Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

of institutions colonoscopy is used instead, although little evidence exists that it is superior to a barium enema.

An overall staging accuracy appears similar for CT and MRI; neither imaging modality detects small mesenteric or small bowel implants.A CT limitation is its inability to detect subtle bowel serosal involvement and early peritoneal spread. Magnetic resonance imaging probably has similar limitations, but the evidence for this is not clear. Somewhat better results are obtained in staging advanced ovarian cancer; The Radiological Diagnostic Oncology Group reported a 92% CT sensitivity, 95% for MRI, and 69% for US in detecting peritoneal metastases (46); both CT and MRI were especially useful in subdiaphragmatic spaces and hepatic surfaces. Preoperative evaluation of pelvic and paraaortic lymph node metastases has a low sensitivity but high specificity, a consequence of assuming that lymph nodes above a certain size (typically 1.5cm or larger) are involved by metastases. With these criteria, the detection of para-aortic lymph node metastases is greater than that for pelvic node involvement. One study achieved a MRI sensitivity of only 28% for pelvic lymph node involvement (47), a not untypical result. Complicating nodal analysis is that some women have positive paraaortic nodes but no pelvic node involvement; para-aortic node metastasis presumably occurs both by spread from pelvic nodes and directly.

Magnetic resonance imaging achieved a sensitivity of 73–77% for detecting bowel and mesentery spread, considerably better than for omental (38%) and lesser sac (43%) involvement (47). Carcinomatosis is detected with about a 90% sensitivity and specificity.

Addition of FDG-PET to CT increases accuracy of staging ovarian cancer considerably (48) and these dual modalities will undoubtedly be employed more often in the future.

Therapy

The current therapy for large, bulky ovarian carcinomas is cytoreductive surgery followed by chemotherapy. Such an approach is often not curative but does result in clinical remission and prolongs survival. Computed tomography aids in identifying those women

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who will not benefit from cytoreductive surgery.

Incidentally, postcontrast CT identified ovarian vein thrombosis in 80% of women after abdominal hysterectomy and bilateral salpingo-oophorectomy (49); no clinical thrombophlebitis was evident.

Follow-up/Metastasis

Follow-up of a woman with a previous ovarian carcinoma includes a physical examination, serum CA-125 levels, and imaging. CA 125 is useful in detecting recurrence of most (but not mucinous) ovarian carcinomas.

A longitudinal study in women with treated ovarian cancer found contrast-enhanced MRI to have a sensitivity of 91% and specificity of 87% in detecting residual tumor—results superior to serum CA-125 level and physical examination (50). Nevertheless, CT has a limited role in routine follow-up after carcinoma resection. Because of a high false negative recurrence rate, a normal CT scan is of limited use, realizing that a true positive study can save reexploration. On the other hand, in women with suspected or known recurrent ovarian cancer who are considered for secondary cytoreductive surgery, CT aids in differentiating between those amenable to debulking and those with an nonresectable tumor (51); hydronephrosis and pelvic sidewall invasion were findings pointing to tumor nonresectability. In some institutions a second-look laparotomy is preferred as a viable follow-up procedure.

Some investigators find that conventional imaging sensitivity and specificity are improved considerably by also performing whole-body FDG-PET (52), results difficult to place in perspective because other studies have found that FDG-PET does not improve the overall diagnostic accuracy in detecting recurrent ovarian carcinoma (compared with CT), especially for small tumor recurrences (53). It does have a role in women with inconclusive other imaging.

Magnetic resonance imaging is useful prior to reexploration in women with surgically staged ovarian cancer. Although MRI misses small implants, it does detect larger ones. Either a hyperintense abnormal structure on T2weighted spin-echo (SE) images or early contrast enhancement on dynamic subtraction images suggests a recurrent tumor. Postopera-

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tive fibrosis is hypointense on both T1and T2weighted MRI, and thus MRI should allow differentiation of fibrosis from recurrent tumor. Postoperative distortion, however, often results in a complex picture. Dynamic postcontrast subtraction MRI appears more accurate than precontrast imaging in differentiating fibrosis from recurrent tumor, although both sequences are often obtained.

In a prospective, blinded study of women with ovarian carcinoma, normal CA-125 levels, and no clinical evidence of disease after primary cytoreductive surgery and cytotoxic chemotherapy, immunoscintigraphy using indium-satumomab pendetide detected disease in all women with histologically proven tumor at reassessment laparotomy (54).

