Atypical and Rare Pancreatic Tumors

Published on 19/07/2015 by admin

Filed under Radiology

Last modified 22/04/2025

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 Extremely aggressive and almost always unresectable

image Large, heterogeneous, moderately enhancing, exophytic mass with necrosis and cystic change
• Small cell carcinoma

image Highly aggressive, with hematologic and lymphatic metastases at time of diagnosis
image Large, homogeneous, mildly enhancing mass with confluent local and distant lymphadenopathy
image May be indistinguishable from lymphoma
• Giant cell carcinoma (pleomorphic or osteoclast)

image Resection often impossible due to large size
image Large, heterogeneous, cystic, low-density mass with frequent hemorrhage, septation, and calcification
• Acinar cell carcinoma

image Slightly better prognosis than adenocarcinoma
image Large, well-circumscribed mass with cystic degeneration, exophytic component, and enhancing capsule
image Usually no biliary/pancreatic duct dilatation
image Vascular occlusion uncommon (20%); may invade the portal vein/superior mesenteric vein
• Pancreatoblastoma

image Most often occurs in children (mean age 2.5 years), but very rarely affects adults (mean age 40 years)
image Poor prognosis: Worse outcomes in adults than children
image Large, heterogeneous mass with frequent internal calcifications and necrosis/hemorrhage
image No pancreatic or biliary duct obstruction
• Pancreatic plasmacytoma

image Consider in patients with known myeloma
image Homogeneous mass without pancreatic/biliary ductal obstruction or pancreatic atrophy
image Mimics lymphoma, but usually no lymphadenopathy
• Pancreatic Lipoma

image Benign fat-containing mass (-80 to -120 Hounsfield units) with surrounding capsule
image Most often occur in pancreatic head
• Pancreatic schwannoma

image Usually benign, with malignant transformation very rare
image Well-circumscribed mass ± cystic degeneration
image Can closely mimic neuroendocrine tumors (usually with less avid vascularity)

TOP DIFFERENTIAL DIAGNOSES

• Pancreatic adenocarcinoma, pancreatic neuroendocrine tumor, lymphoma, mucinous cystic neoplasm
image
(Left) Axial CECT demonstrates a well-circumscribed, encapsulated, enhancing mass image in the pancreatic head with solid and cystic components. This was found to be an acinar cell carcinoma at surgery. As in this case, these tumors often mimic the appearance of neuroendocrine tumors, albeit with less hyperenhancement.

image
(Right) Axial CECT demonstrates a lobulated, well-circumscribed enhancing mass image arising from the pancreatic tail. This mass was found to be an acinar cell carcinoma at surgery.
image
(Left) Axial CECT in a patient with known myeloma demonstrates a well-circumscribed, enhancing mass image in the pancreatic head.

image
(Right) Axial CECT in the same patient shows that the mass causes no pancreatic ductal obstruction or parenchymal atrophy, highly atypical for an adenocarcinoma. The mass was found to be a rare pancreatic plasmacytoma at biopsy.

TERMINOLOGY

Abbreviations

• Anaplastic carcinoma: Pleomorphic carcinoma, undifferentiated carcinoma, sarcomatoid carcinoma
• Small cell carcinoma: Poorly differentiated carcinoma
• Giant cell carcinoma: Pancreatic osteoclastoma
• Acinar cell carcinoma

Definitions

• Rare pancreatic malignancies that may mimic adenocarcinomas and neuroendocrine tumors

IMAGING

General Features

• Best diagnostic clue
• Anaplastic carcinoma

image Large, heterogeneous, moderately enhancing, exophytic mass with necrosis and cystic change
image Locally invasive with frequent lung and liver metastases
• Small cell carcinoma

image Large, homogeneous, mildly enhancing mass with confluent local and distant lymphadenopathy
image May be indistinguishable from lymphoma
image Pancreatic head; homogeneous, hypovascular
• Giant cell carcinoma (pleomorphic or osteoclast)

image Large, heterogeneous, cystic, low-density mass with frequent hemorrhage, septation, and calcification

– Tendency to arise in pancreatic body and tail
– Often grow to very large sizes (mean > 6 cm)
image Local invasion and distant mets (liver, lung) uncommon
• Acinar cell carcinoma

image Large, well-circumscribed mass with cystic and necrotic degeneration and frequent exophytic component

