MR features of primary and secondary malignant lymphoma of the pancreas: a pictorial review
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- Fujinaga, Y., Lall, C., Patel, A. et al. Insights Imaging (2013) 4: 321. doi:10.1007/s13244-013-0242-z
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To describe the imaging findings of primary and secondary pancreatic malignant lymphoma on magnetic resonance imaging (MRI), to help differentiate lymphoma of the pancreas from primary adenocarcinoma and autoimmune pancreatitis among others, and to discuss a few atypical presentations of pancreatitis mimicking lymphoma.
Knowledge of these imaging manifestations of lymphoma may be helpful to arrive at an accurate diagnosis and avoid unnecessary morbidity and mortality from inadvertent surgery.
• Pancreatic malignant lymphoma is shown as a nodular low-density area with mild enhancement on CT.
• It sometimes shows variable manifestations mimicking other tumours and inflammatory conditions.
• MRI provides useful information for differentiating malignant lymphoma from other mimickers.
KeywordsMagnetic resonance imaging Malignant lymphoma Pancreatic cancer Chronic pancreatitis Autoimmune pancreatitis
No evidence of palpable superficial lymphadenopathy,
No enlargement of mediastinal nodes,
Normal leukocyte count,
At surgery, the pancreatic mass predominates, with involved lymph nodes confined to the peripancreatic region,
No hepatic or splenic involvement.
Extranodal lymphoma is classified as secondary if there is involvement of lymph nodes except for those of an adjacent primary organ or with more than one extra nodal site. Lymphomatous involvement of the pancreas is usually of the non-Hodgkin’s or B-cell type. Overall, secondary involvement of the pancreas with lymphoma is more common than primary pancreatic lymphoma, which accounts for less than 1 % of pancreatic tumours [1, 2, 3, 4] and less than 2 % of extra-nodal lymphoma [5, 6]. On the other hand, secondary lymphoma is much more common and can be seen in up to 30 % of patients presenting with widespread lymphoma . However, predominant pancreatic involvement is rare. Diffuse large B-cell is the most common type of non-Hodgkin’s lymphoma (NHL), and more than 50 % of patients have some extra-nodal lesions, comprising less than 0.6–2.1 % of pancreatic NHL [7, 8]. Secondary malignant lymphomas were found in 3 % of autopsy cases with pancreatic secondary tumours , usually appearing as large and bulky masses.
The incidence of pancreatic involvement is as high as 5 % in human immunodeficiency virus (HIV) patients. The gastrointestinal tract is the most commonly affected extranodal site in AIDS-related NHL [10, 11, 12].
Clinical manifestations of pancreatic malignant lymphoma
Primary pancreatic lymphoma appears as variable histopathological subtypes, such as follicular lymphoma, lymphoma of mucosa-associated lymphoid tissue, diffuse large B-cell lymphoma and T-cell lymphoma. It affects patients in the 5th or 6th decade of life and has a slight male predominance. Clinical symptoms are generally nonspecific; abdominal pain, abdominal mass and weight loss are the most common symptoms, followed by jaundice, nausea, vomiting, diarrhoea, pancreatitis and bowel obstruction [13, 14]. Jaundice is sometimes observed because the head of the pancreas is the most common location (more than 80 %) . These findings are similar to those in secondary lymphoma with predominantly pancreatic involvement, although the classic symptoms of NHL, such as fever, chills and night sweats, are rarely seen in primary pancreatic lymphoma. The incessant pain typically encountered with pancreatic adenocarcinoma (PAC) is rare . Therefore, an important clinical aspect differentiating PAC is the clinical manifestation of abdominal pain and palpable mass without jaundice. Primary pancreatic lymphoma can also be associated with immunodeficiency syndromes. There are reported cases of pancreatic lymphoma following solid-organ transplantation or patients infected with HIV [12, 15].
Surgical resection does not play a role in the treatment of pancreatic lymphoma, because chemotherapy is effective in most of the patients. However, pancreatic lymphoma is frequently treated with surgical resection because of the difficulty of differentiating it from PAC [16, 17]. Although biopsy is one of the most useful methods for accurate diagnosis [17, 18], preoperative diagnosis by non-invasive methods is of the utmost importance.
A comprehensive MR protocol to fully evaluate the pancreatic parenchyma and the pancreaticobiliary ductal system at our institution consists of the following sequences: T1-weighted gradient-echo (GRE); T2-weighted axial and coronal sequences, usually fast spin-echo (FSE) or a variant of FSE; diffusion-weighted imaging (DWI); 2D and 3D MR cholangiopancreatography (MRCP); and T1-weighted 3D GRE before and after contrast .
Fat-suppressed T1-weighted images (FST1WI) play an important role in detecting lesions because normal pancreatic parenchyma has either a homogeneous or cobblestone appearance and appears as hyperintense signal areas on FST1WI . Lesions within the pancreas are observed as hypointense signal areas compared with the surrounding pancreatic parenchyma. In addition, the haemorrhagic component in the lesion shows up as hyperintense signal areas.
T2-weighted images (T2WI) clearly demonstrate the internal appearance of the lesion. Presence of necrosis and cystic components is rare in lymphoma but can be seen in other tumours . Thin-slice ultrafast T2WI by a partial Fourier method provides images that clearly demonstrate the association between the lesion and the main pancreatic duct (MPD).
