DOI:10.2214/AJR.07.2761
AJR 2008; 190:643-649
© American Roentgen Ray Society
MDCT of Acute Mild (Nonnecrotizing) Pancreatitis: Abdominal Complications and Fate of Fluid Collections
Dipti K. Lenhart1 and
Emil J. Balthazar
1 Both authors: Department of Radiology, NYU School of Medicine–Bellevue
Hospital Center, 462 First Ave., NB 3W33A, New York, NY 10016.
Received June 21, 2007;
accepted after revision September 28, 2007.
Address correspondence to D. K. Lenhart
(dipti.kandlikar{at}med.nyu.edu).
CME
This article is available for CME credit. See
www.arrs.org
for more information.
Abstract
OBJECTIVE. The objective of our study was to describe the occurrence
of local complications and the fate of fluid collections in milder forms of
acute nonnecrotizing pancreatitis.
MATERIALS AND METHODS. Initial MDCT studies of 169 consecutive
patients with mild acute pancreatitis and 203 follow-up CT examinations were
reviewed. The fate of peripancreatic fluid collections was investigated, and
the incidence and type of local complications were recorded and correlated to
the CT grading system (A–E).
RESULTS. Complications developed in nine of 169 patients, for an
incidence of 5.3%. All morbidity occurred in the subgroup of 73 patients with
initial fluid collections, for an incidence of 12.3%. Follow-up CT
examinations available in 51 of these 73 patients documented rapid fluid
resolution in 35 cases (68.6%) and persistence of fluid more than 2 weeks from
onset in seven asymptomatic patients (13.7%). Acute, life-threatening
complications (hemorrhage, infection, perforation) occurred in five patients,
for an incidence of 6.8% among the 73 patients with initial fluid collections,
or 3.0% in the entire group of 169 patients. Five patients developed acute
pseudocysts. Long-term follow-up studies discovered two patients with chronic
pancreatitis and one with groove pancreatitis.
CONCLUSION. A small number of acute, life-threatening abdominal
complications and chronic complications are expected to occur in patients with
milder forms of acute nonnecrotizing pancreatitis presenting with fluid
collections. In these patients, clinical monitoring and repeated imaging
studies are recommended to document the resolution of fluid or the development
of complications.
Keywords: abdominal imaging • acute pancreatitis • MDCT • pancreas
Introduction
Acute pancreatitis is a common disease in the developed world that is
characterized by a diffuse inflammatory process affecting the pancreas and
triggered by the leakage and extravasation of activated pancreatic secretions.
Acute pancreatitis leads to a wide range of local and systemic
pathophysiologic alterations and to a large variability in the clinical
manifestation and prognosis
[1–5].
For clinical purposes, a useful simplified classification of acute
pancreatitis was proposed by the Atlanta, Georgia International Symposium on
Acute Pancreatitis [6,
7].
According to this classification system, an acute attack of pancreatitis is
divided into two major clinical forms: First, mild acute pancreatitis
occurring in approximately 80% of patients has no CT evidence of necrosis,
exhibits minimal or no distal organ dysfunction, and shows rapid recovery
without complications. It is a self-limiting disease previously called
"edematous" or "interstitial" pancreatitis. Second,
severe acute pancreatitis, also called "necrotizing pancreatitis;"
occurs in approximately 20% of patients; shows CT evidence of parenchymal
necrosis (lack of enhancement); and exhibits systemic manifestations, distal
organ failure, a protracted clinical course, and an increased incidence of
morbidity and mortality [6,
7]. Indeed, most patients who
develop local complications have necrotizing pancreatitis
[8–11].
The mortality incidence is less than 1% in mild pancreatitis, with a striking
increase to 10–23% in the presence of pancreatic necrosis
[3,
10,
11]. Furthermore, more than
50% of deaths do not occur immediately, but rather within a few weeks after an
acute episode secondary to abdominal complications and occur mainly in
patients with pancreatic necrosis
[1,
11]. This clinical
classification emphasizes the importance of pancreatic necrosis as a
predictive indicator, while overlooking intermediary forms of disease
presenting with fluid collections but without necrosis.
