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1 All authors: Department of Diagnostic Radiology, University of Ulsan College of Medicine, Ulsan University Hospital, 290-3 Cheonha-Dong, Dong-Ku, Ulsan 682-714, South Korea.
Received January 27, 2004;
accepted after revision June 1, 2004.
Address correspondence to J. H. Lee
(jhlee{at}uuh.ulsan.kr).
Abstract
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SUBJECTS AND METHODS. A total of 877 subjects were included in this study. This sample population consisted of two groups: 202 control subjects and 675 patients who were suspected of having acute appendicitis. If detection of the appendix failed after a sufficient number of trials using graded compression scanning, appropriate operator-dependent techniques were used to help graded compression scanning to increase the detectability of the appendix further. The detection rate for the appendix in both groups and the diagnostic accuracy for acute appendicitis were obtained.
RESULTS. The initial graded compression sonography examination depicted the appendix in 170 (84%) of 202 subjects in the control group and 601 (89%) of the 675 patients in the patient group. We then added operator-dependent techniques to graded compression sonography for the remaining patients in whom the appendix could not be detected. The additional use of the posterior manual compression technique, low-frequency convex transducer, upward graded compression technique, or left oblique lateral decubitus change of body position allowed graded compression sonography to depict the appendix in an additional 10, eight, six, and four patients in the control group, respectively, and in an additional 27, 23, 11, and seven patients in the patient group. The number of identified appendixes was increased to 198 (98%) of the 202 patients in the control group and to 669 (99%) of the 675 patients in the patient group. Graded compression sonography with operator-dependent techniques in the patient group yielded a sensitivity of 99% (319/321 patients), specificity of 99% (350/354), and an accuracy of 99% (669/675) for acute appendicitis.
CONCLUSION. The addition of various operator-dependent techniques to graded compression sonography is useful for allowing improved visualization of both normal and abnormal appendixes.
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Although a significant limitation of sonography is operator dependency, accumulated operator experience along with advanced sonographic equipment have allowed the appendix to be detected with increased frequency. Only limited reports dealing with operator-dependent techniques helping graded compression sonography to detect the appendix more easily in difficult cases have been published [7, 16–19]. Some of the reports simply described the mechanism. More varied operator-dependent techniques that are readily accessible to imaging practitioners could be used with graded compression sonography to detect the normal or abnormal appendix and to diagnose acute appendicitis.
In our hospital, we have used known or new operator-dependent techniques successfully with graded compression sonography to diagnose difficult cases of acute appendicitis. Therefore, the purpose of this prospective study was to evaluate the value of various operator-dependent techniques with graded compression sonography to help detect the normal or abnormal appendix and to diagnose acute appendicitis.
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Sonographic Techniques
Two gastrointestinal radiologists with approximately 6 and 10 years of
experience in gastrointestinal and sonography-oriented emergency radiology,
respectively, at the start of the study independently performed the graded
compression sonography examinations in a region of the right lower quadrant of
the abdomen to detect the appendix. All examinations included in this study
were performed with a commercially available sonographic unit with
4-7–MHz linear-array, 5-12–MHz linear-array, and 2-4–MHz
curved-array transducers (HDI 5000, Advanced Technology Laboratories).
All examinations began with the patient in the supine position. All sonographic studies initially were performed with graded compression to obtain transverse and longitudinal scans. If detection of the appendix failed despite sufficient attempts of graded compression scanning within an examination time of approximately 15–20 min, the most appropriate operator-dependent technique according to the patient's condition or appendiceal location was attempted to help graded compression sonography within an additional examination time of 15 min. For agreement on sonographic interpretation after and before application of an operator-dependent technique, another gastrointestinal radiologist or a resident was asked to observe the examination.
Operator-Dependent Techniques
Upward graded compression technique.—The false or true
pelvic location of the vermiform appendix with the deep orientation of its
distal portion is a definite limitation for graded compression sonography
because of the increased distance and oblique insonation angle between the
appendix and the high-frequency transducer. An examination using this
technique starts with forced upward sweepings of the high-frequency linear
transducer to move upward the low-lying cecum and appendix. Upward graded
compression of the transducer will squeeze the cecum and vermiform appendix
onto the psoas muscle or anterior to the vertebral body (Figs.
