Causes of Pelvic Pain			Occurrence			Pain Characteristics
	Transabdominal sonography (TSA–US)			Low-frequency probe (convex probe 3–5 MHz).			The standard protocol for examining the female pelvis involves an initial TAS with the urinary bladder completely full, so it can act as an acoustic window. Following bladder emptying, the patient assumes a lithotomy position, and TVS is performed. The two imaging techniques are complementary and often provide different diagnostic information.		The protocol often also calls for the execution of Doppler, power Doppler, and pulsed wave Doppler flowmetry depending on the clinical situation and pathology that emerge from grayscale imaging.			TAS offers a wider field of view than TVS and allows better visualisation of the superficial and distal structures of the vagina by bringing the probe closer to the target organs.			Empty bladder. Obese patients. Retroverse uterus where the fundus is located beyond the focal zone of the transducer. Less effective for characterisation of adnexal masses.
	Transvaginal sonography (TVS–US)
			• Adnexal
	Adnexal torsion		High-frequency probe (endocavitary probe > 7 MHz).			3% of gynecologic emergencies		TVS approach requires a greater penetration depth to avoid the attenuating soft tissues that cover the pelvic organs. Therefore, it requires the use of a higher frequency probe, which, in turn, provides greater resolution of the anatomical details of the uterus, ovary, and adnexal structures.				Limited field of view. Should not be performed on patients who are unable or unwilling to consent to the procedure, as well as on most virgin patients and for those in which the insertion of the probe produces marked discomfort. It is contraindicated in some obstetric patients in the 2nd and 3rd trimester of pregnancy due to the risk of active bleeding or membrane rupture.

However, the characteristics of pelvic pain must be strongly considered before any instrumental diagnostic approach. In this regard, Table 2

Acute persistent (complete torsion) or intermittent (intermittent torsion) right/left pelvic pain
	Ruptured or bleeding ovarian cysts			The incidence is difficult to estimate. A broader estimate calculates about 7% of women worldwide experience a symptomatic cyst during their lifetime			Acute right/left pelvic pain
	Pelvic inflammatory disease			No specific international data are available for PID incidence worldwide. A study reports a prevalence of self-reported lifetime PID of 4.4%			Chronic pelvic pain with reacutization
Chronic pelvic pain
Thrombosis of the gonadal veins
	Referred incidence of about 0.18% of the general population			Acute pelvic pain of variable entity

3. Adnexal Causes of Pelvic Pain

3.1. Adnexal Torsion

Adenxal torsion is the partial or complete rotation of the adnexum on its vascular peduncle resulting in congestion and oedema, due to compromised venous and lymphatic drainage, and subsequent ischaemia and necrosis, due to compromise of the arterial blood supply ^[3][4][3,4]. Although frequently reported in the scientific literature, it is an uncommon cause of pelvic pain, accounting for only 3% of gynecologic emergencies [3]. It can affect the adnexum in its entirety involving both the ovary and the fallopian tube [4]. The torsion is often unilateral, and is more common on the right, presumably due to the reduced mobility of the left gonad due to the presence of the sigmoid colon. Torsion has a higher incidence in women of childbearing age and can be secondary to a space-occupying lesion, either cystic (large cystic lesions) or neoplastic, acting as a lead point ^[1][4][5][1,4,5]. Other potential causes include pregnancy, polycystic ovary syndrome, previous surgery to the pelvis, and hyperlaxity of the mesenteries and ovarian ligaments [1] (Table 3). Adnexal torsion US diagnostic clue.

	Adnexal Causes of Pelvic Pain			US Diagnostic Clue			US Limits
	Endometritis			Thickened endometrium with an irregular profile and the presence of more or less echogenic fluid or pus in the uterine cavity (pyometra)			At US, may be difficult to distinguish severe endometritis from cancer

 

3.5. Endometriosis

3.5. Endometriosis

Endometriosis is a chronic inflammatory condition caused by the abnormal presence of endometrial tissue at sites other than the physiological endometrium. It affects up to 10% of women of reproductive age, is often asymptomatic and, when symptomatic, it manifests with chronic pelvic pain, dysmenorrhea, dyspareunia, and abnormal uterine bleeding ^{[1][13][14][15][16]}[1,15,16,17,18]. Symptoms are often cyclical in nature as endometriosis is a hormone-responsive disease. Infertility is an important consequence of endometriosis, due to the anatomical deformation of the pelvic structures and occlusion of the fallopian tubes. Ectopic sites of endometriosis implantation include the ovarian surface, the suspensory ligaments of the uterus, the uterus itself, the peritoneal surfaces of the pouch of Douglas, and the fallopian tubes ^{[1][13][14][15][16]}[1,15,16,17,18]. When the endometriosis tissue reaches structures deeper than 5 mm from the peritoneal surface causing fibrosis and muscle hyperplasia, it is defined as deep pelvic endometriosis. On US, endometriomas appear as unilocular swellings, which are often bilateral and multiple, with a thick capsule, regular margins, and homogeneously echogenic content, with fine internal echoes, due to the blood cells flaking off the walls, resulting in a “ground glass” appearance (Table 7). Endometriosis US diagnostic clue.

