(Radiographics. 2001;21:1455-1461.)
© RSNA, 2001
Microcystic Features at US: A Nonspecific Sign for Microcystic Adenomas of the Pancreas1
Hsu-Chong Yeh, MD,
Agata Stancato-Pasik, MD and
Robert S. Shapiro, MD
1 From the Department of Radiology, Mount Sinai-NYU Medical Center, One Gustave L. Levy Pl, Box 1234, New York, NY 10029. Presented as an education exhibit at the 2000 RSNA scientific assembly. Received January 31, 2001; revision requested March 6 and final revision received August 28; accepted August 29. Address correspondence to H.C.Y. (e-mail: hsu-chong.yeh@mountsinai.org).
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Abstract
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Microcystic adenoma of the pancreas is a benign tumor with no malignant potential and may not require surgery if it is asymptomatic. In the past, a mass containing more than six small (<2-cm) cysts at ultrasonography (US) has been considered to be diagnostic for microcystic adenoma. However, a retrospective study of 36 patients with focal or diffuse pancreatic lesions containing over six small cysts demonstrated that this finding can occur in a wide variety of neoplastic and inflammatory lesions, most of which are malignant. These lesions included adenocarcinoma (n = 18), mucinous cystadenocarcinoma (n = 2), islet cell carcinoma (n = 1), lymphoma (n = 1), sarcoma (n = 1), metastases (n = 2), pancreatitis (n = 4), and adenoma (n = 7). Thus, a finding of multiple small cysts in a pancreatic mass is not specific for microcystic adenoma, and if diagnosis is based on US findings alone, many malignant tumors will be misdiagnosed as microcystic adenomas. Furthermore, computed tomography provides only limited assistance in this setting due to overlapping findings. Needle biopsy can be highly accurate in diagnosing both microcystic adenoma and other malignant lesions and should generally be performed for all lesions with the US features described earlier.
Index Terms: Pancreas, cysts, 77.312 • Pancreas, diseases, 77.291, 77.312, 77.321 • Pancreas, neoplasms, 77.312, 77.3192, 77.321 • Pancreas, US, 77.12983 • Pancreatitis, 77.291
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Introduction
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Cystic pancreatic neoplasms are rare, accounting for about 10%–15% of all pancreatic cysts and only 1% of all pancreatic neoplasms (1). These tumors may be benign (microcystic adenoma, mucinous macrocystic adenoma) or malignant (mucinous cystadenocarcinoma). Unlike mucinous macrocystic adenomas, microcystic adenomas do not have malignant potential; furthermore, if asymptomatic, they do not require surgical removal (2–4). Therefore, a definitive diagnosis of microcystic adenoma is very important.
The major diagnostic feature of microcystic adenoma at ultrasonography (US) is more than six intratumoral cysts less than 2 cm in diameter (2,4,5). However, we found this US feature in a wide spectrum of neoplastic and inflammatory pancreatic lesions.
In this article, we describe our study in greater detail. We also discuss and illustrate the nonspecific microcystic features seen at US and computed tomography (CT) in various pancreatic lesions, including adenocarcinoma, mucinous cystadenocarcinoma, lymphoma, metastatic lesions, microcystic adenoma, and pancreatitis.
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Patients and Procedures
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We conducted a retrospective study of 36 patients (25 female, 11 male; age range, 33–86 years [mean, 64.7 years]) who, over the past 13 years (30 over the past 9 years), were found to have focal or diffuse pancreatic lesions containing over six small cysts less than 2 cm in size.
US was performed with commercially available real-time scanners (Acuson, Mountain View, Calif; Advanced Technology Laboratories, Bothell, Wash; Diasonics, Milpitas, Calif). A 3.5-MHz mechanical sector transducer was used in the first six cases. In the next 12 cases, a 3.5-MHz curved-array transducer was used. A wide-band 2–4-MHz curved-array transducer was used in all of the remaining cases except one, in which a harmonic 4-MHz curved-array transducer was used. The lesions were scanned carefully to ensure that vascular structures in the lesions were not mistaken for small cysts. Color Doppler US was also used for this purpose and was performed in 23 of 29 cases arising since 1992, the year in which this imaging modality became available in our department. Color Doppler US was also used to avoid puncturing vessels during needle biopsy, which was performed by one of the authors (H.C.Y.) in most cases.
