The importance of visualization of appendix on abdominal ultrasound for the diagnosis of appendicitis in children: A quality assessment review

Muhammad Akhter Hamid, Ruqiya Afroz, Uqba Nawaz Ahmed, Aneela Bawani, Dilnasheen Khan, Rabia Shahab, Asim Salim

1 Scarborough Health Network, Toronto, ON, Canada

2 Department of Paediatrics, University of Toronto, ON, Canada

3 St. Michael's Hospital, Toronto, ON, Canada

4 Grand River Hospital, Kitchener, ON, Canada

5 Brantford General Hospital, Brantford, ON, Canada

KEY WORDS: Abdominal ultrasound; Visualization; Importance; Appendix; Abdominal pain; Acute appendicitis; Children; Paediatric population

INTRODUCTION

Ultrasound is now widely considered as one of the most universally accepted imaging modality for diagnosing abdominal pathologies, including acute appendicitis. Acute appendicitis remains one of the most common surgical emergencies among children. In North America, appendicitis accounts for about 10% of all acute abdominal pain among children.[1,2]The overall lifetime risk of developing acute appendicitis is 8.6% in males and 6.7% in females.[2,3]The most predictive findings of appendicitis include right lower quadrant pain, guarding of the abdominal wall, and migration of periumbilical pain to the right lower quadrant. In addition, anorexia, pain with movement, vomiting, fever, and signs of peritoneal irritation are all supportive fi ndings. These clinical fi ndings may be vague or absent in infant and young children, nevertheless their absence is not a reason to exclude the diagnosis of appendicitis. Furthermore, appendicitis can mimic many other pathologies thus making the diagnosis more challenging in these young individuals.[4]

Ultrasound has a first line investigation role in children as they have reduced abdominal fat, thin build and need to avoid radiation. Ultrasound has many undeniable and useful advantages over other noninvasive imaging modalities. It is easily accessible, painless, cost-effective, and does not emit harmful ionizing radiation. Its real-time imaging is advantageous for capturing images that show the structure and movement of the body’s internal organs.[5]In a study by Gregory et al,[6]they integrated staged imaging with a validated clinical decision rule (CDR) for the diagnosis of appendicitis in children and concluded that ultrasound is a cost-effective and cost-saving approach. For medium and high-risk patients on CDR incorporated with ultrasound, a further 10.9% reduction in the number of CTs was found in contrast to a 19.5% reduction in CDR alone. All this makes ultrasound an attractive and credible investigation tool for diagnosing acute appendicitis, especially in children.

The appendix is not always found in its typical anatomical position; in 15%–20% of cases its retrocecal position can make its visualization rate by sonographers more diffi cult.[7,8]

When appendicitis is suspected, the investigation commences with ultrasound and advances to a CT scan in approximately 34% of cases, if the diagnosis on ultrasound is uncertain or equivocal.[6,9]Sensitivity and specificity of ultrasound between 86%–97% and 81%–91% respectively have been reported in different studies.[5,10-12]Other studies found a wide variation in visualization rate of appendix ranging from the lowest 21% to the highest 97.1%.[5,11,12]CT scan has sensitivity and specificity of 92%–94% and 96% respectively for the diagnosis of appendicitis.[13,6]Owing to the exposure to ionizing radiation, cost and lack of availability in low resources hospitals, it is not always the best option. MRI is another modality which has a benefit of low ionizing radiation but has not been found superior to ultrasound in terms of accuracy.[14,15]Additionally, high cost and lack of availability make this choice less favourable.

With the above depiction, it is evident that ultrasound is the most suitable initial imaging modality in suspected appendicitis. Emergency physicians of two local community hospitals in greater Toronto area discerned that while many ultrasound investigations were requested in an emergency to rule out the causes for acute abdomen in children, they fail to visualize the appendix. This led us to carry out a quality assessment review /audit to analyze the visualization rate of an appendix in community care settings with the premise that the more we see appendix on ultrasound, the more it will help in ruling in or ruling out the diagnosis of acute appendicitis. Our study thus aimed to appraise the importance of the visualization of the appendix on ultrasound in ruling out the causes of the acute abdomen such as appendicitis in paediatric population. To accomplish our objective, we reviewed the findings of all ultrasounds abdomen that were performed for the patients with acute abdominal pain with suspected appendicitis.

METHODS

Retrospective data of patients from two community hospitals in the Greater Toronto Area were retrieved for a 5-year duration from June 1, 2012 until May 30, 2017. Approval from an ethical review board of the hospitals was obtained before commencing the study. Our objective was to perform a qualitative assessment on paediatric ultrasound reports to estimate the visualization of an appendix on ultrasound in patients ranging from 5 to 18 years of age.

