PEDIATRICS Vol. 104 No. 3 September 1999, pp. 440-446

Effect of Computed Tomography on Patient Management and Costs in Children With Suspected Appendicitis

Barbara M. Garcia Peña, MD^*, George A. Taylor, MD, Dennis P. Lund, MD^§, and Kenneth D. Mandl, MD, MPH^*

From the ^* Department of Medicine, Division of Emergency Medicine; the  Department of Radiology; and the ^§ Department of Surgery, Children's Hospital, Harvard Medical School, Boston, Massachusetts.

	ABSTRACT

Top Abstract Methods Results Discussion References

Objective.  Children evaluated in the emergency department for possible appendicitis are often admitted for observation, despite the widespread availability of accurate diagnostic studies, particularly computed tomography (CT). We sought to establish effective and efficient strategies for using CT to diagnose and manage children with possible appendicitis.

Design.  Retrospective chart review and decision analysis.

Setting.  Emergency department of a large, urban tertiary care pediatric teaching hospital.

Patients.  All patients admitted from January 1996 to August 1997 for suspected appendicitis.

Method of Analysis.  Three modeled strategies were empirically applied to the retrospective cohort of patients admitted for observation. Outcomes and costs under the modeled strategies were compared with those under current practice. The three strategies were: 1) to obtain CT scans on all patients and discharge those with normal findings; 2) to obtain CT scans and admit all patients; 3) to selectively obtain CT scans on those patients with a peripheral white blood cell count >10 000/mm³ (10 × 10⁹/L) and admit all. The sensitivity and specificity of CT for diagnosing appendicitis were determined empirically from the data. A sensitivity analysis was performed.

Main Outcome Measures.  The number of preoperative inpatient observation days, total hospital costs, and the rates of both missed appendicitis and negative laparotomies.

Results.  Of 609 patients hospitalized for possible appendicitis, 287 went directly to the operating room and 14 patients had known perforation and abscess. Three hundred eight children were observed and comprised the study cohort. Of the cohort, 112 (36.4%) underwent appendectomy and 26 (23.2%) of these had a normal appendix at pathology. Three patients were discharged from the hospital after observation and were subsequently readmitted with appendicitis (missed appendicitis). Among the 75 patients who had CT performed, the sensitivity and specificity of CT were both 97%. Under the current practice strategy, the cohort collectively accumulated 487 inpatient observation days and incurred a per patient cost of $5831. All three CT strategies would have reduced the total number of inpatient observation days, operations, negative laparotomies, as well as the per patient cost. The strategy of obtaining CT scans on all patients and then admitting them had the lowest rate of missed appendicitis. The additional cost of preventing each case of missed appendicitis under this strategy compared with the strategy of obtaining CT scans and sending home those with negative findings was $150 304. Even at the lowest reported sensitivity and specificity of CT in the literature, the ordering of the three strategies remained constant and continued to reduce total cost per patient.

Conclusion.  Compared with current practice, diagnostic strategies using CT could reduce costs and improve diagnosis, management, and outcomes for children with appendicitis.  Key words:  computed tomography, patient management and costs, appendicitis.

Acute appendicitis is the most common condition requiring emergency surgery in children.^1-3 The potential morbidity and mortality from perforation of the appendix necessitates prompt diagnosis.^4-7 In many cases, the diagnosis of appendicitis can be made from the history, physical examination, and laboratory studies obtained during the initial clinical encounter.^8-10 However, in children and adolescents, accurate diagnosis can be difficult, because the initial presentation of appendicitis may be obscure and closely mimicked by other disease processes.^11-16 In fact, the sensitivity of the clinical examination has been reported to be as low as 63%¹⁷ and that of the standard laboratory evaluation as low as 76%.^18,19

Because of the difficulty in accurate diagnosis, children with suspected appendicitis are often admitted to the hospital for a period of observation.^20-23 Inpatient observation is expensive and patients risk perforation of the appendix if surgery is delayed.^24,25 However, improved diagnostic techniques, allowing rapid diagnosis have recently become available. Advances in computed tomography (CT) with high-resolution techniques have yielded a sensitivity as high as 100% and specificity as high as 98%^26-37 for the diagnosis of acute appendicitis. The highest accuracy has been reported with the new focused appendiceal CT technique in which 3% diatrizoate meglumine saline solution is instilled directly into the colon.^27-31,36,37 These studies have confirmed that optimal CT imaging of the right lower abdominal quadrant effectively establishes a diagnosis of either appendicitis or alternative diagnoses, such as inflammatory bowel disease or mesenteric adenitis.^27-31,36,37

We observed that in our institution, there was variation in the diagnostic approach to appendicitis and that the majority of patients were not having CT imaging as part of their evaluation. Our aim was to model diagnostic testing strategies using CT that could be applied to patients with possible appendicitis who are currently admitted to the hospital for an inpatient observation period. We sought to determine the acute care costs and outcomes under three potential strategies for using CT to diagnose and manage children with suspected appendicitis.

