木村 芙英

Fuyo KIMURA

第二川崎幸クリニック乳腺外科

Department of Breast Surgery, The Second Kawasaki Saiwai Clinic

キーワード : breast, ultrasound, normal anatomy, age-related changes, scanning techniques

乳腺は体表に位置するため，高周波プローブを用いた高分解能な形態観察が可能であり，病変部の詳細な評価と診断に有用である．しかし，乳房構成は年齢や個人差により多様で，正常構造と病変の鑑別が困難な場合も少なくない．本総説では，乳腺の皮下組織，クーパー靭帯，腺葉・小葉構造，終末乳管小葉単位（TDLU）の解剖と超音波所見を概説し，正常構造のバリエーションや加齢による変化，病変との鑑別のポイントを示す．また，乳管や小葉周囲の間質は，超音波上低エコー領域として描出され，glandular tissue component（GTC）と呼ばれている．乳癌発症リスクとの関連性の報告や，GTCが高い症例はマンモグラフィ上も高濃度乳房である傾向があることから，GTC評価がリスク層別化乳癌検診として有用であることが期待されている．乳房超音波は，高周波であるがための超音波の減衰の影響が強く，撮像方法が診断に大きく影響する．基本となる検査体位，プローブの持ち方や圧迫の強さ，操作範囲や速度，動的検査の活用，血流情報やエラストグラフィでの注意点など，診断精度を高めるための操作手技について解説する．正確な診断と不要な精密検査の回避のためには，乳腺の詳細な解剖と生理的変化の理解，超音波像との対応付けが不可欠であり，日常診療に役立てていただければ幸いである．

The mammary gland is located close to the body surface, allowing high-resolution morphological assessment using highfrequency ultrasound probes, which is valuable for the detailed evaluation and diagnosis of lesions. However, breast composition varies considerably with age and between individuals, and distinguishing normal structures from pathological findings can be challenging. This review provides an overview of the anatomy and ultrasound features of the subcutaneous tissue, Cooper’s ligaments, lobular and lobule structures, and terminal duct lobular units（TDLUs）. Variations in normal anatomy, age-related changes, and key points for differentiating these from abnormalities are described. The stroma surrounding ducts and lobules appears as a hypoechoic area on ultrasound, referred to as the glandular tissue component（GTC）. Previous reports have suggested an association between GTC and breast cancer risk, and a high GTC is often associated with mammographically dense breasts, indicating its potential utility in risk-stratified breast cancer screening. Because high-frequency ultrasound is subject to considerable signal attenuation, scanning techniques have a substantial impact on diagnostic outcomes. This review discusses technical considerations to enhance diagnostic accuracy, including optimal patient positioning, probe handling and compression, scanning range and speed, use of dynamic assessment, and precautions when employing vascular imaging and elastography. Accurate diagnosis and avoidance of unnecessary further examinations require a thorough understanding of the detailed anatomy and physiological changes of the breast, as well as their correlation with ultrasound appearances. This review aims to support such understanding in routine clinical practice.