Of the 36 patients in our study, 32 had neoplastic disease and four had pancreatitis. Neoplastic lesions included adenocarcinoma in 18 patients (Figs 1, 2); mucinous cystadenocarcinoma in two (one with a focal mass in the pancreatic head [Fig 3] and the other with diffuse pancreatic lesions with numerous small cysts and a 3 x 2.2-cm cyst [Fig 4]); a large (10.8-cm), nonfunctioning islet cell carcinoma in one; lymphoma in one (Fig 5); a large (11-cm) sarcoma in one; metastatic lesions in two (one with metastasis from bile duct cystadenocarcinoma [Fig 6] and one with metastasis from adenocarcinoma of the gallbladder); and microcystic adenomas in seven (six with focal mass lesions [Figs 7, 8] and one with von Hippel–Lindau disease with diffuse involvement of the entire pancreas).
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Figure 3. Mucinous cystadenocarcinoma in a 75-year-old man. Oblique US image shows a mass in the pancreatic head (arrowheads) containing multiple small cysts. There was also a larger, 2 x 1.8-cm cyst (not shown). The common bile duct (arrow) is dilated due to obstruction by the mass. The gallbladder is also dilated and contains biliary sludge that forms a level.
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Figure 4a. Mucinous cystadenocarcinoma of the entire pancreas in a 68-year-old man. (a) Transverse US image shows multiple small cysts in the pancreatic head and body (arrowhead). A 3-cm cyst is vaguely seen in the pancreatic tail (arrows). A = aorta, V = inferior vena cava. (b) Oblique sagittal US image obtained in the epigastric region and oriented toward the left side shows numerous small cysts in the tail of the pancreas (arrowhead). The 3-cm cyst is now more clearly seen at the distal end of the pancreatic tail (arrows). The walls of these cysts are not clearly delineated, making it more difficult to determine the cystic nature of the lesions at US than at CT. However, good through transmission is evident. Aspiration showed turbid dark brown fluid that revealed mucinous cystadenocarcinoma at cytologic examination. (c) CT scan corresponding to a shows numerous small cysts throughout the entire pancreas. The superior mesenteric artery (a) and superior mesenteric vein (V) are encased by the mass, indicating that the mass may be malignant. (d) CT scan obtained slightly inferior to c shows a 3-cm cyst in the distal tail of the pancreas (arrowhead). a = superior mesenteric artery, V = superior mesenteric vein.
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Figure 4b. Mucinous cystadenocarcinoma of the entire pancreas in a 68-year-old man. (a) Transverse US image shows multiple small cysts in the pancreatic head and body (arrowhead). A 3-cm cyst is vaguely seen in the pancreatic tail (arrows). A = aorta, V = inferior vena cava. (b) Oblique sagittal US image obtained in the epigastric region and oriented toward the left side shows numerous small cysts in the tail of the pancreas (arrowhead). The 3-cm cyst is now more clearly seen at the distal end of the pancreatic tail (arrows). The walls of these cysts are not clearly delineated, making it more difficult to determine the cystic nature of the lesions at US than at CT. However, good through transmission is evident. Aspiration showed turbid dark brown fluid that revealed mucinous cystadenocarcinoma at cytologic examination. (c) CT scan corresponding to a shows numerous small cysts throughout the entire pancreas. The superior mesenteric artery (a) and superior mesenteric vein (V) are encased by the mass, indicating that the mass may be malignant. (d) CT scan obtained slightly inferior to c shows a 3-cm cyst in the distal tail of the pancreas (arrowhead). a = superior mesenteric artery, V = superior mesenteric vein.
