Radiographics 20 3 G00ma12725
Radiographics 20 3 G00ma12725
Radiographics 20 3 G00ma12725
Tailored Helical CT
Evaluation of Acute
Abdomen1
(CME available in print version and on RSNA Link)
Index terms: Abdomen, acute conditions, 72.25, 74.723, 751.291, 76.285, 762.81, 77.291, 81.2121, 82.21 • Abdomen, CT, **.12112 • Appen-
dicitis, 751.291 • Cholecystitis, 76.285 • Computed tomography (CT), helical technology • Computed tomography (CT), utilization • Gallblad-
der, calculi, 762.289, 762.81 • Intestines, stenosis or obstruction, 74.723 • Nephritis, 81.2121 • Pancreatitis, 77.291 • Stomach, ulcer, 72.25
Ureter, calculi, 82.81
more, MD 21287. Received March 8, 1999; revision requested May 5 and received June 3; accepted June 8. Address reprint requests to
B.A.U. (e-mail: burban@jhmi.edu).
2** indicates multiple body systems.
©RSNA, 2000
726 May-June 2000 RG ■ Volume 20 • Number 3
Table 1
Suggested Routine Helical CT Protocol for Nonlocalized Acute Abdominal Pain
Table 2
Variations in Helical CT Protocol for Acute Abdomen Based on Working Clinical Diagnosis
a. b.
Figure 8. Biliary obstruction from an impacted common bile duct stone in an 81-year-old
woman with choledocholithiasis. (a) On an axial CT scan obtained with intravenous con-
trast material, the common bile duct (cbd) is moderately dilated and tortuous. (b) CT scan
obtained inferior to a shows an impacted high-attenuation nidus from a gallstone at the am-
pulla (arrow).
Spleen
Patients with splenic infarction typically present
with left upper quadrant pain, although in some
cases the disease may be clinically silent. Com-
mon causes of splenic infarction include bacterial
endocarditis, portal hypertension, and underlying
splenomegaly (29). Pancreatitis can also extend
into the splenic hilum and result in infarction
(29,30). Tailored helical CT protocol requires
Figure 9. Gallstones in a 75-year-old man with intravenous bolus administration of contrast ma-
choledocholithiasis and pancreatitis. Axial CT scan
obtained with intravenous contrast material shows
terial. At helical CT, focal infarcts appear as
very subtle gallstones within the gallbladder lumen wedge-shaped areas of decreased attenuation that
(white arrow) and common bile duct (black arrow). extend to the surface of the spleen (Fig 10) (41–
Stranding is seen in the peripancreatic fat. 43). Most infarcts are easily appreciated against
the normal inhomogeneous pattern of early
splenic enhancement. Global infarction can
reliable CT finding is a high-attenuation nidus manifest as diffuse areas of decreased attenuation
within the duct (Figs 8, 9) (38,39). Helical CT in the spleen and can mimic splenic abscess or
with narrow collimation and small reconstruction
intervals is particularly helpful in detecting small
stones and the subtle, alternating low- and high-
732 May-June 2000 RG ■ Volume 20 • Number 3
10. 11.
Figures 10, 11. (10) Splenic infarction in a 41-year-old woman. Axial CT scan obtained with
intravenous contrast material demonstrates multiple infarcts in an enlarged spleen (arrows). Most
splenic abnormalities, including infarcts, can be differentiated from normal inhomogeneous splenic
enhancement. (11) Global splenic infarction in a 32-year-old man with human immunodeficiency
virus (HIV) infection who presented with severe left upper quadrant pain. Axial CT scan obtained
with intravenous contrast material demonstrates an enlarged, infarcted spleen (S) resulting from
portal vein thrombosis. The spleen appears similar to a large abscess.
tumor (Fig 11). In some cases of global infarction, hypoperfusion, resulting in a characteristic
the splenic periphery remains enhanced due to “patchy” nephrogram (Fig 12) (48–50). Stria-
perfusion from capsular vessels. Helical CT per- tions result from stasis of contrast material within
formed during peak contrast material enhance- edematous tubules that demonstrates increasing
ment allows reliable depiction of the splenic ar- attenuation over time. The infected kidney is usu-
tery and vein (41). ally enlarged, and there is often stranding in the
perinephric fat (Fig 13). Poorly enhanced areas of
Genitourinary Tract focal pyelonephritis can mimic a renal mass at
conventional CT. Helical CT is probably more
Acute Pyelonephritis.—Acute pyelonephritis is a specific in differentiating infection from tumor
common clinical diagnosis in patients who present (47). It is also helpful in detecting subtle cases of
with fever, chills, and flank tenderness. Infections acute pyelonephritis; clues to the diagnosis in-
typically result from ascending retrograde spread clude loss of normal, sharp corticomedullary dif-
through the collecting ducts into the renal paren- ferentiation and delayed appearance of the corti-
chyma. Patients are referred for CT evaluation of cal nephrogram, abnormalities that are visualized
acute pyelonephritis when symptoms are poorly only during early dynamic contrast enhancement.
