Spiral ganglion degeneration patterns in endolymphatic hydrops.
OBJECTIVE
The mechanistic association between endolymphatic hydrops (ELH) and hearing loss (HL) is unclear. Although ELH severity has been shown to correlate in some studies with HL, injury of vital structures, including hair cells and the cochlear nerve, have failed to demonstrate correlation with ELH severity. The goal of this study is to evaluate the hypothesis that spiral ganglion cell degeneration is the principle pathologic site of ELH-related cochlear injury, correlates with ELH severity, and is most profound in the apical region.


METHODS
Surgical induction of ELH in the guinea pig model was followed by histologic confirmation of ELH and subsequent correlation with segmental spiral ganglion cell densities.


METHODS
Guinea pigs (N = 14) were subjected to unilateral ELH induction and killed after 4 to 6 months. ELH severity and spiral ganglion densities were obtained using computer-aided morphometric analysis. Densities were normalized by calculating a spiral ganglion degeneration index (DI) for each animal.


RESULTS
The apical spiral ganglion demonstrated significantly greater degeneration than that noted in the basal spiral ganglion (DI: 1.93 vs. 1.13; P = .004). The degree of spiral ganglion degeneration in the apex correlates well with a total hydrops index (P = .006) and an apical hydrops index (P = .003). Basal spiral ganglion degeneration however, does not correlate well with hydrops severity (total hydrops index: P > .05; basilar hydrops index: P > .05).


CONCLUSIONS
ELH-related pathology appears to focus initially on the apical spiral ganglion and the degree of deterioration correlates well with the severity of ELH. These findings mirror some reports in the human condition, and imply that the mechanism of cochlear injury in ELH and secondary dysfunction appears to be a neural toxicity that begins in the apex of the cochlea.
Bixenstine
Paul J
PJ
Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University, University Hospitals of Cleveland, Cleveland, Ohio 44106, USA.
Maniglia
Mauricio P
MP
Vasanji
Amit
A
Alagramam
Kumar N
KN
Megerian
Cliff A
CA
D000818:Animals; D003053:Cochlear Duct / Q000473:pathology; D003056:Cochlear Nerve / Q000473:pathology; D004195:Disease Models, Animal; D018159:Endolymphatic Hydrops / Q000473:pathology*; D005260:Female; D006168:Guinea Pigs; D006319:Hearing Loss, Sensorineural / Q000473:pathology; D008575:Meniere Disease / Q000473:pathology; D009410:Nerve Degeneration / Q000473:pathology*; D009474:Neurons / Q000473:pathology; D054738:Scala Vestibuli / Q000473:pathology; D013136:Spiral Ganglion / Q000473:pathology*