Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

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causes. Some of these cancers are mostly exophytic and are seen as an intraluminal uterine soft tissue tumor, at times having a cystic appearance.

Most authorities agree that endovaginal US is superior to transabdominal US in detecting endometrial neoplasms. Although endovaginal US does detect many endometrial cancers with reasonable certainty, detection of subtle cancers revolves around measurement of a thickened endometrium, adjusted for age and possible hormone therapy (discussed earlier; see Endometrial Atrophy and Hyperplasia).

Blood flow through an endometrial cancer can be measured with endovaginal color Doppler US, but intratumoral blood flow analysis does not predict either tumor stage or provide a histologic diagnosis and, in fact, does not discriminate between benign and malignant endometrium.

The MRI findings of benign endometrial disease and carcinoma overlap somewhat (staging is discussed in the next section) (Fig. 12.26). Because T2-weighted images identify uterine zonal anatomy, they are useful both in detecting and staging endometrial cancers. These tumors tend to be isointense to normal endometrium, and thus smaller cancers blend in with the endometrium. With growth, the endometrium widens, a nonspecific finding.

Staging

Clinical: Imaging findings of endometrial carcinoma need to be placed in a surgical perspective. Clinical staging of endometrial carcinoma is sufficiently inaccurate that FIGO recommends surgical staging (FIGO and TNM staging is given in Table 12.8). Currently most surgeons stage endometrial carcinoma at surgery and modify the resultant therapeutic approach accordingly. In a high surgical risk woman or with suspected advanced disease, however, imaging does provide additional information prior to therapy.

Histologic grade and stage establish the prognosis. Prognosis is significantly worse with clear cell adenocarcinomas and mixed endometrial–clear cell types compared with more typical endometrial carcinoma.

The depth of myometrial invasion is of prognostic significance. Many surgeons use an intraoperative visual estimate of myometrial invasion as a guide to surgical aggressiveness in staging these tumors. A 50% depth of invasion is often used to differentiate lower risk from higher risk patients, and a number of imaging efficacy studies have also adopted a 50% myometrial invasion guideline.

In a setting of coexistent adenomyosis and endometrial cancer, depth of myometrial invasion is better defined by contrast enhanced

Table 12.8. TNM Staging of corpus uteri tumors

Source: From the AJCC Cancer Staging Manual, 6th edition (2002), published by Springer-Verlag, New York, NY, used with permission of the American Joint Committee on Cancer (AJCC), Chicago, IL.

ADVANCED IMAGING OF THE ABDOMEN

dynamic T1-weighted MR imaging than by precontrast images (86).

An elevated preoperative CA-125 level is predictive of poor survival.

Imaging: Whether CT or endovaginal US is superior in gauging the depth of myometrial invasion is debatable. Initial reports suggested a similar accuracy for both CT and MRI in detecting cervical extension, although the junction between the uterus and cervix is not clearly identified by CT. A later helical CT study achieved a sensitivity of 83% and specificity of only 42% for detecting deep myometrial invasion and a sensitivity of 25% and specificity of 70% for cervical involvement (87), findings considerably worse than with MRI. The relatively poor CT soft tissue contrast (compared to MR) limits CT use in early staging but it is useful in advanced tumor stages.

Transabdominal US has a limited role in staging. On the other hand, endovaginal US is widely employed, achieving sensitivities of 65% to 90% in differentiating absent or superficial myometrial invasion from deep invasion (where deep invasion is generally defined as >50% myometrial involvement). Ultrasonography both overestimates and underestimates invasion; false positives include the presence of other uterine disease, including polyps.

In many institutions MRI has evolved into a leading role in staging endometrial carcinoma. Reported MR sensitivity and specificity in assessing myometrial infiltration are 87% and 91%, for cervical infiltration 80% and 96%, but for lymph node involvement only 50% and 95%, respectively (88). In assessing myometrial invasion postcontrast MRI is significantly better than nonenhanced MR. T2-weighted FSE and dynamic T1-weighted images are preferred, with parasagittal and coronal imaging assessing cervical and myometrial invasion. Overall, postcontrast MR staging accuracy is about 90%.

Disruption of the hypointense junctional zone by a hyperintense tumor, identified on T2weighted images, implies myometrial invasion, although the junctional zone is not always identified in postmenopausal women. Magnetic resonance imaging staging is degraded by the presence of benign endometrial disease such as endometritis. Most endometrial carcinomas have less MR contrast enhancement than adjacent normal myometrium, with some exceptions. A tumor signal intensity in the outer half

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of the myometrium signifies deep myometrial invasion, while disruption of the outer myometrial stripe is found with tumor extending beyond myometrium. Early, dynamic MRI is especially helpful in gauging myometrial invasion; it is more accurate than contrast-enhanced T1-weighted imaging or conventional T2weighted imaging.

