脛骨遠位部に発生した外傷性骨軟骨腫の1例

Post-traumatic Osteochondroma in the Distal Tibia. Case Report

　足関節捻挫後，脛骨遠位に発生した外傷性骨軟骨腫の1例を経験した．症例は18歳の男性で，足関節捻挫後3カ月後に，脛骨遠位骨幹端部に腫瘍が発生した．腫瘍は骨間膜に沿って増大しており，腓骨との骨性架橋構造が認められた．病理組織学検査では，成熟した軟骨組織と幼若な骨組織が認められたが，その配列は不規則で，通常の骨軟骨腫で認められる成長軟骨帯類似の層構造は認められなかった．臨床経過と組織学的所見から，骨膜胚芽層内や骨膜付着部の幼若な細胞の軟骨化生が原因で発生した傍骨性骨軟骨異型増生（bizarre parosteal osteochondromatous proliferation；BPOP）と考えられた．

　We report a case of posttraumatic osteochondroma in the distal tibia. A 18-year-old man noting a mass on his left ankle 3 months after an ankle sprain was found in radiographic examination to have a wide-based bony tumor on the lateral aspect of the distal tibia, expanded around the interosseous membrane. Histologically, a large amount of hypercellular cartilage had maturaed to tubercular bone, but the bony-cartilaginous interface was irregular, unlike typical osteochondroma. We diagnosed this tumor as bizarre parosteal osteochondromatous proliferation and hypothesized that it arose from the cambium layer of the periosteum or embryonic tissue at insertion of interosseous membrane after injury.