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IV./3.4.: Postpartum uterus vs. endometritis
Its length can be also 15 cm following delivery, its wall is thick. The size decreases rapidly (more rapidly following a per vias naturales delivery compared to the caesarean delivery). In nurturing women the uterus reaches the prenatal size faster compared to the non nurturing women.
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Following birth MR cannot image the zonal distribution and the junctional zone (which regenerates appr. 6 weeks later), and dilated vessels can be detected in the myometrium even a week later, which gives a very heterogeneous signal at this time.
The continuance of the uterine involution can be resulted by various causes: twin delivery, hydramnion, bleeding, prolonged delivery, and various tissues retained in the uterus: blood clot, placenta parts, tissue scrap. Differentiation among these (e.g. blood) is possible by MRI.
US demonstrates a very inhomogeneous image in the postpartum uterus: the uterine cavity might be wider, including smaller-larger echogeneous areas because of the possible blood clots. The borders might have very heterogeneous echogeneicity, they can be irregular. Borderline between normal and pathologic cases can be separated sometimes very difficultly. In endometritis, the appearence of uterus and endometrium can be „normal”, but intrauterine intracavital fluid, endometrial thickening can also occur by showing a heterogeneous echogeneicity, and a gas indicating reflection can also appear. In case of a postpartum bleeding and a „normal” US appearence we should think of uterine atonia, whilst the in the uterine cavity appearing echogeneicities rather indicate retained parts (Doppler US might be of help in the differential diagnosis).
Among the causes of endometritis, intrauterine devices (IUD) must be mentioned. TVUS usually demonstrates well these devices (echogeneous lesions with distal shadows). If IUDs migrated from their original place (even into the peritoneal cavity), CT must be chosen since IUDs are hyperdense due to their metal characteristics.
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As indicated above, MRI is the method of choice in the diagnostics of endometritis. On MRI hematoma gives various but very characteristic signals according to the hemoglobin decomposition products. Fluid/hematoma does not enhance the contrast – in contrast to the e.g. retained placenta parts. The imaging differential diagnostics of the retained placenta parts (placenta accreta, placenta increta, placenta percreta) is provided by the MRI (besides the labor diagnostics, HCG level measurement). Differentiation is important since the therapies are different.
Although air bubble can be visible in the uterine cavity following birth, if it is visible later (2-3 weeks later), – besides additional signs referring to inflammation – we should think of endometritis. Uterinal fluid cannot be differentiated from pus by MRI (only the blood can be differentiated). Strong contrast enhancement of the cervix is a very important sign. Uterus itself is edematously impregnated (high signal on T2), however, if small hyperintensities are included, myometritis should be kept in mind (abscesses).
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