ACCURACY OF ULTRASONOGRAPHY IN DIAGNOSIS OF ACUTE APPENDICITIS; RESULTS OF A CROSS-SECTIONAL SURVEY AT TWO CENTRES.
Objective: To determine the accuracy of ultrasonography in diagnosing acute appendicitis (AA) by taking histopathology as gold standard.
Study Design: A cross-sectional validation study.
Place and Duration of Study: Departments of surgery and radiology, Combined Military Hospitals of Multan and Quetta, from Apr 2014 to Apr 2016.
Material and Methods: Ultrasonography of 200 consecutive patients fulfilling the diagnostic criteria on Modified Alvarado Scoring System for the clinical diagnosis of AA was done and the results were entered in proforma s. Each patient underwent appendicectomy and appendices in all cases were sent for histopathological examination. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated through Med Calc.
Results: Out of 200 patients, 132 were males and 68 were females. The most common age group was 11-30 years. The sensitivity of ultrasonography for AA was 61.43%, with a specificity of 76.67%, PPV of 86%, NPV of 46%, and an accuracy rate of 66%.
Conclusion: With sensitivity, specificity, and accuracy rate of 61.4%, 76.7%, and 66% respectively, ultrasonography is justified as an appropriate diagnostic tool in suspected cases of AA to avoid undue surgical interventions.
Keywords: Acute appendicitis, Accuracy, Appendicectomy, Sensitivity, Specificity, Ultrasonography.
Acute appendicitis (AA) is one of the commonest surgical emergencies1. Approximately 7% of the population will suffer from AA during their lifetime2, with the peak incidence occurring between the ages of 10 and 30 years3. Therefore, much effort has been directed toward early diagnosis and intervention. Diagnosis of AA is mainly clinical but a long list of conditions mimicking this clinical scenario has created a lot of diagnostic confusion, resulting in negative appendicectomy rate that once approached 23% in 1990 and 19% in 20084,5. At the extremes of age (below 5 and above 60 years), it is more likely that appendicitis will present with atypical history and clinical findings and hence diagnosis is often difficult and may be delayed. Pain in the lower abdomen and right iliac fossa (RIF) is a common indication of emergency hospital admission with a suspicion of AA6.
Although early clinical evaluation and surgical intervention are mandatory in AA, at times, conventional diagnostic approaches such as history taking, physical examination, and routine laboratory tests are inconclusive7,8. Hence, imaging tests are commonly used to improve diagnostic accuracy4,5,9 and to rule out conditions mimicking appendicitis. Abdominal ultrasonography is one of the important diagnostic tools in AA. It is now increasingly advocated that all patients with a suspicion of AA should routinely undergo abdominal ultrasonography performed by an experienced radiologist to confirm the diagnosis and prevent negative appendicectomy9. Numerous prospective clinical trials have reported an accuracy of 76.3% to 96%, sensitivity of 44% to 100%, and specificity of 47% to 99% of ultrasonography in the diagnosis of AA9-14.
Keeping in view the common nature of this problem, a need was felt to carry out a study to determine accuracy of ultrasonography in the diagnosis of AA. The results of this study would guide us to formulate a policy, either to request or not, an abdominal ultrasonography in cases of clinically suspected AA.
PATIENTS AND METHODS
This was a cross-sectional validation study, carried out from Apr 2014 to Apr 2016, at the surgery and radiology departments of Combined Military Hospitals of Multan and Quetta, which are tertiary care hospitals, draining serving and retired personnel of armed forces and their families and civilian patients in their surrounding areas, representing all ethnic groups. A sample size of 183 was calculated using a sample size calculator15, while using a sensitivity of 84%9, specificity of 67%9, expected prevalence of 29%16, desired precision of 0.1, and confidence level of 95%. The different study variables were age, gender, and ultrasonographic and histopathological diagnosis of each patient. All patients, presenting in the surgical outpatient department or the emergency department of above named hospitals with complaints of right lower quadrant abdominal pain were evaluated by taking history, performing physical examination, and complete blood count evaluation.
