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1
Departmento de Radiologia, Hospital Criança
Conceição,
Ministério da
Saúde, Av. Francisco Trein, 596, Porto Alegre,
RS, Brazil 91350-200.
2
Departmento de Radiologia do Hospital
Universitário Clementino Fraga Filho da
Universidade Federal do Rio de Janeiro, Rua Thomaz Cameron, 438, 25685-120
Petrópolis, Rio de Janeiro, RJ, Brazil.
Received August 16, 1999;
accepted after revision April 26, 2000.
Address correspondence to M. Baldisserotto, Rua
Eça de
Queiróz, 384/502, 90670-020 Porto Alegre, RS,
Brazil.
Abstract
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SUBJECTS AND METHODS. We evaluated 425 consecutive boys and girls clinically suspected of having appendicitis. Noncompressive sonography used a 5.0-MHz curved-array transducer to assess deep layers. We systematically investigated the possible positions of the appendix by evaluating the right retrocecal region through the flank, the pelvis through the suprapubic region with the urinary bladder full, and the right lower quadrant. Whenever the appendix was not visualized, graded compression examination was performed with 5.0-MHz curved-array and 7.5-MHz linear transducers, and the remainder of the abdomen was thoroughly examined with 5.0- and 3.75-MHz curved-array transducers. Sonographic findings were correlated with pathology findings after surgery in 212 cases and with clinical follow-up in 213.
RESULTS. Of the 425 patients with abdominal pain, 199 had surgically confirmed appendicitis; noncompressive examination accurately identified 135 (31.7%) of these 425 cases, and the combined noncompressive and compressive examinations diagnosed 196 cases. The combined noncompressive and compressive techniques had a sensitivity of 98.5% (95% confidence interval, 96.8-100), specificity of 98.2% (96.5-99.9), positive and negative predictive values of 98.0% (99.9) and 98.7% (97.2-100), respectively.
CONCLUSION. The noncompressive technique is a valuable tool in sonographic investigation of appendicitis.
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In 1986, Puylaert [4] described a sonographic technique that applied graded compression and used high-frequency transducers to visualize the appendix. Since then, this technique has become standard in studies of sonographic investigation of acute appendicitis, and high levels of sensitivity and specificity have been achieved in the diagnosis of this disease [5,6,7,8,9,10,11]. Although several authors report that compression at sonography is usually well tolerated [12, 13] for children who have rebound tenderness with appendicitis, gentle percussion is recommended even at physical examination to make the examination less painful [14]. Moreover, intense abdominal pain and retrocecal appendixes, although infrequent, have been regarded as reasons for false-negative sonographic results [5, 6, 9, 12, 15].
The purpose of this study was to determine, using a noncompressive technique based on imaging the appendix from different positions, whether the sonographic investigation of appendicitis can be less painful and equally or more accurate than the graded compression technique.
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Patients were assigned to one of two groups according to the type of pain the physician who requested the sonography observed at physical examination: at abdominal palpation, some patients presented with pain with guarding and some patients presented with pain without guarding. The addition of this variable to this study was aimed at identifying which group of patients had more intense pain and evaluating the correlation between the intensity of pain and the need for compression.
We classified the appendixes according to the positions in which they were visualized during sonographic imaging as retrocecal; abdominal, located in the abdominal cavity, above the horizontal line defined by the iliac crests; mid pelvic, located below that line; and deep pelvic, located beyond the iliac vessels (Fig. 1).
