ESR Essentials: Gynaecological causes of acute pelvic pain in women: a primer for emergent evaluation—practice recommendations by the European Society of Emergency Radiology

Acute pelvic pain (APP) is a common presentation in women of all ages and has both gynaecological and non- gynaecological causes. In the emergency department, the suspected differential diagnosis dictates the chosen imaging modality. For premenopausal patients with APP, transabdominal ultrasound (TAUS) and transvaginal ultrasound (TVUS) are first-line investigations with high sensitivity and speci ficity for ectopic pregnancy, adnexal torsion, and ovarian cysts and their complications. US may also be valuable in pelvic in flammatory disease. When a non-gynaecological cause is suspected, contrast-enhanced CT (± transabdominal US) is indicated and has the advantage of 24/7 availability and lack of operator dependence. CT, however, may reveal an unexpected gynaecological cause of APP. When available, MRI is an excellent second test to improve diagnostic certainty in pregnant women when US is inconclusive —both for gynaecological and non-gynaecological conditions. MRI has a high diagnostic accuracy for pelvic in flammatory disease and tubo-ovarian abscesses. This article will enable readers to refresh their knowledge of common causes of APP and understand the histopathological processes involved in gynaecological causes of APP and how the imaging findings correlate. It will outline why different modalities are useful in different pathologies and help understand the limitations of each modality, including the requirement for operator expertise (US), relative lack of speci ficity/sensitivity (CT), and limited availability (MRI). This article excludes pregnancy-related causes of APP (apart from ectopic pregnancy) and also excludes non-gynaecological causes of APP. Key Points ● In female patients with acute pelvic pain, ultrasound is the best first modality in suspected gynaecological pathology. ● CT can be used when non-gynaecological causes of pain are suspected and when US is inconclusive. ● MRI has limited availability in an emergency setting and may be used in pelvic in flammatory disease and in pregnancy when US is inconclusive. © The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article ’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article ’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/ licenses/by/4.0/. Ana Blanco and Marcela De La Hoz Polo contributed equally to this work. This article belongs to the ESR Essentials series guest edited by Marc Dewey (Berlin/Germany). *Correspondence: Raffaella Basilico [email protected] Full list of author information is available at the end of the article 1234567890():,;1234567890():,; 1234567890():,; 1234567890():,;

Pelvic pain, Gynaecological examination, Ultrasonography, Computed tomography, Magnetic resonance imaging Key recommendations ● In skilled hands, transabdominal and transvaginal ultrasound is the best first modality in suspected gynaecological pathology. It will help identify ectopic pregnancy, adnexal torsion, causes of ovarian cysts and their complications, and may be of value in pelvic in flammatory disease (Level of evidence high). ● CT is a relatively non-speci fic test which is often the first imaging investigation due to its easy availability 24/7. It can be used when non-gynaecological causes of pain are suspected and when US is non-conclusive (Level of evidence moderate). ● MRI has high diagnostic accuracy and is very helpful in further characterisation after US ± CT. It has limited availability in an emergency setting and may be used in differentiating pelvic in flammatory disease and tubo-ovarian abscesses. MRI is useful in pregnancy when US is inconclusive (Level of evidence moderate).

Imaging modalities and protocols Acute Pelvic Pain (APP) is a common emergency com- plaint (Table 1) with gynaecological and non- gynaecological causes in women of all ages [ 1]. The differential diagnosis determines the choice of imaging modality. Ultrasound (US) is indicated if a gynaecolo- gical cause is suspected and has many advantages, being non-invasive, radiation-free, and with a high diagnostic yield. Transabdominal (TA) and transvaginal (TV) US are often performed together. TAUS allows visualisation of all pelvic contents, including free pelvic fluid. TVUS better depicts the uterus and adnexa. Colour and spec- tral Doppler are useful for vascularity assessment, especially if torsion is suspected [ 2]( T a b l e2). However, CT is increasingly becoming the first emergency imaging test due to 24/7 availability, especially if a non- gynaecological cause of APP is suspected (such as appendicitis or renal colic) and when US is unavailable [2, 3]. CT and US in combination may improve diagnostic certainty in some patients [ 4]. A single venous phase minimises radiation, with an additional arterial phase warranted in suspected active bleeding [ 3, 5]. In dual-energy CT (DECT), iodine mapping can dif- ferentiate haemorrhagic infarction from contrast enhancement in ovarian