localized or complications are suspected (44–46). Delayed views of the infected kidney may dem-
Tailored helical CT in patients with acute pyelo- onstrate a nephrogram with increased attenua-
nephritis usually consists of several acquisitions tion (17).
through the kidneys during various phases of renal
enhancement (47). Typically, images are acquired Renal Infarction.—Patients with renal infarc-
during the corticomedullary phase beginning 30 tion typically present with acute flank pain and
seconds after initiation of injection and during ei- may have hematuria. Renal infarcts are typically
ther the nephrographic phase (70–90 seconds after the result of embolism (usually in a diseased
injection) or the excretory phase (5 minutes after heart), aortic dissection, trauma, or thrombosis
injection). (51,52). Tailored helical CT must include an ac-
Helical CT findings in acute pyelonephritis quisition during the corticomedullary phase of
consist of focal areas of striated or wedge-shaped enhancement (beginning 30 seconds after initia-
tion of injection) when renal arterial and venous
opacification is greatest. Helical CT findings in-
clude one or more focal parenchymal defects that
RG ■ Volume 20 • Number 3 Urban and Fishman 733
12. 13.
Figures 12, 13. (12) Acute bilateral pyelonephritis in a 34-year-old woman. Axial CT scan obtained with intrave-
nous contrast material demonstrates patchy, striated nephrograms. (13) Acute pyelonephritis in a 69-year-old man.
Axial nephrographic-phase CT scan obtained with intravenous contrast material reveals patchy enhancement of the left
kidney. The kidney is minimally enlarged with perinephric stranding, secondary findings that also suggest infection.
14. 15.
Figures 14, 15. (14) Abdominal aortic aneurysm and renal infarction in a 67-year-old man. On an axial arterial-
phase CT scan obtained with intravenous contrast material, the lateral aspect of the left kidney demonstrates the char-
acteristic appearance of renal infarction (arrow). (15) Global infarction in a 67-year-old man with aortic dissection.
The patient presented with acute left flank pain. Axial CT scan obtained with intravenous contrast material reveals a
dissection flap occluding the left renal artery (arrow). Flow to the left kidney is obstructed.
involve both the cortex and medulla and extend medial aspect. With global infarction, the entire
to the capsular surface of the kidney. Segmental kidney is nonperfused (Fig 15). Characteristic
infarcts of the anterior or posterior renal arteries rim enhancement representing collateral capsular
demonstrate a characteristic appearance at CT perfusion may be seen surrounding the nonfunc-
(Fig 14) (53). The larger ventral branch supplies tioning, infarcted kidney (51).
the anterior lateral portion of the kidney, whereas
the smaller dorsal branch supplies the posterior
734 May-June 2000 RG ■ Volume 20 • Number 3
16a. 16b.
Figures 16, 17. (16) Obstructing ureteral
calculus in a 51-year-old woman. (a) Axial
unenhanced CT scan demonstrates right hy-
dronephrosis. (b) CT scan obtained inferior
to a clearly depicts an obstructing calculus in
the midureter (arrow). (17) Ureteral calculus
in a 24-year-old man. Axial unenhanced CT
scan shows focal stranding around the middle
of the right ureter, a finding that helps local-
ize a subtle calculus (arrow).
Gastrointestinal Tract
a. b.
Figure 19. Acute appendicitis. Axial CT scans obtained with intravenous contrast material
in a 27-year-old woman (a) and a 62-year-old man (b) show a minimally distended appen-
dix with an enhancing wall (arrow). Stranding is seen in the periappendiceal fat. These find-
ings are pathognomonic for acute appendicitis.
a. b.
