(Radiology. 2000;216:712-717.)
© RSNA, 2000
Segmental Wall Thickening in the Colonic Loop Distal to Colonic Carcinoma at CT: Importance and Histopathologic Correlation1
Hyun-Jung Jang, MD,
Hyo K. Lim, MD,
Cheol Keun Park, MD,
Seong Hyun Kim, MD,
Jong Min Park, MD and
Yoon-La Choi, MD
1 From the Departments of Radiology (H.J.J., H.K.L., S.H.K., J.M.P.) and Diagnostic Pathology (C.K.P., Y.L.C.), Sungkyunkwan University School of Medicine, Samsung Medical Center, 50, Ilwon-dong, Kangnam-ku, Seoul, 135-710, Korea. Received October 14, 1999; revision requested November 6; revision received December 14; accepted December 21. Address correspondence to H.K.L. (e-mail: hklim@smc.samsung.co.kr).
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ABSTRACT
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PURPOSE: To determine the importance of the finding of segmental wall thickening in the colonic loop distal to colonic carcinoma at computed tomography (CT) by means of histopathologic correlation.
MATERIALS AND METHODS: Thirteen consecutive patients whose helical CT scans showed segmental wall thickening (>1 cm in maximal width, >5 cm in length) in the colonic loop distal to colonic carcinoma were included. The thickness and length of an involved segment, location, morphologic tumor type, CT patterns of wall thickening, and pericolic changes were evaluated. Surgical pathologic findings in all 13 patients were correlated with CT findings.
RESULTS: The involved segment distal to the colonic carcinoma showed circumferential wall thickening with a preserved wall layer pattern at CT. Pericolic changes of varying degrees were seen in 10 patients. Histopathologic examination revealed submucosal and subserosal edema (n = 6), chronic inflammation and fibrosis (n = 5), or both (n = 1), and no histopathologic alteration (n = 1). The tumors were mostly fungating (n = 11), larger than 5 cm in the greatest dimension (n = 12), located in the ascending colon (n = 10), and extended to pericolic adipose tissue (n = 11).
CONCLUSION: Colonic carcinoma, especially a large fungating type involving the ascending colon with pericolic infiltration, can produce segmental wall thickening in the distal segment at CT, which represents edema or colitis at histopathologic examination.
Index terms: Colitis, 75.26 • Colon, CT, 75.12112, 75.12115 • Colon, diseases, 75.26, 75.321 • Colon, neoplasms, 75.321
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INTRODUCTION
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Computed tomography (CT) generally is used as a routine preoperative examination in patients with known colonic carcinoma, and it is important to determine accurately the extent of a tumor in planning surgery (1). Wall thickening of the segment proximal to colonic carcinoma, or obstructive colitis, is a well-known condition both radiologically and pathologically (2–5). Information about the extent of such diseased bowel loops at CT is also crucial in planning surgery because of the frequent anastomotic complications (2–5).
During CT interpretation in routine practice, we have encountered segmental wall thickening of the colonic loop distal to colonic carcinoma. To our knowledge, there have been no descriptions regarding this finding. The clinical importance of the finding is therefore unknown, and the interpretation of the finding may be varied—submucosal spread of the tumor, underlying inflammatory bowel disease, concomitant acute colitis or ischemic colitis, or pseudothickening.
The purpose of this study was to introduce the CT finding of segmental wall thickening distal to colonic carcinoma and to clarify its importance by means of histopathologic correlation.
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MATERIALS AND METHODS
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Patient Selection
We searched the medical record database of our institution for the period from March 1998 to May 1999 for patients with surgically proved colonic carcinoma. Among them (n = 192), using our radiology information system, we obtained a list of 133 consecutive patients who underwent contrast medium–enhanced abdominal and pelvic CT within 1 week before surgery.
