Abdominal Imaging

© Springer Science⫹Business Media, Inc., 2004 Abdom Imaging (2004) 29:658 – 662 Received: 14 November 2003 / Accepted: 19 December 2003 / Published online: 27 May 2004 DOI: 10.1007/s00261-003-0159-y

Multidetector-row CT findings of colonic perforation: direct visualization of ruptured colonic wall T. Miki,1 S. Ogata,2 M. Uto,2 T. Nakazono,2 M. Urata,2 R. Ishibe,2 S. Shinyama,3 M. Nakajo4 1

Department of Radiology, Sendai Citizen Hospital, Japan Department of Surgery, Sendai Citizen Hospital, Japan 3 Department of Pediatric Surgery, Sendai Citizen Hospital, Japan 4 Department of Radiology, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshimashi, Kagoshima 890-8520, Japan 2

Abstract Background: We examined the findings of contrast-enhanced multidetector-row computed tomography (MD-CT) in patients with colonic perforation. Methods: Abdominal contrast-enhanced MD-CT findings in six patients with colonic perforation were reviewed retrospectively. Patients (three men and three women) were 74 to 88 years old (mean age ⫽ 78 years). Colonic perforation was confirmed by surgery. CT findings were correlated with surgical and pathologic findings. Result: The site of colonic perforation was suggested by the following combination of CT findings: free air, dirty mass, dirty fat sign, extraluminal fluid collection, bowel wall thickening, and interruption of colonic wall. The ruptured colonic wall was directly visualized in four cases (67%). Conclusion: Abdominal contrast-enhanced MD-CT may improve the accuracy of diagnosis and localization of colonic perforation. Key words: Colon, perforation—Multidetector-row computed tomography, acute abdomen—Computed tomographic findings Colonic perforation is a life-threatening complication of the colonic diseases, and it requires early recognition and treatment. Preoperative diagnosis is sometimes difficult because of nonspecific clinical findings, and free air is found on only 30% to 59% of plain radiographs [1– 6]. Abdominal computed tomography (CT) is clearly superior to plain radiographs in demonstrating free air and is useful to diagnose Correspondence to: T. Miki; email: [email protected]

colonic perforation [1, 3, 4, 7–9]. Yet, there are only few reports dealing with the CT diagnosis of colonic perforation site [10, 11]. We reviewed six patients with colonic perforation who underwent multidetector-row CT (MD-CT) and examined the CT findings of free air, dirty mass, dirty fat sign, extraluminal fluid collection, bowel wall thickening around the perforation site, and interruption of colonic wall. These findings demonstrate the site of perforation and may help in the diagnosis and management of colonic perforation.

Materials and methods The study population consisted of six patients (three men and three women; average age, 78 years; age range, 74 – 88 years) with colonic perforation who underwent plain abdominal radiography and MD-CT before surgery at Sendai Citizen Hospital between December 2001 and November 2002. Table 1 provides a summary. The causes of colonic perforation were carcinoma in two cases, ischemia in two, diverticulum in one, and idiopathic in one. The sites of perforation were the sigmoid colon in four cases, ascending colon in one, and descending colon in one. Preoperative blood leukocyte levels were decreased and operations were performed in all cases, and two patients died. Plain abdominal radiograms were obtained in four patients in the supine position and two patients in the upright position. CT scans were obtained with the Aquilion CT scanner (Toshiba, Tokyo, Japan) using 0.5 s/rotation, helical pitch of 5.5, 2-mm thickness, and 7-mm thickness reconstruction. Contrast medium was administered intravenously to all patients. One hundred milliliters of iodinated contrast material (Iopamidol 300) was injected at a rate of 2 mL/s by a power

T. Miki et al.: MD-CT findings of colonic perforation

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Table 1. Summary of six patients with colonic perforation Case no.

Age (years)

Sex

Cause of perforation

Level of perforation

Width (mm) of perforated leak

Leukocyte (␮l)

Prognosis

1 2 3 4 5 6

76 88 75 77 75 74

F F M M M F

Ischemia Idiopathic Carcinoma Carcinoma Diverticulum Ischemia

Sigmoid colon Sigmoid colon Descending colon Ascending colon Sigmoid colon Sigmoid colon

20 40 4 6 15 8

1700 1900 3600 900 2000 1600

Improved Improved Improved Died Improved Died

injector. The scanning delay was 90 s. If necessary, 2-mm thickness reconstruction and multiplanar reconstruction (MPR) were performed. Plain radiographic and CT images were analyzed retrospectively by two radiologists. The analyzed finding was free air on plain radiography. With regard to the CT findings, the following six findings were analyzed: free air, dirty mass, dirty fat sign, extraluminal fluid collection, bowel wall thickening around the perforation site, and interruption of the colonic wall (Figs. 1–3). A dirty mass indicates a focal collection of extraluminal fecal matter containing small air bubbles [1]. The dirty fat sign is a diffuse increase in attenuation of mesenteric fat [12]. Interruption of the colonic wall is the direct visualization of bowel wall discontinuity [11]. We also examined the location of free air and the relation between the width of the colonic perforation orifice and findings such as interruption of the colonic wall and dirty mass. Interpretation was made by consensus of two radiologists.

