Abnormal genital bleeding represents the characteristic and most common manifestation of acute uterine disorders and is one of the most common presentations in the emergency gynaecology unit as it accounts for approximately one-third of urgent gynaecologic visits. Causes encompass a wide spectrum of systemic and endocrine disorders, benign conditions (infection and focal abnormalities of the uterine cavity) and malignancies [10].
In reproductive-age women, when pregnancy is ruled out, clinical examination is required to search for vaginal and cervical abnormalities underlying acute bleeding. Additional imaging is required to detect or exclude abnormalities such as endometrial polyps or submucosal fibroids. Endometrial cancer is rarely encountered in pre-menopausal women, very exceptionally under 40 years of age. Dysfunctional uterine bleeding (idiopathic menorrhagia) represents a diagnosis of exclusion, in the absence of a recognizable pelvic pathology [11].
Transvaginal US remains the initial modality of choice in the evaluation of endometrial diseases, but the use of MRI to clarify abnormal or suspicious US findings before hysteroscopy is increasing, as it provides superior detection and characterisation of abnormalities in the uterine cavity [12].
Endometrial polyps
Endometrial polyps (EP) represent a localised overgrowth of endometrial glands with a central stroma composed of fibrous tissue or smooth muscle. Sometimes asymptomatic, EP easily cause either menometrorrhagia in pre-menopausal women or post-menopausal bleeding. The prevalence ranges from 7.8% to 34.9% and increases with age; tamoxifen is a well-established risk factor [13, 14].
On T2-weighted MR images, EP appear as low signal intensity sessile or pedunculated masses projecting into the endometrial cavity, surrounded by high signal intensity fluid and endometrium. Furthermore, a fibrous core (low signal intensity stripe or centre) and intratumoural cysts (discrete, smooth-walled cystic structures of high signal intensity) may be identified within the mass. Cystic spaces correspond to dilated glands but are nonspecific as they may be present within EP, hyperplasia or cancer. On T1-weighted images, EP generally have isointense signal compared to the endometrium, and may become haemorrhagic after ulceration or infarction leading to the appearance of hyperintense region best appreciated using precontrast fat saturation. After gadolinium contrast, EP may show either early persistent or gradually increasing enhancement, equal to or greater than that of outer myometrium (Fig. 1) [10, 15, 16].
Regarding management, hysteroscopic polypectomy is the gold standard for both diagnosis and treatment. Conservative management is reasonable in the case of small polyps in asymptomatic patients [17].
The key differential diagnosis of post-menopausal bleeding is endometrial carcinoma, which usually shows intermediate signal intensity (hyperintense compared with the myometrium) on T2-weighted images [18]. Identification of the central fibrous core and of intratumoural cysts favour the diagnosis of EP. Conversely, myometrial invasion, necrosis, a lower enhancement compared to the adjacent myometrium and irregular internal “cystic” areas suggest carcinoma. Endometrial hyperplasia is a premalignant condition that does not have a characteristic imaging appearance (Fig. 2); therefore, any focal endometrial thickening warrants hysteroscopy and biopsy, especially in post-menopausal women [10, 15, 16].
In post-menopausal women, the normal endometrium measures a mean 4 mm (range 1–12 mm) thickness [19], and endometrial thickness should be regarded as abnormal if ≥ 5 mm or > 9 mm, respectively, in presence or absence or genital bleeding [10].
In reproductive age, the normal endometrial thickness varies according to the menstrual cycle phases. Shitano et al. prospectively investigated the MRI appearance of normal endometrium in 32 healthy pre-menopausal women in follicular phase (FP) and luteal phase (LP). The maximum thickness of the normal endometrium, measured on sagittal T2-weighted images, in FP (mean 6.5 mm, range 2.1–14 mm) was significantly lower than that in LP (mean 10.4 mm, range 3.9–20.4 mm). Furthermore, on T2-weighted sequences, the signal intensity of the normal endometrium in FP was significantly higher than that in LP [20].
Uterine fibroids
The most common gynaecological mass, fibroids (leiomyomas) are benign tumours composed of smooth muscle cells and fibrous connective tissues that develop in almost 20–30% of reproductive-age women. In non-complicated fibroids, CT findings include uterine enlargement with lobulated contours, deformity of the endometrial cavity, and presence of focal masses that vary from exophytic or subserosal to intramural to submucosal. When present, coarse calcification is quite specific. Contrast enhancement is variable, so that fibroids may appear isodense, hypodense or hyperdense relative to the myometrium. MRI is the most accurate modality to detect, localise and characterise leiomyomas, which are typically T2-hypointense compared to the surrounding myometrium and of intermediate signal intensity on T1-weighted images [21].
Acute pain develops in up to 30% of patients, secondary to either acute degeneration or torsion of an exophytic or submucosal pedunculated leiomyoma; in the latter case, vaginal bleeding coexists. Degeneration of leiomyomas results from the volumetric increase that outgrows vascular supply and may take different forms (hyaline, myxoid, cystic and haemorrhagic) according to the rapidity of development. The most common form is the hyaline one, with a deposit of collagen fibres. Among the different types of degeneration, the haemorrhagic one is most likely to cause acute pelvic pain. Haemorrhagic (“red”) degeneration often occurs during pregnancy or in association with the use of oral contraceptives and consists of haemorrhagic infarction of the leiomyoma secondary to venous thrombosis at the periphery of the lesion [21].