	METHODS

Top Abstract Methods Results Discussion References

The Cohort

We applied a decision analytic model to a retrospective cohort of children admitted to the hospital with suspected appendicitis. We defined a cohort of consecutive patients admitted for suspected appendicitis through the emergency department (ED) of Children's Hospital in Boston from January 1996 to August 1997. Children's Hospital is a large, urban pediatric teaching hospital with an ED that sees 50 000 patient visits and a general surgical service that performs 3800 operations annually. All operations were performed by board-certified attending pediatric surgeons. Patients were identified by a query of the hospital database by ICD-9 codes for appendicitis and abdominal pain. A single reviewer using a standardized data collection tool abstracted data on symptoms, laboratory studies, radiographic studies, and pathologic reports. Patients discharged home from the ED or admitted directly to the operating room were excluded.

Diagnostic Tests

White blood cell (WBC) counts measured at Children's Hospital were determined using a Technicon Hemalog cell counter (Bayer, Cherrytown, NY). The supine and upright abdominal radiographs were obtained using standard age-based radiographic techniques.

All right lower quadrant sonographic studies were performed by radiology fellows or attending staff using 5.0- and/or 7.5-MHz linear array transducers (Model XP10, Acuson, Mountainview, CA) using the graded compression technique. The sonographic diagnosis of appendicitis was based on detecting a fluid-filled distended structure (6 mm in diameter), which demonstrated no peristaltic activity, was noncompressible, seemed constant in shape and position, and was located either anterior to the psoas muscle or in a retrocecal position. The presence of pericecal inflammatory changes in the absence of visualizing an abnormal appendix was considered strongly suggestive, but not specific for acute appendicitis.

CT examinations were performed by radiologists who were not blinded to the previous ultrasound interpretations with GE 9800 Hilight scanners (GE Medical Systems, Milwaukee, WI) using sequential rapid thin-section scanning or helical technique. Patients received oral 1.2% diluted barium or 2% meglumine diatrizoate (Gastrografin; Bristol-Meyers Squibb, Wallingford, CT) 1 hour before scanning. Subsequently, a 1 cc/kg bolus of intravenous injection of 43% iodinated nonionic contrast material was administered and sequential 5- to 8-mm CT sections were obtained. The CT diagnosis of appendicitis was based on the visualization of an abnormal appendix and/or pericecal inflammation/abscess with or without the presence of an appendicolith. An abnormal appendix was defined as being a fluid-filled tubular structure with a thickened and enhancing wall, measuring >6 mm in its outer diameter. Findings suggestive, but not indicative, of acute appendicitis included pericecal inflammatory changes, abscess, or phlegmon without visualization of a normal or abnormal appendix.

Diagnostic Strategies

We used Decision Analysis by TreeAge, version 3.5 software (Williamstown, MA) to construct our model. The reference strategy was current practice. To determine the diagnostic value of CT, we used empirical data from our own cohort. The three proposed strategies, modeled using empirical data from the retrospective cohort, are summarized in Table 1. All three strategies involved obtaining CT scans on children who, under current practice, would be admitted to the hospital for an observation period. Two of the strategies involved obtaining CT scans on all patients and then either discharging those patients with negative scans home or admitting them for an inpatient observation period. In the third strategy, CT scans were selectively performed on those patients with peripheral WBC counts >10 000/mm³ (10 × 10⁹/L) and all patients with negative scans were admitted for an inpatient observation period. In all three strategies, patients with positive CT scans went directly to the operating room for appendectomy.

We assumed for all three modeled CT strategies that: 1) the procedure costs of negative laparotomy and positive laparotomy without perforation were the same; 2) the number of postoperative hospital days were the same for both negative and positive laparotomies without perforation; 3) patients sent home with a missed appendicitis would subsequently perforate; and 4) patients with appendicitis having a false-negative CT scan who were then admitted would be properly diagnosed on the floor.

