Abstract
Objective:
To evaluate the diagnostic performance of ultrasound and to determine which ultrasound findings are useful to differentiate appendicitis from non-appendicitis in patients who underwent ultrasound re-evaluation owing to equivocal CT features of acute appendicitis.
Methods:
62 patients who underwent CT examinations for suspected appendicitis followed by ultrasound re-evaluation owing to equivocal CT findings were included. Equivocal CT findings were considered based on the presence of only one or two findings among the CT criteria, and ultrasound re-evaluation was done based on a predefined structured report form. The diagnostic performance of ultrasound and independent variables to discriminate appendicitis from non-appendicitis were assessed.
Results:
There were 27 patients in the appendicitis group. The overall diagnostic performance of ultrasound re-evaluation was sensitivity of 96.3%, specificity of 91.2% and accuracy of 91.9%. In terms of the performance of individual ultrasound findings, probe-induced tenderness showed the highest accuracy (86.7%) with sensitivity of 74% and specificity of 97%, followed by non-compressibility (accuracy 71.7%, sensitivity 85.2% and specificity 60.6%). The independent ultrasound findings for discriminating appendicitis were non-compressibility (p = 0.002) and increased flow on the appendiceal wall (p = 0.001).
Conclusion:
Ultrasound re-evaluation can be used to improve diagnostic accuracy in cases with equivocal CT features for diagnosing appendicitis. The presence of non-compressibility and increased vascular flow on the appendix wall are useful ultrasound findings to discriminate appendicitis from non-appendicitis.
Advances in knowledge:
Ultrasound re-evaluation is useful to discriminate appendicitis from non-appendicitis when CT features are inconclusive.
INTRODUCTION
Although CT is widely accepted and the preferred modality for evaluation of suspected appendicitis because of its excellent diagnostic performance,1–5 rapidity and good interobserver agreement for interpretation regardless of experience, CT diagnosis of acute appendicitis is not always certain. CT diagnosis of appendicitis can be challenging, particularly in thin patients with little fat and during the early stage of appendicitis. In cases of incipient appendicitis, CT findings can be inconclusive owing to minimal or borderline dilatation of the appendix, or lack or minimum of changes in the appendiceal wall and periappendiceal area. Moreover, CT cannot reflect early microscopic mucosal changes. The reported prevalence of inconclusive CT findings in suspected appendicitis varies with a range of 5–13.1%,1,5–9 with up to 30% of these patients being subsequently diagnosed with appendicitis.7
A recent study showed that the addition of ultrasonography can improve diagnostic accuracy and decrease the negative appendectomy rate in equivocal CT cases.10 However, the researchers did not explore the useful ultrasound findings to improve diagnostic yield in patients with equivocal CT features for diagnosing appendicitis. Therefore, the purpose of this study was to evaluate the diagnostic performance of overall and individual ultrasound findings and to determine which ultrasound findings were useful to differentiate appendicitis from non-appendicitis in patients who underwent ultrasound re-evaluation owing to equivocal CT features.
METHODS AND MATERIALS
Study population
Our Institutional Review Board approved this study and waived informed consent.
We included 2629 patients who underwent contrast-enhanced CT because of suspected acute appendicitis between April 2013 and August 2016. Of these patients, 553 patients were excluded for the following reasons: (1) having alternative diagnosis explaining the cause of the abdominal pain (n = 512), (2) follow-up CT during conservative treatment of complicated appendicitis (n = 31) or (3) history of appendectomy (n = 10). Among the remaining 2076 patients, 112 patients showed equivocal finding for diagnosing appendicitis on CT. Of these patients, 63 patients underwent ultrasound re-evaluation. One patient was additionally excluded because of non-applicable predefined structured report form for ultrasound re-evaluation. Finally, 62 patients were included in the study (Figure 1). The study group included patients aged 4–91 years (mean age, 29 ± 20 years) and consisted of 30 female patients (mean age, 32 ± 21 years; age range, 4–91 years) and 32 male patients (mean age, 25 ± 19 years; age range, 5–74 years). The patient medical records were reviewed for demographic and clinical variables.
Figure 1.
Patient flow diagram.