1A and
1B), areas in which the
distance between the vermiform appendix and the high-frequency transducer will
be reduced so the appendix will be more easily accessible for detection using
the graded compression technique.
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Posterior manual compression.—This technique is known to be a nonmechanical operator-dependent technique composed of forced extrinsic compression of the opposite side of the right lower quadrant abdomen in the anterior or anteromedial direction using the left hand, thereby allowing forced compression of the posterior aspects of the cecum or pericecal space with or without anteromedial displacement of the right lower quadrant bowel structures onto the psoas muscle [16]. With anterior and posterior simultaneous graded compression, the depth to be reached using a high-frequency transducer may be approached on the retrocecal or retrocolic spaces and on the anterior margin of the psoas space, thereby increasing the spatial resolution. We used this technique in patients with poorly compressible bowel structure or in obese or muscular patients with poor definition of the posterior aspects of the right colon (Figs. 2A and 2B).
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Left oblique lateral decubitus position of body.—Rioux [7] suggested that the left oblique lateral decubitus position of a patient's body is helpful in visualizing a retrocecal appendix. This is because by turning a patient from a supine position to the left oblique lateral decubitus, the cecum and terminal ileum are displaced medially onto the psoas muscle by postural change and then the depth of the lateral portion of the retrocecal colic area will be reduced subsequently with enough penetration of sound to be reached by the transducer [17] (Figs. 3A and 3B). Position change to the left oblique lateral decubitus position also could have a role in reducing the retroileal area onto the psoas muscle.
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Low-frequency convex transducer.—A pelvic location of the appendix and a patient who is obese present the possibility that the appendix is located off the depth of view of the sonogram using a high-frequency transducer. A currently popular low-frequency convex transducer works well and provides a larger field of view and greater penetration. State-of-the-art equipment of advanced signal-processing technologies such as tissue harmonic imaging and sonoCT (real-time compound imaging technology) are now available with a low-frequency convex transducer. When other adjuvant techniques are not helpful in the examination of an obese patient or in a patient with a deeply located appendix, a low-frequency convex transducer may be used successfully [3, 17, 19–21] (Figs. 4A and 4B).
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Sonographic Evaluation
For the appendix to be detected, the entire course of the appendix was
scanned with the appropriate use of graded compression and operator-dependent
techniques according to each patient's physique and appendiceal location. When
detecting the appendix after using an operator-dependent technique, we
rechecked the inability to visualize the appendix using only graded
compression sonography after discontinuation of the operator-dependent
technique. The sonographic diagnosis of acute appendicitis was based on one or
more of the following findings of the appendix: anteroposterior diameter
greater than 6 mm, incompressibility, increased flow signals in the
appendiceal wall or periappendiceal space using color Doppler sonography,
echogenic periappendiceal inflammatory fat change, and periappendiceal fluid
and gas. The criteria for a normal appendix were based on a compressible,
tubular, blind-ending structure filled with fluid, gas, or feces. The lack of
visualization of the appendix was considered a negative result of acute
appendicitis. The final diagnosis of acute appendicitis was made on the basis
of the pathologic findings in those patients who underwent surgery; five
patients had conservative treatment and imaging follow-up after a definitive
sonographic diagnosis of acute appendicitis. The surgical and pathologic
reports and the medial records of all patients were reviewed and compared with
the official radiology reports after the hospital stay and clinical followup
of these patients.
We calculated the detection rate for the appendix on graded compression sonography before and after the additional use of operator-dependent techniques in the control and patient groups. For statistical analysis, we compared the statistical proportions for the increased detection rates on graded compression sonography after the addition of operator-dependent techniques between the control subjects and the patient group by performing the chisquare test. For the diagnostic results in the patient group, we calculated the sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy for acute appendicitis after an additional application of operator-dependent techniques. The probabilities for acute appendicitis diagnosis using only graded compression sonography also were calculated for comparison with the diagnostic accuracies after the application of operator-dependent techniques.
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We detected the appendix in 601 (89%) of 675 patients who were clinically suspected of having acute appendicitis in the patient group using graded compression sonography. For the remaining 74 appendixes (11%) not visualized on the initial graded compression sonography examination, the additional use of the posterior manual compression technique allowed graded compression sonography to depict the appendix in an additional 27 patients. The use of the low-frequency convex transducer, upward graded compression technique, and change of body position to left oblique lateral decubitus helped graded compression sonography to reveal the appendix in an additional 23, 11, and seven patients, respectively. The number of the identified appendixes therefore was increased to 669 (99%) of the 675 patients (Table 1). Comparing the statistical proportions for the increased detection rates on graded compression sonography with the addition of operator-dependent techniques between the control subjects and the patients showed no significant difference (p = 0.703).
