Abstract
Background. Cystic lesions of the pancreas are being identified more frequently. Deciding which asymptomatic lesions can be safely followed with serial imaging and which require resection due to malignant potential is an increasingly common question. Current clinical practice is to rely on characteristics of the lesions on CT scan, and additional information from endoscopic ultrasound with fine-needle aspiration (EUS-FNA) and cyst fluid analysis or endoscopic retrograde pancreatography (ERCP) to assess malignant potential. Hypothesis. The malignant potential of pancreatic cystic lesions cannot be accurately predicted by CT scan. Methods. CT scans from 48 patients with cystic lesions of the pancreas were stripped of patient identifiers and retrospectively presented to two expert radiologists. The radiologists recorded specific characteristics of the lesions thought to be important in the differential diagnosis and their opinion of the likely diagnosis. Diagnostic accuracy was assessed by comparing the radiologists’ diagnoses to the final pathologic diagnosis after resection. To determine if clinical history, EUS-FNA or ERCP findings improved diagnostic accuracy, medical records were retrospectively reviewed and scored as either supporting or not supporting malignant potential of the lesion. Results. Specific diagnoses based on CT findings alone were correct in an average of 39% of the cases. Even when diagnoses were dichotomized as benign (43%) or potentially malignant (57%, papillary mucinous neoplasms, mucinous cystic neoplasms, cancer), determinations based on CT alone were accurate in an average of 61% of cases. Accuracy rates were 60.4 and 62.5% for the two radiologists, although there was only fair agreement between them (Kappa=0.28, 95% CI=(0.01–0.55), p=0.05). When all clinical information available was considered together as a single dichotomous indicator of malignant potential, the indicator was accurate in 90% of the cases (Kappa=0.73, 95% CI=(0.51–0.95, p<0.0001)). Conclusion. Specific preoperative diagnosis of pancreatic cystic neoplasms by CT alone is substantially inaccurate. Complementary tests such as EUS-FNA with fluid analysis and ERCP should be recommended to improve diagnosis especially if nonoperative treatment is planned.
Keywords: pancreatic neoplasm, cystic neoplasm, computed tomography
Introduction
In the past, cystic neoplasms of the pancreas were thought to be relatively uncommon, and a general recommendation existed that all suspected cystic neoplasms of the pancreas should be resected 1,2,3. In recent years, with the widespread use of modern CT, the identification of incidental asymptomatic cysts of the pancreas has increased markedly. One autopsy study demonstrated that small cystic lesions were present in almost half of the patients studied and the prevalence increased with age 4. Many surgeons now believe that some of these lesions can be safely observed, especially in the elderly patient that may not be an ideal operative candidate. The problem facing surgeons is how to distinguish benign lesions, such as pseudocysts and serous cystadenomas from malignant or premalignant mucinous lesions such as mucinous cystic neoplasms (MCN), and intraductal papillary mucinous neoplasms (IPMN). In the current study, we sought to determine the accuracy of high-quality modern CT scan with expert interpretation in the diagnosis of cystic lesions of the pancreas. Based on our clinical experience, we hypothesized that despite rapid advancements in imaging quality, the accurate diagnosis of pancreatic cystic lesions remains challenging.
Methods
The present study is a retrospective blinded analysis of 48 consecutive cases with a preoperative diagnosis of pancreatic cystic neoplasm who presented to our Pancreas Center over a 32-month period (November 2004–July 2007) for a surgical consultation. Patients with a clear history of acute pancreatitis and subsequent development of a pseudocyst were excluded from the study. Patients diagnosed preoperatively with solid pancreatic neoplasms with no cystic component were also excluded from the study. Patients diagnosed with a cystic neoplasm that have not undergone resection were also excluded.
