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Research Article
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Accuracy of Sonography in Diagnosis of Acute Appendicitis Running |
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A.S. Shirazi,
M. Sametzadeh,
R. Kamankesh
and
F. Rahim
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ABSTRACT
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This study was conducted to assess the efficacy of ultrasound in the diagnosis of acute appendicitis in clinically suspected cases of acute appendicitis. A total of 110 patients clinically suspected to have acute appendicitis admitted to the surgery departments of Golestan and Imam Khomeini hospitals, from March 2006 to 2007. Abdomino-pelvic ultrasonography with focus on RLQ ultrasonographying the graded compression technique was done. Positive ultrasonography was defined as at least one of the criteria of puylaert. The sonographic data were prospectively correlated with clinical, operative and pathological findings. Graded compression ultrasonography results were analyzed and remarked 92.7% sensitivity, 94.5% specificity, 93% accuracy, 94.4% positive predictive value and 92.5% negative predictive value. Ultrasonography is an accurate, safe and reliable method in the diagnosis of suspected cases of acute appendicitis that can help to minimize negative appendectomies and perforation rates.
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INTRODUCTION
Appendicitis is one of the most common causes of acute abdomen requiring surgical
intervention. The preoperative clinical diagnoses are straightforward in 70-80%
of cases with an overall negative appendectomy rate of 20-25% (Yu
et al., 2005; Lee et al., 2005; Birnbaum
and Wilson, 2000; Paulson et al., 2003).
Accurate and prompt diagnoses followed by early surgery are essential to minimize
morbidity. Because of wide spectrum of clinical presentation and a constant
effort to reduce negative appendectomy rate, delay in diagnosis is not uncommon
leading to unacceptable rise in perforation rate and significantly increased
morbidity and mortality. Females of childbearing age have the highest negative
appendectomy rate of 35-45%, because of gynecological conditions simulating
appendicitis (Paulson et al., 2003; Yamauchi
et al., 2008). In recent years, ultrasonography has been widely performed
during the examination of patients with clinically suspected acute appendicitis
because of its safety and diagnostic accuracy (Assefa et
al., 2006; Morin, 2008). Abdominal ultrasonography
was first performed in 1981 to demonstrate an inflamed appendix (Rompel
et al., 2006). Since then, many studies have found promising value
in abdominal ultrasonography for the diagnosis of acute appendicitis (Yu
et al., 2005; Lee, 2003; Zielke
et al., 2001). These studies show a sensitivity of 75 to 98% and
accuracy of 76 to 96% (Yu et al., 2005; Assefa
et al., 2006; Lee, 2003). Thus, negative
appendectomy rate can be significantly reduced by ultrasonography along with
clinical evaluation (Styrated et al., 2000; Fujii
et al., 2000).
The aim of this study was to assess the efficacy of graded compression ultrasonography of the abdomen and pelvis in patients clinically suspected to have acute appendicitis. Many studies have been focused on imaging findings of acute appendicitis but since, the race, diet and normal flora of GI tract in each area can influence on the variety of the human anatomy as well as presentation of appendicitis, with this reason we duplicated the study. MATERIALS AND METHODS
Patients population and evaluation: A total of 110 patients with acute
abdominal pain and tenderness of RLQ, clinically suspected to have acute appendicitis
admitted to the department of surgery of Golestan and Imam Khomeini hospitals
from March 2007 to March 2009. They referred to ultrasound department and ultrasonography
was performed using 3.5 MHz convex and 7.5 MHz linear transducers. After taking
a detailed history, performing a complete physical examination and taking blood
sample for complete blood count, a plain abdominal radiography examination was
performed.
| Fig. 1: | (a)
Transverse section of appendicitis, (b, c) longitudinal image of inflamed
appendix |
The results were judged positive if the examination met at least one of the
criteria of puylaert: (1) non-compressible, swollen appendix with a diameter
greater than 7 mm and a wall thickness greater than 3 mm, (2) lack of normal
wall layer, (3) appendicolith (4) increase and hyperechogenicity of periappendiceal
fat, (5) appendiceal abscess and (6) periappendiceal fluid collection (Fig.
1a-c).
Ultrasonography: We systematically performed a general examination of
the entire abdomen by 3.5 MHz convex transducer and a graded compression ultrasonography
of right lower quadrant and point of maximum tenderness by a 7.5 MHz transducer.
Para-sagittal, transverse and oblique images were obtained until the entire
region of interest was scanned. Sonographic findings of each patient were recorded.
