Pancreatic Neuroendocrine Tumors

 Syndromic tumors: Small in size (usually < 3 cm)

image Nonsyndromic tumors usually much larger (> 5 cm) with frequent cystic and necrotic degeneration

• Usually avidly enhancing on arterial phase images and less conspicuous on venous phase

• Lesions frequently calcify (unlike adenocarcinoma)

• May invade mesenteric veins with tumor thrombus

• Do not usually obstruct biliary/pancreatic ducts unless large

• Cystic NET can mimic other cystic neoplasms
image Peripheral rim of enhancement or hypervascular mural nodularity should suggest correct diagnosis

• Hypervascular lymph node and liver metastases
image Fluid-fluid levels within liver metastases specific for NET

image Liver metastases often very T2 hyperintense on MR and can mimic cysts or hemangiomas


• Pancreatic ductal adenocarcinoma

• Intrapancreatic splenule

• Pancreatic metastases (especially renal cell carcinoma)

• Pancreatic serous cystadenoma (solid serous adenomas)


• Divided into syndromic (produce clinical syndrome with abnormal lab findings) or nonsyndromic tumors

• Most common syndromic tumors include insulinoma, glucagonoma, gastrinoma, somatostatinoma, VIPoma
image Insulinoma: Usually solitary and benign (90%) 
– Presents with Whipple triad (hypoglycemia, low fasting glucose, and relief by IV glucose)

image Gastrinoma: Often multiple, malignant (60%), and associated with MEN1
– Presents with Zollinger-Ellison syndrome: Severe peptic ulcer disease, increased acidity, and diarrhea

• Nonsyndromic tumors tend to be malignant (80-100%)

• Treatment
image Somatostatin analogs (such as Octreotide) provide symptom relief for syndromic tumors

image Surgical resection (enucleation or pancreatectomy), chemoembolization or resection of liver metastases, chemotherapy, and watchful waiting are possible treatment options

(Left) Axial CECT of an insulinoma in the arterial phase shows a subcentimeter hypervascular mass image in the pancreatic tail.

(Right) Gross pathology from the same patient shows the resected specimen confirmed to be a neuroendocrine tumor (NET) image, with its typical well-circumscribed, noninfiltrative appearance. NETs are often referred to by their main hormonal output (e.g., insulinoma), but pathologists call them NETs because of the electron microscopic finding of neuron-specific enolase.

(Left) Axial CECT in a patient with a metastatic nonsyndromic NET shows a large hypervascular pancreatic mass image and additional hepatic metastases image. This constellation of findings is typical of a malignant NET of the pancreas, a glucagonoma in this case. Glucagonomas are more commonly malignant than insulinomas.

(Right) Axial CECT demonstrates a cystic lesion image in the pancreatic uncinate process. The subtle nodular hypervascular rim image around the lesion strongly suggests that this is a cystic NET.



• Pancreatic neuroendocrine tumor (NET)


• Islet cell tumor


• Tumors arising from pancreatic endocrine cells (islets of Langerhans)

Associated Syndromes

• Multiple endocrine neoplasia type 1 (MEN1, gastrinomas), von Hippel-Lindau syndrome, neurofibromatosis type I, tuberous sclerosis


General Features

• Best diagnostic clue
image Well-circumscribed hypervascular pancreatic mass with hypervascular liver metastases

• Location
image 85% arise in pancreas, while 15% are ectopic 
– Most common ectopic locations: Duodenum, stomach, lymph nodes, and ovary

image 90% of gastrinomas arise in gastrinoma triangle 
– Gastrinoma triangle defined by cystic duct and common bile duct (CBD) superiorly, 2nd and 3rd parts of duodenum inferiorly, and pancreatic neck and body medially

– Most commonly arise in duodenal wall

• Size
image Varies from few mm to 10 cm

• Morphology

• General concepts
image More rare than tumors of exocrine pancreas

image Divided into benign (well-differentiated endocrine tumor) or malignant (well/poorly differentiated neuroendocrine carcinoma) based on WHO classification

image No longer divided into functioning or nonfunctioning, as all NET are now considered hormonally active

image Now divided into syndromic (produce clinical syndrome with abnormal lab findings) or nonsyndromic
– Syndromic tumors: Secrete multiple pancreatic hormones, but patients have single clinical syndrome
image Insulinoma, glucagonoma, gastrinoma, somatostatinoma, VIPoma (vasoactive intestinal polypeptide), carcinoid