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This sonographic study was carried out by two pediatric radiologists possessing the equivalent of American Board of Radiology certification. From 8:00 A.M. to 7:00 P.M., one of the radiologists was available at the hospital to perform the sonographic examination, and one was on call at night. The examinations were performed with an SSD-630 scanner (Aloka, Tokyo, Japan). The initial noncompressive examination used a 5.0-MHz curved-array transducer and consisted of the following steps: First, examination of the right retrocecal retroperitoneum by scanning the right flank starting in the transverse plane from the liver and right kidney and extending to the iliac crests, where the sonographic beam is reflected; immediately after that, in the longitudinal plane, beginning anteriorly at the axillary line and continuing around the flank to the posterior axillary line, ending in the lumbar region (Fig. 2A). Second, we used the suprapubic approach with the urinary bladder as an acoustic window (Figs. 2B and 2C). Third, after the patient voided, we examined the superficial and deep intraabdominal structures by applying the transducer to the right lower quadrant. If gas-filled loops were present, the patient's position was changed in an attempt to better visualize all structures. Whenever a dilated appendix was not visualized during these first steps, graded compression sonography was performed with a 5.0-MHz curved-array transducer or a 7.5-MHz linear transducer. The remainder of the abdomen was subsequently surveyed with a 5.0-MHz curved-array transducer or, for obese children, with a 3.75-MHz curved-array transducer.
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Examinations were carried out with adequate urinary bladder filling (defined as the urinary bladder filling the pelvis). Bladder filling was obtained through ingestion of liquids or through the IV administration of a physiologic saline solution for patients with nausea and vomiting. For patients whose urinary bladder was empty at the beginning of the procedure, a noncompressive examination was performed first and, even if an abnormal appendix was identified then, the pelvis was examined after bladder filling to check for the presence of fluid collections. For non—toilet-trained patients (n = 36), bladder filling was evaluated sonographically every 15 min. Patients underwent compressive examination only after bladder voiding to make the maneuver less painful. For non—toilet-trained patients, the examination after voiding was performed once a relative confirmed there was urine in the patient's diaper.
For toilet-trained patients, total examination time was approximately 20 min. The noncompressive examination took about 10 min, including the time to go to the bathroom and empty the bladder. The compressive examination and the full examination of the abdomen took approximately 10 more min. For non—toilet-trained patients, the waiting time was the time necessary for the patient to empty the bladder.
Except for the assessment of appendiceal compressibility, which was carried out only at the graded compression examination, the sonographic criteria for the diagnosis of acute appendicitis during the non-compressive examination were the same as for the graded compression examination—that is, the visualization of an image suggestive of an abnormal appendix (blind-ending tubular structure) with a diameter greater than 6 mm, with or without a fecalith, or the presence of an abscess. The criterion for noncompressive imaging of a diameter greater than 6 mm was based on the criterion for the noncompressive diameter for the CT diagnosis of appendicitis [16].
Sonographic findings were correlated with the findings of pathology after surgery in 212 patients, and with clinical follow-up obtained from a clinician after 1 week in 213 patients.
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Of the four patients with false-positive findings, three were taken to surgery and two of these had Merckel's diverticulitis; sonography had imaged a tubular hypoechoic structure in the iliac fossa that was mistakenly interpreted as an abnormal appendix. For a third patient, sonographic imaging showed a thickened terminal ileum surrounded by an omental mass and a moderate amount of fluid in the peritoneal cavity, which mimicked perforated appendicitis. At surgery, this patient showed signs suggestive of nonspecific peritonitis. In this patient, a clearer interpretation of the suspected image was difficult to obtain because of the presence of gas-filled loops. The fourth patient improved clinically, and follow-up sonography had normal findings.
Of the three false-negative cases, the sonographically suggested diagnosis in two was mesenteric adenitis. At clinical follow-up, pain increased for these two patients, one in 12 hr and the other in 24 hr. For the third patient, sonography was inconclusive because imaging suggested three different diagnoses: Meckel's diverticulitis, an infected enteric cyst, and appendicitis. These three patients were taken to surgery, where appendicitis was confirmed.
Considering the performance of the noncompressive study alone, we obtained a sensitivity of 67.8% (95% confidence interval, 61.3-74.3), specificity of 98.2% (96.5-99.9), and positive and negative predictive values of 97.1% (94.3-99.9) and 77.6% (72.8-82.5), respectively. When the study was completed with the graded compression examination, sensitivity was 98.5% (96.8-100), specificity was 98.2% (96.5-99.9), and positive and negative predictive values were 98.0% (96.1-99.9) and 98.7% (97.2-100).
