1. Ovarian Torsion
Ovarian torsion (OT), also known as adnexal torsion or tubo-ovarian torsion, is an emergency condition that occurs when the ovary twists around its vascular pedicle, frequently with a portion of fallopian tubes
[20][1]. It is considered a relatively frequent condition, accounting for 3% of all gynaecological surgical emergencies. It occurs in females of all ages but is most common in women of childbearing age. Torsion is often associated with the presence of cysts or benign ovarian tumours, with a size greater than 5 cm being considered a risk factor. However, due to ovarian hypermobility, it can occur with no underlying ovarian pathology. There is also an increased risk of OT during pregnancy, most frequently between the 6th and 14th week of pregnancy. OT typically manifests as acute and severe unilateral lower abdominal pain that is accompanied by other symptoms, such as nausea, vomiting, and fever
[20,21][1][2]. If torsion is suspected, immediate diagnosis is essential to avoid infarction and preserve ovarian function
[22,23][3][4].
US combined with colour Doppler is the first-line imaging of choice, and the findings depend on the duration and severity of the torsion. Typical findings are an enlarged (>4 cm), oedematous, and heterogeneous ovary found in an unusual location, for instance, shifted medially or cranially to the uterine fundus. The ovary usually shows a hyperechoic central stroma with peripherally displaced follicles (follicular ring sign)
[24][5]. An underlying ovarian lesion may be seen. Upon the Doppler evaluation, a reduced or absent vascular flow is typically observed, and the twisted vascular pedicle could be seen as whirlpool sign. Free fluid is often observed
[25,26][6][7].
Although CT is not indicated as a first-line technique when OT is suspected, it is usually performed in female patients with aching nonspecific pelvic pain and vomiting. Moreover, it can be helpful for ruling out OT if US does not show ovarian abnormalities or if it is limited due to patient pain. CT scans usually show a large pelvic mass abnormally located at the midline, anteriorly to the uterus. During no-contrast scans, the ovary may appear hyperdense (>50 Hounsfield Unit) due to internal haemorrhage. In contrast-enhanced images, the ovarian twisted pedicle may be detected
[27,28][8][9]. It can also be seen as a triangular enhancing soft tissue between the uterus and the involved ovary. Peripherally displaced follicles, fat stranding near the adnexa, and a small amount of free fluid are also common findings
[26][7].
MRI is usually not available in emergency settings. However, it can be useful for further evaluating equivocal findings seen with other techniques and for characterising an underlying ovarian mass
[26][7]. If haemorrhagic infarction is present, the involved ovary shows a T1 hyperintense signal during MRI, with low or without contrast enhancement, and can show diffusion restriction on Diffusion-Weighted Imaging (DWI) sequences. A T1 thin hyperintense ring, representing methaemoglobin, may also be present.
2. Ovarian Cyst Haemorrhage/Rupture
Acute bleeding or rupture of functional (follicles and corpus luteum) ovarian cysts is one of the most common causes of APP in young women
[30][10]. In severe cases, it can be associated with haemorrhagic shock and hypotension and, thus, can be potentially life-threatening. Clinically, it may overlap with an ectopic pregnancy, which should be ruled out by evaluating serum human chorionic gonadotropin (hCG) levels. In the case of acute haemorrhage, upon a US evaluation, the cyst is isoechoic in comparison with the ovarian stroma. It can mimic an enlarged ovary, while a thick irregular wall of increased peripheral vascularity (“ring of fire”) may be seen during a colour Doppler US
[31][11]. In case of cyst rupture, chronic bleeding, septations, and liquid-sediment levels can be detected. At the CT evaluation, haemorrhagic cysts are typically heterogenous lesions with hyperdense areas. If a haemorrhagic cyst ruptures, hyperdense ascites is generally seen in the pouch of Douglas and sometimes in the upper abdomen
[16,32][12][13]. During MRI, haemorrhagic cystic lesions typically show a high signal on T1-weighted images and an intermediate-to-low signal on T2-weighted ones. In the case of haemorrhagic cyst ruptures, haemoperitoneum can be seen as free peritoneal fluid characterised by areas of both low and high signal intensity depending on the extent of blood-clot formation
[5][14].