The patients scoring 5 or higher on the Modified Alvarado Scoring System for the clinical diagnosis of AA17 were consecutively sampled and admitted in the indoor departments. All cases underwent ultrasonographic evaluation by a senior consultant radiologist using ultra-sonography machine "Mindray DP-50" (Shenzen Mindray Bio-medical Electronics Co., Shenzen, China). The ultrasonographic criteria for the diagnoses of AA given by Maher and Dixon18 was followed. The results were entered in structured proformas. All patients with clinical appendicitis underwent appendicectomy. The removed appendix was sent for histopathological examination in all cases. The histopathological reports were collected, documented in the respective proformas, and compared with the ultrasonographic findings of the patients.
At the end, the data were analyzed using the Statistical Package for Social sciences (SPSS) version 20.0 (IBM Corp., Armonk, NY, USA) and Med Calc (MedCalc Software, Ostend, Belgium). Descriptive data were presented as frequencies and percentages for age, gender, various symptoms and signs, and ultrasonographic and histopathological findings. Sensitivity analysis was performed to assess sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of ultrasonography taking histopathological diagnosis as gold standard.
Table: Summary sensitivity and specificity of Pakistani references identified through electronic searches.
S No.###Authors###Year of publication###Sensitivity(%)###Specificity(%)
1.###Afzal et al25###1997###38.88###83.8
2.###Qureshi et al26###2001###88.8###83.9
3.###Ahmad et al27###2003###71.8###62.5
4.###Saeed et al 28###2009###85###86
5.###Yousaf et al29###2011###68###88
6.###Hussain et al30###2012###31###75
7.###Ahmed et al31###2012###94###68.18
8.###Abbasi et al32###2012###44###89.3
9.###Alia et al12###2013###96.72###89.74
10.###Hussain et al10###2014###88###92
11.###Qureshi et al33###2014###91.5###87.5
12.###Arooj et al11###2015###94###84
13.###Ihsan et al9###2017###84###67
A total of 200 patients were studied. There were 132 (66%) males and 68 (34%) females making a male to female ratio of 2:1. The mean age was 25.7 +- 13.4 years with a range of 8-70 years. The most common age group was 11-30 years (fig-1). Clinically, the pain in RIF was present in all patients. In 52% (n=104), the pain started in the RIF while in 48% (n=96) patients, the pain started in the umbilical or epigastric region and latter migrated to the RIF. Vomiting was present in 61% (n=122), anorexia in 70% (n=140), and fever was present in 22% (n=44) patients. Total leucocyte count was raised in 45% (n=90) patients. Sonographically, 100 (50%) patients had AA (74 male and 26 female). Out of them, 86 had histopathologically proven AA while 14 were having normal appendix. In the rest 100 (50%) patients, a normal appendix was commented by the radiologist in 56 patients and appendix was not visualized in 44 patients. Histopathologically, 140 (70%) patients had positive histopathology.
Thus, 43% (n=86) patients had true positive results, 23% (n=46) patients had true negative results, 7% (n=14) patients had false positive results while 27% (n=54) patients had false negative results making an overall sensitivity of 61.43%, specificity of 76.67%, PPV of 86%, NPV of 46%, and an accuracy rate of 66%. Out of 132 males, 50% (n=66) patients had true positive results, 21.21% (n=28) patients had true negative results, 6.06% (n=8) patients had false positive results, while 22.72% (n=30) patients had false negative results. Out of 68 females, 29.41% (n=20) had true positive results, 26.47% (n=18) patients had true negative results, 8.82% (n= 6) patients had false positive results while 35.29%(n=24) patients had false negative results. The receiver operating characteristic curve interpreting sensitivity and specificity levels has been presented as fig-2.
