Comparison of the retrobulbar and Peterson nerve block techniques via magnetic resonance imaging in bovine cadavers

OBJECTIVE: To use magnetic resonance (MR) imaging to describe and compare the anatomic distribution of a lipid contrast medium injected via the retrobulbar and Peterson nerve block techniques in heads of bovine cadavers. DESIGN: Original study. SAMPLE: 5 grossly normal heads obtained from cattle at necropsy. PROCEDURE: Standardized techniques for the modified retrobulbar and Peterson nerve blocks were established. Each cadaver had 1 treatment performed on a randomly selected side of the head; the second treatment was performed on the alternate side of the head. Injections were performed with canola oil, which is an MR-positive contrast medium. Images of heads in the transverse and dorsal planes were obtained with a 3.0 Tesla short-bore MR system. RESULTS: The retrobulbar technique was characterized by widespread distribution of the contrast medium around the periorbital structures; further distribution of the medium was detected along the optic nerve and in the ethmoid turbinates and nasopharynx. After the Peterson nerve block technique, contrast medium was repeatedly located in the pterygopalatine fossa, but distribution to surrounding structures was minimal. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that the retrobulbar injection technique results in a greater distribution of contrast medium to the target nerves and surrounding structures, compared with that achieved via the Peterson nerve block technique. This may explain the previously reported clinical impression that the retrobulbar block is more reliable than the Peterson nerve block but is associated with a greater risk of complications.