3. Pelvic Inflammatory Disease
Pelvic inflammatory disease (PID) is one of the most common causes of APP and typically occurs in young and sexually active women
[4,33][15][16]. PID includes many conditions, such as endometritis, salpingitis, pyosalpinx, tubo-ovarian abscess (TOA), and pelvic peritonitis
[34][17]. Clinical symptoms’ spectrum is very wide, varying from asymptomatic infection to abdominal pain, malaise, fever, vaginal bleeding, dysuria, or dyspareunia. PID is usually caused by ascending sexually transmitted infections that may involve the endometrium, fallopian tubes, ovaries, and peritoneum. The most common involved pathogens are Chlamydia trachomatis or Neisseria gonorrhoeae
[35][18]. PID pathogens have an important role in producing tubal damage and in the development of adverse sequelae such as infertility or ectopic pregnancy. Thus, early diagnosis and treatment are crucial for preserving fertility and avoiding long-term consequences such as chronic pelvic pain and an increased risk of ectopic pregnancy, since the effectiveness of antibiotic therapy is dependent upon the interval from the onset of symptoms to the initiation of treatment
[36][19]. The diagnosis is based on clinical and laboratory parameters, but imaging plays a crucial role, especially in the case of atypical clinical presentations
[36,37][19][20].
Normal fallopian tubes cannot usually be distinguished upon imaging. In the case of salpingitis, lumen occlusion leads to the retention of purulent secretion and tubes swelling (pyosalpinx). During a US, a tubular structure with hyperechoic content is usually seen in the adnexal area. CT and MRI allow for a better visualisation of the dilated tube. Pyosalpinx is observed as a contrast-enhancing parauterine tubular structure with a thickened wall and incomplete septa (“cogwheel sign”)
[38,39,40,41][21][22][23][24].
When the inflammatory process evolves from the fallopian tubes to the ovaries, it produces a condition known as tubo-ovarian abscess (TOA)
[42][25]. Although US is considered the first method of choice for the diagnosis of PID, contrast-enhanced CT is often needed to confirm the diagnosis of an abscess, assess the extent of peritoneal disease, evaluate possible complications, plan treatment, and exclude non-gynaecological causes. Moreover, multiplanar sequences facilitate the visualisation of the tubular morphology of enlarged tubes. The typical imaging findings of a TOA are bilateral, centrally hypodense, multilocular, thick-walled adnexal lesions. Identifying a pyosalpinx as a tortuous, tubular lesion is essential for the diagnosis of TOA. Frequent findings include free fluid, pelvic peritonitis, and a fluid-filled uterine cavity
[38,43][21][26].
On the contrary, MRI is rarely needed to diagnose PID and is more likely to be used for a better delineation of uterus and adnexal structures, the differential diagnosis of unclear adnexal lesions, and the differentiation of PID from other pathologic processes. During MRI, TOA usually presents with a hypointense signal on T1-weighted sequences and a hyperintense signal on T2-weighted sequences. A T1 hyperintense rim along the inner wall of the abscess cavity, because of the presence of haemorrhage or granulation tissue, is often detected. However, the MRI findings depend on the presence of blood and the protein content of the mass. MRI is also a useful tool for distinguishing pyosalpinx from haematoalpinx because the latter usually does not demonstrate wall thickening and has a higher signal intensity on T1-weighted images due to the presence of blood products
[38][21].
In approximately 4% of cases during PID, right upper quadrant abdominal pain may occur due to inflammation of the hepatic capsule and overlying peritoneum with adhesion formation (perihepatitis). This condition is known as Fitz–Hugh–Curtis syndrome, and during CT imaging, it manifests as a thickened and enhanced liver capsule, transient hepatic perfusion abnormalities in arterial phases, periportal oedema, and inflammatory stranding in the right paracolic gutter
[44,45][27][28].
4. Complicated Uterine Leiomyomas
Uterine leiomyomas are extremely common benign and usually asymptomatic gynaecological tumours.