	Adnexal Causes of Pelvic Pain			US Diagnostic Clue			US Limits
	Endometriosis			Unilocular swellings, which are often bilateral and multiple, with a thick capsule, regular margins, and homogeneously echogenic content, with fine internal echoes, due to the blood cells flaking off the walls, resulting in a “ground glass” appearance. Useful monitoring for differential diagnosis with hemorrhagic ovarian cyst (persistence to follow-up of the endometriotic cyst addresses the diagnosis)			At US, may be difficult to detect millimetric foci of ovarian endometriosis and to detect retrocervical or ligaments thickening, as well as possible intestinal or nerve involvement.

3.6. Peritoneal Inclusion Cyst

Peritoneal inclusion cysts (PICs) are generally benign mesothelial lesions with an estimate incidence of approximately 3–5% of the peritoneal mesotheliomas containing peritoneal fluid that occur in women of childbearing age, often following invasive pelvic surgery, infection, or cancer ^[17][19]. The imaging features of peritoneal inclusion cysts reflect their pathogenesis and allow for their differential diagnosis from an ovarian cystic mass ^[18][19][20,21]. Indeed, the typical US finding is an ovary trapped inside a cyst, surrounded by septa and fluid. The fluid is usually anechoic but may contain echoes in some compartments due to haemorrhage or protein-rich fluid (Table 8). Peritoneal inclusion cyst US diagnostic clue.

	Adnexal Causes of Pelvic Pain			US Diagnostic Clue			US Limits
	Peritoneal inclusion cyst			Trapped ovary inside a cyst, surrounded by septa and fluid. The fluid is usually anechoic but may contain echoes in some compartments due to haemorrhage or protein-rich fluid			At US, can be difficult to differentiate the cystic origin.

3.7. Ectopic Pregnancy

The definition of ectopic pregnancy (EP) is that of a pregnancy that has implanted in a location other than the uterine cavity occurring in 1–2% of all pregnancies ^[20][22]. The most common abnormal implantation site for ectopic pregnancy is in the fallopian tubes, which occurs in up to 97% of cases. Of these, 75% to 80% are found in the ampullary region, 10% in the isthmic portion, 5% in the fimbrial portion, and 2 to 4% in the interstitial portion (Table 9). Ectopic pregnancy US diagnostic clue.

	Adnexal Causes of Pelvic Pain			US Diagnostic Clue			US Limits
	Ectopic pregnancy			When the b-hCG value is below the cut-off value of 2000 mIU/mL (IRP) and there is no intrauterine gestational sac, the diagnosis could be an early intrauterine pregnancy, a miscarriage, or an ectopic pregnancy, and therefore follow-up is indicated		Uterine findings: gestational pseudosac (differential diagnosis with gestational sac: double echogenic wall versus single echogenic wall of the pseudosac). Adnexal findings: echogenic tubal ring or ectopic gestational sac containing the yolk sac or the embryo (with or without cardiac activity)			Related with difficulties in exploring the adnexa and in detecting early pregnancy as well as active bleeding in case of rupture

4. Uterine Causes of Pelvic Pain

4.1. Fibroids: Degeneration, Rupture and Torsion

Fibroids are the most common benign uterine tumours found in women of childbearing age. Although usually asymptomatic, they can manifest with acute or chronic pelvic pain, particularly due to compressive effects on neighbouring organs. Given the high prevalence of fibroids, it is remarkable that acute complications are very rare indeed ^[21][28]. A study examining the incidence of degeneration of leiomyoma in patients referred for uterine fibroid embolisation underwent MRI found an incidence of 5.1% ^[22][29]. Torsion and rupture are a rare entity (reported incidence for torsion of less than 0.25%) ^[23][30] (Table 10). Fibroid torsion US diagnostic clue.

