Transnasal spread of bupivacaine into the pterygopalatine fossa following endoscopically assisted cotton swab placement: a cadaveric study.

Abstract

Background: There are conflicting data on the efficacy of transnasal topical anesthetic approaches intended to achieve a pterygopalatine ganglion block, specifically regarding the extent to which local anesthetics reach the pterygopalatine fossa. This cadaveric study aims to determine whether bupivacaine can reach the pterygopalatine fossa following topical administration near the sphenopalatine foramen using endoscopically assisted cotton ball placement.

Methods: Nine fresh cadavers underwent topical nasal administration of a solution containing bupivacaine, methylene blue, and iodine contrast. Under direct endoscopic visualization, an absorbent cotton ball was positioned intranasally adjacent to the sphenopalatine foramen. CT was used to confirm correct placement and measured relevant anatomical distances. Tissue biopsies from the pterygopalatine fossa were collected via a transmaxillary surgical approach and analyzed using high-performance liquid chromatography-mass spectrometry.

Results: Bupivacaine was detected in all pterygopalatine fossa biopsy samples except one, which was the farthest (17.5 mm) from the sphenopalatine foramen. Concentrations exceeded 1.00 µg/g in 29% and 0.10 µg/g in 71% of samples. The concentration decreased exponentially with distance from the application site, following a one-phase decay model (R²=0.74).

Conclusions: These findings demonstrate that bupivacaine can reach the pterygopalatine fossa from the nasal cavity when topically applied near the sphenopalatine foramen under endoscopic assistance, supporting the feasibility of such an approach. They also suggest the main mean of transport is simple diffusion, meaning that optimizing bupivacaine concentration, duration of application, and precise placement of the absorbent cotton ball are crucial for maximizing the block's clinical efficacy.