Shoulder swelling in a Horse

The mare in Figure 1 presented for a complaint of sudden onset severe swelling at the point of the right shoulder and near non-weight bearing lameness of the same limb. The mare is normally kept with other horses and there is no history of a "equine dispute" or evidence of external trauma. On presentation, the swelling consists of significant edema and the mare is considerably "tender" to pressure and palpation of the swelling. Manipulation of the limb was limited due to the significant pain response that resulted. Radiographic exam of the horse's shoulder is a viable option however due to the pain on manipulation and significant soft tissue swelling, an ultrasound exam was more highly indicated.

Figure 1

The images in Figure 2 and 3 correspond to the soft tissue swelling noted in Figure 1. A large, fluid filled pocket was noted deep to the skin surface. The fluid had a mixed pattern of echogenicity suggesting that the fluid consisted of cellular debris mixed with blood/serum. These findings are most consistent with a large subcutaneous abscess. The two most likely causes for abscess formation in this area would be trauma induced or abscess formation from a bacteria called corynebacterium pseudotuberculosis. This condition is also known as "Pigeon's fever". Pigeon's fever is a serious condition due to the highly infectious nature of the bacteria AND the fact that once the bacteria is present on the premises, it is very difficult to remove from the environment. Correct diagnosis depends on collecting a sample of fluid from the abscess and submitting for laboratory evaluation. Treatment of either condition requires establishing drainage of the abscess and daily  lavage for 10-14 days after drainage. Microbiological identification in this case is pending and the horse is in quarantine on the farm! The abscess was opened and drainage established.

Figure 2

Figure 3

Interestingly, within 7 days of examining the mare above, a gelding presented for similar symptoms. He was found non-weight bearing lame in the pasture with severe swelling of the shoulder region. The referring veterinarian provided digital radiographs which did not identify the cause of the lameness/swelling. On ultrasound exam, a bright, bone-like structure (red dotted line) was noted extending into a fluid filled mass that appeared to be a hematoma (Figure 4 and 5). The bone-like structure was the humerus bone (red dotted line) and it was fractured plus displaced. This gelding was humanely  immediately euthanized!

Figure 4

Figure 5

Although these cases are quite different in outcome, they demonstrate the benefit of soft tissue ultrasound with regards to assessing "swellings". As demonstrated it is possible to evaluate soft tissue changes as well as bony changes.