Management
Surgical excision is generally indicated in symptomatic lesions or lesions with large cystic components. However, since thymic tissue involutes with increasing age, conservative management and follow-up might be appropriate in cases of asymptomatic solid lesions. Notably, ECT could be the only active thymus and an absent mediastinal thymus has been documented in 50% of these patients.3 Wells et al reported that infants who are thymectomized under the age of 1 year show a significant decrease in total T cell counts (especially the CD2 and CD4 subsets) although they have no increase in the frequency of infections.80Therefore, careful consideration should be taken prior to excision of an ECT in children as this might lead to potential immuno-incompetence. Furthermore, thymic involution starts prior to adolescence, with a decline averaging 1% per year81 and therefore a solid ECT could regress over time as the lesion is rarely found in adults. The most relevant findings in our systematic review is that cystic lesions are much bigger and identified at a much older age compared to solid lesions. This is secondary to the natural involution of the thymus tissue with time, and asymptomatic solid ECT could be managed conservatively. In older children, when the ECT has undergone degeneration with formation of large cysts, surgical excision might be appropriate as these will likely not have immunological function.57
One advantage of the surgical excision of an ECT is the potentially malignant transformation of this lesion. However, cervical thymoma is an extremely rare entity, with twenty cases (three malignant) currently reported in the literature, presenting at an average age of 45 years.18
Pirkey in 1954 reported a paediatric case of thymoma arising in a ECT, which was non-metastatic.82 Lewis, in a review of 32 cases of ECT documented malignant cells only in a tracheal mass of a 58-year-old female.83 In addition, there is no data indicating that the incidence of malignant transformation of ECT is any greater than in normal thymic tissue. Furthermore, from our systematic review of the last 20 years, we did not identify any case of malignancy, suggesting that ECT is a benign lesion in children.
Finally, it is important to highlight that surgical excision of an ECT in children might have significant morbidity. As with our described case, the lesion is often adherent to surrounding structures, such as the carotid artery, the jugular vein, and/or the vagus, hypoglossal, phrenic, and recurrent laryngeal nerves. Additionally, 50% have shown a mediastinal connection that could require a sternotomy for complete excision further supporting a conservative approach in asymptomatic lesions.65