Mature intrathoracic teratomas are typically located in the anterior mediastinum. They account for 10% of congenital teratomas and 7% of all pediatric germ cell tumors. Thus, intrathoracic teratomas, including intrapericardial or pericardial teratomas, are extremely rare [4]. Histologically, anterior mediastinal teratomas have associated thymic tissue around the tumor, leading to Schlumberger’s theory of intra-thymic tissue invasion as a possible pathogenesis of mediastinal teratomas [5]. However, there are no report of thymic tissue in intrapericardial teratomas. Friedman's theory of germ cell intrusion is also considered a strong theory considering that teratomas occur in a variety of sites other than the mediastinum, including the pineal gland, retroperitoneum, sacral region, and gonads [6]. In the respect of embryological point, the difference between intrapericardial and extrapericardial teratoma is not certain. Mature intrapericardial teratomas are typically diagnosed during infancy because they manifest in a variety of ways, including pericardial effusion, dyspnea, arrhythmias, respiratory distress, and hypotension [7, 8]. Intrapericardial teratomas rarely present in adults [9, 10], with, to the best of our knowledge, only five cases of intrapericardial teratoma in adults having been reported [3, 9,10,11,12] (Table 1). Four of them were symptomatic, having chest pain, cough, dyspnea, and palpitations secondary to pericardial tamponade and compression of right-sided heart structures. Anterior mediastinal teratomas can rupture, causing cardiac tamponade [10, 11]. Mature teratomas of the mediastinum, which are usually benign, often grow slowly. Thus, our patient had never experienced symptoms of an enlarging intrapericardial mass and her teratoma was discovered incidentally.

A CT scan can identify the location and characteristics of a thoracic tumor, including a mature intrapericardial teratoma. Additionally, MRI is a mandatory modality for assessing pericardial involvement and the relationship between the tumor and surrounding vascular structures [10, 13]. The diagnosis is typically made by pathological evaluation of the resected specimen. The role of transthoracic needle biopsy in debatable. A needle biopsy can cause serious complications and often fails to yield sufficient tissue for an accurate diagnosis [3]. To our knowledge, there are no published reports concerning the usefulness of transthoracic needle biopsy for intrapericardial teratomas. When intrapericardial teratoma is the provisional diagnosis, transthoracic needle biopsy should not be performed because of the risk of complications.

Complete resection of mature teratomas is recommended, including intrapericardial ones. Incomplete resection of benign teratomas to relieve compressive symptoms is indicated if the tumor cannot be excised completely because this would endanger surrounding vital structures. The prognosis of intrapericardial teratomas after complete resection is favorable [14].

There are several reasons for excising intrapericardial teratomas. First, they carry a risk of malignant transformation [15]. Second, intrapericardial teratomas have the potential to rupture and perforate. There are two previous reports of intrapericardial teratoma perforating into the pericardial sac (8, 9). When the tumor perforates into the pericardial sac and causes inflammation, tumor resection becomes more difficult owing to severe adhesion. Third, when intrapericardial, teratomas can result in constrictive pericarditis [16]. Finally, blood supply of these tumor is reportedly derived from the adventitial vessels of the aorta, creating a risk of massive hemorrhage from the aorta during dissection [3]. When dissecting the aortic adventitia, it is necessary to ascertain whether or not feeding arteries are present. To evaluate the blood supply of these tumor, preoperative coronary CT could be informative.