Figure 20. Perforating appendicitis in a 44-year-old man. (a) Axial CT scan obtained with in-
travenous contrast material demonstrates subtle findings of a minimally enhancing, tortuously di-
lated appendix (arrowheads). This finding was initially misinterpreted as the normal terminal ileum.
(b) CT scan obtained inferior to a demonstrates minimal fluid in the pelvis (arrow). B = bladder. In
this case, use of oral contrast material would likely have aided in making the correct diagnosis. Al-
though reported sensitivities for detecting acute appendicitis are similar with any combination of
oral, intravenous, and rectal contrast material (or with none of the three), we prefer using a com-
bination of the first two whenever possible.
sign of inflammation (Fig 19). However, in pa- also demonstrate complications of appendicitis,
tients with adequate intraperitoneal fat, diagnosis including perforation, small bowel obstruction,
can be made without oral or intravenous contrast and mesenteric venous thrombosis (Fig 20).
material because the focal nature of the periap- Many other conditions can lead to inflammation
pendiceal stranding is obvious. Helical CT can and abscess formation in the right lower quad-
rant and mimic findings of acute appendicitis at
both clinical examination and radiography (65–
RG ■ Volume 20 • Number 3 Urban and Fishman 737
24. 25.
Figures 24, 25. (24) Duodenitis in a 72-year-old man. The patient presented with postoperative nausea, vom-
iting, and abdominal pain. Axial CT scan obtained with intravenous contrast material shows moderate duodenal
thickening (arrowheads). (25) Perforated duodenal ulcer in a 62-year-old man. Axial CT scan obtained with
intravenous contrast material demonstrates stranding in the right anterior pararenal space (arrow), a common
location for the traversal of fluid in patients with perforated ulcer. Surgery confirmed the presence of a large
perforated ulcer.
depiction of wall thickening and is best achieved if ful and specific in patients with complications
rectal rather than oral contrast material is used. from penetrating ulcers (Fig 25) (75), who will
Most authors suggest the administration of 400– demonstrate inflammatory changes in the adja-
800 mL of 3% iodinated contrast material (16). cent soft tissues and organs, including the pan-
In practice, however, the diagnosis can be estab- creas, liver, and lesser omentum. These changes
lished in most patients without use of rectal con- are easily identified at helical CT (75,76). CT is
trast material, which can be reserved for the oc- also valuable in the detection of clinically unsus-
casional patient with equivocal findings. pected perforation, although determining the pre-
cise site of perforation is often difficult (76).
Peptic Ulcer Disease.—Patients with peptic ulcer
disease present with epigastric pain, nausea, and Small Bowel Obstruction.—Small bowel ob-
vomiting. At times, symptoms are nonlocalized or struction is a common cause of acute abdominal
indistinguishable from those in acute pancreatitis pain. Patients often present with nausea, vomiting,
or cholecystitis, and CT is often performed in such and abdominal tenderness. Small bowel obstruc-
cases. Alternatively, patients with known ulcer tion has a variety of causes, the most common of
disease may undergo CT for assessment of severe which are adhesions (64%–79% of cases), hernia
complications of ulcer penetration, including pan- (15%–25%), and tumor (10%–15%) (77). The
creatitis, perforation, and abscess formation. utility of CT in the evaluation of small bowel ob-
Tailored helical CT of the stomach and duode- struction depends somewhat on the degree and
num is best performed after adequate distention suspected cause of obstruction. At most institu-
following the ingestion of either water or positive tions, CT has supplanted the small bowel follow-
oral contrast agent. Intravenous bolus administra- through study as the initial examination of choice
tion of contrast material is also necessary if water because it can help confirm the need for or obviate
is used (13,14). Peptic ulcer disease often mani- surgery. CT has proved to be very useful in cases
fests at CT as focal thickening (Fig 24). Unfortu- of high-grade small bowel obstruction, with a sen-
nately, gastric and duodenal thickening are often sitivity of 90%–96%, a specificity of 96%, and an
nonspecific, and correlation with the patient’s accuracy of 95% (78,79). In low-grade obstruc-
symptoms is poor (73). In addition, many patients tion, however, the accuracy of CT is only about
have chronic thickening, often due to infection 50%, and follow-up CT or barium examination
with Helicobacter pylori, which can produce sub- may be indicated. In all cases of small bowel ob-
stantial thickening in the body and antrum of the struction (including low-grade obstruction), sensi-
stomach (74). Helical CT is probably most help- tivity drops to about 60%, with a specificity of
80% and an accuracy of 66% (80). For this rea-
RG ■ Volume 20 • Number 3 Urban and Fishman 739
a. b.