Two experienced abdominal radiologists (H.J.J., H.K.L.) together retrospectively reviewed helical CT scans in these 133 patients. There were 13 patients (seven men, six women; age range, 29–87 years; mean age, 60 years) whose CT scans showed segmental wall thickening (>1 cm in maximal width, >5 cm in length) in the colonic loop distal to colonic carcinoma. These 13 patients formed the study group. The abnormal thickening of the distal segment was mentioned in our initial CT reports in 11 patients. Various possibilities had been suggested for the finding: intramural spread of the tumor, concomitant ischemic colitis, or both (n = 6); nonspecific thickening or pseudothickening at CT (n = 3); misdiagnosis of colonic carcinoma as inflammatory bowel disease (n = 1); or carcinoma associated with possible underlying ulcerative colitis (n = 1).
CT and Barium Enema Examination Techniques
All CT examinations were performed with a helical CT scanner (HiSpeed Advantage; GE Medical Systems, Milwaukee, Wis). The upper abdomen from the level of the hepatic dome to the inferior tip of the liver was scanned with a helical mode: 7-mm collimation at a pitch of 1 and 7-mm reconstruction intervals. The rest of the abdomen and pelvis were scanned with a clustered data acquisition mode: 5-mm collimation and 5-mm interval.
The patient drank 600 mL of 2.5% diluted diatrizoate sodium and diatrizoate meglumine mixture (Gastrografin; Schering, Berlin, Germany) 50–60 minutes before scanning and an additional 300 mL immediately before CT scanning. CT scanning was started 70 seconds after the start of intravenous injection of 120 mL of iopromide (Ultravist 300; Schering) at a rate of 2.5 mL/sec. Water was administered per rectum in 11 of the 13 patients.
Barium enema radiographs were available in 12 of the 13 patients. The studies were performed by using single- (n = 2) or double- (n = 10) contrast techniques, and they had been performed 4–23 days before surgery.
Analysis
CT images in all patients were reviewed by means of consensus by the two radiologists (H.J.J., H.K.L.) for the thickness and length of the involved segment, location, morphologic type of the tumor, CT patterns of wall thickening, and pericolic changes. The readers were aware of formal pathology reports at the time of surgery and barium enema examination findings. The wall thickness was measured at the maximal magnification on a 2,000 x 2,000 picture archiving and communication system, or PACS, monitor (GE Medical Systems Integrated Imaging Solutions, Mt Prospect, Ill). The length was estimated by evaluating all CT sections that showed the thickened segment distal to the colonic carcinoma. The transition point of tumor and nontumorous thickening was determined by comparing CT findings with the site of the tumor seen at barium enema examination and the size described on the pathology report.
CT patterns of wall thickening were evaluated in terms of the preserved wall layer pattern (inner high attenuation, middle low attenuation, and outer high attenuation) and attenuation of the predominantly thickened layer: markedly hypoattenuating, slightly hypoattenuating to the enhancing mucosa, or as hyperattenuating as the enhancing mucosa. These patterns of wall thickening also were assessed regarding the segment proximal to the colonic carcinoma when the proximal segment was thickened at CT.
Pericolic changes were assessed regarding pericolic infiltration and venous engorgement around both the tumor and the thickened distal segment. Pericolic infiltration was graded as follows: severe, areas of soft-tissue attenuation around the colonic wall and adjacent fascial thickening; mild, pericolic haziness or thick pericolic strands; equivocal, a few thin pericolic strands; or absent. Venous engorgement was indicated by the presence of well-enhancing (equal to the enhancement of the aorta) linear or round structures in the pericolic space.
Barium enema radiographs were evaluated with the focus on the presence or absence of abnormality in the segment distal to the colonic carcinoma and the findings in and length of the abnormal segment when present.
The pathology reports focused on the extent of colonic carcinoma, and the findings in the distal segment were not mentioned except in one case. Histopathologic findings in surgical specimens in all patients thus were reviewed retrospectively by one experienced pathologist (C.K.P.) with a special emphasis on changes in the segment distal to the colonic carcinoma as follows: the presence or absence of wall thickening, the predominantly affected layer, pericolic changes, and any other frequent findings. Characteristics of primary tumors and changes in the segment proximal to the colonic carcinoma when thickened at CT also were evaluated.
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RESULTS
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The imaging and histopathologic findings in the 13 patients are summarized in the Table.
