Anatomy Review: What am I looking at?

 

The appendix is a small, blind-ended tubular structure.  The appendix typically arises from the posteromedial aspect of the cecum, just below the ileocecal valve. The tip can have variable position within the right lower quadrant and is often found below or slightly posterior to the terminal ileum and anterior to the iliac vessels.

Less commonly, the appendix can be retrocecal, extending behind the cecum making visualization more difficult, or have a pelvic position, where it extends downward into the pelvis, closer to the bladder and reproductive organs. Additionally, it can sometimes extend laterally from the cecum, which may also affect its visualization.

 

Figure 1: Typical anatomical position of the appendix in the RLQ

 

 

Figure 2: Transverse image of the RLQ demonstrating anatomical landmarks (Iliac vessels & Psoas muscle) used to identify the appendix on PoCUS

 

Figure 3: TTransverse image of the RLQ anatomy, showing the cecum positioned lateral to the psoas muscle and the TI medially—key landmarks for locating the appendix on PoCUS

 

Figure 4: Transverse image of the RLQ showing the “typical” position of the appendix

 

Figure 5: Transverse video of the RLQ anatomy 

Stepwise Technique Overview

Patient position: Supine

 

1. Assess point of maximal tenderness

2. Identify anatomical landmarks of the RLQ

3. Attempt left posterior oblique position to troubleshoot when having difficulty identifying the appendix

4. If a structure of interest is identified:

i. Short axis sweep: slide in short axis to review entire length from base to tip

ii. Long axis rotation: Rotate to view in long axis

– Try to visualize and capture the entire length of the appendix from the cecal junction to the tip

iii. Apply color doppler

–  Select the color doppler function and set the color box over the area of interest, ensuring it is slightly larger to include surrounding tissue

–  Use a low velocity scale and adjust the color gain to enhance sensitivity to flow.

iv. Assess compressibility

– In short axis, apply compression to assess compressibility

– Be sure to document the compressibility with a video clip or a buddy view (split-screen) showing images with and without probe compression. 

v. Assess surround structures: look for secondary signs and document any findings

 

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Point of maximal tenderness

This is the preferred starting point for appendicitis

1. Have the patient point with one finger to the spot that hurts the most

2. Place the probe in this spot, in the transverse position (probe marker toward patients right)

3. Review the immediate region in transverse and sagittal plane

** Tip: Identifying the point of maximal tenderness can require some coaching in smaller children

 

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Anatomical Landmarks with identification of the cecum/ileocecal region

This technique used a systematic approach to identify first the anatomic landmarks in the immediate region of the appendix, then the cecum and ileocecal region. 

1. Place the probe in the transverse position in the right lower quadrant

2. Identify the iliac vessels and psoas muscle (Figure 2)

3. Look laterally (screen left) to identify the cecum (Figure 3)

4. Look for the origin of the terminal ilium posterior/medially from the cecum

–  The appendix typically arises posterior/medially from the cecum and caudal/posterior to the TI, draping anteriorly over the iliac vessels

5. Scan the area in transverse and sagittal planes until you can identify the appendix or any secondary findings

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Indications

• Rule-in test for appendicitis
• Clinical suspicion for appendicitis including but not limited to:
  • Right lower quadrant pain
  • Guarding and rebound tenderness
  • Fever, nausea, vomiting
  • Anorexia
  • Migratory pain from periumbilical region
  • Positive risk calculation (Alvarado score, Pediatric Appendicitis Score, Pediatric Appendicitis Risk Calculator (pARC)) [13-15]

PoCUS is appropriate in the same clinical scenarios that radiology-based imaging would be indicated. Physicians might elect to perform POCUS when this imaging is not available or timely, or in cases where POCUS might facilitate treatment or transfer decisions and expedite care.

