title: Intratympanic Iodine Contrast Injection Diffuses Across the Round Window Membrane Allowing for Perilymphatic CT Volume Acquisition Imaging.
abstract: OBJECTIVE
  Whether the round window membrane (RWM) is permeable to iodine-based contrast agents (IBCA) is unknown; therefore, our goal was to determine if IBCAs could diffuse through the RWM using CT volume acquisition imaging.
  
  
  BACKGROUND
  Imaging of hydrops in the living human ear has attracted recent interest. Intratympanic (IT) injection has shown gadolinium's ability to diffuse through the RWM, enhancing the perilymphatic space.
  
  
  METHODS
  Four unfixed human cadaver temporal bones underwent intratympanic IBCA injection using three sequentially studied methods. The first method was direct IT injection. The second method used direct RWM visualization via tympanomeatal flap for IBCA-soaked absorbable gelatin pledget placement. In the third method, the middle ear was filled with contrast after flap elevation. Volume acquisition CT images were obtained immediately postexposure, and at 1-, 6-, and 24-hour intervals. Postprocessing was accomplished using color ramping and subtraction imaging.
  
  
  RESULTS
  After the third method, positive RWM and perilymphatic enhancement were observed with endolymph sparing. Gray scale and color ramp multiplanar reconstructions displayed increased signal within the cochlea compared with precontrast imaging. The cochlea was measured for attenuation differences compared with pure water, revealing a preinjection average of -1,103 HU and a postinjection average of 338 HU. Subtraction imaging shows enhancement remaining within the cochlear space, Eustachian tube, middle ear epithelial lining, and mastoid.
  
  
  CONCLUSIONS
  Iohexol iodine contrast is able to diffuse across the RWM. Volume acquisition CT imaging was able to detect perilymphatic enhancement at 0.5-mm slice thickness. The clinical application of IBCA IT injection seems promising but requires further safety studies.
authors: *Department of Otolaryngology-Head and Neck Surgery †Department of Radiology-Neuroradiology, Johns Hopkins University School of Medicine, Baltimore, Maryland.
authors: Nicholas B
authors: NB
authors: Abt
authors: Mohamed
authors: M
authors: Lehar
authors: Carolina Trevino
authors: CT
authors: Guajardo
authors: Richard T
authors: RT
authors: Penninger
authors: Bryan K
authors: BK
authors: Ward
authors: Monica S
authors: MS
authors: Pearl
authors: John P
authors: JP
authors: Carey
mesh_terms: D002102:Cadaver; D003051:Cochlea / Q000000981:diagnostic imaging*; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D003287:Contrast Media / Q000008:administration & dosage*; D004432:Ear, Middle; D006801:Humans; D000069555:Injection, Intratympanic; D007455:Iodine / Q000008:administration & dosage*; D010498:Perilymph / Q000000981:diagnostic imaging*; D012405:Round Window, Ear
chemical_list: D003287:Contrast Media; D007455:Iodine