AJR 2004; 183:899-906
© American Roentgen Ray Society
MDCT of Patients with Acute Abdominal Pain: A New Perspective Using Coronal Reformations from Submillimeter Isotropic Voxels
Erik K. Paulson1,
Tracy A. Jaffe,
John Thomas,
John P. Harris and
Rendon C. Nelson
1 All authors: Department of Radiology, Duke University Medical Center, Box
3808, Durham, NC 27710.
Received December 9, 2003;
accepted after revision March 24, 2004.
Address correspondence to E. K. Paulson
(pauls003{at}mc.duke.edu).
Introduction
Numerous studies indicate that CT, when combined with careful physical
examination and evaluation of laboratory results, provides useful diagnostic
information in patients with an acute abdomen
[1–4].
As a result, CT is increasingly used in the emergency department setting. MDCT
is a technologic advance that allows simultaneous acquisition of multiple
images during a single rotation of the X-ray tube
[5]. With the recently
developed 16-MDCT scanner, it is now possible to scan the entire abdomen and
pelvis within a breath-hold at a resolution of less than 1 mm (0.5–0.75
mm) in the x, y, and z axes. These data sets result in
voxels that are both submillimeter in dimension and isotropic, suggesting that
reformations in any desired plane will have a spatial resolution similar to
that of the axial plane. With 4- or 8-MDCT scanners, it was not possible to
cover the entire abdomen and pelvis within a single breathhold at
submillimeter z-axis resolution.
Heretofore, the usefulness of multiplanar reformations was limited by the
speed with which images could be reconstructed and the necessity of performing
several time-consuming steps. First, the source images were reconstructed from
the raw data with at least a 50% overlap. The reconstructed images were
transferred to an independent workstation that, depending on the number of
images and processing speed of the computer, might require significant
computational time. Then to view the images, an operator had to prescribe the
parameters on the workstation. The total time required for this process ranged
from 10 to 30 min, far exceeding the time required to review the axial images
alone. Recently, console systems have become available that have streamlined
and shortened the time required to perform reconstructions.
Radiologists are skilled in interpreting CT scans in the axial plane, but
the development of MDCT coupled with faster reconstruction hardware and
software has piqued interest in viewing the abdomen in planes other than the
axial plane [6]. In some
patients with acute abdominal pain, the coronal plane images may serve as a
useful adjunct to the axial plane images. Images in the coronal plane are
particularly appealing to surgeons because the orientation of structures is
analogous to that encountered during an exploratory laparotomy. We illustrate
our preliminary use of coronal reformations using 16-MDCT scanner as an
adjunct to the axial plane in the evaluation of patients with acute abdominal
pain.
MDCT Protocol
Scanning was performed from the dome of the diaphragm through the pubic
symphysis with a 16-MDCT scanner (LightSpeed, GE Healthcare). Patients
ingested 450 mL of a 2% barium sulfate suspension (Readi-Cat 2, EZ-EM)
1–2 hr before scanning. Then, 150 mL of iopamidol (Isovue, 300 mg I/mL,
Bracco Diagnostics) was injected at a rate of 3 mL per second. Imaging was
performed during the portal venous phase as determined by bolus tracking and
automated triggering technology. The parameters were 140 kVp; 350 mA; 16
x 0.625 mm detector configuration; pitch, 1.75; 17.5 mm per rotation;
and 0.5 sec per rotation. The axial data was reconstructed twice, first with a
5-mm thickness at 5-mm intervals and then with a 0.625-mm thickness at 0.5-mm
intervals. The second set of reconstructed axial images were then reformatted
in the coronal plane with a thickness of 3 mm at 5-mm intervals.
The CT dose index of this 16-MDCT protocol is equivalent to that of a
protocol for an analogous 4-MDCT scanner (LightSpeed, GE Healthcare) using the
technical parameters of 140 kVp; 220 mA; 4 x 2.5 mm detector
configuration; pitch, 1.5; 15 mm per rotation; 0.8 sec per rotation; and 5-mm
reconstruction thickness.