CT technique and interpretation
CT was performed using 64-row (Brilliance 64, Philips Healthcare, Eindhoven, Netherlands) or 128-row (iDose, Philips Healthcare, Eindhoven, Netherlands) multidetector CT (MDCT) scanners. The tube current was automatically modulated and the tube voltage was 100–120 kVp. Other parameters were as follows (16- and 64-row MDCT, respectively): anatomical range, diaphragm to the symphysis pubis; detector collimation, 1.5 mm or 0.6 mm; rotation speed, 0.5 s; and pitch, 1.4 or 0.9. Reconstructions consisted of transverse and coronal sections of 3 or 4 mm. Two i.v. contrast agents were used: iohexol (Omnipaque 300, GE Healthcare, Princeton, NJ) and ioversol (Iversense 320, Accuzen, Seoul, Korea). The i.v. contrast agent was administered at a rate of 2.0 ml s−1 and a dose of 2 ml kg−1 body weight, and CT data acquisition was initiated 70 s after the start of the injection. No oral or rectal contrast material was administered.
All CT interpretations were finally confirmed by three experienced abdominal radiologists (7, 16 and 32 years of experience) with or without initial interpretation by residents (1–4 years of training). Some of the CTs taken during the day were initially interpreted by residents and the attending abdominal radiologist checked the preliminary report within 6 h and made a formal report for these cases. Otherwise, the CT exams were primarily interpreted by the attending abdominal radiologists. Offhour studies were initially interpreted by the residents, and the preliminary reports were reviewed and confirmed on the morning of the next working day by the abdominal radiologists. In our institute, the following CT criteria or their combinations derived from previous studies1,3,11–14 were used for diagnosing appendicitis: appendix diameter of more than 6 mm, measured at the greatest portion of the visible appendix; appendiceal wall enhancement (hyperdense to adjacent small bowel) or appendiceal wall thickening equal to or greater than 3 mm, measured from the outer wall to the inner mucosa; cecal apical wall thickening compared with the normal thickness of the wall of the ascending colon; and periappendiceal fat stranding. The determination for diagnosing appendicitis was relied on the interpreting attending abdominal radiologist. The presence of only one or two of these findings on CT was considered to be equivocal for appendicitis, and we recommended ultrasound re-evaluation in the CT report for these cases. The final decision to proceed with ultrasound re-evaluation for equivocal cases was made by the physician on the basis of clinical and laboratory findings.
Ultrasound examination and evaluation
All ultrasound examinations were performed with an iU22 ultrasound system (Philips Healthcare, Bothell, WA) using C5-2-MHz curved or 5-12-MHz linear probes, or a LOGIQ E9 ultrasound system (GE Healthcare, Milwaukee, WI) using a C5-1-MHz convex or ML6-15 or 9L linear array transducer. Colour Doppler ultrasound was performed using the low-flow settings of the lowest available pulse repetition frequency, highest colour Doppler gain possible without background noise signals and a low wall filter of 100 Hz. All ultrasound examinations included in this study were performed in the daytime by residents (1–4 years of training) under the supervision of two experienced abdominal radiologists (7 and 16 years of experience), or by the attending abdominal radiologists themselves with a graded-compression technique.15 If residents initially performed the ultrasound examinations, the attending abdominal radiologist immediately reviewed and confirmed the results. Ultrasound re-evaluation was not performed during offhours. A predefined structured report form based on a literature review6,15–19 was used in patients who underwent ultrasound re-evaluation owing to suspected appendicitis (Appendix A). The following findings were evaluated with the predefined structured report form: (1) absence or presence of visualization of the appendix; (2) maximal diameter of the appendix; (3) appendiceal wall thickness; (3) appendiceal luminal diameter; (4) absence or presence of increased flow within the appendiceal wall on colour Doppler ultrasound; (5) mucosal discontinuity; (6) non-compressibility of the appendix; (7) ultrasound probe-induced tenderness at the area over the appendix; and (8) absence or presence of increased periappendiceal echogenicity. We did not define specific ultrasound criteria for diagnosing appendicitis and instead relied on the subjective decision of the performing radiologist. On the basis of ultrasound findings, the likelihood of appendicitis was scored as follows: 1, definitely non-appendicitis; 2, probably non-appendicitis; 3, indeterminate appendicitis; 4, probably appendicitis; 5, definitely appendicitis. Scores of 4 or 5 were considered appendicitis.
The time interval between CT and ultrasound re-evaluation was calculated and was a minimum of 36 min and a maximum of 4080 min (mean 1232 ± 2607 min).
