Gastrointestinal - Learning Modules - CTisus.com CT Scanning

Typical and Atypical Appearances of Pancreatic Neuroendocrine Tumors (PNETs): Role of CT Angiography (CTA) and Cinematic Rendering (CR)

Elliot K. Fishman M.D.
Johns Hopkins Hospital

Click here to view this module as a video lecture.

What is PNET (aka Pancreatic Neuroendocrine Tumor)?

Well-differentiated endocrine cell tumors
All hormonally active
- Hyperfunctioning vs Non-hyperfunctioning
  - Hyperfunctioning
    - Insulinoma, gastrinoma, glucagonoma, vipoma, somatostatinoma, etc.
    - Tend to be detected earlier and smaller given patients are symptomatic
Syndromic associations
- VHL, NF1, MEN1, TS

Variable Appearances

SHAPE/SIZE: typically well-circumscribed, ranging from small to large

SOLID/CYSTIC: typically solid however can also be cystic and/or necrotic

ENHANCEMENT: typically hypervascular, however can be hypovascular

VASCULAR INVOLVEMENT: typically invade venous vasculature rather than encasing and narrowing them

CALCIFICATIONS: can occur, typically central/bulky

METASTASES: typically hypervascular lesions - most commonly to the liver and lymph nodes; lesions/nodes can be hypovascular after treatment

DUCTAL INVOLVEMENT: rare, but can occur if tumor is extensively large or PNET that secretes serotonin which leads to ductal fibrosis and obstruction

Differential Diagnosis

PNET

well-circumscribed
hypervascular, avidly enhancing
invade venous vasculature
can calcify (central/diffuse/bulky)
enlarged lymph nodes
hypervascular mets

Adenocarcinoma

poorly marginated
hypovascular
encase/narrow vessels
never calcify
enlarged lymph nodes rare
hypovascular mets

Other considerations/mimics of PNETs:

Hypervascular metastases (ie RCC)
Serous cystadenoma
Intrapancreatic splenule
Peripancreatic hypervascular lesions (retroperitoneal paraganglioma), etc.

Pancreas Protocol

Importance of protocol optimization

Lesion identification
Lesion characterization
- Differentiating from normal pancreas and other pancreatic and peripancreatic lesions
Metastases
Staging
Surgical/treatment planning

Dual Phase Imaging for Pancreas

IV contrast - Omnipaque 350 or Visipaque 320
- Arterial phase: 30 seconds
  - Differentiate between adenocarcinoma and PNET
  - Identify vascular metastases and arterial vascular involvement
- Venous phase: 60-70 seconds
  - Evaluate venous vasculature
  - Assess solid organs and differentiate from other lesions; some PNETs may show up on the venous phase (hypovascular)
Oral contrast - neutral agent (ie water)
- positive agent may obscure small lesions
Post-processing = Multiplanar reconstructions, MIPs, VRT and Cinematic Rendering

Cinematic Rendering

Using complex high dynamic range rendering maps to create a natural lighting environment that results in overall more lifelike and visually appealing 3D images with the ability to create vascular and texture maps for improved identification and visualization relative to volume-rendered images
Potential uses:
- Early disease detection
  - Detect the presence of tumor when the texture differs but a defined mass may not be visible due to texture differences between normal and abnormal tissues
- Improved classification of lesions
  - Analyze texture for specific tumor types and grade (grade 1 PNET vs a grade 3 PNET)
  - Potentially predict optimal treatment outcomes
- Presurgical/treatment planning
- Education

Staging/Management

AJCC 8th Edition Staging

T1: Tumor limited to pancreas, <2 cm
T2: Tumor limited to pancreas, 2-4 cm
T3: Tumor limited to pancreas, >4 cm, or invading duodenum or CBD
T4: Tumor invading adjacent organs (stomach, spleen, adrenals, colon) or large vessels (celiac, SMA)
M1a: Mets to liver
M1b: Mets in an extrahepatic site
M1c: Hepatic and extrahepatic sites

Management

Asymptomatic patient with <2 cm - observation vs surgery (no consensus)
Surgery - parenchyma sparing (enucleation, central pancreatectomy) vs demolitive (pancreaticoduodenectomy, distal or total pancreatectomy)
Follow up should include clinical examination, appropriate biochemical markers, and imaging techniques such as CT scan and MRI adapted to tumor grade and stage

Case 1: Typical Hypervascular PNET

Teaching point(s):

The typical appearance of a PNET is a well-circumscribed, avidly enhancing, hypervascular lesion

Case 1: Typical Hypervascular PNET (cont’d) - cinematic renderings

Case 2: Well-differentiated PNET

Teaching point(s):

CTA and CR can be utilized to differentiate normal pancreas tissue from abnormal tissue as well as vascular mapping for pre-operative planning

Case 3: Atypical Hypovascular PNET

Teaching point(s):

PNETs can be Hypovascular and sometimes appear more conspicuous on venous phase imaging than arterial phase imaging

Case 3: Atypical Hypovascular PNET (cont’d)

Case 4: Incidentally noted PNET

Teaching point(s):

Small PNETs can be easily missed or mistaken for vasculature. CR can be used to detect small pancreatic lesions with texture mapping as seen here.

