Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

(or low malignant potential) tumor category is used by pathologists. Germ cell origin neoplasms are more common in younger women, while epithelial origin neoplasms predominate in postmenopausal women. Mature cystic teratomas predominate among ovarian tumors found in girls under the age of 15 years.

Benign Tumors

A number of benign ovarian and other adnexal tumors are treated with laparoscopic surgery. The major limitation of a laparoscopic approach is the inability to definitely confirm the benignity of the lesion in question. It is not rare to have an initial laparoscopic diagnosis and begin treatment of what is thought to be benign disease, but subsequently discover that the condition is indeed malignant.

Granuloma

Ovarian granulomas are most often a result of an inflammatory reaction—typically a result of a foreign body reaction to suture material introduced at previous surgery. Other causes include infections such as a bacterial tuboovarian abscess or tuberculosis, endometriosis, Crohn’s disease, previous diathermy or a necrotizing reaction to previous surgery. Some are idiopathic.

Sex Cord–Stromal Tumors

These tumors originate from sex cords and mesenchymal tissue. Most are benign. They are rare in young women and most occur in the postmenopausal age group. Some produce estrogen and/or androgen with their resultant clinical manifestations.

A variant of a sex cord tumor is one containing annular tubules, with the predominant component being intermediate between a granulosa cell tumor and a Sertoli cell tumor. Of interest is that some of these tumors are associated with Peutz-Jeghers syndrome.

Fibroma/Thecoma

Both of these solid tumors originate from ovarian stroma. Their pathologic appearance is similar and a tumor is often classified depend-

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ing on the preponderance of thecal cells or fibrous tissue.

Thecomas occur mostly in middle-aged and older women and constitute less than 5% of all ovarian neoplasms. They are rare in prepubertal girls. Most are benign and 90% are unilateral. They tend to be associated with excess estrogen production, a finding not seen with fibromas. Also, some thecomas are associated with endometrial hyperplasia and endometrial carcinoma. An interesting association exists between luteinized thecomas and sclerosing peritonitis. Some of these present with an acute abdomen.

Ovarian fibromas are most common in middle age. Most are asymptomatic but an occasional fibroma is a component of Meigs’ syndrome. An increased incidence occurs in some families and in Gorlin’s syndrome (basal cell nevus syndrome). Ascites is common with larger fibromas and thecomas.

The imaging appearance of fibromas and thecomas is similar. Computed tomography shows most tumors to be solid and homogeneous, but they tend to become inhomogeneous when large. Some develop calcifications. The more homogeneous tumors are hypoechoic by US. The CT and US differential diagnosis includes other solid extraperitoneal tumors such as a teratoma and lymphoma. Fibromas, thecomas, and Brenner tumors have similar imaging and operative findings.

These tumors are hypointense on both T1and T2-weighted MRI, a rather specific appearance differing from that of most other solid ovarian tumors. Degeneration within larger tumors tends to produce a heterogeneous and cystic appearance. Their contrast enhancement varies considerably. Because their appearance is similar to that of uterine fibroids, the tumor origin needs to be established to differentiate these entities.

The MRI appearance of the rare ovarian leiomyoma is similar.

Granulosa Cell Tumor

Granulosa cell tumors are benign tumors found mostly in postmenopausal women. Some produce excess estrogen and, if it is uncorrected, these women are prone to develop endometrial carcinoma. Serum tumor markers tend to be normal. A rare variant is found in the pediatric age and younger women, where some

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of these tumors manifest due to their estrogen or androgen production.

Smaller tumors are solid, but a cystic component often develops with growth, and as a result the imaging findings of larger ones tend to mimic those of cystadenomas. Their imaging appearance ranges from unilocular to multilocular cystic, thickto thin-walled, and homogeneously to heterogeneously solid (39). Bleeding, infarction, and tumor degeneration contribute to their heterogeneous appearance.

Magnetic resonance imaging reveals solid tumors with a variable cystic component and intratumoral hemorrhage; the solid component enhances postcontrast. The uterus is often enlarged, and endometrial thickening is evident (Fig. 12.15).

These tumors tend to recur years after an apparent cure, and thus long-term follow-up is necessary after initial therapy.

Sertoli-Leydig Cell Tumor

This rare tumor occurs mostly in girls and young women, occasionally bilaterally. Some are

associated with elevated serum a-fetoprotein levels. These tumors produce androgen and other hormones, and some women develop masculinization. An occasional one produces renin and is a cause of hypertension. In distinction to other sex cord tumors, a number of Sertoli-Leydig tumors are malignant, at times even being poorly differentiated.

