Lung - Atypia, Cellular

Atypia can be seen in the airways (Figure 1 and Figure 2) or in the alveoli (Figure 3 and Figure 4). Cellular atypia in rodent lungs is characterized by one or more of the following features: cytoplasmic basophilia, hyperchromatic nuclei, loss of nuclear polarity, high nuclear to cytoplasmic ratio, karyomegaly, anisokaryosis, and pleomorphism. The atypical cells are often poorly differentiated and may be binucleated. They may have multiple and/or enlarged nucleoli. In the pathology literature, cellular atypia, atypical hyperplasia, and atypical adenomatous hyperplasia have been used synonymously with dysplasia to signify cells and nuclei with abnormal size, shape, organization, and/or tinctoral properties. While individual cells in the alveoli may have features of atypia, cellular atypia can also be seen in areas of bronchial, bronchiolar, or alveolar epithelial hyperplasia or squamous metaplasia. Some of the features listed above may also be seen in regenerating cells (e.g., cytomegaly, karyomegaly, cytoplasmic basophilia, increased nuclear to cytoplasmic ratio). The biological significance of this lesion is not known; in the absence of obvious regeneration, it may represent a preneoplastic change, particularly when associated with hyperplasia or squamous metaplasia.