Elisa Silvia D’Urso; Chiara De Gennaro; Giuliano Ravasio
Background
Regional anesthesia can reduce perioperative opioid use and attenuate surgical stress in dogs. The cervical plexus in dogs is formed by the ventral branches of the second, third, and fourth cervical spinal nerves (C2–C4), which supply sensory and motor innervation to structures of the ventrolateral neck. Targeting this plexus could provide analgesia for surgical procedures such as arytenoid lateralization, thyroidectomy, parathyroidectomy, ventral neck exploration, and ventral slot surgery. The study aimed to describe the ultrasonographic anatomy of the canine cervical region and evaluate the feasibility and spread of an ultrasound-guided injection targeting the cervical plexus.
Methods
This prospective cadaveric study used six fresh mixed-breed mesocephalic dog cadavers categorized by body weight into small (≤10 kg), medium (10.1–24 kg), and large (>24.1 kg). Under ultrasound guidance, a linear probe was placed near the wing of the atlas and moved caudally to identify the transverse process of the fourth cervical vertebra (C4). A spinal needle was advanced in-plane toward the cervical fascia (CF). Methylene blue (0.15%) was injected within the CF and, subsequently, deeper between the intertransversarius ventralis and longus colli muscles. Injection volumes were adjusted by size category (2.5–10 mL). Bilateral injections were performed, followed by anatomical dissection to assess staining of the ventral branches of C2, C3, and C4. Successful injections were defined as circumferential dye staining of these nerves for more than 2 cm.
Results
Ultrasonographic landmarks, including the atlas wing and C4 transverse process, were consistently identified across cadavers. Injection within the cervical fascia produced successful staining of 100% of the ventral branches of C2, C3, and C4 bilaterally (12/12 nerves for each level). Staining lengths exceeded 2 cm in all cases. In contrast, deeper injections between the intertransversarius ventralis and longus colli muscles did not stain the cervical nerves. Dye spread occurred cranially and caudally within the fascia but did not extend caudally beyond C4; in the smallest cadaver, cranial spread reached the atlas.
Limitations
The study used a small convenience sample and was performed in cadavers, which may alter tissue characteristics compared with living animals, potentially affecting injectate distribution. Differences in muscle tone, vascularization, and temperature may influence dye spread compared with local anesthetic in vivo. Additionally, the same operator performed both injections and dissections, introducing potential assessment bias.
Conclusions
An ultrasound-guided injection within the cervical fascia at the level of C4 consistently stained the ventral branches of C2–C4 in canine cadavers, suggesting this technique is a feasible approach to performing a cervical plexus block in dogs. This locoregional anesthesia method may provide analgesia for various cervical surgical procedures, although clinical studies in live animals are needed to confirm efficacy and safety.
(a) Probe positioning at the level of the transverse process of the fourth cervical vertebra (C4) in the 10 kg cadaver. The needle insertion is performed in-plane in a dorso-ventral direction (white arrow). (b) Scan of the transverse process of C4, creating an acoustic shadowing underlying a hyperechoic edge. The cervical fascia, visible as a double hyperechoic line (white arrowheads), lies between the cleidocephalicus muscle (Cc) and the omotransversarius (Om) and intertransversarius ventralis muscles (Iv). (c) In-plain needle reaching the cervical fascia (n). (d) Anatomical dissection of the neck after injection of 2.5 mL of methylene blue 0.5% in the cervical fascia. Ventral roots from C2 to C4 are exposed after removal of the overlying muscles. At, wing of the atlas; Ca, caudal; Cr, cranial; D, dorsal; Id, intertransversarius dorsalis muscle; Lat, lateral; Med, medial; Sc, subcutaneous tissue; V, ventral.
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