Current Concepts in Imaging of Small Bowel Obstruction

Current concepts in imaging of small bowel obstruction

Dean D.T. Maglinte, MDa,*, Darel E. Heitkamp, MDa,Thomas J. Howard, MD, FACSb, Frederick M. Kelvin, MDc,

John C. Lappas, MDa

aDepartment of Radiology, Indiana University Medical Center, 550 North University Boulevard, UH0279,

Indianapolis, IN 46202-5243, USAbDivision of General Surgery, Indiana University School of Medicine, 545 Barnhill Drive, EH523, Indianapolis, IN 46202, USA

cDepartment of Radiology, Methodist Hospital of Indiana, 1701 North Senate Boulevard, Indianapolis, IN 46202, USA

Despite recent advances in abdominal imaging,

intestinal obstruction remains a difficult disease entity

to diagnose accurately and treat [1–3]. Small bowel

obstruction (SBO) is a common clinical condition,

often presenting with signs and symptoms similar to

those seen in other acute abdominal disorders. Once

intestinal obstruction is suspected based on the

patient’s clinical history and physical examination,

diagnostic imaging is charged with the task of veri-

fying the presence of obstruction and providing cogent

information on the site, severity, and probable cause of

the obstruction. By providing this broad range of

anatomic information, imaging impacts directly on

patient management, specifically addressing the cru-

cial question of whether a trial of nonoperative therapy

should be instituted rather than resorting to immediate

surgery because of the possibility of strangulation

[4,5]. Because of its ability to provide important

anatomic and functional information, radiology has

become a vital tool in the clinical decision making of

patients with known or suspected SBO. This article

examines current concepts in the imaging of SBO.

Clinical considerations

Small bowel obstruction is responsible for 12% to

16% of admissions to the surgical service in patients

with acute abdominal conditions [6]. Establishing the

diagnosis in a timely manner is best accomplished

by relying on the classic investigational triad of a

well-taken history, a careful physical examination,

and appropriate ancillary testing. The diagnosis of

mechanical SBO is straightforward when the classic

findings of crampy abdominal pain, distention, nau-

sea, and vomiting are present along with abdominal

radiographic (plain film) findings of small bowel

distention, multiple air-fluid levels, and decreased

colonic gas and stool [4]. In many cases, the dia-

gnosis is much more subtle because most patients fail

to present with a classic history and often have vague

abdominal findings on physical examination. Plain

abdominal radiographs have been found not to sup-

port the clinical diagnosis of obstruction in nearly one

third of surgically proved cases. Based on these

observations, after a complete history and physical

and abdominal plain films, if the clinical suspicion for

intestinal obstruction remains high, further abdominal

imaging is often indicated [4,7].

The three most common causes of SBO in the

western world are (1) adhesions, (2) Crohn’s disease,

and (3) neoplasia [8]. In the past, hernias represented

a major cause of SBO in the United States, but

improvements in health care availability and the

increase in elective hernia repair has led to a sub-

stantial decline in the incidence of SBO related to

abdominal wall hernias. Hernias, however, still rep-

resent the predominant cause of SBO in many devel-

oping countries. Crohn’s disease has only recently

been acknowledged in the surgical literature as a

0033-8389/03/$ – see front matter D 2003, Elsevier Science (USA). All rights reserved.

doi:10.1016/S0033-8389(02)00114-8

* Corresponding author.

E-mail address: [email protected] (D.T.T. Maglinte).

Radiol Clin N Am 41 (2003) 263–283

leading cause of SBO, a fact that has long been

suspected in many clinical radiology departments [8].

Controversy still exists surrounding the manage-

ment of patients with adhesive SBO. If the obstruction

is partial or early in the postoperative period ( < 6

weeks from operation), many surgeons recommend a

trial of conservative treatment with intestinal decom-

pression in the belief that, with close patient monitor-

ing, surgery frequently can be avoided altogether

[1,9–12]. Other surgeons advocate early surgical

management for all patients, particularly those with

complete intestinal obstruction, based on the high

complication rate associated with delayed operative

intervention in this group of patients [13–16]. Clinical

experience has shown that simple mechanical obstruc-

tion cannot be reliably differentiated from strangulated

obstruction on the basis of clinical, laboratory, or

abdominal plain film findings [9,15,17–21]. Histor-

ical data in patients with surgically proved strangula-

tion show that the preoperative diagnosis is unreliable

in 50% to 85% of cases [2,9,16,22–24]. The current

mortality rate of patients with adhesive intestinal

obstruction is in the 1% to 2% range [25,26], suggest-

ing that the risks associated with conservative man-

agement may be acceptable as long as emergent

surgery is performed at the first sign of patient deteri-

oration or evidence of incarceration or strangulation is

found. Recent clinical series have shown that even

patients with high-grade mechanical SBO can have a

substantial rate of resolution with conservative nasoin-

testinal decompression, further supporting an even-

handed approach to patients with SBO [11,15,27,28].

Abdominal radiography

Despite its limitations, abdominal radiography

remains the initial imaging study in patients with

abdominal symptoms, particularly in those with pos-

sible intestinal obstruction. Its diagnostic value tends

to be highest in patients with signs or symptoms of

biliary or urinary system calculi, intestinal obstruc-

tion, perforation, or ischemia. Plain films are least

helpful in patients with vague abdominal pain and

nonspecific physical findings. Its role in the evalu-

ation of calculi, perforation, or ischemia has been

replaced by CT.

In the setting of SBO, abdominal radiographs are

diagnostic in 50% to 60% of cases [17–20,29]. In an

analysis of plain film findings reported by experi-

enced gastrointestinal radiologists, a sensitivity of

only 66% was found in proved cases of SBO [7].

Twenty-one percent of patients reported as normal

were in fact obstructed. Of patients whose films were

interpreted as abnormal but nonspecific, 13% had

low-grade and 9% had high-grade obstruction. Addi-

tionally, abdominal radiography has shown a low

specificity for SBO, because mechanical and func-

tional large bowel obstructions can mimic the radio-

graphic findings observed in SBO [30]. Despite these

acknowledged limitations of this examination, plain

film radiography remains an important study in

patients with suspected SBO because of its wide-

spread availability and low cost. Although in many

cases the abdominal radiographs are nondiagnostic,

their findings can be valuable in guiding subsequent

imaging, or following disease progression.