Preoperative CT scans from 48 patients with cystic lesions of the pancreas were stripped of patient identifiers, recorded on CD-ROM, and retrospectively presented to two expert radiologists. Both radiologists were fellowship-trained, and board certified by the American Board of Radiology. Each radiologist had at least seven years experience as an attending, dedicated, full-time abdominal CT imager. The two radiologists reviewed the CT scans independently. The radiologists filled out data sheets which recorded the presence or absence of specific characteristics of the lesions thought to be important in the differential diagnosis, and their opinion of the most likely diagnosis. The location of the lesion within the pancreas and its greatest dimension as measured by the radiologist were recorded. The structure of the cyst was documented including a description of the contour of the wall (lobulated or smooth), the thickness of the cyst wall, the presence and thickness of septae, and whether the cyst was unilocular or multilocular. The presence and location within the cyst of calcifications was noted as was the presence or absence of a central scar. The presence or absence of a solid component to the lesion was also recorded. The radiologist was then asked to choose only one of the following diagnoses that they considered the most likely: serous cystadenoma, mucinous cystic neoplasm, intraductal papillary mucinous neoplasm, or pseudocyst. The radiologist was allowed to select “other” and write in a specific diagnosis if none of the previous selections were thought to be most likely.
Diagnostic accuracy was assessed by comparing the radiologists’ diagnoses to the final pathologic diagnosis after resection. Agreement between the two expert radiologists was assessed by Kappa statistics. To determine the increase in sensitivity for detecting malignant potential with additional information beyond CT findings, a more thorough review of each case was performed. Using our prospective database, the clinical history was reviewed along with endoscopic ultrasound with fine-needle aspiration (EUS-FNA), or endoscopic retrograde pancreatography (ERCP) findings. FNA results including the presence of atypical cells, mucin, or cyst fluid CEA level >200 ng/mL were evaluated. An experienced surgeon then considered all of this information along with the two radiologist's diagnoses and categorized the lesion as benign, or of malignant potential. This opinion was also compared to the final pathologic diagnosis after resection.
Results
Among the 48 patients with cystic neoplasms in this series, the majority (69%) were women (33 women, 15 men). The mean age was 60 years, but patients with neuroendocrine tumors tended to be younger with a mean age of 48. Most (81%) of the patients were symptomatic which is not surprising in this surgical series (Table I). The most common symptom was pain (71%), and patients who had weight loss tended to also have nausea or vomiting. Three of the four patients with jaundice in this series had adenocarcinoma.
Table I. Symptoms.
| Pathologic diagnosis | N | Symptomatic N (%) | Jaundice N (%) | Pain N (%) | Wt. Loss N (%) | N/vaN(%) |
|---|---|---|---|---|---|---|
| Adenocarcinoma | 11 | 11 (100) | 3 (27) | 9 (82) | 4 (36) | 6 (55) |
| IPMNb | 9 | 6 (67) | 0 (0) | 5 (56) | 2 (22) | 2 (22) |
| Serous cystadenoma | 7 | 6 (86) | 0 (0) | 6 (86) | 2 (29) | 2 (29) |
| Mucinous cystic neoplasms | 8 | 6 (75) | 0 (0) | 5 (63) | 2 (25) | 2 (25) |
| Pseudocyst | 6 | 6 (100) | 1 (17) | 6 (100) | 1 (17) | 4 (67) |
| PENc | 5 | 3 (60) | 0 (0) | 2 (40) | 1 (20) | 0 (0) |
| Pseudopapillary carcinoma | 1 | 0 (0) | 0 (0) | 0 (0) | 0 (0) | 0 (0) |
| Hemorrhagic cyst | 1 | 1 (100) | 0 (0) | 1 (100) | 0 (0) | 1 (100) |
aN/V: Nausea and vomiting.
bIntraductal papillary mucinous neoplasm.
cPancreatic endocrine neoplasm.
Specific diagnoses based on CT findings alone were correct in an average of 39% of the cases (Table II and III). Even when diagnoses were dichotomized by the radiologist as benign (radiologist 1: 39.6% vs. radiologist 2: 45.8%) or potentially malignant/malignant (radiologist 1: 60.4% vs. radiologist 2: 54.2%; IPMN, MCN, cancer), determinations of malignant potential based on CT alone were accurate in an average of 61% of the cases (Tables II and III). Accuracy rates were 60.4% for radiologist 1 and 62.5% for radiologist 2, although there was only fair agreement between radiologists (Kappa=0.28, 95% CI=(0.01–0.55), p=0.05).
