Diagnostic Ultrasound - Abdomen and Pelvis

Pancreatic Neuroendocrine Tumor
TERMINOLOGY
Synonyms
• Pancreatic/gastroenteropancreatic neuroendocrine tumor
(NET); pancreatic endocrine tumor (pET)
• Historical terms: Islet cell tumor; carcinoid
Definitions
• Solid epithelial neoplasm believed to arise from pluripotent
pancreatic ductal cells with capacity to differentiate along
neuroendocrine lines
IMAGING
General Features
• Best diagnostic clue
○ Well-circumscribed, round hypervascular mass(es); no
pancreatic ductal dilation
○ Calcification, necrosis, and cystic change in larger tumors
• Location
○ 85% within pancreas: Usually body/tail; 15% ectopic
– Duodenum, stomach, lymph nodes, ovaries
○ May be multiple
• Size
○ Variable: Range from < 1 cm to > 20 cm; typically 1-5 cm
– Functioning tumors: Smaller at time of presentation
– Nonfunctioning tumors: Usually larger at diagnosis
• Morphology: Functioning vs. nonfunctioning subtypes
○ Functioning tumors: Small, round, enhancing mass
– May be subtle
○ Nonfunctioning: Large, well-demarcated, lobulated mass
with heterogeneous enhancement pattern
– Areas of cystic change/necrosis and calcification
– Displaces, rather than invades, adjacent structures
Transabdominal Ultrasound (TA US)
• Well-defined, round, hypoechoic mass; can appear
isoechoic (focal contour asymmetry)
• Large tumors may be echogenic ± calcification &/or central
hypoechogenicity (necrosis)
○ Intratumoral calcification suggests malignancy
○ 60-90% have adenopathy and liver metastases at clinical
presentation
– Hyperechoic, hypoechoic, or target lesions
• Color Doppler: Demonstrates intratumoral flow
• Reported sensitivity for detection of small tumors ~ 25-60%
○ Limited role in detection for functional NETs given
typical small tumor size and body habitus limitations
Endoscopic Ultrasound (EUS)
• ↑ sensitivity for detection of small tumors (up to 94%)
• Can guide biopsy and sample cyst fluid
Intraoperative Ultrasound (IOUS)
• Highest sensitivity for small lesions (75-100%)
CT Findings
• CECT
○ Smoothly marginated and hypervascular (arterial/PV
phases)
○ Large lesions: Heterogeneous due to nonenhancing
cystic/necrotic areas ± calcification
○ Cystic variant: Hypervascular rim, central necrosis
(distinguishing feature vs. other cystic pancreatic lesions)
○ Rarely appears infiltrative (poorly differentiated NET)
○ Liver and nodal metastases: Hypervascular, often with
ring-like enhancement in liver lesions
MR Findings
• T1WI ± FS: Hypointense to normal pancreas
○ Unenhanced, FS T1WI has highest sensitivity (75%)
• T2WI ± FS: Usually hyperintense to normal pancreas
• T1 C+: Hypervascular
○ Small tumors: Homogeneous enhancement pattern
○ Large tumors: More heterogeneous with nonenhancing
cystic, necrotic/hemorrhagic areas and hyperenhancing
tumor
○ Liver and nodal metastases: Prominent enhancement,
ring like in liver
Nuclear Medicine Findings
• Octreotide scintigraphy
○ Limitations: Uptake by nontarget sites, ↑ image
acquisition time, poor image resolution
• PET/CT with Ga-68-(DFO)-octreotide
○ Advantages: Rapid excretion from nontarget sites, ↓
acquisition time, CT localization → ↑ precision
• Useful for metastatic disease or if primary lesion
undetected by other imaging modalities
○ Low sensitivity for insulinomas (↓ expression of
somatostatin receptors)
Imaging Recommendations
• Best imaging tool
○ Contrast-enhanced CT or MR
○ Endoscopic US: ↑ detection rate for small tumors
compared to transabdominal US
– Invasive technique
– Performed for localization if CT/MR is negative with
high clinical suspicion or to guide biopsy
○ Even if initial CECT/MR/US are negative, if positive
biochemical evidence exists, further imaging studies are
essential
– Consider somatostatin receptor functional imaging
○ Intraoperative ultrasound helps ensure complete
detection/resection of small tumors
• Protocol advice
○ CT: Dual phase pancreatic protocol should be performed
(late arterial and portal venous phases)
– Arterial phase increases conspicuity of small lesions
○ MR: Include T1/T2 ± FS and C+ T1W FS dynamic imaging
DIFFERENTIAL DIAGNOSIS
Mucinous Cystic Pancreatic Tumor
• Multiloculated cystic mass with septations
• Can appear similar to cystic NET variant
• Usually with larger cystic component and no thick
enhancing rind
Solid Pseudopapillary Neoplasm
• Rare solid and cystic mass than can appear similar to a
nonfunctioning NET
• Occurs in overlapping younger age demographic
Diagnoses: Pancreas
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