Reference standard
For patients who underwent surgery, the reference standard was based on the surgical and pathological findings, while a reference was made based on information retrieved from medical records for clinical follow up, with or without CT or ultrasound examination, for patients who did not undergo surgery. The time interval between ultrasound re-evaluation and last clinical follow up in patients without surgery was a mean of 11.9 ± 8.7 days. Pathological diagnosis of acute appendicitis was based on the presence of neutrophils interrupting the mucosa along with mucosal ulcerations. Neutrophils within the lumen or in the periappendiceal tissues without mucosal interruption were not considered appendicitis.20, 21
Statistical analyses
Categorical variables were summarized as the number (percent) of patients, and continuous variables were summarized as the mean or median (range). Variables were compared between patients with appendicitis and non-appendicitis using the χ2 test or Fisher’s exact test (categorical variables) and the Mann–Whitney test (continuous variables).
The optimal cut-off values of continuous variables for discrimination of appendicitis were obtained by the receiver operating characteristic curve and Youden index.22 The diagnostic performances of overall and individual ultrasound findings to differentiate appendicitis from non-appendicitis were assessed including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy. For subjective variables such as mucosal discontinuity, non-compressibility and probe-induced tenderness, indeterminate results were considered as negative. To assess the independent variables for discrimination of appendicitis, a backward elimination logistic regression procedure was performed using the variables that were significant in the univariate analyses. A p-value of less than 0.05 was considered to indicate a statistically significant difference. All analyses were performed using PASW Statistics for Windows (v. 18.0) software (SPSS, Inc., Chicago, IL).
RESULTS
Patient characteristics
There were 27 (44%) patients (15 males and 12 females; mean age 31 years) in the appendicitis group that included 18 patients who were pathologically confirmed to have suppurative appendicitis, 8 patients with focal appendicitis and 1 patient with gangrenous appendicitis (Figure 2). Focal appendicitis was diagnosed when neutrophil infiltration with mucosal ulceration was confined to the mucosa. After the final diagnosis, there were 35 (56%) patients (17 males and 18 females; mean age 27 years) in the non-appendicitis group. The final diagnoses were as follows: 20 patients with non-specific abdominal pain, 10 with gastroenteritis or enterocolitis, 2 with mesenteric lymphadenitis, 1 with peptic ulcer disease and 1 with pelvic inflammatory disease. The remaining patient was misdiagnosed and underwent a laparoscopic appendectomy which confirmed subserosal congestion on histopathology (Figure 3). Patient characteristics of the two groups are summarized in Table 1.
Figure 2.
A 30-year-old male with acute suppurative appendicitis. (a) Coronal contrast-enhanced initial CT image shows the isolated finding of borderline appendiceal dilatation of 6 mm (arrows). (b) Ultrasonographic examination performed 3 h later shows typical features of appendicitis, i.e. increased vascular flow on the appendiceal wall (not shown), mucosal discontinuity, non-compressibility and probe-induced tenderness as well as appendiceal dilatation of 6 mm (arrows). Laparoscopic appendectomy was performed and acute suppurative appendicitis was pathologically confirmed.
Figure 3.
False-positive case of a 20-year-old female with right lower quadrant pain. (a) Transverse contrast-enhanced initial CT image shows mildly dilated appendix of 7 mm (arrows). (b) Ultrasonographic examination performed 3 h and 30 min later shows a maximal appendiceal diameter of 7.8 mm (arrows) and increased vascular flow on the appendiceal wall (arrow heads) with non-compressibility. The echogenic mucosa is preserved, but probe-induced tenderness is indeterminate. This patient was diagnosed with appendicitis and underwent an appendectomy. (c) Histologic section of appendectomy specimen (haematoxylin–eosin stain, original magnification 100×) demonstrates subserosal congestion with telangiectasia (arrow heads) in the subserosa. Note the intact mucosa (*) and submucosal thickening and fibrosis (double-headed arrow) without infiltration of neutrophils in the appendix wall.
Table 1.
