TL;DR: Testicular asymmetry (one testicle larger than the other) is often caused by tumors or infection; while usually not an emergency, you should seek immediate care if the area is red, hot, or your dog is vomiting.
What causes one of my dog's testicles to look larger than the other?
When one testicle appears larger than the other in a dog, it is known as testicular asymmetry. This condition can be caused by several factors, including:
- Testicular tumors
- Inflammation (orchitis)
- Infection (epididymitis)
- Scrotal hernia
While finding a lump or swelling can be stressful, many of these issues are manageable when caught early by a veterinarian.
When is my dog's testicular swelling considered a veterinary emergency?
- Low Urgency: If your dog is behaving normally, eating well, and does not seem to be in pain, you can typically wait a few days for a scheduled veterinary appointment.
- High Urgency: If the scrotum is extremely red, hot to the touch, or if your dog is lethargic and vomiting, you should contact a clinic immediately as these could be signs of a more acute infection or torsion.
How does sending a photo help the veterinary team triage my dog?
- A visual reference allows a professional to assess the scale of the swelling, the condition of the skin, and the specific shape of the enlargement.
- The veterinary team can better determine how quickly your dog needs to be seen based on the visual severity.
- Photos help the clinic prepare for necessary diagnostic tests before you even arrive.
Clinical Context (Merck Veterinary Manual)
In dogs presenting with one testicle larger than the other, diagnostic tests should include evaluation for *Brucella canis* infection, cytologic examination of semen with bacterial and mycoplasmal culture (although semen collection may be difficult in ill or painful animals), and fine-needle aspiration of testicular or epididymal specimens for cytology and culture. Testicular biopsy for histopathology and bacterial culture may be performed if needed, after less invasive diagnostic tests. Ultrasonography can confirm testicular torsion and focal lesions such as masses or abscesses in the testis or epididymis, and identify less common causes of scrotal enlargement, such as scrotal hernia or hematoma. Cryptorchidism, a failure of one or both testicles to descend into the scrotum, is a relatively common disorder in dogs and can result in one descended and one undescended testicle.
Chapter: Reproduction, Surgery, Congenital
Source: The Merck Veterinary Manual, 11th Edition (Page 2220)