European Journal of Radiology, 10 (1990) 118-123 Elsevier
118
EURRAD
00026
Acute pancreatitis: value of CT as a predictor of outcome C. PCrez, J. Llauger, J. Andreu, J. Palmer and J. Puig Depament of DiagnosticRadiology,Hospital de la Santa Creu i Sant Pau, Autonomous Universityof Barcelona, Spain (Received 8 August 1989; revised version received 8 November
Key words: Pancreatitis,
acute; Pancreatitis,
CT; Pancreatitis,
1989; accepted
10 November
CT grading; Pancreatitis,
1989)
prognostic
signs
Abstract
A prospective study was performed on the relationship of CT findings to the clinical course of 148 patients with acute pancreatitis. The type of pancreatic inflammation seen on CT was classified into six categories based on an overall assessment of size, contour and density of the gland, and peripancreatic abnormalities. The majority (94%) of patients in whom CT showed mild pancreatic changes (grades A, B and C) had two or less positive clinical indicaters of severe pancreatitis (Ranson’s signs). In contrast, 92% of patients in whom CT showed more severe changes of pancreatitis (grades D, E or F) had three or more positive signs. The nine patients who died with pancreatitis-related complications were in grades D, E or F. We wish to draw attention to a CT appearance which we have called ‘fat islets’ (low density intrapancreatic or peripancreatic areas, the contents of which approach fat in attenuation values); there was a strong correlation between this appearance and subsequent infection.
Introduction Inflammation of the pancreas is a common disorder that is manifested clinically from a benign self-limiting disease to one with a protracted clinical course with considerable associated morbidity and mortality. Prognosis depends to a great extent on the local pancreatic and peripancreatic complications (i.e., abscess, pseudocyst, hemorrhage). Diagnostic imaging of the pancreas has been revolutionised in recent years by the introduction of sonography and computed tomography (CT). CT examination is rapidly assuming a primary role in the assessment of the severity of acute pancreatitis. Sonography is a valuable modality for evaluating associated biliary tract disease, but frequently provides an incomplete view of the pancreas and peripancreatic area [ 11. The prognostic value of CT as a predictor of outcome in acute pancreatitis has received little mention in the literature [2-41. We report a prospective study of the relation of CT findings to the
Address for reprints: Dra. Carme Perez, Servicio de Radiodiagnbstico, Hospital de la Santa Creu i Sant Pau, Universidad Autonoma, Avda. S. Antonio M. Claret, 167, 08025 - Barcelona, Spain. 0720-048X/90/$03.50
0 1990 Elsevier Science Publishers
clinical course of patients with acute pancreatitis. The main objective of the study was to assess the prognostic value of CT based on correlation of CT grading with Ranson’s clinical criteria, clinical course and mortality. We have also analysed the predictive value of certain CT findings with regard to early diagnosis of infected foci. Material and Methods This study comprised 148 patients diagnosed from December 1985 to December 1988 as having acute pancreatitis. They were selected from a population of 321 patients with acute pancreatitis admitted to our institution over a 3-year period. Selection was made according clinical course. There were 87 men and 61 women, aged 15-89 years, with a mean age of 55 years. The diagnosis of acute pancreatitis was based on typical symptoms and laboratory evidence of increased serum amylase levels. The etiology of pancreatitis was biliary lithiasis in 58 patients, chronic alcohol abuse in 48, gallstones and alcohol in six, and miscellaneous or unknown in 36. Severe pancreatitis was defined if three or more of the Ranson’s prognostic signs (Table I), were presented
B.V. (Biomedical
Division)
TABLE Prognostic
I signs of acute pancreatitis
At admission
During initial 48 h
Age over 55 years
Hematocrit fall greater than 10% points
White blood cell count over 16. 103/p1, (16 * lo9 1)
Blood urea nitrogen level rise more than 5 mg/dl ( 1.79 mmol/l)
Blood glucose level over 200 mg/dl (11 mmol/l)
Serum calcium level below 8 mg/dl (2 mmol/l)
Serum lactic acid hydrogenase level over 350 IUjl
Arterial POz below 60 mm Hg (7.98 KPa)
Serum glutamic-oxaloacetic transaminase level over 250 IU/dl
Base deficit greater than 4 mEq/l (4 mmol/l)
Estimated fluid sequestration more than 6000 ml (6 1)
within 48 h of admission [ 51. There were 87 patients with mild pancreatitis (zero to two positive signs) and 61 with severe pancreatitis. In all patients, sonograms were obtained within 24-48 h after admission with the main purpose of assessing biliary lithiasis as an etiologic factor of pancreatitis. CT scans were obtained, either as single examination within the first 7 hospital days or as consecutive, follow-up examinations approximately every 8-12 days in patients with severe pancreatitis until death or discharge from the hospital. CT examinations were carried out with a Somaton DR2 Siemens total body scan. Eight millimeter slices were performed at lo-15 mm intervals from the xyphoid process until the entire pancreas had been visualised; when peripancreatic collections were present, the whole of the abdomen was examined. Diluted (5%) megltie diatrizoate (Gastrografm@) was administered orally before examination. Slices were obtained before and after intravenous administration of contrast medium. Patients with severe pancreatitis were also given contrast material by bolus after the initial enhanced CT examination. All CT studies were reported twice: first by the initial radiologist; then prospectively, by one of the authors. If there was discrepancy a consensus report was established. We classified the type of pancreatic inflammation seen on the CT scans into six categories. This classification was based on an overall assessment of size,
Fig. 1. An ill-defined fluid collection occupying the lesser sac and the left anterior pararenal space (Grade D).