The purpose of this retrospective study was to estimate whether and to what
degree milder forms of pancreatitis without necrosis contribute to the
development of local abdominal complications. We attempted to determine the
fate and outcome of extravasated peripancreatic fluid collections and to
assess the incidence and type of local morbidity and patient outcome as
correlated with the CT grading scale
[12] in patients without
pancreatic necrosis.
Materials and Methods
Subjects
A retrospective review of CT scans obtained in patients with acute
pancreatitis presenting to either of our institution's two large tertiary care
centers over a 2-year period (April 2004–April 2006) was undertaken
according to a protocol approved by our institutional review board; patient
informed consent was waived. We identified 233 patients with acute
pancreatitis in our radiology database. By review of their images, 28 patients
were excluded because of the presence of pancreatic necrosis (on either
initial or follow-up CT scans) and an additional 36 patients were excluded
because of either concomitant tumor, complications from prior episodes of
pancreatitis, motion or streak artifacts on the CT scan that limited
evaluation, or unenhanced scans. A total of 169 patients with acute mild
(nonnecrotizing) pancreatitis were included in our study. Clinical staging
criteria (Ranson's signs [13])
were not used.
In addition to the 169 initial CT scans obtained within 24 hours of patient
presentation to the hospital, we reviewed 203 follow-up CT examinations, for a
total of 372 studies or an average of 2.2 examinations per patient. Among the
169 initial episodes, 82 patients (48.5%) had follow-up examinations, for an
average of 3.5 scans per patient in this subgroup. The follow-up time ranged
from 4 to 880 days, with an average time to final CT examination of 124 days.
Seventy-three percent of patients with follow-up studies underwent their first
follow-up CT within 60 days of their initial CT examination.
Our series of 169 subjects was composed of 93 males and 76 females with an
age range of 11–90 years (average age, 49 years). The cause of
pancreatitis was gallstones in 57 patients, alcohol in 44 patients, gallstones
and alcohol combined in nine patients, other causes (including hyperlipidemia,
lupus, pancreas divisum, and post-ERCP) in 10 patients, and unknown in 49
patients.
CT Technique
Initial CT examinations were performed on a 16-MDCT scanner (Sensation 16,
Siemens Medical Solutions) in 103 patients and on a 4-MDCT scanner
(LightSpeed, GE Healthcare) in 66 patients.
One hundred twenty-five patients (74%) were clinically suspected to have
acute pancreatitis and were scanned using our institution's two-phase
acquisition pancreatic protocol. These patients were instructed to drink 500
mL of water for negative opacification of the gastrointestinal tract
immediately before imaging. The initial pancreatic phase (late arterial
dominant phase) of the examination was performed over the upper abdomen from
T11 to L3 vertebral body levels with a scanning delay of 40 seconds after the
start of IV administration of 1.5 mL/kg of contrast material (300 mg I/mL,
Ultravist [iopromide, Bayer HealthCare] or Omnipaque [iohexol, GE Healthcare])
at an injection rate of 4 mL/s. On the 16-MDCT scanner, the images were
acquired at 120 kVp with a detector row configuration of 16 x 0.75 mm
and a table speed of 9.0 mm per rotation with a reconstructed slice thickness
of 3 mm. On the 4-MDCT scanner, the images were acquired at 120 kVp with a
detector row configuration of 4 x 1.25 mm and table speed of 7.5 mm per
rotation with a reconstructed slice thickness of 2.5 mm.
The second portal-dominant phase of the examination was performed from the
diaphragm to the symphysis pubis at an 80-second scanning delay. On the
16-MDCT scanner, the images were acquired at 120 kVp with a detector row
configuration of 16 x 1.5 mm, table speed of 18.0 mm per rotation, and
reconstructed slice thickness of 4 mm. On the 4-MDCT scanner, the images were
acquired at 120 kVp with a detector row configuration of 4 x 2.5 mm,
table speed of 15 mm per rotation, and reconstructed slice thickness of 5
mm.