 

Equipment

• Ultrasound machine
• High frequency linear probe (curvilinear probe for obese or older children)
• Ultrasound gel

Introduction

Acute appendicitis is a common surgical emergency among children and adolescents, affecting tens of millions of patients globally each year, with the highest incidence occurring between ages 10 and 19 [1,2]. Prior to the advent of medical imaging and modern surgical techniques, it accounted for significant morbidity and mortality [3]. In the modern era in North America death secondary to acute appendicitis and its complications have become rare, with decreased incidence, improved diagnosis, increased treatment options, and availability of prompt surgical management all playing a role in the improvement in outcomes [4]. Diagnosis of appendicitis typically involves a combination of clinical evaluation and medical imaging, which plays a central role in confirming the diagnosis and guiding management. While history and physical examination remain important, most major centers rely on imaging before proceeding to surgery, especially in cases with equivocal presentations. Scoring systems may also be used to support decision-making and determine the need for imaging [5,6]

Why Ultrasound?

Ultrasound is a valuable diagnostic tool in cases of suspected appendicitis, particularly in children and pregnant populations, where minimizing radiation exposure is paramount. It is a non-invasive modality and does not require complete stillness, making it particularly suitable for younger children or those who may have difficulty remaining still for cross-sectional imaging such as CT or MRI.

Ultrasound has high sensitivity  in detecting inflammation and structural abnormalities in the appendix, allowing for dynamic assessment of the appendix and surrounding tissues [7]. It also offers sufficient specificity to aid in distinguishing between uncomplicated and complicated appendicitis [7]. Its diagnostic performance can vary depending on factors such as operator experience and patient characteristics, including body habitus, difficulty tolerating probe pressure, and the presence of bowel gas, among others. Despite this variability, ultrasound for the diagnosis of acute appendicitis in pediatric patients by radiology (RADUS) has demonstrated a sensitivity of 97.1% and specificity of 94.8%, and when nondiagnostic studies are excluded, these values increase to 98.8% and 98.3%, respectively [7].

 There is, however, high variability in the sensitivity and specificity reported across the publications included in all three analyses [8-10], but overall, the data supports PoCUS as a valuable tool for diagnosing acute appendicitis, particularly in pediatric patients.

Additionally, PoCUS for appendicitis allows real-time imaging, and can be readily performed at the bedside, facilitating prompt diagnosis and timely initiation of appropriate treatment, thereby reducing the risk of complications associated with appendicitis. Studies have shown that ED PoCUS can significantly reduce pediatric ED length of stay when performed by both fellowship and non-fellowship PoCUS trained emergency physicians [11,12] and reduce CT usage [11].

Considering these advantages, it is important to recognize that PoCUS for appendicitis should be viewed as a useful diagnostic tool, with its strengths in real-time imaging and immediate assessment. However, due to the prevalence of non-diagnostic exams, it is most effective when used as a rule-in test, where a positive result supports the diagnosis—helping guide immediate management decisions, but a negative scan alone does not reliably rule it out.

 

Table 1: Summary chart of Sensitivity and Specificity values for diagnosing appendicitis in pediatric populations

*CI = 95%. EP = Emergency physician

 

 

 

Primary Author: Melissa Skaugset, MD, FRCPC

Secondary Author: Julia Stiz MSc, RDMS

Reviewer(s): Melanie Willimann, MD, FRCPC, Dave Kirschner, MD, FRCPC

 

