Asymptomatic Metastatic Melanoma of the Gallbladder Diagnosed With Contrast-Enhanced Ultrasonography

Abstract

etastatic melanoma of the gallbladder is a rare entity, with series of autopsies reporting prevalence of 15% to 20% among patients deceased from melanoma.1,2 Nevertheless, melanoma is the most frequent tumor metastasizing to the gallbladder, accounting for 50% to 67% of all reported secondary malignancies at this site.3,4 Few cases of primary melanoma of the gallbladder have been reported in the literature, and some authors believe they are more likely metastases from a clinically occult primary tumor.5,6 Gallbladder involvement is typically asymptomatic. Less frequently, acute cholecystitis or obstructive symptoms are present. Ultrasonography is usually the first imaging modality used when gallbladder disease is suspected. Characteristic ultrasonographic features of melanoma metastasis to the gallbladder include a hyperechoic mass and diffuse thickening of the gallbladder.7–9 Gray scale ultrasonography is not able to show the vascularity of the tumor, which can be obtained using Doppler imaging. A low resistive index (<0.65) and a high blood velocity (20 cm/s) are more indicative of malignancy. However there is a great overlap between features of benign and malignant lesions.10 Therefore, contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) are frequently used to characterize masses in the gallbladder. Several reports have also documented the use of contrast-enhanced ultrasonography (CEUS) to evaluate gallbladder disease other than stones.11–13 Advantages of CEUS over CT are the absence of exposure to ionizing radiation and decreased cost of the procedure. In addition, these lesions are usually discovered during a conventional ultrasonographic examination, making it easy to immediately perform CEUS to characterize the lesion. We report a pathologically confirmed case of asymptomatic melanoma metastasis to the gallbladder diagnosed with CEUS and show that in patients with a history of malignancy that tends to metastasize to the gallbladder and in whom a mass is identified in the gallbladder on ultrasonography, CEUS allows the clinician to make a presumptive diagnosis of metastatic disease based on a vascular pattern typical of malignant lesions. Received January 19, 2010, from the Department of Radiology, University of Milan-Bicocca, Milan, Italy (A.A., M.F.M.); Department of Radiology, University of Wisconsin, Madison, Wisconsin USA (P.L.); Department of Radiology, San Gerardo Hospital, Monza, Italy (M.L., M.F.M.); Department of Radiology, University of Messina, Messina, Italy (F.Z.); and Legnano Hospital, Milan, Italy (V.D.). Revision requested January 25, 2010. Revised manuscript accepted for publication February 24, 2010. Address correspondence to Anita Andreano, MD, Department of Radiology, University of MilanBicocca, 33 Pergolesi St, 20052 Monza, Italy. E-mail: a.andreano@campus.unimib.it Abbreviations CEUS, contrast-enhanced ultrasonography; CT, computed tomography; MRI, magnetic resonance imaging