Background : The Primary mucosa-associated lymphoid tissue (MALT) lymphoma of the gallbladder (GB) is an extremely uncommon occurrence. Many patients exhibit symptoms like gallstone disease, and in some cases, the lymphoma may be detected through imaging even without apparent symptoms.

Methods : Differential diagnosis from typical GB carcinoma based solely on imaging findings can be challenging, and definitive diagnosis often requires surgical intervention. We present a patient in an 82-year-old man who was initially diagnosed with prostate cancer but incidentally detected GB wall thickening from magnetic resonance imaging (MRI) conducted for prostatic surgery and and subsequent radical cholecystectomy revealed primary MALT lymphoma of the GB.

Results : The patient was followed up by a oncologist, and after discussion, the decision was made to continue observation with close monitoring without systemic chemotherapy given the asymptomatic presentation. The patient has been free of recurrence for 11 months after the surgery. Although precise diagnosis before the surgery was difficult in this case, preoperative examinations revealed a submucosal tumour-like lesion

Conclusions : MALT lymphomas should be considered when imaging findings are atypical for gallbladder carcinoma.