torsion. Virtual monochromatic images increase the detection of ischaemia in adnexal torsion or peritoneal in flammation. Finally, DECT can replace a true nonenhanced scan with a virtual none- nhanced scan, reducing radiation exposure [ 6]. On CT, normal fallopian tubes are not visible, while normal ovaries can be identi fied by location and follicular structure [ 5]. MRI, if available, enables excellent characterisation of abnormal gynaecological findings already identi fied on US or CT without ionising radiation [ 5]. A full MRI protocol includes fat-suppressed T2W images which Table 1 Causes of acute pain Gynaecological Non-gynaecological Nonpregnant Pregnant Genitourinary  Ovarian functional cyst rupture/ haemorrhage  Haemorrhagic corpus luteal cyst  Distal ureteral calculus  Pelvic in flammatory disease (PID)  Ectopic pregnancy  Lower urinary tract infection  Ovarian torsion  Uterine rupture Gastrointestinal  Fibroid degeneration/torsion  Uterine torsion  Appendicitis  Malpositioned IUD  Placental abnormalities  Diverticulitis  Hematometra  Spontaneous/incomplete abortion  Epiploic appendagitis/intraperitoneal focal fat infarction  Endometriosis/endometriosis cyst rupture  Ovarian hyperstimulation syndrome  Bowel in flammation, ischaemia, haemorrhage  Ovarian hyperstimulation syndrome  Gynaecological tumours  Ovarian vein thrombophlebitis Dick et al . European Radiology (2025) 35:6682 –6695 6683 increase the conspicuity of in flammation, oedema, and ascites. Gradient echo T2* sequences and pre-contrast T1 fat-saturated sequences identify blood products. DWI detects hypercellular fluid/pus [ 7]. In APP, gadolinium-enhanced fat-suppressed T1W demonstrates inflammatory peritoneal enhancement in PID (not visible in endometriosis). It can also characterise leio- myomas, leiomyosarcomas and adnexal masses [ 5, 8] (Table 3, limited protocol). Gynaecological causes of acute pelvic pain Infection/pelvic in flammatory disease (PID) PID refers to the in flammation of female reproductive organs, typically caused by b acterial infection ascend- ing from the vagina, causing cervicitis, endometritis, salpingitis, pyosalpinx, oop horitis, tubo-ovarian abscess (TOA) [ 9], peritonitis and occasionally pyometra and ovarian vein thrombophlebitis [ 10]. Risk factors include multiple sexual partners, intrauterine surgery, intrauterine devices (IUDs ), delivery, and endome- triosis [ 7]. Fever, pelvic pain, vaginal discharge, cervical tenderness and dyspareunia are common presentations. PID requires early antibiotic treatment to avoid complications such as infertility and ectopic pregnancy [ 10, 11]. Imaging helps in clinical uncertainty. Ultrasound is the best modality with CT used if US is inconclusive or there are suspected complications. General CT findings include thickening of the uterosacral ligaments, pelvic fat stranding (sensitivity 60.4%), obscuration of fascial planes, reactive lymphade- nopathy, and pelvic free fluid [ 10, 11]. The most specificC T finding is bilateral tubal thickening (95.1%, n = 190) [ 12]. MRI has a greater sensitivity than CT (0.95 pooled sen- sitivity versus 0.79) [13]. However, MRI is rarely needed to diagnose PID except in doubtful cases, the differential diagnosis of unclear adnexal lesions, and distinguishing non- complex fluid from blood and pus [ 7, 14]. Table 2 US findings of common causes of acute pelvic pain Pelvic in flammatory disease (PID)  Free fluid in the pelvis with internal echoes indicating purulent content  Endometritis/pyometra: thickened heterogenous endometrium, indistinct endometrium, fluid and/or gas within the cavity  Salpingitis: swollen fallopian tube (> 5 mm diameter), thickened walls and endosalpingeal folds showing hyperaemia on Colour Doppler.  Pyosalpinx: dilated fallopian tubes with echogenic fluid that may form levels due to purulent content  Tubo-ovarian abscess: multilocular complex cystic mass in the adnexa with a thick wall and internal echoes, showing hyperaemia on Colour Doppler. The ovary and the fallopian tube cannot be individually identi fied. Gas may be seen as echogenic foci with posterior dirty shadowing. Ovarian cysts  Follicular cyst: thin wall, posterior acoustic enhancement. No internal vascularity on Colour Doppler  Corpus luteum: well-circumscribed cyst ≤ 3 cm with a thick wall showing prominent hyperaemia on Colour Doppler ( “ring of fire” sign), and no internal vascularity. Spectral Doppler: prominent diastolic flow with low- velocity waveform throughout the luteal phase of the cycle.  