Pancreatic neuroendocrine tumors (PanNETs) are neoplasms originating from the endocrine cells (islets of Langerhans) of the pancreas, comprising 1-5% of all pancreatic tumors. Classified as functional (insulinoma, gastrinoma, glucagonoma, VIPoma, somatostatinoma) or non-functional; the non-functional type is the most common form at 60-90%. Incidence has been increasing in recent decades — partly due to increased incidental detection. Mean age at diagnosis is 50-60 with near-equal gender distribution. WHO 2019 classification grades as grade 1 (Ki-67 <3%), grade 2 (Ki-67 3-20%), and grade 3 (Ki-67 >20%); poorly differentiated neuroendocrine carcinoma (NEC) is a separate category. Prognosis is significantly better than PDAC — 5-year survival exceeds 90% for localized disease. May be associated with MEN1, VHL, and tuberous sclerosis.
Age Range
40-70
Peak Age
55
Gender
Equal
Prevalence
Uncommon
PanNETs originate from islet of Langerhans cells — these cells normally secrete insulin (beta), glucagon (alpha), somatostatin (delta), and pancreatic polypeptide (PP). Tumoral transformation increases cell proliferation and in functional tumors leads to excessive secretion of the respective hormone. The most defining imaging feature of these tumors is hypervascularity: neuroendocrine cells are surrounded by a dense capillary network, and this vascularity is preserved or increased in tumoral transformation. Prominent hypervascular enhancement in the arterial phase results from this rich capillary network — showing more intense enhancement than normal pancreatic parenchyma. Low-grade tumors typically enhance homogeneously, while high-grade and large tumors develop necrosis and cystic degeneration creating heterogeneous appearance. Grade 3 NECs can paradoxically be hypovascular and mimic PDAC. Somatostatin receptors (particularly SSTR2) are overexpressed in most PanNETs; this forms the basis of functional imaging with octreotide scintigraphy and Ga-68 DOTATATE PET-CT.
Well-defined solid mass enhancing distinctly more intensely than pancreatic parenchyma in the arterial phase. This hypervascular enhancement pattern is the most critical finding distinguishing PanNETs from the hypovascular pattern of PDAC. The term 'flash enhancement' describes the strikingly bright appearance of the tumor compared to its surroundings in the arterial phase.
Well-defined solid mass showing prominent hypervascular enhancement compared to pancreatic parenchyma in arterial phase. Homogeneous enhancement in small tumors (<2 cm), heterogeneous in large tumors is typical. Enhancement degree generally shows >20 HU increase (compared to unenhanced). Insulinomas present as small (<2 cm), intensely and homogeneously enhancing tumors. Rim enhancement and central necrosis may be seen in large non-functional tumors.
Report Sentence
A well-defined solid mass in the pancreas demonstrating prominent hypervascular enhancement in the arterial phase is identified, consistent with pancreatic neuroendocrine tumor (PanNET).
Hyperintense, well-defined solid mass relative to pancreatic parenchyma on T2-weighted images. T2 hyperintensity reflects the cellular composition and vascular component of the tumor. Areas of cystic degeneration show very high T2 signal. Low-grade PanNETs are homogeneously hyperintense while high-grade tumors show heterogeneous signal.
Report Sentence
A well-defined solid mass showing hyperintense signal in the pancreas on T2-weighted images is identified.
Hyperintense signal on DWI with low ADC values on ADC map. Diffusion restriction in PanNETs correlates with cellularity grade and is more prominent in high-grade tumors. DWI adds value to conventional sequences in detecting small PanNETs. ADC values may inversely correlate with grade — low ADC = high grade.
Report Sentence
The mass demonstrates diffusion restriction on DWI, consistent with increased cellularity.
In large PanNETs (>3-4 cm), central necrosis, cystic degeneration, and calcification may be seen. In portal venous phase, peripheral solid component enhances while central necrotic/cystic area does not enhance. This heterogeneity results from rapid tumor growth outpacing vascular supply. Calcifications may be punctate, coarse, or peripheral — seen in ~20% of cases.
Report Sentence
A large mass in the pancreas is identified with central necrotic/cystic degeneration and peripheral solid component enhancement, to be evaluated for neuroendocrine tumor.
Well-defined, homogeneously hypoechoic solid mass relative to pancreatic parenchyma. Small insulinomas (<2 cm) appear as homogeneous hypoechoic nodules. In large tumors, heterogeneous echostructure, cystic areas, and calcifications (posterior acoustic shadowing) may accompany. Endoscopic ultrasonography (EUS) shows much higher sensitivity than transabdominal US (90-95% vs 30-50%), especially for small functional tumors.