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Figure 4c. Mucinous cystadenocarcinoma of the entire pancreas in a 68-year-old man. (a) Transverse US image shows multiple small cysts in the pancreatic head and body (arrowhead). A 3-cm cyst is vaguely seen in the pancreatic tail (arrows). A = aorta, V = inferior vena cava. (b) Oblique sagittal US image obtained in the epigastric region and oriented toward the left side shows numerous small cysts in the tail of the pancreas (arrowhead). The 3-cm cyst is now more clearly seen at the distal end of the pancreatic tail (arrows). The walls of these cysts are not clearly delineated, making it more difficult to determine the cystic nature of the lesions at US than at CT. However, good through transmission is evident. Aspiration showed turbid dark brown fluid that revealed mucinous cystadenocarcinoma at cytologic examination. (c) CT scan corresponding to a shows numerous small cysts throughout the entire pancreas. The superior mesenteric artery (a) and superior mesenteric vein (V) are encased by the mass, indicating that the mass may be malignant. (d) CT scan obtained slightly inferior to c shows a 3-cm cyst in the distal tail of the pancreas (arrowhead). a = superior mesenteric artery, V = superior mesenteric vein.
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Figure 4d. Mucinous cystadenocarcinoma of the entire pancreas in a 68-year-old man. (a) Transverse US image shows multiple small cysts in the pancreatic head and body (arrowhead). A 3-cm cyst is vaguely seen in the pancreatic tail (arrows). A = aorta, V = inferior vena cava. (b) Oblique sagittal US image obtained in the epigastric region and oriented toward the left side shows numerous small cysts in the tail of the pancreas (arrowhead). The 3-cm cyst is now more clearly seen at the distal end of the pancreatic tail (arrows). The walls of these cysts are not clearly delineated, making it more difficult to determine the cystic nature of the lesions at US than at CT. However, good through transmission is evident. Aspiration showed turbid dark brown fluid that revealed mucinous cystadenocarcinoma at cytologic examination. (c) CT scan corresponding to a shows numerous small cysts throughout the entire pancreas. The superior mesenteric artery (a) and superior mesenteric vein (V) are encased by the mass, indicating that the mass may be malignant. (d) CT scan obtained slightly inferior to c shows a 3-cm cyst in the distal tail of the pancreas (arrowhead). a = superior mesenteric artery, V = superior mesenteric vein.
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Figure 6. Metastasis from cystadenocarcinoma of the bile duct. Transverse US image shows a large mass in the head of the pancreas (arrowheads) containing multiple cysts. Although two cysts are slightly larger (up to 3 cm in diameter), most of the cysts are less than 1.5 cm.
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Figure 7a. Microcystic adenoma in a 78-year-old woman. Transverse US image (a) and corresponding CT scan (b) show a mass in the head of the pancreas (arrowhead) containing multiple small cysts. a = superior mesenteric artery, v = superior mesenteric vein.
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Figure 7b. Microcystic adenoma in a 78-year-old woman. Transverse US image (a) and corresponding CT scan (b) show a mass in the head of the pancreas (arrowhead) containing multiple small cysts. a = superior mesenteric artery, v = superior mesenteric vein.
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Figure 8a. Microcystic adenoma in a 51-year-old woman. (a) Transverse US image shows a mass in the head of the pancreas (arrowheads) containing multiple small cysts. (b) US image obtained with the patient in the decubitus position shows a dilated common bile duct (D) and gallbladder (G) due to obstruction by the pancreatic mass (arrowheads).
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Figure 8b. Microcystic adenoma in a 51-year-old woman. (a) Transverse US image shows a mass in the head of the pancreas (arrowheads) containing multiple small cysts. (b) US image obtained with the patient in the decubitus position shows a dilated common bile duct (D) and gallbladder (G) due to obstruction by the pancreatic mass (arrowheads).
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Three of the four patients with pancreatitis had focal mass lesions (Fig 9), and one had diffuse involvement of the entire pancreas by small cysts (Fig 10).