Haemorrhagic cyst: heterogeneous content, fluid levels, possible complex mass appearance. No internal vascularity. ± Hemoperitoneum  Haemorrhagic corpus luteum: heterogeneous echogenic content, thickened hyperaemic walls. ± Hemoperitoneum Adnexal torsion  Enlarged ovary with peripherally displaced follicles. Heterogeneous ovarian echotexture (echogenic areas = haemorrhage; hypoechoic areas = oedema)  Midline or superior displacement of the affected ovary. Uterine deviation to the side of the twist. Ascites  Colour Doppler: Whirlpool sign indicating the twisted pedicle  Spectral Doppler: absent venous flow, decreased/absent diastolic flow, absent arterial flow. Important: presence of arterial or venous flow does not exclude ovarian torsion. Ectopic pregnancy (serum β-hCG +)  Absence of a normal intrauterine gestational sac (double decidual sac with two concentric hyperechoic rings that surround an anechoic gestational sac)  Tubal pregnancy: ∘ Adnexal mass separate from the ovary ± presence of gestational sac or a living embryo ∘ “Tubal ring sign ” + “ring of fire sign ”: decidual response in the fallopian tube with hypervascularity  Extrauterine findings: pelvic free fluid, hematosalpinx, hemoperitoneum. Hemoperitoneum is highly suggestive of ruptured ectopic pregnancy Dick et al . European Radiology (2025) 35:6682 –6695 6684 Cervicitis and endometritis Both represent early man- ifestations of PID. In cervicitis, the cervix may be enlarged and hyperaemic on US, with an enhancing endocervical canal and parametrial fat stranding and free fluid on CT/MRI. Endometritis can occur in PID, during the peripartum period, and after gynaecological procedures. Findings of a thickened heterogenous endometrium on US, abnormal endometrial enhancement relative to the inner myometrium on CT/MR, and fluid within the cavity suggest endometritis. The uterine border may be indistinct from parametrial tissue [ 2, 10]. Uterine empyema (pyometra) is characterised by complex fluid in the uterine cavity containing gas or air- fluid levels [ 10]. Salpingitis, tubal empyema (pyosalpinx) In salpingitis, the fallopian tube is swollen (> 5 mm diameter) and thickened. In pyosalpinx, pus distends the lumen (echogenic on US) and the mural thickening is hyperaemic on Doppler US, enhancing on CT (Fig. 1). CT may show surrounding pelvic in flammation, includ- ing uterosacral ligament thickening and para-aortic lymphadenopathy [ 2, 10, 15]. CT-multiplanar recon- struction helps identify the tubular contour, while MRI additionally differentiates pyosalpinx from haematosal- pinx by the presence of intratubal blood products. In pyosalpinx, there is tubal wall thickening, enhancement and in flammation. On DWI, restricted diffusion suggests pyosalpinx, while unrestricted diffusion suggests hydro- salpinx [ 7]. Tubo‑ovarian abscess Infection and destruction of adnexal structures result in a TOA. Imagingfindings typically reveal a multilocular complex cystic mass in the adnexa with thick walls, showing hyperaemia on US and uniform enhancement on both CT and MRI (Fig. 2). Associated free peritoneal fluid, surrounding pelvic in flammation, fat stranding and enhancement are common [ 10, 15]. The complex mass can be difficult to differentiate from an ovarian malignancy, but a dilated fallopian tube and restricted diffusion on DWI sequences suggest infection [11]. Peritonitis Pyometra, pyosalpinx, and TOA can cause peritonitis when an abscess ruptures or pus leaks from the infected organ [ 10, 15], but it can also be seen in the absence of such complications. Fitz-Hugh– Curtis syndrome (perihepatitis) In this rare complication, peritoneal spread to the liver capsule results in sharp right upper quadrant (RUQ) pain. CT findings include enhancement and thickening of the anterior liver capsule, geographic areas of variable perfusion in subcapsular and periportal areas, fluid and fat stranding extending from the pelvis into the RUQ, and gallbladder wall thickening [ 10, 15]. Atypical PID forms PID can uncommonly progress to involve other pelvic organs such as the bladder, urethra, or bowel. In addition to typical organisms, two further organisms should be considered, especially in unusual or extensive cases: Actinomycosis is suggested when there is Table 3 Time-efficient non-contrast MRI protocol for urgent study of the female pelvis and non-cooperating patients MRI protocol Axial T2W SSFSE Sagittal T2WFRFSE Oblique coronal/axial T2W FRSE Axial DWI SE EPI Sagittal, oblique coronal/axial T1W 3D GRE LAVA Repetition time/echo time (ms) 765/59 4675/100 4675/100 3000/74 4.4/2.1 Flip angle 90° 90° 90° 90° 12° Section thickness (mm) 6 4 4 8 3.4 Interslice gap (mm) 0.6 0.4 0.4 2 −1.7 Bandwidth (kHz) 31.25 41.67 41.67 62.5 Field of view (cm) 38 32 32 42 40 Matrix 320 × 288 320 × 224 320 × 224 160 × 160 370 × 192 No. of averages 0.54 2 2 2 0.75 No. of images 30 26 26 15 Frequency direction Right to left Anterior to posterior Right to left Anterior to posterior Superior to inferior Acquisition time 24 s 2 min 15 s 2 min 15 s 27 s 22 s β value (s/mm 2)- - - 0 –800 - Reproduced under the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/) from Tonolini et al [ 5] T2W T2-weighted, T1W T1-weighted, SSFSE single-shot fast spin-echo, FRFSE fast recovery fast spin-echo, DWI diffusion-weighted imaging, SE spin-echo, EPI echoplanar imaging, GRE gradient echo, LAVA liver acquisition with volume acceleration Dick et al . European Radiology (2025) 35:6682 –6695 6685 extension across tissue planes and fistula formation in the presence of an IUD. Tuberculosis can cause pyosalpinx, endometritis, and peritoneal thickening with deposits that can mimic