Pancreatic pseudotumors: non-neoplastic solid lesions of the pancreas that clinically mimic pancreas cancer.

In the pancreas, a variety of non-neoplastic conditions may form solid masses that may mimic cancer. Up to 5% of pancreatectomies performed with the preoperative clinical diagnosis of carcinoma will prove to be non-neoplastic by pathologic examination, although this figure is decreasing with improved diagnostic modalities. Chronic inflammatory lesions are the leading cause of this phenomenon ("pseudotumoral pancreatitis"), and among these, autoimmune and paraduodenal pancreatitides (discussed separately in this issue) are most important. In this article, we will focus on the noninflammatory lesions that may form tumor-like lesions of the pancreas. Adenomyomatous hyperplasia of ampulla of Vater is a subtle lesion that is difficult to define; larger examples (>5 mm) have been found to be the cause of obstructive jaundice. Accessory (heterotopic) spleen may form a well-defined nodule within the tail of the pancreas and is typically mistaken for endocrine neoplasm. Lipomatous hypertrophy is the replacement of pancreatic tissue with mature adipose tissue that occasionally leads to moderate to marked enlargement of the pancreas. Hamartomas are very rare if the entity is defined strictly. They are characterized by irregularly arranged mature pancreatic elements admixed with stromal tissue. A cellular, spindle-cell variant with c-kit (CD117) expression is recognized. Pseudolymphoma forms well-defined nodules composed of hyperplastic lymphoid tissue. Rarely, foreign-body deposits, granulomatous inflammations (such as sarcoidosis or tuberculosis), and congenital lesions may form tumoral lesions. In conclusion, it is important to recognize the types of conditions that form pseudotumors in the pancreas so that they can be distinguished from ductal adenocarcinomas, especially clinically, but also pathologically. Nonspecific terms such as "inflammatory pseudotumor" ought to be avoided, and every attempt should be made to classify a "pseudotumor" into a more specific diagnostic category discussed above.