Forty-four patients (26%) were scanned using a single-phase portal venous
acquisition with an 80-second scanning delay at an IV contrast injection rate
of 3 mL/s, using the same CT scanner parameters as the second phase of the
pancreatic protocol. These patients drank 1.5 L of diluted (2%) water-soluble
contrast material (Gastrografin [meglumine diatrizoate], Bristol-Myers Squibb)
beginning 1 hour before imaging.
Data Analysis
Reconstructed axial images were reviewed on our PACS workstation (either
PACS MagicView 1000, Siemens Medical Solutions; or Philips PACS, Philips
Medical Systems) and thinner collimation and coronal or multiplanar
reformation were performed if needed. All images were reviewed together by two
radiologists, one with 40 years of experience in abdominal imaging and the
other a radiology resident, both of whom were blinded to clinical follow-up
information.
The initial episodes of pancreatitis were stratified into five groups
(grades A–E) according to the previously described CT grading scale
[12]
(Table 1). The follow-up
studies were evaluated for the number and type of local complications,
including pseudocysts, hemorrhage, infection, bowel perforation, venous
thrombosis, pseudoaneurysm, and chronic and groove pancreatitis. The
complications were correlated with the initial CT grade. Fluid collections
that develop immediately after an episode of pancreatitis due to leakage of
pancreatic secretions define grades D and E pancreatitis. These are
ill-defined nonencapsulated collections to be distinguished from pseudocysts,
which are completely encapsulated fluid collections that develop more than 4
weeks after the initial episode of pancreatitis
[6,
7].
A two-tailed Fisher's exact test was used to compare the difference in
complication rate between each grade of pancreatitis. It was assumed that
those patients without follow-up examinations who clinically improved and
became asymptomatic did not develop complications. We reviewed our hospital's
clinical electronic data repository for follow-up findings, need for surgical
intervention, and final clinical outcome.
Results
Among the 169 attacks of acute pancreatitis, follow-up CT examinations
depicted local complications in nine patients, for an overall incidence of
5.3%. There were a total of 16 complications, with three patients showing
multiple complications. The number and percentage of patients with
complications, number of complications, and number and percentage of follow-up
examinations were calculated and correlated with the CT grading scale
(Table 2). Follow-up CT
examinations were available for review in 48.5% of the entire group and in 70%
of patients presenting with fluid collections (in 54.2% of grade D and 100% of
grade E patients). Local complications occurred exclusively in patients with
fluid collections. The incidence of complications among the 73 patients with
fluid collections was 12.3%, whereas no complications developed in the 96
patients without fluid collections (Fig.
1). This incidence of complications is based on clinical
evaluation and on CT follow-up studies in 51 of the 73 patients initially
exhibiting peripancreatic fluid collections. A significantly higher
complication rate was seen in patients with fluid collections (grades D and E)
than in patients without fluid collections (grades A, B, and C) (p
0.001); indeed, no complications occurred in those patients without fluid
collections.
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Fig. 2A —Grade E pancreatitis without necrosis in 24-year-old man.
Axial image from initial contrast-enhanced CT examination at admission shows
multiple large peripancreatic fluid collections (arrows). Entire
pancreatic gland shows normal enhancement.
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Fig. 2B —Grade E pancreatitis without necrosis in 24-year-old man.
Axial image from last CT examination 27 days after A reveals
development of 6 x 10 cm partially loculated fluid collection
(arrows) in lesser sac, which may progress to acute pseudocyst if it
becomes fully encapsulated. Patient was lost to follow-up.
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Follow-up CT studies in 51 of 73 patients with retroperitoneal
peripancreatic fluid collections were available and revealed resolution of
fluid within 2 weeks in 35 patients (68.6%), development of abdominal
complications in nine patients (17.6%), and persistence of unencapsulated or
partially encapsulated fluid collections in seven patients (13.7%) who were
clinically asymptomatic at the time of hospital discharge (Fig.