peritoneal carcinomatosis [ 15]. Vaginal infections Isolated vaginal abscesses (without ascending infection) can occur in Bartholin ’s glands (posterolateral vagina) and in a Gartner cyst (anterolat- erally within the proximal vagina) [ 11]. Uterine emergencies: leiomyoma degeneration and uterine inversion Uterine leiomyomas ( fibroids) are a common gynaecolo- gical neoplasm containing smooth muscle and fibrous connective tissue, which can be submucosal, intramural, subserosal, and/or pedunculated [ 11, 16]. In 30% of patients, acute degeneration or torsion can cause APP [16]. Ultrasound is helpful, but MRI is optimal in char- acterisation [ 16]. In acute degeneration, the leiomyoma outgrows its blood supply. Speed of onset of degeneration in fluences pain experienced, histopathological nature (hyaline, myxoid, cystic or haemorrhagic) and imaging findings [16]. Hyaline degeneration is the most common and least painful, with deposition of collagen fibres [11]. Haemorrhagic (so-called ‘red’) degeneration occurs with rapid leiomyoma growth, such as in pregnancy or with oral contraceptive use [ 16]. In red degeneration, CT may show haemorrhage, loss of con- trast enhancement, ± cystic contents [ 11]. On MRI, non- degenerated leiomyomas are ty pically well-circumscribed, low to intermediate signal intensity on T2. Degenerated leiomyomas do not enhance post gadolinium due to infarction and, on T2W imaging, can be low (hyaline or calcific degeneration) or high signal (cystic or myxoid degeneration) [16]. Red degeneration may show peripheral T1 high signal intensity (repr esenting blood products and possibly thrombosed peripher al vessels) with variable T2 signal intensity (Fig. 3). Of patients who have undergone uterine artery embo- lisation of leiomyomas, 10% may require readmission for postembolisation syndrome, which includes pain, fever, and nausea. MRI will demonstrate haemorrhagic infarc- tion (high signal on T1) and lack of enhancement corre- lating with successful embolisation [ 16]. Inversion of the uterine fundus is rare, can extend through the cervix, and occurs either acutely postpartum Fig. 1 Pelvic in flammatory disease (pyosalpinx) in two different patients presenting with acute pelvic pain and fever. a Transabdominal grey-scale US and ( b) transvaginal Doppler image show thick-walled dilated tubular adnexal structures (arrows in a), distended with echogenic fluid-debris levels (dashed arrows) with surrounding vascularity with Doppler ultrasound. c Transabdominal grey-scale US image in a different patient, shows bilateral cystic structures (arrows) surrounding the uterus (U) containing hyperechoic material compatible with pyosalpinx. The ovaries show multiple follicles (arrowheads). d, e Coronal and axial post-contrast CT images, respectively, of the same patient, demonstrate both ovaries with multiple follicles (arrowheads) and bilateral thick-walled dilated tubular structures (arrows) representing the dilated fallopian tubes Dick et al . European Radiology (2025) 35:6682 –6695 6686 or in postmenopausal multiparous women, where it may be associated with a leiomyoma acting as a lead point [ 11]. While this is a challenging clinical diagnosis, sagittal MRI (and, to a lesser extent, CT) demonstrates inversion and indentation of the fundus [ 17]. Ovarian cyst complications, endometriomas, and ovarian hyperstimulation syndrome Haemorrhagic and ruptured ovarian cysts Ruptured or haemorrhagic ovarian cysts are the most common gynaecological cause of APP in a nonpregnant, afebrile premenopausal woman [ 18]. This may be a physiologic, self-limited process involving a corpus luteum (CL) cyst or a follicular cyst [ 6] (Fig. 4). While ovarian endome- triosis is common, rupture of an endometriotic cyst is uncommon [ 19]. Ruptured or haemorrhagic ovarian cysts present clini- cally with severe APP and, occasionally, hypotension due to large intraperitoneal bleed [ 18]. B-hCG levels help to differentiate from ruptured ectopic pregnancy [ 14]. US is the best modality to assess ovarian cyst rupture and haemorrhage/haemoperitoneum. Ruptured ovarian cyst may be sonographically normal if the cyst has completely ruptured and the fluid reabsorbed. Clues to a leaking cyst are crenellated appearance and low-level echoes/clot. Ruptured luteal cysts have a thick, echogenic, and irregular wall with increased peripheral blood flow on Doppler, the so-called “ring of fire” [14, 18]. Sonographic findings of haemorrhagic cysts depend on the age of the haemorrhage. In the early stages, a haemorrhagic cyst exhibits diffuse, low-level internal echoes, thin walls, posterior acoustic enhancement and no internal vascularity (Fig. 4)[ 18]. As the haemorrhage evolves, a lace-like reticular pattern of internal echoes develops. As echogenic thrombus coalesces within the cyst, a heterogeneous avascular mass forms with retractile angular or concave margins. Clots may be adherent or rounded but can be differentiated from mural nodules by lack of vascularity on Doppler US and, where needed, 6 –8 week US follow-up [ 18]. On CT, high-density cyst contents and