contour and density of the gland, and peripancreatic abnormalities. We used the following grades which are similar to those reported in the literature [ 2,3] : grade A, normal pancreas; grade B, focal or diffuse enlargement of the pancreas including contour irregularities, nonhomogeneous attenuation of the gland and foci of small fluid collections within the gland; grade C, intrinsic pancreatic abnormalities associated with haziness and streaky densities representing inflammatory changes in the peripancreatic fat; grade D, single, ill-defined extrapancreatic fluid collection (Fig. 1); grade E, two or more extrapancreatic fluid collections; and grade F, presence of gas in or adjacent to the pancreas and/or massive involvement of the retroperitoneal space by extrapancreatic fluid (Figs. 2 and 3). In some cases of severe acute pancreatitis, other CT findings were recorded. Small, low density areas, the contents of which approached fat in attenuation values, were found both intrapancreatic and extrapancreatic. This feature, called fat islets, did not show any change
Fig. 2. Massive involvement of the retroperitoneal
space (Grade F).
Fig. 3. Gas bubbles in the body and tail of the pancreatic Pancreatic abscess (Grade F).
gland.
after the i.v. bolus of contrast material (Fig. 4). Peripancreatitis consisted of preservation of the pancreatic parenchyma within a large peripancreatic fluid collection (Fig. 5), whereas the opposite finding named pancreatic burst represented fragmental and inhomogeneous uptake of contrast material without attaining visualisation of the pancreatic gland. The presence of high-density areas within peripancreatic fluid collections was also evaluated (Fig. 6). Results Normal CT findings were found in 44 cases, morphologic abnormalities of the gland in 99, and extrapancreatic spread of the inflammatory process in 100 (Table II). The most frequent site of extrapancreatic involvement was the lesser sac followed by the left anterior pararenal space. Involvement of the anterior pararenal spaces was more common than involvement of the posterior ones; however, in both circumstances
Fig. 4. Fat islets: hypodense
areas within a large peripancreatic collection.
Fig. 5. Peripancreatitis: within a peripancreatic
visualisation of the pancreatic parenchyma collection after contrast material given by bolus.
TABLE II CT findings in a group of 148 patients with acute pancreatitis Findings
No. of cases
Normal pancreas Morphologic abnormalities Enlargement of the gland Contour irregularities Intrapancreatic collection(s) Infiltration peripancreatic fat
44 99 99 99 65 81
Extrapancreatic fluid collection(s) Anterior pararenal space Posterior pararenal space Lesser sac Paracolic gutters
100 61 28 45 33
Free peritoneal fluid Pleural effusion Pancreatic calcifications Gallstones Distended gallbladder
24 31 6 9 10
Fig. 6. Hemorrhagic pseudocyst. High-density areas extrapancreatic fluid collection.
