AJR 2002; 179:1375-1388
© American Roentgen Ray Society
Cystic Lesions of the Pancreas
Terrence C. Demos1,
Harold V. Posniak1,
Carla Harmath1,
Mary C. Olson1 and
Gerard Aranha2
1 Department of Radiology, Loyola University Medical Center, 2160 S. First Ave.,
Maywood, IL 60153.
2 Department of Surgery, Surgical Oncology Section, Loyola University Medical
Center, Maywood, IL 60153.
Received January 23, 2002;
accepted after revision March 19, 2002.
Presented at the annual meeting of the American Roentgen Ray Society,
Seattle, April-May 2001.
Address correspondence to T. C. Demos.
Introduction
Cystic pancreatic lesions are regularly encountered on imaging studies of
patients who are symptomatic or as unexpected abnormalities in patients who
are being examined for other easons. A wide variety of cystic lesions of the
pancreas are seen, but pseudocysts are by far most common. Cystic neoplasms
are often misdiagnosed as pseudocysts, which occurred in 22 of 67 patients in
one series [1]. This indicates
the difficulty in diagnosis and at the same time emphasizes the need to obtain
clinical information to provide the most accurate diagnosis by consulting with
the referring physician regarding virtually every patient who is found to have
a pancreatic mass. In addition, knowledge of fundamental clinical
[2,3,4,5],
pathologic [2], laboratory, and
imaging
[6,7,8,9,10,11]
information related to specific cystic pancreatic lesions can be used to
decrease misdiagnosis, to narrow the differential diagnosis, or, in some
cases, to provide a diagnosis.
In this review, a gamut of pancreatic and parapancreatic masses is
illustrated and arranged according to disease category. Basic clinical,
pathologic, and imaging features are presented. Pancreatic lesions are imaged
with CT
[6,7,8],
sonography [9,
11], MR imaging
[10], endoscopic retrograde
cholangiopancreatography (ERCP), and angiography. In this article we emphasize
CT because most lesions are either discovered or evaluated on CT.
Congenital Pancreatic Lesions
Most congenital pancreatic cysts are multiple, and almost all are
associated with underlying congenital diseases that primarily affect other
organ systems. Solitary congenital cysts are rare.
Multiple Pancreatic Cysts
Autosomal dominant polycystic kidney disease.—Extrarenal
cysts are most common in the liver. In decreasing incidence, cysts also occur
in the pancreas, spleen, endometrium, ovaries, seminal vesicles, epididymis,
and thyroid gland [11,
12]. The incidence of cysts
increases with aging. A recent sonographic study based on 213 individuals
reported hepatic cysts in 67% and pancreatic cysts in 5%
[12]. Pancreatic cysts vary
from microscopic to several centimeters in diameter and have an epithelial
lining of cuboidal to flat cells (Fig.
1).
Von Hippel-Lindau disease.—Von Hippel-Lindau disease is an
autosomal dominant condition characterized by central nervous system and
retinal hemangioblastomas, visceral cysts, pheochromocytomas, and renal cell
carcinoma. Pancreatic cysts are found in up to 75% of cases at autopsy but on
only approximately 50% of imaging studies
[11,
13,
14]. Cysts vary in size from
millimeters to centimeters (Fig.
2). Other pancreatic lesions include microcystic adenomas, islet
cell tumors, angiomas, and vascular neoplasms, including hemangioblastomas
[11,
13,
14]. In some members of
families with this syndrome, pancreatic lesions are the first or only
manifestation of the disease, with a delay of years before the development of
lesions at other sites [13,
14]. Therefore, family members
must continue to be screened after their initial evaluation
[14].
Cystic fibrosis.—The most common pancreatic abnormality
found on imaging studies is fatty replacement of the pancreas, but
calcifications and cysts may also be found. True epithelium-lined cysts
probably develop as a result of inspissated mucin that obstructs pancreatic
ducts (Fig. 3). Cysts can be
single or multiple. Most are microscopic, but infrequently cysts up to several
centimeters in diameter are shown on imaging studies
[11]. Rarely, cysts are so
numerous and large that most of the pancreas is replaced. This phenomenon has
been termed "cystosis" and should not be mistaken for a cystic
neoplasm [15].
Solitary Pancreatic Cysts
The most frequent types of these rare lesions are the true cysts and the
lymphoepithelial cysts.