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Imaging and Histopathologic Findings of Colonic Carcinoma and Associated Thickening of the Colonic Segment Distal to the Colonic Carcinoma in 13 Patients
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Imaging Findings
The tumor was seen most commonly (n = 11) as a bulky polypoid mass expanding the colonic lumen and obscuring the wall layer pattern with heterogeneous contrast enhancement at CT. The remaining two cases showed segmental wall thickening with contrast enhancement and obliteration of the wall layer pattern. Pericolic infiltration and venous engorgement around the tumor were seen in 12 and 11 patients, respectively. The tumors were located most commonly in the ascending colon (n = 9).
The distal segments showed circumferential wall thickening 1.1–1.6 cm (mean, 1.3 cm) in maximal thickness and 5–15 cm (mean, 9 cm) in length at CT. The wall layer pattern was preserved in all 13 patients at CT. Wall thickening predominantly affected the middle layer, the attenuation of which was markedly hypoattenuating (n = 5) or slightly hypoattenuating (n = 8). No patient showed hyperattenuation. Pericolic infiltration around these segments was severe in four, mild in one, equivocal in five, and absent in the three remaining patients. Venous engorgement was seen in six patients. Wall thickening of the colonic loop proximal to the colonic carcinoma was observed in eight patients and showed similar appearances to those of the distal segment (eg, wall layer pattern with the thickened hypoattenuating middle layer).
On barium enema radiographs, nine patients showed no recognizable abnormality in the distal segment. Only three patients showed abnormalities: thickening of the mucosal fold (n = 1) and prominent transverse ridges (n = 2). The involved length of these findings in the colon was shorter than that seen at CT: The length on barium enema radiographs was 3, 6, and 5 cm, respectively, whereas that on CT scans was 5, 12, and 6 cm, respectively.
Pathologic Findings
At gross examination of the resected specimens, the tumors were mostly fungating (n = 11) in morphologic type. The remaining two were ulceroinfiltrative. The size of the tumors was 4–12 cm (mean, 8 cm) in the greatest dimension. At microscopic examination, most colonic carcinomas extended to pericolic adipose tissue (n = 11). Marked pericolic infiltration of chronic inflammatory cells and fibrosis of varying degrees were found around the tumor in all 13 patients.
In the colonic segment distal to the tumor in all 13 cases, no mucosal abnormality was observed. Although overlapping features were present to some degree, the histopathologic findings in the segment were categorized into two groups according to the predominant features: colonic edema (n = 6) and colitis (n = 5). One case had two separate areas with predominant colitis and edema: colitis in the segment just distal (hepatic flexure area) to the ascending colonic carcinoma and severe edema in the transverse colon (Fig 1). In the remaining case, no remarkable histopathologic alteration was seen. The edema was seen most prominently in the submucosal and subserosal layers and was 0.3–0.6 cm in the thickness of each layer.
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Figure 1a. Patient 12. Cecal and ascending colonic carcinoma with distal colitis and edema in a 44-year-old man. (a) Contrast-enhanced transverse helical CT scan shows a large ulcerofungating mass (solid arrows) with heterogeneous enhancement obliterating the lumen of the ascending colon. Note the marked pericolic infiltration (open arrows). (b) Contrast-enhanced transverse helical CT scan obtained at the level of the hepatic flexure distal to the colonic carcinoma, 7 cm cephalad to a, shows severe wall thickening with preservation of the wall layer (black arrows) in the distal ascending and proximal transverse colon. Also noted are pericolic infiltration (open white arrows) and venous engorgement (solid white arrows). (c) Photomicrograph of the colonic segment corresponding to b demonstrates markedly thickened subserosa (ss) composed of exuberant fibrosis, chronic inflammatory cells, and lymphoid aggregates that represent colitis. pm = muscularis propria. (Hematoxylin-eosin stain; original magnification, x200.) (d) Contrast-enhanced transverse helical CT scan obtained at a level distal and 4 cm caudad to b shows striking wall thickening with preserved wall layer pattern mainly consisting of a middle hypoattenuating layer of the transverse colon (open arrows). Also seen is the distal portion of the carcinoma in the ascending colon (solid straight arrow). Note that severe pericolic infiltration (curved arrows) is seen around the carcinoma and proximal part of the transverse colon, whereas only equivocal pericolic changes are seen around the farther distal segment. The carcinoma was confined to the subserosa without penetration of the colonic wall at pathologic examination (not shown). (e) Photomicrograph of the transverse colonic segment corresponding to d shows the submucosa (sm) markedly thickened, with dilated lymphatic vessels (curved arrows), congested vessels (straight arrows), and loose connective tissue permeated by abundant extracellular fluid representing edema. Also noted is the intact mucosa (mu). pm = muscularis propria. (Hematoxylin-eosin stain; original magnification, x200.)