within
an
121 TABLE
III
Relationship
TABLE V between CT findings and prognostic
Grade
signs
Patients by number of prognostic
A B C D E F
signs
0 or 2
3 or more
42 16 24 5 0 0
2 1 2 14 30 12
the left side was more frequently affected. Gallstones were seen on CT scans in nine patients, but were missed in the other 55 patients who proved to have biliary lithiasis on sonograms. According to CT findings, there where 44 patients (30%) in grade A, 17 (11%) in grade B, 26 (18%) in gradeC, 19(13%)ingradeD,30(20%)ingradeEand 12 (8%) in grade F. CT and prognostic signs. The relationship between early CT findings and prognostic signs is shown in Table III. Eighty-two (94.2%) of the 87 patients with mild pancreatitis were in grades A, B and C. A small, single extrapancreatic fluid collection was found in only live patients (grade D) and of the 87 patients in this category, only one had a pseudocyst that resolved promptly without surgery. All 29 patients who developed pseudocysts were in grades D, E and F. In the group of 61 patients with severe pancreatitis, 56 (92%) were in grades D, E and F. No grade A, B or C patients had any complications or died. Also the nine patients who died with pancreatitis-related complications were in those grades (Table IV). Eighty patients underwent surgery. Prompt surgery was needed to debride and adequately drain all necrotic foci and extrapancreatic collections in 35 patients (grades D, E and F). The remaining 45 patients under-
TABLE
Relationship between presence of fat islets and/or peripancreatitis on early CT scans and clinical course in 42 patients with severe pancreatitis (Grades D, E and F) CT finding
No.
Abscess (infected pseudocyst)
Pseudocyst
Fat islets
27
23
10
3
Peripancreatitis
15
8
5
4
Both
10
I
3
2
went elective surgery for biliary lithiasis (cholecystectomy and/or endoscopic papillotomy) or unresolved pseudocysts (cystogastrostomy). In 42 patients with severe pancreatitis, early CT examination revealed the presence of fat islets (27 cases) and/or peripancreatitis (15 cases). CT follow-up disclosed pancreatic abscess in 31 (74%) (infected pseudocysts in 15), and pseudocysts in seven (17%) (Table V). The radiological finding of pancreatic burst was documented in two patients. One died a few days after admission due to massive retroperitoneal bleeding. High-density areas within a peripancreatic fluid collection were seen in one patient who had a protracted clinical course and died because of intra-abdominal hemorrhage. In a retrospective evaluation of CT findings in the 29 patients with surgically proven pancreatic abscess, CT demonstrated fat islets in 23 (in association with peripancreatitis in seven) and multiple gas bubbles within the abscess in nine (as a single feature in two, and associated with fat islets in six). In two cases, gas bubbles were preceded by fat islets (Fig. 7). In the 33 patients with pseudocysts, fat islets and/or peripancreatitis were found in nine (infected pseudocysts in six).
IV
Relationship
between CT findings and clinical course
Grade
Patients
Abscesses
Pseudocysts
Hemorrhage
Deaths*
A B C D E F
46 17 26 19 30 12
0 0 0 3 14 12
0 2 4 7 18 2
0 0 0 1 0 1
0 0 0 1 4 4
* Causes of deaths: sepsis (four cases), hemorrhage
(four cases), respiratory
failure (one case).
Fig. 7. (a) Fat islets within a fluid collection in the left anterior pararenal space. (b) Gas bubbles in the same site of fat islets appearing at the 10th day of admission.
Discussion CT cannot always make the diagnosis of acute pancreatitis, as 30% of patients with this diagnosis had a normal appearing gland. However, the relationship between CT findings and the clinical course reported by other investigators [6-121 was also confirmed by us. Ninety-four percent of patients with mild pancreatitis as evaluated by CT (grades A, B and C) were in the group of zero to two positive Ranson’s signs. On the other hand, 92% of grades D, E or F patients had three or more positive signs. In the patients with the more extensive inflammatory reaction and tissue destruction (grades D, E and F), the clinical course was severe, and 92% (56 out of 61 patients) had complications. Also the nine patients who died with pancreatitis-related complications were in those grades. In four cases, death was attributed to vascular complications. The frequency of pseudoaneurysm formation in patients with pancreatitis has been estimated to be as high as 10 % [ 131 with a mortality rate of up to 37%. The splenic or gastroduodenal arteries are the vessels most often involved in acute hemorrhage associated with pseudocysts [ 141. Pseudoaneurysms can be detected by CT as hypercaptant areas after bolus administration. Hemorrhage into a pancreatic pseudocyst should be suspected in the presence of gastrointestinal bleeding, sudden drop in the hematocrit level, the development of a bruit over a mass, and a sudden enlargement of a mass originally presumed to be a pseudocyst. Although angiographic evidence of a pseudoaneurysm usually requires immediate surgical intervention, in rare instances embolisation alone may control bleeding