True cyst.—True cysts, most often found in infants, result
from anomalous development of pancreatic ducts and range from microscopic to
several centimeters in diameter. They can be unilocular or multilocular, have
an epithelial lining, and contain serous fluid
[16,
17].
Lymphoepithelial cyst.—To our knowledge, fewer than 40
lymphoepithelial cysts (Fig. 4)
have been reported in the literature
[18]. Most occur in
middle-aged to elderly men. Lesions vary from 1 to 17 cm, have a squamous
lining, and contain keratinous material
[18,19,20].
Inflammatory and Infectious Pancreatic Lesions
Pseudocyst
Panceatic and parapancreatic fluid collections are most often complications
of pancreatitis. These fluid collections can resolve spontaneously, but those
that do not are recognized as pseudocysts on imaging studies when a
well-defined wall becomes visible (Fig.
5). This wall consists of fibrous tissue, but unlike true cysts,
lymphoepithelial cysts, and most cystic neoplasms, a pseudocyst has no
epithelial lining [21]. When
cysts are chronic, the cyst wall can calcify
(Fig. 6). Imaging studies show
accompanying signs of pancreatitis to a varying degree in most patients
[21]. The appearance of a
pseudocyst on CT, sonography, and MR imaging varies with the cyst content
[22]. On CT, hemorrhagic and
necrotic material can increase the attenuation of fluid, whereas fat decreases
attenuation. Secondary infection can result in gas formation. A typical
pseudocyst, however, is a uniform, low-attenuation fluid collection with a
thin uniform wall that enhances after the administration of IV contrast
material. On sonography, uncomplicated pseudocysts are generally hypoechoic
with variable through-transmission, but hemorrhage or necrotic debris will
produce internal echogenicity. On MR imaging, an uncomplicated, fluid-filled
pseudocyst has uniform low signal intensity on T1-weighted images and high
intensity on T-2 weighted images. Protein content, necrotic debris, and
hemorrhage can alter these signal characteristics.
On imaging studies, a pseudocyst may be indistinguishable from a cystic
neoplasm [1,
5]. The amylase level of
pseudocyst fluid is almost always much higher than the fluid in cystic
neoplasms, but cystic neoplasms with high levels of amylase have been reported
[2,
23,
24]. Extrapancreatic extension
or location of a pseudocyst on imaging studies is evidence against a cystic
neoplasm.
Abscess
Pancreatic abscess is a serious complication of pancreatitis. Abscesses may
have poorly defined margins and are often suspected when gas is present in a
fluid collection (Fig. 7). In
the absence of gas, differentiation of an abscess from pancreatic necrosis or
simple fluid is not possible with imaging. Percutaneous aspiration is often
used to confirm infection or abscess before percutaneous or surgical drainage
[22]. Pancreatic gas, however,
is not pathognomonic of an abscess. A pancreatic—enteric fistula (Fig.
8A,8B),
a previous internal pseudocyst drainage, or a previous drainage of the
pancreas by a pancreati-cojejunostomy can all result in gas in the pancreatic
bed.
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Fig. 7. —Pancreatic abscess containing gas in 54-year-old man. CT scan
shows large fluid collection containing gas bubbles in pancreatic bed due to
abscess complicating acute pancreatitis. Note infiltration of peripancreatic
fat and calcified gallstones.
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Fig. 8A. —Pancreatic gas caused by pancreatic—enteric fistula in
asymptomatic 58-year-old man. CT scan shows small thin-walled collection with
air—fluid level (arrow) in tail of pancreas on follow-up
several weeks after episode of acute pancreatitis.
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Some rare pancreatic infections, including fungi, tuberculosis, and
parasites, can have a cystic appearance
[25,26,27].
Knowledge of the patient's history is essential to suggest the diagnosis.
Exocrine Pancreatic Lesions
Neoplasms that can present as cystic lesions are indicated in Appendix 1,
which is based on the pathologic classification of pancreatic neoplasms
[28].
Mucinous Adenocarcinoma (Colloid Carcinoma)
Adenocarcinoma is by far the most common pancreatic neoplasm. Mucinous
adenocarcinoma is an uncommon variant of adenocarcinoma
(Fig. 9). This neoplasm
produces a large volume of mucin that results in a cystic appearance on
imaging studies [29,
30]. The prognosis is just as
poor as for an adenocarcinoma that has a typical appearance and histology.
