DOI:10.2214/AJR.07.3159
AJR 2008; 190:1521-1526
© American Roentgen Ray Society
Colonic Pseudoobstruction: CT Findings
Ji Soo Choi1,
Joon Seok Lim1,2,
Hoguen Kim3,
Jin-Young Choi1,
Myeong-Jin Kim1,
Nam Kyu Kim4 and
Ki Whang Kim1
1 Department of Diagnostic Radiology, Yonsei University Health System, Republic
of Korea.
2 Institute of Gastroenterology, Yonsei University Health System, 134
Shinchon-dong, Seodaemoon-ku, Seoul, 120-752, Republic of Korea.
3 Department of Pathology, Yonsei University Health System, Republic of
Korea.
4 Department of Surgery, Yonsei University Health System, Republic of
Korea.
Received September 16, 2007;
accepted after revision December 22, 2007.
Address correspondence to J. S. Lim
(jslim1{at}yumc.yonsei.ac.kr).
Abstract
OBJECTIVE. The purpose of this review was to define the imaging
features of colonic pseudoobstruction and to describe the pathologic
findings.
CONCLUSION. Colonic pseudoobstruction can be diagnosed on the basis
of CT findings that show extensive colonic dilatation without an obstructive
lesion at the intermediate transitional zone or adjacent to the splenic
flexure. Pathologic examination reveals that intramural ganglion damage has a
high tendency to occur in cases of chronic colonic pseudoobstruction.
Keywords: colonic pseudoobstruction • CT • ganglion cell • transitional zone
Introduction
Colonic pseudoobstruction is a syndrome in which the clinical
features resemble those of mechanical obstruction, that is, failure of
motility associated with pain and abdominal distention, but there is no
mechanical obstructing lesion. Uncertainty about the pathogenesis of colonic
dilatation without obstruction has led to a variety of terms for the disease,
including pseudoobstruction, Ogilvie's syndrome, false colonic obstruction,
pseudomegacolon, adult megacolon, adynamic ileus, functional obstruction, and
idiopathic large-bowel obstruction
[1]. We favor the term
pseudoobstruction because it is descriptive but not overly specific.
Despite the absence of an obstructing lesion, particularly acute colonic
distention can be rapidly progressive and lead to necrosis and perforation of
the large bowel. Furthermore, an incorrect diagnosis of mechanical obstruction
can lead to unnecessary surgery. Pseudoobstruction of the colon is often
mistaken, both clinically and radiologically, for other abnormal conditions,
such as mechanical obstruction and paralytic ileus. This error may occur
because colonic pseudoobstruction is a relatively unknown entity that has
received scarce attention in the radiologic literature. Our purpose was to
describe the imaging features of colonic pseudoobstruction and to discuss the
pathologic findings.
Materials and Methods
Patients
A computerized search of electronic medical records at our university
hospital over the 5-year period 2002-2006 revealed the cases of eight patients
who underwent CT examinations and had a final diagnosis of colonic
pseudoobstruction or a similar entity. The medical records were reviewed for
demographic features, clinical symptoms, imaging study performed (colonoscopy,
CT), and follow-up results. This retrospective study was approved by our
institutional review board, and informed consent was waived.
CT and Image Evaluation
All patients underwent contrast-enhanced CT. The scans were obtained with a
4-MDCT (Light-speed Plus, GE Healthcare) or a 64-MDCT (Sensation 64, Siemens
Medical Solutions) scanner. Contrast medium with an iodine concentration of
370 mg/mL (iopromide, Ultravist 370, Bayer HealthCare) was administered with a
power injector at a rate of 4 mL/s. Images were acquired in a craniocaudal
direction from the diaphragmatic dome to the level of the symphysis pubis with
2.5 x 4 or 0.6 x 64 beam collimation and 60- to 70-second scan
delay (portal venous phase). A reconstruction section thickness of 3.0 mm or
5.0 mm and an interval of 3.0 mm or 5.0 mm were used to interpret axial and
coronal images.