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Figure 10a. Chronic pancreatitis associated with diffuse cystic changes. (a) Transverse US image shows the pancreatic head and body filled with small (<2-cm) cysts. (b) Coronal US image of the spleen (S) shows small cysts in the tail of the pancreas (arrowheads). (c) CT scan corresponding to a shows the pancreas filled with small cysts. (d) CT scan corresponding to b also demonstrates numerous small cysts filling the tail of the pancreas (arrowhead). Aspiration showed whitish milky or semipurulent intracystic fluid due to chronic infection.
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Figure 10b. Chronic pancreatitis associated with diffuse cystic changes. (a) Transverse US image shows the pancreatic head and body filled with small (<2-cm) cysts. (b) Coronal US image of the spleen (S) shows small cysts in the tail of the pancreas (arrowheads). (c) CT scan corresponding to a shows the pancreas filled with small cysts. (d) CT scan corresponding to b also demonstrates numerous small cysts filling the tail of the pancreas (arrowhead). Aspiration showed whitish milky or semipurulent intracystic fluid due to chronic infection.
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Figure 10c. Chronic pancreatitis associated with diffuse cystic changes. (a) Transverse US image shows the pancreatic head and body filled with small (<2-cm) cysts. (b) Coronal US image of the spleen (S) shows small cysts in the tail of the pancreas (arrowheads). (c) CT scan corresponding to a shows the pancreas filled with small cysts. (d) CT scan corresponding to b also demonstrates numerous small cysts filling the tail of the pancreas (arrowhead). Aspiration showed whitish milky or semipurulent intracystic fluid due to chronic infection.
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Figure 10d. Chronic pancreatitis associated with diffuse cystic changes. (a) Transverse US image shows the pancreatic head and body filled with small (<2-cm) cysts. (b) Coronal US image of the spleen (S) shows small cysts in the tail of the pancreas (arrowheads). (c) CT scan corresponding to a shows the pancreas filled with small cysts. (d) CT scan corresponding to b also demonstrates numerous small cysts filling the tail of the pancreas (arrowhead). Aspiration showed whitish milky or semipurulent intracystic fluid due to chronic infection.
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Cystic Pancreatic Neoplasms
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Microcystic Adenoma
Microcystic adenoma is a benign pancreatic tumor that arises from acinar cells. The tumor contains multiple small cysts lined with cuboidal cellsand containing serous fluid. The fluid is positive at glycogen staining (periodic acid Schiff reaction) (1,4). The US features of microcystic adenoma of the pancreas include more than six small (<2-cm) cysts, a central stellate scar, and calcifications (2,4,5). In a study by Johnson et al (5), central scar was found in only two of 16 patients (13%) with microcystic adenoma, and calcifications were not identified at US in any of 45 patients with microcystic adenoma, macrocystic adenoma, or macrocystic adenocarcinoma. However, calcifications were seen at CT in 38% of patients with microcystic adenoma, 18% of patients with macrocystic adenoma, and 8% of patients with macrocystic adenocarcinoma. None of the seven cases of microcystic adenoma in our series demonstrated central stellate scar or calcifications at US, even though the masses ranged widely from 3 to 12.9 cm. CT was performed in one patient with microcystic adenoma in our study but revealed no calcification. Thus, multiple small cysts are the major distinguishing US feature of microcystic adenoma. However, only seven of the 36 patients in our study had this disease; thus, the specificity of this feature for microcystic adenoma is only 19.4%. It is well known that when cysts are too small and are not clearly visualized, a mass may appear solid (1,4,5). Johnson et al (5) found three solid tumors among the 16 patients in their series with microcystic adenoma. Increased echogenicity may be seen in the solid-appearing area due to sound reflections from numerous small cyst walls. In one case in our series, the mass was initially mistaken for a completely solid tumor; however, the mass was not hyperechoic but nearly isoechoic relative to the liver.