thick enhancing walls can Fig. 2 Surgically con firmed tubo-ovarian abscess in two different patients. a, b Middle-aged woman with lower abdominal pain, fever and vaginal discharge. a Transabdominal grey-scale ultrasound shows a large cystic complex mass representing a tubo-ovarian complex with echogenic content consistent with pus. b Microflow ultrasound imaging demonstrates peripheral vascularity in the walls of the cystic lesion without internal vascularity in keeping with the cystic nature of the mass. c–e Young woman with pelvic pain and raised in flammatory markers. Consecutive axial ( a, b) and coronal (c) CECT images, venous phase, show bilateral pyosalpinx (dotted arrows) and a right ovarian abscess (asterisk). Note the fat stranding around the fallopian tubes (arrows) and the markedly thickened uterosacral ligaments (arrowheads) Dick et al . European Radiology (2025) 35:6682 –6695 6687 be seen. The MR appearance of haemorrhagic cysts is complex, with different signal characteristics at different stages [ 6]. Complicated endometriomas Endometriosis is the presence of ectopic endometrial tissue outside of the uterus. In the ovary, ectopic endometrial tissue can form haemorrhagic cysts or endometriomas due to repeated cyclic haemorrhage causing APP [ 5]. On US, endometriomas are unilocular, homogeneously hypoechoic cysts with diffuse low-level echoes ( ‘choco- late cysts ’)[ 18]. Spontaneous rupture of an endometriotic cyst is rare and torsion rarely occurs because of adhesions, however, these should still be considered in patients with endometriosis. CT can demonstrate features suggestive of endometrioma rupture, including thick-walle d, multilocular or bilateral ovarian cysts, loculated pelvic ascites, and fat stranding [19]. Other acute complications of endometriosis causing APP include endometrioma superinfection, PID, hemo- peritoneum, and bowel and genitourinary complications [20]. MRI is the best technique to diagnose endometrio- mas with ‘shading ’ on T2W due to dependant blood and repeated bleeding episodes (Fig. 4), with bilateral or multiple lesions being typical. In comparison, a non-endometriotic haemorrhagic ovarian cyst is more likely to be unilateral, unilocular, and without shading. Fig. 3 A–C Red degeneration on an intramural fibroid in a postmenopausal patient with acute pelvic pain and known fibroids. Sagittal T2, T1-FS pre and post-gadolinium MRI images, respectively, show intramural fibroids (arrows) with ( A) central heterogeneous T2 signal, ( B) hyperintense on T1 fat sat (haemorrhage) and ( C) non-enhancement in the post-contrast images in keeping with infarction. D, E Myometrial abscess in a patient with pelvic pain and vaginal discharge. Axial and sagittal post-contrast CT images show pelvic fluid (asterisk), fat stranding and thickening and oedema of the uterosacral ligaments (arrows). A uterine intramural hypodense abscess (arrowheads) was noted communicating with the endometrial cavity which is distended with fluid Dick et al . European Radiology (2025) 35:6682 –6695 6688 Ovarian hyperstimulation syndrome Ovarian hypersti- mulation syndrome (OHSS) is a condition that can occur after ovarian stimulation, often in the context of fertility treatments. Imaging plays a crucial role in diagnosing and assessing the severity of OHSS. Ultrasound is the primary imaging modality used to evaluate the ovaries, where findings typically include enlarged ovaries with multiple thin-walled cysts, ranging from small to large, represent- ing enlarged follicles or corpus luteum cysts (Fig. 5). In severe cases, free fluid may be seen in the pelvis or abdomen due to capillary leakage. In more advanced stages, CT or MRI scans may be employed to assess complications such as ovarian torsion, ascites, pleural effusions or other signs of severe OHSS. Particularly, MRI is very helpful in differentiating OHSS from ovarian tumours, including choriocarcinoma, which can also produce high hCG levels, by demonstrating markedly bilateral symmetrically enlarged ovaries with simple cysts of different size, separated by thin septa and lacking inhomogeneous solid tissue consistent with malignancy (Fig. 5)[ 5]. Adnexal torsion Adnexal torsion can involve the ovary, fallopian tube, or (most commonly) both. Isolated fallopian tube torsion spares the ovary, is rare, usually occurs during repro- ductive years and seldom post-menopause [ 6]. Clinically, Fig. 4 Complicated ovarian cyst in a young woman in her late teens presenting with acute pelvic pain, nausea and vomiting. a, b Transabdominal grey- scale and Doppler US shows a complex cystic mass with hyperechoic content (arrow) without vascularisation in Doppler images. c–e Portal venous phase axial and coronal CT images demonstrate a large amount of hemoperitoneum (asterisk) in the abdomen and pelvis. The images through the pelvis show a right para-uterine cystic mass (black arrows) with multiple hyperdense foci within related to active bleeding. Large hemoperitoneum with sentinel clot in the pelvis. Findings suspicious for ruptured ovarian cyst with active bleeding. Surgery