Patient characteristics and ultrasound findings
| All (n = 62) | Appendicitis (n = 27, 44%) | Non-appendicitis (n = 35, 56%) | p-value | |
|---|---|---|---|---|
| Age (years) | 28.5 ± 19.9 | 30.9 ± 19.3 | 26.6 ± 20.4 | 0.4 |
| Sex | 0.59 | |||
| F | 30 (48%) | 12 (44%) | 18 (51%) | |
| M | 32 (52%) | 15 (56%) | 17 (49%) | |
| BMI | 21.5 ± 3.3 | 22.9 ± 2.7 | 20.4 ± 3.4 | 0.005 |
| Appendix visualization on ultrasound | 0.5 | |||
| No | 2 (3%) | 0 (0%) | 2 (6%) | |
| Yes | 59 (95%) | 27 (100%) | 32 (91%) | |
| Partial | 1 (2%) | 0 (0%) | 1 (3%) | |
| Appendix maximal diameter (mm) | 6.1 ± 2.2 | 6.5 ± 2.6 | 5.8 ± 1.8 | 0.24 |
| Appendix wall thickness (mm) | 1.6 ± 0.9 | 2.0 ± 1.1 | 1.3 ± 0.7 | 0.01 |
| Appendix luminal diameter (mm) | 3.3 ± 1.9 | 3.8 ± 2.2 | 3.0 ± 1.5 | 0.09 |
| Increased wall flow in appendix | 0.001 | |||
| No | 42 (70%) | 12 (44%) | 30 (91%) | |
| Yes | 18 (30%) | 15 (56%) | 3 (9%) | |
| Appendix mucosal discontinuity | 0.001 | |||
| No | 48 (80%) | 16 (59%) | 32 (97%) | |
| Yes | 7 (12%) | 7 (26%) | 0 (0%) | |
| Indeterminate | 5 (8%) | 4 (15%) | 1 (3%) | |
| Non-compressibility of appendix | 0.001 | |||
| No | 19 (32%) | 1 (4%) | 18 (55%) | |
| Yes | 36 (60%) | 23 (85%) | 13 (39%) | |
| Indeterminate | 5 (8%) | 3 (11%) | 2 (6%) | |
| Probe tenderness over the appendix | 0.001 | |||
| No | 28 (47%) | 1 (4%) | 27 (82%) | |
| Yes | 21 (35%) | 20 (74%) | 1 (3%) | |
| Indeterminate | 11 (18%) | 6 (22%) | 5 (15%) | |
| Periappendiceal increased echo | 0.039 | |||
| No | 53 (88%) | 21 (78%) | 32 (97%) | |
| Yes | 7 (12%) | 6 (22%) | 1 (3%) | |
| Interval CT to ultrasound (min) | 1232 ± 2607 | 1025 ± 3044 | 1392 ± 2246 | 0.59 |
BMI, body mass index; F, female; M, male.
Equivocal CT findings
The frequency of equivocal findings shown on initial CT interpretation was as follows: 39 patients showing >6 mm in the maximal diameter of the appendix, 4 patients with appendiceal wall enhancement, 2 patients with cecal apical wall thickening, 11 patients showing both >6 mm in the maximal diameter of the appendix and appendiceal wall enhancement, 3 patients showing both >6 mm in the maximal diameter of the appendix and ≥3 mm appendiceal wall thickening and 3 patients with both >6 mm in the maximal diameter of the appendix and periappendiceal fat stranding. The most common finding was >6 mm in the maximal diameter of the appendix in 56 patients followed by appendiceal wall enhancement in 15.
Ultrasound assessment and diagnostic performance
Among all patients who underwent ultrasound re-evaluation, the appendix was not visualized in two (3%), and the appendix was only partially visualized in one patient. Ultrasound assessment was performed for the partially visualized appendix in the patient with incomplete visualization of the appendix.
All of these patients were conservatively managed on the basis of clinical findings. The overall diagnostic performance of ultrasound re-evaluation was 96.3% (95% CI: 81.0, 99.9%) sensitivity, 91.2% (95% CI: 76.3, 98.1%) specificity, 89.7% (95% CI: 72.6, 97.8%) PPV, 96.9% (95% CI: 83.8, 99.9%) NPV and 91.9% (95% CI: 82.2, 97.3%) accuracy. The performance of individual ultrasound findings for diagnosing appendicitis is shown in Table 2. Probe-induced tenderness showed the highest accuracy of 86.7% with sensitivity of 74%, and specificity of 97% to discriminate appendicitis from non-appendicitis, followed by non-compressibility (accuracy 71.7%, sensitivity 85.2% and specificity 60.6%).
Table 2.