The imaging appearance is similar to granulosa cell tumors. Some small Leydig cell tumors are not detected by US in spite of high plasma testosterone levels and virilization.

Cystic Tumors

Clinical

Benign ovarian cysts range from incidental simple cysts, to functional cysts, to a cyst manifesting by its neoplastic nature. The terms simple cyst and functional cyst are often used interchangeably and generally imply a follicular cyst.

Doppler US follow-up in premenopausal women with adnexal cysts reveals that about one third regress spontaneously and thus

are simple (functional) cysts. Ultrasonography cannot differentiate between cysts that will regress and those that will not.

Small, thin-walled, anechoic, nonpalpable ovarian cysts detected by US present a dilemma. What is the malignant potential of these small cysts in a postmenopausal woman? Follow-up US reveals that most of these cysts remain stable, with an occasional one even resolving. The risk of malignancy appears sufficiently low that follow-up with US of stable cysts appears reasonable, assuming there is no family history of ovarian, breast, or colon cancer. The CA-125 antigen serum level should also remain low.

A US pelvic cancer screening program of postmenopausal women defined a simple cyst as an anechoic cyst <5cm in diameter having a morphologic appearance of a typical benign cyst (smooth, aseptate, hypoechoic) (40); women with a cyst were followed at 3- to 6- month intervals and evaluated for possible surgical intervention. Of these simple cysts, 23% resolved spontaneously and 59% persisted (other women were lost to follow-up). No malignancy was identified in women with a persistent cyst who underwent surgery. Of interest, a woman with congenital hypothyroidism had bilateral multicystic ovaries (41); the cysts disappeared after thyroid hormone therapy.

Follicular (Simple) Cysts

The prevalence of simple cysts is <10% in postmenopausal women. Imaging identifies the presence of a cyst, although most functional cysts have a similar appearance. If multiple, these cysts tend to vary in size, in distinction to polycystic disease where cysts tend to be small and about the same size.

Most follicular cysts are under hormonal influence and result from a failure to ovulate or involute. They are benign, most are small, and most regress following a menstrual cycle. Those cysts that do not regress are not under hormonal control and some other tumor, either benign or malignant, is often considered. Follicular cysts are found in McCune-Albright syndrome.

At times US in neonates, infants and young children with a lower abdominal cystic tumor detects a small cyst along the wall of a cystic

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tumor (called a daughter cyst sign); these daughter cysts, pathologically identified as ovarian follicles, occur in ovarian cysts but not in cysts of other etiologies (42).

Simple ovarian cysts have an appearance similar to that of cysts elsewhere; namely, they are entirely cystic, smooth-walled, and homogeneous, and they contain no internal debris. Any septa are thin and smooth. Doppler US reveals no internal vessels. Simple cysts are hypointense on T1and hyperintense on T2weighted MRI.

Ultrasonography reveals a fluid-filled thinwalled structure. Uncomplicated cysts are hypointense on T1and hyperintense on T2weighted images. Blood and other debris within the cyst modify their appearance. Due to a surrounding theca and stromal reaction, functional cysts tend to have hypointense rims on T2weighted images.

Ultrasonography is useful in correlating cyst regression with menstrual cycle.

Some ovarian cysts have thick walls, contain septa, and have internal echoes; in these, US does not differentiate between solid and cystic tumors.

Depending on imaging appearance, the differential diagnosis of an ovarian cyst includes a simple cyst, hemorrhagic cyst, endometrioma, dermoid cyst, and other neoplasms, both benign and malignant. At times, even an appendiceal abscess located in the pelvis is in the differential.

Ultrasound-guided percutaneous aspiration of a simple ovarian cyst is a straightforward procedure associated with few complications. Nevertheless, this is a controversial topic and therapy of these cysts is not settled. Authors discouraging aspiration point to a high cyst recurrence rare (cysts recur in about half or slightly more instances), sampling errors encountered with complex cysts, and possible needle tract seeding by malignant cells. On the other hand, numerous studies have established the relative safety and effectiveness of percutaneous aspiration of preselected cysts. Especially in high surgical risk women, US-guided aspiration of benign-appearing ovarian cysts appears worthwhile to evaluate for malignant potential. If needed, recurrent cysts can be resected, but cysts several cm in diameter are followed. In general, a high concentration of estradiol in

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aspirated fluid predicts a low cyst recurrence rate.

Corpus Luteum Cysts

Corpus luteum cysts are associated with pain, and they may rupture and bleed. They tend to be unilateral and are larger than follicular cysts.