Figure 26. Small bowel obstruction from inguinal hernia in a 55-year-old man. (a) Axial CT scan obtained with
intravenous contrast material shows moderately dilated small bowel loops with minimal mural thickening and en-
hancement. (b) CT scan obtained inferior to a shows a transition point at the site of an incarcerated right inguinal
hernia (arrow).
obstruction and is often associated with an under- obstructions may have a peculiar C- or U-shaped
lying mass that serves as a lead point (84,85). In configuration, and fluid in the mesenteric leaves
the absence of an obstructing mass or hernia at may radiate out from the point of strangulation
CT, small bowel obstruction is most likely due to (Fig 29). An unusual course and diffuse engorge-
adhesions, especially in patients with a history of ment of the mesenteric vasculature with mesen-
surgery (Fig 28). A finding of adhesions as the teric haziness are highly specific for strangulation
cause of small bowel obstruction effectively ex- (86).
cludes an obstructing mass or hernia in the ma-
jority of patients. Ischemic Bowel.—Patients with bowel ischemia
Helical CT can also be useful in differentiating can present with symptoms ranging from rela-
simple from strangulated small bowel obstruction tively minor discomfort to acute abdominal pain,
(86,87). Strangulated small bowel obstruction which makes clinical diagnosis difficult (89). Pre-
involves mechanical obstruction proximal to the dominant causes of intestinal ischemia include
involved loop and closed-loop obstruction with vascular occlusion or thrombosis, whether from
venous congestion of the involved loop (88). Ini- arterial or venous disease, and hypoperfusion.
tially, venous outflow is occluded in the involved Usually, a combination of these factors is seen,
loop, resulting in distention and engorgement of and the degree to which a given factor predomi-
vessels. Bowel hemorrhage ensues, resulting in nates determines patient outcome. Ischemia can
transudation of fluid into the peritoneal cavity. also result from secondary vascular compromise
Findings that suggest strangulation include poorly in patients with bowel obstruction, including
enhanced or unenhanced bowel wall and the ser- closed loop obstruction, hernia, and intussus-
rated beak sign, both of which are 100% specific ception. CT plays a key role in identifying early
for strangulation (86). The serrated beak sign is changes of ischemia and in determining the un-
caused by twisting of bowel with regional engorge- derlying cause of ischemic bowel (90–92). How-
ment of the mesenteric vasculature, mesenteric ever, CT findings in patients with ischemic
edema, and bowel wall thickening. Closed-loop bowel, even when newer helical CT techniques
are used, can be nonspecific (93). In patients
with obstruction, helical CT has only an 80%
positive predictive value for ischemia, and up to
RG ■ Volume 20 • Number 3 Urban and Fishman 741
a. b.
Figure 30. Diffuse bowel ischemia in a 49-year-old woman. The patient presented with recurrent pancreatic
cancer and had a history of Whipple disease. (a) Axial CT scan obtained with intravenous contrast material
reveals a tumor surrounding the pancreas and mesenteric vessels (white arrowheads). The superior mesenteric
artery is patent (straight arrow), but the superior mesenteric vein is thrombosed (curved arrow). Infarcts are seen
in the left kidney (black arrowheads). (b) On a CT scan obtained inferior to a, minimal bowel wall thickening
is seen in both the small and large intestine (arrows). Surgery revealed diffuse ischemia.
33. 34.
Figures 33, 34. (33) Ischemic small bowel and pneumatosis intestinalis in a 41-year-old woman. The patient
presented with acute thrombosis of multiple vessels including the superior mesenteric artery. Unenhanced CT
scan reveals air within the bowel wall (arrow). Pneumatosis is often best appreciated with a lung window setting.
