軸椎歯突起後方偽腫瘍5例の治療経験

Treatment of Retro-odontoid Pseudotumor. Report of Five Cases

　軸椎歯突起後方偽腫瘍(以下，偽腫瘍)は，環軸椎不安定性に起因する非腫瘍性腫瘤と考えられている．5例を経験し治療法を検討した．環軸椎に不安定性のない2例に対し後方除圧術を施行し，そのうち1例に術後腫瘤の増大があり後頭頚椎後方除圧固定術を施行した．環軸椎に不安定性のある3例に対しては後方固定術を施行した．後頭頚椎後方固定を施行した1例で術後速やかに腫瘤が縮小した．偽腫瘍は環軸椎関節への機械的刺激により反応性に形成されるため，固定術を行うことが望ましい．神経症状が急速に悪化している場合に後頭頚椎後方除圧固定術は有効であった．

　Retro-odontoid pseudotumor is regarded as a nonneoplastic mass that arises as a result of instability of the atlantoaxial joint.　We treated five cases of retro-odontoid pseudotumor and assessed the methods of surgical treatment.　We performed posterior decompression surgery in the two cases in which there was no instability of the atlantoaxial joint.　There was an increase in size of the pseudotumor in one case postoperatively, and we treated it by performing occipitocervical posterior fusion.　We performed posterior fusion in the three cases with instability of the atlantoaxial joint.　The pseudotumor regressed immediately postoperatively in one patient who underwent occipitocervical posterior decompression fusion.　Since pseudotumors formed in response to mechanical stress on the atlantoaxial joint, we think that it is better to perform fusion to treat this disease and prevent recurrences.