FISH analysis of intrapulmonary malignant mesothelioma without a clinically detectable primary pleural lesion: an autopsy case.

Patients with malignant mesothelioma typically present with a pleural effusion or pleural thickening and masses. A rare autopsy case of mesothelioma presenting with multiple bilateral lung nodules without clinically detectable pleural lesions is presented. A definitive diagnosis of the video-assisted thoracic surgery specimen could not be made, though a pattern of fibrosis mimicking organizing pneumonia was identified. Despite corticosteroid therapy, follow-up chest computed tomography showed enlargement of multiple nodules accompanied by the appearance of pleural thickening and effusions. The patient died of respiratory failure 11 months after initial presentation. Autopsy and retrospective analysis of the video-assisted thoracic surgery specimen using a p16 fluorescence in situ hybridization assay showed p16 homozygous deletion. The final diagnosis was sarcomatoid mesothelioma, and the lung nodules were intrapulmonary metastases from a clinically undetectable pleural sarcomatoid mesothelioma. It is important both to consider the possibility of mesothelioma with unusual clinical, radiological and pathological presentations and to remember that p16 fluorescence in situ hybridization analysis can play an important role in the diagnosis of mesothelioma.