[W. Pancreatic abscess is a late complication of acute pancreatitis, usually arising from secondary infection of
necrotic pancreatic and peripancreatic tissues. Mortality from a pancreatic abscess is almost 100% if surgical debridement is not done; however, the mortality of surgically treated pancreatic abscesses is commonly [ 12, 16-201. A major factor limiting the suc30-50x cess of surgery is the inability to establish the diagnosis of a pancreatic abscess early in the patient’s course. Reports on the CT findings in pancreatic abscesses have stressed the importance of demonstrating intra- or peripancreatic gas collections [ 181. Detection of gas within the pancreatic abscess occurs in 30-64% of patients [7,18,21]. Conversely, pancreatic gas may be the result of fistula formation [21], rather than abscess alone. Fat islets on CT scans (low-density intrapancreatic or extrapancreatic masses, the contents of which approach the attenuation values of fat) is an early finding suspicious of infection. The feature of fat islets has not been previously described in the literature, although intrapancreatic ill-defined low-density areas presumably due to fluid or undigested fat have been reported [ 6,221. In the present study, CT demonstrated fat islets in 23 of the 29 patients with surgically proven pancreatic abscess. Fat islets within a mass originally presumed to be a pseudocyst should alert the physician to the possibility of infection. In the presence of this sign interventional radiologic techniques - percutaneous aspiration and drainage of fluid collections by CT guidance - are valuable alternatives or adjuncts to surgery [23,241. Preservation of the pancreatic parenchyma within a large peripancreatic fluid collection (‘peripancreatitis’) was also associated with a high rate of local complications. Of the 15 cases in which peripancreatitis was found on early CT scans, 12 developed abscesses or pseudocysts. The combination of fat islets and peripancreatitis was found to be associated with an even
123
higher morbidity; nine of the ten patients with both signs had abscesses or pseudocysts. We conclude that initial CT examination in cases of acute pancreatitis is very helpful in establishing or confirming the clinical diagnosis. CT scan can also be used as an early indicator of the severity of the disease. We found a good correlation between CT grading and the clinical course. The use of CT features improves the original prognostic clinical estimation and contributes to the identification of patients in whom life-threatening complications may develop. References Silverstein W, Isikoff MB, Hill MC, Barkin J. Diagnostic imaging of acute pancreatitis: prospective study using CT and sonography. AJR 1981; 137: 497-502. Balthazar EJ, Ranson JHC, Naidich DP, Megibow AJ, Caccavale R, Cooper MM. Acute pancreatitis: prognostic value of CT. Radiology 1985; 156: 767-772. Hill MC, Barkin J, Isikoff MB, Silverstein W, Kalser M. Acute pancreatitis: clinical vs. CT findings. AJR 1982; 139: 263-269. Nordestgaard AG, Wilson SE, Williams RA. Early computerized tomography as a predictor of outcome in acute pancreatitis. Am J Surg 1986; 152: 127-132. Ranson JHC. Etiological and prognostic factors in human acute pancreatitis: a review. Am J Gastroenterol 1982; 9: 633-638. White EM, Wittenberg J, Mueller PR, et al. Pancreatic necrosis: CT manifestations. Radiology 1986; 158: 343-346. Mendez G Jr, Isikoff MB, Hill MC. CT of acute pancreatitis: interim assessment. AJR 1980; 135: 463-469. Lawson TL. Acute pancreatitis and its complications. Computed tomography and sonography. Radio1 Clin North Am 1983; 21: 495-513. Foley WD, Stewart ET, Lawson TL, et al. Computed tomography, ultrasonography, and endoscopic retrograde cholangiopancreatography in the diagnosis of pancreatic disease: a comparative study. Gastrointest Radio1 1980; 5: 29-35.