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References

1. Liang T, Metcalfe P, Sevcik W, Noga M. Retrospective review of diagnosis and treatment in children presenting to the pediatric department with acute scrotum. AJR Am J Roentgenol. 2013 May;200(5):W444-9.
2. Barbosa JABA, de Freitas PFS, Carvalho SAD, Coelho AQ, Yorioka MAW, Pereira MWA, et al. Validation of the TWIST score for testicular torsion in adults. Int Urol Nephrol [Internet]. 2021;53(1):7–11. Available from: https://doi.org/10.1007/s11255-020-02618-4
3. Barbosa JA, Tiseo BC, Barayan GA, Rosman BM, Torricelli FCM, Passerotti CC, et al. Development and initial validation of a scoring system to diagnose testicular torsion in children. J Urol. 2013 May;189(5):1859–64.
4. Qin KR, Qu LG. Diagnosing with a TWIST: Systematic Review and Meta-Analysis of a Testicular Torsion Risk Score. J Urol. 2022;208(1):62–70.
5. Choudhury P, Saroya KK, Anand S, Agarwal P, Jain V, Dhua AK, et al. Unjumbling the TWIST score for testicular torsion: systematic review and meta-analysis. Pediatr Surg Int. 2023 Feb;39(1):137.
6. Radmayr CB, Burgu B, Castagnetti M, Dogan H, O’Kelly F. EAU guidelines on paediatric urology 2024. European Association of Urology. 2024. 26–29 p.
7. Chan EP, Wang PZT, Myslik F, Chen H, Dave S. Identifying systems delays in assessment, diagnosis, and operative management for testicular torsion in a single-payer health-care system. J Pediatr Urol [Internet]. 2019;15(3):251.e1-251.e7. Available from: https://doi.org/10.1016/j.jpurol.2019.03.017
8. Mori T, Ihara T, Nomura O. Diagnostic accuracy of point-of-care ultrasound for paediatric testicular torsion: A systematic review and meta-Analysis. Emerg Med J. 2022;40(2):140–6.
9. Ramachandra P, Palazzi KL, Holmes NM, Marietti S. Factors influencing rate of testicular salvage in acute testicular torsion at a tertiary pediatric center. West J Emerg Med. 2015 Jan;16(1):190–4.
10. Park JS, Kim D, Chun MK, Choi SJ, Lee JS, Ryu JM, et al. Implementing Point-of-Care Ultrasound for Acute Scrotal Pain in the Pediatric Emergency Department: Screening Testicular Torsion and Patient Flow Analysis. J Ultrasound Med. 2023;42(12):2757–64.
11. Koppel JH, Patt YS, Berant R. Point-of-Care Ultrasound for the Diagnosis of Pediatric Testicular Torsion: A Retrospective Case Series Analysis. Pediatr Emerg Care. 2023;39(8):623–8.
12. Stringer L, Cocco S, Jiang A, Chan EP, Myslik F, Brahm G, et al. Point-of-care ultrasonography for the diagnosis of testicular torsion: A practical resident curriculum. Can J Surg. 2021;64(2):E191–5.
13. Siegel, M. J. (2019). Pediatric sonography (5th ed.). Wolters Kluwer Health.
14. Shields LB, Daniels MW, Peppas DS, Rosenberg E. Sonography Findings Predict Testicular Viability in Pediatric Patients With Testicular Torsion. Cureus. 2022;14(1):1–7.
15. Afsarlar CE, Cakmakci E, Demir E, Guney G, Komut E, Elizondo R, et al. Novel prognostic grayscale ultrasonographic findings in the testis from a comprehensive analysis of pediatric patients with testicular torsion. J Pediatr Urol. 2019 Oct;15(5):480.e1-480.e7.
16. Dogra VS, Bhatt S, Rubens DJ, Sonographic evaluation of testicular torsion) Ultrasound clin. 2006;1:55-66
17. Cassar, S., Bhatt, S., Paltiel, H.J. and Dogra, V.S. (2008), Role of Spectral Doppler Sonography in the Evaluation of Partial Testicular Torsion. Journal of Ultrasound in Medicine, 27: 1629-1638. https://doi.org/10.7863/jum.2008.27.11.1629
18. McDowall J, Adam A, Gerber L, Enyuma COA, Aigbodion SJ, Buchanan S, et al. The ultrasonographic “whirlpool sign” in testicular torsion: valuable tool or waste of valuable time? A systematic review and meta-analysis. Emerg Radiol. 2018;25(3):281–92.
19. Nene R V., Subramony R, Marcias M, Campbell C, Aminlari A. Real-time Point-of-care Ultrasound for the Diagnosis and Treatment of Testicular Torsion. POCUS J. 2021;6(2):70–2. 19
20. Hsu C Te, Chiu PW, Deanehan JK. Successful Outcome of Manual Testicular Detorsion Using Point-of-Care Ultrasound Guidance: A Clinical Experience. Pediatr Emerg Care. 2023;39(10):813–5.
21. Güneş M, Umul M, Çelik AO, Armaʇan HH, Deʇirmenci B. A novel approach for manual de-torsion of an atypical (outward) testicular torsion with bedside Doppler ultrasonography guidance. Can Urol Assoc J. 2015;9(9–10):E676–8.

