Diffuse pulmonary meningotheliomatosis: A diagnostically challenging entity on fine-needle aspiration cytology.

Diffuse pulmonary meningotheliomatosis (DPM) is an exceedingly rare entity consisting of multiple minute pulmonary meningothelial-like nodules profusely involving the lungs. To the best of our knowledge, we present the first cytologic description of this uncommon lesion from a 57-year-old nonsmoking woman. Computerized tomographic-guided fine-needle aspiration cytology from a left upper lobe nodule showed whorled/nested clusters of elongated cells with oval nuclei, clear pseudonuclear inclusions, nuclear grooves/indentations, smooth nuclear contours, fine granular chromatin, inconspicuous nucleoli, and abundant fibrillary cytoplasm with indistinct cell borders. The subsequent pulmonary wedge resections confirmed the diagnosis of DPM. As this condition is exceptionally rare, familiarity with these cytologic features is of the essence to accurately establish this challenging diagnosis.