Morphology sorts out benign and malignant lesions in pancreas

Cystic lesions of the pancreas tend to be a phenomenon of aging. By and large, these lesions are benign, but sorting out the small number that have potential for malignancy is important.

Dr. R. Brooke Jeffrey, chief of abdominal imaging at Stanford University, shared his approach to incidental small pancreatic cystic lesions at the 2008 Stanford International Symposium on Multidetector-Row CT in Las Vegas.

"One unintended consequence of scanning with multislice CT and thin collimation is that you see these incidental findings with disturbing frequency," Jeffrey said. "Pathologists recognize at least six different histologic variants of cystic lesions. We have the ability with imaging, based on morphologic features, to see three of these. We are often not able, however, to distinguish epithelial cysts from mucinous cystic neoplasms."

Jeffrey outlined criteria for making the distinction between benign and potentially serious lesions. The first is size: If the lesion is larger than 3 cm, the risk of malignancy goes up substantially.

"If you have a lesion larger than 3 cm, most centers recommend endoscopic ultrasound needle aspiration, looking specifically for mucin and carcinoembryonic antigen," he said.

If the lesion is under 3 cm, then clinical and imaging features come into play. Clinical features that are more indicative of malignancy are male gender, older age, and symptoms such as jaundice, weight loss, and anorexia (J Gastrointest Surg 2008:12:2:234-242).

On imaging, Jeffrey cited features that should raise red flags: presence of solid tissue in the cystic lesion, ductal obstruction, regional lymphoadenopathy, and interval enlargement.

He cautioned that the overlap between mucinous cysts and thin-walled epithelial cysts cannot be teased out by imaging criteria alone. Shaggy necrotic carcinomas with no definable cyst walls should not be misconstrued as cystic lesions. These findings should be subjected to needle aspiration or even surgery, he said.

Two types of cysts, however, can be called benign based on imaging features and marked for follow-up: side branch intraductal papillary mucinous neoplasms and serous microcystic ademonas. The adenomas are distinguished by a honeycomb-like morphologic appearance, Jeffrey said (Abdom Imaging 2007:32:1:119-125).

The question of follow-up remains open-ended. Empirical evidence states that lesions at 1 cm or smaller should be tracked at a one-year interval, while larger lesions need to be revisited every six months, but these are suggestions and not hard and fast rules, Jeffrey said.

Another option is to treat the cysts with endoscopic ultrasound-guided ethanol ablation. The cysts are aspirated prior to alcohol-based lavage. In a pilot study at Massachusetts General Hospital, patients who underwent enthanol ablation experienced long-term resolution of their cysts (Gastrointest Endosc 2005:61:6:742-746).

"Look for this as a potential therapeutic intervention in the near future," Jeffrey said.