DWI, reflecting changes in water mobility, offers high detectability of the lesions. The respiratory-triggered technique is more effective for providing better image quality, signal intensity characteristics and apparent diffusion coefficient (ADC) measurement than the free-breath technique . ADC values are useful for differentiating between benign and malignant tumours in most studies. However, radiologist should know that ADC values in the pancreas head are lower than those in the tail  and it is sometimes difficult to differentiate malignant tumours from inflammatory lesions .
MRCP, provided by heavily T2WI, is a useful and noninvasive method to assess the MPD and the biliary tree. Free-breathing MRCP obtained by the 3D FSE sequence improves the diagnostic performance, image quality and visibility of the pancreatic duct compared with conventional breath-hold 2D MRCP .
Obtaining a dynamic contrast-enhanced MR image (DCE-MRI) using extravascular gadolinium contrast agents is useful to assess the vascularity of the tumour. FST1WI using a chemical-shift-selective fat-saturation method is recommended to eliminate paradoxical negative enhancement . Overall, the signal-to-noise ratio of 3-T MRI is superior to that of 1.5 T, and high-resolution, thin-slice images can be obtained by 3D-T1WI sequences using the partial-Fourier method .
CT and MR features of pancreatic lymphoma
In previous reports, radiologic findings of secondary lymphoma with predominant pancreatic involvement were similar to those of primary pancreatic lymphoma including nodular, diffuse and multi-nodular types [14, 27, 28].
On CT imaging with intravenous contrast, most lesions are shown as well defined, sometimes bulky and infiltrating, homogeneous low-attenuation masses relative to the enhancing pancreatic parenchyma with only mild enhancement . However, lesions that are less well circumscribed may wrongly be misdiagnosed as pancreatic cancer and result in surgical intervention.
Less commonly, pancreatic lymphoma may present as diffuse enlargement of the gland with an infiltrative tumour that could mimic acute pancreatitis. It is important to note that typical features of acute pancreatitis, including peripancreatic fat stranding and peripancreatic inflammation, are usually minimal if even present. Peripancreatic fluid collections and fat necrosis are typically absent in infiltrating pancreatic lymphoma. To our knowledge, pancreatic ductal disconnection and disruption seen with severe acute pancreatitis has not been reported in lymphoma. Vascular encasement or invasion is rarely seen with pancreatic lymphoma . Although vessels may be stretched because of a mass effect, irregularity and caliber changes due to tumour invasion are generally absent. Intravascular lymphomatosis is a rare type of malignant lymphoma, whose pathologic findings have been reported .
MRI is an excellent modality for detecting and diagnosing pancreatic lesions as well as assessing the extent of involvement, since the tissue contrast is far superior compared with CT. In general, pancreatic lymphomas appear as homogeneous, low-signal-intensity, focal nodular areas on T1WI, with variable, low or high signal intensity on T2WI, and a generally circumscribed, less-enhanced area relative to surrounding parenchyma on DCE-MRI [13, 28]. Unlike CT, MRI shows a slightly heterogeneous character of the lesion, especially on T2WI. Islet cell tumours, although circumscribed, tend to show more hyperintensity than lymphoma on T2W images. There are no reports describing pancreatic lymphoma on DWI; however, whole-body DWI is already playing an important role in detecting and staging in lymphoma patients.
Following administration of intravenous gadolinium-based contrast agents, lymphomatous deposits enhance homogeneously, but to a lesser degree than normal parenchyma. Some lymphomatous lesions can appear mildly inhomogeneous on MRI. On the other hand adenocarcinoma of the pancreas tends to enhance less because of the desmoplastic content and is typically inhomogeneous post gadolinium.
Comparison of MR findings among malignant lymphoma, autoimmune pancreatitis and pancreatic adenocarcinoma
Speckled hyperintensity on FST1WIa
Target appearance on T2WIb
Duct-penetrating sign (in focal lesions)
Marked upstream MPD dilatation
Speckled enhancement on PP DCE-MRIc
Homogeneous enhancement on EP DCE-MRI
Target appearance on PP or EP DCE-MRIb
Without delayed enhancement
Diffuse enlargement (sausage appearance)
Capsule-like rim (in diffuse lesions)
Vascular involvement without obstruction
Lymphadenopathy below the level of the left renal vein
Other organ involvement
None (primary)/common (secondary)
Well-circumscribed nodular type with solitary pancreatic mass
Diffuse type with pancreatic enlargement
Peripheral lymphomatous involvement, mimicking autoimmune pancreatitis
Invasion from an adjacent peri-pancreatic lymphomatous lesion
MRI findings of primary and secondary lymphoma may at times not be sufficiently specific to render a diagnosis, especially when pancreatic involvement is the first or only finding. Rather, other parameters must be considered, including clinical presentation and relevant imaging studies.
Radiologists should, however, be well versed in these varied imaging manifestations, as well as the characteristic findings of pancreatic lymphoma and its mimickers, to avoid misdiagnosis and unnecessary surgery. In a few cases, the findings of pancreatic lymphoma may be confusing and endoscopic biopsy should be suggested to arrive at a definitive diagnosis.
We thank Dr. Hiroyoshi Ota for pathological instructions.
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