Tumoral calcification, inspissated mucin or tumor obstructing bile ducts, and
pseudomyxoma peritonei have all been reported in association with mucinous
adenocarcinomas.
Microcystic Adenoma (Cystadenoma, Serous Adenoma, Glycogen-Rich
Adenoma)
This benign neoplasm, which constitutes 1-2% of all pancreatic neoplasms,
is most frequent in women in the seventh decade (female-to-male ratio, 2:1)
[31,32,33]
(Figs.
10,11A,11B,12A,12B).
Microcystic adenoma is one of the pancreatic lesions found in von
Hippel-Lindau disease. Cysts can be single or multiple and can involve any
part of the pancreas. Most are smaller than 2 cm in diameter, but larger cysts
do occur. A minority of lesions have a central stellate scar, with or without
calcification (Fig. 10). When
it is present, this calcified central stellate scar within a lesion consisting
of cysts smaller than 2 cm has been considered to be diagnostic
[3,
33]. A solitary ovoid lesion
consisting solely of cysts smaller than 2 cm in an asymptomatic patient has
also been considered to be specific enough to allow follow-up without tissue
confirmation [8,
33]. However, if a lesion
contains some cysts larger than 2 cm, fine-needle aspiration biopsy or surgery
has been advocated [3,
8,
32]. Recent medical literature
has reported accurate diagnosis of microcystic adenomas, based on imaging
studies, varying from six of 22 proven microcystic adenomas in one study
[7] to 28 of 36 lesions in
another study [8].
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Fig. 12A. —Microcystic adenoma and adenocarcinoma in 97-year-old woman
with multiple liver metastases. CT scans show microcystic adenoma in
pancreatic head that consists of small cysts (A) and synchronous solid
adenocarcinoma (arrow, B) in tail of pancreas (B).
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Fig. 12B. —Microcystic adenoma and adenocarcinoma in 97-year-old woman
with multiple liver metastases. CT scans show microcystic adenoma in
pancreatic head that consists of small cysts (A) and synchronous solid
adenocarcinoma (arrow, B) in tail of pancreas (B).
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Misdiagnosing a potentially malignant mucinous cystic tumor as a benign
microcystic adenoma is a serious problem that was reported to have occurred in
seven of 28 patients in one study
[7] and in two of 49 patients
in another study [8]. A
microcystic adenoma contains intracellular glycogen but no mucin. This
glycogen content is a feature that is central in using percutaneous aspiration
biopsy to differentiate this neoplasm from a mucinous cystic tumor that is
characterized by mucin content
[31].
On CT, microcystic adenomas can be water, soft-tissue, or mixed density and
have a margin ranging from poorly defined to a thin well-defined capsule.
Enhancement of cyst walls and septa ranges from moderate to marked. Cyst walls
are sometimes visible only, or become more visible, on enhanced images (Fig.
11A,11B).
The central stellate scar is well defined and may be calcified. On sonography,
the lesions may appear cystic, solid, or even echogenic if the cysts are very
small. The central scar is echogenic, and cyst walls are better shown on
sonography than on CT [32,
33]. MR imaging, in general,
shows the same features with low signal intensity on T1-weighted images and
high signal intensity on T2-weighted images, and also shows a central scar and
septa.
Synchronous microcystic adenoma and adenocarcinoma have been reported
[34] (Fig.
12A,12B).
Mucinous Cystic Tumor (Cystadenoma, Cystadenocarcinoma, Macrocystic
Adenoma)
This neoplasm is most common in women in the fifth and sixth decades
(female-to-male ratio, 9:1)
[35,36,37,38,39,40]
(Figs.
13,14,15,16).
Some lesions are frankly malignant, but all are considered potentially
malignant. Survival is related to the extent of invasion, but overall the
prognosis after surgery is better than for adenocarcinoma. Five-year survival
after all resections of adenocarcinomas for cure is less than 10%, although
recent reports indicate survival rates near 25%
[41]. Ten-year survival rates
near 50% have been reported after resection of invasive malignant mucinous
cystic tumors [36], but a
recent study reported a 5-year rate survival of fewer than 20% in these
patients [38]. This disparity
was attributed to difficulties and differences in the histopathologic
classification of these mucinous cystic tumors
[38].