Costs

The 1997 average charges for a perforated appendicitis, nonperforated appendicitis, hospital observation day, abdominopelvic CT scan, and ultrasound were obtained from the hospital charge database at our institution. All costs are in 1997 US dollars. The costs were calculated from the average hospital charge data using a cost-to-charge ratio of 0.72³⁸ (Table 2). The cost of an inpatient hospitalization day includes the daily room cost, laboratory tests, intravenous fluids, and medications administered. ED costs, since incurred by every patient, were not included in the decision model. Costs of the supine and upright abdominal radiographs were also omitted from the model.

Outcome Measures

Main outcome measures were: number of inpatient observation days, number of cases of appendicitis and missed appendicitis, total operations performed, and the number of negative laparotomies. Inpatient observation days were defined as the time period during which patients were being observed and examined on the surgical service before either being discharged from the hospital or undergoing appendectomy. The number of observation days modeled for a patient in each CT strategy was derived empirically from the mean number of days that a similar subgroup of patients spent under current practice. The diagnosis of appendicitis was made by histopathologic examination or clinical outcome. Patients were considered to have a negative laparotomy if the pathologic report indicated no evidence of inflammation of the appendix. If symptoms were resolved by the time of discharge from the hospital, patients were considered to have a normal appendix. Cases of missed appendicitis were defined as those patients who were discharged from the hospital with a diagnosis other than appendicitis and who were then readmitted with the pathologically-proven diagnosis of appendicitis. The per patient cost was calculated for each strategy based on the costs for all operations, perforations, total number of inpatient observation days, number of cases of missed appendicitis, and imaging studies performed.

Sensitivity Analysis

Because of uncertainties in the estimates of some of our parameter values, we performed four one-way sensitivity analyses. We tested the sensitivity of our model to both the specificity and sensitivity of CT as well as to the costs of CT and those of an inpatient observation day.

	RESULTS

Top Abstract Methods Results Discussion References

The Cohort

Six hundred twenty patients were admitted to the hospital from the ED for suspected appendicitis during this 20-month period and 609 (98.2%) charts were available for review (Fig 1). Of these 609 patients, 287 went immediately to the operating room for appendectomy and 14 patients had known perforation and abscess, and were admitted to the hospital for intravenous antibiotics and percutaneous drainage. The study cohort of patients admitted for observation was comprised of 308 children who had a suggestive, but not definitive, diagnosis of appendicitis. During the observation period, children underwent serial abdominal examinations by a surgeon and further laboratory and radiographic studies.

View larger version (38K): [in this window] [in a new window]   Fig. 1.   Breakdown of study participants.

Of the 308 patients in the cohort, 166 were female (53.9%). The mean age was 10.9 years with a standard deviation of 4.9 years and a range of 0.5 years to 25.0 years (Fig 2). Two hundred eighty-two (92%) patients either did not have an ultrasound performed while in the ED, or had one with indeterminate or negative results. One hundred fourteen children had an abdominal ultrasound and 5 had an abdominal CT performed while in the ED. One hundred children had an abdominal ultrasound and 53 had CT scans performed while hospitalized. One hundred ninety (62%) children were admitted without undergoing any radiographic examination other than the supine and upright abdominal radiographs in the ED.

View larger version (11K): [in this window] [in a new window]   Fig. 2.   Age distribution of observation cohort.

Diagnostic Value of CT

Seventy-five of the 609 total patients admitted to the hospital for suspected appendicitis had CT scans performed. The sensitivity and specificity of the scans for these patients were 97% (95% confidence interval 0.92-1.00) and 97% (95% confidence interval 0.89-1.00), respectively.

Compared with patients who did not have CT scans performed, those who did were of similar age (11.3 years vs 10.7 years; P = .26), and had similar rates of appendicitis (57% vs 59%; P = .83). The rate of perforation, however, was higher in the subgroup who had CT scans performed (97% vs 22%; P < .01).

Current Practice

Of the 308 patients in the observation cohort, 58 had abdominopelvic CT scans performed (Table 3). These children had a total of 487 days of inpatient observation. Three patients had missed appendicitis; they were discharged from the hospital after observation and then readmitted with pathologically-proven appendicitis. Two of these patients had perforated by the time of surgery. One hundred twelve eventually underwent appendectomy and 26 (23%) had a normal appendix at pathology. Forty-two (14%) were found to have perforated appendicitis at surgery or at pathology. The total cost per patient in the current practice strategy was $5831.