Red degeneration, also referred to as carneous degeneration, is one of four main types of degeneration that can involve uterine fibroids and is the most frequently occurring type during pregnancy, particularly during the second and third trimesters, and in the case of large fibroids (>5 cm)
[48][29].
Red degeneration primarily occurs secondary to the rupture of intralesional arteries or venous thrombosis, leading to haemorrhagic infarction of leiomyomas. This condition usually manifests with APP, fever, and nausea. Upon US and CT imaging, red degenerated fibroids may appear as large, inhomogeneous, and well-circumscribed intramural masses, with cystic areas and an absence of Doppler signal/flow in infarction areas. MRI examinations may demonstrate a peripheral high-intensity rim on T1-weighted images due to the T1 shortening effects of the methaemoglobin of blood products confined to the thrombosed and dilated vascular structures surrounding the leiomyoma. In gadolinium-enhanced fat-suppressed T1-weighted sequences, red degenerated leiomyomas do not show contrast enhancement
[47,49][30][31].
The degeneration or torsion of uterine leiomyomas usually occurs in subserosa and pedunculated fibroids, and it is a rare but potentially life-threatening cause of APP. The severity of symptoms depends mainly on the degree of rotation: if pedicle torsion is partial and spontaneously untwisting, symptoms are usually mild; nevertheless, a complete torsion leads to venous stasis, with oedema and congestion, and then causes compression of the arterial blood supply. Obstruction of the arterial network produces haemorrhagic necrosis. If not treated, massive bleeding or peritonitis may occur
[50][32]. US, CT, and MRI are all imaging tools that are useful for fibroids torsion. The most typical imaging findings are a para-uterine mass with a twisted pedicle, vascular flow absence, and mild free abdominal fluid
[50,51][32][33].
Infection of leiomyomas (pyomyoma) is an infrequent complication of uterine fibroid but is associated with high morbidity and mortality. It may occur in postmenopausal women, during pregnancy, in the postpartum period, or as a complication of uterine artery embolisation for treating leiomyomas
[52,53][34][35]. Its clinical symptoms usually include fever and PAA. The diagnosis of pyomyoma is tricky because of its insidious presentation and lack of reported imaging and clinically typical findings. However, the presence of air within the myoma at CT evaluation is a crucial finding when there is a suspected infection. MRI may reveal a uterine mass with an inhomogeneous central hyperintensity component, suggesting the presence of blood products, necrotic tissue, and purulent fluids. Air components within the lesion show low signal intensity on T1, T2, and DWI
[54][36].
5. Endometriosis
Endometriosis, defined as the presence of functional endometrial tissue outside the uterine cavity, is a frequent cause of chronic and cyclic pelvic pain
[55,56][37][38]. Nevertheless, it can also present with APP. The most common acute complications of endometriosis have an intestinal aetiology, such as obstruction, perforation, and acute appendicitis caused by endometriosis fibrotic implants. Other acute endometriosis manifestations include endometrioma ruptures, endometrioma superinfection, PID with tubo-ovarian abscess, and urinary tract obstruction
[57,58,59,60][39][40][41][42]. MRI is considered the reference standard imaging modality for the diagnosis of endometriosis
[61,62][43][44].
In the case of gastrointestinal or urinary tract complications in an emergency setting, endometriosis is rarely identified as an aetiologic factor on imaging, even if it should be suspected in the context of known endometriosis with intestinal or urinary tract involvement. The presence of stellar, mildly enhanced, infiltrative, and fibrotic lesions in suggestive areas in female patients of reproductive age may help doctors reach the correct diagnosis
[57,58][39][40]. During MRI, the presence of a hyperintense area on T1-weighted fat-saturated sequences within the lesion can suggest the diagnosis of endometriosis
[44][27].
The rupture of an endometrioma is an infrequent complication. CT signs are similar to those of a corpus luteal cyst rupture, with spontaneously dense ovarian masses and ascites. MRI usually shows a distorted endometrioma and free peritoneal fluid with a high T1 signal. In the case of endometrioma superinfection, CT usually shows a nonspecific hypodense cystic adnexal with adjacent fat stranding. During the MRI, the superinfection of an endometrioma is suggested by the presence of thickened and enhancing walls of the lesion, an increase in size of an already known endometrioma, the loss of the characteristic high signal in T1 and the shading sign in T2, and a marked restriction of diffusion in DWI
[58][40].
