Abnormal bronchus morphology Increased airway neuroendocrine cells 2020-12-23T14:03:04Z Presence of increased numbers of bombesin-immuno-positive neuroendocrine cells (NECs) within distal airways. There are no formal criteria for an increase (which is also dependent on the sensitivity of the staining method), findings of neuroendocrine cells in at least 70% of bronchioles by lung biopsy and at least 10% NECs in an individual airway are consistent with the diagnosis of Neuroendocrine cell hyperplasia of infancy in the appropriate clinical setting. Increases are also seen in other clinical settings. Neuroendocrine neoplasms of the lung encompass NE tumors (NETs), which split into typical and atypical carcinoids, and NE carcinomas (NECs). The bronchial mucosa also contains a small cluster of neuroendocrine cells, also known as Kulchitsky cells. They have neurosecretory type granules and can secrete several factors. This includes catecholamine and polypeptide hormones, such as serotonin, calcitonin, and gastrin-releasing factors (bombesin). Like brush cells, these neuroendocrine cells make up only a small portion of mucosal epithelium, around 3%. Pulmonary neuroendocrine cells (NECs), which produce bioactive products, including bombesin-like peptide and serotonin, are specialized epithelial cells scattered throughout the conducting airways and as innervated clusters (neuroepithelial bodies [NEBs]). In the fetus, NECs are most abundant in the distal airways where they promote branching morphogenesis, epithelial and mesenchymal cell proliferation, and surfactant secretion. Postnatally, NECs function as oxygen chemosensors and degranulate in response to hypoxia. Although NECs decline rapidly in number after the neonatal period, NEC hyperplasia has been described in a number of conditions or disorders, including bronchopulmonary dysplasia, sudden infant death syndrome, pulmonary hypertension, cystic fibrosis, and mechanical ventilation.