 

• Time is testicle. In cases of testicular torsion, outcomes are improved with detorsion in less than 6 hours from symptom onset
• PoCUS may be used as an adjunct to clinical decision making alongside the TWIST score when the suspicion for TT is intermediate.
• PoCUS should be utilized as a rule-in test for testicular torsion but should never delay surgical consultation or formal ultrasound when clinical suspicion of torsion is high
• The most specific signs for testicular torsion are absent/decreased testicle vascularity and whirlpool sign.

Pitfalls & Limitations

 

• PoCUS can be used to rule IN TT, but should not be used to rule OUT in cases with moderate to high pretest probability
• Partial TT may have preserved color doppler flow. It should be decreased when compared to the contralateral testicle.
• Torsion-detorsion may have either reduced or increased signal (hyperemia) depending on the stage of torsion-detorsion, which can mimic orchitis therefore it is imperative to interpret increased perfusion in the clinical context

 

Due to these limitations, if a patient presents with a high TWIST score and a strong history and physical exam suggestive of torsion, but the ultrasound is inconclusive or normal, maintain a high index of suspicion. Consider arranging a repeat scan in the morning or calling in the sonographer if clinically indicated.

 

Manual detorsion is a non-invasive procedure that emergency physicians can perform at the bedside to reverse the torsion and return blood flow to the testicle. The European Urological Association Pediatric Urology Guideline states that manual detorsion should be attempted in all cases of testicular torsion at the physician’s discretion and can be done without anesthesia. In testicular torsion, the testis is typically rotated inwards. Therefore, manual detorsion is typically performed by manually rotating the testicle outward, from medial to lateral. This results in reperfusion in about ⅓ of cases. There are multiple factors which influence success rates for manual detorsion including the degree of torsion and the direction of rotation (19). If you are trying to detort in the wrong direction or you do not rotate enough, vascular flow will not be restored.

PoCUS can be used to help identify direction of rotation of the torsion to help guide the counter-direction for manual detorsion (20). If you identify the whirlpool sign, you can determine the direction of rotation (Figure 14) (20,21). Ultrasound can also be used to assess for reperfusion of blood flow on color doppler and resolution of whirlpool sign. Additionally, the patient should have an abrupt improvement in pain with restoration of blood flow which can be confirmed by direct visualization on ultrasound.

Figure 14. Using the whirlpool sign (B,C) to identify direction of manual detorsion resulting in return of blood flow on color doppler (D) (20).

 

2D Findings: Testicular orientation, volume and texture

Orientation: In testicular torsion, the affected testicle often lies horizontally

Volume: In acute torsion, the testicle is enlarged with increased volume (Video 2). In chronic or missed torsion the testicle undergoes atrophy, leading to a decrease in volume. Unilateral increased volume of the testicle should raise suspicion for partial torsion or torsion-detorsion in the right clinical context but may also be seen in orchitis.

Texture: Testicular heterogeneity (figure 6) is typically a later finding and associated with worse outcomes, including non-viable testis (14). Testicular fragmentation and patching can be seen once the testicle becomes necrotic and increases the risk of testicular loss (figure 7)(15).

 

 

 

Figure 6. Heterogenous echogenicity of enlarged testicle

 

Figure 7. Testicular fragmentation (a,b) and patching (c,d)

 

 

Color Doppler

Absent testicular flow (Figure 8A)

Absence of doppler flow is highly predictive of TT, with 97% positive predictive value and 75% specificity for TT (7). If there is absence of flow, the case should be treated emergently as TT.

