Fig. 1. (A, B) Axial and coronal contrast-enhanced computed tomography scans reveal a 20-mm cystic lesion in the head of the pancreas during the arterial phase, with contrast enhancement observed in the cyst wall. A 4-mm nodule with strong contrast enhancement is also detected. (C) Contrast-enhanced endoscopic ultrasound using Sonazoid reveals contrast (GE Healthcare) enhancement in the cystic wall and nodule (arrow). (D) After puncturing with a 19-gauge fine needle aspiration needle, a biopsy is performed using 0.75-mm micro biopsy forceps (Moray Micro forceps; STERIS).

Fig. 2. (A) Biopsy specimen shows that tumor cells with round nuclei proliferated in a trabecular or alveolar pattern (hematoxylin & eosin [H&E] stain, ×10). Immunohistochemical staining is positive for chromogranin A, leading to the diagnosis of pancreatic neuroendocrine neoplasm. (B) In the loupe image of the resected specimen, a cyst with a thin capsule is observed. (C) In the magnified image of the red-framed area of the image (B) where the biopsy specimen is taken, densely proliferating tumor cells are observed in the cyst wall (H&E stain, ×100). (D) In the loupe image of immunostaining with chromogranin A, positivity is observed in the cyst wall, leading to the diagnosis of cystic degeneration of pancreatic neuroendocrine neoplasm.