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 [8].

Findings: The tubular structure is readily identified as cystic, with high signal intensity on T2- weighted images, which is lower than that of a pure cyst and may present a lack of internal enhancement. The signal intensity of T1-weighted images varies, depending on the protein content of the fluid. There is enhancement of the thickened fallopian tube walls and pelvic fat stranding. Although differentiating between pyosalpinx and hydrosalpinx is difficult, the thick hyper-enhancing tubal walls and surrounding inflammation serve as clues to the diagnosis. In cases of tubo-ovarian abscesses, MR imaging findings depend on the hemorrhagic and protein content of the mass. The abscess is usually hypointense at T1-weighted imaging; however, hemorrhagic or proteinaceous material can be hyperintense. A hyperintense rim along the inner wall of the abscess cavity has been described at T1-weighted imaging and is thought to correspond to granulation tissue and hemorrhage. T2-weighted imaging demonstrates a heterogeneous mass with low-signal-intensity septa, as well as hypointense linear stranding in the adjacent pelvic fat.

Occasionally, 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. CT scanning is very sensitive for the detection of pelvic pathology; however, it may not be as specific as sonography when an adnexal pathology must be differentiated from a tubal or ovarian one. If the diagnosis of PID is still in question, confirmation with ultrasonography is suggested.

The most common general CT findings of PID described in the literature are thickening of the uterosacral ligaments; obliteration of fascial planes; free fluid in the cul-de-sac; loss of definition of the uterine border; pelvic fat infiltration or haziness and pelvic edema; reactive lymphadenopathy; and signs of peritonitis. The uterosacral ligaments are paired structures that extend from the lower uterine segment to the mid-sacrum and are best seen on axial cross-sectional images. The normal thickness of the uterosacral ligaments is subjective and has not yet been established on CT images [11–14]. Salpingitis should be suspected at CT when the fallopian tubes are thickened, measuring more than 5 mm in axial dimension, and show enhancing walls. Associated free fluid may be depicted within the cul-de-sac. For the diagnosis of PID, the CT finding of tubal thickening was found to have a high specificity of 95% [14].

PID is often accompanied by reactive lymphadenopathy affecting the para-aortic lymphatic chain at the level of the renal hila. This lymphadenopathy is caused by the course of drainage of the ovarian and salpingian lymphatic vessels along the gonadal veins [14, 15] (Figs. 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7 and 4.8).