Minute pulmonary meningothelial-like nodules. A clinicopathologic study of so-called minute pulmonary chemodectoma.

The clinicopathologic features of 23 so-called minute pulmonary chemodectomas from nine patients are presented. Eight patients were women and one was a man; age range was 34-75 years (mean, 61). Two specimens were surgical resections and seven were autopsies (incidence, one per 60 autopsies). There was no association with a specific disease process or pathologic condition. Grossly, the lesions were 1-3 mm, tan to yellow, pleural or parenchymal nodules. Six of nine cases had multiple lesions; upper lobes were more often involved. Microscopically, characteristic cell nests expanded alveolar septa. Larger lesions were connected by intervening collagen, often imparting a stellate configuration. Smaller lesions had closely apposed nests with mildly thickened alveolar septa. The nodules were strongly reactive for epithelial membrane antigen (12 of 14) and vimentin (10 of 14), and were uniformly negative for cytokeratin, S-100, neuron-specific enolase, and actin. Ultrastructurally, complex interdigitating cell processes were connected by desmosomes. Occasional cytoplasmic filaments were seen. These nodules lack neuroendocrine features, differ from mesothelium, and strongly resemble meningothelial cells. A more accurate term for these lesions is minute meningothelial-like nodules. Their relationship to larger, solitary pulmonary meningiomas is unclear.