Results Plain abdominal radiographs depicted free air in two of six cases (33%). Free air was identified in the right upper quadrant in case 4 and under the right hemidiaphragm in case 5. In contrast, MD-CT depicted free air in six of six cases (100%), dirty mass in five (83%), dirty fat sign in six (100%), extraluminal fluid collection in six (100%), bowel wall thickening around the perforation site in six (100%), and interruption of colonic wall in four (67%; Table 2). Free air was present in four cases of sigmoid colon perforations (cases 1, 2, 4, and 5); around the liver in three (75%), around the stomach in three (75%), in the mesentery in four (100%), in the pelvis in four (100%), and in the retroperitoneum in two (50%). Free air was present in the retroperitoneum in one case of ascending colon perforation (case 6) and in the mesentery in one case of descending colon perforation (case 3; Table 3). The mean widths of the colonic perforation orifice were 20 mm (range, 6 – 40 mm) in four cases with interruption of the colonic wall (cases 1, 2, 4, and 5) and 6 mm (range, 4 – 8 mm) in two cases without this finding (cases 3 and 6). The mean widths of the colonic perforation orifice were 18 mm (6 – 40 mm) in five cases with dirty mass (cases 1, 2, and 4 – 6) and 4 mm in one case without this finding (case 3).

Fig. 1. Ascending colon perforation caused by carcinoma in a 77-year-old man. A Contrast-enhanced MD-CT demonstrates interruption of thickened and well-enhanced ascending colon wall (arrow). Extraluminal fluid collection (arrowhead) and free air (curved arrow) are also noted around the ascending colon. B MPR clearly demonstrates interruption of the ascending colon (arrow).

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Fig. 2. Sigmoid colon perforation caused by diverticulum in a 75-year-old man. A Free air (arrow) and extraluminal fluid collection (arrowhead) are noted in the subphrenic space. B Contrast-enhanced MD-CT demonstrates interruption of thickened sigmoid colon wall (arrow). A dirty mass (arrowhead) is noted near the site of perforation.

The site of perforation was directly visualized as a discontinuity in the colonic wall in four cases (cases 1, 2, 4, and 5). In another case (case 3), the perforation site was suggested by a mass in the descending colon and the dirty fat sign and extraluminal fluid collection around the mass. In another case (case 6), a dirty mass near the thickened sigmoid colon wall suggested the site of perforation. Thus, the site of colonic perforation was localized in all cases by the findings of MD-CT.

Discussion Perforation is a life-threatening complication of most colonic diseases and occurs in patients of all ages. Acute perforation causes fecal peritonitis, which may be localized or diffuse. Despite aggressive surgical and medical management, fecal peritonitis is associated with high rates of morbidity and mortality [5]. In fact, preoperative blood leukocyte levels

T. Miki et al.: MD-CT findings of colonic perforation

Fig. 3. Idiopathic perforation of the sigmoid colon in an 88-year-old woman. A Although 7-mm slice thickness contrast-enhanced MD-CT demonstrates thickened bowel wall (arrow), a dirty mass (arrowhead), and dirty fat (curved arrow), interruption of the colonic wall is not clear. B Reconstruction MD-CT with 2-mm slice thickness clearly demonstrates interruption of the colonic wall (arrow), the dirty mass (arrowhead), and dirty fat sign (curved arrow). Table 2. Computed tomographic findings of colonic perforation Case no.

Free air

Dirty mass

Dirty fat sign

Extraluminal fluid collection

Bowel wall thickning

Interrupted colonic wall

1 2 3 4 5 6

⫹ ⫹ ⫹ ⫹ ⫹ ⫹

⫹ ⫹ ⫺ ⫹ ⫹ ⫹

⫹ ⫹ ⫹ ⫹ ⫹ ⫹

⫹ ⫹ ⫹ ⫹ ⫹ ⫹

⫹ ⫹ ⫹ ⫹ ⫹ ⫹

⫹ ⫹ ⫺ ⫹ ⫹ ⫺

were decreased in our six cases who were thought to be septic or nearly septic. Surgery was performed in all six cases and two (33%) died. When perforation of the alimentary tract is suspected, the first examination should search for free air on a standard upright or lateral abdominal radiograph in addition to a supine radiograph, even though it is well known that perforation quite often gives no radiologic signs [4]. In fact, we noted free air in two of six our patients. In clinical practice,

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Table 3. Location of free air in six patients with colonic perforation Level of perforation

Around liver

Around stomach

Mesentery

Pelvis

Retroperitoneum

Sigmoid colon Ascending colon Descending colon

3/4 (75%) 0/1 (0%) 0/1 (0%)

3/4 (75%) 0/1 (0%) 0/1 (0%)

4/4 (100%) 0/1 (0%) 1/1 (100%)

4/4 (100%) 0/1 (0%) 0/1 (0%)

