• How often is the lung the site of metastases?
• What are the means by which the tumor cells reach the lung?
• Is it common to see the lung as the only site of metastasis?
• What are the different metastatic patterns?
• Can one predict the probable primary source from a given roentgen pattern?
• What are the modes of presentation?
• What is the best way to make a diagnosis?
• What is the best way to care for it?

Multiple Lesions

• Multiple discrete lung lesions occur due to widely disseminated hematogenous metastasis. 
• The pattern can vary from:
  • diffuse micronodular shadows resembling miliary disease, or
  • to multiple large well defined masses cannon balls.
• Occasionally, cavitation or calcification can be noted. 
• Symptoms:
  • Due to the interstitial location, these lesions are often asymptomatic. 
  • Cough and hemoptysis are the usual symptoms. 
• Needle aspiration or transbronchial biopsy would be the procedure of choice for confirmation of the nature of the lesion. 
• Treatment:
  • Chemotherapy is the choice when the tumor is responsive.
  • Occasional surgical resection of multiple lesions were attempted with some reported success. 
  • In refractory hemoptysis, selective occlusion of bronchial arteries by Teflon is a consideration.

Cannon Balls:

• Neoplasms with rich vascular supply draining directly into the systemic venous system often present in this fashion.

Miliary Pattern: This presentation is seen in patients with the following:

• Thyroid carcinoma 
• Renal cell carcinoma 
• Sarcoma of the bone 
• Trophoblastic disease

Cavitating Lesions:

• Cavitation is identified in 4% of metastatic deposits and, as with primary bronchial carcinoma, is more likely in squamous cell lesions.
• Colon, anus, cervix, breast and larynx account for 69% of such occurrences. 
• Generally, small thin walled metastases usually indicate a primary site in the head or neck, where as most large, thick walled secondaries arise from the gastrointestinal tract. 
• Avascular necrosis of the lesion secondary to vascular occlusion, is the presumed mechanism for cavitation.

Calcification:

• Calcification or ossification is rarely visible in metastasis to the thorax.
  • Calcification of metastasis from ovarian, thyroid, breast and mucin producing gastrointestinal neoplasms. 
  • Calcification in lymphomatous nodes has most often occurred following therapy.
  • Lung metastasis may also calcify following therapy. 
  • Almost all calcified or ossified lung metastasis occurring prior to therapy are due to osteosarcoma or chondrosarcoma. 
  • Isolated cases of such metastasis have also been reported with synovial sarcoma and giant cell tumor of the bone.

Solitary Pulmonary Nodule

• Pulmonary metastases clinically present as a solitary pulmonary nodule.
• Similar to other solitary pulmonary nodular lesions, these are detected by routine chest x-rays. 
• Of the solitary pulmonary nodular lesions, solitary metastases accounts for less than 3% of cases. 
• Colon, chest, sarcoma, melanoma and genitourinary malignancies account for 79% of such instances.
• Solitary metastatic lesion can precede, follow or appear concomitantly with the malignancy. 

Diagnostic Strategy:

• When it appears concomitantly or following definitive therapy of the primary, thin needle aspiration of the lesion is probably the best procedure to establish the nature of the lesion. 
• CT scans are superior to whole lung tomograms in evaluating the presence of other occult metastatic lesions.
• When the solitary pulmonary metastasis precedes clinical recognition of the primary, standard management of the solitary pulmonary nodular lesion should follow.
  • This clinical presentation accounts for less than 1% and routine search for primary is not recommended.

Treatment:

• Surgical resection of single metastasis should be considered:
  • when the primary tumor is resectable
  • no other organ metastasis is evident 
  • and no effective alternate therapy is available
• Surgical resection of solitary lung lesions occurring a few years following curative resection of primary have a better prognosis than the lesions that manifest concomitantly with the primary tumor.

Endobronchial Lesion

• Endobronchial metastases are rare in comparison with parenchymal deposits and account for 2% of patients who died from solid neoplasms.
• Diagnostic challenge:
  • They simulate primary bronchogenic carcinoma in clinical presentation and are often difficult to distinguish, even pathologically.
  •  Simultaneous occurrence of two primaries is a difficult differential to settle on many occasions. 
  • The usual roentgen findings are bronchial obstruction and obstructive atelectasis or pneumonia. 
  • The endobronchial lesion may have characteristic pigment on bronchoscopy in metastatic melanoma. 
• Patients may complain of persistent cough, hemoptysis, wheezing and may have normal chest x-rays.
• Kidney, colon, breast sarcoma and melanoma account for 67% of the cases. 
• The metastases is located subepithelially and is due to hematogenous metastases through the bronchial arteries.
• It is unlikely to be secondary to endobronchial drop metastasis as tumor cells often require fibrin thrombin to impact. The cough and mucociliary reflex may efficiently clear aspirated cells. 
• Palliative radiation or resection becomes necessary if the patient has hemoptysis or refractory obstructive pneumonitis.

Tracheal Metastasis

When the lesion is located in the trachea, patients will present with severe wheezing and have normal chest x-ray findings.