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Figure 1b. Patient 12. Cecal and ascending colonic carcinoma with distal colitis and edema in a 44-year-old man. (a) Contrast-enhanced transverse helical CT scan shows a large ulcerofungating mass (solid arrows) with heterogeneous enhancement obliterating the lumen of the ascending colon. Note the marked pericolic infiltration (open arrows). (b) Contrast-enhanced transverse helical CT scan obtained at the level of the hepatic flexure distal to the colonic carcinoma, 7 cm cephalad to a, shows severe wall thickening with preservation of the wall layer (black arrows) in the distal ascending and proximal transverse colon. Also noted are pericolic infiltration (open white arrows) and venous engorgement (solid white arrows). (c) Photomicrograph of the colonic segment corresponding to b demonstrates markedly thickened subserosa (ss) composed of exuberant fibrosis, chronic inflammatory cells, and lymphoid aggregates that represent colitis. pm = muscularis propria. (Hematoxylin-eosin stain; original magnification, x200.) (d) Contrast-enhanced transverse helical CT scan obtained at a level distal and 4 cm caudad to b shows striking wall thickening with preserved wall layer pattern mainly consisting of a middle hypoattenuating layer of the transverse colon (open arrows). Also seen is the distal portion of the carcinoma in the ascending colon (solid straight arrow). Note that severe pericolic infiltration (curved arrows) is seen around the carcinoma and proximal part of the transverse colon, whereas only equivocal pericolic changes are seen around the farther distal segment. The carcinoma was confined to the subserosa without penetration of the colonic wall at pathologic examination (not shown). (e) Photomicrograph of the transverse colonic segment corresponding to d shows the submucosa (sm) markedly thickened, with dilated lymphatic vessels (curved arrows), congested vessels (straight arrows), and loose connective tissue permeated by abundant extracellular fluid representing edema. Also noted is the intact mucosa (mu). pm = muscularis propria. (Hematoxylin-eosin stain; original magnification, x200.)
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Figure 1c. Patient 12. Cecal and ascending colonic carcinoma with distal colitis and edema in a 44-year-old man. (a) Contrast-enhanced transverse helical CT scan shows a large ulcerofungating mass (solid arrows) with heterogeneous enhancement obliterating the lumen of the ascending colon. Note the marked pericolic infiltration (open arrows). (b) Contrast-enhanced transverse helical CT scan obtained at the level of the hepatic flexure distal to the colonic carcinoma, 7 cm cephalad to a, shows severe wall thickening with preservation of the wall layer (black arrows) in the distal ascending and proximal transverse colon. Also noted are pericolic infiltration (open white arrows) and venous engorgement (solid white arrows). (c) Photomicrograph of the colonic segment corresponding to b demonstrates markedly thickened subserosa (ss) composed of exuberant fibrosis, chronic inflammatory cells, and lymphoid aggregates that represent colitis. pm = muscularis propria. (Hematoxylin-eosin stain; original magnification, x200.) (d) Contrast-enhanced transverse helical CT scan obtained at a level distal and 4 cm caudad to b shows striking wall thickening with preserved wall layer pattern mainly consisting of a middle hypoattenuating layer of the transverse colon (open arrows). Also seen is the distal portion of the carcinoma in the ascending colon (solid straight arrow). Note that severe pericolic infiltration (curved arrows) is seen around the carcinoma and proximal part of the transverse colon, whereas only equivocal pericolic changes are seen around the farther distal segment. The carcinoma was confined to the subserosa without penetration of the colonic wall at pathologic examination (not shown). (e) Photomicrograph of the transverse colonic segment corresponding to d shows the submucosa (sm) markedly thickened, with dilated lymphatic vessels (curved arrows), congested vessels (straight arrows), and loose connective tissue permeated by abundant extracellular fluid representing edema. Also noted is the intact mucosa (mu). pm = muscularis propria. (Hematoxylin-eosin stain; original magnification, x200.)
