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CT AND MRI CORRELATION OF PANCREATIC TUMORS




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Computed Tomography —Involves the use of in- travenous contrast and timed image sequences that en- able the evaluation of vascular structures around the pancreas. Very accurate at determining unresectable disease with positive predictive values for unresectability varying from approximately 89% to 100% [10]. For determining resectability, the sensitivity of spiral CT is 81-90% and specificity is 82%. This is comparable to conventional CT and MRI. However, spiral CT has the added benefit of superior sensivity (91-98%) for the initial diagnosis of pancreatic carcinoma compared to conventional CT (86%) and MRI (84%) [6]. Multidetector CT (MDCT) with multiplanar reformatted images offers improved evaluation of vascular involvement and liver metastases and is more accurate in assessing tumor resectability compared to single detector CT. The positive predictive value for determining resectability is 91%. [3]

CT is a widely used and validated tool for the study of pancreas [7,11]. CT is the primary imaging study for evaluation of patients with symptoms that suggest the presence of the disease. CT is an appropri- ate initial imaging test because it detects tumors in the pancreas and can be used to stage for resectability and to detect liver metastases. Its sensitivity and specificity have increased considerably due to technical improve- ments. Multidetector row CT allows imaging of larger volumes of pancreatic tissue while acquiring both arte- rial and venous phases in shorter periods of time with better delineation of the main pancreatic duct and small intraparenchymal masses. Pancreas imaging protocols can vary from institution to institution, but several prin- ciples should be observed to guarantee the best yield. Since the pancreas is supplied by splanchnic arteries, its peak enhancement occurs after the peak enhance- ment of the aorta (arterial phase) and before the peak enhancement of the liver (hepatic phase) [11]. Studies show that during this phase, there is the maximal con- trast between tumor and normal parenchyma to assess the vascular involvement of the lesion [11]. Pancreatic adenocarcinoma usually appears as a hypodense mass, due to hypoperfusion, but it can also be isodense to the surrounding normal tissue [7,8,11]. Sometimes it could be detectable just by secondary signs such as deviation of surrounding vessels or pancreatic duct or common bile duct dilation [7].

The sensitivity of MDCT for detecting pancreatic adenocarcinoma ranges from 89% to 97%, with higher yield for larger lesions [11].

Magnetic Resonance Imaging (MRI) — is becoming a primary diagnostic tool in the study of pancreatic cancer. Due to its high soft tissue contrast and the mul- tiplicities of different data types that can be acquired, it is reported to be more predictable than CT in the diag- nosis of pancreatic tumors, especially for small non- contour-deforming lesions and in detecting liver metas- tasis and vascular invasion [8,9]. Normal pancreatic pa- renchyma is hyperintense on noncontrast in T1- weighted images, due to the presence of aqueous pro- tein in the pancreatic acinar cells, whereas pancreatic cancer appears as a low-signal (even normal) intensity lesion on precontrast and postcontrast T1-weighted fat suppressed images, because of the abundant fibrous stroma and relatively low tumor vascularity [11,5]. Multiple technological improvements significantly ameliorated the diagnositc yield of MRI over the past decade. This is especially apparent when regarding 3D gradienecho, which has a better signal-to-noise ratio. This allows thinner slices up to 2 mm and more homogeneous fat saturation [5]. In their prospective comparison of MRI with multislice CT Fusari et al. reported similar accuracy, both for tumor detection and for re- sectability evaluation, with non statistically significant differences between these two techniques (98/98% and 95/90%, respectively) [2].

Magnetic resonance cholangio-pancreatography (MRCP) has replaced ERCP in the evaluation of pa- tients with suspected pancreatic mass, since it can displays both CBD and pancreatic duct, with high accu- racy images (90%) [8]. MRCP also plays a relevant role in suspected IPMN, in detecting, staging and follow up tumors, in order to evaluate the best management for these lesions [1]. Kim et al. [4] assessed the accuracy of T1-weighted 3D gradient echo sequence MRI, in dis- tinguishing pancreatic cancer from chronic pancreatitis, in patients with focal lesions, reporting a sensitivity of 93% and a specificity of 75%, since it can determine a relative well-defined demarcation of malignant lesions [4]. Although the contrast resolution of MRI, especially for soft tissue, is superior to CT, the spatial resolution of MRI is lower, as is the capacity of acquiring high- quality multiplanar images. Therefore, CT should be generally preferred over MRI for staging pancreatic cancer. MRI should be reserved to those patients in whom iodine contrast administration should be avoidable and in whom CT findings are uncertain [9,5]. MRI could also be useful in characterization and staging of cystic pancreatic tumors, because of the internal struc- ture, which is made of septations and mural nodules, has prognostic value, and is easier to visualize on MRI than on CT [5].

Conclusion

For primary tumor detection MDCT is appropriate method of choice for pancreas malignancy and MRI with MRCP unchangeable for the diagnosis of pancreatoduodenal zone tumors especially in case of tumors of common bile duct.

References

  1. Baiocchi G.L.; Portolani N.; Missale G.; Baronchelli C.; Gheza F.; Cantu M.; Grazioli L.; Giu- lini, S.M. Intraductal papillary mucinous neoplasm of the pancreas (IPMN): Clinico-pathological correlations and surgical World J. Surg. Oncol. 2010, 8, 25.
  2. Fusari ; Maurea S.; Imbriaco M.; Mollica C.; Avitabile G.; Soscia F.; Camera L.; Salvatore M.: Com- parison between multislice CT and MR imaging in the diagnostic evaluation of patients with pancreatic masses. Radiol. Med. 2010, 115, 453-466.
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  2. Kim J.K.; Altun E.; Elias J., Pamuklar E.; Rivero H.; Semelka R.C.: Focal pancreatic mass: Dis- tinction of pancreatic cancer from chronic pancreatitis using gadolinium-enhanced 3D-gradientecho MRI. J. Magn. Reson. Imaging 2007, 26, 313-322.
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  4. Lee J.K., Kim A.Y., Kim P.N., Lee M.G., Ha H.K.: Prediction of vascular involvement and resecta- bility by multidetector-row CT versus MR imaging with MR angiography in patients who underwent sur- gery for resection of pancreatic ductal Eur J Radiol. 2010;73(2):310-6.
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    . This percentage increases by age to 8.7% in individuals from 80 to 89 years [3]. Pancreatoduodenal zone tumors are 15% of malignant tumors of gastrointestinal system and increasing of inci- dence year by year (Granova A.M. and others 2007). By Skipenko O.G. (2004) mortality rate of pancreatoduodenal zone increased 10-12 times. Among tumors of pancreatoduodenal zone 63-68% tumors are located in the head of pancreas (Yankin A.V. 2004 ). Other authors (Muchmore J.H. et al., 1996; Link K.H. et al., 1997) think tumors of the head of pancreas located 80% in the head of pancreas and 10-20 % — body and tail of pancreas. Next most common tumors of pancreatoduodenal zone is tumors of major papilla (8-26%), which is 1,6-2,0% all of other malignant tumors.» author=»Rakhmonova G.E.» publisher=»БАСАРАНОВИЧ ЕКАТЕРИНА» pubdate=»2017-01-11″ edition=»ЕВРАЗИЙСКИЙ СОЮЗ УЧЕНЫХ_30.11.16_32(1)» ebook=»yes» ]