10 Jeffrey RB, Federle MP, Cello JP, Crass RA. Early computed tomographic scanning in acute severe pancreatitis. Surg Gynecol Obstet 1982; 154: 170-174. 11 Moossa AR. Diagnostic tests and procedures in acute pancreatitis. N Engl J Med 1984; 311: 639-643. 12 Geokas MC, Baltaxe HA, Banks PA, Silva J Jr, Frey CF. Acute pancreatitis. Ann Intern Med 1985; 103: 86-100. 13 Burke JW, Erickson SJ, Kellum CD, Tegtmeyer CJ, Williamson BRJ, Hansen MF. Pseudoaneurysms complicating pancreatitis: detection by CT. Radiology 1986; 161: 447-450. 14 Greenstein A, DeMaio EF, Nabseth DC. Acute hemorrhage associated with pancreatic pseudocysts. Surgery 1971; 69: 56-62. 15 Vujic I, Andersen BL, Stanley JH, Gobien RP. Pancreatic and peripancreatic vessels: embolization for control of bleeding in pancreatitis. Radiology 1984; 150: 51-55. 16 Warshaw AL, Jin G. Improved survival in 45 patients with pancreatic abscess. Ann Surg 1985; 202: 408-417. 17 Jeffrey RB Jr, Grendell JH, Federle MP, et al. Improved survival with early CT diagnosis of pancreatic abscess. Gastrointest Radio1 1987; 12: 26-30. 18 Federle MP, Jeffrey RB Jr, Crass RA, Van Dalsem V. Computed tomography of pancreatic abscesses. AJR 1981; 136: 879-882. 19 Vernacchia FS, Jeffrey RB Jr, Federle MP, et al. Pancreatic abscess: predictive value of early abdominal CT. Radiology 1987; 162: 435-438. 20 Rotman N, Bonnet F, Lard& D, Fagniez P-L. Computerized tomography in the evaluation of the late complications of acute pancreatitis. Am J Surg 1986; 152: 286-289. 21 Alexander ES, Clark RA, Federle MP. Pancreatic gas: indication of pancreatic fistula. AJR 1982; 139: 1089-1093. 22 Crass RA, Meyer AA, Jeffrey RB, et al. Pancreatic abscess: impact of computerized tomography on early diagnosis and surgery. Am J Surg 1985; 150: 127-131. 23 Haaga JR. CT-guided percutaneous aspiration and drainage of abscesses. AJR 1980; 135: 1187-1194. 24 Van Sonnenberg E, Wittich GR, Casola G, et al. Complicated pancreatic inflammatory disease: diagnostic and therapeutic role of interventional radiology. Radiology 1985; 155: 335-340.
118
EURRAD
00026
Acute pancreatitis: value of CT as a predictor of outcome C. PCrez, J. Llauger, J. Andreu, J. Palmer and J. Puig Depament of DiagnosticRadiology,Hospital de la Santa Creu i Sant Pau, Autonomous Universityof Barcelona, Spain (Received 8 August 1989; revised version received 8 November
Key words: Pancreatitis,
acute; Pancreatitis,
CT; Pancreatitis,
1989; accepted
10 November
CT grading; Pancreatitis,
1989)
prognostic
signs
Abstract
A prospective study was performed on the relationship of CT findings to the clinical course of 148 patients with acute pancreatitis. The type of pancreatic inflammation seen on CT was classified into six categories based on an overall assessment of size, contour and density of the gland, and peripancreatic abnormalities. The majority (94%) of patients in whom CT showed mild pancreatic changes (grades A, B and C) had two or less positive clinical indicaters of severe pancreatitis (Ranson’s signs). In contrast, 92% of patients in whom CT showed more severe changes of pancreatitis (grades D, E or F) had three or more positive signs. The nine patients who died with pancreatitis-related complications were in grades D, E or F. We wish to draw attention to a CT appearance which we have called ‘fat islets’ (low density intrapancreatic or peripancreatic areas, the contents of which approach fat in attenuation values); there was a strong correlation between this appearance and subsequent infection.
Introduction Inflammation of the pancreas is a common disorder that is manifested clinically from a benign self-limiting disease to one with a protracted clinical course with considerable associated morbidity and mortality. Prognosis depends to a great extent on the local pancreatic and peripancreatic complications (i.e., abscess, pseudocyst, hemorrhage). Diagnostic imaging of the pancreas has been revolutionised in recent years by the introduction of sonography and computed tomography (CT). CT examination is rapidly assuming a primary role in the assessment of the severity of acute pancreatitis. Sonography is a valuable modality for evaluating associated biliary tract disease, but frequently provides an incomplete view of the pancreas and peripancreatic area [ 11. The prognostic value of CT as a predictor of outcome in acute pancreatitis has received little mention in the literature [2-41. We report a prospective study of the relation of CT findings to the
Address for reprints: Dra. Carme Perez, Servicio de Radiodiagnbstico, Hospital de la Santa Creu i Sant Pau, Universidad Autonoma, Avda. S. Antonio M. Claret, 167, 08025 - Barcelona, Spain. 0720-048X/90/$03.50
0 1990 Elsevier Science Publishers