Diagnostic performance of individual ultrasound findings for appendicitis
| Ultrasound findings | Sensitivity (%) | Specificity (%) | PPV (%) | NPV (%) | Accuracy (%) |
|---|---|---|---|---|---|
| Appendix maximal diameter (7.9 mm)a | 37.0 (19.4, 57.6) | 90.9 (75.7, 98.1) | 76.9 (46.2, 95.0) | 63.8 (48.5, 77.3) | 66.7 (53.3, 78.3) |
| Appendix wall thickness (2 mm)sup>a | 37.0 (19.4, 57.6) | 84.8 (68.1, 94.9) | 66.7 (38.4, 88.2) | 62.2 (46.5, 76.2) | 63.3 (50.0, 75.4) |
| Appendix luminal diameter (4.5 mm)a | 37.0 (19.4, 57.6) | 90.9 (75.7, 98.1) | 76.9 (46.2, 95.0) | 63.8 (48.5, 77.3) | 66.7 (53.3, 78.3) |
| Increased wall flow in appendix | 55.6 (35.3, 74.5) | 90.9 (75.5, 98.1) | 83.3 (58.6, 96.4) | 71.4 (55.4, 84.3) | 63.3 (50.0, 75.4) |
| Appendix mucosal discontinuity | 25.9 (11.1, 46.3) | 100 (89.4, 100) | 100 (59.0, 100) | 62.3 (47.9, 75.2) | 66.7 (53.3, 78.3) |
| Non-compressibility of appendix | 85.2 (66.3, 95.8) | 60.6 (42.1, 77.1) | 63.9 (46.2, 79.2) | 83.3 (62.6, 95.3) | 71.7 (58.6, 82.5) |
| Probe tendernessover the appendix | 74.1 (53.7, 88.9) | 97.0 (84.2, 99.9) | 95.2 (76.2, 99.9) | 82.1 (66.5, 92.5) | 86.7 (75.4, 74.1) |
| Periappendiceal increased echo | 22.2 (8.6, 42.3) | 97.0 (84.2, 99.9) | 85.7 (42.1, 99.6) | 60.4 (46, 73.5) | 63.3 (50.0, 75.4) |
NPV, negative predictive value; PPV, positive predictive value.
Data in parentheses are the 95% confidence interval.
Data in parentheses are the optimal cut-off values of continuous variables for discrimination of appendicitis which were obtained by the receiver operating characteristic curve and Youden index.
Independent ultrasound findings
In univariate analyses of ultrasound findings for diagnosis of appendicitis, the significant variables were wall thickness ≥2 mm (p = 0.01), increased flow on the appendiceal wall (p = 0.001), mucosal discontinuity (p = 0.001), non-compressibility (p = 0.001), probe-induced tenderness (p = 0.001) and periappendiceal increased echogenicity (p = 0.04). The independent ultrasound findings for discriminating appendicitis (Table 3) were non-compressibility (odds ratio, 12.7; 95% CI:2.45,66.23; p = 0.002) and increased flow on the appendiceal wall (odds ratio, 18.0; 95% CI: 3.09,104.6; p = 0.001) in a backward elimination logistic regression procedure.
Table 3.
Ultrasound findings to discriminate appendicitis from non-appendicitis in backward elimination logistic regression analysis
| Variables | Frequency (60)a | Odds ratio | 95% confidence interval | p-value | |
|---|---|---|---|---|---|
| Appendix wall thickness (2 mm)b | 45 | Reference | |||
| 15 | |||||
| Increased wall flow in appendix | 18.0 | 3.09, 104.6 | 0.001 | ||
| No | 42 | Reference | |||
| Yes | 18 | ||||
| Appendix mucosal discontinuity | |||||
| No | 53 | Reference | |||
| Yes | 7 | ||||
| Non-compressibility of appendix | 12.7 | 2.45, 66.23 | 0.002 | ||
| No | 24 | ||||
| Yes | 36 | ||||
| Probe tenderness over the appendix | |||||
| No | 39 | Reference | |||
| Yes | 21 | ||||
| Periappendiceal increased echo | |||||
| No | 53 | Reference | |||
| Yes | 7 | ||||
The number in parentheses is the total number of cases used in this analysis. Two cases among the enrolled patients were excluded owing to the non-visualization of appendix in ultrasound re-evaluation.
The optimal cut-off value for discrimination of appendicitis was obtained by the receiver operating characteristic curve and Youden index.
