A 62-year-old man presented with pain in the abdomen radiating to the back and dyspepsia since one month. There was no history of any other major illness. On examination, there was a well defined palpable mass in the epigastrium associated with mild tenderness. Routine blood investigations were normal. Serum amylase was normal. Serum lipase level was increased (1531 IU/L). Serum levels of CA 19-9 (tumor marker for pancreatic carcinoma) were normal.

RADIOLOGICAL FINDINGS:

Ultrasonographic findings:
There was a large, well-defined, hypoechoic mass (approximately 12x10x10 cm in size ) arising from the body of the pancreas.

CT findings (Figs 1-5):
A soft tissue density mass was noted in the upper abdomen - arising from the body of the pancreas and extending anteriorly and cranially- causing encasement of the celiac artery and its branches and occupying most of the lesser sac. The mass showed minimal homogenous enhancement after intravenous contrast administration. There was loss of fat planes between the mass and the stomach and the left lobe of the liver. There was no calcification seen in the mass. Incidentally noted were a right renal cyst and a simple cyst in the right lobe of the liver. A few calcified granulomas were also seen in spleen.

Fig. 1	Fig. 2
Fig. 3	Fig. 4
Fig.5

MR findings: (Figs 6-9) On T1W images, a well defined homogenously hypointense mass was seen in the upper abdomen, arising from the body of the pancreas. The lesion appeared hyperintense on T2W images .The mass was seen invading the anterior structures including the posterior wall of stomach and the left lobe of the liver. The pancreatic duct was not dilated. The tail of the pancreas was normal. The mass showed encasement of vessels including the celiac artery and its branches and the splenic vein. The liver and spleen were of normal size.

Fig.6			Fig.7
Fig.8			Fig. 9

USG guided biopsy:
An ultrasound guided Tru-Cut biopsy was performed under local anesthesia. .Histopathological evaluation revealed sheets of small round cells of apparent lymphoid origin. The cells showed hyperchromatic nuclei and scanty cytoplasm. These features were suggestive of low grade malignant lymphoma (NHL).

FINAL DIAGNOSIS: Pancreatic lymphoma

DISCUSSION:

In lymphoma, primary involvement of the pancreas is uncommon, representing 2% to 5% of cases of extranodal lymphomas, comprising less than 0.5% of pancreatic tumours. Many of these cases occur in patients who are immunocompromised hosts - particularly patients infected with HIV.

Lymphoma, predominantly the non Hodgkin B cell subtype, involves the pancreas secondarily in approximately 30% of patients with widespread disease. It usually spreads to the pancreas by direct extension from peripancreatic lymphadenopathy.

To distinguish PPL (primary pancreatic lymphoma) from secondary involvement of the pancreas by non-Hodgkin's lymphoma, Behrns' clinical and diagnostic criteria of PPL include:

1. Mass predominantly within the pancreas with grossly involved lymph nodes confined to the peripancreatic region
2. No palpable superficial lymphadenopathy
3. No hepatic or Splenic involvement
4. No mediastinal nodal enlargement on chest radiograph
5. Normal white cell count.

AGE: The disease mainly affects middle age and elderly patients

SEX: Male to female ratio is around 1.4: 1

PRESENTING SYMPTOMS are non-specific, typically including abdominal pain, weight loss, nausea and vomiting, but also jaundice, acute pancreatitis, and small bowel obstruction.

RADIOLOGICAL FINDINGS:

USG Findings:
Sonography reveals a homogeneous, sonolucent, or complex mass. These masses are usually echo-poor and may mimic cystic lesions. Transabdominal sonography allows the detection of enlarged peripancreatic and periaortic lymph nodes and dilatation of the common bile and pancreatic ducts. Doppler waveform scanning, provide information about the patency of the major peripancreatic vessels, the celiac and superior mesenteric arteries, and the portal, superior mesenteric, and splenic veins.

CT Findings:
CT is the most common imaging technique used in the detection and characterization of primary pancreatic lymphoma.
Pancreatic lymphomas generally appear as homogeneous soft tissue mass, showing little enhancement after intravenous contrast administration. Intrinsic involvement of the pancreas may be difficult to differentiate from lymphoma affecting the peripancreatic lymph nodes.
Two distinct CT patterns have been described, including focal and circumscribed single or multiple masses and diffuse enlargement of the gland by an infiltrating tumor. The latter appearance can be associated with involvement of the peripancreatic fat and mimic acute pancreatitis on CT.
Encasement of the peripancreatic vessels may occur, but dilatation of the pancreatic duct is uncommon, despite the presence of bulky tumor, a helpful distinguishing feature from adenocarcinoma.
The presence of associated lymphadenopathy below the level of the renal veins also favors the diagnosis of lymphoma.

MR Imaging :
Two different morphologic patterns of pancreatic involvement are seen on MR imaging that are similar to the CT appearance.
The well-circumscribed tumoral type appears as a low-signal-intensity homogeneous mass within the pancreas on T1-weighted images with subtle enhancement after IV administration of gadolinium-containing contrast medium. On T2-weighted images, a tumoral mass shows a more heterogeneous character with a low to intermediate signal amplitude slightly higher than that of the residual gland but much lower than the signal intensity of fluid.
The diffuse infiltrating type of pancreatic involvement shows similar characteristics of low signal intensity on unenhanced T1- and T2-weighted images, with mild to moderate enhancement after gadolinium injection. In the diffuse infiltrating type, enhancement is predominately homogeneous but may include small foci of little or no gadolinium uptake. Bile and pancreatic ductal dilatation can be easily assessed with MR imaging using MR cholangiopancreatography .

ERCP and Percutaneous Transhepatic Choledochography
Unlike pancreatic adenocarcinoma, moderate to severe dilatation of Wirsung's duct is apparently rare in pancreatic lymphoma because Wirsung's duct is either normal, displaced or simply narrowed in patients with pancreatic lymphoma.
Bile duct dilatation from obstruction is seen more often because jaundice occurs in 42% of patients with non-Hodgkin's lymphoma primarily involving the pancreas.

Diagnosis, Treatment, and Prognosis:
As the prognosis of a pancreatic lymphoma is favorable, its differentiation from a carcinoma is crucial. The correlation of USG , CT and MR findings may result in a correct diagnosis. However, if doubt exists, biopsy may reveal the true nature of the mass.
Percutaneous(usg guided) or endoscopic core biopsy should be performed to establish the diagnosis. In most patients, the diagnosis can be established without surgery; this fact is a major reason to look for findings suggestive of pancreatic lymphoma.

Summary
When the radiologist is faced with a well-circumscribed tumoral mass in the pancreas, knowing when to direct the patient toward non-surgical biopsy instead of surgical biopsy is critical. Lymphoma does not require surgical staging or a palliative Whipple's procedure before chemotherapy or radiation therapy. In patients with primary pancreatic lymphoma, no marked pancreatic ductal dilatation is present even with ductal invasion. Adenocarcinoma commonly dilates the more distal pancreatic duct when more proximal ductal invasion has taken place. Lymph node involvement below the level of the renal veins is another finding not seen with adenocarcinoma. Clinical and imaging findings are otherwise not specific in the differentiation of pancreatic lymphoma and pancreatic cancer, but a bulky homogeneous tumoral mass without alteration of Wirsung's duct or the peripancreatic vessels should suggest the diagnosis. In patients with diffuse infiltration of the pancreatic gland without clinical signs of pancreatitis, the radiologist should be alert to the possibility of pancreatic lymphoma.