Microcystic features at US: a nonspecific sign for microcystic adenomas of the pancreas.

Microcystic adenoma of the pancreas is a benign tumor with no malignant potential and may not require surgery if it is asymptomatic. In the past, a mass containing more than six small (<2-cm) cysts at ultrasonography (US) has been considered to be diagnostic for microcystic adenoma. However, a retrospective study of 36 patients with focal or diffuse pancreatic lesions containing over six small cysts demonstrated that this finding can occur in a wide variety of neoplastic and inflammatory lesions, most of which are malignant. These lesions included adenocarcinoma (n = 18), mucinous cystadenocarcinoma (n = 2), islet cell carcinoma (n = 1), lymphoma (n = 1), sarcoma (n = 1), metastases (n = 2), pancreatitis (n = 4), and adenoma (n = 7). Thus, a finding of multiple small cysts in a pancreatic mass is not specific for microcystic adenoma, and if diagnosis is based on US findings alone, many malignant tumors will be misdiagnosed as microcystic adenomas. Furthermore, computed tomography provides only limited assistance in this setting due to overlapping findings. Needle biopsy can be highly accurate in diagnosing both microcystic adenoma and other malignant lesions and should generally be performed for all lesions with the US features described earlier.