con firmed ruptured corpus luteal cyst. f, g Endometrioma in a young woman with acute left quadrant pain. Axial T1-FS WI ( f) shows a large left ovarian cyst with high signal intensity and a fluid-fluid level (arrow). In the axial T2 WI ( g), the adnexal lesion shows marked signal loss due to cycling bleeding (shadowing sign). Note the right ovarian follicular cyst (arrowhead) Dick et al . European Radiology (2025) 35:6682 –6695 6689 patients present with nausea, vomiting and excruciating unilateral APP [ 18]. A normal ovary rarely undergoes torsion, except occasionally in perimenarchal girls or pregnancy [ 6]. In up to 90% of cases, an underlying ovarian mass serves as the lead point for torsion, particularly if larger than 5c m [ 14, 21]. Malignant ovarian tumours and endo- metriotic cysts are less likely to cause ovarian torsion due to adhesions [ 6]. Other risk factors include ovulation induction, pregnan cy, previous tubal ligation and hypermobility of adnexal structures [ 18]. Ovarian torsion is a surgical emergency. Delayed treat- ment increases the risk of vascular compromise and hae- morrhagic infarction. Torsion occurs when the ovary twists on its vascular pedicle, resulting in partial to complete obstruction of arterial in flow and venous out flow [22]. Pelvic US and colour Doppler is thefirst imaging modality to rule in/out adnexal torsion. The US appearance of torsion Fig. 5 Ovarian hyperstimulation syndrome in two different patients. a–d Women in her 30 ’s undergoing in vitro fertilisation presented with abdominal distention, nausea and vomiting. TAUS ( a, b) and TVUS ( c, d) demonstrate ascites (arrow in a), enlarged ovaries (black arrows) with preserved central flow (b) and multiple follicles of varying sizes ( b–d) consistent with OHSS. e, f Different patient in her early 30 ’s and 15 weeks pregnant presented with abdominal pain. Sagittal T2WI at the level of the right and left adnexal regions show markedly enlarged bilateral ovaries (arrows) containing multip le large, thin-walled cysts consisted with OHSS. P (placenta). MRI can provide better characterisation of the ovarian process in the differential diag nosis of ovarian tumours Dick et al . European Radiology (2025) 35:6682 –6695 6690 is variable and depends on the chronicity and degree of torsion, and whether there is some preservation of arterial flow to the ovary from its dual supply from the ovarian and uterine arteries [23, 24]. Findings greatly depend on factors such as duration and degree of vascular obstruction and whether it is intermittent [23]. Classical sonographic signs of ovarian torsion include increased ovarian diameter (> 4 cm) and volume (> 20 cm 3 premenopausal or > 10 cm 3 post- menopausal); however, in 5% of p a t i e n t s ,n oo v a r i a ne n l a r - gement occurs [ 21]. Other signs of ovarian torsion are peripherally displaced folli cles, midline or superior dis- placement of the affected ovary, heterogeneity of the central stroma with echogenic areas indicating haemorrhage and hypoechoic areas representing oedema, and uterine devia- tion to the side of the affected ovary and ascites [ 14, 18]. Doppler ultrasound flow patterns reflect the degree of vas- cular compromise and duration of torsion with venousflow affected before the high-pressure arterial flow. Signs of complete torsion include absent venous flow, decreased or absent diastolic flow and absent arterial flow. In partial torsion, arterial flow with high resistive spectral signal may be seen, In some cases of nonviable or complete torsion, peripheral arterialflo wc a nb ep r e s e r v e d ,w h i c hm a yb ed u e to the dual arterial supply and relative preservation of flow within the uterine artery [21, 23]. The ‘whirlpool’ sign refers to the twisted ovarian pedicle, and in association with an enlarged ovary, it is diagnostic of ovarian torsion [21]. Many of these findings can also be seen with contrast-enhanced CT and MRI, including the presence of a twisted vascular pedicle or an underlying mass and abnormal enhancement (Fig. 6). Finally, abnormal morphology and cystic degen- eration suggest infarction [21]. Fig. 6 Right adnexal torsion in a woman in her 40 ’s with intense right pelvic pain and vomiting. CT was requested to exclude appendicitis. a–c Post- contrast coronal ( a) and axial CT images ( b, c) excluded appendicitis and showed an enlarged and hypodense right ovary (arrow) posteriorly displaced behind the uterus in the axial images, compared to the normal size and located left ovary (arrowhead) and twisted right fallopian tube (dotted arrows) . d, e Subsequent transvaginal US performed preoperatively by the gynaecologist con firmed the CT findings with an enlarged and oedematous right ovary (arrow) measuring approximately 98 × 42 mm with distended peripheral follicles (curved arrows). f Intraoperative image con firmed right ovarian necrosis Table 4 Factors which increase the risk of ectopic pregnancy [27] Factors which increase the risk of ectopic pregnancy [ 27] Previous PID Previous surgery Endometriosis Use of IUDs Previous EP Assisted