Why Neurovascular Anatomy Matters in Canine Perineal Hernia Repair

Perineal hernia (PH) in dogs is often described as a weakening of the pelvic diaphragm that allows pelvic or abdominal structures to displace into the perineal region. However, beyond the visible muscular defect lies a far more complex surgical challenge involving displacement of blood vessels and nerves within the pelvic cavity. A precise understanding of this neurovascular anatomy is essential because any variation involving the internal iliac artery (IIA) and its branches can influence tissue viability, surgical dissection, and postoperative function¹. 

Classical anatomical descriptions identify the internal pudendal artery (IPA) as the source of the caudal rectal artery, along with the dorsal and ventral perineal arteries (PAs)¹. Yet previous anatomical investigations have reported multiple branching variations that may become especially significant in dogs with PHs. As pelvic structures shift during chronic herniation, the normal location of vessels and nerves may also change, increasing the likelihood of intraoperative complications¹. 

PH predominantly affects older intact male dogs, with reports indicating that nearly 96% of affected animals are male. Certain breeds, including Poodles, Pinschers, and Maltese, appear predisposed¹. Surgical correction remains the preferred treatment approach and commonly involves internal obturator muscle transposition. In more advanced or recurrent cases, surgeons may require polypropylene mesh reinforcement or semitendinosus muscle flap reconstruction¹. 

Vascular Variations and Surgical Risk¹ 

Evidence from anatomical studies suggests that the vascular arrangement of the perineal region is more variable than traditionally believed. The classical short dorsal PA pattern is present in approximately 45.7% of cases and supplies only the dorsal perineum. In this configuration, the perineal nerve does not accompany the artery but continues independently toward the external anal sphincter and surrounding skin. 

Other dogs exhibit a long dorsal PA pattern, identified in approximately 12.5% of cases. This artery extends into both dorsal and ventral regions of the perineum and forms anastomoses with the ventral PA. Anatomical observations indicate that the perineal nerve consistently follows this elongated vessel. 

A third variation involves the presence of a perineal trunk, reported in nearly 41% of dogs, where both dorsal and ventral PAs arise from a common arterial branch. Again, the nerve follows this altered vascular pathway. These differences become highly relevant during surgery because many clinicians rely on expected vascular landmarks when attempting to preserve surrounding neural structures. 

Progressive Degeneration and Anatomical Distortion 

Clinical observations suggest that PH is not simply a mechanical defect but a progressive condition involving muscular degeneration and secondary neurovascular distortion^1,2. Histological changes involving the levator ani and coccygeus muscles include fiber fragmentation, nuclear pyknosis, separation of muscle fibers, and adipose replacement in advanced cases^1,3. 

As the pelvic diaphragm weakens, pelvic organs such as the colon, urinary bladder, and urethra may shift into the hernial sac⁴. This displacement can stretch or compress nearby vessels and nerves, contributing to dyschezia, tenesmus, urinary obstruction, and altered perineal sensation^1,5. 

Notably, the superficial perineal nerve does not consistently accompany the dorsal PA despite the artery often being used as a surgical landmark. This variability may increase the risk of inadvertent nerve injury and postoperative complications such as reduced sphincter tone or fecal incontinence¹. 

Clinical Takeaway 

For veterinary surgeons, individualized anatomical assessment is critical during PH repair. 

Important considerations include: 

• Bilateral PHs often produce greater neurovascular distortion than unilateral cases.  

• Vascular landmarks may not reliably predict nerve location.  

• Progressive muscular degeneration can alter both arterial and neural pathways.  

• Preservation of the superficial perineal and caudal rectal nerves is essential for maintaining continence.  

Conclusion 

Canine PHs are associated with substantial and often unpredictable changes in the vascular and neural anatomy of the perineal region. Variations involving the dorsal and ventral PAs, combined with chronic muscular degeneration and organ displacement, may complicate surgical repair and increase the risk of postoperative dysfunction. Greater awareness of these neurovascular alterations can help veterinarians perform safer dissections, preserve sphincter function, and improve long-term surgical outcomes. 

Reference 

1. Marañón-Almendros M, Avedillo L, Sánchez-Banderas G, Martín-Alguacil N. Preliminary Anatomical and Imaging Characterization of Vascular and Neural Changes in Dogs with Perineal Hernia. Veterinary Sciences. 2026 Apr 3;13(4):353. https://www.mdpi.com/2306-7381/13/4/353 

2. Åhlberg TM, Jokinen TS, Salonen HM, Laitinen-Vapaavuori OM, Mölsä SH. Exploring the association between canine perineal hernia and neurological, orthopedic, and gastrointestinal diseases. Acta Veterinaria Scandinavica. 2022 Dec 17;64(1):39. https://link.springer.com/content/pdf/10.1186/s13028-022-00655-w.pdf 

3. Ashtari MS, Veshkini A, Masoudifard M, Gilanpour H, Bahonar A. Measuring morphological parameters of the pelvic diaphragm muscles using computed tomography in healthy dogs. InVeterinary Research Forum 2021 Dec 15 (Vol. 12, No. 4, p. 493). https://pmc.ncbi.nlm.nih.gov/articles/PMC9010835/pdf/nihpp-rs4169007v1.pdf 

4. Tobias KM, Crombie K. Perineal hernia repair in dorsal recumbency in 23 dogs: Description of technique, complications, and outcome. Veterinary Surgery. 2022 Jul;51(5):772-80. https://www.arfcv.fr/wp-content/uploads/2022/10/Veterinary-Surgery-2022-Tobias-Perineal-hernia-repair-in-dorsal-recumbency-in-23-dogs-Description-of-technique-.pdf 

5. Machado ÂV, Lugoch G, dos Santos AP, Gonçalves ME, de Oliveira MT, Viela JA, Beckmann BV. Perineal hernia in a bitch. Acta Scientiae Veterinariae. 2020 Jan 1;48. https://seer.ufrgs.br/ActaScientiaeVeterinariae/article/download/100110/pdf