clinical course of patients with acute pancreatitis. The main objective of the study was to assess the prognostic value of CT based on correlation of CT grading with Ranson’s clinical criteria, clinical course and mortality. We have also analysed the predictive value of certain CT findings with regard to early diagnosis of infected foci. Material and Methods This study comprised 148 patients diagnosed from December 1985 to December 1988 as having acute pancreatitis. They were selected from a population of 321 patients with acute pancreatitis admitted to our institution over a 3-year period. Selection was made according clinical course. There were 87 men and 61 women, aged 15-89 years, with a mean age of 55 years. The diagnosis of acute pancreatitis was based on typical symptoms and laboratory evidence of increased serum amylase levels. The etiology of pancreatitis was biliary lithiasis in 58 patients, chronic alcohol abuse in 48, gallstones and alcohol in six, and miscellaneous or unknown in 36. Severe pancreatitis was defined if three or more of the Ranson’s prognostic signs (Table I), were presented
B.V. (Biomedical
Division)
TABLE Prognostic
I signs of acute pancreatitis
At admission
During initial 48 h
Age over 55 years
Hematocrit fall greater than 10% points
White blood cell count over 16. 103/p1, (16 * lo9 1)
Blood urea nitrogen level rise more than 5 mg/dl ( 1.79 mmol/l)
Blood glucose level over 200 mg/dl (11 mmol/l)
Serum calcium level below 8 mg/dl (2 mmol/l)
Serum lactic acid hydrogenase level over 350 IUjl
Arterial POz below 60 mm Hg (7.98 KPa)
Serum glutamic-oxaloacetic transaminase level over 250 IU/dl
Base deficit greater than 4 mEq/l (4 mmol/l)
Estimated fluid sequestration more than 6000 ml (6 1)
within 48 h of admission [ 51. There were 87 patients with mild pancreatitis (zero to two positive signs) and 61 with severe pancreatitis. In all patients, sonograms were obtained within 24-48 h after admission with the main purpose of assessing biliary lithiasis as an etiologic factor of pancreatitis. CT scans were obtained, either as single examination within the first 7 hospital days or as consecutive, follow-up examinations approximately every 8-12 days in patients with severe pancreatitis until death or discharge from the hospital. CT examinations were carried out with a Somaton DR2 Siemens total body scan. Eight millimeter slices were performed at lo-15 mm intervals from the xyphoid process until the entire pancreas had been visualised; when peripancreatic collections were present, the whole of the abdomen was examined. Diluted (5%) megltie diatrizoate (Gastrografm@) was administered orally before examination. Slices were obtained before and after intravenous administration of contrast medium. Patients with severe pancreatitis were also given contrast material by bolus after the initial enhanced CT examination. All CT studies were reported twice: first by the initial radiologist; then prospectively, by one of the authors. If there was discrepancy a consensus report was established. We classified the type of pancreatic inflammation seen on the CT scans into six categories. This classification was based on an overall assessment of size,
Fig. 1. An ill-defined fluid collection occupying the lesser sac and the left anterior pararenal space (Grade D).
contour and density of the gland, and peripancreatic abnormalities. We used the following grades which are similar to those reported in the literature [ 2,3] : grade A, normal pancreas; grade B, focal or diffuse enlargement of the pancreas including contour irregularities, nonhomogeneous attenuation of the gland and foci of small fluid collections within the gland; grade C, intrinsic pancreatic abnormalities associated with haziness and streaky densities representing inflammatory changes in the peripancreatic fat; grade D, single, ill-defined extrapancreatic fluid collection (Fig. 1); grade E, two or more extrapancreatic fluid collections; and grade F, presence of gas in or adjacent to the pancreas and/or massive involvement of the retroperitoneal space by extrapancreatic fluid (Figs. 2 and 3). In some cases of severe acute pancreatitis, other CT findings were recorded. Small, low density areas, the contents of which approached fat in attenuation values, were found both intrapancreatic and extrapancreatic. This feature, called fat islets, did not show any change
Fig. 2. Massive involvement of the retroperitoneal
space (Grade F).
Fig. 3. Gas bubbles in the body and tail of the pancreatic Pancreatic abscess (Grade F).
gland.
after the i.v. bolus of contrast material (Fig. 4). Peripancreatitis consisted of preservation of the pancreatic parenchyma within a large peripancreatic fluid collection (Fig. 5), whereas the opposite finding named pancreatic burst represented fragmental and inhomogeneous uptake of contrast material without attaining visualisation of the pancreatic gland. The presence of high-density areas within peripancreatic fluid collections was also evaluated (Fig. 6). Results Normal CT findings were found in 44 cases, morphologic abnormalities of the gland in 99, and extrapancreatic spread of the inflammatory process in 100 (Table II). The most frequent site of extrapancreatic involvement was the lesser sac followed by the left anterior pararenal space. Involvement of the anterior pararenal spaces was more common than involvement of the posterior ones; however, in both circumstances
Fig. 4. Fat islets: hypodense
areas within a large peripancreatic collection.
Fig. 5. Peripancreatitis: within a peripancreatic
visualisation of the pancreatic parenchyma collection after contrast material given by bolus.
