Anterior Mediastinum

Anterior mediastinal tumors may consist of thyroid enlargement for the superior portion of the anterior mediastinum. This usually involves a thyroid goiter, but may involve a thyroid tumor.

Thymomas are the most common anterior mediastinal mass. They are usually benign but may be malignant. The interrelationship between thymomas and myasthenia gravis will be discussed subsequently, suffice it to say that 10% of patients with myasthenia gravis have thymomas, whereas half of patients with thymomas have myasthenia gravis. The thymoma may be benign or malignant with that determination being made by the surgeon at the time of surgery, not by the pathologist since the histology will appear to be the same microscopically and the invasive features are the most reliable means to determine malignancy (Fig. 18.2).

Germ cell tumors can be either benign or malignant. Benign tumors include benign germ cell tumors and benign teratoma or dermoid cyst. The malignant germ cell tumors are much rarer than benign ones. The malignant germ cell tumors may be seminomanous or nonseminomanous. Patients with seminomanous malignant germ cell tumors must undergo ultrasound of the testicles even if physical examination is negative since there may be a nonpalpable focus of tumor still there with the mediastinal component being a metastasis rather than a primary tumor. Seminomanous tumors have low levels of beta HCG and alpha-fetopro-tein unlike its nonseminomanous germ cell counterpart.

The management of seminomanous germ cell tumors when small and localized is surgical resection followed by radiation. This results in nearly 100% cure rate; 60% of these lesions are cured with radiation therapy alone (this is compared to 80% cure rate for radiation therapy for testicular seminomas). If there are distant metastases from the mediastinal primary or testicular primary, then chemotherapy should be utilized with radiation therapy to the primary. For locally advanced disease but no metastases, the treatment is controversial but should internal jugular internal jugular

THYMUS ANATOMIC RELATIONSHIPS

Fig 18.2. Normal thymus anatomic relationships.

probably involve radiation therapy, and for relapses chemotherapy.

Nonseminomanous malignant germ cell tumors include embryonal carcinoma, malignant teratoma, choriocarcinoma or endodermal sinus tumor (yoke sac tumor). These tumors generally have elevated beta HCG and alpha-fetoprotein. The management of these tumors is chemotherapy (initially cis-platnin, bleomycin and vinblastin regimen) and if there is a response with decrease in the beta HCG/ alpha fetoprotein levels, then resection is indicated. Generally, if there is no decrease in beta HCG and alpha-fetoprotein levels with chemotherapy, then this signifies a relatively aggressive tumor and resection is not indicated. The role of adjuvant radiotherapy is not settled at this point.

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