The reconstructions were performed on a commercially available console
system devoted to rapid reconstruction (Xtream, GE Healthcare) that consists
of symmetric multiprocessing dual Intel Xenon 2.66-GHz processors (Intel
Corp.) with a CT image generator capable of reconstructing from six to 10
images per second. The image generator required approximately 2 min to
reconstruct both the axial and coronal images. The entire process was
performed by the technologist at the operator's console. The 5-mm-thick axial
and 3-mm-thick coronal images were transferred to a PACS workstation
(Centricity 1.0, GE Healthcare) as a separate series of images for
interpretation.
Sources of Abdominal Pain
Appendicitis
CT is increasingly used in patients with an equivocal clinical presentation
of acute appendicitis [7] (Fig.
1A,
1B). Although axial CT
performed with IV and oral contrast agents is sensitive and specific for acute
appendicitis, there are patients in whom the diagnosis may be difficult or in
doubt. For example, identifying the appendix may be difficult in patients with
scant intraperitoneal fat tissue (Fig.
2A,
2B), suboptimal opacification
of the terminal ileum (Fig. 3A,
3B), a retrocecal appendix, or
an appendix located low in the pelvis adjacent to the adnexa. In such
patients, coronal imaging may provide improved appendiceal visualization and
enhance confidence as to the presence or absence of acute appendicitis.
Furthermore, some clinical mimics of acute appendicitis may be more easily
seen on coronal images as opposed to axial images. For example, inflammatory
conditions of the cecum or terminal ileum may be seen to better advantage
using images in the coronal plane (Figs.
4A,
4B and
5A,
5B).
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Fig. 1A. —36-year-old woman with diffuse abdominal pain. Axial MDCT
scan obtained with IV and oral contrast agents shows thickened appendix
(arrow) medial to cecum. There is minimal adjacent inflammation.
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Fig. 1B. —36-year-old woman with diffuse abdominal pain. Coronal
reformation of MDCT scan shows entire length of thickened appendix
(arrows) arising from cecum and extending into pelvis. Coronal image
provides confidence in suspected diagnosis of acute appendicitis, which was
confirmed surgically.
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Fig. 2A. —19-year-old woman who presented in emergency department
reporting 10 hr of increasing cramping pain radiating to right lower quadrant.
Axial MDCT scan obtained with IV and oral contrast agents shows collapsed
loops of small bowel and colon in pelvis. It is difficult to identify appendix
with confidence.
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Fig. 2B. —19-year-old woman who presented in emergency department
reporting 10 hr of increasing cramping pain radiating to right lower quadrant.
Coronal reformation of MDCT scan shows portion of normal contrast-filled
appendix (arrows), adjacent to gas-filled sigmoid colon. Appendix has
no wall thickening or adjacent inflammation. In this patient, coronal
reformations aided in identification of normal appendix, and acute
appendicitis could be ruled out with high degree of confidence.
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Fig. 3A. —20-year-old woman with right lower quadrant pain and fever 1
day after uncomplicated vaginal delivery. Ut = uterus. Axial MDCT scan
obtained with IV and oral contrast agents shows gas- and fluid-filled
structure (arrows) medial to cecum with surrounding fluid and
inflammation. On this image, it is difficult to differentiate distended
appendix with perforation from fluid-filled small bowel and to determine
whether rounded high-attenuation structure (arrowhead) represented
oral contrast material or appendicolith. Dome of postpartum uterus is
identified at midline.
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Fig. 3B. —20-year-old woman with right lower quadrant pain and fever 1
day after uncomplicated vaginal delivery. Ut = uterus. Coronal reformation of
MDCT scan shows tubular structure (arrows) medial to cecum in
different perspective. High-attenuation structure (arrowhead) clearly
represents appendicolith. At surgery, gangrenous appendicitis with an
appendicolith and perforation were identified.
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Fig. 4A. —48-year-old man with periumbilical pain who was referred to
rule out acute appendicitis. Axial MDCT scan obtained with IV and oral
contrast agents shows impressive thickening of cecum (arrows) with
adjacent inflammatory changes.
