Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

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yet even brain metastatic is curable in about 50% with chemotherapy and irradiation.

The role of imaging is to detect local and distal spread. Myometrial invasion is identified as small, mostly hyperechoic nodules, better seen with endovaginal than transabdominal US. At times Doppler US detects diffuse myometrial invasion by identifying hypervascularity and low-impedance blood flow. Coronal MR is useful to identify the nodules’ location. Distal spread is evaluated by head CT, chest radiographs, and other appropriate imaging.

Placental Site Trophoblastic Neoplasm

A placental site trophoblastic neoplasm readily infiltrates the myometrium and leads to vascular dilation, visualized by Doppler US as cystic spaces representing blood vessels. The role of MR in this condition is speculative, although a tumor and myometrial invasion can be identified.

With failed initial systemic chemotherapy for metastatic trophoblastic neoplasm, selective chemoembolization is occasionally successful.

endometriosis. Serum hormone levels and US during ovarian cycles identify some of these causes. Impaired uterine blood perfusion can also result in infertility. Aspirin improves uterine perfusion in those women found to have impaired perfusion during their menstrual cycles, as detected with Doppler US.

Ectopic pregnancies do develop after in vitro fertilization. Fallopian tube disease appears to be the main risk factor for ectopic pregnancy after in vitro fertilization.

Use of US-guidance for embryo transfer appears to improve pregnancy rates by optimizing placement of embryos. Implantation rates with US guidance were 29% versus 18% without US-guidance, while the corresponding pregnancy rates in cycles with easy transfers were 63% versus 36% (28).

Sonohysterography combined either with sonosalpingography or sonohysterosalpingography in infertile women achieved a diagnostic accuracy of 98% in detecting submucosal fibroids, 96% for polyps, and 81% for synechiae (29); tubal patency was correctly assessed in 79% with a saline solution and in 92% when using a contrast agent.

Ovarian Hyperstimulation Syndrome

Ovarian hyperstimulation syndrome develops if the ovaries are overstimulated by either medication or idiopathic. Fertility medications stimulate follicle maturation and result in multiple large follicles. Some of these ovaries enlarge to the point that they are palpable. They are readily detected by transabdominal US. Sufficient fluid transudation from follicles manifests as ascites. Pregnancy makes the syndrome worse. It is a potentially life-threatening complication.

The ovarian hyperstimulation syndrome develops during assisted reproduction; elevated serum estradiol levels and retrieved oocyte numbers suggest the ovarian hyperstimulation syndrome, but neither parameter by itself is pathognomonic.

Infertility-Related Conditions

Ovarian causes of infertility include anovulation due to follicular atresia or polycystic disease, empty follicle or unruptured follicle syndromes, chronic anovulation, and ovarian

Tumors

Differential Diagnosis of

Adnexal Tumors

After detecting an adnexal tumor, the primary tasks of imaging are to establish its site of origin and then determine whether it is cystic or solid.

Considerable controversy ensued in the 1990s about whether endovaginal US or MRI was the preferred initial imaging modality in evaluating adnexal tumors. As an example, in women with adnexal tumors, endovaginal US was found superior for simple cysts, hemorrhagic cysts, endometriomas, and ovarian carcinomas; MRI was found superior for dermoids; and both were equally effective for pedunculated fibroids (30). Further advances in equipment and software have rendered many of these and similar conclusions obsolete.

In general, endovaginal US findings are more accurate than those obtained with transabdominal US, although the latter provides a wider overall view. Doppler US is more sensitive in

women with adnexal tumors than gray-scale US; malignant tumors tend to be vascular and have a lower PI and RI than benign neoplasms and inflammatory tumors, yet sufficient overlap exists to make this Doppler US finding of limited clinical use. Serum CA 125 levels achieve high specificity in differentiating malignant from benign tumors.

The prevalence of malignancy in adnexal tumors is considerably greater in postmenopausal women than in premenopausal. Benign versus malignant differentiation of any one adnexal tumor with imaging is imprecise. Many benign and malignant tumors contain a cystic component. As a rough initial differentiation, a completely cystic tumor is most likely benign, while the presence of a solid component raises the possibility of a malignancy. In fact, the most significant US criterion for malignancy is presence of a solid component and ascites. Necrosis in a solid tumor and nodules in a cystic tumor detected with postcontrast MRI suggest a malignancy (31).