Three Strategies Using CT

Applying the calculated values for the sensitivity and specificity of CT to the three strategies, a baseline cost and outcomes analysis was conducted (Table 3). In the CT and home group, in which all children would have undergone CT, no patients would have been admitted for observation. In this strategy, there would have been 3 cases of missed appendicitis, and 93 total operations with 7 negative laparotomies. The total cost per patient would have been $3813, a savings of $2018 per patient compared with current practice.

In the CT and admit group, in which all patients would have undergone CT and subsequently would have been hospitalized for observation, 308 CT scans would have been performed and the cohort would have had 93 total operations with 7 negative laparotomies. Under this strategy, the cohort would have had 363 total days of observation and no cases of missed appendicitis. The total cost per patient would have been $5277, a savings of $554 per patient compared with current practice.

In the final strategy, WBC, CT, and admit, in which patients would have undergone CT scans only if they had WBC >10 000/mm³ (10 × 10⁹/L) and then admitted, there would have been 173 CT scans performed, 370 total days of observation, 2 cases of missed appendicitis, and 97 total operations with 11 negative laparotomies. The total cost per patient would have been $5140, a savings of $691 per patient compared with current practice.

All three of the above CT strategies would have reduced the number of observation days, operations, negative laparotomies, and cost per patient. The CT and admit strategy would have resulted in the lowest rate of missed appendicitis; compared with the CT and home strategy, the cost of preventing each of these cases of missed appendicitis would have been $150 304.

Sensitivity Analysis

To determine if the costs of the three strategies maintained their respective ordering even at the lowest sensitivity and specificity of CT reported in the literature, sensitivity analyses were conducted throughout a range of 80% to 100% (Fig 3A and B). The ordering of the strategies remained constant throughout the range which encompasses the reported sensitivities and specificities of CT in the literature. The current practice strategy was consistently the most expensive, whereas the CT and home strategy was the least costly.

View larger version (27K): [in this window] [in a new window]   Fig. 3.   A, Sensitivity analysis on sensitivity of computed tomography (CT). B, Sensitivity analysis on specificity of CT. C, Sensitivity analysis on cost of CT. D, Sensitivity analysis on cost of hospital observation day.

Sensitivity analyses were also conducted across a range of costs of a CT scan (Fig 3C) and of a day of inpatient observation (Fig 3D). Even if a CT scan were to cost several thousand dollars, the CT and home strategy would remain the least costly. Not until the cost of CT reaches $1650, does the CT and admit strategy become more expensive than current practice. At realistic cost estimates, the current practice strategy always dominates as the most expensive strategy. Similarly, when we varied the cost of an inpatient observation day, the current practice strategy dominated as the most expensive even if the cost of hospitalization were only $100. The CT and home strategy remained the least costly until the cost of a hospitalization day dropped to $175; at this low cost, the WBC, CT, and admit group is the least expensive. Hence, the univariate sensitivity analyses indicate that using CT scans in our cohort of observation patients would provide a net savings under any of the proposed strategies.

	DISCUSSION

Top Abstract Methods Results Discussion References

The diagnosis of appendicitis in children remains a challenge. It has been shown that in up to 20% of children with acute appendicitis, the initial diagnosis is incorrect.^39-42 Studies have also reported false-negative rates of up to 45% in patients with the clinical diagnosis of appendicitis.^43,44 Furthermore, missed appendicitis is the most frequently successful malpractice claim against emergency physicians.^39-42 Although sonography has been widely used as the primary imaging modality in children, the ability to exclude appendicitis requires visualization of the normal appendix, which is a rare occurrence with ultrasonography.^45-47 Ultrasonography propagates less confidence in a negative result and management strategies are not routinely based on negative sonographic findings. In addition, prompt diagnosis is critical because of the morbidity and mortality associated with both perforation and the surgery itself.

We have shown that diagnostic strategies using CT in children would reduce the total number of days of inpatient prediagnosis observation, operations, and negative laparotomies as well as the total cost per patient. Obtaining CT scans on all children who are candidates for inpatient observation for suspected appendicitis would reduce both morbidity and cost. A strategy in which patients with negative CT scans are admitted would result in the lowest morbidity, although there are additional costs related to hospitalization.

