Final answer:
The correct diagnosis code for a patient with a postoperative diagnosis of pancreatic mass is C25.9.
Step-by-step explanation:
The correct diagnosis code for a patient with a postoperative diagnosis of pancreatic mass is C25.9. According to the ICD-10-CM Alphabetic Index, the code C25.9 represents the diagnosis of malignant neoplasm of pancreas, unspecified. This code is used to document a pancreatic mass or tumor without specifying whether it is benign or malignant. Other codes listed (A.K86.89, B.D01.7, D.D37.8) do not specifically correspond to a postoperative diagnosis of pancreatic mass.