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Figure 1d. Patient 12. Cecal and ascending colonic carcinoma with distal colitis and edema in a 44-year-old man. (a) Contrast-enhanced transverse helical CT scan shows a large ulcerofungating mass (solid arrows) with heterogeneous enhancement obliterating the lumen of the ascending colon. Note the marked pericolic infiltration (open arrows). (b) Contrast-enhanced transverse helical CT scan obtained at the level of the hepatic flexure distal to the colonic carcinoma, 7 cm cephalad to a, shows severe wall thickening with preservation of the wall layer (black arrows) in the distal ascending and proximal transverse colon. Also noted are pericolic infiltration (open white arrows) and venous engorgement (solid white arrows). (c) Photomicrograph of the colonic segment corresponding to b demonstrates markedly thickened subserosa (ss) composed of exuberant fibrosis, chronic inflammatory cells, and lymphoid aggregates that represent colitis. pm = muscularis propria. (Hematoxylin-eosin stain; original magnification, x200.) (d) Contrast-enhanced transverse helical CT scan obtained at a level distal and 4 cm caudad to b shows striking wall thickening with preserved wall layer pattern mainly consisting of a middle hypoattenuating layer of the transverse colon (open arrows). Also seen is the distal portion of the carcinoma in the ascending colon (solid straight arrow). Note that severe pericolic infiltration (curved arrows) is seen around the carcinoma and proximal part of the transverse colon, whereas only equivocal pericolic changes are seen around the farther distal segment. The carcinoma was confined to the subserosa without penetration of the colonic wall at pathologic examination (not shown). (e) Photomicrograph of the transverse colonic segment corresponding to d shows the submucosa (sm) markedly thickened, with dilated lymphatic vessels (curved arrows), congested vessels (straight arrows), and loose connective tissue permeated by abundant extracellular fluid representing edema. Also noted is the intact mucosa (mu). pm = muscularis propria. (Hematoxylin-eosin stain; original magnification, x200.)
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Figure 1e. Patient 12. Cecal and ascending colonic carcinoma with distal colitis and edema in a 44-year-old man. (a) Contrast-enhanced transverse helical CT scan shows a large ulcerofungating mass (solid arrows) with heterogeneous enhancement obliterating the lumen of the ascending colon. Note the marked pericolic infiltration (open arrows). (b) Contrast-enhanced transverse helical CT scan obtained at the level of the hepatic flexure distal to the colonic carcinoma, 7 cm cephalad to a, shows severe wall thickening with preservation of the wall layer (black arrows) in the distal ascending and proximal transverse colon. Also noted are pericolic infiltration (open white arrows) and venous engorgement (solid white arrows). (c) Photomicrograph of the colonic segment corresponding to b demonstrates markedly thickened subserosa (ss) composed of exuberant fibrosis, chronic inflammatory cells, and lymphoid aggregates that represent colitis. pm = muscularis propria. (Hematoxylin-eosin stain; original magnification, x200.) (d) Contrast-enhanced transverse helical CT scan obtained at a level distal and 4 cm caudad to b shows striking wall thickening with preserved wall layer pattern mainly consisting of a middle hypoattenuating layer of the transverse colon (open arrows). Also seen is the distal portion of the carcinoma in the ascending colon (solid straight arrow). Note that severe pericolic infiltration (curved arrows) is seen around the carcinoma and proximal part of the transverse colon, whereas only equivocal pericolic changes are seen around the farther distal segment. The carcinoma was confined to the subserosa without penetration of the colonic wall at pathologic examination (not shown). (e) Photomicrograph of the transverse colonic segment corresponding to d shows the submucosa (sm) markedly thickened, with dilated lymphatic vessels (curved arrows), congested vessels (straight arrows), and loose connective tissue permeated by abundant extracellular fluid representing edema. Also noted is the intact mucosa (mu). pm = muscularis propria. (Hematoxylin-eosin stain; original magnification, x200.)
