A case of encapsulated papillary carcinoma of the thyroid

甲状腺被包型乳頭癌は比較的まれであり，非被包型乳頭癌と比べて再発，癌死もほとんどなく予後は良好であるとされている．また，線維性被膜を有することから超音波検査では濾胞性腫瘍 との鑑別は困難な場合がある．症例は38歳の女性．前医の超音波検査で甲状腺左葉に2.2 cm 大の 充実性腫瘤が認められた．穿刺吸引細胞診で濾胞性腫瘍の疑いと診断され，当院に手術目的で紹介された．超音波検査で甲状腺左葉から峡部にかけて2.5 × 2.1 × 1.6 cm 大の境界部低エコー帯を 一部に伴う充実性腫瘤を認めた．濾胞性腫瘍の疑いで甲状腺左葉峡部切除術を施行した．病理組織学的に線維性被膜及び乳頭癌の核所見として矛盾しない腫瘍細胞が乳頭状構造をとる部分が認められたことにより，被包型乳頭癌と診断した．超音波検査で明らかな頸部リンパ節腫大は指摘できなかったため再手術は行わず TSH 抑制療法を行いながらで経過観察中である． Encapsulated papillary carcinoma of the thyroid is a relatively rare disease. Compared with the non-encapsulated form of the disease, it is associated with a better prognosis including lower rates of recurrence and mortality. It is characterized by the presence of a fibrous capsule; as such, it can be challenging to distinguish encapsulated papillary carcinoma from follicular neoplasm on ultrasound. The patient was a 38-year-old woman who had a 2.2-cm solid mass in the left thyroid lobe that was identified on ultrasound performed at a clinic. She was subsequently diagnosed with follicular neoplasm based on the results of fine needle aspiration cytology, and was referred to our hospital to undergo surgery. Ultrasound examination revealed the presence of a 2.5 × 2.1 × 1.6-cm solid mass with a partial halo sign from the left thyroid lobe into the isthmus. Follicular neoplasm was suspected, and left thyroid lobectomy and isthmusectomy were performed. Fibrous capsules were identified on pathology. Furthermore, tumor cells had papillary structures that corresponded to the characteristic nuclear structure of papillary carcinoma. Thus, the patient was diagnosed with encapsulated papillary carcinoma. Since ultrasound did not show any indications of cervical lymph node swelling, reoperation was not performed. The patient is currently being followed up and is on thyroidstimulating hormone (TSH) suppression therapy