沼田 和司, 杉森 一哉, 森本 学, 田中 克明

Kazushi NUMATA, Kazuya SUGIMORI, Manabu MORIMOTO, Katsuaki TANAKA

横浜市立大学市民総合医療センター消化器病センター

Gastroenterological Center,Yokohama City University Medical Center

キーワード : autoimmune pancreatitis, contrast-enhanced ultrasound, pancreatic, Levovist, Sonazoid

自己免疫性膵炎とはびまん性もしくは一部の膵腫大と膵管狭細像，高γグロブリン血症，高IgG血症や自己抗体の存在，ステロイド治療が有効など，自己免疫機序の関与を示唆する所見を伴う稀な慢性膵炎である．多くの症例は総胆管の拡張を伴うが，主膵管の拡張は認めない．ハーモニックイメージによる造影超音波はアーチファクトがなく，膵腫瘤性病変の血管と濃染を評価することが可能である．自己免疫性膵炎と膵臓癌患者におけるLevovist^®とSonazoid^®による造影超音波の撮影方法であるが，両造影剤とも造影剤注入後約一分以内の数十秒間に病変の血管と濃染を経時的に観察し（early phase），造影剤注入後約1分半から3分の間に数秒間で腫瘍濃染を観察した（delayed phase）．膵臓癌ではearly phaseで腫瘍血管を認めるが，自己免疫性膵炎では明らかな腫瘍血管は認めなかった．膵臓癌では病変部の辺縁部が濃染され，自己免疫性膵炎では腫瘤全体が濃染した．自己免疫性膵炎の造影超音波での濃染の程度は，炎症が強く線維化が幼若な状態ほど濃染が強く，炎症が軽く線維化が古いほど濃染が弱かった．ステロイド治療後は炎症が沈静化し，造影超音波では濃染の程度が弱くなった．造影超音波は自己免疫性膵炎の血管性状と濃染の評価に有用であり，自己免疫性膵炎と膵臓癌との鑑別に有用である可能性がある．

Autoimmune pancreatitis is a rare form of chronic pancreatitis characterized by focal or diffuse swelling of the pancreas, irregular narrowing of the main pancreatic duct, hyperglobulinemia, presence of autoantibodies, and marked response to corticosteroid therapy. Patients with autoimmune pancreatitis often have dilatation of the common bile duct without dilatation of the main pancreatic duct. Contrast-enhanced harmonic gray-scale ultrasound has recently been used to evaluate the vascularity of pancreatic mass lesions; it can visualize blood perfusion in pancreatic mass lesions without producing motion artifacts. Patients with pancreatic carcinoma and autoimmune pancreatitis were required to hold their breath from 20 to 50 seconds after administration of Levovist^® (Schering AG, Berlin, Germany) or Sonazoid^® (GE Healthcare, Oslo, Norway) while the vascularity (tumor vessels and tumor enhancement) of the lesion was examined by contrast-enhanced harmonic gray-scale ultrasound (early phase). Lesion enhancement was monitored for about 90 to 180 seconds after the injection with patients holding their breath for several seconds (delayed phase). Although pancreatic carcinoma lesions exhibited some grade of tumor vessels, autoimmune pancreatic lesions showed no apparent tumor vessels in the early phase. Almost all pancreatic carcinoma lesions showed positive enhancement only in the peripheral tumor region; however, autoimmune pancreatitis lesions exhibited enhancement throughout the entire lesion in both the early and delayed phases. Grade of lesion vascularity in the contrast-enhanced harmonic gray-scale ultrasonograms correlated directly with pathologic grade of inflammation and inversely with grade of fibrosis associated with autoimmune pancreatitis lesions. Lesion vascularity had decreased on contrast-enhanced harmonic gray-scale ultrasonograms after steroid therapy. Contrast-enhanced harmonic gray-scale ultrasound was useful in evaluating vascularity of autoimmune pancreatitis lesion and may prove useful in the differential diagnosis between pancreatic carcinoma and autoimmune pancreatitis.