Imaging in Pelvic Inflammatory Disease and Tubo-Ovarian Abscess 

Preferred examination

Ultrasonography should be the first diagnostic imaging examination to be performed in cases of suspected pelvic inflammatory disease (PID) in which there are nondiagnostic clinical findings. This modality is readily available and noninvasive and can be performed at the patient's bedside.^{[1, 2, 3, 4, 5, 6]}

See the PID and tubo-ovarian images below.

Transvaginal sonography (TVS) allows detailed visualization of the uterus and adnexa, including the ovaries. The fallopian tubes are usually imaged only when they are abnormal and distended on physical examination, primarily from postinflammatory obstruction. Transabdominal sonography (TAS) is complementary to the endovaginal examination because it provides a more global view of the pelvic contents. Whether TAS (bladder filling required) or TVS (bladder filling not required) is performed first and whether the complementary examination is needed for a final diagnosis is a matter of individual clinical imaging practice.^{[7, 5, 8, 9]}

Magnetic resonance imaging (MRI) serves as an excellent imaging modality in cases in which the ultrasonographic findings are equivocal. In a study by Tukeva et al, the authors compared findings from MRI with sonograms and found that MRI was more accurate than ultrasonography in the diagnosis of PID.^[10] However, the study was limited to a select group of patients.^{[10, 11, 12]}

Occasionally, computed tomography (CT) scanning may be used as the initial diagnostic study for the investigation of nonspecific pelvic pain in a female, and PID may be found incidentally. Most often, ultrasonography is preferred over CT scanning as the triaging tool in a female child or adolescent with right lower quadrant or pelvic pain, particularly because of concerns about radiation exposure. If the diagnosis of PID is still in question, confirmation with ultrasonography is suggested.

Pelvic inflammatory disease is one of the most serious complications of sexually transmitted diseases.^[1] It is an infection of the female upper genital tract that encompasses a broad category of diseases, including endometritis, salpingitis, salpingo-oophoritis, tubo-ovarian abscess (TOA), and pelvic peritonitis. Prompt diagnosis and treatment of this condition are critical because the complications of PID can be life and fertility threatening.^{[2, 13]}

Annually, there are approximately 1 million women who develop PID.^[3] An estimated 1 in 8 sexually active adolescent girls develop PID before reaching age 20 years. Because PID may be asymptomatic and this condition is frequently undiagnosed, the incidence rate is likely higher.^{[3, 14]}

Pelvic inflammatory disease most commonly results from Chlamydia trachomatis or Neisseria gonorrhoeae infection of the cervix or vagina that then spreads into the endometrium, fallopian tubes, ovaries, and adjacent structures. Less commonly, direct spread from a nearby infection such as appendicitis or diverticulitis may occur. Hematogenous infection is a rare cause of PID except in cases of tuberculous PID.^[15]

Criteria for diagnosis

The Centers for Disease Control and Prevention (CDC) criteria for the diagnosis of PID are as follows^[14] :

Minimum criteria (1 or more) are as follows:

• Lower abdominal tenderness
• Adnexal tenderness
• Tenderness with cervical motion

Additional criteria (patients with PID should have 1 or more) are as follows:

• Signs of lower genital tract inflammation
• Oral temperature higher than 101ºF
• Abnormal cervical and vaginal discharge
• Greatly increased numbers of white blood cells on saline microscopy of vaginal secretions
• Elevated erythrocyte sedimentation rate
• Elevated C-reactive protein level
• Laboratory documentation of cervical infection with C trachomatis or N gonorrhoeae

Elaborate criteria (additional findings) are as follows:

• Histopathologic evidence of endometritis at endometrial biopsy
• Thickened fluid-filled tubes with or without free pelvic fluid or a tubo-ovarian complex on transvaginal sonograms or images from other modalities
• Laparoscopic abnormalities that are consistent with PID

Limitations of techniques

Transvaginal sonography may be limited by the patient's inability to tolerate the transvaginal examination (although this is not usual). In such cases, only transabdominal findings may be available. Occasionally, the higher frequency and the lower position of the transvaginal transducer limits penetration of the sound beam, and TVS imaging of an unusually high adnexa may not be possible. Sometimes, a patient's large body habitus or abdominal wall scarring limits penetration of the sound beam, adversely affecting transabdominal sonography.^[9]

CT scan findings are nonspecific in cases of pelvic inflammatory disease in which there is no evidence of an abscess. Inflammation obliterates the pelvic fat planes, with thickening of the fascial planes. If hydrosalpinx is present, a fluid-filled tubular structure may be seen in the adnexa.^[6]

Typically, a tubo-ovarian abscess (TOA) is depicted as a mass; the mass may have regular margins and contain debris similar to that seen in endometriomas or hemorrhagic cysts. Sometimes, the margins may be thick and irregular. There may also be an associated low-attenuation area that may represent an adjacent or contained fluid-filled fallopian tube.^[7]

Tubular fluid-filled nonvascular structures in the pelvis that are associated with an adnexal mass are suggestive of dilated fallopian tubes that correlate with cases of pelvic inflammatory disease. A finding of an adjacent or surrounding complex mass confirms the diagnosis of TOA.

