Special Regional Edition Asia-Pacific
September 2004

Cover Story

Role of CT expands in gynecologic cases

Ultrasound is the primary investigation for evaluation of any gynecologic disorder, for which the usual symptoms are pelvic pain, a pelvic lump, or menstrual disturbances. MR imaging is often the next most commonly used modality for problem-solving, and it is the modality of choice for the local staging of most gynecologic malignancies.

As the use of CT has grown, however, its application in gynecology has also evolved. The availability of multidetector row CT has increased the spatial resolution achievable, and it also provides isotropic multiplanar reconstructions (Figure 1). The ability to visualize complex pelvic anatomy, delineate the organ of origin, and diagnose other abdominal pathology in one examination has enhanced the use of CT in gynecology.

CT may also be performed if a gynecologic disorder is not initially suspected or if ultrasound findings are equivocal.1 This approach is especially applicable in patients presenting with acute abdomen or with longstanding nongynecologic symptoms such as pain or bowel or urinary symptoms. The latter group of patients may present to a general practitioner. Familiarity with the CT appearance of various gynecologic conditions helps in the diagnosis of these diseases.

ACUTE ABDOMEN

Awareness of several gynecologic causes of acute abdomen is important. Incidentally present findings in relation to the genital tract may mask an unrelated etiology as the cause of presentation. Signs of inflammation such as peritoneal fat stranding and nodularity, localized thickening of the peritoneal reflections, localized ileus, and regional lymphadenopathy around a particular organ help point toward the diagnosis.

In adnexal torsion, the ovary, ipsilateral fallopian tube, or both twist with the vascular pedicle, resulting in vascular compromise.2 Adnexal torsion commonly accompanies an ipsilateral ovarian neoplasm or cyst but can also occur in normal ovaries, usually in children. Ovarian torsion in children has been attributed to excessive mobility of the adnexa.1

CT findings in ovarian torsion include deviation of the uterus to the twisted side, ascites, obliteration of fat planes, and an enlarged ovary displaced from its normal location in the adnexa. Other CT imaging features include fallopian tube thickening and smooth wall thickening of the twisted adnexal cystic mass. Occasionally, the thickened tube can be traced to a complex ovarian mass with peripherally placed cystic areas (Figure 2). Uncommon imaging findings in adnexal torsion that are specific to hemorrhagic infarction include hemorrhage in the thickened fallopian tube, hemorrhage within the twisted ovarian mass, and hemoperitoneum. Early diagnosis can help prevent irreversible structural damage and may allow conservative, ovary-sparing treatment.

Hemorrhage into a corpus luteal cyst or follicular cyst may occur. If cyst rupture occurs, it may be life-threatening due to associated hemoperitoneum and hypotension. CT usually demonstrates a mixed-attenuation mass with a high-attenuation component (45 to 100 HU) in the adnexa. A fluid-fluid level may also be observed. In the case of cyst rupture, hemoperitoneum will also be present. Delayed CT may be useful in demonstrating the site of pooling of contrast-enhanced blood in the pelvis. CT is helpful in excluding other intra-abdominal diseases (e.g., ruptured hepatic adenoma) that can lead to hemoperitoneum in a young woman.1

Ruptured ectopic pregnancy (Figure 3) may have a similar clinical picture as a hemorrhagic cyst, and correlation with beta-hCG (human chorionic gonadotropin) levels to exclude this possibility is essential. If the disease is correctly diagnosed, patients with hemorrhagic ovarian cysts often do well with conservative treatment and supportive therapy, while patients with ectopic pregnancy need surgery. Chronic ectopic pregnancies may be more difficult to diagnose, and they have a greater degree of peritoneal reaction (Figure 4).

Ovarian hyperstimulation syndrome is usually iatrogenic secondary to ovarian stimulant drug therapy for infertility, but it may occur as a spontaneous event in pregnancy.1 The syndrome consists of ovarian enlargement with extravascular accumulation of exudates, leading to weight gain, ascites, pleural effusions, intravascular volume depletion with hemoconcentration, and oliguria in varying degrees. Because the enlarged follicles are often peripheral in location, the overall appearance can be that of wheel spokes, in which stromal ovarian tissue is located centrally with surrounding cysts.

Endometriosis is an important gynecologic disorder primarily affecting women during their reproductive years.3 It results from functional endometrial glands and stroma located outside the endometrium and myometrium. Small implants and adhesions are not well evaluated radiologically, and laparoscopy is performed for diagnosis and staging.

