腰仙椎部移行椎例の脊髄円錐下端の高位分布―MRIによる検討

Variation in the Termination Level of the Conus Medullaris in Patients with Lumbosacral Transitional Vertebrae : Evaluation by MRI

　抄録：MRIを用いて腰仙椎部移行椎を有する症例の脊髄円錐下端高位との関係について検討した．対象症例を，腰下肢痛を主訴に当科を受診した症例のうち，脊椎退行性疾患や腫瘍性疾患などの異常所見が認められない青壮年期（18歳以上50歳以下）に限定した．対象の内訳は，正常群69例，L4/移行椎群（第5腰椎の仙椎化）12例，L5/移行椎群（第1仙椎の腰椎化）15例であった．脊髄円錐下端の高位の中央値は，L4/移行椎群ではL1椎体頭側に，正常群とL5/移行椎群ではL1椎体尾側部に存在していた．L4/移行椎群の脊髄円錐下端の高位分布は，正常群やL5/移行椎群より約1椎体分頭側に局在している．この事実は，L1破裂骨折の場合，L4/移行椎群では脊髄障害が惹起されるのに対し，正常群やL5/移行椎群では馬尾障害が惹起される可能性が高いことを示唆している．すなわち，腰仙椎部移行椎の存在は，惹起される神経障害の病態に影響を与える可能性がある．

　The purpose of this investigation was to identify variations in the termination level of the conus medullaris (TLCM) in patients with lumbosacral transitional vertebrae. The subjects were 96 low back pain patients (18-50 years old). Patients with degenerative changes in the spine or tumors were excluded. The patients were classified into three groups according to the presense and location of lumbosacral transitional vertebrae：1）15 patients with sacralization of the 5th lumbar vertebra, the L4/TV group；2）12 patients with lumbarization of the sacrum, the L5/TV group；3）and 69 patients without lumbosacral transitional vertebrae as a control, the N group. TLCM was assessed by MRI, and the cases were classified into 4groups according to whether termination was at the upper, middle, or lower part of the vertebral body, or at the disk level. The median TLCM was at the lower third of L1 in the N group, the upper third of L1 in the L4/TV group, and the lower third of L1 in the L5/TV group. The TLCM in the L4/TV group was approximately one vertebral craniad to the level in the L5/TV group and the N group (p＜0.005). This means that the presence of lumbosacral transitional vertebrae may affect the type of nerve injury (spinal cord injury or cauda equina injury), when an L1 burst fracture occurs.