岩井 孝仁^{1, 2}, 西田 睦^{1, 2}, 表原 里実^{1, 2}, 薮崎 哲史³, 小川 浩司⁴, 岡村 圭祐⁵, 平野 聡⁵, 三橋 智子⁶, 加畑 馨¹, 清水 力¹

Takahito IWAI^{1, 2}, Mutsumi NISHIDA^{1, 2}, Satomi OMOTEHARA^{1, 2}, Satoshi YABUSAKI³, Koji OGAWA⁴, Keisuke OKAMURA⁵, Satoshi HIRANO⁵, Tomoko MITSUHASHI⁶, Kaoru KAHATA¹, 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診断科, ⁴北海道大学病院消化器内科, ⁵北海道大学病院消化器外科II, ⁶北海道大学病院病理診断科

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

キーワード : liver, inflammatory pseudotumor, contrast-enhanced ultrasonography, Sonazoid<SUP>&reg;</SUP>, case report

症例は40歳代女性．主訴なし．前医にて肝S₆の孤立性壊死性結節を経過観察中であった．造影CTにて，肝S₆結節は経時的にほぼ消失したが，新たに肝S₅に早期濃染を伴う10 mmの腫瘤性病変を指摘された．超音波検査（US）とGd-EOB-DTPA造影MRIを施行し，悪性病変を否定できず，切除希望のため当院紹介となった．当院での初回USにて，肝S₅に境界不明瞭な低エコー腫瘤を認め，Sonazoid^®造影超音波検査（CEUS）では，動脈相で微細点状の豊富な造影効果を認め，その後，結節状に強く造影された．門脈相で造影効果は遷延し，後血管相で造影効果は認めなかった．半年後のUSにて，肝S₅腫瘤に増大はみられず，CEUS動脈相，後血管相に著変はなかったが，門脈相で早期の造影効果減弱を認めた．造影CTでも門脈相，平衡相の洗い出しが明瞭化した．これらの変化は肝細胞癌の脱分化など悪性病変を否定できず，腹腔鏡下肝部分切除術が施行された．病理組織学的所見では，被膜を有さない境界明瞭な腫瘤で，炎症細胞浸潤を背景に小血管の増生を伴っていた．免疫染色でαSMA陽性，ALK陰性，EBER陰性，IgG4陽性細胞をほとんど認めず，炎症性偽腫瘍（IPT）と診断された．IPTは特徴的な画像所見に乏しく，CEUSでIPTを経過観察し得た報告は少ない．今回，経時的にCEUS所見が変化したIPTの1症例を経験したので，若干の文献的考察を含めて報告する．

=Hepatic inflammatory pseudotumor (IPT) is a rare benign disorder with non-specified image findings that depend on the inflammatory stage. Here, we report a case of hepatic IPT with contrast-enhanced ultrasonography (CEUS) findings that changed over time. The female patient in her 40s was referred to us for close examination of a new lesion appearing in hepatic segment 5 on contrast-enhanced computed tomography (CT) during follow-up for a solitary necrotic nodule in hepatic segment 6. Ultrasonography revealed a 13-mm hypoechoic solid lesion with an ill-defined border in her liver. At the first visit, the new hepatic nodule showed a strong homogeneous enhancement pattern in the arterial phase of CEUS, while it showed a prolonged enhancement pattern in the portal phase of CEUS. In the post-vascular phase, the nodule showed an enhancement defect. Six months after these initial findings, the contrast enhancement pattern in the portal phase had changed into a washout pattern. The nodule showed a washout pattern in both the portal and equilibrium phases of contrast-enhanced CT. As dedifferentiation of hepatocellular carcinoma was not ruled out, laparoscopic partial hepatectomy was performed. The resected specimen clearly showed a distinct tumor without a capsule. Pathological findings showed an increased number of spindle cells and small blood vessels with infiltration of inflammatory cells including plasma cells in the tumor. The nodule was diagnosed as IPT. This case suggested that follow-up with CEUS might be useful to diagnose IPTs for hypoechoic solid lesions with ill-defined borders.