomic pelvic structures (24), including any discernible ovarian parenchyma or ligament, and the effect of the mass on the ureter. An ovarian mass not fully replacing the ovary may be draped by recognizable normal ovarian parenchyma, which reveals the true origin of the mass (Fig 16). The location of the ureter relative to a pelvic mass can be a most helpful hint to the ovarian origin of the mass (24) (Fig 17). A mass arising from an ovary in its typical location at the ovarian fossa is usually anterior or anteromedial to the ureter, and when large enough it will displace the ureter posteriorly or posterolaterally. However, a large uterine, bladder, or even bowel mass can also displace the ureter posteriorly or posterolaterally (24) (Fig 18).
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Figure 16. Pelvic cysts of ovarian origin. CT scan shows a simple cyst in each ovary. Both cysts are bordered by recognizable normal ovarian parenchyma, which indicates their ovarian origin. SLA = ovarian attachment of the right suspensory ligament.
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Figure 17a. Determining the origin of pelvic masses in a 32-year-old woman. CT scans show a complex cystic mass in the left lower pelvis, which was identified as ovarian because of its location medial to the ureter (U in a) and by recognizing the attachment of the suspensory ligament (SLA) to the mass. A structure in the right lower pelvis contains a small cystic mass; this structure was also medial to the ureter (not shown) and was confirmed to be the ovary (Ov in b) because the suspensory ligament (SL) leads to it. The bilateral cystic lesions proved to be endometriomas. ULM = uterine leiomyoma pedunculated from the fundus.
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Figure 17b. Determining the origin of pelvic masses in a 32-year-old woman. CT scans show a complex cystic mass in the left lower pelvis, which was identified as ovarian because of its location medial to the ureter (U in a) and by recognizing the attachment of the suspensory ligament (SLA) to the mass. A structure in the right lower pelvis contains a small cystic mass; this structure was also medial to the ureter (not shown) and was confirmed to be the ovary (Ov in b) because the suspensory ligament (SL) leads to it. The bilateral cystic lesions proved to be endometriomas. ULM = uterine leiomyoma pedunculated from the fundus.
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Figure 18. Posterolateral displacement of the ureter by a large myomatous uterus. CT scan shows a large leiomyomatous uterus (Ut) displacing the effaced left ureter (U) posterolaterally against the psoas muscle. The left ovary (Ov), which contains a simple cyst, is uplifted into the anterior upper pelvis away from the ureter. The ureter would be similarly displaced posterolaterally by a large adnexal, bladder, or even bowel mass.
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The unequivocal visualization of the ovarian suspensory ligament leading to and merging with a pelvic mass is a highly reliable finding that indicates the mass is ovarian. The suspensory ligament is in direct continuity with the main ovarian blood vessels but is not consistently depicted with CT as a distinct structure readily distinguishable from the ovarian blood vessels leading into it. Consequently, tracking the ovarian vein along the ventral surface of the psoas muscle caudally to the pelvis may lead to a recognizable suspensory ligament attached to an ovary or ovarian mass (Fig 19), or the ovarian vein may appear to lead directly to an ovary or ovarian mass (Fig 20) without discernible features of a ligament. In the latter situation, the location of the nondiscernible ligament is reflected by the most caudal aspect of the ovarian vein.
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Figure 19a. Tracking the ovarian vein to a recognizable suspensory ligament joining a pelvic mass in a 48-year-old woman. CT scans show a dilated left ovarian vein leading to the fan-shaped suspensory ligament (SL in b), which joins a large complex cystic mass. The tumor proved to be an ovarian mucinous adenocarcinoma. U in a = ureter.
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Figure 19b. Tracking the ovarian vein to a recognizable suspensory ligament joining a pelvic mass in a 48-year-old woman. CT scans show a dilated left ovarian vein leading to the fan-shaped suspensory ligament (SL in b), which joins a large complex cystic mass. The tumor proved to be an ovarian mucinous adenocarcinoma. U in a = ureter.
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Figure 20a. Ovarian vein leading to a pelvic-abdominal mass in a 32-year-old woman. CT scans (a obtained superior to b) show a dilated right ovarian vein, which can be tracked to the posterolateral aspect of a large cystic mass, where it appears to merge with the mass. There are no recognizable features of the suspensory ligament through which the vein passes. The tumor proved to be a mucinous intraepithelial carcinoma arising from the right ovary.
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Figure 20b. Ovarian vein leading to a pelvic-abdominal mass in a 32-year-old woman. CT scans (a obtained superior to b) show a dilated right ovarian vein, which can be tracked to the posterolateral aspect of a large cystic mass, where it appears to merge with the mass. There are no recognizable features of the suspensory ligament through which the vein passes. The tumor proved to be a mucinous intraepithelial carcinoma arising from the right ovary.
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Identification of the suspensory ligament can be very challenging, especially in the presence of very large pelvic masses (such as the one in Fig 20). Furthermore, masses arising from the fallopian tube (Fig 21) are usually difficult to distinguish from ovarian masses because of the intimate relationship of the fallopian tube to the ovary (6) and the ovarian ligamentous attachments. In particular, in some clinical practices, hydrosalpinx is a fairly common finding that is often challenging to distinguish from a cystic ovarian mass (25), especially when a normal-appearing ipsilateral ovary is not identified. Thus, it is not consistently feasible to determine, with a high degree of accuracy, whether an adnexal lesion is ovarian or tubal.
