Nose - Foreign Body

Foreign bodies are a common background finding in rats and mice and are not typically correlated with exposure concentration. The term "foreign body" refers to any aberrant material in the nasal cavity. If the morphology of the foreign material is consistent with the test agent, if the material is seen only in exposed animals, and if the amount of material correlates with the exposure concentration, the term “foreign material” should be used rather than foreign body (see Nose - Foreign Material ). The most common foreign bodies are hair shafts (Figure 1) and plant material (feed or bedding). Hair shafts are translucent and multilayered, and feed or plant-based bedding can be identified by the presence of plant cell walls. Often the material cannot be identified (Figure 2 and Figure 3, arrows). Foreign bodies can be found anywhere in the nasal cavity, in the lacrimal ducts, in the incisive ducts, or embedded in the tissues. The inhaled material typically incites a focal suppurative, pyogranulomatous, or granulomatous reaction and is usually surrounded by accumulations of macrophages and/or neutrophils. The epithelium adjacent to the foreign body may also show changes (e.g., necrosis or degeneration, squamous metaplasia, or hyperplasia).