Accuracy of Ultrasound in the Diagnosis of Acute Appendicitis and Correlation with Histopathology

Introduction: Acute appendicitis is a common surgical condition; yet its diagnosis can be elusive at times and missed diagnosis can lead to attendant complications of perforation and its sequelae. On the contrary, negative appendectomy subjects one to unnecessary surgery and its physiological and psychological consequences. Among the various available modalities of diagnosis of appendicitis, Ultrasonography(USG) is easily accessible, non invasive, less time consuming, low cost investigation no radiation hazards. So, USG is appropriate diagnostic modality in our country. Methods: This prospective observational study was carried out from January 2011 to June 2011, in the radiology department of Bir hospital. Total of 80 cases with clinical impression of acute appendicitis were enrolled. These patients underwent surgery for suspected acute appendicitis. Details of signs and symptoms, lab findings including Total Leukocyte count (TLC), Differential Leukocyte Count (DLC) and USG findings were recorded. Intra-operative and histopathology findings were also recorded. The findings were analyzed to assess accuracy of ultrasonography in acute appendicitis. Histopathological report was considered the goal standard. Results: A total of 93 cases clinically diagnosed as acute appendicitis were subjected for USG. Out of 93 cases, 80 cases underwent surgery. Among 80 cases, sonography showed acute appendicitis in 56 cases out of which 54 was proved by histopathology as well. However, ultrasonography was not able to detect appendicitis in 9 cases. The sensitivity and specificity of USG for acute appendicitis were 87.7% and 88.2% respectively. The positive and negative predictive values were 96.4% and 62.5% respectively. Overall negative appendectomy rate of 21.2% had been used a basis for decision making, the rate of error being 13.7%. Conclusion: Ultrasonography is a fairly accurate and safe modality in acute appendicitis. It can be useful in reducing negative appendectomy rate.

of the vermiform appendix, which is a blind ended tube arising from the caecum.It is vestigial organ but it can become diseased.Appendicitis is a surgical emergency, and if it is left untreated the appendix may perforate and cause potentially fatal complications especially in children and elderly.The overall mortality rate for acute appendicitis is less than 1% but is higher in elderly, more than 5% to 15 %. 1 Despite technological advances, diagnosis of acute appendicitis is still based primarily on history and clinical examination.Prompt diagnosis and surgical referral may reduce the risk of perforation and prevent complications. 2 Patients with acute appendicitis typically present with central abdominal pain shifting to the right lower quadrant (RLQ) or may present with generalized abdominal pain.Vomiting is common in children.Clinical examination reveals signs of acute intra-abdominal process e.g., local and rebound tenderness, muscle guarding, rigidity, cutaneous hyperaesthesia and tenderness on rectal examination.Since about one third of patients with acute appendicitis present with atypical symptoms. 3ifferential diagnosis is diverse and includes gastroenteritis, mesenteric lymphadenitis, ovarian and tubal disorder, renal colic, peptic ulcer and acute cholecystitis.
Ultrasonographic criteria of acute appendicitis include blind-ended, non-compressible, aperistaltic tube, with diameter more than 6 mm, arising from the tip of caecum with a gut signature.Visualization of an appendix with an appendicolith, regardless of appendiceal diameter is also regarded as a positive test.However, normal appendix can also be visible on ultrasound.Normal appendix is compressible with wall thickness of less than or equal to 3 mm.The size of appendix can differentiate normal from acutely inflamed appendix.The threshold level for the diameter of the appendix above which acute appendicitis is very likely is 6 mm. 4 Routine investigations like total leucocyte count, differential count and plain X-ray abdomen, have been recommended to improve the diagnosis.Plain abdominal radiographs have an overall accuracy of only 8%. 5 The routine laboratory examination of blood and urine is mandatory.Leucocytosis is useful but non-specific.It may be absent particularly in very young and old patients. 3ere has been numerous publications on the use of ultrasound as a diagnostic tool.There studies demonstrate sensitivity of 75%-94% and specificity 87%-96%.Several prospective studies have been conducted where the result of ultrasonography were used as an aid for surgeons in making an operative decision. This study was conducted to evaluate diagnostic accuracy of ultrasound in acute appendicitis.The study was based on the presumption that an accurate diagnosis helps to reduce high negative appendectomy rates and thereby benefit the patients.

