AbstractLower abdominal pain is frequently reported and has a diverse differential diagnosis. In cases with atypical presentation and nonspecific findings, further imaging evaluation is required to confirm the clinical suspicion and to distinguish between self-limiting disorders and those requiring immediate intervention. In line with European guidelines, transabdominal ultrasonography is recommended as a first-line imaging modality for clinically suspected acute appendicitis and acute diverticulitis, which respectively represent the predominant causes of right and left lower quadrant abdominal pain. It is similarly the preferred method for evaluating suspected obstetric/gynecologic and genitourinary diseases. Computed tomography is utilized as a secondary option when ultrasonography results are inconclusive. This pictorial essay illustrates the sonographic features of the most common conditions associated with lower abdominal pain and outlines the clinical characteristics of each entity.
IntroductionLower abdominal pain (LAP) represents a common concern with a broad differential diagnosis, ranging from self-limiting conditions to life-threatening surgical emergencies. The presence of overlapping or atypical clinical signs can complicate the evaluation of patients with LAP. A thorough history and physical examination are essential and should be supplemented with laboratory and imaging assessments as clinically indicated.
Recent recommendations suggest that transabdominal ultrasonography (US) should be routinely used in all patients with suspected acute appendicitis and diverticulitis. This approach allows for early risk stratification and reduces the need for additional computed tomography (CT) scans. Under these guidelines, CT should be reserved for cases in which US results are inconclusive [1-3]. Furthermore, the American College of Radiology appropriateness criteria recommend transabdominal US as the first-line imaging modality for suspected obstetric/gynecologic and genitourinary diseases, followed by contrast-enhanced CT when US findings are negative (Fig. 1) [4,5].
This pictorial essay summarizes the US appearances of the most common causes of LAP, accompanied by brief clinical notes intended to increase the clinical awareness of each entity.
Gastrointestinal DisordersAcute Colonic Diverticulitis and Acute AppendicitisClinical presentationAcute colonic diverticulitis (ACD) is the most common cause of left LAP, although individuals with a redundant sigmoid colon may experience suprapubic or right lower quadrant pain. Other potential symptoms include fever, nausea, and constipation. In cases of complicated ACD, patients may present with septic shock, exhibiting generalized guarding and rebound tenderness [6]. Acute appendicitis, which is the leading cause of right LAP, typically begins with periumbilical pain, which migrates to the right lower quadrant after several hours. This pain is often accompanied by peritoneal irritation, and patients also experience anorexia and nausea.
ImagingA step-up strategy employing US as the first-line imaging method, followed by CT when US results are negative or inconclusive, seems to be the most effective approach for suspected acute diverticulitis or appendicitis [1]. The diagnostic accuracy of US can be compromised by factors such as obesity, diverticulitis affecting the distal sigmoid colon, and retrocecal or pelvic positioning of the appendix.
The presence of uncomplicated ACD is suggested by several findings: (1) short-segment colonic wall thickening greater than 5 mm; (2) inflamed diverticula within the thickened wall area, which manifest as focal discontinuities in the bowel wall; (3) inflammation of the perigut fat, appearing as a hyperechoic halo surrounding the bowel serosa or diverticula; (4) pericolic fluid; and (5) sonographic tenderness to compression (Figs. 2, 3) [1]. Complicated ACD is diagnosed based on the presence of intramural, pericolic, or distant abscesses, which appear as well-demarcated fluid collections that may contain echogenic debris, gas bubbles, and/or intraperitoneal fluid (Fig. 4) [1].
The diagnosis of acute appendicitis can be confirmed by the presence of (1) an enlarged, incompressible appendix with an outer diameter greater than 6 mm; (2) sonographic tenderness to compression; and (3) hyperechoic periappendiceal tissue (Figs. 5, 6) [1]. To definitively rule out appendicitis, the entire length of the normal appendix must be visualized. The presence of substantial periappendiceal fluid and submucosal hypoechogenicity suggest perforation (Fig. 7).
Colitis and Colon CancerClinical presentationThe typical presentation of inflammatory bowel disease includes bloody diarrhea, colicky abdominal pain, tenesmus, and fatigue. Physical examination reveals abdominal tenderness to palpation along with fever [7]. Fulminant colitis and toxic megacolon are suggested by continuous bleeding, abdominal pain, and signs of systemic toxicity [8]. In comparison, the predominant symptom of infectious colitis is acute diarrhea, which may be watery or contain mucus and blood. Ischemic colitis typically presents with rectal bleeding and abdominal pain.
