Pleural effusion is a common presenting manifestation of peripheral adenocarcinoma of lung.
Very rarely metastatic pleural tumors spread diffusely within the pleura to form an encasing mass and may be confused with diffuse malignant mesothelioma. We describe a patient who presented with progressive chest pain, dyspnea and weight loss. Thoracic CAT scan revealed unilateral diffuse nodular pleural thickening encasing the lung and producing lung entrapment. Diagnosis of pleural metastasis with lung adenocarcinoma was made by thoracoscopic pleural biopsy. Immunohistochemistry helped distinguish metastatic adenocarcinoma of lung from diffuse malignant pleural mesothelioma.
A 57 year old male, previously healthy presented with progressive dyspnea, right sided pleuritic chest pain, anorexia and weight loss of 30 lbs over a period of 3 months. He denied cough, hemoptysis, anorexia, night sweats, fever, chills. He admitted to 26 pack years smoking history. He was a construction worker and involved in demolition of buildings in NY city since 1980. On physical examination he was in no acute distress, and vital signs were stable. Chest examination disclosed decreased breath sounds and dullness to percussion on lower right lung zone. Routine blood work up was normal. Chest XR showed right sided pleural effusion with volume loss and without mediastinal shift. CT Chest revealed diffuse nodular pleural thickening extending to the fissures with loculated pleural effusion and entrapment of r lung. CT scan guided thoracentesis drained 250cc of fluid . The fluid was grossly hemorrhagic and cytology negative for malignant cells. Thoracoscopic pleural biopsy and immunochemistry were positive for pleural metastasis with primary adenocarcinoma of lung.
Adenocarcinoma of lung is the most common cell type of non-small cell lung carcinoma. Because of the peripheral location, it is not uncommon for adenocarcinoma to present with pleural effusion 1. PMA( Pseudomesotheliomatous adenocarcinoma) is an uncommon variant of peripheral lung cancer first described by Harwood et al in 1976. The majority of these patients were men in fifth and sixth decade of life and were heavy smokers. The presenting symptoms include chest pain, cough and dyspnea2. Radiographic presentation of diffuse nodular pleural thickening with spread along the fissure and bronchovascular bundles mimicks diffuse malignant mesothelioma. Like Malignant mesothelioma, PMA is an aggressive rapidly growing tumor. It has a poor prognosis with a median survival of approximately 6 months. Pleural spread of carcinoma lung usually presents as a pleural effusion but it may spread along the pleura in a fashion grossly similar to that of a mesothelioma. Such spread of carcinoma lung with clinical, radiological and gross appearance mimicking a diffuse malignant pleural mesothelioma is termed as a pseudomesotheliomatous adenocarcinoma. 4The few reported cases in literature indicate that the lesion occurs predominantly in men in fifth and sixth decades of life and 5in second or third decade of life in HIV positive individuals. It is usually seen with a peripherally located adenocarcinoma of the lung. (6,7) Other cell types of lung cancer including small cell and large cell carcinomas have also been reported to present as a pseudomesothelioma. Case reports have documented similar radiological appearance with pleural metastasis in thymomas and angiosarcoma. Pleural thickening with a nodular mass within lung parenchyma and prominent hilar lymphadenopathy favors a diagnosis of adenocarcinoma with pleural involvement. It is difficult to distinguish adenocarcinoma from diffuse malignant mesothelioma based on histological appearance on light microscopy. Microscopically, both tumors can form papillary structures. The tumor cells in an epithelioid mesothelioma are usually more uniform, cuboidal, and less crowded than the tumor cells in adenocarcinoma, which are more pleomorphic, columnar, and crowded with nuclear molding. Electromicroscopic studies and immunohistochemical studies, with special stains for tumor markers are frequently necessary to separate diffuse malignant mesothelioma from adenocarcinoma. Electron microscopy can also help in distinction; adenocarcinomas have short and thick microvilli as compared to mesotheliomas, which have very long, thin microvilli.8 In conclusion, this case was an unusual presentation of adenocarcinoma of lung. The diagnostic difficulties were caused by his rather non-specific presentation and by the pleural thickning on the CT scan. In a patient with known asbestos exposure,the diffuse nodular pleural thickening, spread along the fissure with lung entrapment mimicked diffuse malignant epithelial mesothelioma. Special stains with immunohistochemistry were required to make the distinction.
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