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Fig. 4B. —48-year-old man with periumbilical pain who was referred to
rule out acute appendicitis. Coronal CT reformation of MDCT scan clearly
depicts inflammatory mass (arrows) medial to cecum as well as
inflammatory changes. Portion of appendix (arrowheads) is well
visualized and appears normal. At surgery, inflammatory mass proved to be
contained perforation from diverticulitis. Appendix was normal.
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Fig. 5A. —31-year-old woman with periumbilical pain and fever. Axial
MDCT scan obtained with IV and oral contrast agents shows thickening of cecum
(arrows) and cluster of enhancing lymph nodes (arrowheads)
in adjacent mesentery.
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Fig. 5B. —31-year-old woman with periumbilical pain and fever. Coronal
CT reformation of MDCT scan reveals enlarged lymph nodes (arrowheads)
along ileocolic veins that are more conspicuous in coronal than in axial
plane. Note thickened ascending colon (white arrow). On colonoscopy,
acute colitis was identified, which was likely cause of adenitis. Note
respiratory motion artifact (black arrows) along both sides of
diaphragm.
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Bowel Obstruction
Bowel obstruction is a frequent cause of abdominal pain and accounts for
20% of all surgical admissions. In some patients with a dilated proximal bowel
and a decompressed distal bowel, the specific point of transition may be
difficult to determine using axial images alone. Coronal reformations allow
one to view the presumed site of obstruction from a different perspective and
may help one to determine the presence or absence of a transition point with
greater confidence [8] (Figs.
6A,
6B and
7A,
7B). Identification of the
precise transition point can help in determining the cause of obstruction
(Fig. 8A,
8B). Complications from bowel
obstruction such as ischemia may be identified on coronal reformations
(Fig. 9).
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Fig. 6A. —91-year-old woman with 3-day history of crampy abdominal
pain, nausea, and vomiting. Axial MDCT scan obtained with IV and oral contrast
agents shows dilated small bowel (white arrows) and collapsed colon
(arrowheads). Note dilated bowel in region of inguinal canal
(black arrow).
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Fig. 6B. —91-year-old woman with 3-day history of crampy abdominal
pain, nausea, and vomiting. Coronal CT reformation of MDCT scan shows bowel
dilatation throughout abdomen. "Knuckle" of bowel
(arrows) passes through right femoral canal where there is abrupt
change in caliber. At surgery, incarcerated bowel within femoral hernia was
reduced. Note streak artifact (arrowheads) coursing through abdomen
caused by metallic hardware in lower thoracic and lumbar spine (not
shown).
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Fig. 7A. —57-year-old-woman who presented with nausea, vomiting,
abdominal pain, and no bowel movement for 1 week. Axial MDCT scan obtained
with IV and oral contrast agents shows dilatation of hepatic flexure of colon
(arrows) due to obstructing mass (arrowheads) in splenic
flexure.
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Fig. 7B. —57-year-old-woman who presented with nausea, vomiting,
abdominal pain, and no bowel movement for 1 week. Coronal CT reformation of
MDCT scan shows dilated small bowel and colon up to leading edge of splenic
flexure mass (arrow) described in A. Note enlarged lymph nodes
(arrowheads) in gastrocolic ligament. At colonoscopy, an obstructing
adenocarcinoma was identified.
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Fig. 8A. —58-year-old man with remote history of testicular cancer and
radiation therapy who presented with pain and diarrhea and who was referred to
rule out bowel obstruction. On axial MDCT scan obtained with IV and oral
contrast agents, it is unclear whether central fluid-attenuation structures
(arrows) are dilated loops of bowel or loculated fluid suggesting
abscess.
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Fig. 8B. —58-year-old man with remote history of testicular cancer and
radiation therapy who presented with pain and diarrhea and who was referred to
rule out bowel obstruction. Coronal CT reformation of MDCT scan clarifies
presence of fluid collection (arrows) with enhancing pseudocapsule.
Subsequent percutaneous drainage yielded 125 mL of purulent material. Cultures
grew Klebsiella pneumoniae and Bacteroides fragilis
organisms.
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Fig. 9. —50-year-old woman with nonbilious emesis and colicky
abdominal pain. Coronal reformation of MDCT scan obtained with oral contrast
material shows dilated and thick-walled bowel (arrows) in mid
abdomen. Other loops of bowel are normal and filled with contrast material.
