thymomas are the most common low - grade malignant tumors that often emerge in the 
 anterior mediastinum in adults . while 
 thymectomy by sternotomy is the traditional method of treating thymoma , recently , 
 video - assisted thoracic surgery ( vats ) approaches have been often selected .
vats thymectomy is reportedly feasible and 
 safe and is less invasive than transsternal thymectomy [ 2 , 3 ]
. however , we 
 experienced a rare complication of port - site recurrence that would not have occurred 
 with transsternal thymectomy .
a 60-year - old woman was referred to our hospital with an anterior mediastinal tumor on 
 computed tomography ( ct ) performed for follow - up 6 years after a complete response to 
 chemotherapy for malignant lymphoma .
ct revealed a tumor in the right anterior 
 mediastinum with a diameter of 3.5 cm , round shape and demarcation from the neighboring 
 tissue ( fig .
nmol / l ( within normal 
 range ) . to confirm the diagnosis and treat the patient , we planned tumor resection via 
 vats
. figure 1:initial ct revealed a tumor in the right anterior mediastinum with a diameter 
 of 3.5 cm , round shape , which was clearly demarcated from the neighboring 
 tissue .
initial ct revealed a tumor in the right anterior mediastinum with a diameter 
 of 3.5 cm , round shape , which was clearly demarcated from the neighboring 
 tissue .
the first 
 15-mm thoraco - port for the videoscope was placed in the sixth intercostal space on the 
 mid - axillary line .
the second 15-mm port was placed on the fifth intercostal space on the anterior axillary 
 line .
the third 5-mm port was placed in the fourth intercostal space on the anterior 
 axillary line .
the tumor was easily identified under the mediastinal pleura as an 
 elevated mass in the thymic tissue . through the second and third ports ,
the normal thymus around the tumor was grasped by forceps and cut using an 
 ultrasonic scalpel with marginal tissues .
after the resected tumor was placed into a 
 specimen bag , it was removed through the second port .
frozen sections during the operation revealed that the 
 tumor was capsulated type a masaoka stage i thymoma with sufficient marginal tissue . 

follow - up ct performed 36 months after the operation revealed two pleural tumors located 
 near the second and third ports ( fig .
initially , the operation was performed only by vats with three ports . after removing the 
 severe adhesion between the lung and chest wall
given these findings , we diagnosed these tumors as port - site 
 implantations after the first vats .
figure 2:follow - up ct at 36 months after the operation revealed two pleural tumors 
 locating at the second ( a ) and third ( b ) ports used 
 in the vats operation . 

figure 3:in the operative findings , the tumors were found to have arisen from the 
 intercostal space , and their surfaces were covered with parietal pleura with 
 partial irregularity .
follow - up ct at 36 months after the operation revealed two pleural tumors 
 locating at the second ( a ) and third ( b ) ports used 
 in the vats operation . in the operative findings
, the tumors were found to have arisen from the 
 intercostal space , and their surfaces were covered with parietal pleura with 
 partial irregularity . with no definitive findings suggesting tumor invasion into the rib
we performed mini - thoracotomies just above the 
 tumors and enucleated those two tumors via the mini - thoracotomies using an electric 
 scalpel . to obtain a sufficient surgical margin , we visualized the adequate resected 
 line using a thoracoscope while cutting the intercostal tissue surrounding the tumor . 

the pathological diagnosis was type a thymoma , which was consistent with port - site 
 metastasis of the initial tumor .
after relating these findings and the incomplete 
 resection to the patient , we decided on close follow - up without reoperation .
ishibashi et al . 
 reported a case of port - site recurrence after a vats operation for type b2 thymoma 
 , to our knowledge , this is the only 
 such previous case report . the current type
a and the reported type b2 thymomas are 
 low - grade malignant tumors . despite their mild biological behavior , implantation at
cases of implantation after medical procedures have been 
 reported , not only for malignant tumors , but also for benign tumors .
surgeons should thus be aware that 
 port - site implantation can occur regardless of the tumor 's malignant 
 potential .
willard et al .   reported a case that recurred in the small 
 vats port through which partially resected lung cancer had been extracted without a 
 specimen bag . in our case ,
the implantation developed only at the second and third 
 ports , through which the forceps and ultrasonic scalpel had passed repeatedly .
although 
 we did not detect any tumor exposure during the first operation , we can not help but 
 assume that the implantation occurred due to contamination with tumor cells from either 
 the ultrasonic scalpel or forceps that had grasped tissue near the tumor .
of further 
 note , implantation did not develop in other pleura in which tumor tissue must surely 
 have been disseminated by contaminated equipment .
taken together , these findings suggest 
 that one of the possible causes of port - site implantation was the rubbing of tumor 
 cells , such as thymoma , which might have a high affinity for pleura , against the vats ports .
surgeons should 
 take extreme care to grasp the tissue as far as possible from the tumor and to use a 
 specimen bag even when tumor exposure is not recognized .
given the lack of 
 any definitive clinical findings that the tumors had invaded the neighbor ribs , we 
 believed that the tumors could be enucleated completely while preserving the ribs . 

however , the enucleation of the tumors located mainly in the narrow intercostal spaces 
 with a sufficient margin was very difficult .
although no definitive tumor invasion to 
 the skin or subcutaneous tissue was identified , they might nevertheless invade the ribs 
 pathologically .
ishibashi et al .   successfully performed a curative operation in a case of port - site 
 recurrence via wide chest wall resection and reconstruction . in the process
a small - extent 
 resection of the skin and wide resection of the chest wall is therefore recommended when 
 performing surgery for port - site recurrence after vats thymectomy .
 a 60-year - old woman was referred to our hospital with an anterior mediastinal tumor 
 measuring 3.5 cm in diameter on computed tomography ( ct ) . 
 we performed tumor 
 resection by video - assisted thoracic surgery ( vats ) with three ports . 
 the final 
 diagnosis was type a masaoka stage i thymoma . on follow - up 
 ct performed 36 months 
 after the operation , two pleural tumors were detected at the port sites through which 
 the forceps and ultrasonic scalpel had passed repeatedly during the operation . 
 we 
 therefore performed a second operation and enucleated the tumors while preserving the 
 ribs . 
 however , other tumor tissue was detected along the surgical marginal line 
 during the pathological diagnosis after the operation . 
 surgeons should thus be aware 
 that port - site recurrence can occur after vats resection of type a thymoma , despite 
 its mild biological behavior . 
 wide resection of the chest wall is therefore 
 recommended for operations of port - site recurrence after vats thymectomy . 