Macrocystic Adenoma and Cystadenocarcinoma
Macrocystic adenoma is a benign cystic pancreatic tumor that is lined with columnar epithelial cells and probably arises from the ducts. The cysts in macrocystic adenoma contain mucin, and the columnar cells lining the tumor are well oriented relative to the basement membrane and have a regular alignment with no evidence of anaplasia. In cystadenocarcinoma, the epithelial cells are anaplastic, pile up into irregular proliferative masses, and invade the underlying wall and adjacent structures. US typically demonstrates fewer than six larger (>2-cm) cysts (5). The tumors may be multilocular or, less commonly, unilocular (4,6–9). Papillary projections or solid tissue may be seen in the cystic wall, which may be thickened (5,6). The two cases of mucinous cystadenocarcinoma in our series did not demonstrate these classic US features (Figs 3, 4). Instead, they demonstrated numerous small cysts similar to those seen in microcystic adenoma, although one patient also had a 3-cm cyst. Carlson et al (1) found that one or more larger cysts may also be seen in microcystic adenoma. Curry et al (10) found cysts larger than 2 cm in eight of 22 patients (36%) with microcystic adenoma. Therefore, a finding of small cysts combined with larger cysts is not specific for macrocystic adenoma or adenocarcinoma.
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Diffuse Cystic Changes throughout the Pancreas
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Three patients in our series had diffuse cystic changes throughout the pancreas. One of two patients with mucinous cystadenocarcinomas had tumor involvement of the entire pancreas (Fig 4), which is rather unusual. Diffuse involvement may also be seen in 10% of cases of microcystic adenoma (4) and in von Hippel–Lindau disease. One patient with this disease had diffuse microcystic changes involving the entire pancreas, possibly owing to microcystic adenoma or diffuse cystosis. The third patient had diffuse microcystic changes that were due to pancreatitis (Fig 10). Thus, the three cases of diffuse cystic lesions involving the whole pancreas were due to cancer, adenoma, and pancreatitis, respectively.
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Microcystic Features of Pancreatic Masses
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US Findings
A cyst usually has a thin, well-defined wall. In a small cyst, however, the lateral wall may not be clearly delineated, and only the anterior and posterior walls are seen, appearing as thin, curvilinear echogenic areas. Tiny cysts may be difficult to visualize individually at US but manifest corporately as diffuse, coarse hyperechoic areas. However, in one case in our series, even this finding was absent, and prior to core biopsy, the mass was mistaken for a pure solid lesion. The through transmission of a small cyst may be seen in a homogeneous organ such as the liver. In heterogeneous tissue or tumor, through transmission may not be apparent, but the posterior wall of the cyst may sometimes appear more prominent or thicker than the anterior wall. Multiple cysts packed together may be seen as a multiloculated cyst or multiple irregular cysts: Depending on differences in individual intracystic pressure, one cyst may indent the other, causing an irregular appearance of the cysts. The cystic contents may be anechoic or echogenic, the latter finding perhaps owing to particulate material within the cyst. However, through transmission is still seen in these cysts (Fig 10). A 3.5-MHz transducer is usually adequate for detecting small (0.2–0.3-cm) cysts. Most important is that scanning be performed with a steady pressure and a slow, sweeping motion. In this way, gas in the bowel or stomach will not obliterate the pancreas, and fine details in the mass will not escape observation.
If gray-scale US alone is used, some vascular structures may be mistaken for microcystic lesions. With careful real-time scanning, cysts can be recognized as round structures that cannot be traced like tubular vessels, although markedly tortuous vessels may be more easily mistaken for multiple cysts. Actual real-time scanning was performed by one of the authors (H.C.Y.) in all the patients in our series. In most cases, no tumor vessels other than encased vessels were seen at color Doppler US.