Emerging technologies such as focused appendiceal CT with rectal contrast have reported sensitivities even higher than that used in our model.^27-31,36 A test with these diagnostic characteristics applied to children with suspected appendicitis would reduce the rate of missed appendicitis even below the level we report. Although radiation exposure in children should clearly be minimized,⁴⁸ focused appendiceal CT involves a similar amount of radiation as supine and upright abdominal radiographs.^27,36

Our models only account for the costs and morbidity encountered during the acute episode of disease. Additional costs and morbidity, and even mortality, may be incurred by long-term complications of missed appendicitis. However, we expect the rates of all these complications to be reduced under any of the CT strategies that we present.

Our study has some limitations. First, we do not have follow-up on all patients sent home after their admission, and some may have gone on to be diagnosed with appendicitis at another institution. However, our ED sees >60% of pediatric visits in its catchment area and our hospital performs ~50% of the pediatric surgery in the Boston area.

There may have been some selection bias in the generation of the cohort of observed patients. Although we aimed to apply our testing strategy to the equivocal group most in need of improved diagnosis we were not able to prospectively define this group. Selection bias may have also affected our estimates of CT sensitivity and specificity. Because CT scan has not been applied widely in the diagnosis of appendicitis in children, we had to derive these values empirically. The sensitivity and specificity of the relatively small number of scans performed on members of the cohort may be influenced by a high prior probability of disease; we found that the children who had CT scans performed were significantly more likely to have appendiceal perforation. However, in our sensitivity analysis, the ordering of strategies remained constant throughout the entire range of reported sensitivity and specificity of CT. Thus, our model is robust, even if CT proves to perform more poorly than any previous work would suggest.

Compared with current practice, diagnostic strategies using CT applied to the appropriate patient population could improve management and outcomes and reduce costs of care for children with suspected appendicitis. The high diagnostic accuracy of CT will be optimal when the test is applied to a population of children with right lower quadrant pain and associated clinical and laboratory findings suggestive, but not classic for appendicitis. Clearly, patients at either very low or very high risk of appendicitis need not undergo additional diagnostic procedures exposing them to unnecessary radiation and contrast exposure. Moreover, the decision to use CT in the evaluation of appendicitis should be made in conjunction with an experienced pediatric surgeon.

CT has the potential to reduce the rate of unnecessary laparotomy in children without appendicitis and to expedite the time to appendectomy in those children with appendicitis. Advances in CT technology give clinicians an accurate and sensitive tool to aid in the diagnosis of appendicitis in children. Strategies using CT could markedly reduce morbidity and acute care costs associated with clinically suspected appendicitis.

	ACKNOWLEDGMENTS

We thank Dr Patrick M. Rao for his encouragement and support and Dr Gary R. Fleisher for his invaluable input and careful reading of the manuscript.

	FOOTNOTES

Received for publication Oct 15, 1998; accepted Jan 12, 1999.

Presented at the annual meeting of the Ambulatory Pediatric Association; May 3, 1998; New Orleans, LA.

Reprint requests to (B.M.G.P.) Division of Emergency Medicine, Children's Hospital, 300 Longwood Ave, Boston, MA 02215. E-mail: pena-b{at}a1.tch.harvard.edu

	ABBREVIATIONS

CT, computed tomography; ED, emergency department; WBC, white blood cell count.