The CT images were jointly evaluated by two gastrointestinal radiologists
(9 and 4 years of experience). For patients who underwent multiple CT
examinations (n = 4) during follow-up, the first CT examinations
showing colonic dilatation were used. The presence or absence of a
transitional zone between dilated and collapsed colon was determined. Location
and character of the transitional zone also were analyzed. In the transitional
zone, the presence or absence of a structural obstructive lesion was
determined. The characteristics of transition were classified as smooth,
intermediate, or abrupt. A smooth transition was defined as a slight
discrepancy (less than 50%) between the caliber of the proximal and distal
colonic loops. An intermediate transition was defined as a discrepancy of 50%
or more between the proximal and the distal colonic caliber with residual gas
or fecal material in the distal colon. An abrupt transition was defined as a
discrepancy of 50% or greater between the proximal and distal colonic luminal
caliber and complete collapse of the distal colon. The diameters of the
maximally dilated segment and cecum were measured with electronic calipers as
the longest diameter on axial or coronal images. The location of the maximally
dilated segment was classified as one of five segments: cecum, ascending
colon, transverse colon, descending colon, and rectosigmoid. In the cases of
two patients who underwent follow-up CT examinations immediately before
surgery, the diameters of the maximally dilated colon and cecum were
repeatedly measured.
Pathologic Review
Six of the eight patients underwent surgical resection of the dilated
colonic segments. Sections from various areas of the specimen were stained
routinely with H and E. Our pathologist retrospectively reviewed
paraffin-block specimens of the colonic loops with an emphasis on the change
in ganglion cells.
Results
Clinical Findings
Our study group was composed of two men and six women with an average age
of 52.7 years (range, 31-71 years). All patients presented with abdominal pain
and distention at first admission. The mean duration of the initial symptoms
was 22 days (range, 3-90 days). All patients had a history of chronic
constipation. Two patients also had a history of hypertension; one patient, a
history of diabetes mellitus; and one, a history of epilepsy. Two patients had
had nonspecific colitis 2 and 6 months before colonic pseudoobstruction. The
absence of obstructive lesions was confirmed with colonoscopy in all
cases.
CT Findings
In all cases, CT scans at first hospitalization for colonic obstruction
showed prominent colonic dilatation without distal obstructing lesions (Figs.
1A,
1B,
1C,
1D,
1E,
2A,
2B,
2C,
2D
3A,
3B, and
3C). Six patients had marked
dilatation from the cecum to the transverse colon with transitional zones in
the splenic flexure (Table 1).
In the other two patients, transitional zones were found in the midportion of
the transverse and descending colon. All eight patients had an intermediate
transition. Maximally dilated segments were found in the transverse colon in
five patients and the cecum in three patients. At initial CT examinations, the
average diameters of the maximally dilated colonic segment and cecum were 9.6
cm (range, 8.2-13.7 cm) and 7.4 cm (range, 4.0-10.0 cm). In the six patients
treated surgically, the average diameters of the maximally dilated colonic
segments and cecum were 10.1 cm and 7.2 cm, respectively, at CT examinations
immediately before surgery. Only one of the eight patients had diffuse
small-bowel dilatation.
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Fig. 1A —31-year-old woman with colonic pseudoobstruction. Axial
(A) and coronal (B) contrast-enhanced CT images show markedly
distended transverse colon with large amount of fecal material. Transitional
zone (arrow,A) is at splenic flexure and has no
obstructivelesions.
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Fig. 1B —31-year-old woman with colonic pseudoobstruction. Axial
(A) and coronal (B) contrast-enhanced CT images show markedly
distended transverse colon with large amount of fecal material. Transitional
zone (arrow,A) is at splenic flexure and has no obstructive
lesions.
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Fig. 1D —31-year-old woman with colonic pseudoobstruction.
Photomicrographs show ganglion cells are nearly absent in myenteric (D)
and submucosal (arrow,E) plexuses of pathologic specimen. Few
remaining ganglion cells show decrease in size and nuclei with unusual shape
(H and E, x100).
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Fig. 1E —31-year-old woman with colonic pseudoobstruction.
Photomicrographs show ganglion cells are nearly absent in myenteric (D)
and submucosal (arrow,E) plexuses of pathologic specimen. Few
remaining ganglion cells show decrease in size and nuclei with unusual shape(H
and E, x100).
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Fig. 2A —61-year-old woman with colonic pseudoobstruction. Axial CT
image shows severely distended transverse colon without obstructive lesion.
Diameter of maximally dilated colonic segment was 13.7 cm. Transitional zone
(arrow) is in splenic flexure.