2A,
2B and
Table 3). Three of these seven
patients were lost to follow-up, whereas long-term clinical follow-up in four
patients with residual fluid collections revealed no complaints or abnormal
physical findings.
The type and number of local complications in our series of 169 patients
with acute pancreatitis as correlated to the A–E grad ing system are
presented in Table 4. These
complications developed entirely in our patients with fluid collections
(grades D and E). Acute short-term life-threatening complications (hemor
rhage, infection, or perforation) developed in five of 73 patients with
peripancreatic fluid (6.8%), and chronic long-term morbidity (chronic
pancreatitis or groove pancreatitis) was seen in three of 73 patients
(4.1%).
Among the 73 patients with initial fluid collections, we detected five
patients who developed single pseudocysts from 2 x 1 cm to 7 x 6
cm, for an incidence of 6.8% (Fig.
3A,
3B,
3C). Two of the pseudocysts
developed hemorrhage and rupture with leakage of blood into the peritoneal
cavity (Fig. 4A,
4B). One of these patients also
developed duodenal perforation and required surgery, and the other recovered
without surgical intervention.
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Fig. 3A —Grade D pancreatitis without necrosis in 44-year-old man.
Initial contrast-enhanced axial CT image shows small fluid collection
(arrows) adjacent to tail of pancreas and in left anterior pararenal
space. Entire pancreas including tail (not shown) showed normal
enhancement.
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Fig. 3C —Grade D pancreatitis without necrosis in 44-year-old man.
Axial CT image 2 years after A shows 5 x 4 cm pseudocyst
(arrows) with calcification in wall (arrowhead), indicating
chronic pseudocyst.
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Fig. 4A —Grade E pancreatitis without necrosis in 47-year-old man.
Axial image from contrast-enhanced CT examination performed 5 months after
initial episode for abdominal pain and decrease in hematocrit level shows
hemorrhagic pseudocyst (white arrows) in wall of duodenum and leakage
of blood (arrowheads) into peritoneal cavity. Additionally, small
pseudocyst is present in head of pancreas (black arrow).
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Fig. 4B —Grade E pancreatitis without necrosis in 47-year-old man.
Axial CT image 6 days after A shows that hemorrhagic pseudocyst
(arrows) has eroded and perforated postbulbar duodenum, with leakage
of free air (arrowheads) into abdomen. Patient underwent surgery with
unroofing and drainage of pseudocyst and pyloric exclusion. Hemorrhage and
pseudocyst resolved on follow-up CT examinations (not shown).
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There were two other cases of acute retroperitoneal hemorrhage, for a total
of four cases of hemorrhage (5.5% in 73 patients with fluid collections) (Fig.
5A,
5B). One case of duodenal
perforation (1.4%) (Fig. 4A,
4B), two cases of infection
(2.7%), and one case of splenic vein thrombosis (1.4%) were also diagnosed.
Chronic pancreatitis developed in two of 73 patients (2.7%) and groove
pancreatitis in one patient (1.4%) on long-term follow-up CT examinations. Two
patients with bleeding underwent diagnostic angiography that was negative.
Three patients with complications, including hemorrhage, infection, and
duodenal perforation, had surgical interventions with drainage and
débridement and protracted clinical courses. All patients in our series
survived.
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Fig. 5B —Retroperitoneal hemorrhage in 25-year-old man with grade E
pancreatitis without necrosis. Follow-up axial CT image 21 days later shows
encapsulated, liquefied retroperitoneal hematoma (arrows). Resolution
of hematoma was documented on follow-up CT examinations (not shown).
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Discussion
The development of abdominal complications in patients with acute
pancreatitis leads to a prolonged hospitalization and, when life-threatening
and not detected in time, to an increased mortality rate. Some of these
complications may coexist, occur at any time after an acute attack, and have
different manifestations and clinical repercussions. By and large, they are
closely related to the staging severity of an acute attack of pancreatitis.
