Pelvic inflammatory disease (PID) is a most serious complication of sexually transmitted diseases. The long-term sequelae include infertility, ectopic pregnancy, and disabling pelvic pain.
The sonographic appearances of PID can be divided into five categories:
1. Normal: A normal appearance of all pelvic organs and structures. This is usually seen with acute inflammation involving only the fallopian tubes without dilatation.
2. Endometritis: The endometrial echoes are usually absent. There may be fluid present within the uterus. The uterus is hypoechoic with indistinct margins and can appear enlarged and bulbous. No adnexal mass is identified.
3. Hydrosalpinx (Patient A): While PID is a bilateral disease, ultrasound may only suggest one-sided involvement. When detected, frequently an adnexal structure, which may be separable from the ovary, is seen. The structure is anechoic, tubular, and 1 to 4 cm in diameter with hyperechoic walls.
4. Pyosalpinx (Patient B): This focal extrauterine mass is usually located in the adnexa and about 1/3 of the time will also involve the cul-de-sac. Rarely, the mass is bilateral. The mass may cause bladder indentation if they share a common border. The mass is usually well-defined and clearly separable from the surrounding tissue. In 60% of cases, the walls are sharp and smooth; in the other 40%, they are irregular and ill-defined. The mass is usually between 3 and 8 cm and ovoid in shape. Almost all will have acoustic enhancement, about 2/3 will have internal echoes, and approximately half will have septations. Most will be anechoic or have a mixed pattern of echogenicity. Rarely, the mass will be hyperechoic. The uterus will appear normal. If it shares a common border with the mass, its specular echo can be obliterated.
5. Tubo-ovarian abscess (Patient C): It involves a large portion of the pelvis. The pelvis will contain a disorganized heterogeneous echo pattern having solid and/or cystic areas. One-third of the time it will be impossible to identify the uterus. When the uterus is seen, its specular echo pattern will be absent.
Patterns 4 and 5 are the most common, each occurring about 40% of the time. With any of the patterns, it is possible to see free fluid in the pelvis. It has been reported that a "pseudouterus" can be seen in women with PID who have had a hysterectomy. This is believed to be caused by the presence of adhesions holding bowel loops in the pelvis with an additional inflammatory response. When PID presents as a tubo-ovarian abscess, it will appear as a tube-shaped, fluid-filled, elongated oval which is fixed and tethered to any structure in the pelvis, most commonly the ovary. There may also be thickening of the hyperechoic peritubal fascia.