Table II. Radiologist #1 interpretation.
| Location | Size (mm) | Septations | Unilocular/Multilocular | Cyst wall thickness (mm) | Calcifications | Central scar | Lobulated/Smooth | Solid component | Rad. 1 | Pathologic diagnosis | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Tail | 11 | A | U | 3 | A | A | S | P | Adenocarcinoma | Serous cystadenoma |
| 2 | Tail | 16 | A | U | 2 | A | A | S | A | Pseudocyst | Pseudocyst |
| 3 | Tail | 43 | 6 | M | 2 | A | A | L | P | Adenocarcinoma | Pseudopapillary carcinoma |
| 4 | Tail | 57 | A | U | 3 | Peripherally | A | S | A | Serous cystadenoma | MCN |
| 5 | All | 24 | A | M | 3 | A | A | L | A | Serous cystadenoma | PEN |
| 7 | Head | 21 | A | U | 1 | Peripherally | A | S | A | IPMN | IPMN |
| 9 | All | 27 | 1 | M | 2 | Peripherally | A | L | A | IPMN | IPMN |
| 10 | Head | 44 | 3 | M | 2 | Peripherally | A | L | A | IPMN | MCN |
| 11 | Head | 29 | 2 | M | 2 | A | A | L | A | Serous cystadenoma | IPMN |
| 12 | Tail | 125 | 3 | M | 7 | A | A | L | P | MCN | Adenocarcinoma |
| 13 | Body | 31 | 3 | M | 4 | A | A | L | P | Adenocarcinoma | IPMN |
| 14 | Head | 8 | A | M | 1 | A | A | S | A | IPMN | Adenocarcinoma |
| 15 | Body | 33 | 5 | M | 8 | A | A | L | P | Adenocarcinoma | Adenocarcinoma |
| 16 | All | 10 | A | U | 1 | A | A | L | A | IPMN | Adenocarcinoma |
| 17 | Tail | 120 | A | U | 2 | Peripherally | A | S | A | Pseudocyst | Pseudocyst |
| 18 | Tail | 17 | 1 | M | 4 | A | A | S | A | Serous cystadenoma | PEN |
| 19 | Tail | 23 | 1 | U | 1 | A | A | S | A | Serous cystadenoma | MCN |
| 20 | Head | 14 | 1 | U | 2 | A | A | S | A | Serous cystadenoma | PEN |
| 21 | Head | 22 | A | U | 1 | A | A | S | A | IPMN | IPMN |
| 22 | Tail | 68 | A | M | 2 | A | A | L | P | MCN | Adenocarcinoma |
| 23 | Tail | 44 | A | M | 3 | Centrally and peripherally | P | L | P | Serous cystadenoma | Serous cystadenoma |
| 24 | Head | 65 | A | U | 1 | A | A | L | A | IPMN | Pseudocyst |
| 25 | Body | 51 | 2 | M | 2 | A | A | S | P | MCN | MCN |
| 26 | Tail | 9 | A | L | A | A | A | L | A | Serous cystadenoma | PEN |
| 27 | Tail | 100 | 6 | M | 5 | Peripherally | A | L | A | MCN | MCN |
| 28 | Head | 120 | 5 | M | 5 | Centrally | A | L | A | Serous cystadenoma | Serous cystadenoma |
| 29 | All | 155 | 10 | M | 10 | A | A | L | P | Adenocarcinoma | Adenocarcinoma |
| 30 | Body | 27 | 2 | M | 1 | A | A | S | A | Pseudocyst | PEN |
| 31 | Tail | 51 | 4 | M | 6 | Peripherally | A | S | A | Pseudocyst | Pseudocyst |
| 32 | Head | 14 | A | U | 1 | A | A | S | A | Pseudocyst | Pseudocyst |
| 33 | Tail | 60 | 3 | M | 2 | A | A | L | P | MCN | Adenocarcinoma |
| 34 | Head | 14 | 1 | M | 1 | A | A | S | A | Serous cystadenoma | IPMN |
| 35 | Head | 26 | A | U | 6 | A | A | L | P | Adenocarcinoma | Adenocarcinoma |
| 36 | Tail | 48 | 2 | M | 1 | A | A | L | P | Serous cystadenoma | Serous cystadenoma |
| 37 | Tail | 15 | 2 | M | 1 | A | A | S | A | MCN | MCN |
| 38 | Head | 110 | A | U | A | A | A | S | A | Adenocarcinoma | IPMN |
