Thyroid Carcinoma on the Side of the Absent Lobe in a Patient with Thyroid Hemiagenesis



Introduction

Thyroid hemiagenesis is an extremely rare congenital abnormality, with a reported prevalence of 0.02-0.2%. This pathology is often discovered during detailed examinations for abnormal thyroid function and thyroid diseases such as goiter. Only 13 previous cases of thyroid cancer concurrent with thyroid hemiagenesis have been reported. Tumors in each of those cases occurred in the remaining thyroid tissue; no previous reports have described thyroid carcinoma occurring on the side of the absent thyroid lobe.

Case Report

A 64-year-old woman was referred to our department for evaluation of a thyroid mass discovered incidentally during examinations for symptoms of abnormal sensation during swallowing. The patient had no history of previous surgery or radiotherapy to the neck. She had no significant past medical history. No family history of thyroid disorders was elicited.

Diagnosis

Examination of the neck revealed a firm mass with irregular edges and little mobility. No cervical lymphadenopathy was evident. Examination of the oral cavity, pharynx, and larynx showed findings within normal limits, with mobile vocal cords. Ultrasonography and computed tomography (CT) did not show a left lobe of the thyroid, but the right lobe and isthmus were identified. A 0.7*0.8*1.4cm hypoechoic nodule with small calcifications and attenuation of posterior echo and a 0.8 —0.7 cm enhanced nodule with clear borders were identified on the left side of the isthmus. Ultrasonography and CT did not reveal enlarged lymph nodes on either side of the neck. CT also did not reveal metastatic tumors in the lungs. Serum thyroid-stimulating hormone (TSH) was 1.35 IU/mL, free triiodothyronine (FT3) was 2.87 pg/ mL, free thyroxine (FT4) was 1.43 ng/ dL, and thyroglobulin was 12.93 ng/ mL. Ultrasonography-guided fine-needle aspiration cytology identified the nodule as papillary thyroid carcinoma. The postoperative histopathological examination found that the right lobe and isthmus were present and the left lobe was absent. The tumor was adjacent to the left side of the isthmus, and a clear demarcation was evident between the thyroid and tumor. Most of the tumor was consistent with thyroid papillary carcinoma with a funicular- and microfollicular-shaped ductal structure and nuclear grooves were observed within the tumor cells at high magnification. A honeycomb structure and necrosis were observed in a section of the infiltrating tumor, and a marked difference was seen in the sizes of nuclei, indicative of poorly differentiated thyroid carcinoma. In addition, immunohistochemical staining showed that both the papillary and poorly differentiated carcinomas were thyroid transcription factor- (TTF-) 1-positive, suggesting that the carcinomas originated from thyroid tissue. The final diagnosis was concomitant papillary thyroid carcinoma and poorly differentiated carcinoma pT4pN0pEx2, with recurrent laryngeal nerve invasion.

Treatment

The patient underwent surgery using a standard collar incision. Intraoperative findings confirmed the presence of the right lobe and isthmus, the absence of the left lobe, and the presence of a firm nodule with infiltration into the muscle tissue surrounding the site of the absent lobe on the left of the isthmus after the abduction of the anterior cervical muscles. Total right thyroid lobectomy isthmectomy, resection of the tumor, and central neck dissection were performed concurrently. The tumor had invaded the lateral branch of the recurrent laryngeal nerve, which was also resected, but the medial branch of the recurrent nerve was preserved. On the side of the absent thyroid, the superior thyroid artery, superior thyroid vein, middle thyroid artery, inferior thyroid artery, inferior thyroid vein, and parathyroid glands were in the normal locations. No abnormality was evident in the pathway of the recurrent laryngeal nerve. At 3 months postoperatively, the patient underwent 131I ablation on an outpatient basis. Subsequent thyroid scintigraphy indicated no accumulation of radioactive iodine. The patient has remained recurrence-free as of 3 years postoperatively, and observation is continuing.

Discussion

Thyroid hemiagenesis was first reported by Henle in 1866. The thyroid develops via epithelial cell proliferation from the foramen cecum of the tongue between the tuberculum impar and copula linguae in week 5 of gestation. The gland subsequently descends as a diverticulum dividing into right and left lobes, reaching the anterior of the trachea in week 7 of gestation. Thyroid hemiagenesis is postulated to be caused by a failure of the diverticulum to divide, but some reports have also described associations between a lingual thyroid and hemiagenesis. Confirmation that other locations remain free of abnormal accumulation on thyroid scintigraphy is therefore necessary, even if thyroid hemiagenesis is observed on ultrasonography, CT, or other modalities. In this case, thyroid scintigraphy was not performed before surgery. However, no abnormal accumulation was detected at other sites on thyroid scintigraphy performed postoperatively following 131I ablation. Only 13 cases of thyroid cancer complicated by thyroid hemiagenesis have been reported. These cases included 11 female and two male patients, ranging between 14 and 74 years of age. In eight of these 13 cases, the tumors were discovered by palpation following cervical swelling or nodule detection. Five cases, including ours, were asymptomatic. Papillary carcinoma was the most common histology in 10 cases, with one case of follicular carcinoma, one of medullary carcinoma, and one of combined papillary and follicular carcinoma. Our case showed a combination of papillary and poorly differentiated carcinomas, representing the first case in which poorly differentiated carcinoma was identified. Among cases reported to date, the left side of the thyroid was absent in eight patients, and the right side was absent in five. Tumors in all cases except ours arose in the existing parts of the thyroid (i.e., in the lobe or isthmus). In our case, however, the tumor arose on the side of the absent thyroid. The fact that positive results for TTF-1 were obtained for both the papillary and poorly differentiated carcinoma sites suggested that cancer originated in the thyroid. However, checking for thyroid tissues on the side of the absent thyroid was not possible, so the origin of the thyroid cancer in our patient could not be confirmed.

Keywords

Thyroid hemiagenesis, thyroid function, thyroid cancer

Author : Sato, et al.