Newly Published
Pain Medicine  |   March 2019
Extrafasicular and Intraperineural, but No Endoneural, Spread after Deliberate Intraneural Injections in a Cadaveric Study
Author Notes
  • From the Centro de Estudios Universitarios (CEU) San Pablo University School of Medicine, Madrid, Spain (M.A.R.); the Department of Anesthesiology, Madrid-Montepríncipe University Hospital, Madrid, Spain (M.A.R., E.M.); the Human Anatomy and Embryology Unit, Faculty of Medicine, University of Barcelona, Barcelona, Spain (X.S.-B.); the Division of Acute and Perioperative Pain Medicine, Department of Anesthesiology (O.C.N., A.P.B.) and the Department of Orthopedic Surgery (A.P.B.), University of Florida College of Medicine, Gainesville, Florida; and the Department of Anesthesiology, University of Maryland School of Medicine, Baltimore, Maryland (P.E.B.).
  • Part of the work presented in this article was presented as a lecture at the 37th Annual European Society of Regional Anesthesia Congress in Dublin, Ireland, September 12–15, 2018.
    Part of the work presented in this article was presented as a lecture at the 37th Annual European Society of Regional Anesthesia Congress in Dublin, Ireland, September 12–15, 2018.×
  • Submitted for publication September 4, 2018. Accepted for publication January 16, 2019.
    Submitted for publication September 4, 2018. Accepted for publication January 16, 2019.×
  • Correspondence: Address correspondence to Dr. Boezaart: Departments of Anesthesiology and Orthopaedic Surgery and Rehabilitation, University of Florida College of Medicine, 1600 SW Archer Road, PO Box 100254, Gainesville, Florida 32610. aboezaart@anest.ufl.edu. Information on purchasing reprints may be found at www.anesthesiology.org or on the masthead page at the beginning of this issue. Anesthesiology’s articles are made freely accessible to all readers, for personal use only, 6 months from the cover date of the issue.
Article Information
Pain Medicine / Central and Peripheral Nervous Systems / Pain Medicine
Pain Medicine   |   March 2019
Extrafasicular and Intraperineural, but No Endoneural, Spread after Deliberate Intraneural Injections in a Cadaveric Study
Anesthesiology Newly Published on March 5, 2019. doi:10.1097/ALN.0000000000002647
Anesthesiology Newly Published on March 5, 2019. doi:10.1097/ALN.0000000000002647
Abstract

Editor’s Perspective:

What We Already Know about This Topic:

  • The intraneural injection of local anesthetics is an accepted cause of nerve injury related to regional anesthesia

  • The intrafascicular versus extrafascicular spread of local anesthetics is hypothesized to be necessary for nerve damage to occur

What This Article Tells Us That Is New:

  • Using the ultrasound-guided injection of heparinized blood into the nerves of cadavers, the extrafascicular spread of injectate was observed

  • Intrafascicular spread of injectate was rarely observed, making this an unlikely route of nerve damage after accidental intraneural injection

Background: There is confusion regarding the spread of intraneurally injected local anesthetic agents during regional anesthesia. The aim of this research was to deliberately inject a marker that does not leave the neural compartment into which it is injected, and then to study the longitudinal and circumferential spread and possible pathways of intraneural spread.

Methods: After institutional review board approval, we intraneurally injected 20 and 5 ml of heparinized blood solution under ultrasound guidance into 12 sciatic nerves in the popliteal fossa and 10 median nerves, respectively, of eight fresh, unembalmed cadavers using standard 22-gauge “D” needles, mimicking the blocks in clinical conditions. Ultrasound evidence of nerve swelling confirmed intraneural injection. Samples of the nerves were then examined under light and scanning electron microscopy.

Results: Extrafascicular spread was observed in all the adipocyte-containing neural compartments of the 664 cross-section samples we examined, but intrafascicular spread was seen in only 6 cross-sections of two nerves. None of the epineurium, perineurium, or neural components were disrupted in any of the samples. Spread between the layers of the perineurium was a route of spread that included the perineurium surrounding the fascicles and the perineurium that formed incomplete septa in the fascicles. Similar to the endoneurium proper, subepineural compartments that did not contain any fat cells did not reveal any spread of heparinized blood solution cells. No “perineural” spaces were observed within the endoneurium. We also did not observe any true intrafascicular spread.

Conclusions: After deliberate intraneural injection, longitudinal and circumferential extrafascicular spread occurred in all instances in the neural compartments that contained adipocytes, but not in the relatively solid endoneurium of the fascicles.