表原 里実^{1, 2}, 西田 睦^{1, 2}, 佐藤 恵美^{2, 3}, 工藤 悠輔^{1, 2}, 作原 祐介⁴, 三橋 智子⁵, 柿坂 達彦⁶, 横尾 英樹⁶, 神山 俊哉⁶, 清水 力¹

Satomi OMOTEHARA^{1, 2}, Mutsumi NISHIDA^{1, 2}, Megumi SATOH^{2, 3}, Yusuke KUDOH^{1, 2}, Yusuke SAKUHARA⁴, Tomoko MITSUHASHI⁵, Tatsuhiko KAKISAKA⁶, Hideki YOKOO⁶, Toshiya KAMIYAMA⁶, Chikara SHIMIZU¹

¹北海道大学病院検査・輸血部, ²北海道大学病院超音波センター, ³北海道大学病院放射線部, ⁴北海道大学病院放射線診断科, ⁵北海道大学病院病理部, ⁶北海道大学病院消化器外科I

¹Division of Laboratory and Transfusion Medicine, Hokkaido University Hospital, ²Diagnostic Center for Sonography, Hokkaido University Hospital, ³Department of Radiological Technology, Hokkaido University Hospital, ⁴Department of Diagnostic and Interventional Radiology, Hokkaido University Hospital, ⁵Department of Surgical Pathology, Hokkaido University Hospital, ⁶Department of Gastroenterological Surgery I, Hokkaido University Hospital

キーワード : Inflammatory myofibroblastic tumor, liver, contrast-enhanced ultrasonography, Sonazoid<SUP>&reg;</SUP>

32歳，女性．胃部不快感と発熱で近医受診するも改善せず，右季肋部痛も出現したため当院受診．腹部超音波（US）では，肝S_5，8を主体に径106 mmの境界明瞭輪郭整な等‐低エコー腫瘤および右肝静脈内に連続する超音波像がみられた．Sonazoid^®造影では，動脈優位相血管イメージで腫瘤内に流入する屈曲した索状の造影効果，潅流イメージにて不均一な強い造影効果，門脈優位相で造影効果は軽度減弱．また，造影効果不良域を認め出血，壊死を疑った．Micro Flow Imagingでは右肝静脈内の超音波像内に豊富な血管構築を認め腫瘍栓の所見であった．後血管相では分葉状の欠損像を呈した．CTでは，動脈相で不均一濃染，平衡相でのwash outは認めなかった．造影MRIでは，T1強調像で均一な低信号，T2強調像で不均一な高信号を呈し，肝細胞相では造影剤の取り込みは低下していた．肝細胞癌，癌肉腫，混合型肝細胞癌など悪性腫瘍が疑われ右葉切除施行．病理組織学的に，豊富な粘液浮腫状間質を背景に，紡錘形細胞が個在性に増殖，小型リンパ球様細胞を伴う樹枝状血管が豊富に介在していた．炎症性筋線維芽細胞性腫瘍（Inflammatory myofibroblastic tumor: IMT）と診断された．肝原発IMTはきわめてまれで悪性腫瘍との鑑別が困難とされる．造影USを施行し得た肝IMTを経験したので報告する．

A 32-year-old woman complaining of stomach discomfort and high fever was referred to our hospital because of prolonged symptoms and the appearance of right upper quadrant abdominal pain. Ultrasonography visualized a 106mm iso-hypoechoic nodule with a clearly defined border in mainly hepatic segments 5 and 8. The hypoechoic lesion extended from the nodule to the right hepatic vein. The arterial phase of contrast-enhanced ultrasonography (CEUS) revealed a hypervascular, non-tortuous structure during the vascular image, and then showed a strong, inhomogeneous enhancement pattern during the perfusion image. In the portal phase, the strong enhancement pattern was slightly washed out. On Micro-Flow Imaging, an intense vessel structure was seen in the right hepatic vein that suggested a tumor thrombus. The poorly enhanced area indicated bleeding or a hemorrhage. The nodule was visualized as an enhancement defect in the post-vascular phase. Contrast-enhanced computed tomography showed an inhomogeneous, hyperenhanced pattern in the arterial phase. Contrast media washout was not seen in the delayed phase. MR T₁-weighted imaging showed homogeneous, low signal intensity, while T₂-weighted imaging showed heterogeneous, high signal intensity. The preoperative diagnosis was a malignant tumor such as a hepatocellular carcinoma, carcinosarcoma, or combined hepatocellular and cholangiocarcinoma. A histopathological examination revealed a proliferation of spindle cells in the background of myxoid stroma with arborizing blood vessels and small lymphocytic cells. The tumor was diagnosed as an inflammatory myofibroblastic tumor (IMT). IMT of the liver is rare and difficult to distinguish from malignant tumors. We report a case of IMT of the liver.