METHODS
This prospective observational hospital based study was done at Bir hospital, NAMS after obtaining approval from the Institutional Review Board (IRB) from January 2011 to June 2011.Patients more than 15 years of age diagnosed clinically as acute appendicitis were included in the study.Patients in whom ultrasonography could not be performed and those not undergoing surgery were excluded from the study.Patients were subjected for abdominal ultrasonography.USG diagnosis of acute appendicitis was based on the criteria of Jeffery et al 9 which includes: Non compressible, immobile, blind ended tubular structure with target appearance in transverse view, diameter of visualized structure more than or equal to 6 mm.Supportive features are inflamed perienteric fat, pericaecal collection, appendicolith. 9onographic findings that met all criteria were diagnosed as positive for appendicitis.All attempts were made to rule out or establish other causes of right lower quadrant pain sonographically.
All the findings including history, clinical examination, laboratory investigation and ultrasound findings were recorded.Intraoperative findings were recorded and histopathologic reports of specimen were noted.The histopathological diagnosis of acute appendicitis would be based on the finding of neutrophilic infiltration of the muscularis propria.The operative diagnosis of acute appendicitis would be based on finding of swollen, shiny /dull, granular redness of appendix judged by attending surgeon.
Results of ultrasonographic impression were compared to clinical impression, intraoperative findings and histopathological reports.Sensitivity, specificity, positive predictive value, negative predictive value and accuracy were computed and comparisons made.Fisher's exact test was utilized to compare USG and intraoperative findings while Chi square test was used to compare USG findings with histopathology.

RESULTS
A total of 93 cases were clinically diagnosed as acute appendicitis and subjected for USG.Out of 93 cases only 80 cases underwent surgery, 13 cases being excluded from the study.Out of excluded 13 cases, 7 cases were found to have an early appendicular lump on sonography, 2 cases had appendicular abscess, 2 cases had right ureteric calculus and 1 was normal.One case was diagnosed as acute appendicitis sonographically but patient refused surgery.
In these 80 cases, sonography showed acute appendicitis in 56 cases, of which 54 were confirmed by histopathology.One was normal appendix and another Meckel's diverticulum by histopathology.Intra-operatively 53 were acute appendicitis, 2 were normal appendix and 1 was Meckel's diverticulum.bTwenty four cases were normal by sonography, of which 9 were histopathologically diagnosed as acute appendicitis.
Age range of study group was from 16 to 70 years.The mean age was 27.64 years.Standard deviation was 9.6 years.Sixty three cases were histologically acute appendicitis.There were 40 (63.5%)males and 23 (36.5%) females.Male female ratio was 1.6:1.Sex distribution consisted of 40 (63.5%)male and 23 (36.5%) female.Common age group consisted of 16-25 yrs (47.6%) and 26-35yrs (34.9%).There were no cases in age group 56-65yrs and above 75yrs during the course of this study.
Among 63 cases with histological diagnosis of acute appendicitis, 51 (80.95%) cases had raised leukocyte counts (>11,000/mm3) and 12 (19.05%)cases had normal leukocyte counts (4000-11000/mm3).Out of 63 cases, 41 (65.08%) cases showed target sign and 22 (34.92%)cases had no target sign.Fifty six patients had an appendix diameter more than 6mm, two patients had <6mm and in 22 cases appendix could not be visualized.Among those with non-visualization, 9 actually had appendicitis on histopathology.Fifty four caseswith appendiceal diameter > 6mm diameter.had acute appendicitis histopathologically Out of 80 cases which underwent surgery during the course of study, sonographic diagnosis of acute appendicitis was made in 56 cases and 24 cases were ruled out as acute appendicitis.Among sonographically diagnosed 56 cases, 53 cases were also diagnosed as acute appendicitis intraoperatively, while 1 case diagnosed as Meckel's diverticulum and 2 cases had normal appendix.Among the 24 cases which were sonographically ruled out as acute appendicitis, 15 cases were diagnosed as acute appendicitis and 9 cases as normal appendix intraoperatively.We found ultrasonography has sensitivity of 77.9%, specificity of 75%, positive predictive value of 94.6%, and negative predictive value of 62.5% and accuracy of 77.5 % in acute appendicitis as compared to intraoperative findings.
Out of 80 cases which underwent surgery during the course of study, sonographic diagnosis of acute appendicitis was made in 56 cases and 24 cases were ruled out as acute appendicitis.Among sonographically diagnosed 56 cases, fifty four cases were histopathologically diagnosed as acute appendicitis while 1 case diagnosed as Meckel's diverticulum and 1 case as normal appendix.Among the 24 cases which were sonographically ruled out as acute appendicitis, 9 cases were diagnosed as acute appendicitis and 15 cases as normal appendix histopatholohgically, In our study, ultrasonography has sensitivity of 85.7%, specificity of 88.2%, positive predictive value of 96.4%, negative predictive value of 62.5% and accuracy of 86.25% as compared to histopathology findings in acute appendicitis.Out of 80 cases which underwent surgery during the course of study, intraoperative diagnosis of acute appendicitis was made in 68 cases and 12 cases were ruled out as acute appendicitis.Among intraoperatively diagnosed 68 cases, 62 cases were histopathogically diagnosed as acute appendicitis, 1 case diagnosed as Meckel's diverticulum and 5 cases as normal appendix.Among the 12 cases which were surgically ruled out as acute appendicitis 1 case was diagnosed as acute appendicitis and 11 cases as normal appendix histopathogically.We found intraoperative diagnosis has sensitivity of 98.4%, specificity of 64.4%, positive predictive value of 89.7%, negative predictive value of 91.6% and negative appendectomy of 21.2% as compared to histopathological findings in acute appendicitis.

