Thymomas are uncommon pathologies and a high index of suspicion is usually required to clinch the diagnosis. Patients may present with localized pain, shortness of breath or superior vena cava syndrome (4). Symptoms of myasthenia gravis can be present in up to 50% of patients with thymomas, and up to 30% may be completely asymptomatic and are discovered to have thymomas on routine chest radiographs (5).
They are typically classified according to the World Health Organization (WHO) histologic classification that is based on their oncologic behavior (6). The types that have been defined are A and AB that can be typified as benign tumors, types B1 and B2 that are the borderline type bridging benign and malignant tumors, and types B3 and C that fall into the malignant end of the spectrum, C being thymic carcinoma (6). Another classification that is used is the Masaoka-Koga staging system (7).
Types A and AB thymomas have the best prognosis, with one study involving 200 cases reporting a 100% 5-year survival rate (8). In comparison, the same study reported Types B2, B3 and C thymomas to have 5-year survival rates of 75%, 70% and 48% respectively (8).
CT Thorax is the gold standard diagnostic and preoperative staging tool for thymomas (9). A general consensus of cumulative ionizing radiation that is accepted in pregnancy is <50mGy (10). The exposure from a single chest CT however is only <0.2mGy (11). In the early stages of the disease, they tend to be well-defined round or oval masses with preservation of fat planes between adjacent structures and the thymoma (9). The presence of irregular margins, calcifications, areas of low attenuations and the loss of clear fat planes suggest a more invasive nature (9). CT is a useful tool pre-operatively whereby it assists in identifying whether or not a thymoma can be surgically resected (9). It also aids with post-operative surveillance (9).
Mediastinal masses that appear as benign on CT (small-to medium in size without radiological evidence of local invasion) may be resected without requiring a pre-operative tissue diagnosis (9). In contrast, larger tumors or those with local invasion will require pre-operative biopsies to establish distinction from thymic carcinoma (9). However for our patient, we proceeded with a preoperative biopsy to ascertain the thymoma type preoperatively, as this would affect the decision of whether or not to proceed with surgery first or allow the pregnancy to continue and perform excision post-partum. As she was found to have a type B2 thymoma, the risk of progression to malignancy would have been higher than if she had, for example, a type A thymoma which would represent a relatively more benign pathology. This in turn would have affected her prognosis as the survival rates for types B3 and C thymomas are lower than those with type B2 as mentioned above. As such, surgery was undertaken as soon as the diagnosis was made.
Due to their malignant potential, all thymomas should be completely removed to prevent progression (9). Careful pre-operative planning and multidisciplinary team involvement is key to a successful outcome especially in cases where a resection or reconstruction of adjacently involved important structures such as the great vessels are required (9). Traditionally, thymectomies are performed via an open surgical method, namely gaining access to the thoracic cavity via a sternotomy or thoracotomy approach (12). However, there exist minimally invasive options through a variety of incisions and techniques including transcervical, extended transcervical, video-assisted thoracoscopy and robotic approaches (12). There have been limited reports on video-assisted thoracoscopic thymectomies in pregnancy. Nevertheless, VATS has been shown to be a safe and effective mode of treatment for lung cancer in pregnancy while resulting in less post-operative pain and faster recovery (13). Furthermore, our use of uniportal VATS does not require the use of carbon dioxide insufflation. Insufflation of carbon dioxide especially at high levels over an extended duration has been linked with fetal acidosis (14). Regardless of the approach, the general principle is to perform complete resection of the thymoma, and if this is not possible through a minimally-invasive approach, conversion to open surgery is required (12).
Pregnancy should not be a reason to delay necessary interventions as this can also affect maternal and fetal outcomes (13). Non-obstetric surgeries have been linked to a higher risk of a miscarriage and preterm labor (15). Hence, antenatal corticosteroids can be considered in patients with a viable fetus to promote lung maturity in the event of a preterm delivery (13). Perioperative assessment should take into account physiological changes in pregnancy such as the increase in cardiac output, oxygen consumption and coagulation factors (16). These patients should have a venous thromboembolism risk assessment done and if required, should be commenced on thromboprophylactic agents (13). The current literature shows no evidence of teratogenic effects of anaesthetic agents to fetuses when administered in standard doses (13). Intraoperative fetal monitoring should be decided on a case-to-case basis and subject to certain factors such as gestational age and possibility of accommodating an emergency delivery during the planned procedure (13). Bearing all this in mind, it is paramount that a multidisciplinary team is involved, including the obstetric anesthetist as the ultimate goal is the safety of both mother and fetus (13).
Adjuvant therapy is not required for operable non-invasive thymomas (17). Complete resection of the thymoma precludes the need for post-operative radiotherapy or chemotherapy (8). However, there is a role of multimodal therapy encompassing surgery, radiotherapy and chemotherapy for more advanced stage thymomas that may not be completely resectable (17).
Thymomas can be the most common mass of the anterior mediastinum but when encountered in pregnancy, they pose different challenges altogether. Imaging in pregnancy should be considered where required. Maternal and fetal outcomes should be weighed when undertaking any major surgery in pregnancy especially when fetal viability has been reached. The safety of VATS in obstetric patients has been well described in the literature and its outcomes have been favorable. Complex cases should involve experts from the necessary field of expertise and a mutual decision with the patient should be sought. As with our patient, it is evident that it can be successfully managed with the right team.
The authors would like to thank the department of Obstetrics and Gynecology, Hospital Kuala Lumpur, and the department of general surgery, Hospital Kuala Lumpur.
Conflicts of Interest
The authors have no conflict of interest.