石川 卓哉¹, 川嶋 啓揮², 大野 栄三郎¹, 水谷 泰之¹, 藤城 光弘¹

Takuya ISHIKAWA¹, Hiroki KAWASHIMA², Eizaburo OHNO¹, Yasuyuki MIZUTANI¹, Mitsuhiro FUJISHIRO¹

¹名古屋大学大学院医学系研究科消化器内科学, ²名古屋大学医学部附属病院光学医療診療部

¹Department of Gastroenterology, Nagoya University Graduate School of Medicine, ²Department of Endoscopy, Nagoya University Hospital

キーワード : imaging diagnosis, autoimmune pancreatitis, endoscopic ultrasonography, contrast-enhanced endoscopic ultrasonography, elastography

自己免疫性膵炎（AIP）の診断は容易ではなく，臨床所見，画像所見，血清学的所見，病理学的所見などを総合的に評価する必要がある．超音波内視鏡検査（EUS）は，既存のどの画像診断モダリティよりも詳細に膵実質や膵管所見を評価することが可能であり，AIP診断においても有用性が期待される．この論文では，AIPの診断における，EUSの通常観察，EUSエラストグラフィ（EUS-EG），造影ハーモニックEUS（CEH-EUS）という3つの手法に焦点をあてた．EUS通常観察において，びまん性低エコー域，びまん性腫大，胆管壁肥厚，膵周囲低エコー帯はAIPに特徴的であり，これらの所見の頻度は膵癌（PC）よりもAIPで有意に高い．AIPの膵実質のEUS-EGは均一な硬さを示し，ステロイド治療後には膵臓の硬さが変化する可能性がある．CEH-EUSでは，ほとんどのAIP症例で限局性またはびまん性のiso-enhancement（周囲と同等の造影効果）が，また，ほとんどのPC症例でhypo-enhancement（周囲よりも弱い造影効果）が認められる．しかし，一部のAIP症例はPCと同様の造影パターンを示す．AIPのEUS所見は，病期や疾患活動性によって異なる可能性があることに注意が必要である．AIPの診断過程において，PCとの鑑別はますます重要な課題となっており，通常のEUS観察に加え，EUS-EGやCEH-EUSは，そのための有望な画像診断モダリティとなり得る．

The diagnosis of autoimmune pancreatitis (AIP) is challenging and should be achieved through the comprehensive evaluation of clinical, radiological, serological, and pathological evidence, as there is currently no single reliable diagnostic modality. Endoscopic ultrasonography (EUS) can reveal pancreatic parenchymal and ductal features in much more detail than any other existing imaging modality. In this article, we focused on three applications of EUS, i.e., conventional EUS imaging, EUS elastography (EUS-EG), and contrast-enhanced harmonic EUS (CEH-EUS), for the diagnosis of AIP. Diffuse hypoechoic areas, diffuse enlargement, bile duct wall thickening, and peripancreatic hypoechoic margins on conventional EUS are characteristic features of AIP, and the frequencies of these findings are significantly higher in AIP than in pancreatic cancer (PC). EUS-EG of the pancreatic parenchyma in AIP showed homogenous stiffness and that the elasticity of the pancreas may change after steroid therapy. CEH-EUS revealed focal or diffuse iso-enhancement in most AIP cases and hypo-enhancement in most PC cases. However, some AIP cases show a contrast enhancement pattern similar to that of PC. It should be noted that EUS findings of AIP may differ depending on its stage or disease activity. Differentiation from PC has become an increasingly important issue in the process of diagnosing AIP, and EUS, including elastography and contrast enhancement, could be a promising imaging modality for this purpose.