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Fig. 2B —61-year-old woman with colonic pseudoobstruction. Photograph
of gross specimen shows marked dilatation of ascending and transverse colon.
Transitional zone (arrow) is in splenic flexure.
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Fig. 2D —61-year-old woman with colonic pseudoobstruction.
Photomicrograph of submucosal plexus of specimen shows reduction in number of
ganglion cells. Few remaining cells (arrows) are flattened with
abnormal shape. (H and E, x100)
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Fig. 3A —71-year-old woman with colonic pseudoobstruction and normal
findings at pathologic examination. Axial contrast-enhanced CT image obtained
when colitis was present shows relatively long segmental wall thickening with
mucosal fold thickening in transverse colon. Increased vascularity
(arrows) of marginal vessels is evident.
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Fig. 3B —71-year-old woman with colonic pseudoobstruction and normal
findings at pathologic examination. Six months afterA,patient was
hospitalized with colonic pseudoobstruction. Axial CT image shows marked
colonic distention and transitional zone (arrow) in splenic flexure.
Obstructive lesions are not present in transitional zone.
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Fig. 3C —71-year-old woman with colonic pseudoobstruction and normal
findings at pathologic examination. Photomicrograph of myenteric
(arrow) and submucosal plexuses shows ganglion cells are normal in
shape and number. (H and E, x100)
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Two of the patients in our study group had a medical history of nonspecific
colitis. On the CT images of these two patients when colitis was present, the
involved segments were mainly located in the transverse colon. The CT findings
showed long segmental wall thickening, increased vascularity of marginal
vessels, and mucosal fold thickening (Figs.
3A,
3B and
3C). None of the etiologic
factors was defined at the time. Both of these patients were admitted because
of colonic pseudoobstruction 2 and 6 months after undergoing conservative
therapy for colitis.
Follow-Up Results
At the first hospitalization, all patients were initially treated
conservatively with nasogastric tube placement, fluid resuscitation, or
colonoscopic decompression. The condition of four patients improved after
conservative treatment. The four patients whose condition did not improve
underwent surgery. The four patients treated conservatively had recurrence of
symptoms 6-24 months after therapy. Two of the four had two episodes of
recurrence, and two had one episode. At the time of each recurrence, CT
examinations were performed. The condition of two of these four patients
improved with continued conservative treatment. The other two patients were
treated surgically. One patient underwent surgery at the first recurrence and
the other at the second recurrence. One of the six patients treated surgically
underwent total colectomy; the other five underwent subtotal colectomy. Two
patients whose condition improved with conservative treatment had decreased
colonic distention on follow-up radiography after the last recurrence.
Pathologic Findings
The surgical specimens of six patients exhibited severe dilatation of the
involved colonic segments without obstructive lesions or mucosal defects. In
the dilated colonic segments of four patients, the myenteric and submucosal
plexuses had microscopic evidence of a loss of or reduction in number of
ganglion cells (Figs. 1A,
1B,
1C,
1D,
1E,
2A,
2B,
2C and
2D). The specimens of two
patients with a history of colitis had only flattened mucosa without reduction
in the number of ganglion cells (Figs.
3A,
3B and
3C).
Discussion
Early recognition of colonic pseudoobstruction is important for prompt
treatment. Conservative treatment with nasogastric suction, enemas, and
neostigmine is highly effective in the management of colonic
pseudoobstruction. If the cecum is markedly dilated, the risk of perforation
is high, and direct intervention, such as colonoscopic decompression, must be
prompt. Before these treatments are begun, it is imperative that mechanical
obstruction be excluded. Abdominal radiographs show only nonspecific findings
of gaseous distention of the colon. Although findings at barium enema can
confirm dilatation of the colon without mechanical obstruction, this
examination should be avoided in cases in which complicated cecal perforation
is suspected on clinical grounds
[1]. CT is the single most
useful study because it can yield information about the location and cause of
bowel obstruction [2]. To our
knowledge there have been no studies on the CT findings of colonic
pseudoobstruction. The CT findings in all of our patients were proximal
colonic dilatation with an intermediate transitional zone at or adjacent to
the splenic flexure. Structural obstructing lesions were not visualized.
