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An intrapericardial thymoma resected by uniportal video-assisted thoracoscopic surgery

Thymomas are usually located in the normal location of the thymus in the anterior mediastinum. It is very rare for thymomas to arise primarily intrapericardially. A 76-year-old male patient with a known human immunodeficiency virus positivity and has been under close follow-up for five years was admitted to our clinic. Thoracic computed tomography revealed an intrapericardial mass. Uniportal video-assisted thoracoscopic surgery was performed for the resection of the intrapericardial mass. Pathological examination revealed a type AB thymoma with a 3x3x2.5-cm dimensions (Stage 1). He underwent adjuvant irradiation. He has been doing well without any recurrence for 41 months. In conclusion, resection of intrapericardial masses is feasible and safe. This is the first case with a purely intrapericardial thymoma that was resected via uniportal videoassisted thoracoscopic surgery in the literature.

Thymomas are usually located in the anterior mediastinum as the normal location of the thymus. [1] Involvement of the pericardium by thymic tumors is expected in invasive or metastatic thymoma. [1] Thymomas arise primarily in the pericardium. [1] It is possible that, during the embryologic stage, some thymic tissues are left behind in the pericardium as the thymus develops. [2] Such tissue may turn into an intrapericardial tumor. [2] Intrapericardial thymomasrelated sudden death events have been reported in the literature. [3] Some of the cases were diagnosed during autopsies. [3] In this article, we report a case operated in a certain way that has never been reported before for pericardial thymoma.

CASE REPORT
A 76-year-old male patient was referred to our department after a computed tomography (CT) scan The patient was a non-smoker. His vitals were normal and routine laboratory results were unremarkable. He has been human immunodeficiency virus (HIV)-positive for five years with normal CD4+ T lymphocytes. A chest CT showed a 2.7-cm long, round-shaped intrapericardial mass with soft tissue density ( Figure 1) other than Chiliaditi syndrome. The mass was located adjacent to ascending aorta. Electrocardiography showed normal sinus rhythm. Transthoracic echocardiography did not detect any other abnormalities. A thoracic magnetic resonance imaging (MRI) revealed a tissue plane between the aorta and the mass. Pulmonary function test was between normal limits. Under general anesthesia a single 3-cm incision at the fourth intercostal space from the anterior axillary line to explore the mass directly. The chest cavity showed no abnormalities other than elevated hemidiaphragm. The intrapericardial mass was resected totally (Figure 2). The pericardial defect was primarily sutured using 3/0 polypropylene (Ethicon Inc., Johnson & Johnson, Somerville, NJ, USA). Postoperative course was uneventful and the patient was discharged the next day. Pathological examination showed a spindle type AB thymoma with abundant T lymphocytes ( Figure 3). There was no microscopic capsular invasion. The tumor was a Stage 1 tumor according to the Masaoka-Koga staging system, T1N0M0 according to the International Association for the Study of Lung Cancer (IASLC)/

DISCUSSION
Herein, an intrapericardial Stage 1 type AB thymoma was completely resected with surrounding fatty tissue. In our patient, there was no anterior mediastinal mass. Therefore, thymoma should be named an ectopic intrapericardial thymoma. Stage of this 2.7-cm type A tumor according to Masaoka-Koga system was Stage 1, whereas it was a T1aN0M0 tumor according to 8 th staging system. [4] However, the usability of these systems is questionable, since tumor location is eccentric. Therefore, there is a need for a specific distinction in the expanding chapter of ectopic thymomas. [5] Surgical approach is still controversial; however, the entity was reported to cause sudden death in a patient. [3] Caramori et al. [6] reported a case with an intrapericardial thymoma that was resected via multiportal videothoracoscopy. However, this tumor was previously evaluated to be thymic cyst. Weissferdt and Moran [7] also reported a surgically resected ectopic pericardial thymoma case. However, there is no clear definition whether this pericardial thymoma was intrapericardial or extrapericardial, since they reported the tumor as a pericardial tumor. Also, the surgical approach was not mentioned in the report. It should be noted that extrapericardial ectopic thymomas are not rare. [2] The role of HIV in the pathogenesis of thymoma is unknown. Nonetheless, the patient's CD4+ T lymphocyte count was normal and he has been symptom free for three years.
In our patient, we could not perform a preoperative biopsy due to location of the tumor. The tumor was resected completely.
As it has been well described in the literature, complete (i.e. R0) resection is of great importance in the treatment of thymic tumors. Adjuvant radiotherapy is recommended in patients in whom the resectional margin is unknown or patients with Stage 2 or Stage 3 thymoma. [8] We were able to perform complete resection of tumor with fatty tissue. However, adjuvant radiotherapy was given due to the fact that microscopic foci were found in the pericardial peritumoral fatty tissue. Thanks to the minimally invasive nature of the uniportal videoassisted thoracoscopic surgery (VATS) approach, the patient needed only one day of hospitalization. Since the patient has been well without any recurrence for 41 months, it is plausible to speculate that surgical resection of the thymoma with intrapericardial fatty tissue dissection followed by adjuvant radiotherapy seems to be curative in this extremely rare entity.
To the best of our knowledge, our patient is the only case with resected purely intrapericardial tumor in the literature. Our case is also the first case who underwent uniportal VATS resection for an intrapericardial tumor. Even the tumor was staged as Stage 1 tumor, staging protocol for thymoma does not consist any special definition for intrapericardial tumors.
In conclusion, very rare pure intrapericardial thymomas can be completely and safely resected via uniportal videothoracoscopic approach. However, evaluation of large case series is warranted to define the treatment of choice in patients with an intrapericardial thymoma. Patient Consent for Publication: A written informed consent was obtained from patient.

Data Sharing Statement:
The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflict of Interest:
The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.

Funding:
The authors received no financial support for the research and/or authorship of this article.