Note loculated right subphrenic fluid (arrowheads). At exploratory
laparotomy, ischemic bowel (caused by closed-loop obstruction from volvulus)
was resected.
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Female Pelvis
Female pelvic anatomy and abnormality may be difficult to characterize
using axial images. In particular, it is difficult to delineate the adnexal
structures from the uterus, pelvic side wall, and small and large bowels. As
with pelvic MRI, the coronal plane on MDCT often clarifies confusing anatomy.
For example, differentiating a hydro- or pyosalpinx from a multiseptate cystic
ovarian mass is easier on coronal images
(Fig. 10).
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Fig. 10. —36-year-old woman with right lower quadrant pain. Coronal
reformation of MDCT scan obtained with IV and oral contrast material shows
tubular fluid-filled structure (black arrows) in right adnexa.
Inflammation (arrowheads) is present in fatty tissue in right lower
quadrant. Note appendix (white arrow) is normal and opacified with
oral contrast material. At laparoscopy, tubular structure in right adnexa
proved to represent pyosalpinx.
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Miscellaneous
Various abnormalities may be better visualized in the coronal plane
including ureteral obstruction from a stone; focal bowel diseases such as
intussusception, volvulus, and bowel ischemia; and the extent of bowel
involvement from inflammatory bowel disease (Figs.
11,
12A,
12B,
13). Coronal images nicely
illustrate the mesenteric fat tissue and vessels that often lay within the
coronal plane (Fig. 14).
Inflammatory conditions such as mesenteric adenitis or mesenteric venous or
arterial thrombosis may be well delineated on coronal reformations
[9]. Peritoneum-based disease
such as peritoneal carcinomatosis also may be well depicted in the coronal
plane (Fig. 15A,
15B).
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Fig. 11. —23-year-old woman who presented with abdominal pain after
undergoing heart transplantation for peripartum cardiomyopathy. Coronal
reformation of MDCT scan obtained with IV and oral contrast material shows
free intraperitoneal fluid, pneumatosis coli (arrows), and gas
(arrowheads) in peripheral portal vein branches. Findings are
consistent with colonic ischemia. These findings were also evident on axial
MDCT scans (not shown).
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Fig. 12B. —48-year-old woman with bloody diarrhea. Coronal CT
reformation of MDCT scan shows thickening of descending colon
(arrows). Note excellent visualization of vasa recta
(arrowheads) medial to sigmoid colon. On colonoscopy, ischemic
colitis was identified.
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Fig. 13. —36-year-old man with periumbilical pain referred to rule out
acute appendicitis. Coronal CT reformation of MDCT scan obtained with IV and
oral contrast agents shows left-sided pelvicaliectasis (arrow).
Dilated ureter can be traced to 4-mm obstructing calculus
(arrowhead).
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Fig. 14. —35-year-old man with right lower quadrant pain. Coronal CT
reformation of MDCT scan shows small amount of intraperitoneal fluid
(arrow) adjacent to small bowel. Note excellent visualization of
mesenteric vessels (white arrowhead) and small lymph nodes (black
arrowhead).
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Fig. 15A. —47-year-old woman with ovarian cancer and abdominal pain.
Axial MDCT scan obtained with IV and oral contrast agents shows questionable
soft-tissue abnormality (arrows) anterior to ascending colon.
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Fig. 15B. —47-year-old woman with ovarian cancer and abdominal pain.
Coronal CT reformation of MDCT scan clearly shows peritoneal-based soft-tissue
thickening (arrows) along ascending colon and inferior liver capsule.
Note nodular capsular-based implants (arrowheads) along liver dome,
consistent with peritoneal carcinomatosis.
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Conclusion
In patients with acute abdominal pain, MDCT with coronal reformations from
submillimeter isotropic voxels provides a useful adjunct to axial images. The
coronal reformations should not replace careful evaluation of the axial
images. However, in patients with an acute abdomen, the coronal images may
clarify confusing anatomy, add confidence to interpretation, and provide a
perspective familiar to referring surgeons.
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Top
Introduction
MDCT Protocol