reproductive technology Infertility Smoking Congenital uterine anomalies Advanced maternal age Dick et al . European Radiology (2025) 35:6682 –6695 6691 Haemoperitoneum due to gynaecological causes Gynaecological causes of haemoperitoneum are many and include sexual intercourse, intense exercise, corpus luteum bleeding, ruptured haemorrhagic ovarian cyst, ectopic pregnancy, and ruptured endometriotic cyst. On US, peritoneal or pelvic fluid demonstrates low-level echoes, and US can also identify the cause. On CT, the free peritoneal fluid has a relatively high attenuation. CT can demonstrate the volume of haemoperitoneum, pre- sence of septations or loculation (which suggest endo- metriosis), and active bleeding, which guides interventional management. Active bleeding may be seen on the arterial or, most usually, on the venous phase, reflecting intermittent or venous haemorrhage [ 5]. On Fig. 7 Ectopic pregnancies in three different patients. a–c Teenager with intense abdominal pain and persistent vaginal bleeding. Grey-scale US images show a large amount of partially echogenic abdominal fluid (asterisk) and a pelvic haematoma (star) surrounding the uterus (U). A round, thick-walled para-uterine cystic mass (arrow) with vascularised wall and a fetal pole was noted with Colour Doppler ( d). No gestational sac was identi fied within the endometrial cavity. Laparoscopic surgery con firmed a ruptured ectopic tubal pregnancy with extensive hemoperitoneum. e–g Axial post-contrast CT images in a different patient with a ruptured tubal EP. Normal right adnexa is noted (black arrow), separate from a ring-enhancing right para-uterine cystic mass (dotted arrow) which increases the likelihood that the cystic mass represents an ectopic pregnancy. Active bleeding from the ruptured tu bal pregnancy is visible during the arterial phase (arrowhead). h Woman in her 20 ’s presenting in the emergency department with acute pelvic pain and vaginal bleeding. Coronal T2 WI shows an eccentric gestational sac (arrow) with a fetal pole (arrowhead) located in the interstitial segment of the ri ght Fallopian tube, next to the uterus (U). MRI is more helpful in evaluating ectopic interstitial pregnancy, which is a diagnostic challenge on ultrasou nd Dick et al . European Radiology (2025) 35:6682 –6695 6692 MRI, signal intensity of haemoperitoneum depends on age of the blood [ 25]. Ectopic pregnancy including ruptured ectopic pregnancy Ectopic pregnancy (EP) is a common cause of pregnancy- related APP. Early diagnosis and treatment have decreased the incidence of EP rupture, which is poten- tially life-threatening. In EP, the fertilised oocyte implants outside of the uterine endometrium, most commonly in the fallopian tubes (93 –98% of all EP, of which 75% are ampullary, 13% isthmic and 12% fimbrial) [ 26]. The dif- ferential diagnosis includes non-gynaecological adnexal masses [ 27]. Table 4 outlines factors which increase the risk of EP. A serum β-hCG value > 2000 mlU/mL (IRP Interna- tional Reference Preparation ) without intrauterine preg- nancy but with an extraovarian mass is highly suggestive of an EP [ 28]. On TVUS, an adnexal mass separate from the ovary is seen in most, but not all, tubal pregnancies [29]. Other signs include the “tubal ring sign ”: a thick echogenic ring surrounding an extrauterine gestational sac and the “ring of fire sign ” due to peripheral hyper- vascularity of the hyperechoic ring (Fig. 7). If the tro- phoblast invasively grows into the fallopian tube, EP rupture and hemoperitoneum occurs. Haemoperitoneum in EP is not necessarily indicative of tubal rupture but the larger the amount of fluid, the higher the likelihood of such. CT is now increasingly performed on pregnant women either because pregnancy status is unknown, there is clinical deterioration before serum β-hCG is available, or the early urine pregnancy test is false-negative. On CT, an adnexal area of low attenuation with a dramatic enhanced ring adjacent to the ipsilateral ovary and associated hae- moperitoneum suggests EP. In EP rupture, active bleeding can be seen (Fig. 7). The main CT differential diagnosis of EP is a CL cyst because (1) the wall of a CL may show strong enhancement, (2) a CL cyst may rupture in the peritoneum, and (3) a CL cyst may occur in the setting of early pregnancy. If clinical symptoms and serum β-hCG levels do not allow differentiation of these two entities, the site of the adnexal cystic mass may be a clue: a CL cyst is intraovarian, unlike an EP. MRI is a second-line test in suspected EP, demon- strating haemoperitoneum, a heterogeneous, partly hae- morrhagic adnexal mass representing the gestational sac and haematosalpinx within a dilated tube and mural enhancement [5]. MRI is better than CT at demonstrating direct signs (ectopic gestational sac —92% diagnostic accuracy) (Fig. 7) and indirect signs (haematosalpinx, adnexal haematoma, hemoperitoneum). 