A degree of confusion still exists among radiol-

ogists and clinicians over the meanings of common

descriptors used to identify various intestinal gas

patterns on abdominal radiographs [31,32]. Many

physicians frequently use the term nonspecific bowel

gas pattern to actually mean normal bowel gas

pattern [3]. One survey showed that 70% of radiol-

ogists used the term nonspecific in their interpreta-

tions, with 65% trying to convey a normal or

probably normal bowel gas pattern, 22% meaning

to say that they cannot tell if it is normal or abnormal,

and 13% interpreting this to mean abnormal but

cannot tell if it represents mechanical obstruction or

adynamic ileus. Clearly, the term nonspecific is

imprecise and its use ultimately can lead to serious

errors in patient management. If used at all, it should

be qualified as ‘‘abnormal, but nonspecific,’’ satisfy-

ing a group of plain film findings that fits neither the

‘‘normal’’ nor ‘‘definitely abnormal’’ categories. This

qualification adds its own set of clinical implications

[33]. The use of ambiguous terms, such as ‘‘non-

obstructive gas pattern,’’ which does not indicate

whether the gas distribution is normal or abnormal,

should be abandoned.

The use of well-defined terms for describing bowel

gas patterns is essential for generating understandable

reports for clinicians and other radiologists. (1) The

normal small bowel gas pattern refers to either

absence of small bowel gas or small amounts of gas

within up to four variably shaped nondistended (less

than 2.5 cm in diameter) loops of small bowel. A

normal distribution of gas and stool within a non-

distended colon should also be recognized. (2) Abnor-

mal but nonspecific gas describes a pattern of at least

one loop of borderline or mildly distended small

bowel (2.5 to 3 cm in diameter) with three or more

air-fluid levels on upright or lateral decubitus radio-

graphs. The colonic gas and feces distribution is either

normal or displays a similar degree of borderline

distention. This pattern can also be correctly labeled

‘‘mild small bowel stasis,’’ because many conditions

D.T.T. Maglinte et al / Radiol Clin N Am 41 (2003) 263–283264

can produce it, including low-grade obstruction, reac-

tive ileus, and medication-induced hypoperistalsis. (3)

The probable SBO pattern consists of multiple gas- or

fluid-filled loops of dilated small bowel with a mod-

erate amount of colonic gas. The presence of colonic

gas indicates early complete mechanical SBO, an

incomplete SBO, or nonobstructive ileus. This pattern

can be seen in several acute intra-abdominal inflam-

matory conditions that involve the small bowel (diver-

ticulitis, appendicitis, or mesenteric ischemia). This

diagnosis should trigger further investigation with a

prompt CT enteroclysis in a patient with no objective

clinical findings. (4) The definite SBO pattern shows

dilated gas or fluid-filled loops of small bowel in the

setting of a gasless colon. This constellation of find-

ings is pathognomonic for SBO [4].

Various small bowel gas patterns are shown in

Fig. 1A–N. These patterns should be distinguished

from the distended small bowel occurring secondary to

left-sided colonic obstruction. In this pattern, in addi-

tion to the distended small bowel, a fluid-filled right

colon and fluid and gas distended transverse colon can

also be recognized (Fig. 2). The small bowel distention

seen in this setting is secondary to decompression of

the colonic distention through the ileocecal valve.

Two findings on the upright abdominal radiograph

can help differentiate high-grade obstruction from

lower-grade obstruction: the presence of differential

air-fluid levels in the same bowel loop, and a mean air-

fluid level width of at least 25 mm (see Fig. 1M). The

combined presence or absence of these two radio-

graphic findings has a strong positive (86%) and

negative (83%) predictive value of the degree of

patency of the small bowel lumen [34]. Although

upright radiographs alone are not particularly sensi-

tive for SBO, they may be of value in distinguishing

patients with high-grade or complete obstruction from

those with low-grade or partial obstruction. Because

of its widespread availability, relative low cost, and

high sensitivity in revealing high-grade SBO, the use

of abdominal plain radiographs remains a prominent

imaging tool in the evaluation of suspected SBO [29].

Barium radiography

Because barium does not typically inspissate

within the adynamic gut, it can be used safely to

evaluate SBO [35,36]. Ingested orally, iodinated

water-soluble contrast agents result in poor mucosal

detail on radiography and are quite hypertonic.

Although radiography using water-soluble agents

was once used by some institutions to triage patients

into surgical versus nonsurgical management, the

widespread use of abdominal CT has largely sup-

planted this practice [37–39]. Despite the strong

opinion of a few advocates, the use of water-soluble

contrast has been shown to have no therapeutic effect

in patients with postoperative SBO [40].

Barium evaluation of the small intestine can be

performed by either nonintubation or intubation-infu-

sion techniques [4]. The nonintubation methods

include the retrograde small bowel enema; the per

enterosotomy (colostomy, ileostomy) small bowel

enema; and the small bowel follow-through.

Although the small bowel follow-through is a useful

technique when performed with meticulous fluoros-

copy, it has known limitations in the setting of SBO

[41–43]. In cases of high-grade obstruction, dilution

of barium by fluid in the dilated proximal bowel

typically results in incomplete small bowel opacifi-

cation and poor mucosal detail. The duration of the

small bowel follow-through examination is directly

related to small bowel transit time, both of which are

often markedly prolonged in cases of high-grade

obstruction. Moreover, nonintubation barium tech-

niques are inherently limited in their ability to assess

intestinal distensibility and fixation of small bowel

loops [42]. As a result, they may not detect partially

obstructing lesions that produce only fleeting or

inconspicuous prestenotic dilatations when viewed

under fluoroscopy. Despite these limitations, inter-

mittent fluoroscopic monitoring can often yield

important information making the technique a viable

alternative for radiology departments lacking suf-

ficient expertise in performing enteroclysis [42,43].