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Fig. 13. —Mucinous cystic tumor in 52-year-old woman. CT scan shows
unilocular cystic pancreatic mass that had slightly decreased in size over
3-month interval, but patient had no history of pancreatitis, gallstones, or
abdominal trauma. Pancreatic tail was resected, and mucinous cystic tumor was
diagnosed.
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Fig. 16. —Mucinous cystic tumor (cystadenocarcinoma) in 72-year-old
woman. CT scan shows large cystic mass. Note irregularly thickened wall,
nodular excrescences, and smaller peripheral cysts (arrows).
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Most lesions are located in the pancreatic body or tail. Cysts may be
single or multiple. Cyst walls can be irregular or contain excrescences, both
of which correlate well with malignancy, but a uniform, well-defined wall does
not preclude malignancy. Vascularity is usually marked but is often
heterogeneous. Most, but not all cysts, are larger than 2 cm in diameter.
Microcystic adenomas are characterized by cysts smaller than 2 cm, but some of
them also contain cysts that are larger than 2 cm. In these cases, a
microcystic adenoma cannot be differentiated from a mucinous cystic tumor
[7,
8,
33].
CT shows a near-water-density unilocular or multilocular cystic lesion with
enhancing walls and septa that range from thin and regular to thick and
irregular with excrescences and nodules (Figs.
14,15,16).
Peripheral or curvilinear calcifications in the lesion are located in cyst
walls (Fig. 14). which is
different from the central calcification of microcystic adenomas
[33,
37,38,39]
(Fig.
11A,11B).
Sonography shows the features of cyst walls well and may show echogenicity
caused by cyst wall calcification
[37,
40,
41]. MR imaging shows
variable, heterogeneous signal on both T1-weighted and T2-weighted images and
provides good depiction of cyst wall and septa features
[35]. Calcification, however,
is easier to see on CT than on MR imaging.
Lesions with large cysts and typical peripheral curvilinear cyst wall
calcification can be confidently diagnosed, but mucinous cystic tumors have
often been mistaken for pseudocysts
[1,
37], and, to a lesser extent,
lesions have been diagnosed as microcystic adenomas or other cystic tumors
[7,
8,
33,
35]. The most serious problem
is misdiagnosing a mucinous cystic tumor as a benign microcystic adenoma.
We have encountered several patients with mucinous cystic tumors who
presented with nondescript small cystic pancreatic lesions but who underwent
surgery because they had no history of, evidence of, or reason to have had
pancreatitis that could have led to a pseudocyst. The lesion in one such
patient was indistinguishable from a pseudocyst and actually became slightly
smaller on follow-up before surgery (Fig.
13).
In selected patients, percutaneous aspiration biopsy has been used to
identify characteristic mucin, which is not present in pseudocysts or
microcystic adenomas [23,
31].
Intraductal Papillary Mucinous Tumor (Ductectatic Cystadenoma,
Cystadenocarcinoma, Ductectatic Mucinous Tumor)
The incidence, which appears to be equal in men and women, is unknown, but
the diagnosis has been made more frequently in recent years. Most patients
present in the sixth and seventh decades. Symptoms of abdominal pain are
accompanied by an elevated serum amylase level, so these patients are
frequently thought to have pancreatitis
[42,43,44,45].
Dilatation of the main pancreatic duct on imaging studies is then considered
to be further evidence supporting a diagnosis of chronic pancreatitis (Fig.
17A,17B,17C).
This neoplasm is a low-grade, slowly growing malignancy with a much better
prognosis than adenocarcinomas. The overall 5-year survival rate is
approximately 60% [42].
Imaging studies most often show dilatation of the main pancreatic duct and
side ducts in the pancreatic head and uncinate process. The ducts may be so
dilated that they resemble cysts. On ERCP, inspissated mucin or tumor nodules
can produce filling defects in the dilated ducts
[43,44,45].
In addition, on ERCP abundant mucinous secretions issuing from a bulging
papilla of Vater are highly suggestive of this tumor.
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Fig. 17A. —Intraductal papillary mucinous tumor in 69-year-old woman.
Neoplasm involves both main and pancreatic head side ducts. ERCP image shows
dilated main pancreatic duct and marked dilatation of side branches in
pancreatic head. The patient's clinical diagnosis was chronic
pancreatitis.
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Fig. 17B. —Intraductal papillary mucinous tumor in 69-year-old woman.
Neoplasm involves both main and pancreatic head side ducts. CT scan shows
atrophic pancreatic tail and dilatation of main pancreatic duct.
