Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

FEMALE REPRODUCTIVE ORGANS

Endovaginal Doppler US measures blood flow velocity in uterine arteries and both a resistive index (RI) and pulsatility index (PI) are readily calculated. From a simplistic viewpoint, flow with a high PI is common with a benign tumor, while a low PI value suggests a malignancy. These indices are used together with other imaging findings.

The uterine arteries are assessed using a transperineal approach. No significant differences in PI should be detected between the transperineal and endovaginal routes. Likewise, no differences should be evident between endovaginal color Doppler imaging and color Doppler energy in assessing ovarian blood flow or detecting tumors.

Few studies have evaluated the role of laparoscopic US. In women undergoing both endovaginal US and laparoscopic US, the latter revealed additional morphologic detail, better defined the adnexal masses, and detected more adnexal lesions than endovaginal US (4).

Magnetic Resonance Imaging

Magnetic resonance has evolved into the imaging modality of choice for the study of the female pelvis. The relatively high cost of MRI is generally cited as the reason it is currently not used more often as a screening examination. Nevertheless, a number of studies have concluded that MRI is superior to CT and US in evaluating neoplasms and other gynecologic conditions, and future MR application in gynecologic disorders will undoubtedly increase. Magnetic resonance imaging is useful in women with primary amenorrhea both to detect congenital anomalies and as an aid for surgical planning. It provides the best results if the protocol is tailored to a specific question to be answered. Aside from possible screening, the trend is away from set generalized protocols. Endovaginal and endorectal coils are used only if advantageous for a specific question. Coronal T2-weighted images are very useful, especially in uterine evaluation. In particular for cystic lesions, fluid signal intensity is often expressed relative to the signal intensity of urine.

Magnetic resonance hysterography using saline injection has been proposed, but similar

to US, a possibility of intraperitoneal malignant cell dissemination exists in a setting of endometrial cancer.

One limitation of pelvic MRI is the lack of contrast differentiation between bowel and adjacent soft tissue structures. Prior administration of an oral contrast agent is helpful. Positive oral contrast agents are commonly used, although a negative agent tends to identify bowel wall and adjacent structures better.A suspension of superparamagnetic iron oxide particles (a negative oral contrast agent) shows promise in differentiating bowel loops from adjacent structures. Intravenous contrastenhanced MRI visualizes normal ovarian and uterine anatomy. The uterus normally enhances several seconds before the cervix. Some studies suggest that T2-weighted images are superior to postcontrast T1-weighted images in evaluating both normal and abnormal pelvic structures, although most investigators believe that con- trast-enhanced MRI is superior to precontrast MR in characterizing and differentiating pelvic tumors.

Magnetically labeled water perfusion imaging is a possible noncontrast technique for evaluating uterine blood flow. The use of short inversion delay times reveals the uterine artery dividing into its branches (5); longer inversion delay times reveal intracervical branching, followed by tissue enhancement.

Proton MR spectroscopy, although in clinical use in evaluating brain tumors, is rarely employed in gynecologic practice. This spectroscopic technique detects tumor metabolites, provided that a tumor is sufficiently large to be imaged. Single-voxel proton MR spectroscopy of pelvic tumors identifies a characteristic lactate signal in both malignant and some benign tumors (6); a signal from cholinecontaining compounds was detected only in solid tumors. The presence of lactate signifies anaerobic glycolysis.A high lipid peak is evident in tumors containing a high fat content, such as dermoid cysts.

Scintigraphy

Pelvic scintigraphy occasionally detects a hypervascular uterus. In general, such a blush represents increased uterine vascularity during the secretory and menstrual phases; a similar

blush during earlier phases should be considered abnormal.

Carbon-11-methionine is used as a positron emission tomography (PET) tracer. Preliminary studies suggest that benign or borderline malignant ovarian neoplasms do not accumulate C-11-methionine while carcinomas evidence significant uptake; in some patients this study thus appears useful in differentiating benign from malignant ovarian neoplasms.

