title: MR epidurography: distribution of injectate at caudal epidural injection.
abstract: OBJECTIVE
  To (a) evaluate the feasibility of MR epidurography (MRE) and (b) assess the distribution of injectate using two different volumes at caudal epidural steroid injection.
  
  
  METHODS
  Twenty patients who were referred with symptomatic low back pain for caudal epidural steroid injection were assigned to have either 10 ml (9/20) or 20 ml (11/20) of injectate administered. Gadolinium was included in the injection. The patients proceeded to MRI where sagittal and coronal T1-weighted fat-saturated sequences were acquired and reviewed in the mid-sagittal and right and left parasagittal views at the level of the exit foramina.
  
  
  RESULTS
  Gadolinium was observed at or above the L3/4 disc level in all 11 patients who received 20 ml (100 %), compared with only five of nine patients who received 10 ml (56 %). Injectate was seen to the L4 nerve root level in all 11 patients who received 20 ml (100 %) but only four out of nine patients who received 10 ml (44 %), not even reaching the L5 nerve root level in four further of these nine patients (44 %). Overall, there was a trend to visualize gadolinium at higher levels of the epidural space with higher volumes injected.
  
  
  CONCLUSIONS
  Firstly, MR epidurography is a safe technique that allows excellent visualization of the distribution of gadolinium in the epidural space following injection via the caudal hiatus. Secondly, a volume of 10 ml is unlikely to treat L5/S1 disease in almost half of patients at caudal epidural steroid injection and at least 20 ml of injectate is likely required for any medication to reach the desired level.
authors: Cappagh National Orthopedic Hospital, Finglas, Dublin 11, Ireland, darramurphy@me.com.
authors: Darra T
authors: DT
authors: Murphy
authors: Eoin C
authors: EC
authors: Kavanagh
authors: Ashley
authors: A
authors: Poynton
authors: Vikki O
authors: VO
authors: Chan
authors: Michael R
authors: MR
authors: Moynagh
authors: Stephen
authors: S
authors: Eustace
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000893:Anti-Inflammatory Agents / Q000493:pharmacokinetics; D003287:Contrast Media; D004305:Dose-Response Relationship, Drug; D004824:Epidural Space / Q000033:anatomy & histology; D005240:Feasibility Studies; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D007089:Image Enhancement; D007268:Injections, Epidural; D017116:Low Back Pain / Q000188:drug therapy*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008775:Methylprednisolone / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D000077555:Methylprednisolone Acetate; D008875:Middle Aged; D055815:Young Adult
chemical_list: D000893:Anti-Inflammatory Agents; D003287:Contrast Media; D000077555:Methylprednisolone Acetate; D019786:Gadolinium DTPA; D008775:Methylprednisolone