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The majority of the edema group also had a mild degree of chronic inflammation. Areas of lymphatic dilatation were seen in five of the seven patients in the group with edema. In one case, there was a short intervening normal segment between the colonic carcinoma and edema in the distal segment.
The group with colitis showed diffuse infiltration of chronic inflammatory cells from the mucosa to the pericolic adipose tissue. Fibrosis rather than edema involved the submucosa and subserosa and was 0.2–0.7 cm in the thickness of each layer. At CT, four of these six patients with colitis showed marked pericolic infiltration and venous engorgement around the colitic segments (Fig 2), whereas in the edema group, pericolic changes were absent or equivocal around the edematous segments in six of the seven patients (Fig 3). One patient in the colitis group had lymphatic tumor emboli within part of the thickened distal segment, but there were no differences in the other pathologic findings and wall thickness between the segments with and those without tumor emboli. In the remaining 12 patients, no carcinoma cells were found within the thickened segment distal to the colonic carcinoma.
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Figure 2a. Patient 7. Ascending colonic carcinoma with distal colitis in a 69-year-old man. (a) Contrast-enhanced transverse helical CT scan shows a large mass (black arrow) with heterogeneous enhancement involving the ascending colon. Also seen are severe pericolic infiltration (open white arrows) and pericolic lymph nodes (solid white arrows). (b) Contrast-enhanced transverse helical CT scan obtained 2 cm cephalad to a demonstrates moderate wall thickening with wall layer enhancement involving the hepatic flexure distal to the colonic carcinoma. Also associated are severe pericolic infiltration (open arrow) and venous engorgement (small arrows) around the nontumorous distal segment (large arrows). Histopathologic examination of this segment (not shown) revealed diffuse infiltration of chronic inflammatory cells involving all colonic layers and loosely thickened submucosa and subserosa, which represented colitis. (c) Right anterior oblique single-contrast barium enema radiograph demonstrates fold thickening (open arrows) involving the segment distal to the carcinoma, which is shown as an irregular filling defect (curved arrow).
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Figure 2b. Patient 7.
Ascending colonic carcinoma with distal colitis in a 69-year-old man. (a) Contrast-enhanced transverse helical CT scan shows a large mass (black arrow) with heterogeneous enhancement involving the ascending colon. Also seen are severe pericolic infiltration (open white arrows) and pericolic lymph nodes (solid white arrows). (b) Contrast-enhanced transverse helical CT scan obtained 2 cm cephalad to a demonstrates moderate wall thickening with wall layer enhancement involving the hepatic flexure distal to the colonic carcinoma. Also associated are severe pericolic infiltration (open arrow) and venous engorgement (small arrows) around the nontumorous distal segment (large arrows). Histopathologic examination of this segment (not shown) revealed diffuse infiltration of chronic inflammatory cells involving all colonic layers and loosely thickened submucosa and subserosa, which represented colitis. (c) Right anterior oblique single-contrast barium enema radiograph demonstrates fold thickening (open arrows) involving the segment distal to the carcinoma, which is shown as an irregular filling defect (curved arrow).
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Figure 2c. Patient 7.
Ascending colonic carcinoma with distal colitis in a 69-year-old man. (a) Contrast-enhanced transverse helical CT scan shows a large mass (black arrow) with heterogeneous enhancement involving the ascending colon. Also seen are severe pericolic infiltration (open white arrows) and pericolic lymph nodes (solid white arrows). (b) Contrast-enhanced transverse helical CT scan obtained 2 cm cephalad to a demonstrates moderate wall thickening with wall layer enhancement involving the hepatic flexure distal to the colonic carcinoma. Also associated are severe pericolic infiltration (open arrow) and venous engorgement (small arrows) around the nontumorous distal segment (large arrows). Histopathologic examination of this segment (not shown) revealed diffuse infiltration of chronic inflammatory cells involving all colonic layers and loosely thickened submucosa and subserosa, which represented colitis. (c) Right anterior oblique single-contrast barium enema radiograph demonstrates fold thickening (open arrows) involving the segment distal to the carcinoma, which is shown as an irregular filling defect (curved arrow).
