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Series 1: The Birds & The Bees of Veterinary Reproductive Clinical Sonography

Series 1 - Testicles
Retained Testicle Hunt

Not something we scan for every day, and many may not be familiar with the protocol. And like everything else SDEP, there is a protocol that avoids a hit or miss type of scenario.

Studies show that ultrasound has a high sensitivity for identifying both abdominal and inguinal retained testes, and very high predictive value (that is, once identified on ultrasound the testes were found in their respective locations during surgery).
First, look at the appearance of normal testicles so you know what to search for. You don’t want to go in surgically and discover you imaged a lymph node instead of the testicle…
TIP:  Practice imaging normal testicles in the scrotum of patients presenting for routine castration.


Normal Canine Testicle - The short arrow is pointing to the central mediastinum testes, the classic landmark. The long arrow indicates the tail of the epididymis, mildly hypoechoic to the testicular parenchyma and usually coarser echotexture.

Normal Great Dane Testicle - Critical landmark is the central hyperechoic mediastinum testes; imaged here with the linear probe.


Normal Feline Testicle - Note the central hyperechoic mediastinum testes. Sonographically similar to the canine but with a less prominent epididymis.


Video of a sweep through the scrotum to image the testicles - Note the hyperechoic mediastinum testes. A high-frequency linear probe was used. The central hypoechoic region represents the acoustic shadow of the scrotal septum.


Normal Geriatric Canine Testicle - May present some heterogenous changes within the parenchyma. However, no deviation of parenchyma or capsule should be present.


Key points to retained testicle scanning:


  • Use a high frequency linear probe
  • Use light pressure
  • If unilateral, push the existing testicle dorsally and cranially into the inguinal canal to determine if right or left, then scan the opposite side
  • Inguinal testes range from immediately cranial to the pubis to the inguinal region
  • Abdominal testes range from caudal to the kidneys to lateral to the urinary bladder trigone; may be adjacent to the colon, small intestine, aorta, caudal vena cava
  • Be prepared to scan from the caudal inguinal area to the caudal pole of the kidneys
  • The parenchyma may be uniformly echogenic (coarse, homogeneous texture) or have decreased architectural detail, but the important landmark is that all will have the central linear hyperechoic mediastinum testis (also called a median raphe)as evidenced in the above images.  This helps differentiate a testicle from an abdominal lymph node with similar echogenic texture.
  • The tubular epididymis is mildly hypoechoic to the testicular parenchyma


Intra-Abdominal Retained Testicle - Located adjacent to the trigone of the urinary bladder. Photo courtesy of Bob Hylands, DVM.


Feline Retained Testicle - Located in the left inguinal region. The mediastimum testis is not obvious.



Feline Retained Testicle (same patient)- This time, using a linear probe and taken during intra-operative ultrasound to confirm location, that it is a testicle and not a lymph node or other.



  • Practice imaging normal testicles in the scrotum of patients presenting for routine castration.
  • Annotate your images if you can, and upload to the forum under the post “Reproductive Campaign”.

*We will let you know if you are right, or correct, and archive all of your images to a library for future training!

Take me to Series 2!