Today, I review, link to, and excerpt from Pancreatic Cancer Imaging from emedicine.medscape.com. Updated: Feb 21, 2024
Author: Mahesh Kumar Neelala Anand, MBBS, DNB, FRCR; Chief Editor: John Karani, MBBS, FRCR
All that follows is from the above resource.
- Practice Essentials
- Radiography
- Computed Tomography
- Magnetic Resonance Imaging
- Ultrasonography
- Nuclear Imaging
- Angiography
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- Media Gallery
- References
Practice Essentials
Imaging plays an essential role in the surveillance, diagnosis, resectability evaluation, and treatment response evaluation of pancreatic cancer. [1, 2] Multisection CT should be used first for detection of pancreatic adenocarcinoma. When CT findings are negative, MRI or endoscopic ultrasound (EUS) should be performed for detection and for assessment of resectability. Although conventional angiography is obsolete in primary staging, it is occasionally required to assess peripancreatic vessels before surgery. Modern multislice CT scanners are capable of excellent depiction of arterial and venous branches. The role of MR angiography (MRA) in assessment of mesenteric vessels prior to surgery is not firmly established, although study results are encouraging.
Imaging modalities
Multisection CT scanning is generally accepted to be the first line of investigation in a patient with suspected pancreatic cancer. The best imaging technique is determined by local availability and expertise, but will nearly always be spiral CT (ideally multisection CT). The reasons for this preference include its wide availability, speed, thin sections, optimal enhancement, high spatial resolution, and consistently good images. [3, 4, 5, 6]
The importance of good CT technique cannot be overemphasized. Key elements include the following: oral water as negative intraluminal contrast, 120 to 150 mL of iodinated contrast material administered intravenously at a rate of 3 to 4 mL/s, and scanning with thin (2-3 mm) collimation during the pancreatic parenchymal phase (at 25-35 s), with scanning performed at 60 to 70 s during the liver phase. [7, 8]
Limitations of techniques
Detection of a mass on imaging is nonspecific, and 5-15% of pancreatic resections show benign pathology.
Transabdominal US (TAUS) has relatively poor sensitivity, and its outcomes are not satisfactory for assessment in approximately 20% of patients because of a poor acoustic window due to bowel gas.
MRI is sensitive for detection and staging of pancreatic cancer, with sensitivity and specificity similar to those of multisection CT, but MRI involves expensive equipment and requires meticulous attention to the image technique. Other technical limitations involve movement artifacts due to bowel peristalsis and breathing. Because high sensitivity and specificity of MRI in detecting and staging small tumors have not been achieved consistently and universally, debate continues about the superiority of MRI over CT.
Computed Tomography
Multidetector CT is preferred for both staging and assessing pancreatic adenocarcinoma resectability. [4, 5, 6] In a study of 3567 patients with pancreatic ductal adenocarcinoma, sensitivity, specificity, and diagnostic accuracy were 90%, 87%, and 89%, respectively, for CT. [3] Because of a lack of visible attenuation difference between the tumor and the pancreatic parenchyma, up to 11% of ductal adenocarcinomas may not be detected by MDCT. [17] Emerging techniques such as dual-energy CT and texture analysis of CT and MRI may have potential in improving lesion detection and characterization and in treatment monitoring. [4]
Features suggestive of underlying pancreatic cancer include the following: alterations in morphology of the gland with abnormalities of CT attenuation values, obliteration of peripancreatic fat, loss of sharp margins with surrounding structures, involvement of adjacent vessels and regional lymph nodes, pancreatic ductal dilatation, pancreatic atrophy, and obstruction of the common bile duct (CBD). [18, 19, 20, 21, 22, 23, 24, 25]
Degree of confidence
CT is the most widely used and most sensitive test for evaluation of the pancreas for pancreatic carcinoma. Dynamic CT has a detection rate of approximately 99%. Multisection CT should be the first-line study used for detecting this tumor and for evaluating its resectability.
According to a study by Raman et al, MDCT can accurately stage patients with pancreatic cancer, but its accuracy in excluding distant metastatic disease depreciates over time. The authors concluded from their findings that patients should undergo a repeat MDCT within 25 days of any planned definitive operative intervention for pancreatic cancer to avoid unexpectedly finding metastatic disease at surgery. [27]
Cysts or focal pancreatitis can occasionally cause problems in diagnosis, and it can produce false-positive and false-negative results.
Magnetic Resonance Imaging
MRI is often used as a second-line study in the management of pancreatic adenocarcinoma, reserved for cases where CT results are equivocal or CT with contrast is contraindicated. [2, 28] Compared with other modalities, MRI appears to be more valuable for staging the extent and spread of pancreatic carcinoma than for detecting lesions smaller than 2 cm. The ability of MRI to identify pancreatic adenocarcinoma largely depends on demonstration of deformity of the gland, as reflected in its size, shape, contour, and signal intensity characteristics. [29, 30, 31, 32]
Magnetic resonance cholangiopancreatography (MRCP) is as sensitive as ERCP and may prevent inappropriate exploration of the pancreatic and bile ducts in patients with suspected pancreatic carcinoma in whom interventional endoscopic therapy is unlikely. The sensitivity of MRCP has been estimated at 84%, with specificity of 97% for pancreatic cancer. Findings are complementary to those of ERCP and percutaneous transhepatic cholangiography (PTC).
It has been difficult to prove consistent results when MRI is used to detect tumor and to determine its resectability. The degree of confidence with MRI is less than that with CT because of wide variability in MRI techniques and limitations from motion artifacts. Some studies have confirmed greater reliability with MRI when meticulous technique is applied.
Ultrasonography
US equipment has improved considerably, and this is likely to have reflected on its sensitivity for detecting pancreatic masses. [12] Transabdominal ultrasound (TAUS) examination is still less sensitive than other modalities for detection of pancreatic malignancies smaller than 2 cm. TAUS has been noted to have a sensitivity of 70% and a specificity of 95% for the diagnosis of pancreatic malignancy.
The specificity of EUS for differentiating benign from malignant lesions based on US appearance alone remains unsatisfactory. EUS has high sensitivity and specificity for pancreatic cancer, with overall staging accuracy greater than 80%. The possibility of performing EUS-guided fine-needle aspiration (FNA) significantly improves both diagnostic and staging capability of EUS. EUS-guided FNA is safe, with morbidity less than 2%.
In a retrospective study, Tanaka et al performed contrast-enhanced US and contrast-enhanced CT and found that the sensitivities of contrast-enhanced US and contrast-enhanced CT in characterizing adenocarcinoma were 97.0% and 77.0% for all 100 adenocarcinoma cases, 100% and 76.7% for 43 small cancers (≤20 mm), 100% and 58.3% for 12 smaller cancers (≤10 mm), and 100% and 72.2% for 36 stage IA cancers, respectively. [35]