As it is said that appendicitis is the disease of younger age, our study supports this view. In this series, the commonest age group was 11-30 years (75%). In a comparative international study, the commonest age-group (90%) was 10-30 years3. According to Amir and Shami, 1944. Eight percent cases of AA were in their 2nd decade and 30% cases were in the 3rd decade with a gradual decrease in incidence with age. Ihsan et al9 in a series of 100 patients, had maximum patients between 15-25 years while Parsijani et al20 reported maximum number of patients (57%) between 5 and 16 years of age in a study comprising 377 patients. Pain was the most common presenting symptom in our study and was present in all patients of our study. This is similar to the study of Adesunkanmi et al21 who reported lower abdominal pain in all cases of AA.
In our study, the majority of patients (52%) had pain starting in the RIF while in 48% patients, pain started in the umbilical or epigastric region and latter migrated to the RIF. In the literature, the migration or shifting of pain to RIF is variable and is found in 30-64% of the patients22. Lee et al23 in a large series of 766 patients emphasized migratory pain with PPV of 91% which was more than that of raised leucocyte count, computerized tomography scan, and ultrasonography. Another study showed that there was no difference in the frequency of migration among patients with or without appendicitis24. So, when migration or shifting to RIF is present, appendicitis is likely, while absence of migration does not indicate a normal appendix.
Anorexia was the other most common symptom after pain in this study. It was found in 70% of the patients. This figure, more or less, compares with the literature. According to two studies19,21 anorexia was present in 82% and 77.7% of the sampled patients respectively. In one textbook, it was considered the characteristic symptom of AA, positive in more than 90% cases25. Thus, anorexia is a reliable indicator of AA, and one should deeply inquire about this symptom. In our study, 61% patients had one or two episodes of vomiting, by and large, in the early stage of disease. This complaint always followed the pain. The relevant literature reveals that 51-69% of patients with appendicitis have one or more episodes of vomiting19,22. It seems that this symptom has high sensitivity rate but less specificity, as quite a number of patients (30-50%) with normal appendix also have this symptom19.
In a comparative study by Chaudhary et al26, right lower quadrant pain was present in more than 95% of cases with AA, and in more than 65% of cases, there was history of nausea, vomiting, and anorexia. The overall accuracy, sensitivity, and specificity of the ultrasonographic examination in this study was 66%, 61.43%, and 76.67% respectively. These results can be compared to previous studies carried out in Pakistan. A review of the studies has been shown in table. Out of 13 references9-12,27-35 (table) identified through electronic searches and including the present study, the summary sensitivity and specificity of ultrasonography for diagnosis of AA were 74.1% (95% CI 61.2-86.9%) and 81% (95% CI 75.5-86.4%), respectively. The sensitivity of ultrasonography is less than the specificity because of the large number of false negatives mainly due to poor tolerance by the patient, obesity, presence of gas and unusual location of the appendix36.
The higher specificity of ultra-sonographic examination reported by Pakistani studies endorses this evaluation as a useful tool for the differential diagnosis of associated pathology such as mesenteric lymphadenitis or gynecological disorders in suspected cases of AA37. It is suggested that all patients with pain in the right lower quadrant of the abdomen must be evaluated by ultrasonography so as to decreases the rate of negative appendicectomies. The ultrasonographic examination as a sole diagnostic investigation for AA is debatable. Many studies suggest combining ultrasonography with Alvarado score that is a quick and inexpensive diagnostic tool38-41, though, when used alone, has a high negative appendicectomy rate especially when the scores are less than eight38.
The combined accuracy of both diagnostic tools is considered a reliable evidence to decide surgical intervention without going for other investigations like computerized tomographic scan of the abdomen especially in children41. Based on results of these studies, we also suggest linking results of both these non-invasive and cheap evaluation tools with each other to reduce the frequency of unnecessary surgical interventions.
With sensitivity, specificity, and accuracy rate of 61.4%, 76.7%, and 66% respectively, ultrasonography is justified as an appropriate diagnostic tool in suspected cases of AA to avoid undue surgical interventions.
CONFLICT OF INTEREST
This study has no conflict of interest to declare by any author.
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|Publication:||Pakistan Armed Forces Medical Journal|
|Date:||Aug 31, 2018|
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