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Figure 21a. Fallopian tube lesion simulating an exophytic ovarian cyst in a 28-year-old woman. CT scans show a large cyst in the right lower abdomen and upper pelvis. The dilated right ovarian vein is tracked to the cystic right ovary (Ov in b), which is seen to border the inferior part of the cyst. Thus, the cyst was thought to be an exophytic cystic ovarian neoplasm that was probably benign. At surgery, however, the cyst was found to arise from the fallopian tube and was strongly adherent to the ovary. It was considered to be a benign tubal cyst or an unusually large hydrosalpinx.
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Figure 21b. Fallopian tube lesion simulating an exophytic ovarian cyst in a 28-year-old woman. CT scans show a large cyst in the right lower abdomen and upper pelvis. The dilated right ovarian vein is tracked to the cystic right ovary (Ov in b), which is seen to border the inferior part of the cyst. Thus, the cyst was thought to be an exophytic cystic ovarian neoplasm that was probably benign. At surgery, however, the cyst was found to arise from the fallopian tube and was strongly adherent to the ovary. It was considered to be a benign tubal cyst or an unusually large hydrosalpinx.
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In one study (26), the depiction of direct joining of the ovarian vein to a pelvic mass was identified in 92% of 108 ovarian masses and 13% of 23 subserosal uterine myomas. When used in that combined series to differentiate ovarian from uterine lesions, this CT finding indicated that the mass was ovarian with a 91% diagnostic accuracy, 97% positive predictive value, and 69% negative predictive value (26). The authors labeled the finding as the "ovarian vascular pedicle sign" and stated that the ovarian vascular pedicle anatomically comprises the ovarian vessels exiting and entering the ovary (26). However, this terminology and the associated anatomic description do not conform to the established conventional anatomy as described in the English-language references.
In fact, the mesovarium is actually the primary route of transit for blood vessels entering and exiting the ovarian hilum (3) and the anatomic main ovarian artery and vein do not directly join the ovarian hilum. Furthermore, it seems that the described ovarian vascular pedicle in two of the published images from the aforementioned series (26) corresponds to the suspensory ligament, which is in continuity with the ovarian artery and vein. Conforming to the conventional anatomy would favor calling the finding of tracking the ovarian vein to a pelvic mass the ovarian suspensory ligament sign when the ligament is recognizable at CT and the ovarian vein sign when the ligament is not discernible at CT as a distinct structure (rather than the "ovarian vascular pedicle sign").
The ovarian suspensory ligament sign appears to be more reliable than the ovarian vein sign in indicating the ovarian origin of a mass. Large nonovarian pelvic masses can abut or compress the ovarian vein and thus result in an appearance that simulates the direct joining of the ovarian vein to a pelvic mass. In the aforementioned study (26), the false-positive results associated with such an appearance were encountered with large subserosal uterine myomas measuring more than 20 cm. False-positive results can also be encountered with tubal lesions and nongynecologic masses that obscure the ovary and abut the ovarian vein, but such lesions or masses were not included in the series (26).
When the suspensory ligament is not discernible, a pelvic mass depicted directly joined by the tracked ovarian vein is most likely ovarian but can be tubal, uterine, or occasionally a nongynecologic mass. Identifying an ipsilateral ovary separate from the mass indicates a nonovarian origin, but often the ovary is obscured or is not clearly evident and identifiable (25). US is the recommended modality of choice for the initial imaging of the female pelvis (10) and for further evaluation of the uterus and adnexa when the CT findings are indeterminate. US may be particularly helpful in searching for an ipsilateral ovary distinct from a pelvic mass, in revealing the tubular nature of a hydrosalpinx or morphologic features indicative of tubal rather than ovarian disease, and in further evaluating the internal architecture of cystic ovarian masses.
Furthermore, several nonmalignant gynecologic mass lesions can be accurately characterized with US (10) and some morphologic findings associated with an increased risk for malignancy, such as solid papillary projections and septa with vascular flow, can be detected with US in cystic masses that appear featureless at CT. The size and morphology of an adnexal mass, the results of clinical assessment, and laboratory findings such as cancer antigen 125 (CA-125) level together indicate whether conservative management is prudent or aggressive surgical therapy is warranted (27). US follow-up is an option for patients treated conservatively (27), as most processes in this category are benign and many will be shown to have resolved or remained stable at repeat imaging.
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Conclusions
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The ovary and its relationship to the anatomic pelvic structures are usually well depicted with CT (19). A thorough understanding of the ovarian morphologic features and ligamentous attachments, the relationship of the ovary to the ureter, and the course of the ovarian artery and vein is necessary to confidently identify the ovaries and facilitates accurate CT interpretation of the female pelvis. In problematic cases, tracking the ovarian vein to the pelvis is often helpful in locating the region of the ovary and determining whether a pelvic mass is ovarian.
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Acknowledgments
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The authors thank Mary C. Myrand for the illustrations and photography and Mary Strawsine for assistance in preparing the manuscript. Figures 1–6 were adapted and redrawn from sources cited in the references.
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References
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- Reproductive system. In: Bannister LH, Dyson M, eds. Gray’s anatomy: the anatomical basis of medicine and surgery. 38th ed Edinburgh, Scotland: Churchill Livingstone, 1995; 1861-1880.
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- McLean JM. Embryology and anatomy of the ovaries. In: Fox H, Wells M, eds. Haines and Taylor obstetrical and gynaecological pathology. 4th ed. New York, NY: Churchill Livingstone, 1995; 673-698.
- Sawyer RW, Walsh JW. CT in gynecologic pelvic diseases. Semin Ultrasound CT MR 1988; 9:122-142.
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Abstract
LEARNING OBJECTIVES
