This is a biopsy-proven case of primary B-cell lymphoma of the duodenum. The duodenal mass results in obstruction of the common bile duct. The patient was managed with stenting of the common bile duct and chemotherapy. 

Lymphoma is the most common malignancy of the small bowel, and the distal ileum is the most common site of B-cell lymphoma because of the higher concentration of lymphoid tissue. 

Small bowel lymphoma can present as a circumferential bulky mass which extends into the mesentery and regional lymph nodes. It characteristically dilates the lumen without obstruction the GI tract (obstruction is more associated with adenocarcinoma). 

The differential diagnosis in this case would be lymphoma, adenocarcinoma and gastrointestinal stromal tumor. A biopsy could be performed endoscopically at the time of biliary decompression or with ultrasound/CT guidance.