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Original Report |
1
Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC
27710.
2
Department of Medicine, Duke University Medical Center, Durham, NC
27710.
3
Department of Surgery, Duke University Medical Center, Durham, NC 27710.
Received July 27, 2001;
accepted after revision October 17, 2001.
Address correspondence to E. K. Paulson.
Abstract
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CONCLUSION. Simple pancreatic cysts are typically an incidental finding in adults who have no history of pancreatic disease. The imaging characteristics of simple pancreatic cysts on CT and endosonography are similar to those of benign cysts.
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Simple pancreatic cysts, also termed "true cysts," are lined by a single layer of cuboidal epithelium and do not communicate with the pancreatic duct [2]. To date, most pancreatic simple cysts have been described in children or in patients with polycystic disorders such as autosomal dominant polycystic kidney disease [2,3,4]. Simple cysts of the pancreas rarely occur in adults [5, 6]. These cysts are benign, without neoplastic potential. With the widespread use of thin-collimation multidetector CT and the evolution of endosonography at many institutions, we anticipate that simple cysts of the pancreas will be identified with increasing frequency. This report describes the CT and endosongraphic features of pathologically proven simple pancreatic cysts in three adult patients.
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Patient 1 was a 35-year-old man who presented to the emergency department with left-sided renal colic. A CT scan was obtained to evaluate for acute obstructive urolithiasis. An incidental pancreatic lesion was detected on CT. Patient 2 was a 48-year-old woman who was referred from an outside institution for a surgical opinion regarding a mass in the head of the pancreas that had been detected on CT. She had a history of chronic lower back pain dating to a motor vehicle collision 9 months previously. Patient 3 was a 49-year-old man who underwent CT of the chest and abdomen to determine the cause of chronic lower back pain. A pancreatic lesion was identified as an incidental finding on CT.
All three patients were treated in consultation with a gastroenterologist and a pancreatic surgeon. Patient 1 had a history of intermittent epigastric discomfort without specific aggravating or relieving factors. Patients 2 and 3 had no specific symptoms relating to the pancreas. Laboratory analyses confirmed normal levels of serum amylase and lipase in all three patients.
All patients underwent abdominal CT; these examinations were performed using a dual-phase protocol routinely performed at our institution to evaluate pancreatic lesions. Patients 1 and 2 were scanned using a single-detector helical scanner (HiSpeed CT/i; General Electric Medical Systems, Milwaukee, WI). These patients received oral contrast material (175 mL iopamidol 300 [Isovue]; Bracco Diagnostics, Princeton, NJ) using a power injector (Medrad, Pittsburgh, PA) at a rate of 4 mL/sec. Unenhanced images to locate the pancreas were acquired using a 10-mm collimation with a 10-mm interval. Arterial phase imaging through the entire pancreas was performed with a 15-sec delay after the IV administration of contrast material. Images obtained during the arterial phase were helically acquired using a 3-mm collimation and were prospectively reconstructed at 3-mm intervals with a 1:1 pitch. Portal venous phase images through the entire liver and pancreas were acquired 70 sec after the commencement of IV administration of contrast material using a 5-mm collimation and were prospectively reconstructed at 5-mm intervals at a 1.5:1 pitch. For patient 3, a dual-phase pancreatic protocol was performed using a multidetector helical scanner (LightSpeed QX/i; General Electric Medical Systems). Unenhanced images were obtained using a 5-mm collimation at 5-mm intervals and a table speed of 15 mm per revolution. With a delay of 30 sec after the IV administration of contrast material, images were acquired during the arterial phase using a 1.25-mm collimation at a 6:1 pitch, a 1.25-mm interval, and a table speed of 7.5 mm per revolution through the entire pancreas. Portal venous phase images were acquired using a 5-mm collimation, a 5-mm interval, a 3:1 pitch, and a table speed of 15 mm per revolution after a 65-sec delay.
For patients 2 and 3, a gastroenterologist performed endosonography using a scanner (model GF-UM130; Olympus America, Lake Success, NY) with a 7.5- to 12.0-MHz radial array transducer and another scanner (model FG-36UX; Pentax Precision, Orangeburg, NY) with a 5- to 7.5-MHz linear array transducer. In both patients, cystic fluid aspiration was performed during the procedure. With sonographic guidance, clear serous fluid was aspirated from both cysts at endoscopy. Samples of cystic fluid were obtained for cytologic and cystic fluid analyses. Cytopathologic analysis of cystic fluid from both patients showed no evidence of malignancy. The levels of amylase and lipase in the cystic fluid were within the normal serum range for both patients. In patient 3, the levels of two tumor markers, carcinoembryonic antigen (CEA) and carbohydrate antigen (CA) 19-9, within the cystic fluid were also determined. In this patient, the level of CEA was higher than normal, measuring 15.9 ng/mL (expected value, <0.6 ng/mL). The CA 19-9 level was also elevated at 6,000 U/mL (serum reference, <37 U/mL). Patient 1 did not undergo endosonography.
