山下 泰伸, 北野 雅之

Yasunobu YAMASHITA, Masayuki KITANO

和歌山県立医科大学第2内科

Second Department of Internal Medicine, Wakayama Medical University

キーワード : endoscopic ultrasound, contrast-enhanced harmonic endoscopic ultrasound, endoscopic ultrasound-fineneedle aspiration, pancreatic solid lesion

予後不良の膵がんの罹患数と死亡数は急速に増加している．超音波内視鏡検査（endoscopic ultrasonography: EUS）は，経腹壁超音波検査，コンピューター断層撮影（CT），磁気共鳴映像法（MRI）などと比較して，空間分解能が優れており，膵疾患診断における最も有用な診断モダリティの1つと考えられている．EUSは膵充実性病変の診断および膵がんの病期分類に重要な診断ツールである．また，EUSは，膵がんのリスクファクターを持つ患者のスクリーニングでも重要な役割を果たす．EUSは膵小病変の検出に有効であるが，BモードEUSを用いて，鑑別診断を行うには限界がある．これは，ほとんどの膵充実性病変は，低エコー腫瘤として描出されるからである．この観点から，膵病変の鑑別診断において，造影ハーモニックEUS（contrast-enhanced harmonic EUS: CH-EUS）が重要な役割を果たす．CH-EUSはBモードEUSに比べ，膵がんの病期分類においても有用である．さらに，超音波内視鏡下穿刺吸引法（EUS-guided fine-needle aspiration: EUS-FNA）を用いて，病理学的診断が可能であり，他のモダリティよりも優れている．EUS-FNAのみでも膵がんの診断能は高いが，EUS-FNAとCH-EUSを組み合わせると，偽陰性症例数が減るため診断能が改善する．そのため，BモードEUS，EUS-FNA，CH-EUSは，膵充実性病変の診断，膵がん病期分類するために不可欠である．

The incidence and mortality rates of pancreatic cancer, which has a poor prognosis, are rising rapidly. Endoscopic ultrasonography (EUS) provides superior spatial resolution compared with other imaging modalities such as transabdominal ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI), and it is considered among the most reliable and efficient diagnostic modalities for pancreatic diseases. In this review, we show that EUS is useful for detection of pancreatic solid lesions and staging of pancreatic cancer. EUS also plays an important role in screening patients with high-risk factors for pancreatic cancer. Although EUS is useful for detection of small pancreatic lesions, pancreatic lesions are difficult to characterize using this modality, because most pancreatic solid lesions appear hypoechoic on EUS. From this point of view, contrast-enhanced harmonic EUS (CH-EUS) plays an important role in the differential diagnosis of pancreatic lesions. EUS and CH-EUS are also useful for staging pancreatic cancer. Moreover, EUS-guided fine-needle aspiration (EUS-FNA) is superior to other modalities in terms of cytopathological diagnosis. Although EUS-FNA has a high diagnostic ability for pancreatic cancer, the combination of EUS-FNA and CH-EUS improves the diagnostic ability by decreasing the number of false-negative cases. Thus, conventional EUS, EUS-FNA, and CH-EUS are essential in clinical practice for the diagnosis of pancreatic solid lesions.