(34) Bowel necrosis and mesenteric air in a 53-year-old woman. Unenhanced CT scan demonstrates air within the
mesenteric vessels (arrowheads). Surgery revealed transmural necrosis of the distal ileum, cecum, and sigmoid co-
lon.
positive oral contrast agent in patients with pre- Perforation generally indicates a catastrophic com-
sumed ischemia, especially in the setting of ob- plication that can result from a multitude of po-
struction. In these patients, intravenous contrast tential causes, including severe intestinal inflam-
material is essential for depiction of the thickened, mation, peptic ulcer disease, diverticulitis, infarc-
edematous bowel wall, which can easily be appre- tion, trauma, and closed-loop obstruction (97).
ciated against the obstructed, fluid-filled intestine. Perforation can also complicate neoplasms, and
Air within the bowel wall (pneumatosis intesti- the search for an underlying mass is warranted in
nalis), mesentery, and portal venous system are late the appropriate clinical setting. Iatrogenic perfora-
CT signs of bowel ischemia and usually portend a tion is occasionally seen following endoscopic pro-
grave prognosis (Figs 33, 34). A multitude of en- cedures, especially endoscopic biopsy or sphinc-
tities can manifest with air in the bowel wall, in- terotomy (Fig 35) (98).
cluding conditions that disrupt the bowel mucosa Helical CT is ideally suited for rapid evaluation
(eg, bowel obstruction, inflammatory bowel dis- of the abdomen in patients with acute pain from
ease), entities that increase bowel permeability suspected perforation. CT is often indicated when
(eg, graft-versus-host disease, acquired immuno- free air is seen but the perforation site is unclear at
deficiency syndrome, steroid therapy), and pul- conventional radiography. Because CT is more
monary disease (eg, chronic obstructive pulmo- sensitive than conventional radiography in the de-
nary disease) (95,96). CT findings must always tection of subtle pneumoperitoneum, it is also in-
be correlated with clinical history and symptoms dicated when free air is strongly suspected despite
in patients with pneumatosis intestinalis (96). normal abdominal radiographic findings (99,100).
Unenhanced CT is often performed to expedite
Gastrointestinal Perforation.—Patients with evaluation. If possible, oral and intravenous con-
bowel perforation usually present with obvious in- trast material should be used to help localize the
dications of peritonitis, although symptoms can perforation and characterize complications includ-
be masked in immunosuppressed patients or in ing peritonitis and abscess formation. In supine
patients undergoing steroid therapy. Spontaneous CT, the anterior peritoneal surface of the liver is
bowel perforation usually occurs with underlying the most nondependent portion of the body and is
disruption of the mural integrity of the intestine. often the location where extraluminal air can first
be detected. However, detection of the actual site
of perforation is often challenging because the lo-
cation of the free air does not necessarily correlate
with the site of perforation (76,101). Extravasation
RG ■ Volume 20 • Number 3 Urban and Fishman 743
35. 36.
Figures 35, 36. (35) Perforating gastric cancer in a 61-year-old man who had undergone endoscopy. Axial
CT scan obtained with intravenous contrast material demonstrates extensive extraluminal air, predominantly
in the retroperitoneum. The exact site of perforation can be difficult to determine if there is a large amount of air,
especially in patients with iatrogenic perforation. (36) Perforated benign gastric ulcer in an elderly man. Axial CT
scan obtained with intravenous contrast material demonstrates free air anterior to the liver (black arrow) as well
as focal extraluminal oral contrast material (white arrow), which helped localize the perforation in the stomach.
Figure 43. Hematoma in a 38-year-old man with he- Figure 44. Renal cell carcinoma in a 74-year-
mophilia who presented with acute abdominal pain. old man. Axial CT scan obtained after rapid intra-
Axial CT scan obtained with intravenous contrast ma- venous administration of contrast material demon-
terial demonstrates bilateral hematomas with heteroge- strates hemorrhage in the right kidney (arrow).
neous attenuation causing minimal enlargement of the Surgery revealed hemorrhagic cystic degeneration
psoas muscles (arrows). from renal cell carcinoma.
muscular hemorrhage is the psoas muscle (Fig 6. Heiken JP, Brink JA, Vannier MW. Spiral (heli-
43). Bleeding can also result from an underlying cal) CT. Radiology 1993; 189:647–656.
7. Fishman EK. Spiral CT: applications in the
abdominal tumor, especially renal cell carcinoma emergency patient. RadioGraphics 1996; 16:
(Fig 44) (116). 943–948.
8. Baker SR. Unenhanced helical CT versus plain
Conclusions abdominal radiography: a dissenting opinion.
Helical CT is a rapid and efficient means of evalu- Radiology 1997; 205:45–47.
9. Fishman EK. High-resolution three-dimensional
ating patients with acute abdominal pain. Atten- imaging from subsecond helical CT data sets:
tion to proper technique and protocol is essential applications in vascular imaging. AJR Am J
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AT. Diagnosis of acute flank pain: value of un-
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