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Intrapancreatic accessory spleen: findings on MR Imaging, CT, US and scintigraphy, and the pathologic analysis.

Kim SH, Lee JM, Han JK, Lee JY, Kim KW, Cho KC, Choi BI - Korean J Radiol (2008 Mar-Apr)

Bottom Line: In particular, inhomogeneous enhancement of an IPAS in its early phases may be a diagnostic clue.Superparamagnetic iron oxide (SPIO)-enhanced MRI and Levovist-enhanced US, and the mechanisms of which are theoretically similar to that of Tc-99m scintigraphy, can be used as alternative tools to confirm the diagnosis of IPAS.We review and illustrate the differential points between IPAS and hypervascular pancreatic tumors in this manuscript.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology, Seoul National University Hospital, Seoul, Korea.

ABSTRACT
Although the tail of the pancreas is the second most common site of an accessory spleen, intrapancreatic accessory spleen (IPAS) has rarely been noted radiologically. However, as the imaging techniques have recently advanced, IPAS will be more frequently detected as an incidental pancreatic nodule on CT or MRI. Because accessory spleens usually pose no clinical problems, it is important to characterize accessory spleens as noninvasively as possible. An IPAS has similar characteristics to those of the spleen on the precontrast and contrast-enhanced images of all the imaging modalities. In particular, inhomogeneous enhancement of an IPAS in its early phases may be a diagnostic clue. Superparamagnetic iron oxide (SPIO)-enhanced MRI and Levovist-enhanced US, and the mechanisms of which are theoretically similar to that of Tc-99m scintigraphy, can be used as alternative tools to confirm the diagnosis of IPAS. An IPAS shows a significant signal drop similar to the spleen on the SPIO-enhanced T2 or T2*-weighted imaging and prolonged enhancement on the delayed hepatosplenic phase of contrast-enhanced US. We review and illustrate the differential points between IPAS and hypervascular pancreatic tumors in this manuscript.

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Atypical CT appearance of small intrapancreatic accessory spleen in 52-year-old man with advanced liver cirrhosis. On precontrast axial CT scan (left upper), lesion (arrow) shows iso-attenuation compared to pancreas. Axial CT image obtained during arterial phase (right upper) depicts round, well-demarcated and low-attenuating nodule (arrow) in pancreas tail. However, lesion shows attenuation that's identical to spleen (S). On oblique coronal multiplanar reconstruction images obtained during pancreatic (left lower) and portal (right lower) phases, intrapancreatic accessory spleen (arrows) shows low attenuation compared to pancreas on pancreatic phase (left lower), iso-attenuation compared to pancreas on portal phase (right lower) and iso-attenuation compared to spleen (S) on both phases. Even though main spleen still shows slight heterogeneity on portal phase (right lower), intrapancreatic accessory spleen can not be distinguished from adjacent pancreas on portal phase due to its small size. Retarded splenic perfusion due to liver cirrhosis is regarded as possible cause for such low attenuation of both spleen and intrapancreatic accessory spleen on early CT phases.
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Figure 6: Atypical CT appearance of small intrapancreatic accessory spleen in 52-year-old man with advanced liver cirrhosis. On precontrast axial CT scan (left upper), lesion (arrow) shows iso-attenuation compared to pancreas. Axial CT image obtained during arterial phase (right upper) depicts round, well-demarcated and low-attenuating nodule (arrow) in pancreas tail. However, lesion shows attenuation that's identical to spleen (S). On oblique coronal multiplanar reconstruction images obtained during pancreatic (left lower) and portal (right lower) phases, intrapancreatic accessory spleen (arrows) shows low attenuation compared to pancreas on pancreatic phase (left lower), iso-attenuation compared to pancreas on portal phase (right lower) and iso-attenuation compared to spleen (S) on both phases. Even though main spleen still shows slight heterogeneity on portal phase (right lower), intrapancreatic accessory spleen can not be distinguished from adjacent pancreas on portal phase due to its small size. Retarded splenic perfusion due to liver cirrhosis is regarded as possible cause for such low attenuation of both spleen and intrapancreatic accessory spleen on early CT phases.

Mentions: The multidetector-row CT (MDCT) appearance of IPAS largely depends on the CT phases that are used. In our hospital, if a hypervascular nodule is detected in the pancreas on single phase CT images, we usually recommend performing triple-phase (arterial, pancreatic and portal phases) CT for further characterization of that nodule. The same as in normal spleen, IPAS may demonstrate heterogeneous enhancement on the early CT phase (usually within 70 seconds after contrast administration) because of the different rates of flow through the cords of the red and white pulp (10). With the introduction of MDCT scanners and the recent advances of techniques to deliver contrast agent, this inhomogeneous enhancement pattern might be more frequently observed even in small IPASs and it can be a helpful feature to differentiate them from other hypervascular pancreatic tumors (Fig. 5). The attenuation of IPAS on all the dynamic CT phases is usually similar to that of the spleen (Figs. 5, 6). In general, because attenuation of the spleen is higher than that of the pancreas on the arterial, pancreatic and portal venous phases, we can easily presume that IPAS will be brighter than the pancreas on all three dynamic CT phases. Indeed, according to a previous study that examined seven IPASs, the mean HU value of the IPASs was higher than that of the pancreas on all three enhanced CT phases (7). However, the attenuation of IPAS can, on rare occasions, be lower than that of the pancreas on the arterial and pancreatic phases (Fig. 6). It can occur under a condition when splenic enhancement is retarded, such as liver cirrhosis (11). Indeed, one of our patients (Fig. 6) was followed-up due to advanced liver cirrhosis. Nonetheless, the attenuation of IPAS is equal to that of the spleen (Fig. 6).