Patients with colon cancer may represent emergent cases, with symptoms such as intestinal obstruction, perforation, or acute non-profound gastrointestinal bleeding. These manifestations display incidence rates of 8%- 20%, 3%- 10%, and 2.3%, respectively. Typically, the patient’s history reveals a recent onset of hematochezia, iron deficiency anemia, and/or changes in bowel patterns.
ImagingAlthough CT is considered the modality of choice, US is recognized as a first-line modality for the initial diagnosis of colitis when performed by experienced practitioners. For initial imaging investigations, it is crucial to accurately characterize US abnormalities associated with colitis, as this can assist in diagnosis or inform the selection of the most appropriate CT protocol.
Crohn disease is characterized by moderate wall thickening, with a cutoff of 4 mm displaying high specificity. Wall hypervascularization and mesenteric hypertrophy are indicative of disease activity [9]. Involvement of the appendix in Crohn disease may mimic acute appendicitis; however, concurrent thickening of the terminal ileum and cecum can help differentiate between the two conditions [9]. Ulcerative colitis typically presents with less extensive bowel thickening than Crohn disease, affecting the mucosa and submucosal layer while usually preserving stratification. In turn, pseudomembranous colitis exhibits more pronounced wall thickening than inflammatory bowel disease. This thickening consists of two layers: a thick echogenic inner layer of redundant mucosa stemming from edema and pseudomembranous formation, and an outer hypoechoic layer corresponding to the muscularis propria (Fig. 8) [10]. Ischemic colitis generally affects the left colon and causes segmental wall thickening. Stratification is commonly preserved, but a hypoechoic pattern may be observed (Fig. 9).
Colorectal cancer typically presents as a bulky, often lobulated mass with an intra- or extraluminal location, or as segmental, eccentric, or circumferential mural thickening (Figs. 10, 11). The irregular contour and hypoechoic wall pattern represent features that help differentiate carcinoma from colitis.
Epiploic AppendagitisClinical presentationEpiploic appendagitis is a self-limiting condition resulting from the ischemic infarction of a long epiploic appendage, leading to localized LAP that can mimic acute diverticulitis or appendicitis [11]. The typical absence of rebound tenderness may help differentiate between these conditions.
ImagingWhile CT is the preferred method for diagnosing epiploic appendagitis, US not only reveals indicative findings in certain cases but also has the benefit of correlating the lesion’s location with the point of maximum tenderness.
US typically reveals an avascular, ovoid, hyperechoic mass measuring 2-4 cm that is adherent to the anterior colonic wall. This mass is encased by a hypoechoic layer that corresponds to a thickened serosal/peritoneal covering (Fig. 12). The absence of bowel wall thickening, central blood flow, and ascites assists in differentiating epiploic appendagitis from acute diverticulitis [12].
Genitourinary DisordersTesticular TorsionClinical presentationTesticular ischemia resulting from torsion of the testis on the spermatic cord can arise due to arterial flow obstruction or venous congestion. This condition typically presents with acute scrotal pain, diffuse tenderness, and a negative cremasteric reflex, which are often accompanied by nausea and vomiting. Notably, in 22% of adolescent patients, the sole presenting symptom is ipsilateral LAP [13]. Testicular torsion is most common among individuals between the ages of 12 and 18 years. The optimal window for detorsion, known as the "golden time," is the 4-6 hours following the onset of symptoms.
ImagingColor Doppler US is the preferred imaging method for suspected testicular torsion. A side-by-side comparison of the testicles is essential to assess differences in size, echogenicity, and color Doppler signals. Testicular enlargement is an early sign; this may present with either a homogeneous echotexture or a heterogeneously hypoechoic pattern, indicating a potentially viable testis or ischemia, respectively [14]. Notably, in the initial stages of testicular torsion, the echogenicity of the affected testis may appear normal. The diagnosis of torsion is supported by the absence or marked reduction of blood flow (Fig. 13). In addition, compensatory increased vascularity may be evident in the scrotal wall, and the whirlpool sign, which indicates a spiral twist of the spermatic cord components, may sometimes be observed cephalad to the testis.
