Radicality of thoracoscopic thymectomy – an anatomical study

Evidence suggests that there is a direct relationship between the completeness of thymectomy (Thx) and outcome of myasthenia gravis (MG) [1]. The question of the most suitable surgical approach is still controversial [2,3]. The main drawback of all approaches traditionally competing with median sternotomy is their lack of radicality [1,3]. An anatomical study therefore investigated the radicality of Thx using the new thoracoscopic approach (tThx) and the question which side should be preferred for tThx. After approval by the Ethics Committee and informed consent by the next of kin, ten consecutive human cadavers were alternately assigned to left- or right-sided tThx. Eight special locations within the anterior mediastinum were evaluated for complete dissection: the main thymic lobes, the pretracheal tissue, the tissue behind the phrenic nerve and anonymous vein, the aorto-pulmonary window, the aorto-caval groove, and the pericardio-phrenic tissue. tThx was performed as described earlier [2,4], comparing the 0 and 30° telescopes during each procedure.

With the cadaver in a 30° elevated lateral decubitus position, the trocar sites were defined between the 3rd and 6th intercostal spaces and medioclavicular and anterior axillary lines following the submammary line. Preparation started at the lower ends of the main thymic lobes with incision of the mediastinal pleura along the phrenic nerve, which has to be carefully preserved. The incision of the mediastinal pleura was continued at the upper edge to open the connection to the neck tissue. During further mobilization of the anterior mediastinal tissue portion by retrosternal incision down to the diaphragm, the arterial thymic supply was divided. The whole tissue portion was then mobilized from the pericardial surface. After complete exposure of the innominate vein all thymic veins were transsected. Each operation was documented by video. The size and weight of each specimen were determined. Immediately thereafter, extended median sternotomy was done for independent control of radicality: one of the authors (D.C.) looked at all eight mediastinal locations for residual tissue. Histology served to evaluate the mediastinal distribution of thymic tissue. Only the 30° telescope allowed for complete visualization of the anterior mediastinum with special attention to the contralateral side. The resected mediastinal tissue was 79.3±36.4 g (mean±SD). The specimen sizes and the presence of aberrant thymic tissue did not show significant differences between left- and right-sided tThx (Table 1) . The left thymic portion, however, was found to be larger in all ten corpses. All of the eight specified regions, except the aorto-caval groove, were visualized better from the left side. The radicality of tThx in this study is shown in Table 2 . Incomplete resection was slightly more frequent with the approach from the right (Table 2). Our study thus confirms the arguments favoring the left-sided approach: the larger left side of the thymus, the innominate vein running mainly in the left anterosuperior mediastinum, and the aorto-pulmonary window as a frequent site of ectopic thymic tissue [5]. To the best of our knowledge, no other experimental data addressing the radicality of tThx have been published so far. This study provides evidence that tThx achieves radical Thx. Based on these data it appears reasonable to proceed with the clinical investigation of long-term results after tThx for MG.

Table 1

Comparison of specimen sizes and mean weight, and presence of aberrant thymic tissue with left- as compared to right-sided tThx in the experimental setting for Thx^a

Table 2

Proportion of incomplete dissection in relation to eight distinct mediastinal locations (comparison between left- and right-sided tThx)

✩

Presented in part at the 7th European Conference of General Thoracic Surgery, Nancy, France, October 22, 1999.