‘Tis the season for migrating foreign bodies

Amanda Mansz    

Animal Health Laboratory, University of Guelph, Guelph, ON. 

AHL Newsletter 2025;29(2):26.

With the warm weather approaching, disease caused by migration of penetrating environmental foreign bodies is expected to be on the rise. Season, geographic location (rural vs. urban) and even the density of an animal’s haircoat are all potential risk factors for foreign body penetration and migration. The warmer months are thought to be of the highest risk for plant material foreign bodies (grass awns), but chronic migration and delayed disease can happen at any time of the year.

Over several years at AHL, memorable cases caused by foreign body migration include a range of objects such as grass awns or other plant material (Figs. 1,4), toothpicks (Fig. 2b), porcupine quills (Fig. 3), and even BBQ brush metal bristles.

Initial differential diagnoses, clinical histories and chronicity of disease for these cases were highly varied. Clinical signs and speed of onset can depend on the final location of the material and the type of inflammation. The inflammatory response can be sterile - centered only on the foreign body – however, plant or other foreign material can often implant bacterial or fungal microorganisms within migration tracts, leading to a more widespread or septic inflammatory reaction.

Plant material and natural environmental debris have a propensity to lodge in interdigital spaces, ears, eyes, and oral/pharyngeal/nasal cavities. Following implantation, foreign material will follow the path of least resistance and migrate in a unidirectional path through tissues, ultimately lodging, sequestering, and triggering an inflammatory response. Clinical signs vary greatly depending on the primary site of implantation and the path of migration, but typically include swellings/masses of the skin and deeper soft tissues of the ear canal, head, face, neck, thorax, flank, and interdigital areas. Conjunctiva, oral, and nasal mucosal membranes may also be affected. Distant migration through the body has been reported to cause pyothorax (Fig. 1), spinal empyema, and even brain abscessation.

Diagnosis of disease resulting from plant material/foreign body migration can be challenging. Microscopically, polarized light can aid in the detection of inconspicuous foreign plant material by producing a refractile glow (Fig. 4c). Ultrasound (Fig. 2a), radiographs or other imaging may be helpful in some cases with larger fragments or radiodense material; however, foreign material is most often found during surgery, biopsy (histologic examination), or at postmortem.  

Figure 1. Lung/mediastinum/pericardial histopathology submission from a 2-year-old English springer spaniel hunting dog with a clinical history of lethargy, anorexia, pyrexia, dyspnea, pleural effusion, bronchopneumonia and draining tracts in the chest wall. 1a. Lung section with suppurative pleuritis and pyogranulomatous inflammation centered on foreign material (black arrow), consistent with plant fragments (H&E, 4x). 1b. Closer view of the entrapped plant material (H&E, 20x). 1c. Comparison of foxtail plant (grass awn) with plant material retrieved from the formalin-fixed section of lung submitted for histopathology.

Figure 2. Pathology submission of a spleen from a 12-year-old pug with a history of lethargy, decreased appetite, vomiting, “hunched” posture, and pyrexia. 2a. Ultrasound detection of a foreign body (red circle) embedded in a thrombosed spleen. 2b. Gross view of the formalin-fixed spleen and the migrating foreign body (toothpick - red arrow) presumed to have been ingested with subsequent migration through the stomach wall into the spleen.

Figure 3. Postmortem of a 17-month-old black bear cub that entered a sanctuary 6 months prior to submission with a history of being quilled by a porcupine. The cub suffered acute death during activity. 3a. A focal region of chronic fibrous pericardial adhesion to the epicardial surface of the heart (blue circle) indicating a possible migration tract. 3b. A migrating porcupine quill (blue circle) penetrating through the left atrium/aortic valve surrounded by a rim of fibrosis. Photo credit to Dr. Rebecca Egan.

Figure 4. Histopathology submission of tissue from an 8-year-old whippet with a 2-month history of an expansile submandibular mass. 4a. Subcutaneous tissue from the submandibular region containing a central aggregate of plant material (presumed foxtail/grass awn) surrounded by pyogranulomatous inflammation (PGI) and an outer fibrous capsule (FC); skeletal muscle (SM). (H&E 4x). 4b. A closer view of the embedded plant material (H&E 20x). 4c. Refractile plant material under polarized light (H&E 20x).

Reference

1. Brant BJ, Singleton DA, Noble PJM, Radford AD. Seasonality and risk factors for grass seed foreign bodies in dogs. Prev Vet Med. 2021;197:105499.