海綿状血管腫類似のMRI所見を示した甲状腺乳頭癌（thyroid papillary carcinoma）の孤発性脳転移

Solitary Brain Metastasis of Thyroid Papillary Carcinoma Mimicking a Cavernous Angioma by MRI

Ⅰ．はじめに

　甲状腺乳頭癌（thyroid papillary carcinoma；TPC）は，甲状腺悪性腫瘍の65～85％を占めている^1,15,17)．遠隔転移は1～14％にみられ，主に肺や骨に転移し，脳への転移は0.1～5％と少ない^1,3-5)．しかも，脳転移が発見された時点で，既に肺や骨など他臓器に遠隔転移していることが多く，脳のみに遠隔転移が発見される症例は稀である^1,3,11-13)．また，原発巣や他の遠隔転移巣の症状ではなく，脳転移巣の症状で初発する症例も稀である^2,5,6,11,12)．われわれは，TPCの脳への単独転移によるけいれんで初発した症例を経験した．

　本症例のMRI所見は海綿状血管腫と類似していた．海綿状血管腫の術前診断で手術を施行したが，病理組織検査でTPCと診断され，原発巣の発見，治療，全身検索につながった．MRIで海綿状血管腫が強く疑われても，転移性脳腫瘍も考慮して対応することが重要である．

　We report a case of a brain metastasis of thyroid papillary carcinoma. A 50-year-old man suffered generalized convulsion. MRI showed a mixed intensity mass with a perifocal low intensity rim in T2WI, mimicking cavernous angioma. The patient underwent craniotomy and total removal of the mass. The resected specimen revealed thyroid papillary carcinoma. Further examination showed a mass in his thyroid gland. Other distant metastases were not revealed. This is a case of a solitary brain metastasis of thyroid papillary carcinoma and the patient's initial symptom was caused by brain metastasis. Such cases are extremely rare. The mass was presurgically diagnosed as a cavernous angioma but was actually a case of brain metastasis. If we had not performed mass removal, we would not have been able to diagnose it as brain metastasis from thyroid papillary carcinoma and would have not taken appropriate steps toward further examinations and treatment. We must manage carefully a mass resembling cavernous angioma in MRI in consideration of the possibility of its being another diseases such as a metastatic tumor.