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The sonographic diagnosis of acute appendicitis was made in 323 of the 675 patients, 19 of whom had a new diagnosis of acute appendicitis after the use of operator-dependent techniques. A total of 322 patients including two patients with a sonographic diagnosis of mucocele underwent surgery, and five patients with a sonographic diagnosis of acute appendicitis improved after conservative treatment and imaging follow-up. A pathologic diagnosis of acute appendicitis was proven in 316 of the 322 patients who underwent surgery.
Of 323 patients with a sonographic diagnosis of acute appendicitis, sonography established the diagnosis in 319 of the 321 patients who had been proven pathologically and clinically to have appendicitis: There were four patients with false-positive results and two patients with false-negative results. The two false-negative cases were diagnosed preoperatively with acute appendicitis by following CT, and the four false-positive cases were confirmed pathologically as lymphoid hyperplasia. No false results were acquired after using the operator-dependent techniques.
Graded compression sonography in addition to operator-dependent techniques in the patient group yielded a detection rate of 99% (669/675 patients) for the vermiform appendix; a sensitivity of 99% (319/321); specificity of 99% (350/354); positive and negative predictive values of 99% (319/323) and 99% (350/352), respectively; and an accuracy of 99% (669/675) for acute appendicitis. When diagnostic results for acute appendicitis with the application of various operator-dependent techniques were compared with probabilities for those with only graded compression sonography, the former showed more improvement (Table 2). Probabilities for acute appendicitis diagnosis with single-use graded compression sonography yielded a detection rate of 89% (601/675 patients) for the appendix; a sensitivity of 94% (302/321); specificity of 99% (350/354); positive and negative predictive values of 99% (302/306) and 95% (350/369), respectively; and an accuracy of 97% (652/675).
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The usual downward sweeping of the high-frequency linear transducer on starting graded compression sonography may cause the low-lying or false or true pelvis-located appendix more downward squeezing and displacement into a deeper pelvic area in which it is more difficult to detect the vermiform appendix. Under this circumstance, examiners would be better to start graded compression sonography with upward sweeping of the probe because the upward action of the probe can prevent the low-lying or pelvis-located appendix from downwardly displacing into a deeper pelvic area and can often make the low-lying cecum and appendix displace upwardly onto the psoas muscle or anterior to the vertebral body. The right lateral decubitus position coupled with this upward graded compression technique often can achieve upward displacement of the low-lying cecum and appendix more easily.
Rioux [7] mentioned that the left lateral decubitus position is helpful for visualizing a retrocecal appendix, but he simply described that in only one sentence of his article. Besides medial postural change of the cecum and terminal ileum with subsequent reduction of the retrocecal and subcecal or retroileal areas onto the psoas muscle, a position change to left oblique lateral decubitus also could have a role in relocating the appendix to the subcecal or retroileal area, which are more accessible to graded compression sonography. This technique can be used instead of posterior manual compression if that is not helpful or synchronously with it. This technique can be a first-line sonographic technique for use in pregnant women suspected of having acute appendicitis, whereas the graded compression technique could not be helpful [18]. Position change from supine to left oblique lateral decubitus causes medial displacement of the cecum and terminal ileum or the appendix onto the psoas muscle or enlarged uterine wall by postural change, so the depth of the subcecal or retroileal area will be reduced with enough penetration to be reached by a linear or convex transducer [17].