The CT manifestation of endometriomas is variable and can range from a predominantly solid to a predominantly cystic mass (Figure 5). A focal hyperattenuating area representing clot in a cystic mass has been described as a CT finding suggestive of endometrioma,1 but this is seen in only a minority (15%) of cases. Bilaterality and multiple lesions are ancillary findings that support the diagnosis with any imaging modality. Patients who have previously undergone abdominal surgery or amniocentesis may have implantation in the region of the scar with an endometrioma in the abdominal wall. On CT, an enhancing soft-tissue mass is visualized.

Pelvic inflammatory disease (PID) is one of the most common causes of acute pelvic pain in women, and imaging findings vary with the stage of disease.1 CT findings in early PID include obscuration of the normal pelvic floor fascial planes, thickening of the uterosacral ligaments, cervicitis, oophoritis, salpingitis, and accumulation of simple fluid in the endometrial canal, fallopian tubes, and pelvis. As the disease progresses, this simple fluid may become complex and the inflammatory changes may progress to frank tubo-ovarian or pelvic abscesses.4 As pyosalpinx develops, enhancing, thickened fallopian tubes filled with complex fluid and debris are seen.

In the later stages of the disease, tubo-ovarian and pelvic abscesses appear on CT as bilateral thick-walled, low-attenuation adnexal masses with thick septations, often with an associated serpiginous structure corresponding to a dilated, pus-filled fallopian tube.1 In addition, numerous other pelvic and abdominal structures, including the bowel and upper urinary tracts, can become inflamed, infected, and obstructed.

Discrete endometritis occurs most often after parturition or instrumentation, and it is the most common cause of postpartum fever.1 In endometritis, the endometrial cavity is usually thickened and distended with fluid on CT. The diagnosis should usually not be considered solely on the basis of the presence of air within the endometrial cavity. The advantage of CT over ultrasound is that it can identify associated inflammation in the parametrial soft tissues and extra-uterine pelvic abscess. The visualization of enhancing soft tissue within the endometrial cavity suggests the presence of retained products of conception.

Ovarian vein thrombosis, or thrombophlebitis, occurs most commonly in postpartum patients but may occur following pelvic surgery or pelvic trauma. It may complicate other disorders such as PID or complicate treatment of tumors with chemotherapy. In 80% to 90% of cases, the right ovarian vein is involved.1 Characteristic CT findings consist of a tubular structure with an enhancing wall and low-attenuation thrombus in the expected location of the ovarian vein. This finding should not be confused with hydroureter, acute appendicitis, or a thrombosed inferior mesenteric vein.

CT is the initial imaging modality of choice for postoperative complications such as pelvic abscess and hematoma.1 Uterine perforation resulting from dilatation and curettage or occurring after delivery may appear as an enhancing parametrial fluid collection and discontinuity of the uterus. In patients presenting with fistulae, a CT sinogram is useful in delineating the track.

PELVIC MASSES

For incidentally detected pelvic masses, it is vital to identify the organ of origin and characterize the lesion and determine its malignant potential. The only ovarian mass that can be confidently diagnosed on CT is a germ cell tumor or a dermoid. On CT, fat attenuation within a cyst, with or without calcification in the wall, is diagnostic for a mature cystic teratoma. Fat is seen more commonly than teeth or calcifications. Immature teratomas appear on CT as masses with a large, irregular solid component containing coarse calcifications and small foci of fat.5

Epithelial ovarian tumors represent 60% of all ovarian neoplasms and 85% of malignant ovarian neoplasms.5 The two most common types of epithelial neoplasms are serous and mucinous tumors. A tumor that manifests as a unilocular or multilocular cystic mass with homogeneous CT attenuation, a thin regular wall or septum, and no endocystic or exocystic vegetation is considered a benign serous cystadenoma (Figure 6). A tumor that manifests as a multilocular cystic mass that has a thin regular wall and septa or that contains liquids of different attenuation or signal intensity but has no endocystic or exocystic vegetation is considered a benign mucinous cystadenoma (Figure 7). Mucinous cystadenomas tend to be larger than serous cystadenomas at presentation.

Features that are more suggestive of benign epithelial tumors include a diameter less than 4 cm, entirely cystic components, a wall thickness less than 3 mm, lack of internal structure, and the absence of both ascites and invasive characteristics such as peritoneal disease or adenopathy.5 Imaging findings suggestive of malignant tumors include a thick, irregular wall, thick septa, papillary projections, and a large soft-tissue component with necrosis. Ancillary findings of pelvic organ invasion, implants (peritoneal, omental, or mesenteric), ascites, and adenopathy increase diagnostic confidence for malignancy.5 Features such as wall thickening, septa, and multilocularity are less reliable indicators of malignancy because they are frequently seen in benign neoplasms, particularly cystadenofibromas, mucinous cystadenomas, and endometriomas.