	REFERENCES

Top Abstract Methods Results Discussion References

1. Lund DP, Murphy EU Management of perforated appendicitis in children: a decade of aggressive treatment. J Pediatr Surg. 1994; 29:1130-1134 [CrossRef][Medline]
2. Crady SK, Jones JS, Wyn T, Luttenton CR Clinical validity of ultrasound in children with suspected appendicitis. Ann Emerg Med. 1993; 22:1125-1129 [CrossRef][Medline]
3. Adolph VR, Falterman KW Appendicitis in children in the managed care era. J Pediatr Surg. 1996; 31:1035-1037 [CrossRef][Medline]
4. Wagner JM, McKinney WP, Carpenter JL Does this patient have appendicitis? JAMA. 1996; 276:1589-1594 [Abstract/Free Full Text]
5. Brender JD, Marcuse EK, Koepsell TD, Hatch EI Childhood appendicitis: factors associated with perforation. Pediatrics. 1985; 76:301-306 [Abstract/Free Full Text]
6. Wilcox RT, Traverso LW Have the evaluation and treatment of acute appendicitis changed with new technology? Surg Clin North Am 1997; 77:1355-1370 [CrossRef][Medline]
7. Rappaport WD, Peterson M, Stanton C Factors responsible for the high perforation rate seen in early childhood appendicitis. Am Surg. 1989; 55:602-605 [Medline]
8. Fenyo G, Lindberg G, Blind P, Enochsson L, Oberg A Diagnostic decision support in suspected acute appendicitis: validation of a simplified scoring system. Eur J Surg. 1997; 163:831-838 [Medline]
9. Lewis FR, Holcroft JW, Boey J, Dunphy JE Appendicitis: a critical review of diagnosis and treatment in 1,000 cases. Arch Surg 1975; 110:677-684
10. Wilson DH, Wilson PD, Walmsley RG, Horrocks JC, DeDombal FT Diagnosis of acute abdominal pain in the accident and emergency department. Br J Surg. 1977; 64:250-254 [Medline]
11. Dison JM, Elton RA, Rainey JB, Macleaod DAD Rectal examination in patients with pain in the right lower quadrant of the abdomen. Br Med J. 1991; 302:386-388
12. Gamal R, Moore TC Appendicitis in children aged 13 years and younger. Am J Surg. 1990; 159:589-592 [Medline]
13. Putnam TC, Gagliano N, Emmends RW Appendicitis in children. Surg Gynecol Obstet. 1990; 170:527-532 [Medline]
14. Horowitz JR, Gursoy M, Jaksic T, Lally KP Importance of diarrhea as a presenting symptom of appendicitis in very young children. Am J Surg. 1997; 173:80-82 [CrossRef][Medline]
15. Siegel MJ, Carel C, Surratt S Ultrasonography of acute abdominal pain in children. JAMA. 1991; 266:1987-1989 [Abstract]
16. Scholer SJ, Pituch K, Orr DP, Ditus RS Clinical outcomes of children with acute abdominal pain. Pediatrics. 1996; 98:680-685 [Abstract/Free Full Text]
17. Wade DS, Marrow SE, Balsara ZN, Accuracy of ultrasound in the diagnosis of acute appendicitis compared with the surgeon's clinical impression. Arch Surg. 1993; 128:1039-1044 [Abstract]
18. Dueholm S, Bagi P, Bud M Laboratory aid in the diagnosis of acute appendicitis. Dis Colon Rectum. 1989; 32:855-859 [Medline]
19. Skaane P, Schistad O, Amland PF, Solheim K Routine ultrasonography in the diagnosis of acute appendicitis: a valuable tool in daily practice? Am Surg. 1997; 63:937-942 [Medline]
20. Whilte JJ, Santillana M, Haller JA Intensive in-hospital observation: a safe way to decrease unnecessary appendectomy. Am Surg. 1975; 41:793-798 [Medline]
21. Nauta RI, Magnant C Observation versus operation for abdominal pain in the right lower quadrant: roles of the clinical examination and the leukocyte count. Am J Surg. 1986; 151:746-748 [CrossRef][Medline]
22. Graff L, Radford MJ, Werne C Probability of appendicitis before and after observation. Ann Emerg Med. 1991; 20:503-507 [CrossRef][Medline]
23. Senbanjo RO Management of patients with equivocal signs of appendicitis. J R Coll Surg Edinb. 1997; 42:85-88 [Medline]
24. Korner H, Sondenaa K, Soreide JA, Incidence of acute nonperforated and perforated appendicitis: age-specific and sex-specific analysis. World J Surg. 1997; 21:313-317 [CrossRef][Medline]
25. Puylaert JBCM, Rutgers PH, Lalisang RI, A prospective study of ultrasonography in the diagnosis of appendicitis. N Engl J Med. 1987; 317:666-669 [Abstract]
