Solid pancreatic masses

Anatomy, embryology, pathophysiology

Adenocarcinoma: inactivation of multiple antioncogenes, as well as issues with deoxyribonucleic acid mismatch repair ( BRCA2 ). Smoking, diet high in meat and solvent exposure are risk factors.
Neuroendocrine tumors: multiple chromosomal losses. Associated with Von-Hippel Lindau syndrome and multiple endocrine neoplasia.
Pancreatic lymphoma: usually non-Hodgkin lymphoma.
Acinar cell carcinoma: mutations in adenomatous polyposis coli beta-catenin gene and loss of chromosome 11.

Techniques

Computed tomography

Detects and characterizes the lesion based on the enhancement pattern on dynamic imaging.
Pancreatic adenocarcinomas are hypodense on pancreatic phase whereas neuroendocrine tumors are hyperdense.
Venous phase imaging allows for evaluation of vascular invasion and metastases, including regional lymph nodes, hepatic and omental metastases.
Used as primary imaging tool for staging of pancreatic cancer at most institutions.

Magnetic resonance imaging

Problem solving tool.
Good for detection of small tumors and metastases.
Used as primary imaging tool for local staging at some institutions.
Magnetic resonance (MR) angiography can be used to assess vascular involvement.
MR cholangiopancreatography (MRCP) can be used to visualize the effect of the tumor on the biliary tree.
Secretin enhanced MRCP can improve assessment of ductal stenosis and help differentiate benign from malignant strictures.

Ultrasonography

Operator dependent with limitations based on bowel gas and patient body habitus.
Endoscopic ultrasound usually performed by gastroenterologists. Provides high resolution images of pancreas and allows biopsy (fine needle aspiration) of lesions.

Nuclear medicine

Positron emission tomography (PET)/computed tomography (CT).
- Normal pancreas should not have significant fluorodeoxyglucose (FDG) uptake.
- Focal uptake is abnormal and could represent a primary malignancy.

Specific disease processes

Pancreatic adenocarcinoma

90% of malignant pancreatic tumors.
- Fifth leading cause of death in Western countries.
- Five-year survival of 4%.
- Males more than females between seventh and eighth decade.
- Presentation: painless jaundice (75% of patients), new onset diabetes (10%), vague abdominal pain, weight loss.
- Tumors at head are more common (two-thirds) ( Figs. 13.1–13.3 ) and have better prognosis. Smaller at presentation with average size of 3 cm.
  
  Fig. 13.1
  
  Locally invasive pancreatic adenocarcinoma arising from the uncinate process on axial (A) and coronal (B) multidetector computed tomography images, manifesting as a hypodense mass ( thin arrow ), which circumscribes the superior mesenteric artery ( thick arrow ) for more than 180 degrees and invades the duodenum ( curved arrow , B), rendering the tumor inoperable.
  
  (From Sahani DV, Samir AE. Abdominal Imaging, ed 2. Philadelphia: Elsevier; 2017.)
  
  Fig. 13.2
  
  Adenocarcinoma of the pancreas shown on coronal (A) and curved reconstructed (B) multidetector computed tomography images. Note a poorly enhancing mass ( thin arrow ) that obstructs the main pancreatic duct ( thick arrow ) and infiltrates the duodenum ( curved arrow ).
  
  (From Sahani DV, Samir AE. Abdominal Imaging , ed 2. Philadelphia: Elsevier; 2017.)
  
  Fig. 13.3
  
  Pancreatic adenocarcinoma. (A) The in-phase (T1-weighted) image in a patient with pancreatic adenocarcinoma in the pancreatic head ( arrow ) shows relative hypointensity compared with normal parenchyma ( arrowhead ). (B) The T2-weighted image exemplifies the usual hypointensity ( arrow ) with little contrast between normal tissue and neoplasm. (C) The enhanced image bears the highest tissue contrast between the lesion ( arrow ) and normal pancreatic tissue ( arrowhead ).
  
  (From Roth C, Deshmukh S. Fundamentals of Body MRI, ed 2. Philadelphia: Elsevier; 2016.)
- Tumors in body (5%–15%) or tail (10%–15%) may present with back pain. Worse prognosis. Larger at prognosis with average size of 5 cm ( Fig. 13.4 ).
  
  Fig. 13.4
  
  Pancreatic adenocarcinoma—arterial phase imaging. Infiltrative mass enlarges the body of the pancreas ( arrows ), which can be seen in the in-phase T1-weighted (A) and the precontrast fat-suppressed T1-weighted gradient recalled-echo (D) images in contrast to the normal pancreatic parenchyma in the head of the pancreas. This mass demonstrates mildly increased signal intensity in T2-weighted (B) images, which is pronounced in fat-suppressed T2-weighted (C) images. In addition, distal gland atrophy and duct dilatation ( arrowheads ) can be seen in the T2-weighted (B) and fat-suppressed T2-weighted (C) images. Furthermore, this mass demonstrates decreased enhancement, compared with the normal pancreas, and is most pronounced in early arterial phase fat-suppressed T1-weighted gradient recalled-echo (E) imaging, with gradual enhancement in delayed phase, fat-suppressed T1-weighted gradient recalled-echo imaging (F) related to desmoplastic content.
  
