There are several reasons for a sudden suborbital (below the eye) swelling in dogs – insect bites are indeed possible, but more commonly we should think of trauma, foreign body, tumor and definitely dental disease.
When a tooth is the cause of a suborbital swelling, most commonly we will find a fractured and/or severely periodontally affected and/or non-vital upper fourth premolar tooth. Suspicion of dental disease can be raised by an oral examination on an awake dog (if possible), but it is of an utmost importance to perform a thorough oral and dental examination with dental radiographs with the animal under general anaesthesia to rule in or out dental disease as a cause of a suborbital swelling. In some cases, a diagnosis cannot be reached by dental exam and radiographs and head CT or CBCT is recommended in such cases as superior imaging modality; at the same time these imaging techniques provide an insight into other tissues in the periorbital region.
Sudden suborbital swelling, especially if it enlarges quickly, is considered an emergency – the cause should be determined as soon as possible and appropriately treated. Namely, if dental disease is the cause, infection/inflammation can spread fast to involve larger area of the face. In many cases suborbital swelling will “open”, resulting in a small suborbital wound secreting fluid. This is so called draining tract. These wounds (draining tracts) are not treated per se (no flushing, debridement, suturing or similar is indicated), but the cause (i.e., diseased tooth) must be treated (either extracted or root canal treatment performed).
If you have noted any problems with your animal, please consult your veterinarian.