Cochlear Fluid is the one of the most important fluid not only for hearing sensation but also for the balance of human body. It is very important to know the embryology, anatomy, and physiology of cochlear fluid mechanism to know the various pathological conditions of inner ear.

1. Cochlear Fluid
By Dr. Yousuf F. Choudhury
PGT, ENT Dept.
Silchar Medical College
Moderated By Prof. Dr. Shams Uddin
HOD, ENT Dept.
Silchar Medical College

3. • The inner ear consists of the cochlea and vestibular apparatus. The
cochlea is a component of osseous labyrinth that contains
perilymph and the cochlear duct. The cochlear duct is a component
of membranous labyrinth and contains endolymph.
• The cochlea makes 2.75mm round in man around a core of bone
(called the modiolus) through which the cochlear nerve passes. The
entire complex resembles a snail’s shell ( hence the term cochlea is
derived).
• Within the cochlea, the cochlea duct (scala media) separates two
perilymph chambers: the scala vestibuli, which contacts the oval
window membrane, and the scala tympani, which contacts the
round window membrane.
• Perilymph can flow from one scala to the other through an opening
(helicotrema) at the apex of the cochlea.
• The helicotrema is non-functional with respect to the physiology of
hearing, it merely precludes perilymph stagnation

7. • The cochlear duct (scala media) is triangular in
cross-section. A thin vestibular membrane
separates cochlear duct from scala vestibuli,
presenting an ionic barrier between perilymph &
endolymph. Vestibular membrane can be ignored
in regard to the mechanics of hearing.
• An osseous spiral lamina and basilar membrane
separate cochlear duct from the scala tympani.
Within the cochlear duct, a spiral organ sits atop
the basilar membrane along its entire length from
the base to the apex of the cochlea.

8. • The basilar membrane is critical in the physiology of
hearing. It consists of radial fibers that extend outward
from the osseous spiral lamina. The fibers are shortest and
stiffest at the base of the cochlea and they are longest at
the apex. (Conversely, the osseous spiral lamina, a spiral
ledge that projects outward from the modiolus, is longest
at the base and shortest at the apex of the cochlea.)
• The spiral organ (organ of Corti) features receptor cells
(hair cells) arranged along one inner row and three outer
rows. Each hair cell has dozens of stereo-cilia on its free
surface. Hair cells are held in place by a reticular
membrane (plate) anchored to the basilar membrane.
Stereo-cilia project above the reticular plate, making
contact with a tectorial membrane. The tectorial
membrane arises from the limbus, a tissue mass set
solidly on the osseous spiral lamina.

9. • Afferent neurons of the cochlear nerve have
bipolar cell bodies located in a spiral ganglion,
within the modiolus.
• From the spiral ganglion, axons traverse the
osseous spiral lamina. More than 90% of the
axons synapse on inner hair cells.
• Less than 10% of the axons synapse on outer
cells, which have mostly a mechanical function
adjusting the position of the tectorial
membrane via cellular elongation.

10. • Centrally, axons leave the spiral ganglion and
pass through the center of the modiolus to
form the cochlear division of the vestibular-
cochlear nerve. In the brain, axons synapse in
dorsal and ventral cochlear nuclei.
• The cochlear nerve also contains inhibitory
efferent axons (from dorsal nucleus of the
trapezoid body) that synapse on dendritic
endings of afferent neurons and on outer hair
cells. Via efferent axons, the brain selectively
“tunes” ear sensitivity (attention) to different
ranges of sound pitch.

14. • The principal divisions of the fluid space in the
cochlea are the perilymphatic space,
consisting of the scala vestibuli and the scala
tympani, and the endolymphatic space,
consisting of the scala media.
• The walls surrounding the endolymphatic
space have occluding tight junctions between
the cells, obstructing the movement of ions
into and out of the endolymph

15. • The perilymphatic space surrounds the
membranous labyrinth and opens into the
cerebrospinal fluid (CSF) by way of the
cochlear aqueduct.
• The endolymphatic space, as well as
continuing throughout the membranous
labyrinth, is joined to the endolymphatic sac
by means of the endolymphatic duct.

16. FORMATION AND ABSORPTION OF THE ENDOLYMPH
ENDOLYMPH
• Endolymph is produced primarily by the stria vascularis in the
cochlea and also by the planum semilunatum and the dark cells in
the vestibular labyrinth
• The stria vascularis has a high concentration of N+/K+ATPase,
adenyl cyclase and carbonic anhydrase, which are enzymes
associated with active pumping of ions and transport of fluid into
the endolymph, and high levels of oxidative enzymes associated
with glucose metabolism, as would be needed to provide fuel for a
vigorous active transport system. The basal and marginal cells are
true epithelial cells, whereas the intermediate cells are
‘melanocyte-like’. Intricate vasculature provides the oxygen and
nutrients needed for the stria vascularis to function correctly.

