Pancreatic Neuroendocrine Tumors

Published on 18/07/2015 by admin

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Last modified 18/07/2015

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 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

TOP DIFFERENTIAL DIAGNOSES

• Pancreatic ductal adenocarcinoma
• Intrapancreatic splenule
• Pancreatic metastases (especially renal cell carcinoma)
• Pancreatic serous cystadenoma (solid serous adenomas)

CLINICAL ISSUES

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

image
(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.
image
(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.

image
(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.

TERMINOLOGY

Abbreviations

• Pancreatic neuroendocrine tumor (NET)

Synonyms

• Islet cell tumor

Definitions

• 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

IMAGING

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

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