Histologic findings in cases with fatal retinoic acid syndrome.

(A) Histologic appearance of normal lung tissue. L shows lung alveolae in normal lung; * indicates normal neutrophil in microvasculature. (B) Lung tissue showing infiltration of alveolae with leukocytes from a patient who succumbed to the retinoic acid syndrome. W shows myeloid cells in the airspace (most leukocytes to left of “w”); the lobated nuclei of myeloid cells is prominently seen. Arrows indicate fibrinous exudate due to vascular leak of serum fibrin.