Related narrative: Mediastinal Mass
The thymus is an organ of immunologic function. In early development it is responsible for the selection of lymphocytes precursors in the selection of mature T-cells. The majority of activity occurs prior to puberty and the thymus is later mostly replaced by fat.
The mediastinum is divided into 3 compartments: the anterior mediastinum ("anterior compartment", the middle mediastinum ("visceral compartment") and the posterior mediastinum ("paravertebral sulcus"). For the purpose of our discussion we will focus on the anterior compartment.
The differential diagnosis of the anterior compartment is classically known by the four-T algorithm. These include thymoma, teratoma, thyroid lesions and "terrible" lymphoma. These four conditions comprise over 90% of all anterior mediastinal masses. In addition, careful history and associated radiologic findings can often narrow the diagnosis even further.
Thymic tumors are the most common mediastinal neoplasm representing 15% of all mediastinal tumors and 40 - 50% of all anterior compartment masses. Of those masses thymoma is the most common tumor and the biology of the tumor is generally favorable with wide surgical excision leading to good long term survival in most patients. Adjuvant or neoadjuvant chemotherapy is recommended in advanced stages. The most widely accepted staging system for thymoma was proposed by Masaoka in 1981.
Masaoka Staging System for Thymoma with Associated Survival:
The mainstay of treatment is surgical excision. There are several principles driving successful therapy:
Lifelong follow-up is required with patients with thymoma for two reasons. Firstly thymomas are indolent tumors and may recur more than 10 years after the initial therapy (even in the early stages). Also patients with a history of thymoma are at increased risk for a second primary malignancy. In fact 20 - 30% of patients presenting with a thymoma develop a primary malignancy.
Discussion Author: Richard Peterson
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Rourke LL, Kesler KA. Mediastinal Tumors. In Cameron JL, ed. Current Surgical Therapy. 8th ed. Philadelphia, PA: Elsevier-Mosby, 2004.
de Perrot M, Keshavjee S. Primary Tumors of the Thymus. In Cameron JL, ed. Current Surgical Therapy. 8th ed. Philadelphia, PA: Elsevier-Mosby, 2004.