– Usually a well-defined enhancing capsule
– Hypodense on both arterial and venous phases
– Usually no biliary/pancreatic duct dilatation (even with large tumors)
– Vascular encasement or occlusion uncommon (20%), and may invade portal vein or SMV
image Commonly misdiagnosed as neuroendocrine tumor
image No predisposition for any specific location in pancreas
image Metastasizes to liver and local lymph nodes
• Pancreatoblastoma

image Can resemble either pancreatic adenocarcinoma or neuroendocrine tumors
image Associated with Beckwith-Wiedemann and familial adenomatous polyposis
image Large, heterogeneous mass with frequent internal calcifications and necrosis/hemorrhage

– May be either well circumscribed or infiltrative
image No pancreatic or biliary duct obstruction
image Most common site of metastasis is liver
• Pancreatic plasmacytoma

image Homogeneous mass without pancreatic/biliary ductal obstruction or pancreatic atrophy
image Mimics lymphoma, but usually no lymphadenopathy
image Consider in patients with known myeloma
• Pancreatic lipoma

image Benign fat-containing mass (-80 to -120 HU) with a surrounding capsule

– Most often occur in pancreatic head
• Pancreatic schwannoma

image Well-circumscribed, mildly hyperenhancing mass ± cystic/necrotic degeneration
image Can closely mimic neuroendocrine tumors (usually with less avid vascularity)

Imaging Recommendations

• Best imaging tool

image CECT or MR

DIFFERENTIAL DIAGNOSIS

Pancreatic Neuroendocrine Tumors

• Hypervascular mass with frequent liver metastases

Pancreatic Ductal Carcinoma

• Ill-defined, hypoenhancing mass obstructing pancreatic duct with upstream pancreatic atrophy

Mucinous Cystic Neoplasm

• Encapsulated cystic mass (± mural nodularity or soft tissue component) in pancreatic tail of middle-aged woman

Non-Hodgkin Lymphoma Involving Pancreas

• Hypodense, homogeneous mass without pancreatic atrophy, ductal dilatation, or vascular narrowing/occlusion
• Usually associated with widespread lymphadenopathy
• Difficult to differentiate from small cell carcinoma of pancreas

Metastatic Small Cell Carcinoma

• Metastases from primary small-cell carcinoma of lung indistinguishable from primary small cell carcinoma of pancreas

PATHOLOGY

General Features

• Etiology

image Anaplastic carcinoma: Most likely originates from ductal epithelial cells of pancreas
image Giant cell carcinoma: Proliferating undifferentiated epithelial and mesenchymal cells admixed with nonneoplastic osteoclast-like giant cells
• Associated abnormalities

image Concurrent pancreatic ductal carcinoma is seen in anaplastic carcinoma

Gross Pathologic & Surgical Features

• Anaplastic carcinoma: Extensive necrosis, cystic areas
• Giant cell carcinoma: Multicystic, extensive, intratumoral hemorrhage and necrosis

Microscopic Features

• Anaplastic carcinoma

image Mixture of undifferentiated and pleomorphic cells
image Spindle cells with abundant eosinophilic cytoplasm may be seen
• Small cell carcinoma

image Sheets and nests of small, oval, or round (“oat”) cells, with markedly hyperchromatic nuclei and poorly defined cytoplasm
• Giant cell carcinoma

image Extensive necrosis and hemorrhage
image Mixture of anaplastic mononuclear polygonal cells, occasional spindle cells, and osteoclast-like cells
• Acinar cell carcinoma

image Sheets of cells in well-formed acini and fibrovascular stroma

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Weight loss, abdominal pain, palpable mass, jaundice
• Other signs/symptoms

image Nausea, vomiting, diarrhea, jaundice, palpable mass
image Small cell carcinoma: Paraneoplastic syndromes (ectopic ACTH, hypercalcemia, Cushing syndrome)
image Acinar cell carcinoma: Lipase hypersecretion syndrome

– Fevers, arthralgias, skin rash, and fat necrosis due to elevated lipase levels (often > 1000 U/L)
– Other laboratory markers (CA 19-9, CEA) normal

Demographics

• Age

image Mostly occur in older (> 60 years) men
image Pancreatoblastoma most often occurs in children (mean age 2.5 years), but very rarely affects adults (mean age 40 years)
• Epidemiology

image Anaplastic carcinoma

– 2-7% of all pancreatic cancers
– Mean age of 61 years with slight male predominance
image Small cell carcinoma