Table 2 shows the performance of the technique used according to the type of pain, the percentage of cases for which compression was unnecessary, and the sensitivity and specificity for the combined noncompressive and compressive techniques according to the type of pain. The rate of compression was greater for the group of patients who presented with pain without guarding at physical examination (85.6%) than for the group who presented with pain and guarding (53.9%). Of the 425 patients with abdominal pain, noncompressive sonography diagnosed appendicitis in 139, of which 135 were true-positive and four were false-positive. Of the 286 patients who underwent graded compression examination, 222 examinations had true-negative findings, 61 had true-positive, and three had false-negative results. Of the 196 true-positive cases, 135 (68.9%) were diagnosed without compression (Table 3), and 110 of these patients presented with abdominal pain with guarding.
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Table 3 shows the percentage of patients for whom the noncompressive technique identified the appendix in its different positions. The noncompressive technique accurately identified 86.5% of the cases of retrocecal appendixes (Figs. 3 and 4), 100% of the deep pelvic appendixes (Figs. 5 and 6), 51.9% of the mid pelvic, and 59.5% of the abdominal (Fig. 7) appendixes. Table 4 lists the different regions where the transducer was positioned for the identification of the appendixes in their different positions. Surgery confirmed the appendiceal position of all the 196 sonographically true-positive cases and also showed that the three false-negative cases presented appendixes in the abdominal position.
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Most patients with an empty or half-filled bladder on arrival at the radiology department took about 30 min to fill the bladder. A smaller group of patients, whose bladders were full, were examined immediately. Another small group of patients were dehydrated, had an empty bladder, and had to wait for approximately 1 hr 30 min to be examined. Non—toilet-trained patients filled the bladder easily, and the average wait time was approximately 30 min, although for a few patients it was up to 1 hour. For non—toilet-trained patients, an additional 15-30 min was necessary to empty the bladder.
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The technique described here attempted to determine the diagnosis of appendicitis using an examination that is more comfortable for the patient. For this purpose, we avoided compression by choosing the approach according to the probable position of the appendix (i.e., retrocecal, mid pelvic, deep pelvic, or abdominal), then trying to place the transducer as close as possible to the appendix; by using a 5.0-MHz curved-array transducer that offered us a broader view of the field for deeper planes; by avoiding overlying bowel loops; and by examining the pelvis through a full urinary bladder.
The compressive examination was performed only in the patients for whom initial sonographic diagnosis of appendicitis was not obtained without compression—that is, the examination was concluded as soon as an abnormal appendix was identified. One hundred thirty-nine patients underwent only noncompressive sonography, and results were true-positive for 135 patients with appendicitis (97.1%, 135/139). Of the 135 patients with appendicitis diagnosed using the noncompressive examination, 110 presented with pain and guarding, and this was the group that benefited the most from this technique. Compressive sonographic examinations were performed for 286 patients and had true-negative findings in 222 (77.6%, 222/286).
These results show that the noncompressive technique was more useful in the patients having appendicitis with more intense pain—exactly those patients who would likely suffer from more discomfort had Pulyaert's compressive technique been used. At the same time, the compressive procedure was useful in identifying the cases of appendicitis not visualized at the noncompressive examination. Therefore, the use of the compressive technique was beneficial to most patients who did not have the disease.
Some studies have considered retrocecal appendixes to be one of the reasons for false-negative results [5, 15]. In 1990, Ceres et al. [21] described the sonographic diagnosis of retrocecal appendicitis through the examination of the right flank. Because a retrocecal appendix is located in a posterior, posterolateral, or lateral position with respect to the cecum and the ascending colon, there are no overlying bowel loops between the appendix and the right flank. Therefore, by applying the transducer to the right flank from the posterior aspect, next to the lumbar region, the retrocecal appendix can be identified without using compression. The study of Ceres et al. found that 28% of patients had retrocecal appendixes. These researchers obtained a sensitivity of 94.5% for the diagnosis of such appendixes. In our study, all cases of retrocecal appendicitis were diagnosed sonographically, and the prevalence of this appendiceal position was 26.1% (52/199). Forty-five of these cases (86.5%) were visualized without compression (Table 3). In 42 of these retrocecal cases, the appendix was identified in the right flank; in eight cases in which the appendixes were in a posteromedial position in relation to the cecum, visualization was obtained through the anterior wall in the lower quadrant; in the other two cases, appendixes were found in the hypochondrium.