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Figure 3a. Patient 8.
Descending colonic carcinoma accompanied by a long distal segment of edema in a 29-year-old man. (a) Contrast-enhanced transverse helical CT scan shows a large heterogeneous mass (m) in the splenic flexure with pericolic strands (arrows). Splenectomy was performed during the surgery for colonic carcinoma because of severe adhesion with the colonic carcinoma. s = spleen. (b) Contrast-enhanced transverse helical CT scan obtained at the level of the iliac wing, 9 cm caudad to a, shows the distal descending colon (arrows) is thickened moderately, with preservation of the wall layer pattern. No pericolic changes are seen. At microscopic examination (not shown) of the distal segment, severe widening of the submucosal layer owing to edema and the intact mucosa were observed, similar to findings visible in Figure 1e.
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Figure 3b. Patient 8.
Descending colonic carcinoma accompanied by a long distal segment of edema in a 29-year-old man. (a) Contrast-enhanced transverse helical CT scan shows a large heterogeneous mass (m) in the splenic flexure with pericolic strands (arrows). Splenectomy was performed during the surgery for colonic carcinoma because of severe adhesion with the colonic carcinoma. s = spleen. (b) Contrast-enhanced transverse helical CT scan obtained at the level of the iliac wing, 9 cm caudad to a, shows the distal descending colon (arrows) is thickened moderately, with preservation of the wall layer pattern. No pericolic changes are seen. At microscopic examination (not shown) of the distal segment, severe widening of the submucosal layer owing to edema and the intact mucosa were observed, similar to findings visible in Figure 1e.
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Of the eight patients with thickened segments proximal to colonic carcinoma at CT, seven showed edema or colitis similar to that seen in the distal segment. The proximal segment in the one remaining patient showed no pathologic alteration, whereas colitis was seen in the distal segment. None of the patients had mucosal ulceration or hemorrhage in the segment either distal or proximal to the colonic carcinoma.
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DISCUSSION
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Many investigators have reported ischemic colitis proximal to an obstructing colonic carcinoma (obstructive colitis), with a prevalence of 1%–7% of colonic carcinomas (2–5). The characteristic pathologic features include marked mucosal or submucosal hemorrhage, congestion, and circumscribed or confluent ulcers (2,3). Understanding of this condition and preoperative radiologic suggestion of this condition are considered important, because anastomoses through unrecognized areas of obstructive colitis may break down, with a prevalence of up to 25% of cases (2–5). In contradistinction to the well-known proximal obstructive colitis, the finding of segmental colonic wall thickening distal to colonic carcinoma has not been described previously, to our knowledge. In the studies in which proximal obstructive colitis was reported (2–5), no pathologic abnormality was described in the segment distal to an obstructing colonic carcinoma, and this fact was considered important in differentiating it from colonic carcinoma associated with underlying inflammatory bowel diseases (3).
According to our results, the frequency of colonic wall thickening distal to colonic carcinoma found at CT is not low (13 [10%] of 133). It was associated most frequently with bulky, fungating carcinoma of the ascending colon, with extension to pericolic adipose tissue. The thickened distal segments did not have tumor infiltration except for one case.
The segmental colonic wall thickening distal to colonic carcinoma reported in this study has many features different from those of proximal obstructive colitis. First, the mucosa of the distal segments was intact in all patients in our study, whereas proximal obstructive colitis typically demonstrates mucosal lesions such as ulceration or hemorrhage. Second, in contrast to proximal obstructive colitis (2–5), there was no case complicated with anastomotic failure in this study despite the fact that pathologic changes were found at the distal margin of the resected specimens. Third, distal segmental wall thickening was associated most commonly with carcinoma of the ascending colon, whereas proximal obstructive colitis occurs most commonly in sigmoid colonic carcinoma (2). Fourth, the cases in our study showed no intervening normal segment between the pathologic portion of the distal segment and the colonic carcinoma except in one case. A skipped area between colonic carcinoma and obstructive colitis is a well-known characteristic finding in proximal obstructive colitis (2,3). Taking our observations together, segmental wall thickening in the colonic loop distal to colonic carcinoma seems to be a separate condition from proximal obstructive colitis.