After the initial curative therapy, distant metastases are more common than local spread. Metastasis to the peritoneal cavity or even the stomach is not uncommon even with normalsized preoperative ovaries.

Lymphatic spread is common. Enlarged paracardiac lymph nodes, detected by CT, represent a significant adverse prognostic factor.

Peritoneal involvement can be followed with peritoneal washings, which are often positive prior to imaging detection. Cul-de-sac aspiration cytology is useful in detecting tumor recurrence; it can be the only indication of recurrence. If needed, an implanted reservoir provides peritoneal washings for cytology at set intervals. Paracentesis and laparoscopy are not without risk, however; abdominal wall metastases develop in a minority of women at laparoscopic or paracentesis sites. Most of these metastases occur in a setting of FIGO stages IIIC to IV.

Metastasis to the liver as the first site is unusual, although eventual liver involvement, detected at autopsy, is relatively common. Abdominal or pelvic recurrence usually precedes lung metastases, but lung metastases, in the absence of disease in the abdomen and pelvis, occurs in 3% to 5% of women (55,56), and those with chest involvement usually also have elevated serum tumor markers.

Ovarian carcinoma metastasizes to the central nervous system. Most of these are serous cystadenocarcinomas. Unusual sites for metastases include axillary lymph nodes, inferior vena cava, breast, and bone.

Squamous Cell Carcinoma

Most primary ovarian squamous cell carcinomas are part of a dermoid cyst or associated with endometriosis, although an isolated squamous cell carcinoma also occurs. Some are associated with a cervical neoplasm. Human papilloma virus is identified in some of these tumors.

Ovarian squamous cell carcinomas tend to be solid except for regions of necrosis.

Brenner (Transitional Cell) Tumor

Brenner tumors, or transitional cell tumors, are of epithelial-stromal origin. Their appearance is similar to transitional cell uroepithelium, most are considered benign, but an occasional one is of low malignancy or even represents a transitional cell carcinoma. Some are associated with mucinous ovarian neoplasms. Occasionally found are bilateral Brenner tumors.

Imaging reveals most to be solid tumors, at times quite large. Extensive calcifications are a characteristic finding. A cystic component found in some of these tumors probably represents another cystic neoplasm.

These tumors tend to be hypointense on both T1and T2-weighted MRI and thus appear similar to an ovarian fibroma or uterine leiomyoma.

Psammoma Tumors

Psammoma ovarian carcinomas tend to be of low malignancy, comparable to borderlinemalignant ovarian tumors. Some contain extensive calcifications and can mimic a leiomyoma.

Sarcoma

Primary ovarian sarcomas are rare. Most are mixed müllerian tumors and include such components as endometrioid stromal sarcoma, rhabdomyosarcoma, or even a chondrosarcoma or adenocarcinoma. These tend to be rather aggressive tumors. A primary ovarian leiomyosarcoma developed in an adolescent who had prior radiation therapy for a medulloblastoma (57).

An ovarian fibrosarcoma contains solid, CT contrast-enhancing regions and a cystic component consisting of hemorrhage, degeneration,

and necrosis. Fibrosis is not a prominent feature with these tumors and MR is nonspecific.

Similar to other sites, a primary ovarian angiosarcoma is a solid tumor usually containing multiple necrotic and hemorrhagic foci.

Malignant Germ Cell Tumor

Malignant ovarian germ cell tumors account for 2% to 5% of all ovarian cancers. Age at presentation is considerably younger than with epithelial carcinomas. These tumors are mostly solid, heterogeneous, tend to necrose with growth, and develop amorphous calcifications (Fig. 12.19). Any septa present tend to be thick.

Generally a biopsy is necessary for diagnosis. 2-[18F]-fluoro-deoxy-D-glucose–PET in women after therapy reveals residual viable tumors to have an intense FDG uptake, allowing differentiation from mature teratomas, necrosis,

or scar (58).

Dysgerminoma

Dysgerminomas are malignant, undifferentiated germ cell tumors. They represent the female counterpart to testicular seminomas. They occur almost always in adolescents and young women; some develop during pregnancy and some are bilateral. Increased prevalence is found in gonadal dysgenesis.