The presence of transitional zones in all cases can be used to
differentiate colonic pseudoobstruction from paralytic ileus. This finding
also is very similar to the features of adhesional obstruction. Adhesive
bands, how ever, seldom obstruct the colon
[3]. Furthermore, whereas the
transition of adhesive obstruction has an abrupt pattern, that of
pseudoobstruction in our cases was intermediate. The location of the
transitional zone can be somewhat characteristic. In all cases, the transition
zones were at the splenic flexure or adjacent to it. Bachulis and Smith
[4] report ed that the
transitional region in pseudo obstruction tends to be at the splenic flexure
or within a short distance to one side or the other. At this point the
para-sympathetic innervation of the colon undergoes transition from the vagal
nerve for the proximal portion to the sacral nerve for the distal portion.
This finding may indirectly implicate an autonomic neuronal imbalance as a
causative factor in colonic pseudoobstruction
[5,
6].
The decision to pursue colonic decompression is partly based on cecal
diameter as determined on abdominal radiographs. When the cecal diameter
exceeds 12 cm, colonic decompression is indicated
[7]. We believe that CT may be
more helpful than abdominal radiography for accurate measurement of cecal
diameter because fluid or fecal material can obscure the margin of the cecum
on radiographs.
All of the cecal diameters in our cases were less than 12 cm. However, six
patients underwent surgical resection of the colon because conservative
treatment failed or obstructive symptoms recurred repeatedly. In 1948, Ogilvie
[8] described two cases of
isolated colonic pseudoobstruction. The term Ogilvie's syndrome, however, has
been used loosely for acute and chronic forms of colonic pseudoobstruction.
Anuras and Baker [1] suggested
that isolated colonic pseudoobstruction can occur in two forms: acute and
chronic. The acute form is a transient reversible illness that occurs in
conjunction with severe medical illness and major surgical procedures
[9-11].
The chronic form usually recurs or persists
[1,
10]. Several characteristics
in our patients, including chronic constipation, no major surgical procedures
or illnesses, and repeated obstructive symptoms, suggest that our patients
probably had the chronic form. In contrast to the acute form, the chronic form
rarely is accompanied by perforation. In addition, there is no effective
medical therapy for chronic pseudoobstruction, whereas a parasympathomimetic
agent is the choice of management of the acute form
[1]. It has been suggested
[12,
13] that subtotal colectomy
gives symptomatic relief to most patients with the chronic form of colonic
pseudoobstruction.
Small-bowel dilatation was found in only one of our patients. Ileocecal
valve incompetence may be a causative factor in the finding, as it is in
mechanical obstruction of the large bowel. At pathologic examination, four of
six patients who underwent surgery were found to have atrophic changes and
decreased numbers of intramural ganglions. Intramural plexus damage in chronic
pseudoobstruction has been reported
[14-16]
as a remote phenomenon in carcinoma, neuronal disease, and viral infection.
These pathologic findings indicate irreversible changes, in contrast to the
reversible changes of the acute form. These results may be indirect evidence
that the acute and chronic forms are different disease entities, as suggested
by Anuras and Baker [1]. In the
two patients with pseudoobstruction after colitis, no changes in intramural
ganglions were detected. The relation between infection and pseudoobstruction
has been documented [1,
14], but most reports have
shown that the pseudoobstruction developed during the active phase of
infection. We cannot explain the cause of delayed development of
pseudoobstruction 2 and 6 months after colitis. Further pathophysiologic
evaluation should be done to investigate the delayed development of
pseudoobstruction after infection.
There might have been selection bias in our study because we selected
patients who underwent CT. Acute and reversible colonic pseudoobstruction
would be diagnosed only with radiographs. CT examination would be performed on
patients with the chronic form. This factor might have been responsible for
the high incidence of surgical treatment in our cases.
For early diagnosis of colonic pseudoobstruction, thorough knowledge of the
condition is required by both radiologists and clinicians, because the
clinical symptoms can mimic those of mechanical obstruction and paralytic
ileus. Colonic pseudoobstruction can be diagnosed on the basis of the CT
finding of extensive colonic dilatation without obstructive lesions at the
intermediate transitional zone at or adjacent to the splenic flexure. The
pathogenesis of colonic pseudoobstruction is not clear, but intramural
ganglion damage has a high tendency to occur in at least chronic colonic
pseudoobstruction.
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Abstract
Introduction