TABLE II CT findings in a group of 148 patients with acute pancreatitis Findings
No. of cases
Normal pancreas Morphologic abnormalities Enlargement of the gland Contour irregularities Intrapancreatic collection(s) Infiltration peripancreatic fat
44 99 99 99 65 81
Extrapancreatic fluid collection(s) Anterior pararenal space Posterior pararenal space Lesser sac Paracolic gutters
100 61 28 45 33
Free peritoneal fluid Pleural effusion Pancreatic calcifications Gallstones Distended gallbladder
24 31 6 9 10
Fig. 6. Hemorrhagic pseudocyst. High-density areas extrapancreatic fluid collection.
within
an
121 TABLE
III
Relationship
TABLE V between CT findings and prognostic
Grade
signs
Patients by number of prognostic
A B C D E F
signs
0 or 2
3 or more
42 16 24 5 0 0
2 1 2 14 30 12
the left side was more frequently affected. Gallstones were seen on CT scans in nine patients, but were missed in the other 55 patients who proved to have biliary lithiasis on sonograms. According to CT findings, there where 44 patients (30%) in grade A, 17 (11%) in grade B, 26 (18%) in gradeC, 19(13%)ingradeD,30(20%)ingradeEand 12 (8%) in grade F. CT and prognostic signs. The relationship between early CT findings and prognostic signs is shown in Table III. Eighty-two (94.2%) of the 87 patients with mild pancreatitis were in grades A, B and C. A small, single extrapancreatic fluid collection was found in only live patients (grade D) and of the 87 patients in this category, only one had a pseudocyst that resolved promptly without surgery. All 29 patients who developed pseudocysts were in grades D, E and F. In the group of 61 patients with severe pancreatitis, 56 (92%) were in grades D, E and F. No grade A, B or C patients had any complications or died. Also the nine patients who died with pancreatitis-related complications were in those grades (Table IV). Eighty patients underwent surgery. Prompt surgery was needed to debride and adequately drain all necrotic foci and extrapancreatic collections in 35 patients (grades D, E and F). The remaining 45 patients under-
TABLE
Relationship between presence of fat islets and/or peripancreatitis on early CT scans and clinical course in 42 patients with severe pancreatitis (Grades D, E and F) CT finding
No.
Abscess (infected pseudocyst)
Pseudocyst
Fat islets
27
23
10
3
Peripancreatitis
15
8
5
4
Both
10
I
3
2
went elective surgery for biliary lithiasis (cholecystectomy and/or endoscopic papillotomy) or unresolved pseudocysts (cystogastrostomy). In 42 patients with severe pancreatitis, early CT examination revealed the presence of fat islets (27 cases) and/or peripancreatitis (15 cases). CT follow-up disclosed pancreatic abscess in 31 (74%) (infected pseudocysts in 15), and pseudocysts in seven (17%) (Table V). The radiological finding of pancreatic burst was documented in two patients. One died a few days after admission due to massive retroperitoneal bleeding. High-density areas within a peripancreatic fluid collection were seen in one patient who had a protracted clinical course and died because of intra-abdominal hemorrhage. In a retrospective evaluation of CT findings in the 29 patients with surgically proven pancreatic abscess, CT demonstrated fat islets in 23 (in association with peripancreatitis in seven) and multiple gas bubbles within the abscess in nine (as a single feature in two, and associated with fat islets in six). In two cases, gas bubbles were preceded by fat islets (Fig. 7). In the 33 patients with pseudocysts, fat islets and/or peripancreatitis were found in nine (infected pseudocysts in six).
IV
Relationship
between CT findings and clinical course
Grade
Patients
Abscesses
Pseudocysts
Hemorrhage
Deaths*
A B C D E F
46 17 26 19 30 12
0 0 0 3 14 12
0 2 4 7 18 2
0 0 0 1 0 1
0 0 0 1 4 4
* Causes of deaths: sepsis (four cases), hemorrhage
(four cases), respiratory
failure (one case).
Fig. 7. (a) Fat islets within a fluid collection in the left anterior pararenal space. (b) Gas bubbles in the same site of fat islets appearing at the 10th day of admission.