The histopathologic nature of wall thickening of the distal segment could be categorized largely into "edema" and "colitis." The edema was seen most prominently in the submucosal and subserosal layers, mostly along with a mild degree of chronic inflammation and mild lymphatic dilatation. The colitis findings were transmural infiltration of chronic inflammatory cells and a varying degree of fibrosis rather than edema involving the submucosa and subserosa. At CT, pericolic changes tended to be prominent in cases with colitis, whereas they were minimal in those with edema. Thus, colonic carcinoma in the colitis group was apt to be overstaged easily at CT.
The exact cause or mechanism of the distal colonic thickening was not understood clearly through this study. We can only speculate on some possible explanations from the following information. In both the edema and colitis groups, the carcinomas were mostly large and extended to the pericolic adipose tissue. Furthermore, the carcinoma was always associated with remarkable pericolic inflammation at pathologic examination, regardless of the presence or absence of carcinoma cells in the pericolic adipose tissue. In the cases in the edema group, lymphatic obstruction secondary to pericolic spread of tumor or inflammation might be one of the possible causes: The majority showed dilatation of submucosal lymphatic vessels at pathologic examination. The cases in the colitis group frequently were accompanied by striking pericolic infiltration and venous engorgement at CT. The pathologic findings in the colitis group were nonspecific regarding cause, but they were suggestive of more chronic changes than those seen in the edema group.
Considering all these findings along with the intact overlying mucosa, spread of inflammation from the serosal side, adhesions, and subsequent impaired venous or lymphatic drainage might be the possible initial processes that produce segmental wall thickening of the distal segment. Further investigations are warranted to clarify the mechanisms that are yet only speculative.
Distal colitis or edema had a strong propensity to involve the ascending colon. Such a predilection also is seen in congestive colonopathy of hepatic cirrhosis (6). This edematous colonic wall thickening, which mainly is attributable to portal hypertension, usually is localized to or more severe in the distribution of the superior mesenteric vein, where collateral vessels are less likely to develop (6). In addition, the ascending colon is known to be sensitive to localized vasospasm, since the ascending colon possesses relatively poor collateral networks and the vasa recta are fewer and originate farther away from the ascending colon than those in the left side of the colon (7,8). In consideration of these factors, the predilection for the ascending colon in this study might support our speculations: possible connection of distal colonic thickening to the localized impairment of venous and lymphatic drainage or the involvement of vasa recta owing to severe pericolic changes.
CT has been reported as helpful in distinguishing tumoral from ischemic segments in patients with ischemic colitis proximal to colonic carcinoma (2). Although we analyzed CT images with knowledge of the pathologic and barium enema examination findings in this study, CT distinction alone of the tumoral segment and its thickened distal segment seemed not to be a problem. The wall layer pattern was preserved in the nontumoral segment, and the thickened wall never showed high attenuation, whereas the wall layer pattern was obliterated with heterogeneous enhancement in the tumoral segment. On barium enema radiographs, no abnormality was seen in the distal segments in all but three of 12 cases. This might be partly due to the intervals between the barium enema examination and CT being different. The discrepancy is, however, more likely due to the fact that CT is superior for demonstrating mural and extraintestinal changes than is barium enema examination.
In conclusion, colonic carcinoma, especially a large fungating type involving the ascending colon with pericolic infiltration, can produce segmental wall thickening in the distal colonic segment at CT, which represents edema or colitis at histopathologic examination. Awareness of this condition may be helpful in the accurate diagnosis and assessment of the true extent of colonic carcinoma at CT.
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FOOTNOTES
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Author contributions: Guarantor of integrity of entire study, H.J.J.; study concepts, H.J.J.; study design, H.J.J., H.K.L.; definition of intellectual content, H.K.L.; literature research, H.J.J.; clinical studies, S.H.K., Y.L.C., J.M.P.; data acquisition, S.H.K., J.M.P.; data analysis, H.K.L., H.J.J., C.K.P.; manuscript preparation and editing, H.J.J.; manuscript review, H.K.L., C.K.P.
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ABSTRACT
INTRODUCTION