Fibroids, or leiomyomas, are the most common disorder of the uterus, found in more than 20% of women over the age of 30. CT is not the primary modality for diagnosing or evaluating fibroids, but fibroids are often found incidentally on CT.

Uterine enlargement with associated focal masses-which may be submucosal, intramural, or subserosal in location-and uterine contour deformity are the most common CT findings.1 Fibroids that have undergone hyaline degeneration or necrosis have a more cystic appearance, with diminished contrast enhancement and areas of low attenuation. Solid mass-type calcifications in a uterine mass are the most specific sign for a leiomyoma, but these occur in only 10% of cases. Fibroids that are subserosal in location may be confused with adnexal masses, and multiplanar imaging can help confirm a uterine rather than an adnexal origin. A degenerating fibroid may also present as an acute abdomen.

CANCER STAGING

CT is the preferred modality for staging ovarian cancer.6 MR is usually the modality of choice for all other gynecologic malignancies.7 The spread of ovarian malignancy is usually to the peritoneum and retroperitoneal nodes and bowel, all of which are better visualized using CT.

Intraperitoneal dissemination is the most common mode of tumor spread in ovarian cancer, with approximately 70% of patients having peritoneal metastases at staging laparotomy. The three most commonly involved sites found at laparotomy are the greater omentum, right subphrenic region, and pouch of Douglas (Figure 8). Thickening, nodularity, and enhancement are all signs of peritoneal involvement. Ovarian cancer may also metastasize through the lymphatic system.

For more advanced disease with hematogenous dissemination, which is the least common mode of tumor spread in ovarian cancer, the most common site of involvement is the liver, followed by the lung. Other locations include the brain, bone, adrenal gland, kidney, and spleen. CT can be used effectively to image these areas. Research suggests MR and CT show similar sensitivity in staging disease.8 Currently, however, no imaging modality allows microscopic spread of disease to be ruled out, and a full staging laparotomy is always required.6 CT is also excellent for follow-up of patients with ovarian cancer (Figure 9).

Krukenberg tumors are bilateral metastatic solid ovarian masses that form primary cancers in the stomach (Figure 10), breast, gallbladder, and colon.

Invasive cervical cancer is the third most common gynecologic malignancy.9 Prognosis is based on the stage, size, and histological grade of the primary tumor and the status of the lymph nodes. Assessment of the stage of disease is important in determining whether the patient may benefit from surgery or should receive radiation therapy.

MR is the modality of choice for evaluation of local disease. Visualization of the primary tumor is limited on CT, and it is now used mostly in staging cases of advanced disease and in monitoring patients for recurrence. CT and MR urography are also indicated in diagnosing hydronephrosis associated with cancer invasion, para-aortic lymph node metastases, or other distant metastases.7 Distant metastases are seen with primary or recurrent disease and can involve the liver, lung, and bone, for which CT is useful.

For other gynecologic malignancies, CT is not indicated and is used only for advanced or metastatic disease evaluation.

The wide availability of CT scanners worldwide and their high usage in clinical practice will result in both incidental and requested gynecologic studies. Radiologists and others need to be aware of the appearances of various pathologies using this modality.

Dr. Aggarwal, Dr. Rajan, and Dr. Gothi are consultant radiologists at the Diwan Chand Satyapal Aggarwal Imaging Research Centre in New Delhi, India. Assisting in the preparation of this manuscript were Ajay Aggarwal, MBBS, M.D., and Mihir Munshi, MBBS. This article is based on a presentation made at the 10th Asian Oceanian Congress of Radiology, held in Singapore in April.

References

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2. Rha SE, Byun JY, Jung SE, et al. CT and MR imaging features of adnexal torsion. Radiographics 2002;22:283-294.

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4. Sam JW, Jacobs JE, Birnbaum BA. Spectrum of CT findings in acute pyogenic pelvic inflammatory disease. Radiographics 2002;22:1305-1325.

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6. Okamoto Y, Tanaka YO, Nishida M, et al. MR imaging of the uterine cervix: imaging-pathologic correlation. Radiographics 2003;23:425-445.

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8. Tempany CMC, Zou KH, Silverman SG, et al. Staging of advanced ovarian cancer: comparison of imaging modalities (report from the Radiological Diagnostic Oncology Group). Radiology 2000;215:761-767.