| 39 | Tail | 69 | A | U | 2 | A | A | S | A | Cyst/Lymphangioma | Hemorrhagic cyst with fibrosis |
| 40 | Head | 32 | 10 | M | A | A | P | L | A | MCN | Serous cystadenoma |
| 42 | Body | 38 | 3 | M | 9 | A | A | L | P | Adenocarcinoma | Adenocarcinoma |
| 43 | Head | 30 | 1 | M | 2 | A | A | L | A | IPMN | IPMN |
| 44 | Head | 16 | A | U | 1 | A | A | S | A | Serous cystadenoma | MCN |
| 45 | Tail | 33 | 8 | M | 4 | A | A | L | P | Adenocarcinoma | MCN |
| 46 | Head | 5 | A | U | 1 | A | A | S | A | Serous cystadenoma | Pseudocyst |
| 49 | Body | 32 | 8 | 4 | Centrally | A | L | P | Adenocarcinoma | Adenocarcinoma | |
| 50 | All | 8 | A | U | 1 | A | A | S | A | IPMN | Serous cystadenoma |
| 53 | Body | 13 | A | U | A | A | A | S | A | Pseudocyst | IPMN |
| 56 | Head | 30 | A | M | 2 | A | A | L | P | Adenocarcinoma | Adenocarcinoma |
| 57 | Body | 22 | 1 | M | 2 | A | P | S | P | Serous cystadenoma | Serous cystadenoma |
Note: IPMN, intraductal papillary mucinous neoplasm; MCN, mucinous cystic neoplasm; PEN, pancreatic endocrine neoplasm.
Table III. Radiologist #2 interpretation.
| Location | Size (mm) | Septations | Unilocular/Multilocular | Cyst wall thickness (mm) | Calcifications | Central scar | Lobulated/Smooth | Solid comp. | Rad. 2 | Pathologic diagnosis | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Tail | 14 | 1 | M | 2 | A | A | L | A | Serous cystadenoma | Serous cystadenoma |
| 2 | Head | 21 | 2 | M | 2 | Centrally and peripherally | A | L | A | Serous cystadenoma | Pseudocyst |
| 3 | Tail | 43 | 2 | U | 1 | A | A | S | P | MCN | Pseudopapillary carcinoma |
| 4 | Tail | 55 | A | U | 2 | A | A | S | A | Pseudocyst | MCN |
| 5 | Head | 26 | 1 | M | 0.5 | A | A | L | A | IPMN | PEN |
| 7 | Head | 25 | A | U | <1 | A1 | A | S | A | IPMN | IPMN |
| 9 | Head | 30 | <1 | M | 1 | A | A | L | A | IPMN | IPMN |
| 10 | Head | 50 | 1.5 | M | <1 | Centrallyand peripherally | A | L | A | Serous cystadenoma | MCN |
| 11 | Head | 31 | <1 | M | <1 | A | A | L | A | IPMN | IPMN |
| 12 | Tail | 122 | 1.5 | M | 2.5 | A | A | S | A | Pseudocyst | Adenocarcinoma |
| 13 | Body | 33 | 1 | M | 2 | A | A | L | A | IPMN | IPMN |
| 14 | Head | 20 | <1 | M | 1.5 | A | A | L | A | IPMN | Adenocarcinoma |
| 15 | Body | 30 | 1 | U | 2 | A | A | S | A | MCN | Adenocarcinoma |
| 16 | Head | 15 | <1 | M | 1.5 | A | A | L | A | IPMN | Adenocarcinoma |
| 17 | Tail | 123 | A | U | <1 | A | A | S | A | Pseudocyst | Pseudocyst |
| 18 | Body | 40 | A | 2.2 | A | A | S | A | MCN | PEN | |
| 19 | Tail | 28 | A | U | 1 | A | A | S | A | Pseudocyst | MCN |
| 20 | Head | 17 | A | U | 2 | A | A | S | A | Pseudocyst | PEN |
| 21 | Head | 27 | A | U | <1 | A | A | S | A | IPMN | IPMN |
| 22 | Body | 27 | A | U | ! | A | A | L | A | Pseudocyst | Adenocarcinoma |
| 23 | Tail | 48 | <1 | M | 1.5 | Peripherally | A | L | A | Serous cystadenoma | Serous cystadenoma |
| 24 | Head | 28 | A | 1 | A | A | S | A | Pseudocyst | Pseudocyst | |
