INTRALUMINAL GAS IN NON-PERFORATED ACUTE APPENDICITIS: A predictor of gangrenous appendicitis

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1 INTRALUMINAL GAS IN NON-PERFORATED ACUTE APPENDICITIS: A predictor of gangrenous appendicitis DM Plata Ariza, MD; E Martínez Chamorro, MD; D Castaño Pardo, MD; M Arroyo López, MD; E Peghini Gavilanes, MD; S Borruel Nacenta, MD. Emergency Radiolody Section, Department of Radiology 12 de Octubre Hospital, Madrid, Spain.

2 INTRODUCTION Acute appendicitis is recognized as the most frequent cause of nontraumatic surgical abdominal pain. Although there are some typical and frequent clinical manifestations, the possibilities of a wide variety of symptoms with atypical presentations and symptoms that can be very subtle at the beginning of the process make the diagnosis difficult in some patients. Therefore it is important that when the diagnosis remains unclear a imaging technique is required to do a prompt diagnosis and to support the surgical decision minimizing morbidity and mortality, which are higher when gangrene and perforation occurs, with consequent increase in hospitalization stay and higher costs to the health system. There are several radiographic signs of acute appendicitis at CT and many studies have focused on identifying signs to difference perforated from non-perforated appendicitis (1-4).

3 INTRODUCTION However, few studies have focused on differentiating gangrenous appendicitis from phlegmonous appendicitis at CT and this could have implications for the management, complications and prognosis of the patient. The computed tomography has an important role as the standard imaging test with a reported sensitivity and specificity of 87% - 99% and 92% - 99% respectively (1). Traditionally intraluminal appendicular air in abdominal plain radiography has been identified as a sign indicating a patent lumen and thus a normal finding in most of the cases and some studies described that US-based detection of gas within the appendix helps to rule out acute appendicitis (5). However, some studies have reported intraluminal appendicular gas at plain radiography and at CT in both, the normal and the inflamed appendix (6,7).

4 PURPOSE -To determine if the presence of gas within the appendix at CT in the context of proven appendicitis correlates with a gangrenous appendix by using pathologic/surgery examination as the reference standard. - To compare the differences in length of hospital stay between the groups of phlegmonous and gangrenous appendicitis as an indicator of hospital costs.

5 METHOD AND MATERIALS PATIENTS We retrospectively reviewed the charts of 1249 adult patients with pathologically proven appendicitis. We had obtained from our hospital information system a list of all patients who had undergone appendicectomy and pathologic examination of the appendix during a 45-month period, between January 2009 and September Of the all patients listed 197 underwent MDCT examination. Patients with classic perforated appendicitis CT findings (phlegmon, extraluminal air, abscess, extraluminal appendicolith, and focal defect in enhancing appendiceal wall) were excluded (93 cases), this in order not to include cases that obviously have gangrene and perforation. This elimination resulted in a final study population of 104 patients who underwent preoperative abdominal multidetector CT (MDCT) and had an appendicitis pathological outcome (Fig 1).

6 Proven acute appendicitis 1249 patients Preoperative MDCT 197 patients No MDCT 1052 patients Patients excluded MDCT signs of perforated appendicitis 93 patients FINAL STUDY GROUP 104 patients Figure 1. Flow diagram of patients exclusions leading to selection of final study group. MDCT: multidetector CT.

7 METHOD AND MATERIALS CT TECHNIQUE All CT examinations were performed using a 16-slice CT scanner. Scanning parameters included slice thickness 3 mm with 1,5 -mm image reconstruction and, in some cases, multiplanar reconstructions were performed. There was no special preparation before the CT. The use of oral/rectal contrast medium was not routinely administered except in some cases depending on the clinical history provided (oral contrast was administrated to eight patients and rectal contrast to one) and the examinations were performed with intravenous contrast medium unless there were contraindications or technical problems in its administration. Intravenous non-ionic contrast media was administered to eighty-eight patients and it was injected at a rate of 3 ml/sec, with image acquisition performed in the portal venous phase with a 70-second scanning delay.