Discussion CT cannot always make the diagnosis of acute pancreatitis, as 30% of patients with this diagnosis had a normal appearing gland. However, the relationship between CT findings and the clinical course reported by other investigators [6-121 was also confirmed by us. Ninety-four percent of patients with mild pancreatitis as evaluated by CT (grades A, B and C) were in the group of zero to two positive Ranson’s signs. On the other hand, 92% of grades D, E or F patients had three or more positive signs. In the patients with the more extensive inflammatory reaction and tissue destruction (grades D, E and F), the clinical course was severe, and 92% (56 out of 61 patients) had complications. Also the nine patients who died with pancreatitis-related complications were in those grades. In four cases, death was attributed to vascular complications. The frequency of pseudoaneurysm formation in patients with pancreatitis has been estimated to be as high as 10 % [ 131 with a mortality rate of up to 37%. The splenic or gastroduodenal arteries are the vessels most often involved in acute hemorrhage associated with pseudocysts [ 141. Pseudoaneurysms can be detected by CT as hypercaptant areas after bolus administration. Hemorrhage into a pancreatic pseudocyst should be suspected in the presence of gastrointestinal bleeding, sudden drop in the hematocrit level, the development of a bruit over a mass, and a sudden enlargement of a mass originally presumed to be a pseudocyst. Although angiographic evidence of a pseudoaneurysm usually requires immediate surgical intervention, in rare instances embolisation alone may control bleeding
[W. Pancreatic abscess is a late complication of acute pancreatitis, usually arising from secondary infection of
necrotic pancreatic and peripancreatic tissues. Mortality from a pancreatic abscess is almost 100% if surgical debridement is not done; however, the mortality of surgically treated pancreatic abscesses is commonly [ 12, 16-201. A major factor limiting the suc30-50x cess of surgery is the inability to establish the diagnosis of a pancreatic abscess early in the patient’s course. Reports on the CT findings in pancreatic abscesses have stressed the importance of demonstrating intra- or peripancreatic gas collections [ 181. Detection of gas within the pancreatic abscess occurs in 30-64% of patients [7,18,21]. Conversely, pancreatic gas may be the result of fistula formation [21], rather than abscess alone. Fat islets on CT scans (low-density intrapancreatic or extrapancreatic masses, the contents of which approach the attenuation values of fat) is an early finding suspicious of infection. The feature of fat islets has not been previously described in the literature, although intrapancreatic ill-defined low-density areas presumably due to fluid or undigested fat have been reported [ 6,221. In the present study, CT demonstrated fat islets in 23 of the 29 patients with surgically proven pancreatic abscess. Fat islets within a mass originally presumed to be a pseudocyst should alert the physician to the possibility of infection. In the presence of this sign interventional radiologic techniques - percutaneous aspiration and drainage of fluid collections by CT guidance - are valuable alternatives or adjuncts to surgery [23,241. Preservation of the pancreatic parenchyma within a large peripancreatic fluid collection (‘peripancreatitis’) was also associated with a high rate of local complications. Of the 15 cases in which peripancreatitis was found on early CT scans, 12 developed abscesses or pseudocysts. The combination of fat islets and peripancreatitis was found to be associated with an even
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higher morbidity; nine of the ten patients with both signs had abscesses or pseudocysts. We conclude that initial CT examination in cases of acute pancreatitis is very helpful in establishing or confirming the clinical diagnosis. CT scan can also be used as an early indicator of the severity of the disease. We found a good correlation between CT grading and the clinical course. The use of CT features improves the original prognostic clinical estimation and contributes to the identification of patients in whom life-threatening complications may develop. References Silverstein W, Isikoff MB, Hill MC, Barkin J. Diagnostic imaging of acute pancreatitis: prospective study using CT and sonography. AJR 1981; 137: 497-502. Balthazar EJ, Ranson JHC, Naidich DP, Megibow AJ, Caccavale R, Cooper MM. Acute pancreatitis: prognostic value of CT. Radiology 1985; 156: 767-772. Hill MC, Barkin J, Isikoff MB, Silverstein W, Kalser M. Acute pancreatitis: clinical vs. CT findings. AJR 1982; 139: 263-269. Nordestgaard AG, Wilson SE, Williams RA. Early computerized tomography as a predictor of outcome in acute pancreatitis. Am J Surg 1986; 152: 127-132. Ranson JHC. Etiological and prognostic factors in human acute pancreatitis: a review. Am J Gastroenterol 1982; 9: 633-638. White EM, Wittenberg J, Mueller PR, et al. Pancreatic necrosis: CT manifestations. Radiology 1986; 158: 343-346. Mendez G Jr, Isikoff MB, Hill MC. CT of acute pancreatitis: interim assessment. AJR 1980; 135: 463-469. Lawson TL. Acute pancreatitis and its complications. Computed tomography and sonography. Radio1 Clin North Am 1983; 21: 495-513. Foley WD, Stewart ET, Lawson TL, et al. Computed tomography, ultrasonography, and endoscopic retrograde cholangiopancreatography in the diagnosis of pancreatic disease: a comparative study. Gastrointest Radio1 1980; 5: 29-35.
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