Distribution of Ectopic Thymus Tissue Present Within Extended Thymectomy

Extended thymectomy is performed to excise the ectopic thymic tissue around the thymus; however, the distribution of the ectopic thymic tissue in the adipose tissue remains unclear. This study investigated the distribution of ectopic thymic tissue in extended thymectomy. This study included 31 patients who underwent extended thymectomy. Pathological specimens were reviewed to examine the distribution of ectopic thymic tissues in six locations: the right and left outer sides of the thymus tissue and the upper and lower ends of the resected tissue in extended thymectomy. The frequency of ectopic thymic tissue and the ratio to the surrounding adipose tissue were estimated. In our study, all patients, including patients >60 years, had thymic tissue in the surrounding adipose tissue removed during extended thymectomy. The probability of an ectopic thymus existing near the diaphragm, i.e., at the caudal end of the resection, was 13–19%, and the ratio of the area of the ectopic thymus to that of adipose tissue was <1% in almost all cases. In three patients with myasthenia gravis, an ectopic thymus was found in the adipose tissue around the diaphragm at a rate of >1%; there were no cases exceeding 10%. This value is extremely low compared with those of the other excision areas of extended thymectomy. Ectopic thymic tissues are far less likely to be present in adipose tissue on the diaphragm compared with that of other areas. This finding may help surgeons during the excision of adipose tissue around the thymus.