Enteroclysis overcomes the limitations of the non-

intubation techniques by challenging the distensibil-

ity of the bowel wall and exaggerating the effects

of mild or subclinical mechanical obstruction (see

Fig. 1B, C). Intubating the small bowel bypasses the

pylorus, enabling delivery of a nondiluted barium or

iodinated contrast bolus directly into the jejunum.

Sequential infusion of barium and methylcellulose or

iodinated contrast during CT enteroclysis promotes

antegrade flow of contrast toward the site of obstruc-

tion despite the presence of diminished bowel peri-

stalsis. The resultant luminal distention facilitates

detection of both fixed and nondistensible bowel

segments. Clinical studies have shown that the

intubation infusion method of small bowel examina-

tion can correctly predict the presence of obstruction

in 100%, the absence of obstruction in 88%, the level

of obstruction in 89%, and the cause of obstruction

86% of patients [7].

SBO is excluded by enteroclysis or CT enter-

oclysis when unimpeded flow of contrast material is

observed within normal-caliber small bowel loops

D.T.T. Maglinte et al / Radiol Clin N Am 41 (2003) 263–283 265

Fig. 1. Small bowel gas patterns. (A) Normal bowel gas

distribution. There is a small amount of gas in the duodenal

bulb (arrow) and distal ileum (curved arrow); otherwise

there should be no gas in the small bowel. There is no

evidence of colonic or gastric distention. Colonic folds are

apparent in intraperitoneal segments of the colon. (B)

Abnormal but nonspecific gas pattern. Mildly dilated loops

of small bowel are noted in the right hemiabdomen

(arrows). There is no colonic distention. Gas is present in

the duodenal bulb (near clips) and in distal ileum (curved

arrow). (C) Enteroclysis done following (B) shows a

moderately tight adhesive band obstruction (open arrow)

involving a pelvic loop of ileum. Note retained fluid in

dilated prestenotic (or sentinel) loop.


Fig. 1. (D) Abnormal but nonspecific gas pattern. Small

amounts of gas (arrows) are noted in nondistended small

bowel loops in left hemiabdomen and pelvis in addition to

usual gas in distal ileum in chronic renal patient presenting

with abdominal pain, nausea, and vomiting who also had

recent ventral herniorrhaphy and subsequent wound infec-

tion. Note semisolid fecal debris in right colon. This

distribution is also known as small bowel stasis pattern.

(E) Enteroclysis radiography shows no significant distention

proximal to intraluminal filling defects (curved arrow) in

ileum. (F) Further infusion of methylcellulose shows distal

movement of intraluminal filling defects towards cecum

(curved arrow).


Fig. 1. (G) Infusion radiograph shows that the filling defects

in distal ileum have been flushed into the right colon and the

distal and terminal ileum (arrow) are normal confirming that

the abnormal but nonspecific small bowel gas pattern is

secondary to medication-related hypoperistalsis. The small

bowel stasis pattern is not uncommon in hospitalized patients

on analgesics or sedatives. C, cecum. (H) Probable small

bowel obstruction (SBO) pattern. Upright abdominal radio-

graph shows air-fluid levels in multiple moderately distended

loops of small bowel. Gas and fluid are present in transverse

colon (arrow in a haustrum) and sigmoid. The pattern is

suggestive of mechanical SBO but can be seen in sigmoid

diverticulitis or appendicitis. (I) CT obtained following (H)

shows a lower abdominal anterior parietal peritoneal fixation

of decreased-caliber small bowel loops (arrow) secondary to

dense adhesions. Note dilated small bowel proximal to

adhesions. (From Maglinte DDT, Reyes BL, Harmon BH,

et al. Reliability and the role of plain film radiography and CT

in the diagnosis of small-bowel obstruction. AJR Am J

Roentgenol 1996;167:1451–5; with permission.)


Fig. 1. (J) Probable SBO pattern. Multiple dilated loops of

small bowel are noted. Gas is still present in normal-caliber

colon making diagnosis of mechanical SBO not unequivocal

but highly suggestive. (K) CT obtained following (J) shows

acute perforative appendicitis with abscess formation.

Appendicolith is present, which is not seen on the plain

film. Small bowel loops are dilated proximal to inflamma-

tory changes. (L) Definite SBO pattern. Supine abdominal

radiograph of a female patient with abdominal distention,

nausea, and vomiting shows markedly dilated gas-filled

loops of small bowel with a normal-caliber colon making

diagnosis of mechanical SBO unequivocal.


from the duodenojejunal junction to the right colon.

The diagnosis of mechanical SBO is confirmed by

the demonstration of a transition zone, defined as a

change in the caliber of the intestinal lumen from a

distended segment proximal to the site of obstruction

to a segment that is either collapsed or decreased in

caliber distal to the site of obstruction [4,5,7,44,45].

By enteroclysis criteria, 3 cm is the upper limit of

normal for the caliber of the jejunal lumen, and 2.5 cm

is the upper limit for the ileal lumen [42]. The level of

obstruction is identified during the single-contrast

phase of the examination, whereas the cause of the

obstruction is best evaluated during the double-con-

trast phase of the study when observation of mucosal

detail is optimal. In partial SBO, enteroclysis has

been shown to be approximately 85% accurate in

distinguishing adhesions from metastases, tumor

recurrence, and radiation damage [46]. Obstructions

can occur synchronously at multiple levels, such that

if dilated fluid- or gas-filled small bowel loops are

encountered distal to a transition zone, additional

downstream obstructions need to be assessed. Enter-

oclysis is particularly helpful in patients about whom

the diagnosis of low-grade SBO is clinically uncer-

tain [47]. Its ability to distinguish low-grade obstruc-

tion from a normal examination makes it an important

tool in this difficult clinical problem [47–51].