– Nonsyndromic tumors
image Hypofunctioning or clinically silent large tumors

image PPoma which secretes pancreatic polypeptide does not produce a clinical syndrome

image Larger than syndromic tumors at diagnosis due to lack of symptoms or laboratory abnormalities

image Cystic NETs more likely to be non-insulin-producing and nonsyndromic

CT Findings

• Well-circumscribed pancreatic mass with noninfiltrative margins that is usually (but not always) hypervascular and most conspicuous on arterial phase
image Lesions usually hyperenhance to lesser degree on venous phase, making smaller lesions difficult to detect 
– Rarely can be most conspicuous on venous phase

image Syndromic tumors tend to be smaller at presentation (usually < 3 cm with insulinomas < 2 cm)
– May be undetectable on NECT and difficult to perceive on venous phase CECT due to small size

image Nonsyndromic tumors much larger at presentation (average > 5 cm)
– Usually hypervascular, but less so than syndromic

– Large tumors are more likely to demonstrate central necrosis, cystic change, and calcification

– Liver metastases are often extensive even in asymptomatic patients

image Large tumors (syndromic and nonsyndromic) tend to be highly invasive with more aggressive appearance
– Calcification, necrosis, and cystic change more common

– Lesions with early portal vein invasion → widespread liver metastases

• Lesions often demonstrate calcification (central or diffuse)

• Usually no biliary or pancreatic duct obstruction (unless large) or upstream pancreatic atrophy
image Some small tumors may rarely secrete serotonin that can cause fibrosis and obstruction of pancreatic duct

• Invasion (rather than encasement) by tumor of mesenteric veins (portal vein or superior mesenteric vein)

• Cystic NET can mimic other pancreatic cystic lesions
image Presence of peripheral enhancement or nodularity on arterial phase should strongly suggest diagnosis

• Metastases demonstrate similar characteristics to primary tumor: Hypervascular lymph node and liver metastases
image Most common sites of metastases include liver, local lymph nodes, and bone (sclerotic lesions)

image Fluid-fluid levels within neuroendocrine liver metastases described as specific feature

• Zollinger-Ellison syndrome (gastrinoma): Avid enhancement and wall thickening of proximal stomach

MR Findings

• NETs tend to be hypointense (relative to normal pancreas) on T1WI, hyperintense on T2WI, and enhance similarly to CECT on T1WI C+ images
image Homogeneous enhancement for small tumors < 2 cm

image Heterogeneous enhancement with areas of necrosis for larger lesions

• Liver metastases can often be very hyperintense on T2WI and mimic hemangiomas or cysts
image Fluid-fluid levels may be visualized within liver metastases, particularly on T2WI

image Liver metastases usually T1WI hypointense but may show hyperintensity due to intratumoral hemorrhage

• DWI: Lesions show variable ADC values, but DWI can help identify tiny lesions that are otherwise occult

Ultrasonographic Findings

• Endoscopic US: Sensitivity and specificity > 90%
image Can be helpful to identify small NET that may be missed on CT/MR in patients with high clinical suspicion

image Can “tattoo” lesion to guide laparoscopic surgery

image No specific imaging features, as lesions tend to be hypoechoic or isoechoic to surrounding pancreas

• Intraoperative US: Can detect small nonpalpable lesions and help guide surgical resection

Angiographic Findings

• Functioning and nonfunctioning tumors
image Hypervascular (primary and secondary)

• Hepatic venous sampling after arterial stimulation
image Functioning tumors (esp. gastrinoma/insulinomas): Elevated levels of hormones suggests occult tumor

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Nov 16, 2016 | Posted by in GASTROINTESTINAL IMAGING | Comments Off on Pancreatic Neuroendocrine Tumors

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