	Uterine Causes of Pelvic Pain			US Diagnostic Clue			US Limits
Adnexal torsion			Twisted vascular peduncle (whirl sign) with absent flows or with increase in resistance indices if represented			Transabdominal US may be limited in obese patients or when the ovaries are masked by intestinal meteorism.		Endovaginal US may be limited in cases of large ovarian masses causing cranial displacement of the ovary, hindering the exploration of the ovarian vessels.
	Endometritis			Pregnancy-related endometritis with an incidence of 1–3% after a vaginal delivery and of 13–90% following cesarean delivery, and endometritis unrelated to pregnancy that may occur in up to 70–90% of documented cases of PID			Chronic pelvic pain with reacutization
	Endometriosis			It affects up to 10% of women of reproductive age			Asymptomatic/poorly symptomatic/chronic pelvic pain with reacutization during menses
	Peritoneal inclusion cysts			Approximately 3–5% occur in women of childbearing age following invasive pelvic surgery, infection, or cancer			Asymptomatic/poorly symptomatic/chronic pelvic pain with reacutization (especially if complicated)
	Ectopic pregnancy			1–2% of all pregnancies			Acute pelvic pain
			• Uterine
	Fibroids: degeneration, rupture, and torsion			A study examining the incidence of degeneration of leiomyoma in patients referred for uterine fibroid embolisation underwent MRI found an incidence of 5.1%.		Torsion and rupture are a rare entity (reported incidence for torsion of less than 0.25%)			Acute pelvic pain
	Post-embolisation syndrome			Occurs in about 40% of women undergoing uterine artery embolisation			Pelvic pain of variable entity
			• Vascular
	Pelvic congestion syndrome			In patients with presenting complaints of chronic pelvic pain, the prevalence of PCS is nearly 30%

3.2. Ruptured or Bleeding Ovarian Cysts

Ovarian cysts are growths that develop in the ovaries during follicular maturation and are defined as functional cysts as they represent a physiological phenomenon related to ovarian function ^[1][6][1,6]. Functional ovarian cysts are caused by the overgrowth of a follicle due to the accumulation of fluid inside it, which is usually spontaneously reabsorbed without causing pain [6]. In some cases, they can rupture, releasing fluid into the peritoneal cavity, causing intense pain and bleeding complications. Haemorrhagic or ruptured ovarian cysts are common in women of reproductive age; however, the actual incidence is difficult to estimate, as many ruptured cysts are asymptomatic or found incidentally [7]. A broader estimate calculates about 7% of women worldwide experience a symptomatic cyst during their lifetime and in this event, US is the primary investigative tool ^[6][7][8][6,7,8] (Table 4) [1].

Table 4.

Ruptured or bleeding ovarian cysts US diagnostic clue.

	Adnexal Causes of Pelvic Pain			US Diagnostic Clue			US Limits
	Ruptured or bleeding ovarian cysts			Cystic mass with an inhomogeneous echo structure in relation to hemoglobin degradation often with evidence of haematic sediment or in an advanced phase with relief of thin internal echoes arranged in a “fishing net” or fibrin bundles not vascularized by colour-Doppler or CEUS (differential diagnosis with tumor mass).			US cannot detect and quantify the active bleeding

3.3. Pelvic Inflammatory Disease

Pelvic inflammatory disease (PID) is an infection of the female genital tract caused by the ascent of microorganisms from the vagina to the uterus, fallopian tubes, and ovaries. Common causes are Neisseria gonorrhoeae and Chlamydia trachomatis, which are sexually transmitted ^[1][9][1,9]. Other aerobic and anaerobic bacteria can cause bacterial vaginosis with retrograde spread of vaginal microorganisms [1]. The continuum of infection begins with cervicitis causing mucopurulent discharge and progresses to endometritis and salpingitis. Pus can collect in the tube (pyosalpinx) and form a tubo-ovarian abscess. PID can be acute, chronic, or subclinical and is often underdiagnosed. Symptoms include lower abdominal pain, fever, mucopurulent discharge, and abnormal uterine bleeding during or after menstruation. Untreated PID can lead to chronic pelvic pain, infertility, ectopic pregnancy, and intra-abdominal infections. The diagnosis is made primarily on clinical suspicion ^[10][11].  (Table 5). Inflammatory disease US diagnostic clue.

	Adnexal Causes of Pelvic Pain			US Diagnostic Clue			US Limits

^][33]. The repeat US allows for the observation of changes in the appearance of the fibroid. The physician may note the presence of air inside the fibroid, which is represented on US with internal echoes and reverberation artifacts in the context of a poorly defined mass following infarction and tissue necrosis (Table 11) ^[1][24][1,33]. Post-embolisation syndrome US diagnostic clue.

	Uterine Causes of Pelvic Pain			US Diagnostic Clue
	Pelvic inflammatory disease			The fallopian tubes with thickened and hyperemic walls, dilated in the presence of pyosalpinx with occluded ovarian fimbria, echogenic intraluminal sediments, and echoes stratified by exudate. The inflamed fallopian tube appears adjacent to or adhering to the ovary with the formation, in more advanced cases, of an ovarian tube abscess represented on US by an inflammatory mass that engulfs the ovary and the fallopian tube, no longer making the ovary distinguishable.			US may suffer from limited panoramicity and, in cases of extensive adhesions, can be difficult to discriminate each anatomical structure.

