力久 翔太¹, 芳賀 真代¹, 脇田 佑哉¹, 齊藤 夏彦¹, 田口 秀彦¹, 下田 絵美子¹, 井上 正義¹, 磯野 友美², 岡田 博司¹, 平井 都始子¹

Shota RIKIHISA¹, Masayo HAGA¹, Yuya WAKITA¹, Natsuhiko SAITO¹, Hidehiko TAGUCHI¹, Emiko SHIMODA¹, Masayoshi INOUE¹, Tomomi ISONO², Hiroshi OKADA¹, Toshiko HIRAI¹

¹市立東大阪医療センター放射線科, ²市立東大阪医療センター呼吸器外科

¹Department of Radiology, Higashiosaka City Medical Center, ²Department of Thoracic Surgery, Higashiosaka City Medical Center

キーワード : periosteal chondroma, chondroma, ultrasonography, lung sliding, pleura

症例は20歳代男性．検診の胸部単純エックス線写真で右下肺野の結節を指摘され精査目的に当院呼吸器外科を紹介受診した．胸部CT検査では，右胸壁に接する約20mm大の境界明瞭な腫瘤を認めた．腫瘤は肋軟骨浸潤を伴わず，脂肪成分や石灰化を認めず，造影効果を認めなかった．超音波検査を施行し，Bモードで右第6肋軟骨の背側表面から連続し胸腔側に突出する約20mm大の腫瘤を認めた．腫瘤は境界明瞭，分葉状で内部均一な低エコーを示し，後方エコーは増強していた．ドプラで血流表示を認めなかった．呼吸運動に伴った臓側胸膜の水平方向への反復移動（lung sliding）を認めたが腫瘤は連動せず，腫瘤が胸壁由来であると考えた．生検も兼ねて胸腔鏡下腫瘤切除術を施行した．術中所見では，腫瘤は壁側胸膜に覆われて肋軟骨と連続していた．腫瘤は脆く白色半透明で硬性であった．病理組織で検体は硝子軟骨組織からなり，異型はなく悪性所見を認めず，軟骨腫と診断された．術中所見や超音波所見から肋軟骨と連続が確認でき，骨膜軟骨腫を考えた．胸壁腫瘤に対する超音波検査のまとまった報告はないが，本症例はlung slidingと連動しないことで胸壁由来であることが良好に描出できた．肋骨の骨膜軟骨腫は稀であるが，超音波検査で肋軟骨と連続を認める点や，腫瘤が軟骨基質を反映し，内部均一な低エコーを示し血流がない点が，特徴的と考えた．

The patient was a 20-year-old man in whom a nodule in the right lower lung field was detected during routine chest radiography, leading to a referral to our Department of Thoracic Surgery for further evaluation. Chest computed tomography revealed a well-defined, 20-mm tumor adjacent to the right chest wall. There was no evidence of costal cartilage invasion, fat components, calcification, or contrast enhancement. Ultrasonography （US） revealed a 20-mm tumor on the posterior side of the right sixth costal cartilage. The tumor had a well-defined border, a lobulated shape, and homogeneous hypoechoic signals with posterior echo enhancement. Doppler US showed no blood flow. Repetitive horizontal movement of the visceral pleura corresponding to respiratory motion （lung sliding） was observed; however, the tumor did not move with lung sliding, suggesting a chest wall origin. Thoracoscopic tumor resection, which also served as a biopsy, was performed. Intraoperatively, we observed that the tumor was covered by the parietal pleura and was continuous with the costal cartilage. It appeared to be fragile, white, translucent, and firm. Histopathological examination revealed hyaline cartilage tissue without atypia or malignant features, leading to a diagnosis of chondroma. Continuity within the costal cartilage was also confirmed ultrasonically, indicating that the tumor was a periosteal chondroma. While comprehensive reports on US for chest wall tumors are limited, the lack of lung sliding in this case effectively demonstrated the origin of the tumor in the chest wall. Although rare, periosteal chondroma of the rib has characteristic ultrasonographic features, including continuity with costal cartilage, a homogeneous hypoechoic internal texture reflecting the cartilaginous matrix, and the absence of blood flow.