Acute Epididymo-orchitisClinical presentationAcute epididymo-orchitis is the most common cause of scrotal pain in adults. Although it typically results from infection, trauma or autoimmune diseases can also be causative factors. The affected epididymis is edematous and painful on palpation. In more advanced cases, the testis may become involved, leading to testicular pain and swelling.
ImagingIn the acute setting, epididymo-orchitis is characterized by the thickening, enlargement, and hypoechogenicity or coarse echotexture of the epididymis, with initial involvement typically occurring at the tail. Testicular involvement is generally indicated by diffuse hypoechogenicity, although it presents with a focal pattern in approximately 10% of patients. Color Doppler imaging typically reveals testicular and/or epididymal hypervascularity relative to the asymptomatic side (Fig. 14). Reactive hydrocele and skin thickening are also common findings.
UrolithiasisClinical presentationUrolithiasis can lead to renal colic in cases of acute obstruction of the ureter or renal pelvis. Patients typically report sudden, intense flank pain that radiates to the ipsilateral abdomen and groin, frequently accompanied by hematuria. The site of the pain can suggest the level of obstruction. Additional symptoms include nausea, vomiting, and dysuria [7].
ImagingAlthough non-contrast CT is the preferred initial imaging method for urolithiasis, US may also be utilized, particularly for pregnant patients. If the initial findings are inconclusive, further evaluation with contrast-enhanced CT is recommended [5].
US can detect calculi of 5 mm or larger, which appear as echogenic foci that cause acoustic shadowing and may produce a "twinkle" artifact on color Doppler. However, the sensitivity of US in detecting urinary stones, particularly those located in the ureters, is lower than that of CT. Additionally, US is more limited in estimating stone size compared to CT, often resulting in an overestimation of the stone’s dimensions. US can reveal obstruction with accuracy comparable to CT, characterized by dilatation of the collecting system and ureter up to the level of the calculus (Fig. 15).
Acute PyelonephritisClinical presentationThe diagnosis of acute pyelonephritis is primarily based on clinical findings. Typical clinical features include fever, nausea, and/or vomiting, and symptoms of cystitis may also be present. Atypical cases may present with LAP. Physical examination often reveals tenderness in the flank, costovertebral angle, or suprapubic area, but without rebound tenderness or abnormal bowel sounds [15].
ImagingContrast-enhanced CT is the preferred method for evaluating suspected pyelonephritis, particularly in cases with atypical clinical findings or when differential diagnosis is challenging. While US is less sensitive, with prior research indicating that it detected abnormalities in only approximately 25% of patients, this modality resembles CT in the key features it can be used to identify. These include wedge-shaped parenchymal areas with reduced vascularity and abnormal echogenicity, which may be hypoechoic or hyperechoic, corresponding to edema or hemorrhage, respectively. US may also detect the loss of renal sinus fat, hydronephrosis, or abscess formation (Fig. 16) [16].
Obstetric/Gynecologic DisordersOvarian CystsClinical presentationOvarian cysts larger than 4 cm can cause unilateral, sharp, intermittent, and sudden pain in the lower quadrant, potentially accompanied by tenesmus or radiating to the ipsilateral leg [17]. Ovarian cyst rupture is indicated by moderate to severe pelvic pain, typically arising suddenly following strenuous physical activity; other signs include vaginal bleeding and nausea. The presence of generalized tenderness and hypovolemia should raise the suspicion of massive intraperitoneal hemorrhage.
ImagingCombined pelvic transabdominal and transvaginal US is the most valuable initial imaging technique for suspected obstetric and gynecologic disorders. In cases of uncertain diagnosis, particularly regarding conditions such as ovarian torsion, pelvic inflammatory disease, and tubo-ovarian abscess, contrast-enhanced CT and magnetic resonance imaging serve as secondary diagnostic tools.
Follicular cysts appear as thin-walled, most commonly unilocular, anechoic cysts measuring 3-6 cm (Fig. 17A) [17]. Corpus luteal cysts, which are functional cysts that form when the corpus luteum fails to regress, present as thick-walled structures with prominent peripheral vascularization (Fig. 17B). Hemorrhagic cysts initially appear isoechoic relative to the ovarian stroma, but as clotting occurs, a distinctive "lace-like" reticular pattern emerges (Fig. 17C, D). Common findings include a fluid-debris level or the appearance of a peripheral clot that may mimic a nodule. The absence of internal vascularity is a useful feature for ruling out solid ovarian lesions. Collapse of the cyst, along with the presence of intraperitoneal fluid containing low-level echoes, indicates cyst rupture (Fig. 18) [17]. Endometriomas are characterized by their homogeneous, low-level echogenicity and tend to be multiple and stable over time (Fig. 19).