Abdominal complications occur predominantly between the second and fifth week
after one or several episodes of acute pancreatitis and with decreasing
frequency months to years later
[14]. They are mostly seen in
patients with severe necrotizing pancreatitis. However, a smaller number of
patients with no CT evidence of pancreatic necrosis can manifest severe
systemic alterations and develop significant local complications. The nature
and incidence of complications in this subset of patients, representing more
than 80% of cases of acute pancreatitis, have not received much attention in
the literature.
Digestion of the pancreatic gland or of peripancreatic tissues after the
leakage of activated pancreatic secretions from acinar cells is responsible
for the development of local complications
[14]. Enzymatic fluid
secretions dissect fascial planes and have a deleterious effect on vascular
structures, adjacent hollow or solid organs, and retroperitoneal fat,
producing fat necrosis. Extensive retroperitoneal fat necrosis interferes with
the rapid absorption of extravasated, and sometimes hemorrhagic, fluid
collections. When these transitory collections are not rapidly absorbed or
continue to increase in size, they tend to organize and loculate by developing
partial capsules. Because liquefied necrotic tissue, blood products, and
retained fluid are excellent media for bacterial growth, infection may develop
[14]. In the initial 1–2
weeks after an acute attack, however, the natural evolution of sterile fluid
collections remains unpredictable, so we recommend that these collections be
followed up with imaging examinations in symptomatic patients.
In our series of 169 patients, fluid collections were detected in 73
patients (43.2%) and almost totally resolved within 7–10 days in most
patients. We were able to document resolution in 35 of the 51 patients (68.6%)
in whom follow-up CT studies were available for review
(Table 3). The remaining 22
patients in whom long-term follow-up studies were not obtained all had small
fluid collections (grade D). These patients had an uneventful clinical course
and rapid improvement, and it may be presumed that because these patients
remained asymptomatic, their small fluid collections resolved as well.
The occurrence and fate of fluid collections in acute pancreatitis have
been previously reported in a series of 48 patients with and without
pancreatic necrosis [15]. In
that series, fluid was found in 37% of patients. It resolved spontaneously in
about half the patients and led to complications (pseudocyst, abscess,
infected necrosis) in the other half. As was also seen in our collected data,
the incidence of spontaneous resolution of extravasated fluid is substantially
higher (70–80%) in patients without pancreatic necrosis.
The overall incidence of acute and chronic complications in our series of
169 acute attacks of pancreatitis is 5.3%. As expected, complications did not
occur in the mild forms of grades A, B, and C pancreatitis, but occurred
exclusively in the more severe forms, grades D and E pancreatitis, after the
extravasation of pancreatic secretions. Even in this subgroup of 73 patients
with fluid collections, the morbidity rate was relatively low in the absence
of pancreatic necrosis, with an incidence of complications of 12.3%. Acute
life-threatening complications such as hemorrhage, infected collections, and
duodenal perforation were seen in only five patients, representing 6.8% of the
73 patients with fluid collections or 3.0% of 169 cases overall.
When the initial peripancreatic fluid collections are not absorbed, they
tend to organize and slowly evolve into fully encapsulated collections called
"acute pseudocysts." This evolution heralds the beginning of a
potentially more complex and uncertain clinical course. The development
usually takes more than 4 weeks, but because the timing is somewhat variable,
the diagnosis is established only when a sharply defined circumferential
capsule is clearly detected. As opposed to chronic pseudocysts, acute
pseudocysts have a thin friable capsule and an unstable natural history. They
can diminish or grow in size, resolve, rupture, drain into the pancreatic
duct, or fistulize into the gastrointestinal tract. Spontaneous resolution has
been reported in 40% of acute pseudocysts known to be present for less than 6
weeks, whereas they tend to remain stable when older than 12 weeks
[16]. Complications such as
rupture, hemorrhage, or infection have been reported in 18–50% of cases
[16–19].