Decreased testicular flow (Figure 8B)

Early or partial testicular torsion (usually <360 degrees) may have preserved arterial flow since the arterial flow is impaired, but not completely obstructed. The color doppler signal may be decreased compared to the other side. Radiology ultrasound includes evaluation of arterial and venous waveform using spectral doppler to confirm this diagnosis.

Increased Blood Flow (Figure 8C)

In cases of torsion-detorsion, rebound reperfusion can result in hyperemia of the affected testicle. It may mimic the sonographic appearing of orchitis which may also have increased color flow. It is imperative to interpret increased perfusion in the clinical context.

 

Figure 8. Abnormal testicular flow of the affected testicular (blue star) in the transverse plane A) Absent flow B) Decreased flow C) Increased flow on color doppler [15]

 

Figure 9. A) Heterogenous echogenicity of enlarged testicle and B) Heterogenous testicle with absent blood flow [15]

 

 

Video 2. Testicular torsion with absent flow and increased volume to left testicle

Spectral Doppler

Although not routinely used in PoCUS, spectral Doppler is commonly employed in Radiology when assessing for testicular torsion. Using spectral doppler in addition to color doppler to confirm torsion has been associated with a higher PPVs in predicting testicular torsion (7)

Pulsed wave spectral doppler can be used to confirm the presence of arterial and venous flow in the testicle in addition to color doppler since color doppler can be subject to motion artefact (16), but obtaining spectral waveforms can be difficult due to size of vessels and angle correction

Normal Spectral Doppler:

With spectral doppler, arterial wave forms are pulsatile with distinct systolic and diastolic phases. Systolic phases begin with a sharp upstroke followed by a diastolic component that varies with resistance. Venous waveforms are continuous or monophasic (no systolic or diastolic peaks) and generally have lower velocity and some respiratory variation.

Normal arterial flow within the testicle will be pulsatile and exhibit high flow, low resistance, waveforms (16,17) (figure 10), whereas venous flow will exhibit low-velocity, continuous waveforms with minimal pulsatility (figure 11).

 

Figure 10: Arterial spectral doppler of the testicle

 

 

Figure 11: Venous testicular spectral doppler

 

 

Abnormal Spectral Doppler: In early or complete torsion, the arterial waveforms will be absent or diminished. When comparing to the non-affected testicle, you may observe blunted waveforms with decreased flow velocity in the affected testicle and higher velocity flows in the non-affected testicle (16,17). Venous waveforms will be absent (17).

 

Figure 12: Torsed testicle with blunted arterial waveform. Image courtesy of Colin Bell, used with permission.

 

Secondary Findings:

Whirlpool Sign:The whirlpool sign is an US image of the spermatic cord above the testicle displaying a spiral with concentric circles. The finding is due to visualization of the twisted spermatic cord. A metanalysis looking at radiology performed US in patients over 3 months old with TT found a pooled sensitivity of 0.92 and pooled specificity of 0.99 for presence of whirlpool sign (18). The sensitivity of whirlpool sign is low in neonates < 30 days (18).

It’s important to note that this sign may not always be present. An important differential to consider is an epididymal abscess, although rare, can also present with a similar appearance.

 

Video 3. Whirlpool sign

 

Epidydimal Swelling: (Figure 13A)

Secondary to the inflammatory process within the scrotum, the ipsilateral epidydimis may become swollen with testicular torsion.

Reactive Hydrocele: (Figure 13B)

Presence of hydrocele is nonspecific to testicular torsion but can be frequently encountered during ultrasound examination of the acute scrotum. The hydrocele fluid is anechoic and surrounds the testicle.

 

Figure 13. Testicular ultrasound in the longitudinal plane demonstrating A) enlarged epidydimal head (blue star) and reactive hydrocele (red star)