Ovarian TorsionClinical presentationThe most common symptom of ovarian torsion, also termed "adnexal torsion" when the fallopian tube is involved, is the sudden onset of moderate to severe pain in the lower quadrant [18]. Patients with ovarian torsion experience nausea and vomiting more frequently than those with other gynecologic causes of pelvic pain. Furthermore, the presence of an ovarian mass increases the likelihood of ovarian torsion.
ImagingOvarian enlargement with peripherally located follicles is the most consistent finding indicative of torsion (Fig. 20). Stromal echogenicity may vary based on the duration of the condition, and an ovarian tumor that predisposes to torsion can sometimes be detected. The characteristics observed on color Doppler imaging depend on the extent of vascular compromise. The most sensitive of the early signs is a reduction or absence of venous flow, whereas arterial flow tends to be affected in more advanced stages [19,20]. The presence of free pelvic fluid is a common associated finding.
Ectopic PregnancyClinical presentationTypical symptoms of ectopic pregnancy include vaginal bleeding and/or abdominal pain. The characteristics of the pain can vary depending on the site of implantation and the volume of hemoperitoneum, presenting as suprapubic, lateralized, or generalized pain. In rare instances, profound hemorrhage can lead to hemodynamic instability. Beta-human chorionic gonadotropin (β-hCG) levels serve as an important marker for ectopic pregnancy. Although women with an ectopic pregnancy typically exhibit lower β-hCG levels than those with intrauterine pregnancy, these ranges display considerable overlap. When ectopic pregnancy is strongly suspected, serial measurement of β-hCG concentrations may be useful while the diagnosis remains uncertain.
ImagingOvarian ectopic pregnancy most commonly manifests as a thick-walled adnexal cyst with a hypervascular rim (Fig. 21) [19,20]. Tubular ectopic pregnancy typically presents as a complex, extra-adnexal cyst or mass-like lesion. The presence of a thick, echogenic endometrium within the uterine cavity, coupled with the absence of an intrauterine pregnancy, are consistent findings.
Less Common CausesIliopsoas BursitisClinical presentationIliopsoas bursitis typically causes pain in the anteromedial thigh, which can radiate to the leg and lower back and is often provoked by activity. In atypical cases, patients may experience pain in the lower quadrant.
ImagingUS should be the initial imaging modality performed in cases of suspected iliopsoas bursitis, followed by magnetic resonance imaging for further characterization when necessary. US is superior to CT in determining the nature of the bursal contents.
Iliopsoas bursitis is characterized by a well-defined, thin-walled, echo-free collection that is either heterogeneous or septated, situated along the iliopsoas tendon. A crucial imaging characteristic is the demonstration of a connection between the bursa and the hip joint (Fig. 22).
Spontaneous Retroperitoneal HematomaClinical presentationPatients with spontaneous retroperitoneal hematoma typically present with symptoms such as abdominal pain, anemia, or hypovolemia. The presence of the Grey Turner sign, characterized by ecchymosis or discoloration of the flanks, and the Cullen sign, which represents periumbilical ecchymosis, can aid in the diagnosis.
ImagingCT angiography is the recommended imaging modality for determining the cause of retroperitoneal hemorrhage and investigating active extravasation. Depending on patient body habitus, ultrasound may detect retroperitoneal fluid if it is located in US-accessible areas, such as the posterior renal space or behind the external iliac vessels (Fig. 23).
Rectus Sheath HematomaClinical presentationThe typical symptoms of rectus sheath hematoma (RSH) include acute, lateralized abdominal pain and a palpable abdominal mass. Physical examination often reveals abdominal tenderness and guarding. The tenderness does not change when the patient sits up from the supine position, a phenomenon known as the Carnett sign. Additionally, the palpable mass is bounded medially by the midline, which is referred to as the Fothergill sign.
ImagingTypical features of RSH include heterogeneity in the rectus abdominis muscle and fluid collection that may be homogeneous or heterogeneous, depending on the stage of hematoma evolution. This fluid collection is confined to the abdominal wall (Fig. 24).
