title: MR-guided perineural injection of the ganglion impar: technical considerations and feasibility.
abstract: OBJECTIVE
  Perineural ganglion impar injections are used in the management of pelvic pain syndromes; however, there is no consensus regarding the optimal image guidance. Magnetic resonance imaging (MRI) provides high soft tissue contrast and the potential to directly visualize and target the ganglion. The purpose of this study was to assess the feasibility of MR-guided percutaneous perineural ganglion impar injections.
  
  
  METHODS
  Six MR-guided ganglion impar injections were performed in six human cadavers. Procedures were performed with a clinical 1.5-Tesla MRI system through a far lateral transgluteus approach. Ganglion impar visibility, distance from the sacrococcygeal joint, number of intermittent MRI control steps required to place the needle, target error between the intended and final needle tip location, inadvertent punctures of non-targeted vulnerable structures, injectant distribution, and procedure time were determined.
  
  
  RESULTS
  The ganglion impar was seen on MRI in 4/6 (66 %) of cases and located 0.8 mm cephalad to 16.3 mm caudad (average 1.2 mm caudad) to the midpoint of the sacrococcygeal joint. Needle placement required an average of three MRI control steps (range, 2-6). The average target error was 2.2 ± 2.1 mm. In 6/6 cases (100 %), there was appropriate periganglionic distribution and filling of the presacrococcygeal space. No punctures of non-targeted structures occurred. The median procedure time was 20 min (range, 12-29 min).
  
  
  CONCLUSIONS
  Interventional MRI can visualize and directly target the ganglion impar for accurate needle placement and successful periganglionic injection with the additional benefit of no ionizing radiation exposure to patient and staff. Our results support clinical evaluation.
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Science, Musculoskeletal Radiology, Johns Hopkins University School of Medicine, 601 North Caroline Street, JHOC 3140A, Baltimore, MD, 21287, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Marker
authors.affiliation: Department of Mechanical and Materials Engineering, Queen's University, 99 University Avenue, Kingston, ON, Canada.
authors.forename: Paweena
authors.initials: P
authors.lastname: U-Thainual
authors.affiliation: School of Computing, Queen's University, 557 Goodwin Hall, Queen's University, Kingston, ON, Canada.
authors.forename: Tamas
authors.initials: T
authors.lastname: Ungi
authors.affiliation: Siemens Corporate Research, Center for Applied Medical Imaging, Baltimore, MD, USA.
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Flammang
authors.affiliation: School of Computing, Queen's University, 557 Goodwin Hall, Queen's University, Kingston, ON, Canada.
authors.forename: Gabor
authors.initials: G
authors.lastname: Fichtinger
authors.affiliation: Department of Mechanical Engineering and Laboratory for Computational Sensing and Robotics, Johns Hopkins University, 3400 N. Charles St., Hackerman 112, Baltimore, MD, 21218, USA.
authors.forename: Iulian I
authors.initials: II
authors.lastname: Iordachita
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Science, Musculoskeletal Radiology, Johns Hopkins University School of Medicine, 601 North Caroline Street, JHOC 3140A, Baltimore, MD, 21287, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Carrino
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Science, Musculoskeletal Radiology, Johns Hopkins University School of Medicine, 601 North Caroline Street, JHOC 3140A, Baltimore, MD, 21287, USA. jfritz9@jhmi.edu.
authors.forename: Jan
authors.initials: J
authors.lastname: Fritz
mesh_terms: D000368:Aged; D001340:Autonomic Nerve Block / Q000379:methods*; D002102:Cadaver; D005240:Feasibility Studies; D005260:Female; D005728:Ganglia, Sympathetic / Q000000981:diagnostic imaging*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D053783:Magnetic Resonance Imaging, Interventional / Q000379:methods*; D008875:Middle Aged; D017699:Pelvic Pain / Q000000981:diagnostic imaging* / Q000517:prevention & control*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: Ganglion impar; Interventional MRI; Nerve block; Nerve injection; Pelvic pain