Elastography in the Diagnosis of Chronic Pancreatitis

Chronic pancreatitis is a chronic inflammatory condition where progressive fibrosis and scarring leads to loss of pancreatic exocrine and endocrine function and can lead to development of malnutrition, weight loss, abdominal pain and impaired quality of life. Patients with chronic pancreatitis have a high risk of pancreatic adenocarcinoma compared to the general population so it is vital that they are identified early in the disease. There are numerous causes of chronic pancreatitis therefore early detection and treatment can prevent irreversible changes and symptoms developing.

Trans-abdominal ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) are currently used to investigate patients with symptoms suggestive of chronic pancreatitis. These tests may, however, fail to show early changes in the bile ducts or small areas of inflammation in pancreatic tissue. In areas of diagnostic uncertainty, endoscopic ultrasound (EUS) is currently used to provide a more detailed assessment.

EUS uses a flexible endoscope (similar to a gastroscope) passed into the stomach via the mouth. The EUS scope has the addition of a tiny ultrasound probe on the tip which is used to acquire high resolution detailed images of the pancreas and other extra luminal structures (lymph nodes, bile ducts, mediastinum) lying only centimeters from the tip of the probe. Despite the advantages of EUS, image interpretation can be extremely challenging and in the presence of inflammation. Morphological changes of chronic pancreatitis seen at EUS have been classified according to the Rosemont classification; however, the findings are subjective with sub-optimal intra-observer agreement.

Elastography is an ultrasound technique used to assess stiffness of tissues in the body. It has established applications in detecting chronic liver disease, and improving diagnostic accuracy in breast and prostate cancers. Pancreatic elastography is now able to be performed during a standard EUS examination using the existing equipment (in a similar manner to Doppler). Tissue elasticity is measured and represented with different colours (on a scale of 1 to 255). The colour signal (red-green-blue) is then superimposed on the conventional grey-scale image. Areas of increased stiffness are marked with dark blue, intermediate areas with green and soft tissue areas with red. Areas of interest are able to be marked to give an elasticity reading and this is also compared to a control area of stomach wall to calculate a ratio (strain ratio).

Elastography has now become part of the routine EUS exam following several studies that have shown elastography can be successfully used to identify malignant pancreatic and lymph node masses with high sensitivity allowing accurate targeting of fine needle aspiration (FNA) biopsies and early confirmation or exclusion of cancer.