An Incidentaloma Not Located in the Adrenal Gland

Abstract

INTRODUCTION: Thymomas and thymic carcinomas are rare tumors of the anterior mediastinum. We present a case of a thymoma incidentally discovered on chest imaging. CASE PRESENTATION: A 74 year old female was admitted to the hospital with decompensated heart failure. Initial workup included plain films of the chest which showed new multifocal left upper lobe opacities. Computed tomography (CT) of the chest without contrast obtained to better characterize these infiltrates showed a new 5-6cm anterior mediastinal mass.CT guided core biopsy of the mass showed variable-sized islands of epithelial cells within a fibrous stroma with rare scattered lymphocytes and total absence of normal thymic tissue. Extensive immunohistochemical staining suggested a diagnosis of thymoma. Acetycholine receptor antibodies were negative.The patient underwent median sternotomy and thymectomy with total apparent removal. Pathology showed a type A thymoma, T1a N0 M0, with some transcapsular invasion into the mediastinal fat.The patient was scheduled to undergo postoperative radiation therapy.DISCUSSION: Thymomas may be incidentally seen on chest imaging, and patients may present with symptoms due to the presence of a mass in the thorax or to paraneoplastic phenomenon such as myasthenia gravis (MG) which is present in up to half of patients with thymomas.Imaging of mediastinal masses with CT or MRI is key in determining resectability. MG should be ruled out in patients with anterior mediastinal masses given its high prevalence in thymic neoplasms and the implications MG has on anesthesia. The World Health Organization (WHO) morphologically classifies thymomas based on their compositions of epithelial and lymphoid cells. Tumors with high spindle cell density or lymphoid density have a better prognosis than those with high epithelioid density. Our patient had a type A thymoma, comprised mostly of spindle cells with few scattered lymphocytes. However, the prognosis of thymic neoplasms is mostly dependent on their TNM stage and resectability. Prognosis is excellent for local, resectable tumors; however, 10 year survival in metastatic disease is about 47%. Postoperative radiation therapy is indicated in most thymic neoplasms aside from cases with no capsular invasion. Chemotherapy with or without immunotherapy may be indicated in metastatic disease or partially resectable/unresectable tumors. CONCLUSIONS: Thymic neoplasms often present as incidentalomas. Multidisciplinary medical and surgical teams are needed to manage thymic cancer. It is often a resectable disease, frequently causes paraneoplastic phenomena, is amenable to radiation and systemic therapies, and has a widely variable prognosis.