| 25 | Body | 50 | 2 | U | 2 | A | A | L | A | MCN | MCN |
| 26 | Tail | 12 | A | U | 1 | A | A | L | A | Serous cystadenoma | PEN |
| 27 | Tail | 60 | A | U | 12 | A | A | S | P | Pseudocyst | MCN |
| 28 | Head | 130 | 1 | M | 2 | Centrally and peripherally | P | L | A | Serous cystadenoma | Serous cystadenoma |
| 29 | Tail | 35 | 2 | M | 1 | A | A | L | A | IPMN | Adenocarcinoma |
| 30 | Body | 25 | A | U | 1 | A | A | L | A | Pseudocyst | PEN |
| 31 | Tail | 60 | A | U | 1.5 | Peripherally | A | S | A | Pseudocyst | Pseudocyst |
| 32 | Head | 15 | 1 | M | 2 | A | A | L | A | IPMN | Pseudocyst |
| 33 | Tail | 60 | 2 | U | 1.5 | A | A | S | A | Pseudocyst | Adenocarcinoma |
| 34 | Head | 12 | 2 | M | 1 | A | A | L | A | Serous cystadenoma | IPMN |
| 35 | Head | 25 | A | M | 2 | A | A | L | A | IPMN | Adenocarcinoma |
| 36 | Tail | 45 | 2 | M | 1 | A | A | S | A | IPMN | Serous cystadenoma |
| 37 | Tail | 13 | 2 | U | 1 | A | A | S | A | Serous cystadenoma | MCN |
| 38 | Head | 100 | 2 | M | 1 | A | A | L | A | IPMN | IPMN |
| 39 | Tail | 75 | A | U | <1 | A | A | S | A | Pseudocyst | Hemorrhagic cyst with fibrosis |
| 40 | Body | 32 | 1 | M | 1 | A | P | L | A | IPMN | Serous cystadenoma |
| 42 | Body | 38 | 4 | M | A | A | S | A | IPMN | Adenocarcinoma | |
| 43 | Head | 26 | 1 | M | 1 | A | A | L | A | IPMN | IPMN |
| 44 | Head | 22 | 4 | M | 2 | A | A | L | A | Serous cystadenoma | MCN |
| 45 | Body | 36 | 2 | M | 3 | A | A | L | A | MCN | MCN |
| 46 | Head | 8 | A | U | 2 | A | A | S | A | MCN | Pseudocyst |
| 49 | Body | 49 | 1 | M | 2 | Centrally | A | L | A | IPMN | Adenocarcinoma |
| 50 | Head | 14 | A | U | 2 | A | A | S | A | IPMN | Serous cystadenoma |
| 53 | Body | 20 | 1 | M | 2 | A | A | L | A | IPMN | IPMN |
| 56 | Body | 32 | 0.5 | M | 1 | A | A | L | A | MCN | Adenocarcinoma |
| 57 | Body | 25 | 1 | M | 0.5 | A | A | L | A | Pseudocyst | Serous cystadenoma |
Note: IPMN, intraductal papillary mucinous neoplasm; MCN, mucinous cystic neoplasm; PEN, pancreatic endocrine neoplasm.
After resection (42 cases) or biopsy (six cases), the majority (71%) of the cystic lesions in this series were determined to be of malignant potential or malignant. There were 11 cases (23%) with adenocarcinoma. One additional patient had carcinoma in situ (CIS) arising in a mucinous cystic neoplasm. Serum CA 19-9 and/or CEA were elevated in seven out of 11 cases (64%) with adenocarcinoma but both were normal in the remaining cases except for one patient with an IPMN who had a serum CEA of 4.9 ng/mL. Eleven (23%) of the patients had EUS in addition to CT and eight (73%) of these exams included FNA. When all clinical information available including the clinical history, radiologist's interpretations, ERCP and EUS-FNA results were considered together as a single dichotomous indicator of malignant potential, the indicator was accurate in 90% of the cases with substantial agreement (Kappa = 0.73, 95% CI=(0.51–0.95), p<0.0001) (Table IV).
