CT Findings of Various Cystic Pancreatic Tumors Overlap

Abstract & Commentary

Synopsis: Substantial overlap exists in the CT findings of benign and malignant cystic pancreatic neoplasms, so differential diagnosis requires a cautious approach.

Source: Curry CA, et al. CT of primary cystic pancreatic neoplasms: Can CT be used for patient triage and treatment? AJR Am J Roentgenol 2000;175:99-103.

Although pseudocysts are the most common cystic lesions of the pancreas, other cystic lesions also are encountered occasionally at CT, including simple cysts, serous (microcystic) neoplasms, and mucinous (macrocystic) neoplasms. Serous pancreatic neoplasms are cystadenomas without malignant potential, whereas mucinous pancreatic neoplasms can be cystadenomas that have a definite potential to become malignant, or they can be frankly malignant cystadenocarcinomas. Serous pancreatic neoplasms can be managed by periodic imaging follow-up (to assess for lesion stability), but mucinous pancreatic neoplasms should be surgically excised.

Curry and colleagues tested the ability of three radiologists to retrospectively distinguish serous from mucinous primary cystic pancreatic neoplasms at CT in 50 patients. They found that the reviewers could correctly diagnose serous neoplasms in only 23-41% of cases. Serious errors occurred; for example, eight mucinous tumors were categorized as benign serous tumors by two of the three radiologists. Using a consensus between at least two of the radiologists, all of the mucinous tumors were correctly categorized as either mucinous or indeterminate. Multivariate logistic regression analysis revealed that a tumor whose largest cyst was smaller than 2 cm had a statistically significant likelihood of being a serous tumor. Peripheral calcifications were seen only in mucinous tumors. Curry et al concluded that CT is not an accurate technique for distinguishing between serous and mucinous cystic neoplasms of the pancreas, and thus the findings at CT must be interpreted cautiously to appropriately guide patient triage and treatment.

COMMENT BY DAVID M. PANICEK, MD

Cystic lesions of the pancreas are commonly found at CT in patients with current or previous pancreatitis, and occasionally as incidental findings in patients being scanned for indications unrelated to the pancreas. The nature of many cystic pancreatic lesions can be deduced from the combination of clinical, laboratory, and radiologic findings. However, particularly in the case of the cystic pancreatic lesion incidentally discovered on CT, the exact diagnosis may remain elusive. Some serous cystadenomas of the pancreas exhibit classic radiologic features, with all cysts measuring smaller than 2 cm and some coarse calcifications occurring in the center of the tumor; similarly, some typical mucinous pancreatic neoplasms consist of large cysts containing mural nodules, with calcifications in the periphery of the tumor. However, as Curry et al illustrated, a serous cystadenoma can manifest as a large unilocular cyst (9 cm in diameter in the case illustrated in their figure 5), and a mucinous cystadenoma can be quite small (1.8 cm in diameter in the case illustrated in their figure 6). And, as Curry et al note, other types of pancreatic lesions (including pseudocysts) that could mimic cystic pancreatic neoplasms at CT were not included in their study, further emphasizing the difficulties one can anticipate when evaluating cystic pancreatic lesions.

The existence of such overlap mandates that the radiologist use considerable caution in formulating an appropriate differential diagnosis of a primary cystic pancreatic lesion, with particular attention to specifying the need for further evaluation. Careful integration of clinical, laboratory, and radiologic features may allow a specific diagnosis of pancreatic pseudocysts, cysts, and some serous cystadenomas with a high degree of certainty; in such cases, periodic follow-up imaging to assess for stability of the lesion should be recommended. For cystic pancreatic lesions that exhibit any atypical features for these particular diagnoses, or that show features typical of mucinous cystadenoma or cystadenocarcinoma, surgical biopsy and/or excision are indicated.