Morphological imaging sorts out cystic lesions of pancreas

Cystic lesions of the pancreas tend to be a phenomenon of aging. These lesions tend to be benign, but sorting out the small number with 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 signs and symptoms such as jaundice, weight loss, and anorexia (J Gastrointest Surg 2008;12:234-242).

Jeffrey also cited features observed on imaging 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 cannotbe 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;32:119-125).

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

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 ethanol ablation experienced long-term resolution of their cysts (Gastrointest Endosc 2005; 61:742-746).

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

PIECE OF PANCREAS PUZZLE

Recent research has bolstered CT's role in differentiating among pancreatic lesions. Drs. Stephan Anderson and Jorge Soto of Boston University Medical Center found that portal venous phase 64-slice CT images were moderately sensitive and highly specific for detecting pancreatic duct stricture, stones, and pancreas divisum and moderately accurate for detecting communication between pancreatic ducts and cystic pancreatic lesions (Abdom Imaging April 29, 2008, DOI 10.1007/s00261-008-9396-4).

Similarly, investigators in South Korea determined that shape and wall thickness are the main CT features for differentiating benign from premalignant and malignant macrocystic pancreatic lesions (Euro J Radiol April 28, 2008, DOI10.1016/ j.ejrad. 2008. 03.012).

Promising studies aside, CT is just one part of the total workup that pancreatic lesions call for, said Dr. Irving Waxman, director of the Center for Endoscopic Research and Therapeutics at the University of Chicago.

"Imaging is not a substitute for tissue (samples)," Waxman said. "I do think that there are CT features of lesions that can sway our decision one way or the other, but imaging is just one piece of the puzzle. CT is an invaluable tool, but it's still not at a level where we can rely on the CT and know exactly what to do."

Waxman emphasized that in addition to CT results, patient characteristics (age, comorbidities) and pathology results (cancer markers, fine-needle aspiration results) drive the course of clinical intervention.

"Patients are usually reluctant to undergo surgery because the CT looks abnormal," he said. "But when you tell them the cancer marker is elevated, or there are suspicious cells on an aspirate, both surgeons and patients are more convinced that it's worth taking the risk of a surgical resection."

Ms. Pal is deputy editor of Diagnostic Imaging.