Because none of the three patients had a history of pancreatitis, a presumptive diagnosis of pancreatic neoplasm was made in all patients. All patients underwent laparotomy and surgical exploration. Patient 1 had resection of a cystic lesion in the tail of the pancreas by distal pancreatectomy. Patient 2 had a Whipple procedure for a serous adenoma in the head of the pancreas and an excision biopsy of a cystic lesion in the neck of the pancreas. At laparotomy, patient 3 had a frozen-section biopsy and aspiration of a cystic lesion arising from the head of the pancreas. Histologically, each lesion was lined by a single layer of cuboidal epithelium, which is consistent with a simple pancreatic cyst. There was no evidence of malignancy. All patients tolerated the surgery well and had an unremarkable postoperative course. At 6-month follow-up, all three patients were asymptomatic.
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Endosonography performed in patients 2 and 3 confirmed the presence of a single unilocular pancreatic cyst in each patient. Both cysts exhibited the same characteristics as benign cysts: an imperceptible wall and posterior acoustic enhancement. Patient 2 had a 1.5-cm anechoic lesion in the neck of the pancreas. Endosonography revealed a 4-cm anechoic lesion that was well defined and arising from the head of the pancreas in patient 3. In both patients 2 and 3, the pancreatic duct was normal in caliber. Patient 1 did not undergo endosonography.
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CT is the imaging modality of choice for preoperative assessment of a pancreatic lesion at our institution. On CT, all three simple pancreatic cysts exhibited characteristics suggestive of an uncomplicated cyst. In the context of a simple pancreatic cyst, important additional CT findings include a normal pancreatic duct and the absence of CT features suggestive of pancreatitis. The CT appearance of simple pancreatic cysts described in this report corroborates the findings described in prior case reports [5,6,7,8,9,10].
Two of the three simple pancreatic cysts in this series were imaged on endosonography. Endosonography confirmed that both lesions had characteristics of benign cysts with a uniformly imperceptible wall and posterior acoustic enhancement. To our knowledge, the imaging characteristics of simple pancreatic cysts on endosonography have not been described in previous reports.
Analyses of the levels of amylase, lipase, and tumor markers in aspirated cystic fluid and cytologic analysis of aspirated cystic fluid have been suggested as methods for preoperative differentiation of cystic masses in the pancreas [11,12,13,14]. In two of three patients in this series, preoperative aspiration revealed that the cystic fluid was clear and of low viscosity—similar to the fluid described in prior reports [12,13,14]. In both patients, cytopathology showed no evidence of malignancy, and the amylase and lipase levels within the cystic fluid were in the normal serum range. Of interest, levels of the tumor markers CEA and CA 19-9 within the cystic fluid were measured in patient 3, and results indicated that both markers were elevated. Elevated levels of tumor markers are more commonly associated with mucinous cystic tumors [12, 13]. However, both normal and increased tumor marker indexes have been reported in simple pancreatic cysts [11, 13, 14]. Thus, analysis of tumor marker levels in the aspirate from simple pancreatic cysts may be of limited value.
Correct preoperative differential diagnosis of pancreatic cystic masses is important to select appropriate treatment [5, 7, 15]. The differential diagnosis for unilocular pancreatic cystic lesions includes pseudocysts, unilocular mucinous tumors, and simple cysts. Pseudocysts typically occur in patients with a history of pancreatitis [1], are classically unilocular on CT, and may have ancillary features of pancreatitis such as pancreatic duct dilatation or pancreatic calcification [1, 5]. On endosonography, a pseudocyst almost never has anechoic contents or a sharply defined internal wall, whereas both findings are revealed on endosonography of simple pancreatic cysts [16]. The lack of an epithelial wall at histology and fluid aspirate with an elevated level of amylase allow confirmation of a pseudocyst [1, 5]. Mucinous tumors, which have premalignant potential, are the other main differential diagnosis for a unilocular pancreatic cystic lesion [12]. All three patients in this series had the presumptive diagnosis of a mucinous tumor before surgery. In the absence of other distinguishing imaging characteristics such as mural nodularity, calcification, or enhancement after IV administration of contrast material, imaging features alone may not allow differentiation of a unilocular mucinous tumor from a simple pancreatic cyst.
In conclusion, the simple pancreatic cyst exhibits characteristics of benign cysts on CT and endosonography. With the increased use of CT and endosonography, the radiologist should be aware that these benign lesions are an important differential diagnosis for a unilocular pancreatic cystic lesion in patients without a history of pancreatitis. Although the decision about surgical management depends on the size and location of the lesion, the patient's symptoms, and the degree of clinical suspicion for potential malignancy, follow-up serial imaging may be an alternative approach to management in the appropriate clinical setting.
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