Table IV. Prediction of malignant potential.
| Radiologist #1 | Radiologist #2 | Multidisciplinary opinion | Final pathology | |
|---|---|---|---|---|
| Benign | 19 | 22 | 11 | 14 |
| Malignant/Malignant potential | 29 | 26 | 37 | 34 |
In this series of 48 patients with cystic neoplasms of the pancreas, 18 premalignant lesions (MCN, IPMN) were resected and cured, theoretically preventing the development of cancer in some cases. Thirteen benign lesions: six serous cystadenomas, six pseudocysts and one hemorrhagic cyst were resected. All of these lesions were causing symptoms. There were five patients with a pancreatic endocrine neoplasm who would be expected to have a prolonged survival. Among the 11 patients with adenocarcinoma, the outcome was poor as expected (Table V).
Table V. Outcome in malignant cases.
| Stage | Surgery | Status | Length of follow-up (months) | |
|---|---|---|---|---|
| 14 | IB | Whipple | NED | 15 |
| 16 | IIB | Whipple | NED | 17 |
| 22 | IIB | Whipple | DEAD | 29 |
| 35 | IIB | Whipple | RECURRED | 22 |
| 49 | IIA | Distal | NED | 13 |
| 56 | IIB | Whipple | NED | 13 |
| Locally advanced or metastatic unresectable | ||||
| 12 | III | None | DEAD | 24 |
| 15 | IV | None | DEAD | 2 |
| 29 | IV | None | DEAD | 6 |
| 33 | IV | None | DEAD | 21 |
| 42 | IV | None | DEAD | 8 |
Among 38 patients who had a pancreas resection, exocrine insufficiency developed in 13 patients (34%), and endocrine insufficiency developed in six patients (16%). Comparing patients who had a Whipple vs. distal pancreatectomy, no difference in terms of endocrine insufficiency was detected (p=0.402, Fisher's exact test) but a significant difference in exocrine insufficiency was observed (p=0.035, Fisher's exact test) (Table VI).
Table VI. Pancreas function after resection of cystic neoplasms.
| Surgery |
|||
|---|---|---|---|
| Whipple N=18 | Distal N=17 | P* | |
| Endocrine insufficiencya, n (%) | |||
| Yes | 2 (11) | 4 (24) | 0.402 |
| No | 16 (89) | 13 (76) | |
| Exocrine insufficiencyb, n (%) | |||
| Yes | 10(56) | 3 (18) | 0.035 |
| No | 8 (44) | 14 (82) | |
*P-value were based on Fisher's exact test.
sRequiring insulin or oral hypoglycemics six or more months following resection.
bRequiring pancreatic digestive enzymes six or more months following resection.
Discussion
Cystic neoplasms of the pancreas may be more frequent than previously recognized and are being identified with increasing frequency as the use of abdominal CT scanning has increased. Some of these neoplasms undergo malignant transformation and thus represent an opportunity to surgically cure or prevent pancreatic adenocarcinoma. Pancreatic cancer usually presents in an advanced stage due to a delay in diagnosis and the overall five-year survival is 5%. Therefore, considering the current safety of pancreatic resection, it is not surprising that there has been an increase in the number of operations for pancreatic cystic lesions 5. However, some cystic lesions of the pancreas are benign or slow growing and the true rate of malignant transformation is unclear.
The dilemma for the surgeon is an accurate assessment of the risk benefit ratio of resection versus observation of these lesions in individual patients. Radiologic features including the size of the lesion and its growth rate, the density of the lesion, characteristics of the wall such as nodules, septations, or calcifications, and the relationship between the lesion and the pancreatic duct have been proposed as criteria that can help categorize these lesions.
Although a thorough history and radiographic findings often suggest a particular diagnosis, EUS-guided FNA and analysis of cyst fluid or ERCP provide useful additional information to guide clinical decision making. Cysts that contain thick fluid with mucin, elevated CEA, or atypical cells must be treated as potentially malignant. CEA appears to be the most useful tumor marker to measure in pancreatic cyst fluid 6. The cut-off value for benign versus potentially malignant varies in the literature, however, about 200 ng/mL seems to provide optimal specificity without significantly impacting sensitivity 6,7,8. Ongoing studies of molecular analysis of pancreatic cyst fluid, particularly genetic analysis, may improve diagnostic specificity in the future.