Endovaginal US of adnexal tumors achieves a high sensitivity but low specificity for identifying solid tissue within a partly cystic tumor, with false-positive US results being due to the presence of blood and other debris. Postcontrast MRI, on the other hand, differentiates between tumor and blood and achieves high sensitivity and specificity.

The differential diagnosis of adnexal tumors is best approached by subdividing into those found in premenopausal and postmenopausal

ADVANCED IMAGING OF THE ABDOMEN

women.Adnexal tumors during pregnancy were discussed in a previous section.

Premenopausal

A majority of adnexal tumors in premenopausal women are benign. Simple cysts, in particular, are benign and often resolve. The differential includes inflammatory tumors, ectopic pregnancy, functional cysts, and (benign and malignant) neoplasms (Table 12.4). An imaging finding of a cystic component includes in the differential a nonneoplastic cyst, most often a functional cyst, and a cystic neoplasm. Follicular cysts are the most common functional cyst, and most resolve within several months. Benign complex cysts include hemorrhagic cysts and endometriomas.A mature cystic teratoma is also in the differential diagnosis of cystic neoplasms in a premenopausal woman.

Ovarian tumors in girls tend to be large when first detected; an exception is with tumors having endocrine activity.

A follow-up US study in about 6 weeks appears reasonable for a complex adnexal cystic tumor detected by US in a premenopausal woman; if unchanged in size or larger, exploration is indicated.

Cystic malignant neoplasms have thick septa and varying amounts of a solid component, findings lacking in most benign tumors. Also, Doppler US reveals increased blood flow and lower pulsatility and resistance indexes in malignant neoplasms.

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Postmenopausal

An adnexal tumor in a postmenopausal woman is generally considered to be malignant until proven otherwise and resection is warranted, especially if associated with an elevated CA-125 level.

Ultrasonography detection of a simple cystlike tumor in a postmenopausal woman raises a management dilemma. While most of these cysts are benign,an occasional one is malignant. One option is to follow smaller cysts (about 5cm or less in diameter) with serial imaging and resect those showing any evidence of enlargement. Larger ones generally are resected. A complex cyst or solid tumor detected by US is assumed to be malignant; preoperative CT (or, perhaps even more appropriate, MRI) is useful for staging.

With a known previous nongynecologic malignancy, differential diagnosis of an adnexal tumor also includes a metastasis. Among women with breast cancer and US-detected adnexal tumors, histopathologic study revealed 74% to have benign adnexal disease and 26% malignant—of the latter half were primary ovarian cancers and half breast metastases (32). Similarly, with a history of colorectal carcinoma and a new adnexal tumor, a majority of these tumors are metastatic colon cancers rather than primary ovarian neoplasms.

What imaging tests are appropriate in a woman with a clinically asymptomatic suspicious adnexal mass detected by screening US? Endovaginal US, MRI, and PET achieved sensitivities of 92%, 83%, and 58%, respectively, and specificities of 59%, 84%, 78%, respectively, in tumor characterization (33); MRI using contrast-enhanced fat-saturated T1-weighted sequences was especially useful with dermoid cysts and endometrial cysts, but all three modalities revealed uncertainty with borderline tumors. The high sensitivity of endovaginal US argues for this modality as the next test in this clinical setting.

Major MRI findings pointing towards malignancy are ascites and nodules on the wall and septum of a cystic tumor (34); other features associated with malignancy include a part solid-part cystic tumor, irregular tumor wall, a large tumor and early contrast enhancement.

Some tumors are difficult to differentiate between an ovarian and a subserosal uterine

origin. Presence of an ovarian vascular pedicle for a tumor, detected with helical CT, confirms an ovarian origin with a high degree of sensitivity (35).

Endometriosis

Clinical

Endometrial tissue in an ectopic location outside the uterus, called endometriosis, and involving ovaries, fallopian tubes, and adjacent structures is discussed here. Endometriosis at more distal sites is discussed in each corresponding chapter. Endometrial tissue invading the uterine myometrium is known as adenomyosis and is covered later in this chapter. Some authors label uterine endometrial tissue as endometriosis interna and endometrium outside the uterus as endometriosis externa, or simply as pelvic endometriosis. Endometriosis often involves multiple pelvic sites, presenting as adnexal tumors.