6. Complicated Ovarian Teratomas
Mature ovarian teratoma, also known as a dermoid cyst, is the most common benign tumour in premenopausal females
[63][45]. Although it is typically asymptomatic, teratoma may undergo several complications, such as adnexal torsion, rupture, malignant transformation, or infection. The incidence of spontaneous teratoma rupture is thought to range from 0.3% to 2.5%
[64][46]. The discharge of fatty content into the abdominal cavity can cause aseptic peritonitis. Ruptured ovarian teratomas can be suspected when imaging shows discontinuity of the cyst wall, an irregular shape of the teratoma, extra-tumoral fatty nodules, and ascites. CT is the most sensitive technique for detecting intraperitoneal fatty nodules, which are commonly observed around the liver surface
[64,65][46][47].
7. Ovarian Hyperstimulation Syndrome and Hyperreactio Luteinalis
Ovarian hyperstimulation syndrome (OHSS) is a side effect of ovarian stimulation therapy used for in vitro fertilisation. Rarely, it may also occur spontaneously during pregnancy
[66][48]. OHSS is characterised by cystic enlargement of the ovaries and a fluid shift from the intravascular to the third space due to increased capillary permeability and ovarian neo-angiogenesis. It is usually a self-imitating condition, presenting with pelvic pain but, in rare cases, can turn into a life-threatening emergency due to hypovolemic shock
[67][49]. Imaging demonstrates bilateral enlarged ovaries with multiple follicular cysts of varying sizes arranged in a “spoke-wheel” pattern. Peritoneal and pleural effusion may also be present
[68][50].
Hyperreactio luteinalis (HS) is a condition that shares many clinical and pathogenetic characteristics with OHSS. Both entities are characterised by bilateral clusters of luteinised ovarian cysts that show a characteristic “spoke-wheel” appearance during an US, accompanied by a physiologic flow on colour Doppler velocimetry
[69][51].
8. Gynaecological Malignancies
Pelvic malignancies, most commonly ovarian, cervical, and endometrial uterine cancers, can induce pain of different intensities and durations. Gynaecological cancer may present with sudden onset in cases of advanced stages, with the invasion of adjacent structures that lead to several complications, such as intestinal perforation, thrombosis, and intestinal or ureteral obstruction
[71,72,73][52][53][54].
9. Ectopic Pregnancy
Ectopic pregnancy (EP) is the implantation of a fertilised ovum outside the uterine cavity and, due to the risk of massive bleeding, is a potentially life-threatening gynaecological emergency, representing the leading cause of maternal mortality in the first trimester, with an incidence of 5–10% of all pregnancy-related deaths
[74,75][55][56]. Predisposing risk factors are a previous EP, tubal ligation, a copper intrauterine device (IUD), and artificial insemination. EP most often occurs along the fallopian tubes (97%), especially close to the ampulla. Still, it can only occur in the cervix, in the ovaries, along a previous Caesarean scar, or within the abdominal cavity
[76][57]. EP rupture with massive intra-abdominal bleeding often occurs after 10 to 14 weeks of gestation. A sign of a rupture is severe APP with vaginal bleeding and even haemorrhagic shock. Due to the risk of life-threatening haemorrhages, an early diagnosis of this condition is pivotal. In addition to the pregnancy test, both transabdominal and transvaginal US are essential and show an empty uterine cavity with decidualised endometrium (“decidual sac sign”). The ovarian region should be closely evaluated since a complex extra-adnexal cyst/mass or dilatated tubes are frequently detected in a tubal EP. Usually, a large amount of free peritoneal fluid and/or haemoperitoneum is also observed. The gestational sac appears during the US examination as a ring-shaped lesion with an anechoic centre and a broad, hyperechoic, hypervascular rim (tubal ring sign)
[77][58].