Anatomy of the vestibulum esophagi and surgical implications during prosthetic laryngoplasty in horses.

OBJECTIVE: To describe the anatomy of the entry to the equine esophagus (vestibulum esophagi) and to assess the risk of penetrating its adventitia and/or lumen during laryngoplasty. STUDY DESIGN: Ex vivo cadaveric study. SAMPLE POPULATION: Five isolated equine larynges and 39 equine head and neck specimens. METHODS: The anatomy of the vestibulum esophagi was studied by dissection of 5 cadaver specimens. Then, a bilateral laryngoplasty was performed, including 5 suture placements through the muscular processes, caudal, rostral, and sagittal, with straight and curved needles. Two of the 3 surgeons performing the implantations were unaware of the goals of the study. Suture positions and iatrogenic trauma to the lumen and/or adventitia of the vestibulum esophagi were identified during dissection of the specimens. Risk factors for penetrating the adventitia were evaluated with a multivariate regression model. RESULTS: The vestibulum esophagi spans between both wings of the thyroid cartilage over the entire width of the larynx, covering the rostral spine (arcuate crest) of the arytenoid cartilages. It is covered by the thyropharyngeus and cricopharyngeus muscles. Masked surgeons were associated with a significantly higher number of adventitia penetrations (72%) compared to the nonmasked surgeon (9%). The lumen of the vestibulum esophagi was penetrated in 4.6% of suture placements and only by the 2 masked surgeons. CONCLUSION: Penetration of the adventitia was more common when surgeons were unaware of the anatomical extent of the vestibulum esophagi. CLINICAL SIGNIFICANCE: Anatomical knowledge of the extent of the vestibulum esophagi reduces the risk of penetrating its lumen or adventitia during suture placement on the muscular process of the arytenoid cartilage.

Comparison of morphological changes and tactile sensitivity of the pharynx and larynx between four standing sedative and analgesic protocols in eight adult healthy horses.

OBJECTIVE: To compare the topographic modifications and tactile sensitivity of the pharynx and larynx after administration of four sedative and analgesic protocols in standing horses. STUDY DESIGN: Experimental, observer-blinded, crossover study. ANIMALS: Eight healthy mares. METHODS: Five protocols were evaluated: 1) xylazine and butorphanol administered intravenously (IV); 2) detomidine and butorphanol administered IV; 3) xylazine administered IV and lidocaine topically; 4) detomidine administered IV and lidocaine topically and 5) no analgesia or sedation (control). Quality of sedation, head height and sudden head movements were recorded. The degree of arytenoid cartilage displacement, the degree of pharyngeal collapse and the occurrence of soft palate displacement were scored using standardized scales. Tactile sensitivity was tested on 10 different pharyngeal and laryngeal regions using an atraumatic transendoscopic probe. Statistical analysis was performed using linear or generalized mixed-effects models. RESULTS: Head height was significantly decreased in protocols with xylazine (p = 0.002). Head movements were significantly increased in protocols with butorphanol (p = 0.0001). No changes in abduction grade or degree of soft palate displacement were observed between all sedative protocols and the control group. Pharyngeal collapse was significantly more frequent in protocols with lidocaine (p < 0.001) or xylazine (p = 0.017). For the pharyngeal regions, no tactile sensitivity difference was observed between the control and treatment protocols. All treatment protocols led to greater desensitization of all the laryngeal regions compared with the control protocol. CONCLUSION AND CLINICAL RELEVANCE: All the protocols provided adequate sedation and analgesia for the manipulation of the larynx and pharynx but significant differences were noted. Xylazine produces a more profound sedation compared with detomidine, but can induce dorsal pharyngeal collapse. Lidocaine caused pharyngeal collapse and its use should be limited to the target area. Butorphanol can be added to improve analgesia in the other regions but frequent head jerking can be expected.