Pathophysiology of the Cysts
The nature and causes of small cystic areas in various masses in our series are not certain. Possible causes include focal necrosis or hemorrhage, cystic degeneration, or encasement of the pancreatic duct and its branches, which become dilated due to obstruction by tumor. Shawker et al (11) found small cystic spaces within or immediately adjacent to four of 52 pancreatic tumors (8%). Numerous small cysts seen in focal pancreatitis may be due to obstruction of small branches of the pancreatic ducts causing cystic dilatation of the ducts distally, cystic changes due to multiple small focal areas of necrosis, or focal necrosis or hemorrhage containing fibrin that forms numerous septations. As mentioned earlier, there were two cases of metastases in our study. In one case, metastasis was from primary cystadenocarcinoma of the bile duct; naturally, metastasis from this cancer may also contain cysts. In the other case, metastasis was from gallbladder cancer, which originally was not cystic. In such a tumor, the cysts are intratumoral and are probably not due to obstruction of small branches of the pancreatic ducts; they more likely have other causes such as focal necrosis or hemorrhage.
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Conclusions
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In our experience, a wide spectrum of neoplastic or inflammatory lesions appear similar to microcystic adenoma at US, and most of these lesions are malignant neoplasms. Therefore, if diagnosis is based on US findings alone, many malignant tumors will be misdiagnosed as microcystic adenomas. Furthermore, although Johnson et al (5) reported that US and CT features can help differentiate microcystic adenoma from macrocystic adenocarcinoma or adenoma in more than 90% of cases, Curry et al (10) found that CT provides only limited assistance in such differentiation due to overlapping CT findings. The authors were able to diagnose microcystic adenoma at CT in only 23%–41% of cases with independent readings and in 27% with consensus readings. Because needle biopsy can be highly accurate in diagnosing both microcystic adenoma (1) and other malignant lesions, it should be performed for all lesions with similar US features unless prohibited by clinical findings.
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References
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Carlson SK, Johnson CD, Brandt KR, Batts KP, Salomao DR. Pancreatic cystic neoplasms: the role and sensitivity of needle aspiration and biopsy. Abdom Imaging 1998; 23:387-393.[Medline]
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Compangno J, Oertel J. Mucinous cystic neoplasms of the patient with overt and latent malignancy (cystadenocarcinoma and cystadenoma): a clinico-pathologic study of 41 cases. Am J Clin Pathol 1978; 69:573-580.[Medline]
-
Hyde GL, Davis JB, McMillin RD, McMillin M. Mucinous cystic neoplasm of the pancreas with latent malignancy. Am Surg 1984; 50:225-229.[Medline]
-
Wolfman NT, Ramquist NA, Karstaedt N, Hopkins MB. Cystic neoplasms of the pancreas: CT and sonography. AJR Am J Roentgenol 1982; 138:37-41.[Abstract/Free Full Text]
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Johnson CD, Stephens DH, Charboneau JW, Carpenter HA, Welch TJ. Cystic pancreatic tumors: CT and sonographic assessment. AJR Am J Roentgenol 1988; 151:1133-1138.[Abstract/Free Full Text]
-
Hill MC. Pancreatic sonography: an update. In: Sanders RC, eds. Ultrasound annual 1982. New York, NY: Raven, 1982; 1-42.
-
Buetow PC, Rao P, Thompson LDR. Mucinous cystic neoplasms of the pancreas: radiologic-pathologic correlation. RadioGraphics 1998; 18:433-449.[Abstract]
-
Carroll B, Sample F. Pancreatic cystadenocarcinoma: CT body scan and gray scale ultrasound appearance. AJR Am J Roentgenol 1978; 131:339-341.[Medline]
-
Freeny PC, Weinstein CJ, Taft DA, Allen FH. Cystic neoplasms of the pancreas: new angiographic and ultrasonographic findings. AJR Am J Roentgenol 1978; 131:795-802.[Abstract]
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Curry CA, Eng J, Horton KM, et al. CT of primary cystic pancreatic neoplasms: can CT be used for triage and treatment?. AJR Am J Roentgenol 2000; 175:99-103.[Abstract/Free Full Text]
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Shawker TH, Garra BS, Hill MC, Doppman JL, Sindelar WF. The spectrum of sonographic findings in pancreatic carcinoma. J Ultrasound Med 1986; 5:169-177.[Abstract]
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Abstract
Introduction