Malignant ovarian tumors show 2-[18F]- fluoro-deoxy-D-glucose (FDG)-PET uptake. The limitations are that inflammatory processes and endometrial and follicular cysts also have an affinity for FDG, while borderline carcinomas tend to be false negative. Intrauterine accumulation of this agent occurs during menstruation. In general, FDG-PET is more helpful in detecting recurrent ovarian carcinoma.

Radioimmunoscintigraphy has a role in detecting the spread of ovarian cancer. A common agent used is indium-111–satumomab pendetide (OncoScint)-labeled antibody to tumor-associated antigen.

ADVANCED IMAGING OF THE ABDOMEN

Table 12.1. Müllerian duct abnormality classification

I.Segmental müllerian agenesis or hypoplasia

A.Vaginal

B.Cervical

C.Fundal

D.Tubal

E.Combined

II.Unicornuate

A.With rudimentary horn With endometrial cavity

Communicating Noncommunicating

Without endometrial cavity

B.Without rudimentary horn

III. Didelphys

IV. Bicornuate

A.Complete

B.Partial

C.Arcuate V. Septate

A.Complete

B.Incomplete

VI. DES related

Source: Adapted from Buttram and Gibbons (7).

Biopsy

Endovaginal US-guided biopsy and drainage are established diagnostic and therapeutic procedures. Most complications are self-limiting and consist of infection and hemorrhage.

Congenital Abnormalities

Müllerian Duct Anomalies

Bilateral fallopian tubes develop from Müllerian (paramesonephric) ducts, with the fused caudal ductal segments forming the uterus, cervix, and upper part of vagina. The lack of development or a müllerian duct fusion defect results in a specific developmental abnormality. Several müllerian duct anomaly classifications have been proposed; the one used here is a classification proposed by Buttram and Gibbons in 1979, and adopted by others since then (Table 12.1).

Congenital uterine malformations include agenesis, unicornuate, bicornuate, and septate uterus. The prevalence of these malformations

is <5%. Most affected women are not at an increased risk for sterility; however, they have a higher rate of spontaneous abortion and premature births compared to those with a normal uterus. Also, these women are at an increased risk for urinary tract abnormalities, including renal agenesis.

Imaging

Congenital uterine malformations are commonly studied with hysterosalpingography, although US is often the first imaging modality employed and is believed by some to be more sensitive. Three-dimensional US is useful in the study of müllerian duct abnormalities, achieving a sensitivity and specificity of close to 100% in defining these abnormalities. Nevertheless, MRI has evolved as the preferred imaging modality in evaluating suspected müllerian duct abnormalities. In particular, MRI is useful in differentiating a bicornuate uterus from a septate uterus. It aids in locating gonadal tissue

FEMALE REPRODUCTIVE ORGANS

not visualized by US and is useful in identifying ambiguous genitalia.

Coronal T2-weighted MR images of the uterus are easier to interpret if their oblique axis is placed parallel to the endometrial canal. The degree of obliquity can be estimated from sagittal images.

Prior surgery makes interpretation of imaging findings more difficult; this is especially true with MRI.

Agenesis/Hypoplasia

The Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome consists of congenital absence of the vagina and uterus and represents complete cessation of müllerian duct development; this syndrome is believed to be due to a deficiency of estrogen and other receptors. Ovarian neoplasms develop in young girls in association with this syndrome.

Some authors divide this syndrome into a typical or isolated form, consisting of symmetrical nonfunctioning muscular buds (müllerian duct remnants) and normal fallopian tubes, and an atypical, more generalized form consisting of aplasia of one or both buds and with or without fallopian tube dysplasia. Some duct remnants are cystic. Differentiation between the two forms is made on the basis of laparoscopic findings, although MRI can often suggests a diagnosis. The atypical form is associated with skeletal, renal, and ovarian abnormalities. Lack of adequate müllerian duct development leads to vaginal agenesis; with a functioning uterine anlage, MRKH syndrome results in hematometra. With a laparoscopic finding of an atypical MRKH syndrome, appropriate imaging is reasonable, often beginning with MR (Fig. 12.1).

