Imaging and Anatomical Insights into the Canine Perineal Region

Perineal hernia (PH) is a clinically significant condition in dogs that alters not only the pelvic diaphragm but also the surrounding vascular and neural anatomy. Although the anatomy of the internal iliac artery (IIA) and its branches has traditionally been described through cadaveric dissections, little information exists regarding how these structures appear on diagnostic imaging or how chronic herniation changes their anatomical relationships¹. 

This gap is clinically important because variations involving the internal pudendal artery (IPA), dorsal and ventral perineal arteries (PAs), and associated nerves may influence surgical planning, tissue viability, and postoperative continence. Previous anatomical reports by Avedillo et al. demonstrated that the vascular arrangement of the canine pelvis is highly variable, particularly in the perineal region¹. 

Combining Fluoroscopy with Anatomical Dissection 

To better understand these variations, fluoroscopic imaging was combined with latex-injected anatomical dissections in both healthy dogs and dogs affected by PHs. Unlike conventional dissection alone, fluoroscopy allowed real-time visualization of contrast-filled arteries without vascular overlap. By injecting contrast into a single internal iliac artery, clearer images of branching patterns could be obtained before tissue dissection^1,2. 

Although contrast-enhanced CT remains the preferred imaging modality for vascular evaluation, fluoroscopy provided valuable insight into how perineal vessels may appear during future angiographic assessment. Correlating fluoroscopic findings with direct anatomical dissection also helped identify clinically relevant vascular deviations that may otherwise remain undetected¹. 

In healthy dogs, the vascular arrangement generally followed the classical NAV pattern described in anatomical literature¹. However, dogs with PHs demonstrated deviations involving the origin and course of the dorsal and ventral PAs as well as the displacement of surrounding nerves and pelvic organs. 

Anatomical Changes in Advanced Perineal Hernias 

Evidence suggests that chronic herniation progressively alters both muscular and neurovascular anatomy^3,4. Degeneration of the levator ani and coccygeus muscles contributes to the collapse of the pelvic diaphragm and displacement of surrounding structures^1,5. 

Histological observations from affected dogs revealed muscle fiber fragmentation, nuclear pyknosis, separation of fibers, and adipose replacement, particularly in advanced bilateral cases. As muscular support deteriorates, organs such as the colon, urinary bladder, and urethra may enter the hernial sac⁶. This displacement places traction on nearby arteries and nerves, contributing to distortion of the regional anatomy and worsening clinical signs including dyschezia, tenesmus, and urinary obstruction¹. 

The superficial perineal nerve was also found to follow variable pathways in dogs with PHs. Clinical observations indicate that chronic displacement and stretching of tissues may alter the expected relationship between the nerve and dorsal PA¹. This finding is particularly important because surgeons often use the artery as a landmark during dissection. 

Clinical Takeaway 

Recognition of altered neurovascular anatomy is essential during surgical planning for PH repair. 

Key clinical considerations include: 

• Bilateral PHs often demonstrate more extensive anatomical distortion.  

• Long- and short-type arterial variations may alter expected surgical landmarks.  

• Displacement of the superficial perineal nerve may increase the risk of postoperative dysfunction.  

• Advanced imaging techniques such as CT angiography may improve preoperative anatomical assessment in complex cases.  

Conclusion 

Perineal hernias in dogs are associated with progressive muscular degeneration and significant neurovascular alteration within the pelvic cavity. Combining fluoroscopic imaging with anatomical dissection provides valuable insight into these changes and highlights the importance of individualized anatomical assessment during surgery. Improved understanding of vascular and neural variations may ultimately support safer surgical techniques, better preservation of continence, and improved long-term outcomes in dogs affected by PHs. 

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. Ibrahim MH, Degner DA, Stanley BJ. Arterial supply to the scrotum: A cadaveric angiographic study. Veterinary Surgery. 2022 May;51(4):658-64. https://www.arfcv.fr/wp-content/uploads/2023/04/Ibrahim-et-al.-2022-Arterial-supply-to-the-scrotum-A-cadaveric-angiog.pdf 

3. 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 

4. Sangmanee P, Kovitvadhi A, Sutthiprapa W, Choochalermporn P, Limmanont C. Canine Perineal Hernia Associated with Prostatic Disorders: Is Castration Really Beneficial? A Retrospective Study. Animals. 2025 Apr 23;15(9):1206. https://www.mdpi.com/2076-2615/15/9/1206 

5. 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 

6. 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