Role of imaging in endometriosis
ABSTRACTEndometriosis—the presence of endometrial tissue outside the uterine cavity—is first suspected on the basis of its signs and symptoms. The diagnosis is confirmed by imaging and surgery. Imaging, particularly transvaginal ultrasonography and magnetic resonance imaging, is essential to confirm the diagnosis and guide surgical treatment.
KEY POINTS
- The diagnostic evaluation should always start with transvaginal ultrasonography of the pelvic structures followed by magnetic resonance imaging, especially if deeply infiltrating endometriosis is suspected.
- An inaccurate imaging evaluation may lead to an incomplete excision of lesions if the patient undergoes surgery.
- Transvaginal ultrasonography and magnetic resonance imaging allow the assessment of the size, location, and extent of the lesions.
- Given the multifocal nature of the disease, a thorough evaluation of all pelvic structures, including the bowel, the bladder, and the ureters, is always recommended.
INCLUDE IMAGING IN THE DIAGNOSTIC WORKUP
Surgical treatment is frequently offered to patients who have severe pelvic pain that does not respond to medical treatment, or in cases of infertility. Imaging investigations are mandatory both to ascertain the diagnosis and to assess involvement of internal organs before surgery. Moreover, imaging helps minimize the surgical risks.
The primary aim of the radiologic examination is to describe the precise location, the depth, and the number of pelvic endometriotic lesions. Furthermore, imaging is useful to check for endometriotic foci in pelvic organs such as the bowel, ureters, and bladder, which are often involved in the pathologic process.
Transvaginal ultrasonography and magnetic resonance imaging (MRI) can accurately delineate deeply infiltrating lesions of endometriosis that are not easily accessible laparoscopically.
Transvaginal ultrasonography
Transvaginal ultrasonography is the first-line imaging study when endometriosis is suspected: it is powerful, simple, widely available, and cost-effective. In particular, it is recommended for diagnosing endometriotic ovarian cysts (endometriomas)8,9 and endometriosis of the bladder.10 However, its value for the assessment of superficial peritoneal lesions, ovarian foci, and deeply infiltrating endometriosis is questionable.
Although uncomfortable for the patient, transvaginal ultrasonography should be performed during menses, or when the pain reaches its highest level. In fact, during menstrual bleeding the endometrial implants grow and become easier to detect.
Mais et al8 reported that transvaginal ultrasonography has a sensitivity of 88% in differentiating endometriomas from other ovarian masses, and a specificity of 90% (Figure 2). Furthermore, its specificity is as high as that of MRI.8,9
Endometriotic nodules detected in the uterosacral ligaments, rectovaginal septum, vagina, vesicouterine pouch, bladder (Figure 3), and ureters can be signs of deeply infiltrating endometriosis. Pelvic adhesions can be suspected when pelvic organs appear fixed to each other, when hyperechogenic plaques are found between the serosal surfaces of the different organs, and when the pouch of Douglas is partially or completely obliterated.
The accuracy of transvaginal ultrasonography strongly depends on the operator’s skill. Furthermore, lesions of the sigmoid colon are impossible to visualize by transvaginal ultrasonography; hence, further diagnostic procedures are required. Transvaginal ultrasonography is the most accurate technique in detecting endometriotic nodules of the bladder wall in patients with urinary symptoms.
Transvaginal ultrasonography combined with color Doppler can also demonstrate the flow of urine through the ureters to the bladder, thereby ascertaining the patency of the ureters and clarifying the anatomic relationship between the ureters and any endometriotic lesions in the detrusors.10 Hydronephrosis can arise from ureteral restriction caused by endometriotic nodules. Thus, transabdominal ultrasonography of the kidneys is always recommended when deeply infiltrating endometriosis is suspected.
Some centers use a bowel-preparation protocol consisting of a laxative taken 24 hours before the procedure, combined with a low-residue diet and an enema 1 hour before the examination to cleanse the rectosigmoid colon of fecal content and gas, which can interfere with the visual examination of the pelvic structures.11
Transabdominal ultrasonography
Transabdominal ultrasonography can be used instead of transvaginal ultrasonography, eg, in young girls and women who have never been sexually active. When transabdominal ultrasonography is selected, the patient should have a full bladder to maximize the visualization of the pelvic structures. However, transvaginal ultrasonography is generally more sensitive than transabdominal in detecting adnexal masses and pelvic nodules.12
Magnetic resonance imaging
MRI has been recently introduced in the diagnosis of endometriosis. MRI is less operator-dependent than transvaginal ultrasonography and is more sensitive for detecting foci of deeply infiltrating endometriosis, because of its ability to completely survey the anterior and posterior compartments of the pelvis. However, its diagnostic value in cases of bladder endometriosis, superficial peritoneal lesions, and ovarian foci is still controversial.13–16
On MRI, lesions of deeply infiltrating endometriosis mainly appear as areas or nodules with regular, irregular, indistinct, or stellate margins. A distortion of the normal pelvic anatomy or the detection of a loculated fluid collection can indirectly signal the presence of adhesions.
MRI has high specificity for the diagnosis of endometriomas as a result of its ability to detect aged hemorrhagic content (Figure 4).17 Despite the many studies that point to the limits of MRI in detecting small endometriotic lesions, recent studies demonstrated that MRI also has good sensitivity for small peritoneal implants and adhesions.18,19 The injection of gadolinium contrast is still a debatable measure, because contrast-enhanced imaging cannot differentiate infiltrating lesions from other normal fibromuscular pelvic anatomic structures.15,20
Bowel preparation can be done with an oral laxative the day before imaging, complemented by a low-residue diet. A single dose of a ready-to-use enema is given 30 minutes before the examination to cleanse the terminal section of the intestinal tract. To avoid motion artifacts caused by bowel peristalsis, images are obtained after intramuscular injections of a myorelaxant are given, if there is no contraindication. Bowel preparation is useful to eliminate fecal residue and gas, thereby allowing proper visualization of lesions of deeply infiltrating endometriosis, but it is not routinely prescribed in all centers.11
In most cases, endometriotic lesions have an MRI signal intensity that comes very close to that of the surrounding fibromuscular structures. In this regard, vaginal and rectal distention and opacification using ultrasonographic gel clearly help to delineate the cervix, vaginal fornices, and vaginal wall, as well as the rectum and wall of the rectosigmoid junction (Figure 5).20
PRESURGICAL IMAGING
Rectal endoscopic ultrasonography
Even though it should not be included in the routine diagnostic workup, rectal endoscopic ultrasonography, using a flexible echoendoscope, is suitable in certain presurgical cases. The aim of this imaging technique is to assess the depth of bowel wall infiltration thanks to the visualization of the different layers.21
Double-contrast barium enema and multislice computed tomography
Double-contrast barium enema is extensively used for the diagnosis of bowel endometriosis, once the decision to perform surgery has been made. It allows evaluation of the degree and length of the bowel occlusion at the level of the sigmoid or high rectosigmoid tract, but it does not permit differentiation of bowel endometriosis from other pathologies.
Multislice computed tomography offers the opportunity to evaluate the depth of the lesions with excellent precision. 22
The most relevant disadvantage of both procedures is the exposure of women of reproductive age to ionizing radiation. In addition, multislice computed tomography requires the administration of an intravenous iodinated contrast medium and a retrograde colonic distention with about 2 L of water.