Other conditions that can mimic pelvic abscess/tubo-ovarian abscess include necrotic pelvic neoplasm, hematoma, hemorrhagic physiologic cyst, and endometrioma.

Hydrosalpinx is depicted as a tubular structure with low signal intensity on T1-weighted MRIs and high signal intensity on T2-weighted images. If the walls are thickened, pyosalpinx should be considered in the differential diagnosis.^{[11, 12]}

Oophoritis may be evidenced by enlarged, polycystic-appearing ovaries with ill-defined margins and adjacent fluid.

Tubo-ovarian abscesses (TOAs) often appear as thick-walled masses with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Occasionally, the TOA may be isointense or hyperintense on T1-weighted images, and they may have heterogeneous signal intensity on T2-weighted images.

Ultrasonography is the most frequently ordered imaging examination when pelvic inflammatory disease (PID) is suspected. Most commonly, the ultrasonographic results for PID are normal, because salpingitis alone is not usually associated with imaging findings.^{[7, 4, 5, 8, 9]}

Positive findings of PID on ultrasonography may include the following:

• The uterus may be ill defined because of inflammation; however, inflammation of the uterus is an unusual finding
• Endometritis may result in central-endometrial-cavity echo thickening and heterogeneity (see the image below)This sonogram shows a markedly heterogeneous and thickened endometrium, a finding that is compatible with endometritis.
• Hydrosalpinx is depicted as a fluid-filled tube; if the tube walls are thickened and if debris is present within the tube, pyosalpinx should be considered in the differential diagnosis; however, a pyosalpinx may occasionally be imaged as an echoless tube, whereas an imaged echo-filled tube may be due to proteinaceous but noninfected fluid in a hydrosalpinx (see the images below) Transabdominal ultrasound scan. This image shows anechoic tubular structures in the adnexa; the finding is compatible with a hydrosalpinx. Endovaginal ultrasound scan. This image shows anechoic tubular structures in the adnexa; the finding is compatible with a hydrosalpinx. Endovaginal ultrasound scan. This image reveals a tubular structure with debris in the left adnexa; the finding is compatible with a pyosalpinx.
• Oophoritis results in enlarged ovaries with ill-defined margins that often appear adherent to the uterus; adjacent free fluid may be present in the adnexa or cul-de-sac (see the images below) Endovaginal ultrasound scan. This image shows a relatively enlarged right ovary in a patient who had pain, increased flow, and a small amount of adjacent free fluid. These findings are compatible with oophoritis. Endovaginal ultrasound scan. This image shows a relatively enlarged right ovary, increased flow, and a small amount of adjacent free fluid. These findings are compatible with oophoritis.
• Tubo-ovarian abscesses (TOAs) are depicted as complex adnexal masses with thickened walls and central fluid^[9] (see the images below) This sonogram reveals bilateral complex masses in a patient who had pyometrium. The finding is compatible with tubo-ovarian abscesses. This sonogram reveals bilateral complex masses in a patient who had pyometrium, a finding that is compatible with tubo-ovarian abscess. Power Doppler sonogram. This image shows increased flow to the wall of a tubo-ovarian abscess. The inner hypoechoic regions are due to the presence of purulent material. Transabdominal ultrasound scan. This image demonstrates an echogenic region within the endometrium with dirty shadowing, a finding that is compatible with air in the endometrium and endometritis. Additionally, bilateral complex masses are present; this finding is compatible with tubo-ovarian masses. Endovaginal ultrasound scan. This image was obtained for a better depiction of the clinical details. Endometritis with air in the endometrial cavity and bilateral tubo-ovarian abscesses are shown.

Degree of confidence

Thickening of the endometrium is nonspecific for PID because this finding may also be seen with endometrial hyperplasia, polyps, or cancer. Knowledge of the patient's clinical findings and other signs of infection can help in the differential diagnosis.

Hydrosalpinx and pyosalpinx can usually be readily distinguished from pelvic veins and bowel by visualizing the color flow within the patent blood vessels and peristalsis within the bowel.

Imaging findings in TOAs are usually nonspecific and must be distinguished from endometriomas, ectopic pregnancies, hemorrhagic cysts, ovarian tumors, and abscesses from adjacent organs.