Nontherapeutic thymectomy, inevitable or avoidable?

Abstract

Approaching anterior mediastinal lesions remains a challenge despite several available imaging modalities. These lesions range from benign cystic lesions like thymic cysts, to slow-growing malignant lesions like thymomas and to invasive and rapidly growing malignant lesions like thymic carcinomas, lymphomas or germ cell tumours. Apparently, the gold standard diagnostic method is core-needle biopsy. This is an invasive procedure that bears risks like bleeding and pneumothorax. More importantly, there is an additional risk of stage upgrading by pleural implantation, particularly in the case of thymoma. For this reason, the NCCN guideline recommends tissue diagnosis with core-needle biopsy only in locally advanced or unresectable cases [1]. Both the NCCN guidelines and 91% of the Centers of the European Society of Thoracic Surgeons recommend upfront surgery without biopsy whenever a resectable thymoma is strongly suspected [1, 2]. This trend has resulted in a significant rate (22–68%) of nontherapeutic thymectomies [3, 4], some for asymptomatic benign thymic lesions like true thymic cysts and thymic hyperplasia (in the absence of myasthenia gravis), and some in the case of malignant lesions that do not require surgical resection like mediastinal lymphomas. A thorough history and physical examination for any associated paraneoplastic syndromes like myasthenia gravis, red cell aplasia or B symptoms and any peripheral lymphadenopathies, as well as results from blood tests like a CBC, α-Fetoprotein, β-HCG and LDH, can narrow the differential diagnosis. The remaining lesions are either thymic epithelial tumours that should be resected, or thymic hyperplasia without myasthenia gravis, asymptomatic thymic cysts and mediastinal lymphomas that clearly do not require resection. Although MRI, particularly with the chemical shift, and CT have been shown to be highly sensitive and specific in differentiating thymomas from thymic hyperplasia or thymic cysts [5], they are not ideal for differentiating thymoma from lymphoma. PET–CT scan has also been investigated for such differentiation with some inconsistent results [6]. This diagnostic dilemma remains present and has resulted in a significant number of unnecessary thymectomies.