Enteroclysis can also objectively gauge the sever-

ity of intestinal obstruction, an important advantage

over other imaging modalities [7,45]. In low-grade

partial SBO there is no delay in the arrival of contrast

to the point of obstruction, and there is sufficient flow

of contrast through the point of obstruction such that

fold patterns in the postobstructive loops are readily

Fig. 1. (M) Upright abdominal radiograph of same patient (L) shows air-fluid levels and multiple fluid-filled loops of distal small

bowel (arrow in one). The rectosigmoid appears dry. (N) Enteroclysis done following overnight long tube decompression shows

fixation and decreased caliber of small bowel loops, multiple kinks, and strictures (arrow in one) from chronic radiation

enteropathy in a patient with a history of carcinoma of the cervix. C, cecum. (From Maglinte D, Herlinger H. Plain film

radiography of the small bowel. In: Herlinger H, Maglinte D, Birnbaum B, editors. Clinical imaging of the small intestine.

2nd edition. New York: Springer; 1999. p. 47–80; with permission.)


defined. High-grade partial SBO is diagnosed when

the presence of retained fluid dilutes the barium and

results in inadequate contrast density above the site of

obstruction, allowing only small amounts of contrast

material to pass through the obstruction into the

collapsed distal loops. Complete obstruction is diag-

nosed when there is no passage of contrast material

beyond the point of obstruction as shown on delayed

radiographs obtained up to 24 hours after the start of

the examination [7]. The authors have applied this

severity scoring to CT enteroclysis [45]. The term

closed-loop obstruction implies acute obstruction with

a tendency to progress toward infarction and the need

for urgent surgery. If a patient displays clinical signs of

a bowel compromise including localized tenderness,

fever, tachycardia, or leukocytosis, immediate resus-

citation and urgent laparotomy should be done. If

further anatomic information is required in a chal-

lenging patient (ie, multiple prior surgeries, dense

adhesions, or morbid obesity) CT should be the ini-

tial choice of imaging. Further investigation using

barium enteroclysis or positive contrast CT entero-

clysis can provide complementary information about

the obstruction, such as how much contrast material

is moving through the transition zone [29,52]. Partial

closed-loop obstruction has been demonstrated by

enteroclysis in the subacute setting [53].

Because enteroclysis requires conscious sedation,

nasointestinal intubation, and near-constant radiolo-

gist involvement, it can be impractical to perform

adequately in the outpatient clinic setting. Many

institutions also lack individuals with the proper

expertise to perform the study. If expertise is lacking,

a dedicated small bowel follow-through with close

fluoroscopic monitoring is an acceptable substitute,

provided that high-grade obstruction is not present

[41,42]. In patients with complete or high-grade

obstruction, dilution of barium occurs proximal to

the site of obstruction and makes diagnostic evalu-

ation suboptimal. Moreover, barium retained in the

small bowel can degrade the diagnostic quality of

subsequent CT examinations. In the acute setting

where time is of the essence, CT should be the initial

method of examination. In the authors’ department,

CT enteroclysis with positive enteral contrast is now

performed more frequently than barium enteroclysis

for further assessment of clinically stable patients

with SBO.

CT

CT has become important in the preoperative

evaluation of patients with suspected intestinal

Fig. 2. Left-sided colonic obstruction plain film pattern. (A) Diffuse small bowel distention is seen. In addition, fluid is seen in

the right colon (arrow) and gas- and fluid-filled transverse colon (open arrow). The rectosigmoid region is empty. (B) CT done

following (A) shows obstruction of the proximal descending colon from carcinoma (arrow). The retained fluid and gas in the

colon correspond to the gas and fluid distribution in (A). (From Maglinte D, Herlinger H. Plain film radiography of the small

bowel. In: Herlinger H, Maglinte D, Birnbaum B, editors. Clinical imaging of the small intestine. 2nd edition. New York:

Springer; 1999. p. 47–80; with permission.)


obstruction. Although some studies report a low

overall sensitivity (63%) of CT for all grades of

SBO, sensitivity improves to 81% when high-grade

obstruction alone is considered. Conversely, sensitiv-

ity worsens to 48% in the detection of low-grade

obstruction [45]. Although CT is accurate for high-

grade SBO, it is not as sensitive for the lower grades

of obstruction that present at the subacute level or in

the outpatient setting [29].

The speed of multidetector row helical CT and its

ability to reveal the cause of obstruction make it

particularly valuable in the acute setting. CT is able to

show the cause of obstruction in 93% to 95% of cases

[29,45,54,55], at the same time revealing the more

serious conditions of closed-loop obstruction and

strangulation [27,56–64]. The exclusion of these

two complications is of great concern to many

surgeons, particularly those who believe a trial of

conservative nonoperative management is warranted

in simple mechanical SBO. Although the specificity

of contrast-enhanced CT for intestinal ischemia is

reported to be as low as 44%, its high sensitivity

(90%) and negative predictive value (89%) [61] are

quite helpful in making decisions concerning contin-

ued nonoperative management versus surgery [11].

Most cases of strangulation occur as complications

of intussusception, volvulus, torsion, or other types of

closed-loop obstruction. Interruption of the blood

supply typically occurs either from twisting of the

bowel on its mesentery or from pressure generated by

markedly distended small bowel loops. Attention to

the course of vascular arcades in the bowel on CTwith

the use of coronal mesenteric vascular mapping may

help identify cases of closed-loop obstruction before

they progress to strangulation. In a recent report [65]

the whirl sign [60], described as the convergence of

mesenteric vessels toward a twisted site [63], and

the reversal of the normal relationship between the

mesenteric artery and vein [66] were identified as the

two most important vascular indicators of closed-

loop obstruction caused by midgut volvulus as seen

on CT. The ability of CT reliably to show signs of

closed-loop obstruction, ischemia, and infarction

likely represents the most important imaging contri-

bution to the management of acute SBO. If CT is used

appropriately, its higher initial cost may result in

overall cost savings within an episode of care by

either expediting surgery or avoiding surgery in

appropriate patients, reducing comorbidities and hos-

pital length of stay.

