Representative images from haematoxylin and eosin stained sections of ketamine cystitis tissue. (A) Typical ketamine-induced changes with increased sub-epithelial capilliarisation and oedema of the lamina propria. In this sample there is early lymphoid aggregate formation which is not uncommon. The overlying urothelium is reduced to a patchy single layer of epithelial cells showing atypical cytological changes. (B) Lamina propria with prominent nerve fascicles and conspicuous perineurium; some eosinophils in the background. Scale bar represents 100 μm.