Pulmonary Metastasis

Pathology and Pathogenesis

Although metastasis to the lung can occur along multiple routes (through pulmonary or bronchial arteries, lymphatics, or airways), the radiologic manifestations of such disease demonstrate considerable overlap. The four patterns of metastatic disease to the lung parenchyma are parenchymal nodules (Fig. 19.2), interstitial thickening (lymphangitic carcinomatosis), tumor emboli with or without pulmonary hypertension or infarction, and airway obstruction from endobronchial tumor [7].

Symptoms and Signs

Surprisingly, signiÞcant number of patients with pulmonary metastasis showing multiple nodules or masses is asymptomatic. NonspeciÞc symptoms including cough, vague chest discomfort, and dyspnea can result from a very large tumor burden. Hemoptysis can occur. Constitutional symptoms such as weight loss, anorexia, and generalized weakness may be the only manifestation in the absence of respiratory symptoms.

CT Findings

CT Þnding of hematogenous pulmonary metastasis consists of multiple nodules (Fig. 19.2). The size of nodules range from a few millimeters to several centimeters in diameter, and nodules are usually of varying size. They tend to be most numerous in the outer third of lungs, particularly the subpleural regions of the lower lung zones, and have a random distribution within the secondary pulmonary lobules [8, 9]. Most nodules are round and have smooth margins. They may be lobulated, however, and have irregular margins. Occasionally, a ground-glass opacity (GGO) halo can be seen in highly vascular or hemorrhagic tumors such as angiosarcoma [10]. Cavitation of nodular metastasis can occur in 4 % of metastases. (Please note section ÒCavitiesÓ in Chap. 23.) CalciÞcation in nodular metastasis is very uncommon and usually indicates that the primary neoplasm is osteogenic sarcoma, chondrosarcoma, synovial sarcoma, or carcinoma of the colon, ovary, breast, or thyroid [8].

CT–Pathology Comparisons

The margins of nodular metastases on thin-section CT may depend on their histologic appearance at the growing edge of the tumor [11]. Smooth margins on CT scans

correspond to the expanding (tumors that compress the surrounding normal lung) and alveolar space-Þlling (tumors that inÞltrate and Þll the alveolar spaces) types, nodules that have poorly deÞned margins tend to be the alveolar cell type (tumors that grow along the alveolar walls), and those that have irregular margins are predominantly the interstitial proliferation (tumors that inÞltrate the interstitium) type. A GGO halo surrounding nodular metastasis reßects the presence of hemorrhage in the parenchyma adjacent to the nodule or the spread of tumor cells along the alveolar walls [8].

Patient Prognosis

Prognosis of the patients with pulmonary metastasis presenting with multiple nodules or masses is poor unless the primary tumor is highly responsive to anticancer chemotherapy.

Pulmonary Lymphoma

Pathology and Pathogenesis

Extranodal marginal zone B-cell lymphoma of bronchialassociated lymphoid tissue (BALT lymphoma) may be the most common type of pulmonary lymphoma and frequently shows nodular interstitial inÞltrate of lymphoma cells along bronchovascular bundles and interlobular septa. Sheets of inÞltrating lymphoma cells can obliterate underlying lung architecture. Lymphoepithelial lesions, characterized by epithelial inÞltration by lymphoma cells, are common [12].

Symptoms and Signs

Median age of primary pulmonary lymphoma is about 60 years [13]. Patients often present with pulmonary symptoms such as cough, dyspnea, chest discomfort, occasional hemoptysis, or constitutional symptoms. However, a majority of low-grade lymphoma patients are asymptomatic.

CT Findings

Typical CT Þndings of primary or secondary pulmonary lymphoma include single or multiple nodules or masses (Fig. 19.3) of mass-like airspace consolidation with air bronchograms [1, 14]. Less common CT Þndings include interlobular septal thickening, thickening of bronchovascular bundles, centrilobular nodules, and areas of GGO.