From the two hospital sites, we retrieved the abdominal ultrasound reports of patients who presented to the emergency department with complaints suggestive of appendicitis. The keywords used to collect the ultrasound data from the hospital emergency medical record were included as follows: (i) acute abdomen; (ii) right lower quadrant (RLQ) pain; (iii) suspected appendicitis; and (iv) acute appendicitis. Cases with concomitant pathology or other identified diagnosis such as pyelonephritis, renal calculi, hydronephrosis, intussusception, ovarian torsion and those require immediate intervention or emergent surgical procedure were excluded. Children less than 5 years of age were also excluded due to their limitations in verbal skills, non-specifi c symptoms and atypical presentations.

Ultrasounds were performed and digital images were taken by non paediatric certified sonographer and reported and confirmed by specialist radiologist on duty in variable time round the clock. Linear or convex array paediatric transducers were used for ultrasound examinations whereas graded compression was the technique of choice. We classified ultrasound results in two main categories of completely visualized or nonvisualized. Completely visualized appendices were further classifi ed as positive or negative for appendicitis. The diagnostic criteria used for visualizing appendix on ultrasound include identifi cation of a compressible fl uidfilled, blind-ended tubular structure in the right lower quadrant with sonographic features indicating intestinal origin, whereas the criteria for identifying acute appendicitis using ultrasound include enlarged, noncompressible fluid-filled tubular structure arising from the cecum, with pericecal fat suggestive of infl ammatory changes and occasional appendicolith. Appendiceal diameter of less than 6 mm was taken negative whereas more than 6 mm was considered positive for appendicitis. Findings of the ultrasound results reported in the electronic data sheet.

Results of the two hospital sites were calculated to see the visualization rate that is a percentage of abdominal ultrasound when the appendix was seen. A two-proportion z-test was performed to find whether the visualization of appendix increases the likelihood of diagnosing appendicitis.

RESULTS

Considering the inclusion criteria, a total of 1,386 ultrasound reports were retrieved from site 1. The appendix was visualized in only 153 reports indicating 11.0% visualization rate of an appendix on ultrasound (153/1,386), whereas 93 out of 153 (60.7%) visualized appendices were finally diagnosed as appendicitis on ultrasound (Figure 1). From site 2, a total of 1,167 ultrasound reports were analyzed. Visualization rate of the appendix was 23.2% (271/1,167), whereas 137 out of 271 (50.5%) visualized appendices were confirmed as appendicitis. Table 1 illustrates the comparison of imaging results of initial ultrasound performed in two sites respectively.

Depending on clinical fi ndings and physician discretion some of the patients were followed according to the hospital guidelines by repeat ultrasound and/or CT scan when the appendix was not visualized on the first ultrasound. A data result from repeat ultrasound in cases where the appendix was not visualized in the first ultrasound has been demonstrated in Table 2. We didn’t collect the data for the children that underwent CT scan as this was beyond the scope of the study. None of the examinations were abandoned due to non-cooperative child.

Figure 1. Visual abstract.

A two-proportion z-test was performed to see if the visualization of the appendix can help in making the diagnosis of appendicitis. The results indicated that the visualization of the appendix (P=0.52), significantly improved the diagnosis of appendicitis (z=34, P<0.001).

DISCUSSION

Ultrasound is now widely used as the initial imaging modality to diagnose infl amed appendix. However, accurate diagnosis of any pathology using ultrasound rest upon skillful visualization of the target organ or tissue. Variable visualization rates have been reported in the literature with the lowest reported of 21 percent. In our study, the visualization rate of the appendix on ultrasound was 11.0% and 23.2% at site 1 and site 2 respectively. Contrary to our study, Junewick et al[16]have reported visualization rates of appendix between 52.5% and 66.7% when performed by paediatric sonographers. The low visualization rate of appendix found at our two local institutions limited the utility of ultrasound as a reliable diagnostic modality for acute abdomen. Furthermore, the low visualization also unjustifiably bolsters the use of the CT scan as a substitute for diagnosing appendicitis.[4]Nevertheless, it is important to note that the rate of visualization of the appendix on ultrasound varies due to many factors, including:

(i) Operator skills. Soft and deep tissue identifi cation requires considerable skills, experience, and the right equipment. Dedicated paediatric sonographers can easily identify the appendix at a significantly higher rate than non-pediatric sonographers.[16]In our study, ultrasound examinations were not performed by paediatric sonographers, which may explain the lower rate of visualization.

(ii) Patient characteristics and cooperation. High BMI in a patient is now arguably considered a limitation to optimal abdominal compression for visualizing appendix.[15,17]It also adversely affects the penetration of high-frequency ultrasound beams, thus leading to poor image quality. In children, there is a relative lack of adipose tissue, so this factor contributes positively.[17,18]Children are often anxious and less cooperative during the examination, hence making it diffi cult to obtain quality images.[18]

Table 1. Comparison of imaging results of initial ultrasound appendix between site 1 and site 2

Table 2. Comparison of imaging results of repeat ultrasound appendix between site 1 and site 2

(iii) Location. Most appendix lies within the right lower quadrant of the abdomen. In the case of a retrocecal appendix or deep pelvic appendicitis visualization on ultrasound become more challenging for the operator.[7,8,18]

