We have previously suggested the usefulness of the subxiphoid approach in thymectomy.1–4 We recently expanded the indications of thoracoscopic thymectomy to include large thymic cystic lesions. Surgeons have hesitated to perform thoracoscopic thymectomy for large thymic cystic lesions because of the possibility of intraoperative rupture of the cystic lesions. However, such rupture may not be entirely avoided even when using median sternotomy if the wall is thin and fragile. With an appropriate degree of skill, delicate thoracoscopic thymectomy without intraoperative rupture of the cystic lesions seems possible. We herein report a case of myasthenia gravis (MG) with a large thymic cystic lesion in which thoracoscopic extended thymectomy was performed using a subxiphoid approach.
A 42-year-old woman was referred to our hospital due to sudden onset of optic-type MG and the finding of a large anterior mediastinal cystic lesion on chest computed tomography (CT). Anti-acetyl-choline receptor autoantibodies were positive (4.1 nmol/L). The cystic lesion, with a maximum tumor diameter of 11.0 cm, was not enhanced by contrast CT, and the fluid density was uniform. No other neoplastic lesions were found around the cystic lesion (Fig. 1) (Video 1, Supplemental Digital Content 1, http://links.lww.com/SLE/A191). As the preoperative diagnosis was optic-type MG with a large thymic cyst, we selected a thoracoscopic operation.
Thymectomy was initiated under general anesthesia with the patient in the lithotomy position using a single-lumen tracheal tube. A 3-cm transverse skin incision was made 1 cm below the lower edge of the xiphoid (Video 2, Supplemental Digital Content 2, http://links.lww.com/SLE/A192). A GelPOINT Mini (Applied Medical, Rancho Santa Margarita, CA; access platform of single-port surgery) was inserted and fixed. A 5-mm thoracoscope with a 30-degree angle was inserted through a port of the GelPOINT Mini. Using carbon dioxide insufflation of 8 mm Hg, the view was rapidly extended. A LigaSure Maryland (Covidien, Mansfield, MA) was also inserted through the second port of the GelPOINT Mini. Without expectation, the right pleura was opened. A thoracic 5-mm port was inserted at the sixth intercostal space on the right anterior axillary line. The cystic lesion was apparent, and it overhung on the right phrenic nerve. We started dissection of the thymus from the left side, and an additional thoracic 5-mm port was inserted at the sixth intercostal space on the left anterior axillary line. Following the dissection of the left side and bilateral upper portions of the thymus, the thymus and thymic cystic lesion was rolled down to the right thoracic cavity. The thymic arteries and veins were exposed and cut by the LigaSure Maryland. The running of the right phrenic nerve was recognized. The thymus and thymic cystic lesion were resected, and extended thymectomy was completed.
In a plastic bag, the cystic lesion was punctured, and 80 mL of yellowish serous fluid was collected. The diminished thymus and thymic cystic lesion were removed from the subxiphoid incision (Fig. 2). The blood loss was minimal (<1 g) and the operation time was 210 minutes. The weight of the resected specimen, including the fluid, was 132 g. The chest drain was removed on the first postoperative day. The patient was discharged on the third postoperative day without any postoperative complications.
The final pathologic diagnosis of the lesion was a multilocular thymic cyst with lymphoid follicular hyperplasia (Fig. 3A). In addition, a 7-mm WHO type A thymoma (Fig. 3B) and adjacently scattered micronodular thymoma were found (Fig. 3C). The pathologic stage of the thymic epithelial tumors was T1aN0M0, stage IA.5 Cytology of the fluid in the thymic cyst was negative. There was no evidence of recurrence of thymoma 6 months after the operation. The MG symptoms have since improved, but the serum anti-acetyl-choline receptor autoantibodies remain relatively high (4.2 nmol/L).
We herein report a case of MG with a large thymic cystic lesion in which thoracoscopic extended thymectomy was performed using a subxiphoid approach. The wall of the cystic lesion was thin and seemed to be easy to be ruptured. However, we were able to avoid rupturing the cystic lesion by carefully performing dissection using LigaSure Maryland. Its tips were dull and ideally curved, making it ideal for dissection of fragile cystic lesions.1 However, the running of the bilateral phrenic nerves was difficult to recognize due to the overhang of the large cystic lesion. An optimum view was achieved via the 3 bilateral ports and the subxiphoid window. Rolling the lesion down to the right thoracic cavity allowed us to visualize the running of the right phrenic nerve, helping us avoid injuring the phrenic nerve.
Recently, robotic operation has been utilized for anterior mediastinal lesions and the usefulness has been reported.6 However, at present, there is little variety in the available instruments for robotic surgery. It is therefore urgent to develop new appropriate instruments for dissection and sealing that exceed the quality of the LigaSure Maryland. In addition, the thoracoscopic view is usually fixed at one port and cannot be easily switched to other ports. Thoracoscopic thymectomy may thus be a more convenient procedure.
We preoperatively diagnosed the present patient with MG with a large thymic cyst and diagnosed the large thymic lesion as a congenital unilocular thymic cyst. However, the cystic lesion was diagnosed as multilocular thymic cyst. Multilocular thymic cysts are associated with type A and micronodular thymomas. Micronodular thymoma, first defined by Suster and Moran,7 is a rare subtype of thymoma. A micronodular pattern of the epithelial components is found in ∼10% of type A and type AB thymoma.8 Multilocular thymic cysts following mediastinal infections or especially those with neoplastic cystic lesions should not be confused with congenital unilocular thymic cysts. Multilocular thymic cyst associated with thymomas are rare cases,9 and micronodular thymoma accompanied by multilocular thymic cyst is rarer still.10 A large congenital thymic cyst mimicking a congenital cyst and accompanied by type A thymoma and micronodular thymoma with MG is an exceedingly rare condition.
In the present case, a small thymoma was concealed in the hyperplastic thymic tissue and not diagnosed preoperatively using enhanced CT. We preoperatively diagnosed this patient with MG and a large thymic cyst. The treatment for unilocular congenital thymic cysts remains controversial. However, we suggest a surgical indication for unilocular cystic lesion with MG, even if the symptoms are mild, due to the possibility of the presence of small thymoma concealed in the rich thymic tissues.
In conclusion, thoracoscopic extended thymectomy via the subxiphoid approach is a safe and useful approach for treating anterior mediastinal tumor. It is possible to treat even a large thymic cystic lesion without causing rupture. We suggest a new surgical indication for unilocular thymic cyst with MG symptoms due to the possibility of a concealed small thymoma.
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