To develop an ultrasound-guided interfascial plane technique for injection of the
pudendal nerve near its sacral origin in cats.
Prospective, randomized, anatomical study.
A group of 12 feline cadavers.
Gross and ultrasound anatomy of the ischiorectal fossa, the pudendal nerve relationship
with parasacral structures, and the interfascial plane were described. Computed tomography
was employed to describe a cranial transgluteal approach to the pudendal nerve. Bilateral
ultrasound-guided injections were performed in eight cadavers using low [(LV) 0.1
mL kg–1] or high volume [(HV) 0.2 mL kg–1] of ropivacaine–dye solution. Dissections were performed to determine successful
staining of the pudendal nerve (>1 cm) and inadvertent staining of the sciatic nerve,
and any rectal, urethral, or intravascular puncture. Pudendal nerve staining in groups
LV and HV were compared using Fisher's exact and Wilcoxon rank-sum test as appropriate
(p = 0.05).
The pudendal nerve and its rectal perineal and sensory branches coursed through the
ischiorectal fossa, dorsomedial to the ischiatic spine. The pudendal nerve was not
identified ultrasonographically, but the target plane was identified between the sacral
transverse process, the ischiatic spine, the pelvic fascia and the rectum, and it
was filled with dye solution. Both branches of the pudendal nerve were completely
stained 75% and 87.5% in groups LV and HV, respectively (p = 1.00). The dorsal aspect of the sciatic nerve was partially stained in 37% of injections
in group HV. Rectal or urethral puncture and intravascular injection were not observed.
Conclusions and clinical relevance
In cats, ultrasound-guided cranial transgluteal injection successfully stained the
pudendal nerve in at least 75% of attempts, regardless of injectate volume. Group
HV had a greater probability of sciatic nerve staining.