CT is also useful in differentiating SBO from ileus

or other causes of small bowel dilatation [67,68]. In

cases of high-grade obstruction, CT has a reported

sensitivity of 100% for distinguishing obstruction

from other causes of small bowel dilatation, as com-

pared with 46% for that of plain radiographs [67]. The

literature shows that by differentiating paralytic ileus

from obstruction, CT findings modified management

in 21% of patients either by changing conservative

management to a surgical one (18%) or vice versa. CT

can expedite the need for surgery and also avoid

unnecessary laparotomy, important goals in the man-

Fig. 3. Decompression-enteroclysis catheter. (A) The catheter is introduced transnasally similar to the conventional nasogastric

tube. The black marker (arrow) in the proximal third of the tube when seen at the level of the external nares indicates the tube tip

position in the body of the stomach and allows the tube to be positioned at bedside in the emergency department or hospital ward

without fluoroscopic guidance similar to the positioning of conventional nasogastric tubes. A rubber adapter (1) allows

connection of the decompression lumen (D) (also infusion lumen) to existing suction devices. A small plastic cap (2) prevents

fluid from leaking out of the sump port (S) when suction is disconnected. The balloon (B) is used only during contrast material

infusion and is inflated by first pressing in the balloon inflation one-way valve attachment (curved arrow). (B) A Teflon-coated

stainless-steel braided torque guidewire with interchangeable ends is provided. The straight tip of the guidewire is introduced to

the level of the nasal marker (arrow in A) of the suction-infusion lumen before intubation. The 45% angle proximal to the

opposite tip of the 195-cm long guidewire allows the operator to change the direction of the tube tip when necessary. The angled

tip is used only in occasional situations of difficult directional control and to allow atraumatic nasopharyngeal tube passage in

patients with acute nasopharyngeal posterior wall angulation. The straight tip is all that is necessary to provide torque in most

transgastric intubations.


agement of adhesive SBO. CT is particularly helpful

and should be used as the primary imaging technique

for patients in whom the obstructive symptoms are

associated with specific medical conditions, such as a

history of a previous malignant abdominal tumor,

known inflammatory bowel disease, palpable abdom-

inal mass, or sepsis [56].

Several caveats need to be considered in the

application of CT to SBO. If the plain radiograph

shows probable or definite SBO, oral contrast should

not be used for the CT, because it often does not reach

the site of obstruction by the time of examination. If it

does, the moderately increased intraluminal attenu-

ation created when bowel fluid dilutes the oral con-

trast bolus can nearly match the attenuation of a

contrast-enhanced bowel wall, making it difficult to

assess the bowel wall for thickening. Administration

of oral contrast in the emergent setting also has the

potential to cause delays in performing the CT exam-

ination. The use of water as an intraluminal contrast

agent is preferred in this setting and in patients with

suspected mesenteric ischemia. Positive oral contrast

in this situation often interferes with vascular recon-

struction algorithms. In the emergent setting, sick

patients are able to tolerate water better than water-

soluble contrast. With multidetector row CT, many

small bowel diseases including inflammatory condi-

tions, obstruction, or masses can be diagnosed with

water as enteral contrast in conjunction with intrave-

nous enhancement. In addition, with the use of water,

further diagnostic investigations are not interfered

with because of residual contrast in the bowel.

Compared with barium enteroclysis or CT enter-

oclysis, abdominal CT is faster, more readily avail-

able, noninvasive, less contingent on technical

expertise, and able to provide a more global evalu-

ation of the abdomen and alimentary tract. This last

advantage is of considerable importance, particularly

in the acute setting when intestinal obstruction rep-

resents only one of many possible etiologies in

patients presenting with acute abdominal conditions.

The CT examination should be monitored closely and

additional sections should be obtained through the

transition zone if the cause of obstruction is unclear

on the initial axial sections. Although identification of

the transition zone is usually not difficult in higher

grades of obstruction, the less distended loops found

with low-grade obstruction can be quite confusing to

follow on axial CT images [69]. When CT results are

equivocal in the search for a transition zone, and

closed-loop obstruction has been ruled out, CT enter-

oclysis or barium enteroclysis can often help establish

the diagnosis by providing volume-challenge disten-

tion of the proximal loops.

Box 1. Suggested instructions for suc-tion with the decompression-enterocly-sis catheter

The following instructions are providedas a guide. This peelable ‘‘suction order’’instruction, which is attached to the cath-eter box cover, can be removed andattached to the physician’s orders sheeton the patient’s chart.

1. Connect decompression (suction)port identified by rubber adapter)to low (___) intermittent (___) con-tinuous suction. Modify as needed.

2. Remove cap from sumping port andinject 2 cc of air into the channel assoon as suction is started. Do notrecap the air channel while suctionis being applied. During section thisport will allow air to enter andbubble back up the suction channelalmost continuously. If ‘‘bubbling’’is not observed, proceed to Step 3.Check that all connections are tight.

3. Irrigate decompression port every4 hours with 20 cc of saline andp.r.n. to prevent clogging of thesuction port.

4. Inject the sumping port with 2 cc ofair every 4 hours and p.r.n. Do notaspirate this port. Steps 3 and 4 canbe done at the same time.

5. Any time the decompression port isdisconnected, reapply caps to boththe decompression and the sumpports to prevent fluid leak. RepeatStep 2 each time the decompressiontube is reconnected for suction.

6. If tube is to be anchored for morethan 2 days, apply Bacitracin orNeosporin ointment to nasal cavityonce daily.

7. Do not use balloon channel. Thisport is used only during enteroclysis.

8. Remove long tube at the discretionof the attending physician. Notifyradiology if there is difficulty inremoving tube.

Signed:________________


CT enteroclysis has emerged as a promising new

method of investigating the small bowel. In this

technique, water-soluble contrast is infused through

an enteroclysis catheter into the proximal small

bowel, followed immediately by CT cross-sectional

imaging of the distended small bowel loops. Multi-

planar reconstructions of the CT data can be

obtained either routinely or on an as-needed basis

for problem solving in difficult cases. Theoretically,

the volume challenge provided by the intubation-

infusion technique of enteroclysis overcomes the

unreliability of CT for diagnosing low-grade obstruc-

tion, whereas the cross-sectional imaging provided

by CT complements the recognized limitations of

conventional enteroclysis in assessing the gut wall

and providing information on extraintestinal causes

of obstruction. In addition to precise three-dimen-

sional localization of small bowel pathology, CT

enteroclysis allows objective determination of the

severity of SBO as has been previously defined

using standard enteroclysis criteria [70]. Initial

reports indicate that the reliability of CT enteroclysis

is equivalent to that of conventional enteroclysis

(sensitivity 88% and specificity 82%) in patients

suspected of having a low-grade partial SBO

[71,72]. Other reports show that it has greater

sensitivity and specificity (89% and 100%, respec-

tively) than CT alone (50% and 94%, respectively) in

patients suspected of having a partial SBO, a differ-

ence that was even greater when a history of abdom-

inal malignancy was known or suspected [72]. CT

enteroclysis is emerging as a promising tool in the

further work-up of SBO. This topic is reviewed in

detail elsewhere in this issue.