Two case reports [22, 23] have shown the difficulty of identifying deep pelvic appendixes using the graded compression technique because of overlying bowel loops. For such cases, sonographic transvaginal examination has been suggested as the alternative technique for adult female patients. In our study, sonography of the pelvis through the urinary bladder proved to be useful in the visualization of such appendixes in children. Prevalence of deep pelvic appendixes was 12.8% (25 patients), and all were identified without compression. Our review of the medical literature did not produce any report that focuses on the use of the urinary bladder as an acoustic window in the noncompressive identification of abnormal appendixes in these positions. In these patients, the filled urinary bladder displaces the overlying bowel loops but does not displace the appendix, probably because of the presence of inflammation, adhesion, and omental thickening, and this made it possible to visualize the appendix without compression.
Total examination time for most patients was approximately 50 min; for a smaller group of patients whose bladder was full at arrival, the examination took 20 min; for a few patients who were dehydrated, the total time was 1 hr 50 min (adding bladder-filling and examination times); the examination of non—toilet-trained patients took 35-50 min.
Unenhanced helical CT [24] has been broadly used as a method that can rapidly define the diagnosis of appendicitis without bladder filling. However, two factors limit its use in our environment: the cost of an abdominal CT examination ($405) is high when compared with the cost of abdominal sonography ($60); and, in our institution, as well as in many others, CT, is not always available—we have a single CT unit for two hospitals (an adult and a pediatric hospital).
For several cases of appendixes deeply set in the abdominal cavity between distended bowel loops, we changed the patient's position so that bowel gas was displaced, and visualization of the appendix without compression was possible. In other cases, visualization of a fecalith helped in the identification of the appendix. Some appendixes that were already gangrenous showed the presence of gas, and the overall constellation of findings could be mistakenly identified as merely representing a bowel loop. In these cases, the presence of fixed gaseous images surrounded by hyperechoic walls, which corresponded to the pneumoappendix, helped in the differentiation from bowel loops. Poljak et al. [25] have already called attention to the difficulty of diagnosing appendixes with such presentation at sonography. Abdominal and mid pelvic appendixes located close to the anterior abdominal wall in the right lower quadrant were identified without compression in 59.5% and 51.9% of the cases, respectively (Table 3).
In conclusion, the technique described here accurately identified appendicitis in most patients with appendicitis. The appendix was otherwise imaged by varying the position of the transducer so that optimal transducer-to-target distance and focus were obtained. The use of a transducer with deeper penetration, the correct positioning of the transducer on the patient, and the pelvic examination through the distended urinary bladder eliminate the need for abdominal compression for the visualization of the abnormal appendix in most cases. For patients clinically suspected of having appendicitis, the noncompressive examination may be attempted before the graded compression study and may successfully establish the diagnosis for some cases, thus avoiding compression in patients with abdominal pain. According to the results of this study, we believe that, in certain clinical situations, the noncompressive sonographic technique can be a useful alternative to both CT and compressive sonography.
Acknowledgments
We thank Leonard Swischuk for his invaluable contribution to the
development and editing of this paper; Mário
Wagner and Mauro Soibelman, who helped us with the statistic calculations; and
Manoel Angelo de Araújo, who also performed
sonographic examinations for this study. We also thank residents Simone
Gianella Valduga and Luciano Vieira Targa for their assistance in collecting
the data for this study, Anelise Burmeister for her assistance in writing and
proofreading the text, and Johny Acosta for his assistance with computer
issues.
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