– 1-1.4% of all pancreatic cancers
– Mean age of 60 years
image Giant cell carcinoma

– < 1% of all pancreatic cancers
– Affects males and females equally with mean age of 61 years
image Acinar cell carcinoma

– 1% of all pancreatic cancers
– Mean age > 60 years with mild male predilection
image Pancreatoblastoma

– < 1% of all pancreatic tumors
– Most often occurs in children (mean age 2.5 years), but very rarely affects adults (mean age 40 years)
– Associated with Beckwith-Wiedemann and familial adenomatous polyposis
– Asian (> 50%) predominance in adults with males > females

Natural History & Prognosis

• Anaplastic carcinoma

image Extremely aggressive with rapid local and distant spread and almost always unresectable at diagnosis
image Mean survival of 2-3 months; 3-year survival rate = 3%
• Small cell carcinoma

image Highly aggressive, with hematologic (usually liver and lungs) and lymphatic metastases at time of diagnosis

– > 90% have metastases at diagnosis
image Without treatment survival is less than a few months
image May respond to chemotherapy ± radiotherapy
• Acinar cell carcinoma

image Slightly better prognosis than adenocarcinoma
image Metastatic disease at presentation in ∼ 50%
• Giant cell carcinoma

image Resection often (> 50%) impossible due to lesion size
image Median survival of 11 months
image Median survival of 6.5 months if unresectable
• Pancreatic plasmacytoma

image Very sensitive to both radiation and chemotherapy
• Pancreatoblastoma

image Poor prognosis, with likely worse outcomes in adults compared to children
• Pancreatic schwannoma

image Usually benign, with malignant transformation very rare

Treatment

• Small cell carcinoma: Chemotherapy, radiotherapy
• Giant cell carcinoma: Complete surgical resection can be curative
image
(Left) Axial CECT demonstrates a very well circumscribed, encapsulated low-density mass image with internal cystic foci image that was found to be a benign pancreatic schwannoma at resection.

image
(Right) Axial CECT in a 56-year-old man shows an infiltrating hypodense mass image in the pancreatic body and tail. While the appearance suggests adenocarcinoma, this is a rare pancreatoblastoma in an adult patient, a tumor much more common in children.
image
(Left) Coronal volume-rendered CECT demonstrates a benign lipoma image within the pancreatic head. The mass is quite simple in appearance, with only a few linear strands interspersed in the midst of fat density.

image
(Right) Axial CECT in a patient with small cell carcinoma shows a hypodense mass image in the neck of the pancreas. Note that the mass is homogeneously enhancing and conforms to the contours of adjacent structures. There is no biliary obstruction. However, multiple liver metastases image are noted.
image
(Left) Axial CECT in a patient with anaplastic carcinoma shows a bulky mass image involving the body of the pancreas with central necrosis image. Note the obstruction of the common duct image, which contains a metallic stent.

image
(Right) Axial CECT in a patient with anaplastic carcinoma shows a large mass image arising from the pancreatic tail with moderate vascularity and central necrosis image. Note the invasion of the left kidney image by the mass.
image
(Left) Axial CECT in a patient with giant cell carcinoma shows a multiseptate, complex cystic mass image arising from the tail of the pancreas. Note the focal calcification in one of the septations image.

image
(Right) Transverse intraoperative ultrasound shows a mass image in the body of the pancreas that contains both solid image and cystic image elements. At pathology, this lesion was proven to be a rare giant cell carcinoma.
image
(Left) Axial CECT demonstrates a large, aggressive, hyperenhancing mass image arising from the pancreatic tail and invading the spleen. The appearance would be more typical for an aggressive neuroendocrine tumor, but the mass was found at biopsy to be an acinar cell carcinoma.

image
(Right) Coronal volume-rendered CECT shows an extremely well circumscribed, encapsulated, homogeneously hypodense mass image arising exophytically from the pancreatic head, found to represent a rare acinar cell carcinoma.
image
(Left) Axial CECT in a patient with neurofibromatosis type I demonstrates a soft tissue density mass image that follows the course of the splenic vein along the dorsal surface of the pancreas. There is no evidence of local invasion, metastases, or ductal obstruction. This was found to be a plexiform neurofibroma.

image
(Right) Curved planar reformation from a CECT shows a small, well-defined hypodense mass image in the head of the pancreas. The mass does not obstruct the pancreatic duct image and was found to be benign peripancreatic schwannoma.

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