In this article, we first introduced the comprehensive clinical application of new or known operator-dependent techniques being used to help conventional graded compression sonography to detect the normal or abnormal appendix and for the diagnosis of acute appendicitis in patients. Because those techniques would reflect the development of state-of-the-art sonographic equipment and accumulated operator knowledge of real practice, graded compression sonography applying more operator-dependent techniques yielded an increased detection rate of the appendix in both the control and patient groups in our study. The detection rates of the appendix after the combined use of operator-dependent techniques helping graded compression sonography for the control subjects and the patients in our study were 98% and 99%, respectively, which are higher than those rates of 63–68% and 83–87%, respectively, when using only graded compression sonography for the control and patient groups in more recent studies [13, 16, 20, 21]. The reason for the increased detection rate when using various operator-dependent techniques is thought obvious because the use of various operator-dependent techniques helping graded compression sonography works well on increasing the detection rates of normal and abnormal appendixes. When comparing the proportions for the increased detection rates on graded compression sonography helped by each operator-dependent technique between the control subject and patient groups, and between the control subject and patient groups having acute appendicitis, no statistically significant differences were detected. Moreover, when diagnostic accuracies for acute appendicitis with the application of operator-dependent techniques were compared with probabilities for that with only graded compression sonography, the former showed more improved diagnostic accuracies.
We studied the responsibility of each operator-dependent technique in the comprehensive value of overall operator-dependent techniques for diagnosis of acute appendicitis. The smallest proportion of the increased diagnostic accuracies in the comprehensive value of overall operator-dependent techniques for diagnosis of acute appendicitis was made by the change of body position to lateral decubitus. The probabilities for accurate diagnosis of acute appendicitis using the lateral decubitus body position for graded compression sonography yielded a detection rate of 90% (608/675) for the vermiform appendix; a sensitivity of 94% (303/321); specificity of 99% (350/354); positive and negative predictive values of 99% (303/307) and 95% (350/368), respectively; and an accuracy of 97% (653/675). The largest proportion in the increased diagnostic accuracies by operator-dependent techniques for diagnosis of acute appendicitis was made using the posterior manual compression technique. Probabilities for acute appendicitis using the posterior manual compression technique for graded compression sonography yielded a detection rate of 93% (628/675) for the appendix; a sensitivity of 97% (310/321); specificity of 99% (350/354); positive and negative predictive values of 98% (310/314) and 97% (350/361), respectively; and an accuracy of 98% (660/675). This may suggest that the increased spatial resolution of the posterior manual compression technique over other operator-dependent techniques would yield an increased detection rate of the appendix. This is undoubtedly because the posterior manual compression technique is most effective in overcoming the limitations of obesity and retrocecal appendix.
The outer diameter of the vermiform appendix is the most important diagnostic criterion in the evaluation of acute appendicitis. However, the outer appendiceal diameter may be changed somewhat with the different transverse shape of the vermiform appendix from round to ovoid depending on the availability of compression (Figs. 5A and 5B). It therefore could be assumed that application of the round shape of the vermiform appendix on a transverse scan as a sign of incompressibility with high specificity would be possible if it is preceded by the proper compression of the vermiform appendix detected on sonography. The aims of posterior manual compression, upward graded compression technique, and change of body position to left oblique lateral oblique for our operator-dependent techniques are to increase the detection rate of the vermiform appendixes and to acquire increased spatial resolution and their better compression over those expected with only graded compression sonography. For obese patients or a pelvic or a more deeply located appendix, a low-frequency convex transducer could be used rather than a high-frequency linear transducer. A convex transducer is preferable to compress the appendix in a deep location or in the true pelvis.
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The sonographic detection rate of the appendix depends on the complexity of the case, including personal differences in physique. All the operator-dependent techniques may not be applicable to every patient population because of obesity. A greater than 98% detection rate of the vermiform appendix may not be expected in an obese group. In one study, obesity was the reason for nondetectability of the appendix in only 9% of patients without appendicitis and in only 1% of patients with appendicitis, even though a considerable proportion of the patients in that country were obese [21]. We believe the use of operator-dependent techniques would decrease some proportion of the nondetectability of the appendix that is caused by obesity. The detection rate of the normal appendix using only graded compression sonography in more recent studies for a control group was approximately 63–68% [13, 20, 21], which is lower than the 84% detection rate achieved using only graded compression sonography in our control subject group. This difference would be due to the racial differences that cause differences in physique, with the general population in our country being less obese.
In conclusion, the application of our operator-dependent techniques to graded compression sonography helped increase the detection rate of the appendix and helped increase the spatial resolution of the appendix. The scrupulous evaluation of the highly detected appendixes with the help of various operator-dependent techniques will achieve a high diagnostic accuracy for the diagnosis of acute appendicitis.
Acknowledgments
We thank Bonnie Hami, Department of Radiology, University Hospitals of
Cleveland, for her editorial assistance in the preparation of this
manuscript.
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