Case 5: Incidentally noted PNET

Teaching point(s):

PNETs can sometimes be more conspicuous on venous phase imaging
Additionally, given that this lesion was incidentally noted, < 2 cm, and patient was asymptomatic with normal biomarkers, the team decided to opt for surveillance rather than surgery.

Case 5: Incidentally noted PNET (cont’d)

Case 6: Multiple PNETs in patient with Von Hippel Lindau

Teaching point(s):

PNETs are associated with multiple syndromes such as VHL, NF1, MEN1, and tuberous sclerosis. Consider these when multiple PNETs or associated features are present.

Case 6: Multiple PNETs in patient with Von Hippel Lindau (cont’d)

Case 7: PNET with Hepatic Metastases and Splenic Vein Occlusion

Teaching point(s):

The most common site of metastasis of PNETs is the liver
PNET metastases are typically Hypervascular

Case 7: PNET with Hepatic Metastases and Splenic Vein Occlusion

Teaching point(s):

CR can be used to assess vascular involvement and for pre-surgical/treatment planning
Image on the right demonstrates splenic vein occlusion with resulting collaterals

Case 8: PNET with Metastases and Vascular Involvement

Teaching point(s):

PNETs can metastasize to extrahepatic locations such as the lymph nodes, retroperitoneum, spleen, vessels, etc.

Case 8: PNET with Metastases and Vascular Involvement (cont’d)

Teaching point(s):

Tumor thrombus of the splenic vein (green arrow)
PNET tends to invade and expand venous vasculature, rather than encase and narrow them adenocarcinoma/other masses

Case 9: PNET with calcification

Teaching point(s):

PNETs can have calcification (purple arrow) which are often central and bulky
- differential diagnosis can include serous cystadenoma/carcinoma

Case 9: PNET with calcification (cont’d)

Case 10: Cystic PNET (uncinate)

Teaching point(s):

PNETs are typically solid, however can also be cystic in nature
CR can be used to accentuate the irregular wall thickening or nodularity of these lesions

Case 11: Cystic PNET (Tail)

Case 12: PNET with Central Necrosis

Case 13: Pancreatic Tail PNET, 1cm

Teaching point(s):

With CR you can change the parameters to better visualize lesions therefore assisting in identifying smaller lesions or abnormalities when there is no defined mass

Case 14: PNET Obstructing the Pancreatic Duct

Case 14: PNET Obstructing the Pancreatic Duct (cont’d)

Teaching point(s):

Unlike adenocarcinoma, PNET rarely results in ductal dilatation or obstruction
May occur when there is a very large PNET or if its a serotonin secreting PNET which results in fibrosis and obstruction of the duct

Case 14: PNET Obstructing the Pancreatic Duct (cont’d)

Future of Cinematic Rendering

Need for clinical studies that measure radiologist accuracy and patient outcomes with and without cinematic rendering
Utilizing AI/deep learning to:
- optimize study visualizations and image quality
- detect findings hidden in the dataset
- predict tumor types/grades

References

Chu, L. C., Johnson, P. T., & Fishman, E. K. (2018). Cinematic rendering of pancreatic neoplasms: preliminary observations and opportunities. In Abdominal Radiology (Vol. 43, Issue 11, pp. 3009–3015). Springer Science and Business Media LLC. https://doi.org/10.1007/s00261- 018-1559-3
Ciaravino, V., De Robertis, R., Tinazzi Martini, P., Cardobi, N., Cingarlini, S., Amodio, A., Landoni, L., Capelli, P., & D’Onofrio, M. (2018). Imaging presentation of pancreatic neuroendocrine neoplasms. In Insights into Imaging (Vol. 9, Issue 6, pp. 943–953). Springer Science and Business Media LLC. https://doi.org/10.1007/s13244-018-0658-6
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Tamm, E. P., Bhosale, P., Lee, J. H., & Rohren, E. M. (2016). State-of-the-art Imaging of Pancreatic Neuroendocrine Tumors. In Surgical Oncology Clinics of North America (Vol. 25, Issue 2, pp. 375–400). Elsevier BV. https://doi.org/10.1016/j.soc.2015.11.007
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