Focal disruption of the entire myometrial thickness implies serosal invasion. It is in detecting serosal invasion that MR achieves its lowest sensitivity, with false-positive results occurring mostly when the myometrium is <5mm thick. Magnetic resonance imaging achieves an accuracy of about 90% in detecting cervical invasion. Normally the cervical epithelium is hyperintense on postcontrast images; continuous cervical epithelial enhancement on dynamic sequences aids in excluding cervical invasion (89). Compared to cervical squamous cell carcinomas, MRI of adenocarcinomas invading the cervix reveals a larger tumor and less overall tumor contrast enhancement but show greater enhancement at the tumor periphery compared to patients with a cervical squamous carcinoma. Occasionally a cancer has a polyp-like appearance in the cervical canal without invading cervical epithelium.

Computed tomography and MRI are similar in detecting nodal involvement, and both are superior to US. Both CT and MRI simply detect lymph node enlargement rather than identify direct tumor involvement.

Intraperitoneal metastases consist of solid or cystic tumors. Ascites is common. Small intraperitoneal tumor foci, however, are readily missed with imaging.

Bladder or rectal invasion is seen as an asymmetric wall thickening, with tumor at times extending intraluminally. A hyperintense bladder or rectal wall segment suggests invasion.

A chest radiograph aids in assessing lung involvement.

Recurrence/Metastasis

Metastasis to bone by endometrial carcinoma is unusual, although an occasional isolated, solitary bone metastasis is detected even before the primary tumor. An occasional metastasis is to the umbilicus (umbilical metastases of an abdominal cancer are also called Sister Mary

Joseph nodes). Malignant pericardial effusion and brain metastases are rare.

A complication of locally advanced cervical carcinomas is uncontrolled hemorrhage. Embolization of the bleeding site is a therapeutic option.

Other Carcinomas

Only a limited number of endometrial transitional cell carcinomas have been reported. They have no distinguishing imaging findings.

A primary endometrial squamous cell carcinoma is rare. No specific imaging findings are available. In fact, even curettage specimens may not be diagnostic, revealing only differentiated squamous epithelium.

Several hepatoid adenocarcinomas have been described in the uterus, where they are considerably less common than in the ovaries. An endometrial hepatoid adenocarcinoma should be suspected if a-fetoprotein levels are elevated with a suspected endometrial carcinoma.

Sarcoma

Sarcomas represent 3% to 5% of all uterine malignancies. Leiomyosarcomas and stromal sarcomas are most common, with mixed müllerian sarcomas and rhabdomyosarcomas being occasionally encountered.

Most sarcomas are large at initial detection and imaging simply detects a large, irregular, necrotic tumor. Often the uterine outline is difficult to identify.

Stromal Sarcoma

Histologically an endometrial stromal sarcoma reveals intramural nests of endometrial stromal cells without endometrial glands. Most often originating from the endometrium, an occasional one arises from adenomyosis or endometriosis. A minority of these sarcomas are associated with antecedent pelvic radiation therapy. Anecdotal reports describe various uterine sarcomas developing years after tamoxifen therapy for breast cancer. Some exhibit complex histology and contain ovarian sex cord-like structures. Smaller ones tend to be confused histologically with adenomyomatosis containing few glands; imaging has a limited

role in differentiating between these two conditions. Also, uterine leiomyosarcomas have a similar imaging appearance.

Imaging reveals a complex cystic tumor within the myometrium. The solid component enhances with contrast. T2-weighted MRI of patients with endometrial stromal sarcoma reveals hypointense bands within regions of myometrial involvement, with pathologic study identifying these bands as preserved myometrium (90); these sarcomas tend to spread along vessels.

Leiomyosarcoma

Many uterine leiomyosarcomas are an unexpected finding after a hysterectomy for uterine fibromyomas. They have a poor prognosis, except for the occasional small, noninfiltrating tumor exhibiting little mitotic activity. Occasionally lung metastases regress after oophorectomy, presumably due to the lack of further ovarian hormone stimulation.

Ultrasonography findings are similar to those seen with a leiomyoma, except these tumors tend to have a more heterogeneous pattern with hyperechoic and anechoic regions and with cystic degeneration. Endovaginal color Doppler US reveals abnormal tumor vessels within sarcomas, a finding seen only in a minority of leiomyomas.

The MRI findings of most sarcomas are similar to those seen with a large leiomyoma. These tumors have a heterogeneous MR signal intensity.

Metastases developing after a hysterectomy for leiomyoma imply a missed low-grade leiomyosarcoma.