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Fig. 17C. —Intraductal papillary mucinous tumor in 69-year-old woman.
Neoplasm involves both main and pancreatic head side ducts. CT scan shows
cystlike dilated branches of side ducts (arrows) in pancreatic
head.
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This neoplasm may exclusively involve the main pancreatic duct (Fig.
18A,18B)
or predominantly involve side ducts in the body instead of the head of the
pancreas. These less common variations have resulted in subdivisions of the
neoplasm being classified by the predominant site of ductal involvement
[44,
45].
Endocrine Pancreatic Neoplasms
Insulinomas, glucagonomas, gastrinomas, and nonfunctioning endocrine tumors
can all present as cystic lesions
[46,
47]. These tumors can be
isolated or associated with the multiple endocrine neoplasia syndrome type 1
(MEN 1), which is characterized by the triad of parathyroid, pituitary, and
pancreatic lesions [48,
49]. All types of pancreatic
islet cell neoplasms have been reported in patients with this syndrome. These
neoplasms can be solitary, multiple, or diffuse; different histologic types
may occur in the same patient. Most patients with MEN 1 present with either
hyperparathyroidism or the Zollinger-Ellison syndrome. Gastrinomas, however,
are an uncommon pancreatic neoplasm in MEN 1 because most gastrinomas are
located in the duodenum rather than in the pancreas
[49].
Insulinoma
Insulinoma is the most common functioning islet cell tumor. The clinical
triad leading to the diagnosis is fasting hypoglycemia, symptoms of
hypoglycemia, and immediate relief of symptoms after the administration of IV
glucose. Symptoms and signs are caused by both hypoglycemia and the secondary
release of catecholamines and include palpitations, headache, confusion,
pallor, sweating, slurred speech, and coma. Despite this striking list of
symptoms, the clinical presentation is often insidious. Fasting hypoglycemia
with no decrease in insulin level is confirmatory. Approximately 10% of
insulinomas are multiple, 10% are malignant, and 10% of patients have
hyperplasia rather than neoplasia
[47,
48]. Most insulinomas are
small and hypervascular. Some contain calcification. Malignant tumors tend to
be large. Cystic lesions are rare
[50]
(Fig. 19).
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Fig. 19. —Cystic insulinomas in 36-year-old woman with multiple
endocrine neoplasia type 1. CT scan shows small cystic masses
(arrows) in body and tail of pancreas. Patient presented with primary
hyperparathyroidism.
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Gastrinoma
Gastrinoma is the second most common functioning islet cell tumor. Most are
sporadic and associated with the Zollinger-Ellison syndrome. The initial
manifestations are most often in young adults who have peptic ulcer disease
that suggests the diagnosis when ulcers are recurrent, intractable, multiple,
or in unusual locations. Diarrhea due to the large volume of hydrochloric acid
and a direct effect of gastrin on the small bowel is common. Most, but not
all, patients have high unstimulated gastric acid secretory rates, but the
diagnosis is confirmed by increased serum gastrin concentrations
[48]. Gastinomas are
frequently multiple, extrapancreatic, difficult to locate, and malignant.
Hepatic metastases are associated with a poor prognosis, whereas patients with
metastases isolated to lymph nodes often have long-term survival. The tumor
size is variable, but pancreatic lesions average 3-4 cm. The lesions are often
hypervascular, so they may be visible on arterial phase CT and angiography.
Rare cystic lesions have been reported
[50].
Glucagonoma
Most lesions are malignant and present with equal incidence in middle-aged
men and women. Most patients present with a necrolytic migratory rash and
various other elements of the "glucagonoma syndrome" including
diabetes mellitus, stomatitis, diarrhea, anemia, and weight loss. The
characteristic rash involves the lower extremities and the perineum, begins
with erythema and progresses to coalescent blisters and pustules, waxes and
wanes, and is pruritic. An elevated plasma glucagon level establishes the
diagnosis, but there are often increased blood levels of other hormones,
including insulin, serotonin, and gastrin
[48]. Approximately 50% of
patients survive at least 5 years after diagnosis.
Tumor size is variable, but most are large and have metastasized at the
time of diagnosis. Most are located in the distal pancreas and are vascular.
Tumors may be solid or contain central low-attenuation areas on CT. Cystic
lesions are rare [51]
(Fig. 20).
