Early cochlear response and ICAM-1 expression to cochlear implantation.
OBJECTIVE
To examine the early cochlear response and intercellular cell adhesion molecule-1 (ICAM-1) expression to implantation of a cochlear electrode into the scala tympani.


BACKGROUND
Understanding the early response of the cochlea to implantation may inform the duration which drug therapies should be delivered to protect hearing.


METHODS
Guinea pigs were implanted with a cochlear electrode and survived 1, 2, or 7 days before they were euthanized, cochleae harvested, processed, and cryosectioned for light microscopy or ICAM-1 immunohistochemistry.


RESULTS
On hematoxylin and eosin staining, scala tympani was characterized by the presence of fibrin and blood clot at 1 to 2 days after surgery, with a leukocytic infiltrate, primarily of neutrophils and macrophage-like cells. By 7 days after surgery, fibroblasts had infiltrated the clot, and the numbers of red blood cells (RBCs) and neutrophils had diminished. ICAM-1 expression was greatest in the lateral cochlear wall with highest expression found in the basal turn in the region of the electrode at 24 hours postimplantation.


CONCLUSIONS
The cochlear vasculature is maximally primed to recruit cells from the circulation, as evidenced by ICAM-1 expression levels, at 24 hours after cochlear implantation. This response is similar to that seen after other types of injury. Where cochlear implantation differs is the predominance of fibrin and clot early after electrode insertion before infiltration by fibroblasts by the end of the first postoperative week. These results suggest that anti-inflammatory drugs aimed at reducing the extravasation of immunecompetent cells into the cochlea must be effective over the first few days after surgery. Whether this can be achieved through preoperative treatment alone, or whether therapy will need to continue postoperatively, awaits further experimentation.
*Department of Otolaryngology, University of Melbourne; and †Department of Surgery, Monash University, Clayton, Melbourne, Victoria, Australia.
Gordana Elizabeth
GE
Kel
Justin
J
Tan
Hayden Timothy
HT
Eastwood
Sarin
S
Wongprasartsuk
Stephen John
SJ
O'Leary
D000818:Animals; D003051:Cochlea / Q000378:metabolism* / Q000601:surgery; D019929:Cochlear Implantation; D003054:Cochlear Implants; D006168:Guinea Pigs; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism*; D012533:Scala Tympani / Q000378:metabolism* / Q000601:surgery
D018799:Intercellular Adhesion Molecule-1