Evaluation of injectate distribution after ultrasound-guided peribulbar injections in canine cadavers.

Objective: To describe a contrast medium distribution pattern after peribulbar injection in cadavers.

Study Design: A cadaveric study.

Animals: A group of eight male dogs and four canine cadaver heads.

Methods: In phase 1, ultrasound-guided peribulbar injections (1.0 mL dye) were performed in four orbits using a subzygomatic approach. After dissection, the procedure was considered successful if 1) no dye was found in the retrobulbar space, 2) the peribulbar compartment was stained and 3) the dye reached the orbital fissure. In phase 2, using 16 orbits, the same technique was used to inject 0.1 mL kg contrast medium into (group A, n = 8) or outside (group B, n = 8) the peribulbar compartment. After freezing at -20°C, orbits were imaged using computed tomography, and the contrast medium distribution was analysed.

Results: In phase 1, the procedure was successful in all four eyes. In phase 2, two orbits (one in each group) were removed from the study: one was not injected and the other was injected twice. The contrast medium was found inside the peribulbar compartment in six of seven (85.7%) group A orbits and two of seven (28.6%) group B orbits. In all of these cases, distribution to the orbital fissure, rostral alar foramen, mandibular foramen and inside the skull was observed. The oval foramen was reached in three of seven (42.9%) group A orbits and one of seven (14.3%) group B orbits. In one/seven (14.3%) group A orbits and five/seven (71.4%) group B orbits, the contrast medium was found inside the masseter and temporal muscles, and no distribution towards the aforementioned structures was observed.

Conclusions And Clinical Relevance: Ultrasound-guided peribulbar injection of 0.1 mL kg contrast medium in canine cadavers can lead to an extensive distribution of the injectate that reaches the orbital fissure, the rostral alar, oval, and mandibular foramina and can be found intra-cranially.