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Fig. 20. —Cystic glucagonoma in 34-year-old woman. CT scan shows large
cystic mass in tail of pancreas. Patient had diabetes and presented with
characteristic eczematous dermatitis termed "necrolytic migratory
erythema."
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Nonfunctioning Endocrine Tumors
This is the third most common endocrine tumor after insulinoma and
gastrinoma. Non-functioning endocrine tumors occur throughout the pancreas,
can be calcified, and may be cystic
[52]
(Fig. 21).
Even though termed "nonfunctioning" and clinically silent, most
produce some hormone detectable by sensitive assays. These tumors are usually
low-grade malignancies, but most are large and have metastasized to the liver
by the time of diagnosis. Symptoms occur late when the bile ducts, pancreatic
duct, or nerves become involved
[53].
Rare Exocrine Neoplasms of the Pancreas
Solid Papillary Epithelial Neoplasm (Solid Pseudopapillary Tumor,
Papillary Cystic Tumor)
These lesions account for approximately 1% of pancreatic neoplasms. The
high incidence in young women (mean, 24 years old) is especially noteworthy.
Distinctive clinical features include eosinophilia and polyarthralgia. A solid
papillary epithelial neoplasm is a low-grade malignancy, and resection is
usually curative [54].
These neoplasms can be solid, but they often present as thick-walled cysts
on CT (Fig. 22) and
sonography. Attenuation is high when hemorrhage occurs. CT will show
peripheral or central stippled calcification in some lesions. Tumor
vascularity is moderate [55,
56].
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Fig. 22. —Solid papillary epithelial neoplasm in 13-year-old girl. CT
scan 1 day after blunt abdominal trauma shows sharply defined water-density
mass deforming pancreatic head. Before trauma and this serendipitous
discovery, patient was asymptomatic.
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Giant Cell Tumor
This rare neoplasm has two histologic types: pleomorphic and osteoclastic.
The pleomorphic type is highly malignant and has a poor prognosis, similar to
that of adenocarcinoma. The osteoclastic type, which has the same histology as
giant cell tumors of the bone, has a better prognosis. Most lesions are large
and highly vascular. A cystic appearance is the result of central necrosis
[57,58,59]
(Fig.
23A,23B).
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Fig. 23A. —Giant cell tumor, osteoclastic type, in 66-year-old woman.
Unenhanced T1-weighted spin-echo MR image shows lobulated,
low-signal-intensity mass (arrows) protruding from tail of
pancreas.
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Nonepithelial Neoplasms of the Pancreas
Sarcoma
Most sarcomas originate in the parapancreatic tissues and secondarily
invade the pancreas. Primary origin in the pancreas is rare. Leiomyosarcoma is
the most common cell type, but only 21 cases have been reported to our
knowledge [60]. These
neoplasms are most often poorly differentiated and are diagnosed when they are
at an advanced stage. The prognosis is similar to that of adenocarcinoma of
the pancreas [60].
The gross morphology ranges from solid to cystic when central necrosis is
present. The solid lesions have an appearance similar to that of
adenocarcinoma, whereas necrotic lesions can stimulate mucinous cystic tumors
[61,
62]
(Fig. 24).
Metastases to the Pancreas
In one series of 2587 consecutive autopsies, 261 patients (10%) had
metastases to the pancreas. When lymphoma was excluded, breast, lung,
melanoma, and gastrointestinal tract were the most common primary sites
[63]. The incidence of
metastases is much lower in patients who present with solitary pancreatic
lesions and, in addition, several series of metastases identified by imaging
studies have reported renal cell carcinoma to be the most common primary
neoplasm [64]. Some of these
metastases developed many years after the initial diagnosis and treatment.
Cystic metastases can be the result of central necrosis or cystic
degeneration (Figs.
25,26,27,28).
A cystic lesion in a patient presented here proved to be multiple myeloma
(Fig. 27). The imaging
characteristics of pancreatic metastases tend to mirror the characteristics of
the primary neoplasm (Fig.
28).
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Fig. 25. —Metastatic colon carcinoma in 55-year-old man. CT scan shows
multiple cystic pancreatic (arrows) and parapancreatic metastases.
Retrocaval lymph node metastasis has same cystic appearance. Note liver
metastasis.