Fig. 4. Therapeutic and diagnostic use of multipurpose long tube. (A) Axial CT of patient who had a history of prior colon

resection for carcinoma who presented with abdominal pain and distention. The ‘‘dirty feces sign’’ (arrow) suggests chronic

obstruction of small bowel with fluid and debris accumulating proximal to the point of obstruction. (FromMaglinte D, Herlinger

H. Plain film radiography of the small bowel. In: Herlinger H, Maglinte D, Birnbaum B, editors. Clinical imaging of the small

intestine. 2nd edition. New York: Springer; 1999. p. 47–80; with permission.) (B) Following nasogastric suction, no clinical

improvement was noted. Enteroclysis and long tube decompression were requested. The nasogastric tube was replaced with the

multipurpose tube and was advanced under fluoroscopic guidance to the proximal jejunum. The proximal small bowel was atonic

and fluid filled. Long tube suction was done. (C) Following overnight decompression, an abdominal radiograph done before

enteroclysis shows satisfactory decompression of the distended small bowel. (D) Radiograph obtained during barium

enteroclysis shows the ‘‘cobra head’’ appearance (arrow) suggestive of dense adhesive band obstruction, which was confirmed at

surgery. (From Maglinte D, Herlinger H. Plain film radiography of the small bowel. In: Herlinger H, Maglinte D, Birnbaum B,

editors. Clinical imaging of the small intestine. 2nd edition. New York: Springer; 1999. p. 47–80; and Maglinte DDT, Reyes BL,

Harmon BH, et al. Reliability and the role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR Am

J Roentgenol 1996;167:1451–5; with permission.)


MR enteroclysis

MR imaging has played only a limited role in the

clinical evaluation of SBO. The emerging technique

of MR enteroclysis, however, has the potential to

change the assessment of the small bowel through

its direct multiplanar imaging capabilities, its lack of

ionizing radiation, and the functional information

and soft tissue contrast that it can provide [73].

Compared with CT enteroclysis, MR enteroclysis

provides the distinct advantages of direct imaging in

the coronal plane and real-time acquisition of func-

tional information. Additionally, the accuracy of the

MR imaging technique does not rely as heavily on

fluoroscopist experience as do conventional enter-

oclysis techniques [73]. To be the primary method

of investigation for small bowel disease, MR enter-

oclysis has to provide reliable evidence of normalcy,

allow diagnosis of early or subtle structural abnor-

malities, influence treatment decisions in patient

management, and be cost effective [41]. Further

research and experience will help clarify whether it

will become a primary method for investigating the

small bowel or be used solely as a problem-solving

examination. This topic is discussed elsewhere in

this issue.

The role of radiology in the conservative

management of SBO

The gastrointestinal tract normally secretes up to

8.5 L of fluid daily, most of which is reabsorbed in

the small intestine [74]. In cases of SBO, kinking and

gas-trapping within distended loops of bowel above

an obstruction impairs the ability of the small intes-

tine to reabsorb secreted fluid and over time results in

a net flux of fluid out of the bowel wall into the

lumen [75,76]. The physiologic derangements of an

intestinal obstruction are borne predominantly by the

bowel immediately proximal to the point of occlusion

[74]. As this part of the gut becomes distended, its

Fig. 4 (continued ).


increased intraluminal pressure slows capillary blood

flow leading to mesenteric venous congestion putting

this segment of bowel at risk for ischemia, gangrene,

and perforation.

With an intact pylorus, nasogastric tubes cannot

decompress the small bowel until the pressure of

backed-up intestinal fluid and gas is strong enough

to overcome the strength of the pyloric sphincter. The

results of several studies have shown that the efficacy

of decompression is inversely proportional to the

distance between the tube tip and the site of the

blockage, such that advancement of the tube beyond

the pylorus into the small bowel significantly im-

proves decompression efficacy over the standard

gastric positioning [77]. These pathophysiologic prin-

ciples explain why nasointestinal rather than naso-

gastric intubation is considered the optimal method of

decompressing the distended small bowel. An added

advantage to using a long tube is that as soon as the

tube passes the pylorus and begins to decompress the

small bowel, the colicky pain of obstruction is largely

relieved. Because nasogastric tube decompression is

limited to the stomach, a patient’s abdominal pain

persists until either the obstruction is relieved or

effective decompression is achieved, either sponta-

neously or surgically [78].

Fig. 5. Radiographic demonstration of partial or incomplete closed-loop obstruction. (A) Abdominal radiograph of a 72-year-old

woman who presented with abdominal pain, distention, and vomiting and a history of prior appendectomy and lysis of adhesions.

