星 進悦

Shin-etsu HOSHI

釜石市民病院消化器科

Department of Gastroenterology, Kamaishi Municipal Hospital

キーワード : Bile duct cystadenocarcinoma, <I>De novo</I> cystadenocarcinoma, Cancerization of simple cyst, Malignant transformation of cystadenoma, Ultrasonography

A 49-year-old woman with occasional pain in the upper abdomen was found to have a hemangioma-like tumor in the lateral segment of the left hepatic lobe on US and CT examination, and was hospitalized for acute hepatitis of unknown cause. The hepatitis improved rapidly under conservative treatment. At first the tumor was an irregular hyperechoic mass 2 cm in diameter with a relatively distinct boundary in the US images. Its diameter grew to 4 cm, a two-fold increase over 2 years, and the tumor became a well-demarcated hyperechoic mass with a halo. There was an internal hypoechoic region on the ventral side, and the hyperechoic structure appeared to be lobulated. On CT, an oval tumor showed a heterogeneous low-density internal structure; some structure was found inside of the tumor on contrast-enhanced CT, although the contrast was not distinct. MRI suggested that the tumor tended to be lobulated, having what, doubtfully, may have been septal structures. Gd-DTPA enhanced most of the center, but not the ventral side of the tumor, thus indicating cystic structure of the ventral region. DSA showed only vessel proliferation around the tumor, but there was no pooling of the contrast medium, which was characteristic of hemangiomas. A metastatic tumor, which was doubted following detailed analysis of the images, was also negative, because the primary lesion was not identified, in spite of careful analysis. Surgery was finally performed, because of the increase in tumor size and suspicion that it might be a malignant hepatic tumor, as suggested by the diagnostic images. The histologic diagnosis after surgery was bile duct cystadenocarcinoma without an adenomatous component. Diagnosis of this case was more difficult than that of previous cases because, here, a cystadenocarcinoma on the epithelium of the bile duct developed directly and unifocally into a single cyst, displaying rapid papillary tumor growth and a cystic component that is small because of the low cyst-forming ability of this lesion, explaining why this tumor was not recognized as a cystic lesion. Imaging findings for a bile duct cystadenocarcinoma in the past were based upon those of cancerization of a simple cyst, malignant transformation of a bile duct cystadenoma, or both. Imaging findings of a de novo cystadenocarcinoma, the rarest of the three types of bile duct cystadenocarcinoma, may resemble a solid tumor with a small cystic component rather than a cystic tumor, especially when it is small.