2/4 (50%) 1/1 (100%) 0/1 (0%)

however, many patients with acute abdomen are too sick or debilitated to stand or lie on their sides, so that a supine abdominal radiograph may be the only film obtained. Supine radiography also may demonstrate pneumoperitoneum but lacks sensitivity when compared with upright or left lateral decubitus radiography [6]. Miller and Nelson showed that as little as 1 to 2 mL of free intraperitoneal air can be detected by plain chest radiography in the upright position [13]. However, overall, plain radiography demonstrates free air in 30% to 59% of alimentary tract perforations [1– 6]. However, plain radiography is limited in depicting free air caused by colonic perforation. In contrast, CT demonstrates free air in 70% to 100% of alimentary tract perforations [1, 3, 4]. In our six cases, free air was found in all of them: around the liver in three (50%), around the stomach in three (50%), in the mesentery in five (83%), in the pelvis in four (75%), and in the retroperitoneum in three (50%; Table 3). Maniatis et al. [14] summarized the correlation between the location of free intraabdominal air and the site of perforation: (a) upper alimentary tract and small bowel perforations are the main sources for free air around the liver; (b) air around the stomach may be due to gastric, sigmoid colon, or duodenal rupture; (c) gastric perforation is not correlated with mesenteric free air, in contrast to the rest of the gastrointestinal tract; (d) colon perforation is almost always the explanation for free air in the pelvis; (e) retropneumoperitoneum is caused by duodenum and colonic ruptures; and (f) free air in the pelvis and around the liver implicates the sigmoid colon as the source. The location of free air is an important indirect CT finding to localize the site of the alimentary tract perforation. The other CT findings observed in colonic perforation were: dirty mass, dirty fat sign, extraluminal fluid collection, and bowel wall thickening around the perforation site [1, 8]. We observed these CT findings in our six cases: dirty mass in five (83%), dirty fat sign in six (100%), extraluminal fluid collection in six (100%), and bowel wall thickening around the perforation site in six (100%). These findings on conventional CT were reported in 29 cases by Saeki et al. [1]: dirty mass in 15 (52%), dirty fat sign in 18 (62%), extraluminal fluid collection in 16 (55%), and bowel wall thickening around the perforation site in 13 (49%). MD-CT seems to detect such CT findings of colonic perforation more frequently than conventional CT. Ongolo-Zogo et al. [15] reported a new direct CT finding of acute gastroduodenal peptic ulcer perforation: interruption of the enhanced gastroduodenal wall marked by a hypodense

line perpendicular to the gastroduodenal wall. Mirvis et al. [11] reported direct visualization of bowel wall discontinuity in three cases after blunt abdominal trauma. In our study, the finding of interruption of the colonic wall was observed in four cases (67%). This is a direct finding of colonic perforation indicating the perforation site. In another case (case 3), the perforation site was suggested by a mass due to carcinoma of the descending colon and to dirty fat sign and extraluminal fluid collection around the mass. In another case (case 4), a dirty mass near the thickened sigmoid colon wall suggested the site of perforation. In our study, the colonic perforation site could be identified in all cases by MD-CT. The thinner collimation of MD-CT may improve visualization of CT findings suggesting colonic perforation. The use of thin-section MD-CT should increase their recognition by decreasing motion and volume averaging [16]. Reconstruction with 2-mm thickness (Fig. 3) and MPR (Fig. 1) clearly visualized interruption of the colonic wall when compared with routine axial images using 7-mm thickness. We studied the relation between the width of the colonic perforation orifice and findings such as interruption of the colonic wall and dirty mass. The ruptured colon wall was directly visualized on MD-CT when the orifice was 6, 15, 20, and 40 mm (average, 20 mm) in width and was not visualized when the orifice was 4 and 8 mm in width. The dirty mass was visualized when the orifice was 6, 8, 15, 20, and 40 mm (average, 18 mm) in width and was not noted when it was 4 mm in width. Thus, the CT findings of a ruptured wall and a dirty mass may suggest that the perforation orifice is relatively large. This small retrospective study cannot allow any definite conclusions in terms of the sensitivity or specificity of MD-CT for the diagnosis of colonic perforation and localization of the perforation site. However, we believe that contrast-enhanced MD-CT improves the diagnostic accuracy of colonic perforation. References 1. Saeki M, Hoshikawa Y, Miyazaki O, et al. (1998) Computed tomographic analysis of colonic perforation: “dirty mass,” a new computed tomographic finding. Emerg Radiol 5:140 –145 2. Wood CD (1977) Acute perforation of the colon. Dis Colon Rectum 20:126 –129 3. Stapakis JC, Thickman D (1992) Diagnosis of pneumoperitoneum: abdominal CT vs. upright chest film. J Comput Assist Tomogr 16:713– 716 4. Schneider PA, Hauser H (1982) Diagnosis of alimentary tract perforation by CT. Eur J Radiol 2:197–201 5. Lozon AA, Duff JH (1976) Acute perforation of the colon. Can J Surg 19:48 –51

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