DISCUSSION
Our study showed that ultrasound re-evaluation in patients with equivocal CT findings provided excellent performance of 96.3% sensitivity, 91.2% specificity, 89.7% PPV, 96.9% NPV and 91.9% accuracy for diagnosing appendicitis. This result was similar to a recent study by Sim et al10 which found that adding ultrasound in patients with equivocal CT findings improved diagnostic accuracy and decreased the rate of negative appendectomies. Our result for diagnostic performance of ultrasound seems to be better compared with the prior study (overall sensitivity of 78% and specificity of 83%) which was based on a meta-analysis of paediatric and adult studies of prospective trials published between 1996 and 2006.23 However, our study is different from this previous study since we used a retrospective method, ultrasound as the second-line imaging modality rather than the first-line imaging modality and excluded complicated appendicitis cases except for one case of gangrenous appendicitis.
Imaging strategies for evaluating suspected appendicitis could be debatable. European Association of Endoscopic Surgery recommended that ultrasound be performed as a first-level diagnostic imaging, and CT or MRI should be performed only if ultrasound diagnosis is inconclusive.24 Several studies have demonstrated that the use of CT conditional on a negative or inconclusive ultrasonography result had the highest sensitivity with the lowest overall exposure to radiation compared with the immediate use of CT for suspected appendicitis.25, 26 Whereas, American College of Radiology preferred CT for evaluating suspected acute appendicitis except for children and pregnant females for whom ultrasound is preferred initially.27 Given the high rate of CT utilization as an initial imaging modality in adolescents and adults with suspected acute appendicitis in our institution as like metropolitan Seoul, Korea (93.1%),28 complementary ultrasound following CT was performed rather than a reverse strategy in this study. The overwhelming preference of CT to ultrasound might be because CT outperforms ultrasound in terms of diagnostic performance, rapidity and provision of alternative diagnosis,29–31 as mentioned in "Introduction". In addition, previous study revealed that the use of CT instead of ultrasonography as the initial imaging modality significantly decreased negative appendectomy rate.28
In our study, an enlarged appendix (90%) was the most common CT finding in equivocal cases of appendicitis which is similar to prior findings.10 Appendiceal enlargement is sometimes an isolated finding of appendicitis and has been reported to indicate acute appendicitis in up to 52% of symptomatic patients.7 However, the numeric threshold of 6 mm for diagnosing appendicitis originated from the ultrasound literature15, 18, 32 based on the technique of graded compression of the appendix and is, therefore, difficult to extrapolate to CT interpretation. Prior studies have shown that in up to 42% of patients, the normal appendix measures greater than 6 mm in outer wall-to-outer wall diameter on CT.25, 33 Appendiceal diameter, in particular, may increase when a normal appendix has intraluminal content such as air, fluid or faeces.33 Therefore, the simple measurement of appendiceal diameter may be limited and not always a reliable indicator of appendiceal inflammation. Whereas, ultrasound can overcome this limitation through the graded-compression technique which can help distinguish acute appendicitis from dilatation owing to air, fluid or faeces. This benefit of ultrasound was supported by our finding that non-compressibility on ultrasound re-evaluation was significant in discriminating appendicitis in patients with equivocal CT features (odds ratio, 12.7; p = 0.002). However, assessment of non-compressibility is subjective and requires technical expertise for interpretation, thus, five patients (8%) had an indeterminate result in the interpretation of non-compressibility in our study. In addition, it is well known that technical failures (<5%) can occur in cases with severe pain or patient obesity that preclude satisfactory graded-compression.
The presence of increased flow within the appendiceal wall was another significant finding for discriminating appendicitis (odds ratio, 18.0; p = 0.001). There were false-positives in 3 of the 35 patients who did not have appendicitis. Of these three patients, two were diagnosed as non-appendicitis preoperatively because the appendix was compressible without or with equivocal probe-induced tenderness (Figure 4) despite the presence of minimally increased vascular flow (2–3 flow spots) on the appendix wall. The remaining one patient who underwent an appendectomy because of the preoperative diagnosis of appendicitis was histopathologically confirmed as subserosal congestion with mild telangiectasis in the serosa. The appendix of this patient showed moderately increased vascular flow on the wall and a maximal diameter of 7.8 mm with non-compressibility (Figure 3). Prior researchers demonstrated that vascular flow on the appendiceal wall showed good correlation with the site of inflammation and was increased in acute uncomplicated appendicitis, while there were few or no signals in cases with necrosis or perforation.34, 35 In our study, there were false-negative findings in 12 (44.4 %) patients. Of these 12 patients, 5 were diagnosed with acute focal appendicitis, and 7 with acute suppurative appendicitis with serosal inflammation. In a prior study by Quillin et al,35 2 of 11 patients with early appendicitis and 1 of 23 patients with acute suppurative appendicitis did not show increased flow on the appendiceal wall, whereas 3 of 5 patients with acute gangrenous appendicitis showed increased flow. It is unclear why there is an inconsistent flow pattern within the same pathological category of acute appendicitis. We believe that there may be differences in the severity of inflammation within the same pathological category, which could contribute to this finding.