Some dysgerminomas result in hypercalcemia, leading to renal medullary calcinosis and

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vascular calcifications. A minority contain syncytiotrophoblasts and result in elevated b-hCG levels, but the a-fetoprotein levels are normal. As an example, a dysgerminoma with syncytiotrophoblastic giant cells was found in an 18-year-old phenotypic woman with 46,XX gonadal dysgenesis (59).

Lymph node involvement and intraperitoneal tumor nodules are common, with the nodules generally being small and few in number, but ascitic fluid cytology is positive in over half.

Imaging reveals a solid, multilobulated tumor. Internal fibrovascular septa are common. At times color Doppler US reveals prominent flow within septa.

These tumors are radiosensitive.

Immature Teratoma

Immature teratomas are rare, malignant germ cell origin neoplasms found mostly in girls and young women. These are rapidly growing, mostly solid tumors. Similar to their benign counterpart (mature cystic teratoma), they contain tissue from all three germ cell layers, but some of this tissue is immature or embryonic in origin. Some contain yolk sac tumor elements, and this component presumably accounts for the occasionally elevated serum a-fetoprotein levels. Any cystic component contains fluid ranging from water density to blood or sebaceous material (Fig. 12.20). Some immature

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Figure 12.20. Longitudinal US scan in an 8-year-old girl reveals a cystic tumor containing mural nodules. It was an immature ovarian teratoma. (Source: Garel L, Dubois J, Grignon A, Filiatrault D,Vliet GV. Ultrasonography of the pediatric female pelvis: a clinical perspective. Radiographics 2001;21:1393–1407, with permission from the Radiological Society of North America.)

teratomas are associated with an ipsilateral mature teratoma.

At initial presentation most immature teratomas are larger than mature teratomas. Solid, irregular components predominate. Many contain amorphous calcifications and often also fat and old blood. Peritoneal spread is common.

MRI reveals solid tumors containing numerous cysts and punctate foci of fat (60); the solid components are heterogeneous on T2-weighted images. Cysts tend to contain simple fluid, in distinction to the sebaceous fluid in most mature cystic teratomas. Presence of ascites suggests peritoneal spread.

After chemotherapy some immature teratomas undergo maturation and resemble mature teratomas.

Embryonal Cell Carcinoma

A pure embryonal cell carcinoma is rare. More often it is part of another tumor. It is associated with elevated serum a-fetoprotein and b-hCG levels. It is the female equivalent of male testicular carcinomas.

In the appropriate clinical setting this tumor and choriocarcinoma result in precocious puberty.

Yolk Sac (Endodermal Sinus) Tumor

A yolk sac tumor, or endodermal sinus tumor, occurs mostly in girls and young women. It is a highly malignant ovarian and occasionally vaginal tumor. These tumors are believed to originate from an embryonal carcinoma differentiating into yolk sac structures. They are associated with contralateral or ipsilateral ovarian mature cystic teratomas. Yolk sac tumors are characterized by their rapid growth, early metastasis, and rapid recurrence following therapy. Abdominal pain and a palpable mass are typical presentations.

Computed tomography reveals yolk sac tumors to be complex, having a heterogeneous appearance, with hemorrhage and necrosis often present. They range from predominantly cystic to solid. Ultrasonography findings vary from hypoechoic to hyperechoic. They reveal marked MR contrast enhancement; FDG-PET identifies a metabolically active tumor.

The imaging differential diagnosis includes a tubo-ovarian or appendiceal abscess and other ovarian cysts and neoplasms.

These tumors tend to result in an elevated serum a-fetoprotein level; thus if imaging reveals a complex, mostly cystic pelvic mass in a young woman, it seems reasonable to obtain serum a-fetoprotein level. Also, the serum a- fetoprotein level is useful in gauging the response to therapy. Surgery combined with chemotherapy achieves a high survival if the tumor is limited to the ovary.

Hepatoid Carcinoma

Primary ovarian hepatoid tumors histologically resemble hepatocellular carcinomas, although they are a variant of a yolk sac tumor. These rare, aggressive tumors found in young women tend to be large at initial presentation. Admixed yolk sac tumors are common, but if the tumor is primarily hepatoid, a metastatic hepatocellular carcinoma is in the differential. Some are associated with elevated serum a-fetoprotein levels.

Choriocarcinoma

Similar to embryonal cell carcinomas, pure primary ovarian choriocarcinomas are rare and