Question: A 38-year-old woman presentedwith a 2-month history of abdominal discomfort. She denied fever orweight loss. The physical examinationwas normal. She underwent a transabdominal ultrasound and computed tomography of the abdomen,which found a mass with annular calcification in the uncinate process of the pancreas. The cyst was almost completely encircled by calcification (Figure A, arrow). T2-weighted MRI showed a high-intensity cystic mass that was 3 cm in diameter (Figure B, arrow). Laboratory tests excludedpancreatic hydatid cyst and tuberculosis, and tests for echinococcal antigens andQuantiFERON-TBwere negative. Endoscopic ultrasonography revealed a cyst that had an almost completely calcified wall in the uncinate process and an acoustic shadow close to the mesenteric vessels (Figure C, arrow). The surrounding parenchyma was normal. An endoscopic ultrasound-guided biopsy of the cyst was performed with a 19-G needle, and 10 mL of a yellowish fluid were obtained. A few seconds after aspiration, thefluid in the syringe became gelatinous. The carcinoembryonic antigen level in the fluidwas 1.4 ng/mL, and amylase was 222 U/L. Cytologic examination showed inflammatory cells, but no malignant cells were observed. After prophylactic endoscopic stenting of the main pancreatic duct, the patient underwent surgical enucleation of the mass. The lesion was as stiff as a bone. Figure D shows a gross section of the pancreatic cyst. Figures E shows a hematoxylin and eosin–stained microscopic section of the cystic wall that had calcification and osseous metaplasia. Figure F shows a hematoxylin and eosin–stained microscopic section with bland polygonal cells with pseudopapillary arrangement and immunohistochemical cytoplasmic and nuclear labeling for b-catenin. The patient’s postoperative recovery was complicated by a low-output pancreatic fistula that spontaneously resolved in 15 days. What is the diagnosis? Look on page 321 for the answer and see the Gastroenterology web site (www.gastrojournal.org) for more information on submitting your favorite image to Clinical Challenges and Images in GI.