Many institutions have created a staged approach for the management of acute appendicitis. In our facilities, risk stratification of a child with suspected appendicitis is done by using a combination of clinical assessment, lab investigations, and imaging studies. If clinical assessment and blood work are supportive of the diagnosis of appendicitis, an abdominal ultrasound is performed. In cases where the diagnosis is uncertain, a repeat ultrasound and/or CT scan is performed after 12 to 24 hours at the prudence of the responsible physician. Repetition of ultrasound did not improve the visualization rate in this study. A study conducted by Ross et al,[19]found that patients with at least one secondary sign have an odds ratio of 6.5 of having appendicitis. Data suggest that an adequately performed US examination has negative predictive value (NPV) of 84% for appendicitis. This increases to more than 95% if associated with WBC count of more than 7.5×109/L assuming that the appendix is visualized and there are no other abnormalities.[20-22]

When a conditional CT (i.e., a CT study after a negative or inconclusive ultrasound exam) is used instead of an immediate CT strategy, the conditional CT exams correctly identified as many patients with acute appendicitis as the immediate CT strategy.[23]Although CT can demonstrate the normal appendix, as well as the variation in its anatomical positions, it may be considered as an immediate option in atypical patients with equivocal presentation and/or clinical suspicion of appendiceal abscess where it gives the benefit of draining the abscess during the scanning.[23]

Lastly, our main aim will always remain to diagnose appendicitis accurately, in a timely fashion and lessen negative appendectomies and complications associated with delayed diagnosis. The delay in diagnosis and timing of intervention are a major risk factor for perforation.[21]It is also important to note that the delay in diagnosis (i.e., time from symptom onset to ED) is usually attributed to atypical presentations, non-specifi c symptoms, overlapping of symptoms with other common childhood illnesses, inability to express symptoms and diffi culty with the abdominal examination. To overcome such obstacles, several investigators have devised clinical scoring systems. These scoring systems are used to aid in clinical decision making. The Alvarado Pediatric Appendicitis Scoring System (APASS),[23]and Raja Isteri Pengiran Anak Saleha Appendicitis (RIPASA),[24]are examples of such scoring systems. Even though Alvarado Scoring is advisable for any patient with suspected appendicitis (typically with right lower quadrant abdominal pain), the Alvarado Score also require supportive laboratory values in addition to history and physical exam findings.[23,24]We are in a process of structured guidelines for the diagnosis of acute appendicitis in our community hospital. One such clinical scoring system will be incorporated in these guidelines.

Limitations

Major limitations to this study were an absence of follow up data of the patients’ post imaging investigations and absence of surgical or pathological confirmations towards the suspected appendicitis. The non-appendiceal diagnosis was beyond the scope of this study. In our study, we could not determine the cause of non-visualization of appendix specifically. We did not collect the data for the patients who underwent complementary imaging like CT scan and MRI. This study also did not follow up with patients whose parent/guardian refused to provide consent for CT or in whom CT contrast was contraindicated due to renal or other anomalies. Often the ultrasound findings for appendix by the radiologists are neither negative nor positive. This leaves the clinicians in a quandary, when the interpretation for such fi ndings suggested “equivocal”, “non-visualized”, “limited”, or “inconclusive”. Our study is lacking the data for equivocal and inconclusive examinations.

CONCLUSION

Since ultrasound is a non-invasive, cost-effective test to diagnose appendicitis, improving its visualization rate (i.e., 11.0% and 23.2% at site 1 and 2 respectively) can increase the probability of accurately diagnosing appendicitis. Ultrasound plays an important role in ruling out the causes of an acute abdomen. This imaging tool can be enhanced by incorporating a systematic reporting method to help the sonographers report, record and interpret the ultrasound findings thoroughly. The template can be tailored as per hospital protocol and recommendations. Training/teaching and refresher courses to the staff may also help enhance their skills in establishing clinical decision-making strategies to rule out acute appendicitis.[25]

Our study evidently affirms that low visualization of appendix constrains the diagnosis of appendicitis. It is also an irrefutable testament that review and improvement of the ultrasound scanning techniques to optimize the visualization, and only then consider using standard or low-dose CT imaging as an alternate method of choice in individuals who present with a high clinical scoring systems. Use of low-dose CT scan has been gaining interest for the diagnosis of appendicitis, but it lacks randomized controlled trials in children.[26]In future, this quality assessment audit will be presented in hospital departmental round, and guidelines will be formulated for diagnoses and treatment of appendicitis so that visualization rate can be improved. This will be followed by another audit to close the loop.

Funding:None.

Ethical approval:Approval from an ethical review board of the hospitals was obtained before commencing the study.

Conflicts of interest:The authors confirm that no conflict of interest or any fi nancial relationship that relates to the content of the manuscript has been associated with this publication.

Contributors:MAH proposed the study and wrote the paper. All authors contributed to the design and interpretation of the study and to further drafts.