Multiple distended loops of small bowel with little gas in colon are suggestive of small bowel obstruction. Clips are seen in right

lower abdomen from her prior surgery. A nasogastric tube is in the stomach. (B) Intravenous contrast-enhanced axial CT image at

level of lower abdomen shows mild dilatation of small bowel loops and possible edema of an ileal segment (arrow). (C) Axial

CT image at level of upper pelvis shows clips (curved arrow) from prior surgery and normal-caliber loops (arrow) and some

dilated loops. (D) Preliminary abdominal radiograph obtained after 12 hours of long tube decompression shows partial

decompression of distended small bowel and more gas in colon. (E) Early enteroclysis radiograph shows focal narrowing with

proximal dilatation of the small bowel at the level of the clips (curved arrow). The poststenotic loop containing a small amount of

contrast and gas, however, is also dilated (arrow). (F) Further contrast infusion shows the dilated poststenotic segment coursing

back toward the region of the clips (arrow). (G) Delayed radiograph shows two loops of small bowel obstructed at the same level

(curved arrow) consistent with a partial volvulus secondary to dense adhesive band. Collapsed loops are seen distal to

obstruction. This was confirmed at surgery. This is an illustration of how to diagnose multiple points of obstruction by

enteroclysis. (From Maglinte D, Herlinger H. Plain film radiography of the small bowel. In: Herlinger H, Maglinte D, Birnbaum

B, editors. Clinical imaging of the small intestine. 2nd edition. New York: Springer; 1999. p. 47–80; with permission.)


The Salem pump nasogastric tube (Sherwood

Medical, St. Louis, MO) cannot be used for enter-

oclysis and is too short to be advanced into the small

bowel for nasoenteric decompression. Patients who

initially undergo nasogastric tube placement but

later require enteroclysis or CT enteroclysis for the

evaluation of SBO experience the trauma of mul-

tiple intubations. The multipurpose intestinal tube

(MDEC-1400, Cook, Bloomington, IN) was de-

veloped in 1992 to be used for both diagnostic and

therapeutic purposes to eliminate the need for mul-

tiple intubations [79]. This multipurpose tube, a

modification of the standard balloon enteroclysis

catheter [80], is a 14F catheter, 155-cm long, triple-

lumen disposable catheter made of radiopaque poly-

vinyl chloride that is adapted for use with hospital



wall suction devices. The important addition of a

sumping mechanism prevents occlusion of the tube’s

side ports from collapse of the bowel wall against the

tube during suctioning, thereby allowing effective

small bowel decompression (Fig. 3) [81]. The multi-

purpose tube kit also includes a preprinted adhesive-

backed order sheet that can be affixed to the orders

page on a patient’s chart (Box 1). This sheet provides

unambiguous instructions to the patient’s caregivers.

In the nonemergent setting, if CT does not answer

all questions relevant to a particular patient’s man-

agement and nasogastric intubation is desired clin-

ically, the multipurpose tube can be positioned in the

stomach for initial gastric decompression. CT enter-

oclysis or barium enteroclysis can then be performed

after advancing the tube, under fluoroscopic guid-

ance, into the jejunum. The long tube can then be

anchored in the proximal jejunum after the study for

further decompression (Fig. 4) [5].

Closed-loop obstruction

Prompt preoperative recognition of closed-loop

obstruction is crucial, because strangulation represents

a dangerous complication that carries a much higher

risk of mortality than simple mechanical SBO. Accu-

rate and early detection of strangulation can expedite

surgery and significantly improve overall patient pro-

gnosis [82,83]. Most closed-loop obstructions result

from entrapment of the small bowel either within an

internal or external hernia. Unless the classic pseudo-

tumor or coffee bean signs are present, plain film

radiography often yields nonspecific and unreliable

results [84]. CT is the imaging modality of choice for

evaluating closed-loop obstruction in the acute setting,

whereas CT or barium enteroclysis serve more com-

plementary roles by establishing the presence of an

incomplete closed-loop obstruction or by helping to

clarify the cause of obstruction (Fig. 5) [37].

The enteroclysis findings of closed-loop obstruc-

tion are similar to those seen in single-band adhesive

obstruction, except that the crossing defect traverses

two adjacent segments of a single loop of bowel [85].

Volvulus is diagnosed if the afferent and efferent

limbs seem to cross or intertwine with twisting of

the folds at the point of obstruction. A separation

between the two obstructed limbs excludes the pres-

ence of volvulus. In patients with moderate to high-

grade obstruction, it may be difficult to exclude

volvulus if the involved limbs appear closely approxi-

mated, tightly compressed, and angulated at the point

of obstruction [85]. It is often impossible to differ-

entiate closed-loop obstructions caused by herniation

through mesenteric defects from those caused by

prolapse of bowel under adhesive bands [40]. If the

constriction is tight, there is usually delayed filling

and delayed emptying of the contrast from the incar-

cerated loop [85].

CT is a particularly valuable diagnostic tool

because it can establish the diagnosis of both

closed-loop obstruction and strangulation [27,48,

51–53,55,56,58,60]. The appearance of closed-loop

obstruction on CT depends on the length of the

closed loop, the degree of bowel distention, and the

three-dimensional orientation of the closed loop with

respect to the axial imaging plane [52,53]. If the

incarcerated loop is oriented horizontally, it appears

U- or C-shaped in the axial plane. If an elongated

segment of bowel is involved, sequential axial images

demonstrate a characteristic radial distribution of

dilated bowel loops having stretched and thickened

mesenteric vessels converging to the point of obstruc-

tion (Fig. 6). The incarcerated segment of bowel

appears almost entirely fluid-filled, whereas loops

Fig. 6. CT of closed-loop obstruction. Axial CT of an elderly

man obtained to investigate abdominal pain and distention.

Intravenous contrast-enhanced CT at the level of the lower

abdomen shows congested mesentery with distended small

bowel loops converging toward a central point (o) adjacent

to a pointed segment of bowel suggesting closed-loop

obstruction. At surgery volvulus was confirmed; the

mesentery was congested but there was no evidence of

strangulation. Note normal enhancement of mucosa without

evidence of bowel wall thickening. (From Maglinte D,

Herlinger H. Plain film radiography of the small bowel. In:

Herlinger H, Maglinte D, Birnbaum B, editors. Clinical

imaging of the small intestine. 2nd edition. New York:

Springer; 1999. p. 47–80; with permission.)


of bowel proximal to the site of obstruction contain

greater amounts of air. Images obtained near the site

of torsion demonstrate progressive, fusiform tapering

of the afferent and efferent limbs manifested as the

beak sign when imaged in longitudinal section. If a

volvulus is present, the whirl sign of a tightly twisted

mesentery may be seen [56]. CT signs of strangula-

tion are related to the appearance of the incarcerated

bowel wall and its mesentery [52,53]. Ischemia is

suggested by the presence of circumferential wall

thickening, increased mural attenuation, and the tar-

get or double halo sign seen on the intravenous

contrast-enhanced examination. In the setting of

examinations without intravenous contrast, increased

bowel wall attenuation is suggestive of ischemia.