At CT, haemorrhage and loss of contrast enhancement within a pedunculated, subserosal or intramural fibroid with a development of a cystic-like appearance may suggest the possibility of degeneration or infarction (Fig. 3). At MRI, haemorrhagic leiomyomas display diffuse or peripheral high signal intensity on T1-weighted images, reflecting the effect of methaemoglobin. On T2-weighted sequences, they show variable signal intensity with peripheral hypointensity secondary to haemosiderin formation. After gadolinium contrast agent administration, the lack of enhancement reflects interrupted blood supply (Figs. 4 and 5) [2, 9].
The most challenging differential diagnosis of benign degenerating leiomyomas is from uterine leiomyosarcomas that may exhibit different MR imaging patterns: (a) lobulated mass with high signal intensity on T2-weighted sequences, (b) well-marginated mass with low signal (similar to that of a leiomyoma), or (c) mass with extensive invasion and infiltrative margins. The suspicion of leiomyosarcoma may also be raised by the identification of haemorrhage and coagulative necrosis. The latter can present as areas of slightly high signal intensity on T1-weighted sequences and heterogeneous signal intensity on T2-weighted sequences [22]. In the differential diagnosis between leiomyomas and leiomyosarcomas, intravenous contrast agent administration is mandatory to identify solid components of leiomyosarcomas [23]. Lakhman et al. identified four qualitative MR features (nodular borders, haemorrhage, “T2 dark” areas and central unenhanced areas) strongly associated with leiomyosarcomas. In particular, the combination of at least three of these MR features may distinguish leiomyosarcomas from atypical leiomyomas with a specificity of > 95% [24].
As for the role of DWI, restricted diffusion may represent a pitfall since it is observable in benign cellular leiomyomas as well as in leiomyosarcomas, although some authors demonstrated significantly lower mean ADCs in leiomyosarcomas than in degenerated leiomyomas [25]. Although invasion, necrosis and above all rapid growth are suggestive of malignancy, the differentiation between benign degenerating leiomyomas and leiomyosarcomas still remains particularly challenging and the final diagnosis is often established histologically [22].
In patients with symptomatic uterine leiomyomas, embolisation is recognised as a minimally invasive uterine-sparing treatment option. Although embolisation is generally safe, post-procedural pain may occur: pain may range from mild to severe, is more frequent during the first week after embolisation and forms the “post-embolisation syndrome” along with fever, loss of appetite, nausea and malaise. Post-procedural readmission is needed in about 10% of cases [26, 27]. Severe pain is partly explained by myometrial ischaemia and is correlated with the percentage and volume of ischaemic tissue [28].
Contrast-enhanced MRI is the imaging method of choice to evaluate post-embolisation appearances of fibroids. At follow-up, treated leiomyomas may show increased signal intensity on T1-weighted images, due to the shortening effect of methaemoglobin, and variable signal intensity on T2-weighted images, a finding consistent with haemorrhagic infarction induced by the procedure (Fig. 6). On contrast-enhanced T1-weighted images, the lack of enhancement within fibroids is indicative of successful complete infarction without residual viable tissue [29, 30]. Since imaging appearances of treated leiomyomas can be very similar to that of leiomyomas with red degeneration and, to some extent, of leiomyosarcomas with coagulative necrosis, particular attention should be paid in the anamnesis of patients with pelvic pain, with thorough questioning regarding possible previous interventional procedures.
Uterine inversion
Uterine inversion (UI) refers to inside-out overturning and protrusion of the uterine fundus downwards up to or through the cervix that may occur either as an acute (within 24 h) life-threatening obstetric complication of mismanaged labour or in multiparous post-menopausal women from pulling effect of submucosal or pedunculated leiomyomas attached to the fundus; in the latter case, symptoms include pelvic tenderness or pain, vaginal discharge and irregular uterine bleeding. Physically, the vagina is occupied by the inverted uterus, but the clinical diagnosis is challenging without a high index of suspicion. Imaging is crucial to avoid misinterpretation as cervical tumour and to obviate biopsy which may cause profuse bleeding [31, 32].
Whereas the nature of the “mass” protruding into the vagina is difficult to identify at US, MRI generally clinches the diagnosis. The hallmark of UI on sagittal viewing is a U-shaped uterus with indentation and depression of the fundus, and a “bulls-eye” transverse configuration reflecting the zonal anatomy (Fig. 7d, f). Additionally, MRI may detect the possible presence of T2-hypointense submucosal fibroids or heterogeneously hyperintense mass-forming tumours. Albeit with limited contrast resolution, in acute settings, CT with adequate image reformation may also allow recognition of UI (Fig. 7a, c) [34].
Treatment of UI should consider the fertility and reproductive wishes of the patient, stage of inversion and underlying (benign or malignant) pathology. Whereas in puerperium manual repositioning is possible, post-menopausal UI requires abdominal or vaginal hysterectomy [35].