ConclusionElucidating the numerous causes of LAP remains a challenging task that requires a high degree of clinical suspicion. A thorough physical examination, typically accompanied by imaging evaluation, is essential for prompt patient work-up. US plays a pivotal role, particularly as a first-line imaging modality, while CT primarily serves as a problem-solving tool. Awareness of the imaging algorithm and familiarity with the appearances of entities associated with LAP are important for accurate diagnosis.
NotesAuthor Contributions Conceptualization: Perysinakis I, Vassalou EE. Data acquisition: Perysinakis I, Vassalou EE. Data analysis or interpretation: Perysinakis I, Vassalou EE. Drafting of the manuscript: Perysinakis I, Vassalou EE. Critical revision of the manuscript: Perysinakis I, Vassalou EE. Approval of the final version of the manuscript: all authors. References1. Dirks K, Calabrese E, Dietrich CF, Gilja OH, Hausken T, Higginson A, et al. EFSUMB position paper: recommendations for gastrointestinal ultrasound (GIUS) in acute appendicitis and diverticulitis. Ultraschall Med 2019;40:163–175.
2. Expert Panel on Gastrointestinal Imaging, Weinstein S, Kim DH, Fowler KJ, Birkholz JH, Cash BD, et al. ACR Appropriateness Criteria(R) left lower quadrant pain: 2023 update. J Am Coll Radiol 2023;20(11S):S471–S480.
3. Expert Panel on Gastrointestinal Imaging, Kambadakone AR, Santillan CS, Kim DH, Fowler KJ, Birkholz JH, et al. ACR Appropriateness Criteria(R) right lower quadrant pain: 2022 update. J Am Coll Radiol 2022;19(11S):S445–S461.
4. Bhosale PR, Javitt MC, Atri M, Harris RD, Kang SK, Meyer BJ, et al. ACR Appropriateness Criteria(R) acute pelvic pain in the reproductive age group. Ultrasound Q 2016;32:108–115.
5. Coursey CA, Casalino DD, Remer EM, Arellano RS, Bishoff JT, Dighe M, et al. ACR Appropriateness Criteria(R) acute onset flank pain: suspicion of stone disease. Ultrasound Q 2012;28:227–233.
6. Bahadursingh AM, Virgo KS, Kaminski DL, Longo WE. Spectrum of disease and outcome of complicated diverticular disease. Am J Surg 2003;186:696–701.
7. Townsend CM. Sabiston textbook of surgery: the biological basis of modern surgical practice. 21st ed. St. Louis, MO: Elsevier, 2022.
8. Silverberg MS, Satsangi J, Ahmad T, Arnott ID, Bernstein CN, Brant SR, et al. Toward an integrated clinical, molecular and serological classification of inflammatory bowel disease: report of a Working Party of the 2005 Montreal World Congress of Gastroenterology. Can J Gastroenterol 2005;19 Suppl A:5A–36A.
9. Fraquelli M, Colli A, Casazza G, Paggi S, Colucci A, Massironi S, et al. Role of US in detection of Crohn disease: meta-analysis. Radiology 2005;236:95–101.
11. Giannis D, Matenoglou E, Sidiropoulou MS, Papalampros A, Schmitz R, Felekouras E, et al. Epiploic appendagitis: pathogenesis, clinical findings and imaging clues of a misdiagnosed mimicker. Ann Transl Med 2019;7:814.
12. Singh AK, Gervais DA, Hahn PF, Sagar P, Mueller PR, Novelline RA. Acute epiploic appendagitis and its mimics. Radiographics 2005;25:1521–1534.
13. Vasconcelos-Castro S, Soares-Oliveira M. Abdominal pain in teenagers: beware of testicular torsion. J Pediatr Surg 2020;55:1933–1935.
14. Kaye JD, Shapiro EY, Levitt SB, Friedman SC, Gitlin J, Freyle J, et al. Parenchymal echo texture predicts testicular salvage after torsion: potential impact on the need for emergent exploration. J Urol 2008;180:1733–1736.
15. Loscalzo J, Fauci A, Kasper D, Hauser S, Longo D, Jameson JL. Harrison’s principles of internal medicine. 21st ed. New York: McGraw Hill, 2022.
16. Craig WD, Wagner BJ, Travis MD. Pyelonephritis: radiologic-pathologic review. Radiographics 2008;28:255–277.
18. Roche O, Chavan N, Aquilina J, Rockall A. Radiological appearances of gynaecological emergencies. Insights Imaging 2012;3:265–275.
|