26. Rhea JT, Rao PM, Novelline RA, McCabe CJ A focused appendiceal CT technique to reduce the cost of caring for patients with clinically suspected appendicitis. AJR Am J Roentgenol. 1997; 169:113-118 [Abstract/Free Full Text]
27. Rao PM, Rhea JT, Novelline RA, Helical CT technique for the diagnosis of appendicitis: prospective evaluation of a focused appendix CT examination. Radiology. 1997; 202:139-144 [Abstract/Free Full Text]
28. Rao PM, Rhea JT, Novelline RA, McCabe CJ The computed tomography appearance of recurrent and chronic appendicitis. Am J Emerg Med. 1998; 16:26-33 [CrossRef][Medline]
29. Rao PM, Rhea JT, Novelline RA, Mostafavi AA, Lawrason JN, McCabe CJ Helical CT combined with contrast material administered only through the colon for imaging of suspected appendicitis. AJR Am J Roentgenol. 1997; 169:1275-1280 [Abstract/Free Full Text]
30. Rao PM, Rhea JT, Novelline RA Sensitivity and specificity of the individual CT signs of appendicitis: experience with 200 helical appendiceal CT examination. J Comput Assist Tomogr. 1997; 21:686-692 [CrossRef][Medline]
31. Rao PM, Rhea JT, Novelline RA Appendiceal and periappendiceal air at CT: prevalence, appearance, and clinical significance. Clin Radiol. 1997; 52:750-754 [CrossRef][Medline]
32. Taourel P, Baron MP, Predel J, Fabre JM, Seneterre E, Bruel JM Acute abdomen of unknown origin: impact of CT on diagnosis and management. Gastrointest Radiol. 1992; 17:287-291 [CrossRef][Medline]
33. Balthazar EJ, Birnbaum BA, Yee J, Megibow AJ, Roshkow J, Gray C Acute appendicitis: CT and US correlation in 100 patients. Radiology 1994; 190:31-35 [Abstract/Free Full Text]
34. Birnbaum BA. CT evaluation of patients with acute lower abdominal pain. In: Balfe DM, Levine MS, eds. RSNA 1997 Syllabus. Categorical Course in Diagnostic Radiology: Gastrointestinal. Oak Brook, IL: RSNA Publications; 1997:199-209
35. Balthazar EJ, Megibow AJ, Siegel SE, Birnbaum BA Appendicitis: prospective evaluation with high-resolution CT. Radiology 1991; 180:21-24 [Abstract/Free Full Text]
36. Rao PM, Rhea JT, Novelline RA, Mostafave AA, McCabe CJ Effect of computed tomography of the appendix on treatment of patients and use of hospital resources. N Engl J Med. 1998; 338:141-146 [Abstract/Free Full Text]
37. Rao PM, Rhea JT, Novelline RA CT diagnosis of mesenteric adenitis. Radiology. 1997; 202:145-149 [Abstract/Free Full Text]
38. Gold MR, Siegel JE, Russell LB, Weinstein MC. Cost-effectiveness in Health and Medicine. New York, NY: Oxford University Press; 1996:205
39. Reynolds SL Missed appendicitis in a pediatric emergency department. Pediatr Emerg Care. 1993; 9:1-3 [CrossRef][Medline]
40. Trautlein JJ, Lambert RL, Miller J Malpractice in the emergency departmentreview of 200 cases. Ann Emerg Med. 1984; 13:709-711 [CrossRef][Medline]
41. Rothrock SG, Skeoch G, Rush JJ, Johnson NE Clinical features of misdiagnosed appendicitis in children. Ann Emerg Med. 1991; 20:45-50 [Medline]
42. Rusnack RA, Borer JM, Fastow JS Misdiagnosis of acute appendicitis:common features discovered in cases after litigation. Am J Emerg Med. 1994; 12:397-402 [CrossRef][Medline]
43. Izbicki JR, Knoefel WT, Wilker DK, Accurate diagnosis of acute appendicitis: a retrospective and prospective analysis of 686 patients. Eur J Surg. 1992; 158:227-231 [Medline]
44. Berry J Jr, Malt RA Appendicitis near its centenary. Ann Surg. 1984; 200:567-575 [Medline]
45. Skaane P, Amland PF, Nordshus T, Solheim K Ultrasonography in patients with suspected acute appendicitis: a prospective study. Br J Radiol. 1990; 63:787-793 [Abstract]
46. Jeffrey RB, Laing FC, Townsend RR Acute appendicitis: sonographic criteria based on 250 cases. Radiology. 1988; 167:327-329 [Abstract/Free Full Text]
47. Puylaert JB Imaging and intervention in patients with acute right lower quadrant disease. Baillieres Clin Gastroenterol. 1995; 9:37-51 [CrossRef][Medline]
48. McColl I More precision in diagnosing appendicitis. N Engl J Med. 1998; 338:190-191 [Free Full Text]