100% diagnostic INVESTIGATION OF FEMALE WITH ACUTE PELVIC PAIN History, examination, investigations Depending on local expertise US or CT β HCG + (POS) Post-menopausal MRI Pre-menopausal CT β HCG is essential in pre-menopausal patients Ectopic pregnancy Ovarian hyperstimulation Gynaecological causes * Non-gynaecological causes ** CT CT β HCG (NEG) or not available (or clinical condition worsening) Gynaecological causes Uterine & placenta complications * Gynaecological causes * US +/ CT If US non-conclusive OR non-gynaecological causes ** ^ Gynaecological causes * PID Malignancy Ovarian torsion Cyst complications Leiomyoma torsion / degeneration CT or MRI (if available) Non-gynaecological causes ** Appendicitis ^ Diverticulitis Perforation Omental infarct Vascular disease Bowel obstruction Bowel inflammatory disease ^ Urinary lithiasis / infection (when complicated) MRI / CT If US non-conclusive OR non-gynaecological causes ** ^ Ectopic pregnancy Ovarian hyperstimulation US MRI US Fig. 8 Flowchart of investigation of a female with acute pelvic pain. β HCG, beta humanchorionic gonadotropin; POS, positive; NEG, negative; US, ultrasound; CT, computed tomography; MRI, magnetic resonance imaging; PID, pelvic in flammatory disease. *Gynaecological causes, **Non- gynaecological causes, and ^MRI: consider MRI in these clinical scenarios in pregnant or very young women Dick et al . European Radiology (2025) 35:6682 –6695 6693 accuracy is achieved if the gestational sac is visible along with two indirect signs [ 30]. MRI protocol should include T2*W sequences in 3 planes to identify low signal fresh haematoma within the adnexal mass with a sensitivity, specificity and accuracy of 95%, 100% and 96%, respec- tively, in diagnosing EP [ 31]. Summary statement Both gynaecological and non-gynaecological pathologies can cause acute pelvic pain, and both the clinician and radiologist have to bear this in mind when requesting and interpreting imaging. Pregnancy and pre- and post- menopausal status will direct investigation pathways Fig. 8. Common gynaecological causes include ovarian cyst hae- morrhage, corpus luteum rupture, endometriomas, adnexal torsion, ectopic pregnancy, uterine leiomyoma degenera- tion, and a spectrum of infective pelvic in flammatory dis- ease. Although ultrasound followed by MRI is often the preferred imaging pathway, the ubiquity of CT and the possibility of non-gynaecological causes means that for many patients with gynaecological causes of acute pelvic pain, CT is the first imaging modality. Patient summary Acute pelvic pain in women can have both gynaecological and non-gynaecological causes. Gynaecological causes include corpus luteum rupture, ectopic pregnancy, twist- ing/loss of blood supply to fibroids or ovary, and infection of the cervix, uterus, fallopian tubes, and ovary. Ultrasound is the best first test if there is high suspicion of a gynae- cological cause, whereas CT is often performedfirst if other causes, such as appendicitis or kidney stones, are suspected. MRI is usually a second-line test which con firms the sus- pected diagnoses seen on ultrasound or CT. Abbreviations APP Acute pelvic pain CT Computed tomography DECT Dual-energy CT DWI Diffusion-weighted imaging EP Ectopic pregnancy IUD Intrauterine device MRI Magnetic resonance imaging RUQ Right upper quadrant TAUS Transabdominal ultrasound TOA Tubo-ovarian abscess TVUS Transvaginal ultrasound US Ultrasound β-hCG Beta human chorionic gonadotropin

This paper was endorsed by the Executive Council of the European Society of Radiology (ESR) and the Executive Committee of the European Society of Emergency Radiology (ESER) in March 2025. The authors wish to thank Ms Miranda Leff and Ms Cordelia Leff for their help with manuscript preparation. Funding Open access funding provided by Università degli Studi G. D ’Annunzio Chieti Pescara within the CRUI-CARE Agreement. Compliance with ethical standards Guarantor The scienti fic guarantor of this publication is Professor Raffaella Basilico. Conflict of interest Professor Elizabeth Dick has received funding and support for conferences and lectures from Everlight Radiology and GCG Global Healthcare. Marcela De La Hoz Polo is an employee of Everlight Radiology. The authors of this manuscript declare no other relationships with any companies, whose products or services may be related to the subject matter of the article. Statistics and biometry No complex statistical methods were necessary for this study. Informed consent Written informed consent was not required for this paper. Images included are anonymised. Ethical approval Institutional Review Board approval was not required. Study subjects or cohorts overlap Not applicable. Methodology ● Practice recommendations Author details 1Imperial College NHS Trust, London, UK. 2Imperial College, London, UK. 3Emergency Section, Department of Radiology, Hospital Universitario Morales Meseguer, Murcia, Spain. 4Everlight Radiology, London, UK. 5Raffaella Basilico, Department of Medical, Oral and Biotechnological Sciences, University G. D’Annunzio Chieti-Pescara, Chieti, Italy. Received: 4 November 2024 Revised: 22 January 2025 Accepted: 11 February 2025 Published online: 21 May 2025

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