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Fig. 28. —Metastatic renal cell carcinoma in 70-year-old woman. CT scan
shows large cystic mass with irregularly thickened wall in pancreatic body and
tail. Note similarity to renal cell carcinoma of right kidney. Pancreatic mass
proved to be metastatic lesion.
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Parapancreatic Neoplasms
Lymphomas are the most frequent parapancreatic neoplasm and, in some cases
it may not be possible to differentiate parapancreatic lymphadenopathy from a
primary lesion in the pancreas. Homogeneous lymphomatous lymph nodes can
appear to be cystic on sonograms, and tumor necrosis
[65] can result in a cystic
appearance on CT scans.
Although rare, many different types of retro-peritoneal neoplasms, some of
which can be cystic, occur in the in the area of the pancreas. These include
lymphangiomas (Fig. 29),
paragangliomas (Fig.
30A,30B),
cystic teratomas, and metastases (Fig.
31). Lymphangiomas are most often homogeneous, thin-walled,
fluid-filled cysts, but they may have septa, thick walls, calcification, and
internal debris. These lesions have an epithelial lining but do not contain
keratin, which differentiates them from lymphoepithelial cysts
[66].
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Fig. 31. —Parapancreatic metastasis from testicular carcinoma in
21-year-old man. CT scan shows large low-attentuation lymph node metastasis
displacing pancreatic head anteriorly and inferior vena cava laterally.
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Approximately 10% of paragangliomas are extraadrenal. Those in the
retroperitoneum are most often located near the origin of the inferior
mesenteric artery in Zuckerkandl's organs or near the kidney. Many produce
hormones, and approximately 10% are malignant. Rarely, these lesions are both
cystic and parapancreatic
[67].
Most retroperitoneal cystic teratomas have been reported in children and
young adults. The imaging appearance is similar to that of cystic teratomas
found in other parts of the body and reflects variable cystic, solid, fat, and
calcific content [68]
(Fig. 32).
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Fig. 32. —Parapancreatic retroperitoneal cystic teratoma in 8-year-old
girl. CT scan shows heterogeneous lesion displacing pancreas and kidney and
containing large central calcification, peripheral water-attenuation cystic
areas, and small focus of fat (arrow).
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|
Parapancreatic metastases can appear cystic if they become necrotic or if
they are from a primary neoplasm that has a cystic appearance.
Fine-Needle Aspiration Biopsy of Cystic Pancreatic Lesions
Fine-needle aspiration biopsy of the pancreas is a simple, cost-effective
procedure with relatively low risk. Analysis of the aspirate includes
cytology; viscosity; and the presence of mucin and glycogen, enzymes (amylase
and lipase), and antigenic tumor markers
[2,
3,
23,
69,70,71,72,73,74].
Cytologic identification of an epithelial lining can be used to differentiate
a cystic neoplasm from a pseudocyst because the latter is devoid of
epithelium, but the lining of neoplasms may be denuded and lead to a
false-negative result. Also, sampling of heterogeneous neoplasms may miss
small foci of malignancy. The fluid in most pseudocysts contains high levels
of amylase, microcystic adenomas contain intracellular glycogen, and mucinous
cystic tumors stain positively for mucin. Fewer data are available for the
accuracy of tumor markers, but some reports are promising
[70,
74].
Controversy continues about the accuracy of the preoperative diagnosis and
management of patients with cystic lesions of the pancreas. Some investigators
advocate surgery for all patients who have cystic lesions other than
pseudocysts [23,
31,
71,
72]. Determination of
malignancy of mucinous cystic tumors is generally agreed to be inaccurate, but
several studies report high sensitivity in differentiating pseudocysts from
cystic neoplasms and microcystic adenomas from mucinous cystic tumors on the
basis of the results of fine-needle aspiration
[2,
70,
73]. Contrarily, one
retrospective study reports more accurate differentiation of pseudocysts from
neoplasms by combining a history that excludes pancreatitis with CT findings
as compared with all other preoperative imaging and pathologic evaluation
[75]. Fine-needle aspiration
has been recommended to establish a diagnosis in asymptomatic elderly patients
and in patients who are not good candidates for surgery because of debility,
additional medical problems, or advanced disease
[72]. With increasing
experience and reports documenting the ability to more accurately diagnose
lesions on the basis of cyst contents, the number of patients who are
diagnosed using imaging studies combined with fine-needle aspiration may
increase.
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Introduction
Congenital Pancreatic Lesions