  (From Roth C, Deshmukh S. Fundamentals of Body MRI , ed 2. Philadelphia: Elsevier; 2016.)
- May be focal masses or may be infiltrative.
- Cystic changes may happen because of necrosis or ductal obstruction.
- Incites extensive desmoplastic reaction leading to main pancreatic ductal (MPD) obstruction ( Fig. 13.5 ), pancreatitis, and/or parenchymal atrophy.
  
  Fig. 13.5
  
  Pancreatic adenocarcinoma in two different patients on multidetector computed tomography pancreatogram (A) and three dimensional magnetic resonance cholangiopancreatography (MRCP) (B) as a small and barely visible lesion ( thin arrow ) causing abrupt narrowing of the main pancreatic duct and upstream dilatation ( thick arrow ). The main pancreatic duct dilatation is better evaluated on MRCP images.
  
  (From Sahani DV, Samir AE. Abdominal Imaging , ed 2. Philadelphia: Elsevier; 2017.)
- Mode of spread: local ( Fig. 13.6 ), retroperitoneum, peritoneal lymph nodes ( Fig. 13.7 ), and liver.
  
  Fig. 13.6
  
  Axial (A) and coronal maximum intensity projection (B) multidetector computed tomography images show an advanced adenocarcinoma ( thin arrow ) infiltrating the superior mesenteric artery ( SMA, thick arrow ) that appears as the “tear drop” sign. Lymph node metastases are present ( curved arrow ).
  
  (From Sahani DV, Samir AE. Abdominal Imaging , ed 2. Philadelphia: Elsevier; 2017.)
  
  Fig. 13.7
  
  Advanced pancreatic adenocarcinoma seen on T2-weighted (A) and pancreatic phase (B), portovenous phase (C), and late phase (D) contrast-enhanced T1-weighted magnetic resonance images as a heterogeneously hyperintense infiltrating lesion ( thin arrow ) on T2-weighted imaging and showing poor, heterogeneous, progressive contrast enhancement over time. Peritoneal metastases coexist ( long thin arrow , D), and necrotic lymph node metastases ( curved arrow , D) are also noted.
  
  (From Sahani DV, Samir AE. Abdominal Imaging , ed 2. Philadelphia: Elsevier; 2017.)
- Mass conspicuity higher in pancreatic phase. Appears as low density mass compared with surrounding parenchyma but may be isoattenuating in 10% of cases.
- Indirect evidence: ductal dilation ( Fig. 13.8 ), parenchymal atrophy, double duct sign (common bile duct and MPD dilation) ( Fig. 13.9 ).
  
  Fig. 13.8
  
  Multidetector computed tomography–pancreatogram image showing abrupt obstruction of the main pancreatic duct with upstream dilatation ( thick arrow ) secondary to a small tumor ( thin arrow ).
  
  (From Sahani DV, Samir AE. Abdominal Imaging , ed 2. Philadelphia: Elsevier; 2017.)
  
  Fig. 13.9
  
  Infiltrating pancreatic adenocarcinoma ( thin arrow ) causing obstruction and upstream dilatation of both the main pancreatic duct and the common bile duct ( thick arrows ) and showing the “double duct” sign on coronal multidetector computed tomography (A), coronal steady state fast spin echo T2-weighted (B) magnetic resonance image, and three-dimensional magnetic resonance cholangiopancreatography (C).
  
  (From Sahani DV, Samir AE. Abdominal Imaging , ed 2. Philadelphia: Elsevier; 2017.)
- Portal venous phase important for evaluation of metastases, visualization of tumor in respect to vasculature.
- Vessel encasement evaluation on CT is important prognostic factor in resection.
  - Less than 90 degrees, less than 3% infiltration; 90 to 180 degrees, 29% to 57% infiltration; more than 180 degrees, more than 80% infiltration.
- T1 hypointense, variable T2 signal (usually hypointense), enhances less than parenchyma but demonstrates progressive enhancement.
- MRCP can demonstrate ductal abnormalities, including stenosis, double duct sign, etc. Secretin MRCP better at characterization than MRCP.
- On ultrasound, pancreatic mass appears hypoechoic.
- Endoscopic ultrasound is most accurate for detection of duodenal infiltration and lymph node staging ( Fig. 13.10 ).
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