Middle Mediastinal Mass

Neoplastic Adenopathy

The neoplastic involvement of middle mediastinal lymph nodes is usually metastatic. ³⁷⁹ It must be emphasized that lung cancer usually metastasizes to the middle mediastinal nodes. ⁵⁴² In fact, nodal metastases frequently constitute the bulk of the masses produced by carcinomas that arise in the mainstem bronchi. Small cell lung cancer ( Fig 10.5, A-C ) commonly presents with extensive middle mediastinal adenopathy, which may involve nodes in the other mediastinal compartments and in the hila. ⁷⁹ Metastases from peripheral lung tumors and even distant primaries may also produce metastatic deposits in the middle mediastinum. ¹⁰¹

The challenge of detecting masses that are deep in the mediastinum with minimal contact with the lung, such as subcarinal masses, is similar in all three compartments of the mediastinum. Both CT and magnetic resonance imaging (MRI) are very sensitive methods for detecting small mediastinal masses and are of particular value in staging lymphomas and carcinomas, which have a tendency to metastasize to mediastinal nodes. The two techniques are especially useful for detecting nodal metastases from primary lung cancer and local extensions of esophageal carcinoma. 402, 403, 550

Lymphomas, particularly Hodgkin lymphoma, more frequently arise in the anterior mediastinum but are also an important cause of middle mediastinal adenopathy. ²¹ Lymphoma may arise in the middle mediastinum, and chronic lymphocytic leukemia is a less common hematologic malignancy that involves the middle mediastinal nodes. As many as 25% of patients with leukemia are reported to have mediastinal adenopathy in the late stages of their disease. Like lymphoma, the adenopathy that occurs in patients with leukemia is often not confined to the middle mediastinum, but may also involve the bronchopulmonary (hilar) nodes.

The diagnosis of a neoplastic condition is frequently suggested by clinical information. When a patient is being followed up for a known primary carcinoma located elsewhere and develops a middle mediastinal mass, a metastatic lesion is the most likely diagnosis. A primary lung tumor should be suspected in patients who have associated hemoptysis and a history of smoking. Patients with primary lung tumors frequently have other indirect radiologic signs of the tumor, including atelectasis or obstructive pneumonia. These signs of an obstructing lesion are helpful for distinguishing primary lung cancer from metastases because endobronchial metastases are infrequent (see Chapter 13 ). On the other hand, associated pulmonary opacities and even atelectasis are unreliable features for distinguishing a primary lung cancer from lymphoma. Both types of tumor may invade the pulmonary interstitium locally with a resultant ill-defined perihilar opacity that may be associated with a mediastinal mass. This is best known in the case of small cell carcinoma, which can completely mimic the appearance of lymphoma in the chest because of its early metastases to the regional lymph nodes. Small cell carcinoma ⁵⁷ may even produce massive mediastinal adenopathy before the primary tumor is radiologically detectable.

Calcification of lymph nodes that are enlarged by tumor is very rare. It is reported to occur as a result of bone-forming metastases from malignant bone tumors (osteosarcoma) and even more rarely from primary lung cancer. ³⁶⁰ Calcification has also been observed to develop in nodes affected by Hodgkin lymphoma, usually after treatment with radiation therapy. 51, 327 In both cases, serial examinations and the history should permit a correct diagnosis.