Original Research
Abdominal Imaging
March 2008

MDCT of Acute Mild (Nonnecrotizing) Pancreatitis: Abdominal Complications and Fate of Fluid Collections

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.

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 [15]. 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 [811]. 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 × 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 × 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 × 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 × 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].
TABLE 1: CT Grading of Acute Pancreatitis
GradeCT Finding
ANormal pancreas
BEnlarged edematous pancreas
CPancreatic and peripancreatic inflammation (peripancreatic stranding)
DSingle small peripancreatic fluid collection
E
Large or several fluid collections or retroperitoneal air
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.
TABLE 2: Complications of Acute Pancreatitis in Patients Without Necrosis
GradeNo. (%) of PatientsNo. (%) of Patients with Local ComplicationsNo. of Local ComplicationsNo. (%) of Patients with Follow-Up CT in ≥ 4 Days
A12 (7.1)0 (0)01 (8.3)
B24 (14.2)0 (0)011 (45.8)
C60 (35.5)0 (0)019 (31.7)
D48 (28.4)6 (12.5)726 (54.2)
E25 (14.8)3 (12.0)925 (100)
D and E
73 (43.2)
9 (12.3)
16
51 (69.9)
Total
169 (100)
9 (5.3)
16
82 (48.5)
Fig. 1 Development of complications in patients with and without peripancreatic fluid collections on initial CT examination.
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.
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 × 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.
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.
TABLE 3: Fate of Fluid Collections in 51 Patients with Follow-Up Examinations
GradeNo. of PatientsNo. (%) of Patients with Rapid ResolutionaNo. (%) of Patients with Local ComplicationsNo. (%) of Patients with Partially Encapsulated or Persistent Fluid
D2618 (69.2)6 (23.1)2 (7.7)
E2517 (68)3 (12)5 (20)
D and E
51
35 (68.6)
9 (17.6)
7 (13.7)
a
Within 2 weeks.
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%).
TABLE 4: Type, Number, and Incidence of Complications in 169 Patients with Acute Pancreatitis
GradePseudocystHemorrhageAbscess or Infected FluidPerforationThrombosisChronic PancreatitisGroove PancreatitisTotal
A00000000
B00000000
C00000000
D32100107
E22111119
D and E
5
4
2
1
1
2
1
16
Total
5 (3.0)
4 (2.4)
2 (1.2)
1 (0.6)
1 (0.6)
2 (1.2)
1 (0.6)
16 (9.5)
Note—Data are numbers of patients. Numbers in parentheses are percentages.
Among the 73 patients with initial fluid collections, we detected five patients who developed single pseudocysts from 2 × 1 cm to 7 × 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.
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.

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.
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.
Fig. 3B Grade D pancreatitis without necrosis in 44-year-old man. Axial CT image 2 months after A reveals development of 7 × 6 cm acute pseudocyst (arrows) adjacent to tail of pancreas.
Fig. 3C Grade D pancreatitis without necrosis in 44-year-old man. Axial CT image 2 years after A shows 5 × 4 cm pseudocyst (arrows) with calcification in wall (arrowhead), indicating chronic pseudocyst.
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).
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).
Fig. 5A Retroperitoneal hemorrhage in 25-year-old man with grade E pancreatitis without necrosis. Initial contrast-enhanced axial CT image reveals large retroperitoneal hematoma (arrows).
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).
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 [1619]. 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.

Footnotes

Address correspondence to D. K. Lenhart ([email protected]).
CME
This article is available for CME credit. See www.arrs.org for more information.

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Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: 643 - 649
PubMed: 18287434

History

Submitted: June 21, 2007
Accepted: September 28, 2007

Keywords

  1. abdominal imaging
  2. acute pancreatitis
  3. MDCT
  4. pancreas

Authors

Affiliations

Dipti K. Lenhart
Both authors: Department of Radiology, NYU School of Medicine–Bellevue Hospital Center, 462 First Ave., NB 3W33A, New York, NY 10016.
Emil J. Balthazar
Both authors: Department of Radiology, NYU School of Medicine–Bellevue Hospital Center, 462 First Ave., NB 3W33A, New York, NY 10016.

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