岡庭 信司¹, 岩下 和広²

Shinji OKANIWA¹, Kazuhiro IWASHITA²

¹飯田市立病院消化器内科, ²飯田市立病院放射線技術科

¹Department of Gastroenterology, Iida Municipal Hospital, ²Department of Radiological Technology, Iida Municipal Hospital

キーワード : ultrasonography, pancreatic carcinoma, risk factor, high-risk individuals, cancer screening

超音波検査（US）は簡易で低侵襲なことから，人間ドックや集団検診といったスクリーニングにも広く用いられている．しかし，従来のUS検診では腫瘤像や肝外胆管・主膵管拡張といった間接所見に着目していたため，膵癌の発見率は低く発見されても大半が進行癌であった．膵癌には未だ早期癌の定義はないが，Stage 0膵癌と10 mm以下のStage I A膵癌は予後良好な膵癌と考えられる．これらの病変を拾い上げるためには，膵癌の危険因子を複数有する高危険群に対して精密検査や定期的な経過観察を行うことが有用であり，主膵管拡張や嚢胞性病変を有する高危険群を拾い上げることもUSの役割である．一方で，膵臓は解剖学的な位置関係が複雑であるだけでなく，肥満や消化管ガスにも影響を受けやすいため描出困難な部位が存在する．膵頭部は予後良好な膵癌の好発部位であるが，groove領域と鉤状突起の病変は間接所見を伴わないことが多いため特に注意が必要である．描出不良部位を減らすためにはプローブでただ強く圧迫するのではなく，描出不良部位に応じて左右側臥位，坐位，立位といった体位変換や飲水法を活用すべきである．さらに，高危険群の精密検査や経過観察時に高周波プローブを用いた拡大観察を行うことにより，小病変や膵管の異常像を拾い上げることが可能になると考える．

As ultrasound (US) is simple and minimally invasive, it is widely used for mass screening. However, since conventional US screening focused on mass lesions and indirect findings such as the dilated extrahepatic bile duct and main pancreatic duct, the detection rate of pancreatic cancer was low, and most detected lesions were advanced. Although there is still no definition of early-stage pancreatic cancer, Stage 0 and Stage 1A pancreatic cancers less than 10 mm are considered pancreatic cancers with good prognosis. To detect these lesions, it is useful to perform detailed examinations and regular follow-up for high-risk individuals who have multiple risk factors for pancreatic cancer. It is also the role of US to identify high-risk individuals who show a dilated main pancreatic duct or cystic lesion. The pancreas is sometimes difficult to visualize not only because of its complicated anatomical location but also because of its susceptibility to obesity and gastrointestinal gas. Although the pancreatic head is a common site of pancreatic cancers with good prognosis, it is important to pay attention to lesions in the groove region and uncinate process, which are often not accompanied by indirect findings. To minimize poorly visualized areas, positional changes such as right and left decubitus, sitting and standing positions, and the liquid-filled stomach method should be applied. Furthermore, employing magnified observation with high-frequency transducers for the detailed examination and follow-up of high-risk individuals could detect smaller mass lesions and abnormalities of the pancreatic ducts.