Gastrointestinal neuroendocrine tumours

Gastrointestinal neuroendocrine tumours (GI NETS) can be functional or non-functional:

  • functional NETS can be challenging to localise as: 
    • they are often small in size at the time of diagnosis 
    • arise in many sites throughout the body
  • non-functioning and/or malignant NETs often are larger at presentation and therefore easier to locate

Types of gastrointestinal - pancreatic neuroendocrine tumours

  • insulinoma
    • account for 50% of pancreatic NETS
    • usually <2cm diameter          
    • 99% of insulinomas found in pancreas          
    • 10-15% are malignant 
  • gastrinoma
    • account for 20-30% of pancreatic NETS
    • found in pancreas, lymph nodes and duodenum           
    • vary in size           
    • 60-75% are malignant 
  • non functioning tumours and pancreatic polypeptide secreting tumours   
    • account for 15-20%           
    • almost exclusively found in pancreas          
    • usually malignant           
    • often large at presentation 
  • vasoactive polypeptide secreting tumour (VIPoma)          
    • account for 3%           
    • 90% found in the pancreas          
    • 10% found in adrenal gland          
    • 50-60% are malignant 
  • glucagonomas and somatostatinomas           
    • rare           
    • most commonly located in pancreas           
    • often malignant

There is no consensus on the best single imaging modality for NETS and depends on the suspected location and local expertise. Combined modalities and techniques are often used 1-3.

CT
  • used for suspected gastric, enteric and pancreatic NETS pre and post IV iodinated contrast
  • bowel distension with fluid, either by oral intake (CT enterography) or via a nasojejunal tube (CT enteroclysis) improves detection of primary GI NETS 
MRI

Used for suspected hepatic, pancreatic or retroperitoneal NETS, often with gadolinium contrast. MRI enterography also possible.

Ultrasound
  • used for monitoring slow growing tumours and/or follow up of metastases. 
  • ultrasound can also be used to guide biopsies
  • endoscopic/endoluminal US can be used to identify and characterised GI NETS as well as obtaining samples for cytology or histology
Nuclear medicine
  • common radiopharmaceutical is 111-indium-pentetreotide, which is a ligand for somatostatin receptor on the cell membrane of many NETS 4,5
  • multiple tumour sites and/or metastasis can be identified using a gamma-camera to detect the emitted radiation 
  • can be used in combination with cross-sectional imaging modalities to aid staging e.g. SPECT or PET-CT or PET-MRI 6
  • can be used to predict response to nuclear medicine based therapies, and, in some cases, to assess response to treatment. 
  • care should be taken with interpretation of images as drugs can interfere with somatostain receptor expression, e.g. interferon. 
  • NETS can differentiate into tumours that do not express somatostatin receptors can become ‘image negative’ making reoccurrence or metastases more challenging to detect 
  • other radiopharmaceuticals are also used, based on certain physiological characteristics e.g. cell surface receptors or uptake of molecules. 
    • gallium-68 labelled somatostatin analogues (PET/CT) – thought to be more sensitive in detecting NETS expect pulmonary and hepatic metastases 
    • for aggressive, rapidly growing tumours (i.e. high metabolism) Fluoro-di-glucose-PET/CT can be used (FDG-PET) 
    • F18 DOPA and C11 Hydroxytryptophan may be used in future but are not routinely available
Angiography
  • venous sampling can be used in small functional NETS where cross sec-tional imaging is equivocal.
  • multiple endocrine neoplasia type 1 can present with multiple lesions; functional NETS can be identified from these, using calcium stimulation with venous sampling. 
  • angiography and endovascular procedures, such as trans-arterial chemo-embolization (TACE), can be used to treat hepatic metastases.
Assessing specific gastrointetsinal NET imaging based on location
  • gastric or colonic - endoscopy 
  • small bowel
    • c-enhanced CT/MR enterography, +/- radiopharmaceuticals or gallium PET/CT to localize NETS as classically high concentration of Somatostatin receptors and are very vascular      
    • capsule endoscopy may be helpful to detect small bowel NETs not identified by CT or MRI but precise location difficult 
  • pancreatic NETs   
    • non - functioning NETS present late and tend to be larger and have mass effect or non-specific symptoms or signs; these can be identified using CT.           
    • functioning NETs present early with signs and symptoms, leading to clinical suspicion of tumour which is often smaller and more challenging to locate                     
      • triple Phase thin multi-slice CT (pre-contrast/arterial/portal-venous)                     
      • high resolution MRI with T2, T1, fat saturated and dynamic contrast administration                     
      • PET 
Assessing malignancy and staging

Signs on CT of malignant NETs include 7

  • larger size
  • necrosis
  • calcification
  • invasion of the surrounding structures
Assessing metastases
  • commonly metastases to lymph nodes and the liver, as well as bone, lung and mesentery 
  • 40-80% of midgut NETs present with metastases at presentation. 
  • union for International Cancer Control (UICC) TNM (tumour, node, metastasis) systems or the European Neuroendocrine Tumour Society (ENETS) have TNM staging systems which differ slightly from each other
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Article information

rID: 25754
Section: Pathology
Synonyms or Alternate Spellings:
  • Gastrointestinal neuroendocrine tumours
  • Gastrointestinal neuroendocrine tumors
  • Gastrointestinal neuroendocrine tumour
  • Gastrointestinal neuroendocrine tumor
  • Gastrointestinal tract neuroendocrine tumours
  • GI tract neurendocrine tumours
  • Gastrointestinal tract endocrine tumours

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