The cyst wall of corpus luteum cyst is thicker and more nodular than a simple cyst. The wall enhances post–MR contrast. Also, bleeding modifies cyst content. The overall appearance of some of these cysts overlaps with endometriomas and cystic ovarian malignancies.

Theca-Lutein Cysts

Theca lutein cysts are associated with pregnancy, tend to be large, and occur bilaterally. Multiple theca-lutein cysts develop in ovarian hyperstimulation syndrome during therapy for infertility and in association with gestational trophoblastic disease, resulting in gross ovarian enlargement. In fact, in the appropriate setting the presence of theca-lutein cysts and an endometrial tumor should suggest gestational trophoblastic disease.

Some of these cysts manifest by rupture and bleeding. Ascites is evident in some women.

Ultrasonography reveals a smooth-walled cyst, with no blood flow to the cyst identified by Doppler US. The cysts’ MR appearance varies considerably.

Hemorrhagic Cyst

A hemorrhagic cyst is a descriptive term for a ruptured corpus luteum cyst or follicular cyst that bleeds internally and contains blood. Sudden onset of midcycle pain is a common presentation. These cysts tend to resolve within several menstrual cycles. Their size varies considerably.

Ultrasonography of these cysts ranges from hypoto hyperechoic, varying considerably depending on the age of hemorrhage. Some are associated with peritoneal fluid. An occasional one is thick-walled and mimics the adnexal ring sign of an ectopic pregnancy (19); a key difference is that a ring sign with a hemorrhagic cyst is intraovarian, while with an adnexal pregnancy it is extraovarian.

Bleeding into a cyst increases the usually low signal intensity on T1-weighted MRI, and many of these cysts appear hyperintense both on T1and T2-weighted images.

The overall appearance of some hemorrhagic cysts mimics a ruptured ectopic pregnancy with its surrounding blood.

Paraovarian and Paratubal Cysts

Some of these cysts are located within the broad ligament. A paraovarian cyst should be suspected if US detects a separate and normal ipsilateral ovary,although this diagnosis is not often made. Paraovarian cysts tend to be misdiagnosed as ovarian cysts, while paratubal cysts are not detected due to their small size.

Peritoneal inclusion cysts are in the differential diagnosis. These cysts are discussed in Chapter 14.

Mature Cystic Teratoma/Dermoid Cyst

Clinical: Mature cystic teratomas, also called dermoid cysts, are the most common neoplasms of germ cell origin. They are almost always benign, in distinction to other malignant germ cell tumors (discussed later). These tumors are composed of all three germ cell layers, although ectodermal components tend to predominate.

About 10% of cystic teratomas develop bilaterally. They grow slowly, and are found in pediatric and postmenopausal age groups, but are most common in young women. They are the most common ovarian tumor in pediatrics. They are slow-growing tumors and most tend to be asymptomatic, but they are also prone to torsion, rupture, and malignant degeneration; therefore, surgical resection is usually considered when discovered.

These cysts tend to be unilocular, and septations are present in some; the cysts are lined by squamous epithelium and contain sebaceous material; only a rare teratoma consists of a mostly solid tumor.

Most mature cystic teratomas undergo surgical resection and thus image-guided biopsy is moot.

Imaging: Fat detected by imaging within an ovarian tumor should suggest a mature teratoma. Magnetic resonance imaging identifies fat in about 90% of ovarian teratomas. Fat

is mostly in the cystic cavity, occasionally in the cyst wall. Fat is associated with sebaceous glands, which are prominent in most dermoids. The MR appearance of teratomas without fat is similar to that of other cystic ovarian tumors.

Some teratomas contain a fluid (fat)-fluid level, debris, or calcifications, findings identified by CT or MRI and, at times, with conventional radiography (Fig. 12.16). Calcifications, including teeth, generally in an associated soft tissue nodule, are characteristic of a mature cystic teratoma.

A teratoma typically has a cystic component and contains focal or diffuse regions of increased echogenicity consisting of hyperechoic lines and nodules, with the latter representing a dermoid plug consisting of fat (sebum), hair, or calcifications. An acute bleed into a simple cyst may be sufficiently hyperechoic to mimic a dermoid plug; a follow-up examination should differentiate these two. A cystic teratoma can also mimic loops of bowel with US and be overlooked.

Doppler US detects blood flow only in a minority of dermoid cysts, and only from peripheral tissue surrounding the tumor (but see below for struma ovarii tumors).

On T1-weighted MRI fatty regions are hyperintense, while calcifications and fibrosis are hypointense. Similar to US, MRI using T1and T2-weighted sequences cannot readily differentiate teratomas and cystic hemorrhagic tumors;

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the use of fat-saturation sequences increases tumor characterization considerably.

