INTRODUCTION: Minute meningothelial-like nodules are a rare cause of both solitary and multiple pulmonary nodules that may be mistaken for malignacy. They are usually asymptomatic and diagnosed incidentally within surgical specimens or at autopsy. Here we present a case of a 73 year old man who presented for evaluation of nodules found during imaging studies.
CASE PRESENTATION: A 73-year-old man was referred to pulmonary clinic for an abnormal chest computed tomography scan obtained during a calcium score cardiac examination. He had a 12 pack -year smoking history and quit 44 years prior. On review, he denied cough, shortness of breath, fever, night sweats, weight loss, anorexia, or malaise. He denied exposure to tuberculosis, asbestos, or birds. He was raised in Ohio and worked as a Navy pilot until retiring to Washington, DC where he worked in the defense industry.On physical examination, his vital signs were normal. Chest auscultation revealed normal breath sounds. The remainder of his exam was unremarkable.All laboratory values including a hypersensitivity pneumonitis panel were normal. Full pulmonary function testing showed normal spirometry, lung volumes, and diffusing capacity for carbon monoxide. CT of the thorax revealed diffuse, bilateral, non-calcified nodular opacities. Cardiomediastinal structures appeared normal without evidence of mediastinal lymphadenopathy. The patient underwent flexible bronchscopy with bronchial alveolar lavage and transbronchial biopsies of the right upper and lower lobes. Imunohistochemical stains showed positive staining for vimentin and negative staining for CD 31 and chromogranin. Transbronchial biopsy was performed because of concern for underlying granlomatous lung disease or malignancy despite his asymptomatic clinical presentation. The bronchial alveolar lavage fluid showed a macrophage predominance and all cultures including fungal and acid fast bacilli were negative. Currently, there is no consensus on disease monitoring, however given that multiple MPMNs may represent transition to neoplastic proliferation, serial imagining will be performed annually or sooner should symptoms arise.
DISCUSSIONS: MLNs were first described by Korn and colleagues in 1960 as an incidental finding in lungs at necroscopy. The lesions were found to be hundreds in number and present in all lobes with a peripheral predominance. Further analysis of structure, immunohistochemistry, and genomics have better defined the etiology of MLNs. On Histology, these lesions show small nests or whorls of epitheliod cells that can be associated with small vessels or unrelated to any structure. Imunohistochemical and electronmicroscopy show that MLNs lack neurosecratory granules, endocrine granules, nerve association, or other distinctive organelles. The radiographic presentation of minute pulmonary -like nodules in the medical literature is scarce. On plain chest radiograph, these lesions are often not appreciated even in the setting of diffuse disease. Chest CT is more sensitive and a single nodule may be visualized, however, numerous, randomly distributed, bilateral nodules less than 3mm in diameter have been reported. Ground glass nodules and reticularnodular infiltrate have also been described. The differential diagnosis for diffuse pulmonary nodules is quite broad with MPMNs representing a very rare cause. Clinical misinterpretation of this entity for metastatic disease may occur for non-pulmonary pathologists.
CONCLUSION: Minute pulmonary meningothelial like- nodules are rare, commonly asymptomatic, and found incidentally. Single MPMNs are reactive in nature, but diffuse MPMNs may represent a transition to neoplastic proliferation. Multiple MPMNs should be considered in the differential diagnosis in an asymptomatic patient with diffuse bilateral nodular infiltrates and transbronchial biopsy may be a reliable option in obtaining the diagnosis.
DISCLOSURE: Nichole Tanner, No Financial Disclosure Information; No Product/Research Disclosure Information