A 64-year-old man comes to the office due to 4 weeks of progressive dyspnea. For the past several months, he has had a nonproductive cough and fatigue. The patient's medical conditions include degenerative joint disease and peptic ulcer disease. He smoked 2 packs of cigarettes daily for 38 years but quit 4 years ago. On examination, there are decreased breath sounds and percussive dullness at the base of the right lung. Chest CT scan reveals a right-sided pleural effusion and diffuse nodular thickening of the pleura. On thoracentesis, bloody fluid is obtained. Pleural biopsy shows proliferation of epithelioid-type cells that are joined by desmosomes, contain abundant tonofilaments, and are studded with very long microvilli. Which of the following is the most likely diagnosis?

Question

A 64-year-old man comes to the office due to 4 weeks of progressive dyspnea.  For the past several months, he has had a nonproductive cough and fatigue.  The patient's medical conditions include degenerative joint disease and peptic ulcer disease.  He smoked 2 packs of cigarettes daily for 38 years but quit 4 years ago.  On examination, there are decreased breath sounds and percussive dullness at the base of the right lung.  Chest CT scan reveals a right-sided pleural effusion and diffuse nodular thickening of the pleura.  On thoracentesis, bloody fluid is obtained.  Pleural biopsy shows proliferation of epithelioid-type cells that are joined by desmosomes, contain abundant tonofilaments, and are studded with very long microvilli.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

This patient with progressive dyspnea and cough has nodular pleural thickening and a pleural effusion. This presentation, in conjunction with characteristic histopathology, suggests mesothelioma. Mesothelioma is a rare, malignant neoplasm arising from mesothelial cells, which line body cavities (eg, pleural, peritoneal, pericardial). Histopathology shows tumor cells with numerous long, slender microvilli and abundant tonofilaments. Immunohistochemical markers (eg, pancytokeratin) are useful in diagnosis. Mesothelioma typically presents with slowly progressive dyspnea, cough, and chest pain. Pleural effusions are common and are often hemorrhagic. Radiography may demonstrate nodular or smooth, unilateral pleural thickening (yellow arrow) and plaque formation; the lung parenchyma is typically uninvolved. Asbestos exposure is the primary risk factor; individuals involved in asbestos mining and industrial applications (eg, insulation, shipbuilding) are at risk for mesothelioma. (Choice A) Adenocarcinoma cells (which can display glandular or papillary characteristics) have short, plump microvilli that distinguish them from mesothelioma cells. Adenocarcinoma tends to involve peripheral lung parenchyma. (Choice B) Carcinoid tumors are neuroendocrine malignancies that most commonly affect the gastrointestinal tract and lungs. They sometimes cause carcinoid syndrome (flushing, diarrhea, wheezing), which is seen more commonly with gastrointestinal tumors. They tend to involve the large bronchi and can appear histologically as sheets of uniform cells with a "salt and pepper" pattern (chromatin with fine and coarse clumps). (Choice D) Small cell carcinoma is associated with smoking but usually arises from the major bronchi. On chest imaging, it is seen as a hilar mass. Pathology shows flat, oval-shaped cells with scant cytoplasm and hyperchromatic nuclei. Neuroendocrine markers such as chromogranin and synaptophysin are usually positive. (Choice E) Squamous cell carcinoma is associated with smoking but arises from the major bronchi; a hilar mass would be expected on imaging. Although desmosomes (intercellular bridges) are seen in squamous cell carcinoma, they are nonspecific and can be found in any tissue that experiences mechanical stress (eg, mesothelium, epithelium, heart). In addition, keratinization (keratin pearls) is expected on histologic examination. Educational objective: Malignant mesothelioma is a rare neoplasm typically arising from the pleura. It is strongly associated with asbestos exposure and presents with progressive dyspnea, cough, and chest pain. Unilateral pleural thickening or plaque formation is seen on imaging; pleural effusions are also common and may be hemorrhagic. Histopathology reveals tumor cells with numerous long, slender microvilli and abundant tonofilaments.

A 64-Year-Old Man Comes to the Office Due to 4