A follow-up CT series of 75 patients with acute pseudocysts reported
enlargement or complications requiring surgery in about half and resolution or
stable size in asymptomatic individuals in the other half
[20].
Follow-up CT examinations in our 73 grades D and E patients with fluid
collections documented five patients with single pseudo-cysts, for an
incidence of 6.8%, or 3.0% of the entire group of 169 cases. Hemorrhage from
rupture of a pseudocyst occurred in two patients, necessitating surgical
intervention. The prevalence of hemorrhagic pseudocysts, similar to the two
cases in our series, varies in different reports from 2% to 31% of acute
pseudocysts [17,
21]. After an acute attack of
pancreatitis, hemorrhage is usually not associated with ruptured
pseudoaneurysms, which tend to occur later after an acute episode
[22]. Rather, in the acute
phase, hemorrhage most often occurs secondary to capillary bleeding in the
wall of the pseudocyst or in the retroperitoneum. Because the natural history,
clinical significance, and surgical management are uncertain, a conservative
noninterventional approach, particularly for asymptomatic pseudocysts smaller
than 5 cm, has been accepted in clinical practice
[20]. Surgical or
interventional drainage procedures are reserved for complications (such as
hemorrhage or infection) and for symptomatic enlarging pseudocysts diagnosed
by follow-up imaging studies.
Three individuals in our series of 169 patients developed chronic
complications (two cases of chronic pancreatitis and one case of groove
pancreatitis), for an incidence of only 1.8%. Groove pancreatitis was
diagnosed when there was focal inflammation exclusively or predominantly
involving the head of the pancreas and associated fluid in the groove between
the head of the pancreas and the second portion of the duodenum
[23]. Although these are
important long-lasting, irreversible, and clinically debilitating developments
[23,
24], their true incidence rate
is difficult to establish without close patient supervision and repeated
long-term follow-up examinations.
Our retrospective survey of 169 patients with attacks of nonnecrotizing
acute pancreatitis has several limitations that may affect the veracity of our
results. Because of its retrospective nature, this is not a controlled study,
and long-term follow-up examinations in some of our patients with unresolved
fluid collections and acute pseudocysts were not always available. Follow-up
imaging studies were available for review in approximately 50% of our entire
patient population and in 70% of patients with fluid collections, including
100% of grade E patients with larger collections and more severe and
protracted clinical presentations. We likely underestimated the true incidence
of acute and chronic complications because longer-term follow-ups in some of
our patients with unresolved fluid collections and acute pseudocysts may have
yielded additional complications. On the other hand, long-term follow-up
examinations could have missed other unrecorded subliminal intervening acute
episodes of pancreatitis, particularly in alcoholic patients, that might have
contributed to the development of late complications. Patients may also have
sought follow-up care and undergone imaging at an outside institution, and
they may have developed complications of which we were not aware. In addition,
despite the improved accuracy of MDCT examinations, small superficial patchy
areas of pancreatic necrosis that might have contributed to the severity of
the acute attack in the development of subsequent complications could have
been missed.
In conclusion, in this series of 169 patients with milder forms of acute
pancreatitis, 16 abdominal complications developed in nine patients, for an
incidence of 5.3%. All complications occurred in grades D and E patients with
fluid collections. Fluid was rapidly absorbed in most patients but led to
complications in 12.3% in this subgroup of patients. Acute, life-threatening
complications (hemorrhage, infection, perforation) were seen in five patients,
for an incidence of 6.8%, among 73 episodes with fluid collections, or 3.0% of
169 total cases. Single acute pseudocysts were seen in five patients, and
long-term chronic complications were documented in three patients. Severe
abdominal morbidity can occasionally occur after an episode of acute
pancreatitis in the absence of necrosis. In patients with milder
interstitialforms of pancreatitis, routine follow-up CT examinations are
indicated only in patients with fluid collections to document resolution of
fluid or the development of complications.
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Abstract
Introduction
