A 34-year-old woman presenting with abdominal pain, chest pressure, weight loss and tachycardia was found to have an 11.4 cm anterior mediastinal mass associated with intrathoracic lymphadenopathy on chest CT. Core needle biopsy was concerning for a type B1-thymoma.
Importantly, during this patient’s initial work up, she was found to have both clinical and laboratory evidence of Graves’ thyroiditis, raising diagnostic suspicion for thymic hyperplasia (TH) rather than thymoma. The case discussed here highlights the unique challenges that arise in the evaluation and management of thymic masses and serves as a prudent reminder that both benign and malignant disorders may present with mass-like changes.
Thymomas are a heterogenous group of tumors that vary in clinical behavior, and prognosis is dependent on pathologic stage, histologic classification, and surgical resectability. Notably, neither the histologic subtype nor pathologic stage can be confirmed on core needle biopsy due to the limited architecture visible on small tissue samples—thus, large biopsy specimens and/or complete surgical resection are often required for definitive diagnosis and classification.
TH is a reactive phenomenon that develops in the setting of physiologic stress or systemic disease (e.g., autoimmunity, HIV) and will generally regress upon treatment of the underlying process. This concept is perhaps best illustrated by the relationship between TH and Graves’ autoimmune thyroiditis.
Ongoing evaluation of the patient’s thymic mass was pursued. A second core needle biopsy showed features of both type B1-thymoma and TH. A repeat chest MRI obtained one month after anti-thyroid initiation demonstrated no interval change in the size of the thymic mass. Despite extensive multidisciplinary efforts, diagnostic uncertainty persisted. The patient ultimately underwent a total thymectomy, confirming a diagnosis of massive benign thymic hyperplasia.
The diagnostic uncertainties manifested in this case serve as an important reminder that thymectomy for a benign process is not a rare occurrence. While the relationship between Graves’ thyroiditis and thymic hyperplasia is well described in the endocrine literature, we believe that this is an area of unmet need for the thoracic oncology community. Furthermore, there have only been a handful of reports describing massive thymic enlargement as seen in this case. As oncology experts, it is critical that our multidisciplinary teams recognize benign and malignant thymic disorders alike and that we are agile in the strengths and shortcomings of standard diagnostic tools (i.e. cross-sectional imaging and limited biopsy samples) in the diagnostic evaluation of such entities—particularly so as to avoid unnecessary and invasive diagnostic and therapeutic interventions in such cases. Thus, clinical evaluation of thymic disease necessitates a comprehensive assessment for both benign and malignant causes of thymic enlargement—particularly thyroid function— so as to avoid unnecessary or invasive diagnostics. Multidisciplinary specialists evaluating such patients should be reminded of the nuanced differences between benign TH and thymic neoplasms. We provide a review of the published literature, with emphasis on the radiographic and pathologic findings associated with thymoma vs. benign thymic hyperplasia, so as to provide guidance on optimal diagnostic evaluation in such cases.