尾上 篤志¹, 秋山 隆弘²

Atsushi ONOUE¹, Takahiro AKIYAMA²

¹高橋計行クリニック超音波室, ²堺温心会病院泌尿器科

¹Division of ultrasound diagnosis, Takahashi Kazuyuki Clinic, ²Department of Urology, Sakai-Onshinkai Hospital

キーワード : contrast enhanced echo, renal cell carcinoma, renal angiomyolipoma, acquired cystic disease of kidney, cyst associated carcinoma

腎癌は高齢者に多く発生する腫瘍であり，我国の人口の高齢化に伴って今後ますます増加するものと考えられる．また，腎癌は症状が無い時期に見つかるほうが，患者の生命予後が明らかに改善するため，スクリーニングによる早期発見が有効である．しかし，スクリーニングの普及に伴い，より小さな腎腫瘤が発見され，腫瘤の鑑別診断が困難となってきた．腎臓の腫瘤は良性腫瘍と悪性腫瘍に別れ，良性では腎血管筋脂肪腫が，悪性では腎細胞癌の頻度が最も高く，腎に腫瘤性病変を認めた場合，まず嚢胞性と充実性に分けて診断する．嚢胞性腫瘤は，ほとんどが良性であるが，断層法で嚢胞壁や隔壁に肥厚した部分が無いかを注意深く検索する必要がある．さらに，腎動脈瘤や腎動静脈瘻などの腎血管性病変の可能性も考えられるためカラードプラ法で嚢胞内に血流信号が無いか確認する．一方，充実性腫瘤の場合，臨床上最も頻度が高く，かつ鑑別診断が困難な腫瘤は高エコーを呈する小さな腫瘤であり，断層法とカラードプラ法を駆使しても鑑別診断が困難であることも多く，造影超音波検査が有用である．さらに，透析患者においては腎癌の発症が高率であり，特に透析導入後に発生する多嚢胞化萎縮腎に多く発生する．この場合も，断層法やカラードプラ法では鑑別診断が困難であり，造影超音波法が有用であることから，積極的に多用されるべき検査法である．本稿では腎臓の超音波診断に必要な基本的知識から造影超音波法の最新の知見までをまとめた．

Renal cell carcinomas (RCC) commonly occur among older people, and the prevalence of RCC is predicted to increase further in the future as the population ages. Early detection of RCC is significant because diagnosis in the symptomless stage obviously improves patient survival. However, the differential diagnosis of small intrarenal masses has recently become more difficult with easier detection of extremely small masses thanks to advances in screening techniques. Renal mass diseases include benign and malignant tumors. Angiomyolipoma (AML) is the most common among benign renal tumors, and renal cell carcinoma is the most common among malignant tumors. Meanwhile, renal mass lesions consist of solid and cystic masses. Almost all cystic masses are benign, but they can be malignant in some cases; therefore, a careful search for thickening of the site of involvement with US tomography is required. Moreover, intrarenal cystic masses may be renal vascular diseases such as aneurysm or aneurysmal type of arteriovenous fistula. Color Doppler US can be used for differentiation of a mass by confirming the presence of a vascular signal. Distinguishing RCC and AML from a hyperechoic small solid mass is needed in many patients, but differential diagnosis between them is mostly impossible even using color Doppler US with B-mode tomography. Contrast-enhanced US is helpful in these cases. A high rate of occurrence of RCC is well known in patients receiving maintenance hemodialysis, usually occurring due to acquired cystic disease of kidney (ACDK). B-mode and color Doppler are also ineffective for differentiating RCC and AML from those masses, and contrast US should be applicable in all patients. Information ranging from fundamental knowledge necessary for ultrasound diagnosis of the kidney to recent findings on contrast-enhanced US is summarized here.