Mixed Müllerian Tumors (Carcinosarcomas)

Mixed müllerian tumors, also called carcinosarcomas and müllerian adenosarcomas, commonly have a benign, at times pedunculated appearance. In some immunohistochemical staining reveals estrogen and progesterone hormone receptors. A rare one produces a- fetoprotein. The relationship of such a tumor with hepatoid carcinomas (discussed previously) is conjecture. A cystic carcinosarcoma is rare.

ADVANCED IMAGING OF THE ABDOMEN

Dynamic MRI of four revealed focal early and persistent enhancement, similar to the myometrium, mixed with regions of delayed enhancement (91); histology of the early enhancing component revealed mostly sarcomatous tissue containing prominent vascularity.

Rhabdomyosarcoma (Botryoides)

Sarcoma botryoides (embryonal rhabdomyosarcoma) typically occurs in the pediatric age group and is rare in an adult. In infants it usually involves the vagina and spreads by direct invasion and lymphatics, while in older girls a cervical origin is more common. These are soft tissue tumors. Necrosis and calcifications develop in some. They exhibit heterogeneous contrast enhancement.

Lymphoma

Primary malignant non-Hodgkin’s lymphoma of the uterus is rare. Cervical lymphoma is difficult to diagnose because the lymphomatous infiltrate often mimics an inflammatory condition (Fig. 12.27). MRI of one primary cervical lymphoma revealed sparing of mucosa, most of stroma and uterine junctional zone, differentiating this condition from a carcinoma (92).

Secondary uterine involvement is common in the late stages of systemic lymphoma.

Cervical Carcinoma

Clinical

The current evidence suggests that HPV plays a role in cervical cancer. The HPV DNA is present in most cervical cancers. Immunosuppression and smoking are also risk factors for cervical cancer.

Most cervical carcinomas arise at the squamocolumnar junction. In younger women this junction tends to be located on the ectocervix, but with age evolves into the endocervical canal. These cancers range from adenocarcinomas and adenosquamous carcinomas to squamous cell carcinomas. A rare cervical adenocarcinoma contains other carcinomatous tissue; thus both choriocarcinomatous and hepatoid differentiation have developed, probably either from aberrant differentiation or neometaplasia of underlying epithelial cells.

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uterine cavity with cervical canal obstruction. It is unusual to find a cervical carcinoma invading the endometrium, although an occasional one extends into myometrium. Because these tumors are centered in the cervix, most can be differentiated from endometrial carcinomas, which are centered in the endometrium. Computed tomography detects a cervical carcinoma as a soft tissue tumor either in the ectoor endocervix. These tumors enhance less with contrast than do the surrounding soft tissues.

Endorectal US reveals cervical carcinomas as poorly defined tumors having indistinct margins in an enlarged cervix, ranging from hypoechoic to isoechoic relative to normal uterine tissue. Endovaginal color Doppler US of uterine arteries reveals a RI and PI significantly lower than normal.

In consecutive women, using a 0.5 tesla (T) unit, endovaginal MRI provided more information with stage I cervical carcinoma than an external phased array coil MR technique (94); endovaginal MR sensitivity was 96% and specificity 70% for tumor detection, while the external coil technique sensitivity was only 54% but at a higher specificity of 84%. The authors believe that the higher specificity with the external coil technique was because small abnormalities were seldom identified.

Magnetic resonance imaging reveals a cervical tumor isointense to muscle on T1and hyperintense on T2-weighted images (Fig. 12.28). Most tumors are better defined on T2-weighted images, although smaller ones enhance with contrast and tend to be best seen postcontrast. Contrast enhancement occurs slightly earlier in a carcinoma than in normal cervical tissue. Postcontrast images occasionally show a hyperintense rim.

Staging

Clinical Staging: Initially cervical carcinoma spreads by direct extension into surrounding tissues. Pelvic lymph node involvement is common, with subsequent spread to para-aortic nodes. Hematogenous metastases are generally a late finding. Metastases have occurred in an episiotomy scar, scalene lymph nodes, pericardium, brain, and leptomeninges.

Clinical staging guidelines of cervical carcinoma by FIGO include chest radiography,

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Figure 12.28. Cervical carcinoma. Contrast-enhanced sagittal MR image identifies a cervical tumor (arrows) having similar enhancement to uterus. (Source: Burgener FA, Meyers SP, Tan RK, Zaunbauer W. Differential Diagnosis in Magnetic Resonance Imaging. Stuttgart: Thieme, 2002, with permission.)

barium enema, and IV urography, but do not include CT, US, or MRI findings (Table 12.9). A number of investigators have empirically modified the FIGO staging classification to

Table 12.9. Staging of cervical tumors

Source: From the AJCC Cancer Staging Manual, 6th edition (2002), published by Springer-Verlag, New York, NY, used with permission of the American Joint Committee on Cancer (AJCC), Chicago, IL.