Report Sentence
A well-defined hypoechoic solid mass in the pancreas is identified; contrast-enhanced CT or MRI is recommended for further characterization.
Intense radiopharmaceutical uptake in the tumor on Ga-68 DOTATATE PET-CT. SSTR2-positive PanNETs show distinctly increased uptake compared to surrounding tissue (SUVmax typically >15-20). This modality demonstrates all primary and metastatic lesions throughout the body in a single session. Sensitivity reaches 90-95% for well-differentiated PanNETs. SSTR expression decreases in grade 3 NEC and poorly differentiated tumors, and FDG PET-CT becomes more informative (flip-flop phenomenon).
Report Sentence
Intense somatostatin receptor uptake in the pancreatic mass on Ga-68 DOTATATE PET-CT, supporting the diagnosis of neuroendocrine tumor.
Criteria
Insulin-secreting functional PanNET. Most common functional type (35-40%). 90% benign, 90% solitary, 90% <2 cm (rule of 90s).
Distinct Features
Whipple triad (hypoglycemia, low blood sugar, correction with glucose). Difficult to detect due to small size — EUS is the most sensitive modality. Intense homogeneous enhancement in arterial phase. Small nodule hypointense on T1, hyperintense on T2 on MRI.
Criteria
PanNET not producing clinical hormone syndrome. 60-90% of all PanNETs. Usually larger at diagnosis (>3-4 cm) as it does not produce early symptoms.
Distinct Features
Larger size, cystic degeneration and calcification more common. Mass effect symptoms (pain, obstruction) or incidental detection. Grade 2-3 proportion higher than functional types. Liver metastases more common at diagnosis (40-60%).
Criteria
Gastrin-secreting functional PanNET. Second most common functional type. 60-90% localized in the 'gastrinoma triangle' (pancreatic head-duodenum region).
Distinct Features
Refractory peptic ulcer, diarrhea, gastric mucosal hypertrophy. 25% associated with MEN1 (multiple tumors). Malignancy rate 60-90% — much more aggressive than insulinoma. Duodenal gastrinomas can be very small (<1 cm) and difficult to detect on imaging.
Distinguishing Feature
PDAC is hypovascular (hypodense) in arterial phase while PanNET enhances hypervasculary (hyperdense) — the most fundamental distinguishing point. PDAC is infiltrative with irregular margins and ductal obstruction/atrophy; PanNET is well-defined, round, and ductal obstruction is rare.
Distinguishing Feature
SPN occurs in young women (20-30 years), is large and encapsulated; contains hyperintense areas on T1 due to hemorrhage. PanNET shows no age or gender predilection, hemorrhage is rare. SPN shows heterogeneous and progressive enhancement while PanNET enhances intensely in the arterial phase.
Distinguishing Feature
Pancreatic metastases (especially RCC, melanoma) can be hypervascular and mimic PanNET. Known primary malignancy history, multiple pancreatic lesions, and presence of extra-pancreatic disease favor metastasis. In RCC metastases, primary tumor in the kidney or nephrectomy history should be investigated.
Distinguishing Feature
PanNET with cystic degeneration may be confused with serous cystadenoma. In serous cystadenoma, microcystic honeycomb pattern and central stellate scar are pathognomonic, while PanNET has a prominent solid component showing arterial enhancement. Serous cystadenoma lacks a solid enhancing component.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
specialist-referralPanNET management is determined by grade, stage, and functional status. Surgical resection (enucleation, distal pancreatectomy, or Whipple) is curative for localized PanNETs. Active surveillance may be considered for small (<2 cm) non-functional grade 1 tumors. In functional tumors (insulinoma, gastrinoma), control of hormone hypersecretion symptoms is urgent. For advanced/metastatic disease, somatostatin analogues (octreotide, lanreotide), everolimus, sunitinib, and peptide receptor radionuclide therapy (PRRT — Lu-177 DOTATATE) are available options. Ki-67 index determination via EUS-FNA or biopsy is mandatory for grading.
PNETs have a better prognosis compared to PDAC. Functional tumors present early with hormonal symptoms. 90% of insulinomas are benign. Non-functional tumors are diagnosed later and at larger sizes. WHO 2019 grading (G1-G3) is important for prognosis and treatment planning.