Caring about medullary anesthesia in Saimiri sciureus : the conus medullaris topography

Saimiri sciureus is a New World non-human primate (NHP) that inhabits Brazilian rain forests. Surgical interventions in wild NHPs can be considered common both for experimental studies procedures and corrective procedures for endangered species. Among various anesthetic procedures, the epidural anesthesia or blockades, depending on the surgical procedure, might be considered elective for wild monkeys, mostly based on its safeness, efficiency and nontime consuming characteristics. However its safeness would be limiting because of the spinal cord arrangement. Notwithstanding the available former studies on New World NHP anatomy, the description of the medullar cone of Saimiri sciureus is still scarce. Therefore, we believe that the better understanding the medullar cone of Saimiri sciureus would contribute to improve the applicability of epidural procedures in the species. Vertebrae architecture of Saimiri sciureus was composed by 9 lumbar, 3 sacral and 18 coccygeal vertebrae, and the medullar cone measured about 3.3 cm. We can conclude that the conus medullaris in Saimiri sciureus is situated more caudally in comparison to other species.


INTRODUCTION
Saimiri sciureus is a New World non-human primate (NHP) that inhabits Brazilian rain forests and whose life differs from Old NHPs because it is entirely developed on trees, being rare its ground descending (Coimbra Filho 1982, Rylands et al. 2000).Surgical interventions in wild NHPs can be considered common both for experimental studies procedures and corrective procedures for endangered species.
Among various anesthetic procedures, the epidural anesthesia or blockades, depending on the surgical procedure, might be considered elective for wild mon-keys, mostly based on its safeness, efficiency and nontime consuming characteristics.However its safeness would be limiting because of the spinal cord arrangement (Dyce et al. 2004, Fantoni and Cortopassi 2002, Hopkins 1935).Meanwhile, it has been considered that small volumes of anesthetic applied on the virtual space between the yellow ligament and duramater near the medullary cone would be safer and prevent injuries over the spinal cord (Hilbery 1992), which emphasizes the necessity of a full control of the sight of application and its regular anatomy.Epidural anesthesia presents innumerable applications, as well as it might be very welcome as an adjuvant procedure to promote postoperative analgesia that would prevent or diminishes the animal stress thus improving recovery.
Notwithstanding the available former studies on New World NHP anatomy, the description of the medullar cone of S. sciureus is still scarce.Therefore, we believe that the better understanding the medullar cone of S. sciureus would contribute to improve the applicability of epidural procedures in the specie.

MATERIALS AND METHODS
Animals that have deceased from natural causes were donated by the National Center of Primates (Cenp).All procedures were carried out according to the international practices for animal use and care under the control of an internal committee of the Evandro Chagas Institute, Ananindeua, PA, under authorization number 008/2010.Two male and two female specimens were perfused and immersed in a 10% aqueous formaldehyde solution for fixation.The dissection procedure was carried out by a dorsal median line incision and skin removal from the thorax to the tail basis.Epiaxial musculature and vertebral arcs were also removed in order to reveal the medulla and its covering tissues.Medullar cone was dissected and measured with the aid of a caliper rule.Veterinary Medicine Anatomical Nomina (Schaller 1999) illustrations were followed to name the structures.InStat 3 software was used for statistical analyses.

DISCUSSION
The caudal portion of the spinal cord of S. sciureus was presented as a cylindrical and prolonged mass, being slightly flattened at the lumbar intumescence.The conus medullaris was observed caudally to the lumbar intumescence being similar to the one of other mammals (Erhart 1992, Getty 1975).This region is a site of epidural anesthesia when anesthetic drugs are applied in a virtual space under duramater to promote analgesia of waist and pelvic limbs.
We can conclude that the conus medullaris in Saimiri sciureus is situated more caudally in comparison to other species.Its base is situated between L7-L8, and the apex between S3-Cc1, which would provide a suggestive site for epidural anesthesia procedures regarding analgesia to waist and pelvic limbs in this species.