Pneumatosis intestinalis may be seen with advanced

ischemia and infarction. Mesenteric congestion

and hemorrhage are important findings whose pres-

ence increases the specificity of the CT diagnosis

of strangulation.

Optimizing the imaging investigation of SBO

Open communication among radiologists, primary

care physicians, and surgeons is essential in the work-

up and management of SBO [86]. The selection of

imaging is based on knowledge of the patient’s

history, physical examination, laboratory results,

and abdominal plain film findings. The dilemma that

radiologists face is not the use of one technique over

the other, but the decision of which examination to

use first in the context of the clinical presentation and

abdominal plain film findings [56,85].

Fig. 7. Problem solving with CT enteroclysis. (A) Supine abdominal radiograph of a 26-year-old woman who presented with

abdominal distention and vomiting following colectomy and ileoanal pouch construction. Multiple distended loops of small

bowel are noted initially interpreted as consistent with mechanical small bowel obstruction. Conventional abdominal CT with

intravenous contrast (not shown) was unable to differentiate between ileus and mechanical obstruction. Oral contrast given was

vomited and patient refused nasogastric intubation. (B) CT enteroclysis with multipurpose long tube introduced following

conscious sedation was requested. Overnight long tube decompression was performed before infusion of water-soluble contrast.

The patient had a relief of the abdominal distention. Coronal CT image obtained 3 hours after initial infusion of contrast because

of slow flow shows the tip of the multipurpose long tube in proximal jejunum. There is moderate distention of remaining small

bowel with continuity of distention to the ileoanal pouch ( p). (C) Axial image at the level of the upper abdomen shows dilated

loops with retained fluid. (D) Axial image at level of pouch ( p) shows an intact pouch without evidence of peripouch

complications. Additional coronal and axial images did not show a transition point confirming a diagnosis of severe

postoperative ileus. The patient responded to long tube small bowel decompression with return of small bowel peristalsis and

passage of gas and contrast after the examination.


Definitive SBO on plain film radiography con-

firms the clinical diagnosis and opens the door for a

decision on whether to perform surgery or use a trial

of conservative nonoperative management. Factors

that favor early surgical exploration include no prior

history of abdominal surgery; clinical signs of bowel

compromise; incarcerated hernia; or the presence of a

complete SBO (obstipation). Factors that favor initial

conservative management include the presence of a

partial SBO; history of resected abdominal tumor;

prior radiation therapy; history of inflammatory

bowel disease; and early ( < 6 weeks) postoperative

obstruction (see Fig. 1M, N). When initial conserva-

tive management is entertained, CT examination is

helpful in evaluating the presence and extent of

neoplastic or inflammatory disease and in excluding

a strangulated obstruction. Postsurgical patients pre-

senting early after operation with abdominal disten-

tion and no signs of bowel compromise (tachycardia,

leukocytosis, localized tenderness, or fever) are

treated conservatively for several days, with CT

advised only if the clinical findings and abdominal

plain films do not improve, or if signs of sepsis or

bowel compromise develop. CT enteroclysis with

positive enteral contrast is a good problem-solving

tool and is easier to perform than barium enteroclysis

particularly in the postoperative patient or those who

are clinically ill (Fig. 7). CT enteroclysis should be

used after the conventional CT study only if addi-

tional management questions are left unanswered

[29,53]. In departments where CT enteroclysis is

not practical, barium enteroclysis is the preferred

investigation [5].

If the abdominal plain film shows colonic disten-

tion in addition to small bowel dilatation, a CT or

contrast enema should be performed. In this clinical

setting, CT is preferred in elderly or infirm patients,

patients with a clinical suspicion of abscess or diver-

ticulitis, and in patients with a history of previously

resected colon carcinoma. CT is also necessary in the

acute setting in patients with poor anal sphincter tone

(see Fig. 2) [82]. Where CT is not readily available,

the contrast enema is the method of choice.

Discordance between the clinical presentation and

plain film findings often requires additional radiologic

imaging. In patients with acute abdominal symptoms

who have normal or abnormal but nonspecific bowel

gas pattern on abdominal plain films, CT is recom-

mended (see Fig. 1J, K). CT is not only reliable in

showing many of the acute abdominal conditions that



can mimic SBO, but it also has a high sensitivity for

high-grade or complete SBO and can reveal closed-

loop and strangulating obstruction. When the CT

examination is not diagnostic, enteroclysis (CT,

barium, or MR) or a fluoroscopy-based barium small

bowel study can be performed as a complementary

examination. CT enteroclysis is the best initial

imaging technique in patients with a history of lap-

arotomy who complain of mild intermittent abdominal

pain and have few physical findings and a normal or

abnormal but nonspecific abdominal plain film. Low-

grade intermittent obstructions and intraluminal

tumors can be detected and evaluated better using this

technique. Barium enteroclysis can be performed later

if the CT enteroclysis does not provide enough

mucosal detail to detect small ulcerations or mild

inflammatory changes. MR enteroclysis can also give

additional information, particularly in patients with

inflammatory bowel disease.

The specific indications for diagnostic imaging

procedures are receiving intense scrutiny because of

the need to control health care costs. Radiologic

services are now being evaluated by criteria that

assess whether the use of a particular diagnostic

method influences clinical management, improves

patient outcome, or lowers medical costs. [83,84].

Unfortunately, erroneous application of imaging stud-

ies is frequent in clinical practice. Recent improve-

ments in CT and enteroclysis technology have

changed the approach to the evaluation of patients

suspected of having SBO [86]. These modalities are

complementary and serve as essential adjuncts to

abdominal plain film radiography in the diagnosis

and management of SBO.

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Current Concepts in Imaging of Small Bowel Obstruction

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