Although several pathogenetic mechanisms have been proposed, transtubal retrograde dissemination appears to be the most likely mechanism in a majority of women; an increased prevalence occurs in a setting of obstructed normal menstrual outflow. Vascular, lymphatic, and mechanical spread during surgery probably also play an occasional role. Endometriosis has developed in a surgical scar, especially after a cesarean section or hysterectomy. It is estrogen dependent. In the absence of hormone replacement therapy and obesity, symptomatic endometriosis is rare in postmenopausal women. The immunologic factors involved in endometriosis constitute an active research field.

The prevalence of endometriosis is about 10% to 20% in menstruating women. It ranges from diffuse to focal, with the latter known as an endometrioma, and can develop anywhere in the abdomen, including abdominal wall, inguinal canal, umbilicus, or surgical scar. Endometriosis of the mesentery, omentum, or bowel wall is less common than peritoneal involvement. Prevalence of endometriosis is increased in women with a cystic mesothelioma and in a setting of disseminated leiomyomatosis. Endometriosis is one of the causes of bloody ascites, in an occasional patient evolves in peritonitis and eventually evolves into scarring. A

rare endometrioid carcinoma develops at a scar endometriosis site. Ectopic endometrial tissue bleeds during menses, is surrounded by inflammation, and eventually fibrosis develops. Pain and infertility are the most common presentations. Nevertheless, symptoms are not always cyclic and often are nonspecific. In fact, an incidentally detected focus of extrauterine endometrial tissue in an otherwise asymptomatic and fertile woman is not uncommon.

Traditionally, laparoscopy is the primary study in patients with suspected endometriosis, being supplanted in a number of institutions by MR as the initial study, which also serves as a guide to subsequent laparoscopy and histologic confirmation.

Percutaneous endometrioma aspiration results in a high recurrence rate. Whether the use of hormonal suppression therapy decreases recurrence is conjecture.

Imaging

Imaging reveals endometriosis as one or multiple thick-walled cystic tumors. An occasional one is solid. Surrounding fibrosis is common and with long-standing disease extensive pelvic distortion is evident, at times mimicking widespread metastases (Fig. 12.13). Intraperitoneal endometriosis most often consists of solid or partly cystic tumors, at times mimicking metas-

Figure 12.13. Severe endometriosis resulting in a frozen pelvis. Barium enema reveals a long rectal stricture (arrow). The sigmoid colon is also infiltrated.

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tasis. The cystic component is partly filled with blood products; their CT density ranges from water to soft tissue. Blood clots, generally adjacent to the wall of a cyst, are hyperdense. Fallopian tubes involved by endometriosis have an irregular, beaded appearance on hysterosalpingography.

An endovaginal approach is preferred with US. These tumors’ echogenicity spectrum reflects their varied cystic-to-solid appearance. The solid component in larger tumors often appears nodular. A homogeneous hypoechoic cyst containing low-level echoes is a common finding; at times septations and a multilocular appearance are evident. No specific US features point toward an endometrioma, but in an adnexal tumor with these findings an endometrioma is suggested if neoplastic features can be excluded. Endovaginal US sensitivity and specificity of about 90% can be expected in suggesting an endometrioma. Color and pulsed Doppler US provides limited additional information except for excluding blood flow within cystic regions.

The reported endorectal US sensitivity and specificity percents are in the high 90s for detecting rectovaginal endometriosis (36); the sensitivity for uterosacral ligament infiltration is about 80%, perhaps reflecting the greater distances involved, but the specificity percents remain in the high 90s.

Magnetic resonance is the imaging procedure of choice in detecting and defining subtle endometrial implants; fat suppression aids in visualizing small implants, being especially useful for implants <5mm. Sensitivity and specificity of MRI in detecting pelvic endometriosis are >90% (37). Although MR findings vary considerably, MR will often differentiate an endometrioma from other adnexal tumors. With conventional MRI small implants have an appearance similar to fat—hyperintense on T1and hypointense on T2-weighted images relative to myometrium, often being homogeneous when small. Some foci appear as small cystic tumors. Endometrioma fluid due to a prior bleed is hyperintense on both T1and T2-weighted images. Recent bleeding is hypointense and the overall appearance thus can vary considerably. Solid nodules enhance postgadolinium. In general, hyperintense fluid on T1-weighted MRI in dilated fallopian tubes suggests pelvic endometriosis.