Intrapancreatic accessory spleen: findings on MR Imaging, CT, US and scintigraphy, and the pathologic analysis.

Kim SH, Lee JM, Han JK, Lee JY, Kim KW, Cho KC, Choi BI - Korean J Radiol (2008 Mar-Apr)

Atypical CT appearance of small intrapancreatic accessory spleen in 52-year-old man with advanced liver cirrhosis. On precontrast axial CT scan (left upper), lesion (arrow) shows iso-attenuation compared to pancreas. Axial CT image obtained during arterial phase (right upper) depicts round, well-demarcated and low-attenuating nodule (arrow) in pancreas tail. However, lesion shows attenuation that's identical to spleen (S). On oblique coronal multiplanar reconstruction images obtained during pancreatic (left lower) and portal (right lower) phases, intrapancreatic accessory spleen (arrows) shows low attenuation compared to pancreas on pancreatic phase (left lower), iso-attenuation compared to pancreas on portal phase (right lower) and iso-attenuation compared to spleen (S) on both phases. Even though main spleen still shows slight heterogeneity on portal phase (right lower), intrapancreatic accessory spleen can not be distinguished from adjacent pancreas on portal phase due to its small size. Retarded splenic perfusion due to liver cirrhosis is regarded as possible cause for such low attenuation of both spleen and intrapancreatic accessory spleen on early CT phases.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2627219&req=5

Figure 6: Atypical CT appearance of small intrapancreatic accessory spleen in 52-year-old man with advanced liver cirrhosis. On precontrast axial CT scan (left upper), lesion (arrow) shows iso-attenuation compared to pancreas. Axial CT image obtained during arterial phase (right upper) depicts round, well-demarcated and low-attenuating nodule (arrow) in pancreas tail. However, lesion shows attenuation that's identical to spleen (S). On oblique coronal multiplanar reconstruction images obtained during pancreatic (left lower) and portal (right lower) phases, intrapancreatic accessory spleen (arrows) shows low attenuation compared to pancreas on pancreatic phase (left lower), iso-attenuation compared to pancreas on portal phase (right lower) and iso-attenuation compared to spleen (S) on both phases. Even though main spleen still shows slight heterogeneity on portal phase (right lower), intrapancreatic accessory spleen can not be distinguished from adjacent pancreas on portal phase due to its small size. Retarded splenic perfusion due to liver cirrhosis is regarded as possible cause for such low attenuation of both spleen and intrapancreatic accessory spleen on early CT phases.
Mentions: The multidetector-row CT (MDCT) appearance of IPAS largely depends on the CT phases that are used. In our hospital, if a hypervascular nodule is detected in the pancreas on single phase CT images, we usually recommend performing triple-phase (arterial, pancreatic and portal phases) CT for further characterization of that nodule. The same as in normal spleen, IPAS may demonstrate heterogeneous enhancement on the early CT phase (usually within 70 seconds after contrast administration) because of the different rates of flow through the cords of the red and white pulp (10). With the introduction of MDCT scanners and the recent advances of techniques to deliver contrast agent, this inhomogeneous enhancement pattern might be more frequently observed even in small IPASs and it can be a helpful feature to differentiate them from other hypervascular pancreatic tumors (Fig. 5). The attenuation of IPAS on all the dynamic CT phases is usually similar to that of the spleen (Figs. 5, 6). In general, because attenuation of the spleen is higher than that of the pancreas on the arterial, pancreatic and portal venous phases, we can easily presume that IPAS will be brighter than the pancreas on all three dynamic CT phases. Indeed, according to a previous study that examined seven IPASs, the mean HU value of the IPASs was higher than that of the pancreas on all three enhanced CT phases (7). However, the attenuation of IPAS can, on rare occasions, be lower than that of the pancreas on the arterial and pancreatic phases (Fig. 6). It can occur under a condition when splenic enhancement is retarded, such as liver cirrhosis (11). Indeed, one of our patients (Fig. 6) was followed-up due to advanced liver cirrhosis. Nonetheless, the attenuation of IPAS is equal to that of the spleen (Fig. 6).

Bottom Line: In particular, inhomogeneous enhancement of an IPAS in its early phases may be a diagnostic clue.Superparamagnetic iron oxide (SPIO)-enhanced MRI and Levovist-enhanced US, and the mechanisms of which are theoretically similar to that of Tc-99m scintigraphy, can be used as alternative tools to confirm the diagnosis of IPAS.We review and illustrate the differential points between IPAS and hypervascular pancreatic tumors in this manuscript.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology, Seoul National University Hospital, Seoul, Korea.

ABSTRACT
Although the tail of the pancreas is the second most common site of an accessory spleen, intrapancreatic accessory spleen (IPAS) has rarely been noted radiologically. However, as the imaging techniques have recently advanced, IPAS will be more frequently detected as an incidental pancreatic nodule on CT or MRI. Because accessory spleens usually pose no clinical problems, it is important to characterize accessory spleens as noninvasively as possible. An IPAS has similar characteristics to those of the spleen on the precontrast and contrast-enhanced images of all the imaging modalities. In particular, inhomogeneous enhancement of an IPAS in its early phases may be a diagnostic clue. Superparamagnetic iron oxide (SPIO)-enhanced MRI and Levovist-enhanced US, and the mechanisms of which are theoretically similar to that of Tc-99m scintigraphy, can be used as alternative tools to confirm the diagnosis of IPAS. An IPAS shows a significant signal drop similar to the spleen on the SPIO-enhanced T2 or T2*-weighted imaging and prolonged enhancement on the delayed hepatosplenic phase of contrast-enhanced US. We review and illustrate the differential points between IPAS and hypervascular pancreatic tumors in this manuscript.

Show MeSH
Related in: MedlinePlus