8 METHOD AND MATERIALS DATA INTERPRETATION 104 MDCT-scans of patients with radiological findings and pathologically proven appendicitis were reviewed and classified in two groups depending on the presence of air in the appendix after a consensus by 2 senior radiologists and 1 resident. Results were compared to surgical and pathological reports looking for a gangrenous or phlegmonous appendix. Both, surgical and pathology reports combined, were considered the reference standard to determine gangrene. Then we reviewed the length of hospital stay by groups and the results were analyzed by comparing the mean hospital stay with the pathology outcome. All reviewed images were considered to be of diagnostic quality and all patients had CT signs of non-perforated appendicitis. STATISTICAL ANALYSIS Odds ratios, sensitivity, specificity and predictive values with 95% confidence intervals for intraluminal gas as sign of gangrenous appendicitis were determined. Statistical analysis used Fisher s exact test and p value < 0.05 was considered statistically significant.

9 RESULTS Our study population consisted of 104 patients, there were 58 male and 46 female patients and the mean age was 40 years (range, years). There were 25 patients with intraluminal appendiceal gas (24%) and a majority group of 79 patients without intraluminal gas (76%). Gangrenous appendicitis was present in 21 of the group of 25 patients with nonperforated appendicitis that contained gas, whereas such finding was present in 7 patients of the 79 without intraluminal gas (84% vs 9%, p < ) (Fig. 2).

10 Figure 2. Graph illustrates the distribution of patients with gangrenous or phlegmonous appendicitis depending on the presence of intraluminal appendicular gas at MDCT.

11 RESULTS By using the presence of appendix with intraluminal gas at CT in patients with other radiological findings of non-perforated acute appendicitis the sensitivity of detecting gangrenous appendicitis was 75% (60-84 %) with a specificity of 94% (89-98%) and positive and negative predictive values of 84 % (67 94 %) and 91% (86 94%) respectively. The presence of intraluminal gas showed an odds ratio for gangrenous appendicitis of 54 (12-262) and a positive likelihood ratio of 14.2 ( ) with an association between intraluminal appendiceal gas in patients with proven appendicitis and gangrenous pathologic/surgical outcome statistically significant (p < 0.01). The mean hospital stays were 2,5 and 5 days for phlegmonous and gangrenous appendicitis, respectively.

12 a. a. c. c. d. b. b. e. Figure 3. Coronal (a), sagital (b) and consecutive axial (c e) MDCT images with intravenous contrast medium in 40 year-old man with nonperforated appendicitis (histopathological report) showing a dilated appendix with intraluminal gas (yellow arrows), fat stranding and a three intraluminal appendicoliths (one is not on the picture) (red arrowheads). The final result was gangrenous appendicitis.

13 b. b. a. a. Figure 4. Appendicitis in a 63-year-old woman. Sagital (a) and axial (b-c) MDCT images with intravenous contrast media show a dilated appendix (red arrowheads) with intraluminal gas (yellow arrows), hyperenhancement of appendicular wall and adjacent fat stranding. Gangrenous appendicitis was the final outcome. c. c.

14 b. b. a. a. Figure 5. MDCT with intravenous contrast medium in a 33 year-old man with acute gangrenous appendicitis (histopathological outcome). Coronal (a-b) and axial (c) images of the dilated appendix with intraluminal gas bubbles (yellow arrows), fat stranding and free fluid adjacent to the appendix. c. c.

15 a. b. a. b. c. d. e. c. d. e. Figure 6. Appendicitis in a 39 years-old man. MDCT with intravenous contrast medium. Coronal (a), sagital (b) and axial (c-e) images showing a dilated appendix gas filled (yellow arrows) with a minimal adjacent fat affectation. The final outcome was gangrenous appendicitis.

16 a. a. c. c. b. d. b. d. Figure 7. MDCT images with intravenous contrast medium in two different patients with acute appendicitis. (a-b) Coronal and axial images in 39 years-old woman and (c-d) sagital and axial images in 17 years-old man showing CT signs of acute appendicitis with intraluminal appendicular gas (yellow arrows) and appendicolith (red arrowheads) (c-d). However the histopathological diagnosis was phlegmonous appendicitis in both cases. These are two examples of false positive cases found in the study.

17 CONCLUSION In patients with CT signs of non-perforated appendicitis the presence of gas within the appendix strongly suggests gangrenous appendicitis. Length of hospital stay is longer in gangrenous appendicitis and may generate higher hospital costs. CLINICAL RELEVANCE Gangrene is a step prior to perforation, with higher morbidity and longer hospitalization time. CT signs of gangrene help surgeons to avoid delays in surgery, complications and a longer hospital stay.

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