Figure 4.
A 16-year-old male with abdominal pain. (a) Transverse contrast-enhanced initial CT image shows a mildly dilated appendix of 7 mm (arrows) without periappendiceal changes. (b) Ultrasonographic examination performed 16 h and 6 min later reveals a maximal appendiceal diameter of 7 mm with sparse flow on the appendix wall (arrows). However, this patient was diagnosed as non-appendicitis because the appendix was compressible without probe-induced tenderness. His symptom was relieved by conservative treatment.
The advantage of ultrasound re-evaluation after initial CT examination is that the operator has information about the position of the appendix. Ultrasound can provide successful detection of the appendix in cases of variable locations such as subhepatic, retrocecal or retroileal locations or an unusual position under rotation anomaly of the intestine. In our study, the appendices in 60 of 62 patients (97%) could be visualized in ultrasound re-evaluation including 1 case of an incompletely visualized appendix. This appendiceal detection rate was superior to that of prior studies (31–85%) which were performed with ultrasound as an initial imaging modality.36, 37
Our study has several limitations. First, the retrospective nature of this study may have biases in patient selection and information. However, the data for enrolled patients who had equivocal CT features and followed by ultrasound exam was prospectively collected. Second, the present study was performed at a single centre with a relatively small sample size. Additional multi-institutional studies with larger sample sizes are required to validate our results. Third, in the non-appendicitis group, the reference standard was mainly based on clinical follow up except in one patient who underwent appendectomy. In these cases, appendicitis which occasionally resolves spontaneously may be included.18 In addition, in the appendicitis group, the objective ultrasound measures (appendiceal diameters and vascular wall flow) were not correlated with pathological findings. Finally, the diagnostic performance of subjective measures such as mucosal discontinuity, non-compressibility and probe-induced tenderness can be affected according to the assignment of an indeterminate result. Considering indeterminate results as positive will result in lower specificity and PPV, and higher sensitivity and NPV for individual ultrasound findings. However, this did not affect the results of the independent ultrasound findings for the diagnosis of appendicitis.
CONCLUSION
Our study found that if there are equivocal CT findings of acute appendicitis, ultrasound re-evaluation might provide useful information and can be used to improve diagnostic accuracy for acute appendicitis. The presence of non-compressibility and increased vascular flow on the appendix wall are useful ultrasound findings that may help discriminate appendicitis from non-appendicitis. However, isolated individual ultrasound findings may be limited. Therefore, comprehensive assessment with various sonographic findings as well as clinical features would be needed to diagnose appendicitis in cases with equivocal CT findings.
Appendix A
Structured report for appendicitis
| Visualization of appendix | ⌧ Yes | ⌧ No | |
| Non-compressibility | ⌧ Yes | ⌧ No | ⌧ Indeterminate |
| Probe-induced tenderness | ⌧ Yes | ⌧ No | ⌧ Indeterminate |
| Mucosal discontinuity | ⌧ Yes | ⌧ No | ⌧ Indeterminate |
| Increased flow on appendiceal wall | ⌧ Yes | ⌧ No | |
| Periappendiceal increased echo | ⌧ Yes | ⌧ No | |
| Maximal diameter of the appendix (mm) | |||
| Appendiceal wall thickness (mm) | |||
| Appendiceal luminal diameter (mm) | |||
| Likelihood of appendicitis | ⌧ 1. Definitely non-appendicitis. Clinical observation is recommended. | ||
| ⌧ 2. Probably non-appendicitis. Clinical observation is recommended. | |||
| ⌧ 3. Indeterminate appendicitis. Clinical observation or surgical exploration is recommended. | |||
| ⌧ 4. Probably appendicitis. Surgical exploration is recommended. | |||
| ⌧ 5. Definitely appendicitis. Surgical exploration is recommended. | |||
| Alternative diagnosis | ⌧ ⌧ ⌧ | ||
Contributor Information
Mi Sung Kim, Email: misung70.kim@samsung.com.
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Kyung A Kang, Email: kyunga.kang@samsung.com.
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