Diseases of The Middle Ear
Most potential route for transmission of Meningitis from CNS toJnner ear is: (DNB June 2011)
Cochler aqueduct is a bony canal that connects the cochlea to the intracranial subrachnoid space. Perilymph within the cochlear aqueduct is in direct continuation with the CSF and hence Cochlear Aqueduct is the most important route for meningitis to spread to the inner ear.
a. Vestibular.Aqueduct.is also A.bony connection between the cerebral subarachnoid space and the inner ear.
b. Vestibular Aqueduct contains the endolymphatic duct which contains the endolymph. The endolymph within the endolymphatic duct does not however communicate freely with the CSF as it forms a closed space and ends in a cul-de-saC. Because the endolymph does not directly communicate with the CSF. Vestibular aqueduct is less important in allowing spread of meningitis from CSF to inner ear than Cochlear Aqueduct.
a. Hyrtle's fissure is an embryonic remnant that normally obliterates by 24 weeks. .
b. When persistent, Hyrtle's fissure provides a connection from the middle ear to the subarachoid space
c. Hyrtle's fissure does not directly communicate the internal ear with CSF and usually obliterates early in life and hence is not an important route of spread of infection from CSF to internal ear.
Encjolymphatic sac is a cul-de-sac containing endolymph that does not directly communicate with CSF.