When considering the cost of care, the value of multiple diagnostic tests to achieve the most accurate preoperative diagnosis must be considered. The current literature suggests that as many as 75% of cystic pancreatic lesions are asymptomatic incidental findings 9. Although asymptomatic pancreatic cysts are being discovered with increasing frequency, some patients present with symptoms of biliary obstruction, pancreatitis, or abdominal pain. Patients who are symptomatic, such as those in this series, generally proceed to surgical resection. In this surgical series, 81% of the patients presented with symptomatic lesions. In symptomatic patients with CT findings of a cystic neoplasm, further characterization of the lesion with EUS-FNA, or ERCP is probably not cost-effective. However, of the 39 patients in our series with symptomatic lesions, 11 (28%) still had either EUS-FNA, ERCP, or both prior to surgical referral.
Also important in the cost considerations is the long-term expense of serial CT scans and EUS-FNA in cases where observation is recommended. This is particularly true for younger patients. However, surgery is not without its long-term costs. Calculating the cost of managing exocrine or endocrine pancreatic insufficiency after pancreatic resection is difficult. In our series, although the incidence of endocrine dysfunction after resection was relatively low, about a third of the patients required chronic pancreatic enzyme supplementation after surgery, particularly after the Whipple procedure.
The value of resection is removal of a symptomatic lesion or a malignant or potentially malignant lesion. Of the lesions in our surgical series 39 (81%) were symptomatic and 34 (71%) were determined to be malignant or of malignant potential after resection. Series with asymptomatic lesions may not be comparable. Other series have reported that only 20% of resected asymptomatic pancreatic cysts have malignant pathology 10. Little is known about the natural history of asymptomatic pancreatic cysts without features suggesting malignant potential. During the 32-month time period of this study we encountered eight additional patients with asymptomatic cysts who were excluded from the present study because they were observed rather than resected. All patients had small lesions, <3 cm, underwent EUS-FNA and had no mucin-producing or atypical cells, and cyst fluid CEA <200 ng/mL. Our algorithm is to repeat CT imaging at three-month intervals for the first year then yearly for at least five years. Repeat EUS-FNA of the cyst is performed if the lesion enlarges. Although we would advise operative management in patients with cysts that become symptomatic, enlarging cysts, or cysts with new fluid analysis suggesting malignant potential, none of the eight patients have come to surgery after a mean follow-up of 18 months. Walsh et al. reported their results with a similar treatment algorithm for asymptomatic pancreatic cysts 8. They followed 98 patients for a mean of 24 months and only four patients came to operation for increasing size and/or development of symptoms. One was a mucinous cystic neoplasm (initial cyst fluid CEA was 896 ng/mL). Pathology on the other patients was benign (lymphoepithelial cyst, pseudocyst, and serous cystadenoma) indicating that it may be safe to follow asymptomatic lesions using this algorithm.
In our study, the latest CT equipment and techniques combined with expert interpretation allowed an accurate specific diagnosis in only 39% and accurate prediction of malignant potential in 61%. This is consistent with the 25–60% range for diagnostic accuracy of CT for cystic neoplasms reported in the literature 11,12,13. The diagnostic accuracy of CT diminishes in small unilocular lesions that are seen more commonly in asymptomatic patients that are more likely to be treated nonoperatively. In our study, accuracy rates were 60.4 and 62.5% for the two radiologists, although there was only fair agreement on each case between radiologists (Kappa = 0.28, 95% CI=(0.01–0.55), p=0.05). Poor interobserver consensus of the etiology of cystic pancreatic lesions has been reported in other studies 14. Recent studies have also reported similar diagnostic accuracy rates for MRI and CT in the characterization of cystic pancreatic masses as benign or malignant 15.
Conclusion
Our data, and the literature, support the opinion that CT alone is not sufficient in determining the malignant potential of pancreatic cystic lesions. If a nonoperative approach is chosen, repeat imaging must be combined with further analysis such as EUS-FNA with analysis of cyst fluid.
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