DISCUSSION
In our study out of 80 total cases, 63 cases were acute appendicitis histopathologically, out of them 40 (63.5%) were male and 23 (36.5%) were female, male female ratio was 1.6:1 and mean age was 27.64 years.The most common age group was 16-25 years followed by 26 -35 years.In a study by Sigdel et al 10 done in Kathmandu, mean age was 27.5 years and male to female ratio was 2.6.In most other studies too there is male preponderance. 11Our study was supported by Berry et al 5 .In his study of 246 cases, there was male predominance with 60.2% male and 39.5% females.In a study by Khattaket al 12 out of 663 cases, 447 were male and 216 were female with male female ratio of 2:1.Peak incidence was 2 nd and 3 rd decade which is also comparable to our study.

Figure 1: Age and sex distribution
In another study by Omranet al 13 , 58% of patients were male and age specific incidence of acute appendicitis followed similar pattern for male and female which is also comparable to our study.In our study, increased Leukocyte was found in 80% cases of histopathologically diagnosed acute appendicitis.However increased leukocytosis is not reliable indicator.Our study was supported by several other studies. 14,15,16 I the present study, USG showed a transverse diameter of appendix of > 6mm in 54 cases, <6mm in 2 cases and appendix was not visible in 22 cases.The visibility of normal appendix on sonography is controversial.Puylaert 6 in his study concluded that normal appendix is not seen in USG.In contrary to this, studies done by Jeffery et al 17 and Rioux 18 documented the visibility of normal appendix.Transverse diameter >6mm was highly significant in diagnosing acute appendicitis.
Our study showed a strong correlation between appendicular transverse diameter of >6mm on USG and histopathology (P<0.001).The sensitivity and specificity using transverse diameter as a criteria for diagnosing acute appendicitis in present study was 85.7% and 88.2% respectively.Study done by Kesller et al 19 also concluded that threshold diameter of 6 mm is the most accurate USG finding for appendicitis.
In our study, USG diagnosis, when compared to histopathology, had an accuracy of 86.25%.Ultrasonography correctly identified 54 cases with appendicitis while it also identified 15cases who had no appendicitis.However there were 9 false negative cases and 2 false positive cases.Had USG been used as a basis for decision making, 9 cases that actually had appendicitis would have been missed.However of these 9 cases, in 7 patients initial clinical diagnosis was also non-confirmatory; they had been conservatively managed initially and decision to operate was taken after 24 hours in view of changed clinical picture.In our study USG had sensitivity of 85.7% and specificity of 88.2%.Thus USG was found to be more specific than sensitive.Karstrupet al 21 , Rioux 18 and Masek et al 24 have reported higher sensitivities while Fung el at 23 , Horton et al 25 and Mohammed et al 20

CONCLUSION
The sensitivity and specificity of USG in our study was comparable to most other studies; it was more specific than sensitive; thus USG can be more useful to help to confirm the diagnosis of appendicitis rather than ruling it out, i.e. a normal USG cannot rule out appendicitis.

NJR VOL 8
No. 2 ISSUE 12 July-Dec; 2018 Shrestha A et al.Ultrasound in Acute Appendicitis

VOL 8 No. 2 ISSUE 12 July-Dec; 2018 Shrestha A et al. Ultrasound in Acute Appendicitis in
20d lower sensitivity levels.Similarly, our specificity rate was comparable to that by Fung et al23.It was lower than that reported by Abu-Yousef et al22, Rioux18and Masek et al24.Karstrup et al21and Mohammad et al20had lower specificity levels.The PPV of USG in our study was 96.4% and NPV was 62.5%.Abu et al23had lower PPV but higher NPV than ours.Rioux et al18and Fung et al23obtained similar results.Mohammad et al20had both lower PPV and NPV values compared to our study.There are certain limitations to our study.Firstly the sample size is small and we have not included pediatric population.Secondly, ultrasonography findings vary when the same patient is examined at different points in time or by different clinician, i.e. inter observer variation may be present.So the findings, and consequently the diagnostic accuracy may improve when a review scan is done, especially NJR those cases that present very early.