脊椎カリエスに類似する画像所見を呈した甲状腺癌脊椎転移の1例

Spinal Metastasis from Thyroid Carcinoma with Radiological Findings that Mimic Tuberculous Spondylitis : Case Report

　抄録：症例は31歳の女性で，特に誘因なく強い背部痛が出現し両下肢麻痺を生じた．既往として14年前に甲状腺腫瘍切除術を施行され濾胞腺腫と診断されていた．ツベルクリン反応が強陽性で，MRIではT6～8椎体はT1強調画像で低～等輝度，T2強調画像で高輝度を呈し，造影画像で比較的均一な増強効果を認めた．病巣はT6/7，7/8椎間板にも浸潤し硬膜外腫瘤による脊髄の強い圧迫を認めた．さらにX線上椎間板腔の狭小化も認めたため，転移性脊椎腫瘍と脊椎カリエスの鑑別診断が困難であった．生検術の結果は濾胞状甲状腺癌の脊椎転移で，脊椎再建術を施行し独歩可能となった．一般に転移性脊椎腫瘍では椎間板は温存されるが，甲状腺癌のような発育の遅い腫瘍の転移巣では画像上椎間板腔への浸潤を認めることもあり得る．

　A healthy 31 year-old woman suddenly presented with severe backache and paraparesis. She had undergone resection of follicular adenoma of thyroid fourteen years before. Magnetic resonance images (MRI) demonstrated low and intermediate signal intensities in the 6^th, 7^th, and 8^ththoracic vertebral bodies on T1 weighted images (WI), high intensities on T2WI, and homogeneous enhancement with Gd-DTPA. The lesion invaded not only vertebral bodies but intervertebral discs as well. Paraparesis of the patient was attributed to kyphotic angulation and encroachment of the lesion on the cord. Plain radiographs showed disc space narrowing at T6/7 and 7/8. Tuberculin skin test showed significantly positive reaction. Some of these findings were consistent with spinal metastasis and others with spinal tuberculosis. In order to reach a definite histological diagnosis, we performed biopsy via transpedicular approach. Histopathologic examination proved the lesion to be spinal metastases from thyroid follicular adenocarcinoma. The affected vertebral bodies were replaced with a titanium mesh cage from anterior and reinforced with pedicular screws from posterior. After surgery, she became pain-free and regained ambulation without any support. In the current case, disc space narrowing distracted us from a definite diagnosis of the lesion, since disc spaces are generally kept intact in patients with spinal metastases. However, there is a report which reveals histological involvement of discs as often as 9.7％of autopsy cases with metastatic spinal tumors. MRIs might demonstrate disc involvement when the tumor is extremely slow-growing such as thyroid carcinoma.