3.4. Endometritis

Endometritis is inflammation of the endometrial lining of the uterus that could also involve the myometrium and, occasionally, the parametrium too, and clinically manifest with fever, chills, lower abdominal pain, and foul-smelling lochia or PID related symptoms ^[11][12][12,13]. It can be divided into pregnancy-related endometritis with an incidence of 1–3% after a vaginal delivery and of 13–90% following cesarean delivery, and endometritis unrelated to pregnancy that may occur in up to 70–90% of documented cases of PID ^[11][12][12,13] (Table 6). Endometritis US diagnostic clue.

	Adnexal Causes of Pelvic Pain			US Diagnostic Clue			US Limits
	US Limits
	Post-embolisation syndrome			Fibroid with internal echoes and reverberation artifacts in the context of a poorly defined mass following infarction and tissue necrosis			Difficulties in exploring the whole uterus in cases of multiple fibromas

5. Vascular Causes of Pelvic Pain

5.1. Pelvic Congestion Syndrome

Pelvic congestion syndrome (PCS) is characterized by chronic symptoms that may include pelvic pain, perineal heaviness, urinary urgency, and postcoital pain, caused by valvular insufficiency of the ovarian veins, resulting in reflux to the pelvic veins and vulvar, perineal, and lower limb varices. In patients with presenting complaints of chronic pelvic pain, the prevalence of PCS is nearly 30% ^[25][26][34,35]. US examination permits to exclude pelvic masses, cystic changes in the ovaries, and uterine pathologies as potential causes of pain and represents the first line diagnostic test to evaluate pelvic congestion syndrome ^[27][28][37,39]. Indeed, on US examination, it is possible to observe multiple veins with a diameter greater than 5 mm adjacent to the ovary and uterus and enlarged arcuate veins also with a diameter greater than 5 mm, which can cross the myometrium and connect to varicosities (Table 12) ^[1][29][1,36]. Pelvic congestion syndrome US diagnostic clue.

	Vascular Causes of Pelvic Pain			US Diagnostic Clue			US Limits
	Fibroids torsion			Hypovascular or avascular mass distinct from the ovary and with a twisted or “pointed” peduncle			Difficulties in exploring the whole uterus in cases of multiple fibromas and in detecting the twisted pedicle

 

4.2. Post-Embolisation Syndrome

4.2. Post-Embolisation Syndrome

Uterine artery embolisation for the treatment of fibroids is indicated in symptomatic women as an alternative to hysterectomy. Post-embolisation syndrome, which occurs in about 40% of women undergoing this procedure, is characterised by fever, pelvic pain, and vaginal bleeding, which subsides within 24 to 48 h ^[2443,44]. Affected patients present with acute pain, often with fever and leucocytosis on laboratory examination. Thrombosis is observed more frequently on the right, probably due to the greater pressure present in the right gonadal vein than on the left, where the pressure would be protected by the retrograde flow of the left renal vein; the right ovary, the ipsilateral iliopsoas muscle, and the inferior vena cava are therefore frequently affected ^[1][30][1,43]. Uterine venous plexus thrombosis is also an unusual site of thrombosis often asymptomatic and incidental detected by TSV–US, which is decisive in the diagnosis and subsequent therapeutic choices ^[32][45]. US approach of gonadic vein thrombosis combines TSA–US and TSV–US. The latter is referred to the US method to explore the intere gonadic vein decourse and it is performed through transverse and longitudinal scans of the retroperitoneum showing an avascular structure with a tortuous tubular appearance, with adjacent anechoic or hypoechoic areas without any flow detection on the colour Doppler evaluation (Table 13) ^[33][46]. Thrombosis of the gonadal veins US diagnostic clue.

	Vascular Causes of Pelvic Pain			US Diagnostic Clue			US Limits
	Pelvic congestion syndrome			Multiple pelvic veins with a diameter greater than 5 mm and a venous reflux greater than 1 s			Possible difficulties in sampling the vessel and correctly evaluate the blood flow, and in detecting eventual complications such as thrombosis.

 

 

 

5.2. Thrombosis of the Gonadal Veins

5.2. Thrombosis of the Gonadal Veins

Gonadal vein thrombosis is a condition that can occur in postpartum women or those undergoing pelvic surgery, with a referred incidence of about 0.18% of the general population ^[30][31][

Thrombosis of the gonadal veins

Avascular structure with a tortuous tubular appearance, with adjacent anechoic or hypoechoic areas without any flow detection on the colour Doppler evaluation.

Possible limits in panoramicity that hinder the detection of thrombosed vessels. Difficulties in Doppler evaluations.