A complex of renal dysgenesis, Gartner’s duct cyst, and ipsilateral müllerian duct obstruction in 10 girls resulted in a dilated Gartner’s duct protruding into the bladder and presenting as a ureterocele in some and extending posterior to the bladder in others (8); all had unilateral müllerian duct obstruction.

Agenesis of a portion of the müllerian ducts and congenital absence of the uterus and vagina is also found in male pseudohermaphrodites. Occasionally genitography is helpful in defining the underlying anatomy.

The appearance of a hypoplastic uterus is that of a normal uterus except for a smaller size. This condition is not common. A small uterus is also seen in such conditions as prior diethylstilbestrol (DES) exposure.

Isolated fallopian tube agenesis is rare and is associated with maldevelopment of mesonephric and paramesonephric ducts, possibly on an ischemic basis. Hysterosalpingography simply reveals fallopian tube nonfilling. Tubal obstruction due to other causes, including prior fallopian tube torsion causing hemorrhage and eventual reabsorption, must be excluded.

Unicornuate Uterus

Abnormal unilateral development of one of the Müllerian ducts results in an unicornuate uterus. These women have a high prevalence of associated urinary tract abnormalities, including an ectopic kidney, renal agenesis, double renal pelvis, horseshoe kidney, and medullary sponge kidney. They also suffer from a high spontaneous abortion rate and a high rate of ovum implantation in a rudimentary horn and subsequent rupture during pregnancy.

Hysterosalpingography reveals a fusiformshaped uterus tapering to its connection with the single fallopian tube. The uterus is displaced toward the side of the functioning tube. When performing this study, one must be careful not to confuse a bicornuate or septate uterus with a unicornuate one. Even if hysterosalpingography does demonstrate what appears to be a unicornuate uterus, a contralateral noncommunicating uterine horn may still be present but simply not communicate with the main uterine cavity, a finding not detected with hysterosalpingography. Such a rudimentary noncommunicating horn is detected by CT, US, or MRI, although US may be nonspecific, defining only a single cavity but without providing sufficient detail. Magnetic resonance imaging is the procedure of choice to provide both uterine and adnexal region anatomic details.

A pregnancy in a noncommunicating rudimentary horn is associated with a high rate of perforation and thus, if detected, resection of this cavity is generally performed. Such a cavity also predisposes to endometriosis, presumably due to retrograde expulsion of menstrual products.

Didelphys

A didelphic uterus results from fusion failure of müllerian duct caudal segments (Fig. 12.2). In complete didelphys each uterine cavity has a separate cervix and a variable septum is present in the vagina (Figs. 12.3 and 12.4). Some women also have associated renal agenesis, dysplasia, or hypoplasia, and an ectopic ureter to Gartner’s duct cysts. A duplicated uterus can be occluded unilaterally. Girls with unilateral occlusion of a duplicated uterus develop hydrocolpos, hydrometrocolpos, hematometrocolpos, and hematosalpinx.

During hysterosalpingography uterus didelphys is confused with a unicornuate uterus if only one of the uterine cavities is injected with contrast. Magnetic resonance imaging is the examination of choice in defining these abnormalities and providing preoperative guidance (Figs. 12.5 and 12.6). It should be noted that a congenital anomaly of cloacal exstrophy is also associated with two vaginas and hemiuteri.

Bicornuate

It is necessary to differentiate between a bicornuate and a septate uterus because of the differences in pregnancy outcome and because therapeutic approaches for these two conditions are different. A bicornuate uterus tends to be associated with a normal pregnancy while abortion rates with a septate uterus are about double that of a bicornuate uterus.

Obstruction of one uterine horn leads to a unilateral hematometra. A variant is a partial vaginal septum and resultant hematometrocolpos. Complicating the diagnosis is that an occasional bicornuate uterus reveals unilateral intermittent occlusion.

During hysterosalpingography a bicornuate uterus resembles a septate uterus. It is also similar to uterus didelphys, except that a bicornuate uterus has only one cervical os. Measurement of the angle of divergence between the two uterine cavities during hysterosalpingography has been used in an attempt to differentiate between a bicornuate and a septate uterus. A