Mature cystic teratomas without fatty fluid (sebum) have an atypical MR appearance. They are hypointense on T1and hyperintense on T2weighted images, consistent with fluid in the cyst. They show heterogeneous postcontrast enhancement, yet even in these teratomas MRI often identifies fat as focal hyperintense regions in the cyst wall.

The rare solid mature teratoma has an imaging appearance similar to an immature teratoma (Fig. 12.17). A biopsy diagnosis of a solid mature teratoma should be made with caution because many immature teratomas also contain histologically mature-appearing tissue.

Occasionally a leiomyoma contains calcifications or fat and the CT and US appearance mimics a cystic teratoma. A perforated appendix with a stone can have a similar echogenic appearance. On the other hand, chemical shift gradient echo MRI differentiates cystic teratomas from endometriomas.

Complications: Cystic teratoma complications include bleeding, perforation (rupture), malignant degeneration, and, rarely, torsion. The fatty component tends to be preserved after torsion (imaging findings of ovarian torsion were discussed earlier).

Perforation of a cystic teratoma ranges from gradual leakage leading to a granulomatous peritonitis or ascites to sudden rupture and an acute abdomen. Spill of cyst content, resultant

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Figure 12.17. Mature ovarian teratoma in a 2-year-old girl. Transverse US scan reveals a solid retrovesical tumor with echogenic shadowing (arrow). (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.)

chemical peritonitis, and ascites are identified with postcontrast T1-weighted MRI. The resultant appearance can mimic carcinomatosis or chronic peritonitis.

Immature teratomas are malignant and are discussed in a later section. Mature teratomas do not evolve into immature teratomas; thus the occasional malignancy in a mature cystic teratoma represents a de novo malignant transformation, generally a squamous cell carcinoma, less often an adenocarcinoma, and a rare one believed to be of thyroid origin. Sarcomas are least common; some of these are part of a carcinosarcoma and occur in association with a squamous carcinoma or, very rarely, an adenocarcinoma. Most malignancies occur in postmenopausal women. The time to malignant degeneration varies, at times being decades after initial diagnosis. A rare woman first presents with metastases, later shown to be from a primary small cell carcinoma arising in an ovarian mature cystic teratoma. Interestingly, some younger women developing ovarian mucinous tumors are found to also have a teratoma, an association greater than by chance.

A prominent soft tissue component in a cystic teratoma, detected by any imaging modality, should raise suspicion of a malignancy. These tumors spread by transmural invasion and thus differ from primary epithelial

cancers. MRI of some of these tumors thus reveals not only a solid component, but also transmural and surrounding structure invasion. At times a solid lobulated tumor extends into surrounding fat The malignant component enhances postcontrast. Some dermoid/carcinoma tumors are huge and consist of mural intracavitary nodules containing regions of necrosis and hemorrhage. A retrospective study of women with squamous cell carcinoma in an ovarian mature cystic teratoma, treated by the Tokai Ovarian Tumor Study Group, revealed a 5- year survival of 95% for those with stage I and 80% for stage II, but 12 of 13 patients with stage III died within 20 months (43).

Struma Ovarii

Struma ovarii is an uncommon, usually benign ovarian neoplasm, with only rare malignant ones reported. Most investigators classify struma ovarii as a mature cystic teratoma variant containing predominantly or exclusively one tissue, namely thyroid. These tumors occur unilaterally in adult women. An occasional one is associated with a mature cystic teratoma. Most are not hormonally active.

Histologically, these tumors contain varyingsize cysts separated by fibrous septa. The hallmark of this tumor is the presence of thyroid follicles, albeit at times scant in nature. The correct diagnosis is readily overlooked if only a few thyroid follicles are identified. Immunohistochemical staining for thyroglobulin is helpful if the diagnosis is in doubt. A histologic diagnosis of malignancy is difficult with these tumors, especially in a setting of a welldifferentiated follicular stroma.

Imaging reveals both cystic and solid components; even nonfunctional struma ovarii can show iodine-123 uptake by the tumor. In distinction to mature cystic teratomas, struma ovarii do not contain fat and the cystic spaces are filled with a gelatinous colloid material. Ultrasonography typically identifies a complex solid and cystic tumor. Doppler US detects blood flow not only in the capsule but also within the solid component. Detection of flow within an apparent cystic teratoma should thus suggest struma ovarii.

Magnetic resonance imaging of struma ovarii tumors reveals complex solid and cystic components. The cyst fluid varies from hypointense