Full-Thickness Uterine Biopsy in Dogs: is It Worth the Invasiveness?

The use of uterine biopsy in canine reproductive medicine is still evolving, with ongoing debate regarding the most appropriate technique and its diagnostic value. Among the available methods, full-thickness biopsy offers comprehensive tissue evaluation but comes with increased invasiveness. This raises an important clinical question, does the additional information justify the procedure? 

Biopsy Techniques in Perspective 

Two main approaches are described for obtaining uterine biopsies in dogs¹: 

• Transcervical partial-thickness biopsy using forceps 

• Full-thickness biopsy via surgical access 

While partial biopsies are less invasive, they are limited to superficial layers of the endometrium. Full-thickness biopsies, on the other hand, provide access to deeper structures, including the myometrium, potentially revealing lesions that would otherwise go undetected. 

Why Depth Matters¹ 

Emerging evidence suggests that some clinically significant lesions may not be confined to the endometrium. In particular, lymphoplasmacytic inflammation has been observed deep within the endometrium and even extending into the myometrium. 

In one analysis, nearly half of such inflammatory changes were located deep within the endometrium, with additional involvement of the myometrium. This finding has important clinical implications, superficial sampling alone may miss critical pathology contributing to subfertility. 

Inflammation and Diagnostic Yield¹ 

Inflammation remains the most significant histopathological difference between fertile and subfertile bitches (p=0.004). More importantly, the type and location of inflammation provide valuable diagnostic clues. 

Lymphoplasmacytic inflammation, strongly associated with subfertility (p<0.001), may represent a chronic process that disrupts normal uterine function. Detecting such changes often requires deeper tissue sampling, supporting the use of full-thickness biopsy in selected cases. 

Limitations and Practical Challenges^1,2 

Despite its advantages, full-thickness biopsy is not without limitations. The invasive nature of the procedure means it is often reserved for cases where other diagnostic methods have failed or when surgical intervention is already planned, such as during a cesarean section. 

Additionally, variability in sampling location, number of samples, and timing within the reproductive cycle can affect interpretation. For example, samples taken during pregnancy may show changes related to placentation, complicating comparisons with non-pregnant animals. 

Interpreting Findings in Context 

Another challenge lies in differentiating pathological findings from normal physiological changes. Certain inflammatory responses, particularly neutrophilic and histiocytic types, may occur naturally during specific stages of the estrous cycle. 

This underscores the importance of timing and clinical context when interpreting biopsy results. Without this, even full-thickness samples may lead to misinterpretation. 

Breed and Size Considerations 

There is some evidence suggesting that larger breeds may be more prone to subfertility. However, uneven breed distribution and sampling bias limit the strength of this conclusion. Importantly, no significant association was found between body size and the presence of inflammation. 

For clinicians, this means that biopsy findings should not be overinterpreted based on breed or size alone. 

When Should You Consider Full-Thickness Biopsy? 

In clinical practice, full-thickness biopsy may be most valuable in: 

• Repeated unexplained breeding failure 

• Suspected chronic uterine disease 

• Cases requiring surgical intervention where biopsy can be obtained opportunistically 

It is less likely to be justified as a first-line diagnostic tool in routine infertility workups. 

Future Directions 

There is a clear need for standardization in biopsy techniques, including optimal sampling locations and the number of samples required. Prospective studies incorporating complete reproductive histories and whole uterine evaluations will be essential in refining its clinical utility. 

Conclusion 

Full-thickness uterine biopsy offers a deeper and potentially more informative assessment of uterine pathology in the bitch. While its invasive nature limits routine use, it can provide critical insights, particularly in identifying deep-seated inflammatory lesions associated with subfertility. 

For veterinarians, the key lies in selecting the right cases, interpreting findings within clinical context, and integrating biopsy results with other diagnostic modalities to make informed reproductive decisions. 

References: 

1. McRae GR, Coutinho da Silva MA, Runcan EE, Stephens JA, Premanandan C. Histological Studies in the Endometrium of Fertile and Subfertile Bitches. Reproduction in Domestic Animals. 2025 Apr;60(4):e70055. https://onlinelibrary.wiley.com/doi/pdf/10.1111/rda.70055 
2. Premanandan, C., and E. Runcan. 2019. “Canine Placentation: Normal Gross and Histologic Structure, and Confounding Features of Evaluation.” Clinical Theriogenology 11, no. 4: 623–625. https://doi.org/ 10.58292/ct.v11.9463