Lymphadenopathy

• The incidence of lymph node metastasis is high with extrathoracic primaries, as well as bronchogenic carcinoma. 
• Autopsy incidence related to various primaries range from 20-60%.
• However, the reported incidence and radiographically visible lymphadenopathy vary greatly.
• Radiographically visible enlargement is probably found in less than 5% of all patients with extrathoracic primary neoplasms. 
• Head and neck and genitourinary tract neoplasms most often cause visible intrathoracic enlargement followed by malignant melanoma and breast carcinoma.
• Diagnostic challenge
  • Lymphadenopathy may be hilar, mediastinal or both. 
  • This opposed to sarcoidosis, which rarely causes mediastinal nodular enlargement without hilar enlargement.
  • Lymph node metastasis is not always associated with lung metastasis. 
  • The radiographic appearance may, therefore, be indistinguishable from sarcoid, non-infectious granulomatous disease, lymphoma, leukemia or a primary mediastinal tumor. 
  • Diagnostic problems arise in the minority of patients who do not have known primary neoplasms.
  • Asymptomatic patients with symmetric hilar enlargement usually have sarcoidosis. 
  • Metastatic disease may cause bilateral hilar enlargement. However, these patients are usually symptomatic. 
  • Anterior mediastinal node masses are common in lymphoma but rare in sarcoid, as seen on chest radiographs.

   

Pleural Effusion

• Pleural effusion is one of the common metastatic patterns. 
• The effusions often tend to be massive, recurrent and associated with shortness of breath. 
• This pattern is associated with extensive underlying lung and systemic metastases. 
• Most patients expire within three months.
• Malignant effusions account for more than 50% of exudative pleural effusions. 
• Lung, breast, stomach and ovary account for 81% of cases.
• Pleural biopsy and fluid cytology establish the malignant nature of the process.
• Pleural sclerosis with tetracycline instillation is the palliative procedure of choice in problem effusions.

• Significant pleural masses can exist without recognition (as in the adjoining CXR), even in the absence of pleural effusion.
•  Iatrogenic pneumothorax facilitates visualization of pleural masses.
• CT scan can reveal pleural masses that are not seen on routine x-rays.
• Thymoma, multiple myeloma and cystadenocarcinoma lung are reported to give such a metastatic pattern.

Spontaneous pneumothorax Pneumothorax occurring secondary to pulmonary metastasis is rare.  This mode of presentation occurs secondary to necrosis of subpleurally located metastases with the resultant bronchopleural fistula.  Cavitating sarcoma is reported to present in this manner.  In some instances, the subpleural metastases are not sufficiently large enough to be recognized in x-rays and pneumothorax is the presenting manifestation.

Chest Wall Lesion

• Metastatic lesions to ribs are common. 
• Occasionally, these lesions expand and encroach on the lung, masquerading as a lung lesion.
• The characteristic extrapleural signs, namely the peripheral location, indistinct outer margin with a sharp inner margin and biconcave edges help point towards the true location of the lesion.
• Recognition of such lesions focuses ones attention to the ribs and facilitates easy biopsy by percutaneous techniques.

Alveolar Pattern

• Alveolar form of metastases is relatively rare and is often an unrecognized form of metastatic pattern. 
• Histologically, they are indistinguishable from primary alveolar cell lung carcinoma.
• Pancreatic carcinoma is the most common primary to present in such a fashion. 
• Metastatic liposarcoma and laryngeal carcinoma have occasionally been reported to give a similar pattern. 
• The metastatic lesions from choriocarcinoma also have features of alveolar pattern. 
  • However, this is secondary to bleeding into the lesions rather then due to tumor, per se.

Interstitial Pattern

• Less than 10% of lung metastases have a lymphangitic pattern.
• Pathogenesis:
  • Lymphangitic metastatic disease in the lung is generally believed to be the result of tumor spread along the perivascular lymphatic after initial deposition of tumor embolus in a pulmonary capillary by hematogenous route. 
  • There is evidence that gastric carcinoma is an exception to this with direct lymphatic extension occurring from the abdomen to chest, across the diaphragm.
• The stomach, lung and breast account for 80% of cases. 
• The large majority of patients with unilateral diseases have bronchogenic carcinoma. 
• Most patients have dyspnea with or without cough. Initially, symptoms can be mild.
• Diagnostic challenge:
  • There is evidence of lung tissue disease on chest radiographs: small linear and nodular densities, reticular nodular pattern, septal lines. 
  • The appearance is similar to interstitial changes seen in pulmonary edema, pneumoconiosis, usual interstitial pneumonitis or sarcoid. 
  • There is frequent pleural effusion on hilar lymphadenopathy.
  •  Some symptomatic patients have normal radiographs.
• Transbronchial lung biopsy or needle aspiration can provide tissue for diagnosis. 
• In the absence of suitable chemotherapy, only symptomatic therapy can be provided. 
• Most patients become severely dyspneic and expire within a few months.

Subacute Cor Pulmonale This form of presentation occurs when small subliminal tumor deposits obstruct a sufficient cross section of the pulmonary vascular bed.  The spectrum of pulmonary symptoms is identically to thromboembolism.  Patients are in prolonged respiratory distress with normal chest x-ray, and with or without signs of pulmonary hypertension.  Choriocarcinoma, hepatoma, breast and stomach tumors account for most of the primaries with such presentation.  This entity should be considered in a female with severe respiratory distress with a history of recent abortion or delivery chorionic gonadotropin levels are high.  When recognized, chemotherapy offers a favorable prognosis in patients with choriocarcinoma.  Prognosis is poor with other primary malignancies.

Conclusion

• Lung metastases occur in approximately 30% of malignant disease cases.
• Frequently, it is the presenting manifestation and search for the primary is lengthy and cumbersome. 
• The roentgen patterns of thoracic metastases vary. Awareness of the common primaries presenting with a metastatic pattern facilitates the search for the source. 
• The venous and lymphatic drainage of the organ and the cell type are some variables that seem to determine the metastatic pattern. 
• Each metastatic pattern has a unique clinical presentation because of its locale and extent. 
• Each pattern raises a distinct differential diagnosis, differs in the best diagnostic procedure and the choice of therapeutic modality.