Preoperative and histopathological findings of all subjects who underwent appendectomy
were also recorded separately. The investigators analyzing the data were unaware
of the final diagnosis and outcome in each case.
Statistical analysis: Statistical analysis was performed with SPSS software (v.12.0; SPSS Inc., Chicago, IL, USA). Results were expressed as Mean±SD. A probability value of less than 0.05 was considered to be statistically significant. Sensitivity and specificity were calculated according to standard formulas, namely:
and
where, TP is true positives, FN is false negatives, TN is true negatives and FP is false-positives. The predictive values (PV), whether positive (+) or negative (), were similarly calculated, with +PV being (TP) / (TP + FP) and -PV being (TN) / (TN + FN). RESULTS
A total of 110 clinically suspected cases of acute appendicitis were examined
by sonography. There were 46 (41.82%) male and 64 (58.18%) female patients with
mean age of 28.9 years (range 4 to 70 years). Diagnostic results of graded compression
ultrasonography are shown in Table 1. There were 56 patients
with negative ultrasonography. Of these, four were falsely negative, all four
patients had surgery because of persistent pain and acute appendicitis was confirmed
on pathological examination. The diagnoses for the 52 patients who tested true
negative on diagnostic ultrasonography are shown in Table 1.
The sensitivity, specificity, accuracy, positive predictive value and negative
predictive value were 92.7, 94.5, 93, 94.4 and 92.5%, respectively. There were
54 patients who had positive ultrasonography studies and subsequently had surgery.
Of these, 51 patients had pathological confirmation of acute appendicitis and
three were falsely positive. Of the latter, one had a ruptured ovarian cyst
and the other two had normal appendix without any problem (Table
2).
Table 1: | Diagnostic
indices of sonography for all study patients |
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Study
group (n = 110) |
Table 2: | Ultrasonography
findings in sonographically positive patients |
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The
patients had either a single or a combination of the above findings |
Table 3: | Diameter
of appendix (mm) in cases of appendiceal swelling |
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Table 4: | Diagnoses
of patients who tested true negative on ultrasonography for acute appendicitis |
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Ultrasonography findings of the 54 sonographically positive patients are shown
in Table 3. Of these, the swollen appendix with the mean diameter
of 8 mm was the most imaging finding (Table 4).
DISCUSSION
Acute appendicitis remains the most common surgical emergency with a life-time
occurrence of 7% (Friday, 2006). The key to successful
management of acute appendicitis depends on prompt diagnosis and early surgical
intervention. The clinical diagnosis of acute appendicitis is not always straightforward
and negative appendectomy rate of 20-25% is not uncommon. There is an inverse
relationship between negative appendectomy rate and perforation rate. So, the
challenge for a surgical specialist is how to balance between efforts to reduce
negative appendectomy rate without increasing the perforation rate. Imaging
can play a great role in making an early diagnosis of appendicitis and also
suggest alternative diagnosis thereby reducing both negative appendectomy rate
as well as perforation rate.
Graded compression ultrasonography as popularized by puylaert is a readily
available, noninvasive, highly accurate mean of diagnosing appendicitis and
a variety of relevant disease (Chan et al., 2005).
Prospective studies have shown the overall accuracy of ultrasonography in diagnosing
acute appendicitis ranges between 87-98% (specificity 89-99%, sensitivity 86-97%),
respectively (Fujii et al., 2000; Chan
et al., 2005; Khanal et al., 2008;
Himeno et al., 2003; Wiersma
et al., 2009). However, in pregnant women and children, the error
rate is reported to be much higher, 35-45% but, in this series of 110 patients
included 7 children under age 10 years and 3 pregnant women, sonographic diagnoses
was correct (Wiersma et al., 2009; Basaran
and Basaran, 2009). Of the 7 children, 4 had negative ultrasonography findings
and 3 were positive (two cases with swollen appendix measuring 7 and 7.4 mm
in total diameter and one with appendiceal abscess). Our data (sensitivity 92.7%,
specificity 94.5%, accuracy 93%, positive predictive value 94.4% and negative
predictive value 92.5%) confirmed the value of ultrasonography in the diagnosis
of acute appendicitis and has produced comparable results to the current literature.
CONCLUSION Ultrasonography is an accurate, safe and reliable method in the diagnosis of suspected cases of acute appendicitis that can help to minimize negative appendectomy and perforation rates.
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