17. • The endolymphatic sac contributes to the
homeostasis of the endolymph, affecting the
ionic composition of the endolymph and being
capable of both increasing and decreasing its
volume ( absorption).
• The cells in the sac have a columnar shape and
contain long microvilli on the luminal surface,
with many pinocytotic vesicles and vacuoles. It
has also been suggested that free phagocytic cells
cross the epithelium to remove cellular debris
and foreign material from the endolymph.

18. FORMATION AND ABSORPTION OF THE PERILYMPH
• There are two types of perilymph: the perilymph of the
scala vestibuli, and that of the scala tympani. Both
have a composition similar to cerebro-spinal fluid
(CSF): rich in sodium (140mM) and poor in potassium
(5mM) and calcium (1.2mM).
• The perilymph in the scala vestibuli comes from blood
plasma across a hemto-perilymphatic barrier, whereas
that of the scala tympani originates from CSF.
• The perilymph is absorbed in the loose connective
tissue of the modiolum.

19. COMPOSITION OF PRILYMPH &
ENDOLYMPH

20. POTASSIUM CYCLE
• K+ ions are cycled through the cochlea: the K+
ions of the endolymph flow into the sensory
hair cells through the mechano-transduction
channels and then into the perilymph via
basolateral K+ channels in the hair cells. K+ can
then be taken up by fibrocytes in the spiral
ligament and transported via gap junctions
into strial intermediate cells before being
secreted into the endolymph again.

24. • Mutations in the K+ channels KCNQ1, KCNE1
or KCNQ4, or in the genes encoding the gap
junction proteins connexin-26, connexin-30 or
connexin-31, can lead to hearing losses due to
defects the K+ cycling.
• Mutations in the gene for connexin-26
account for half of all cases of autosomal non-
syndromic pre-lingual hearing impairment.

26. COCHLEAR PHYSIOLOGY IN BRIEF
• The basilar membrane and the hair cells of the cochlea function as a sharply tuned frequency
analyzer. Sound is transmitted to the inner ear via vibration of the tympanic membrane,
leading to movement of the middle ear bones (malleus, incus, and stapes). Movement of the
stapes on the oval window generates a pressure wave in the perilymph within the cochlea,
causing the basilar membrane to vibrate. Sounds of different frequencies vibrate different
parts of the basilar membrane, and the point of maximal vibration amplitude depends on the
sound frequency.
• As the basilar membrane vibrates, the hair cells attached to this membrane are rhythmically
pushed up against the tectorial membrane, bending the hair cell stereocilia. This opens
mechanically gated ion channels on the hair cell, allowing influx of potassium (K+) and
calcium(Ca2+) ions. The flow of ions generates an AC current through the hair cell surface, at
the same frequency as the acoustic stimulus. This measurable AC voltage is called the
cochlear microphonic (CM), which mimics the stimulus. The hair cells function as a
transducer, converting the mechanical movement of the basilar membrane into electrical
voltage, in a process requiring ATP from the stria vascularis as an energy source.
• The depolarized hair cell releases neurotransmitters across a synapse to primary auditory
neurons of the spiral ganglion. Upon reaching receptors on the postsynaptic spiral ganglion
neurons, the neurotransmitters induce a postsynaptic potential or generator potential in the
neuronal projections. When a certain threshold potential is reached, the spiral ganglion
neuron fires an action potential, which enters the auditory processing pathway of the brain

27. MENIERE’S DISEASE
• Meniere’s disease is defined as a symptom
complex associated with:
1.Roaring tinnitus
2.Sensorineural hearing loss (Low frequency)
3.Vertigo (episodic)
4.Fullness of the ear
5.These symptoms are associated with dilated
membranous labyrinth filled with endolymph

28. • Idiopathic
• Anatomical (small vestibular aqueduct)
• Viral infection (HSV type 1)
• Traumatic (physical, acoustic)
• Allergy
• Autoimmunity
• CSOM
• Syphilis
• Otosclerosis
AETIOLOGY

29. • Endolymphatic hydrops causes distortion of
membranous labyrinth
• Pressure building up in the scala media may
cause micro ruptures of membranous
labyrinth
• This would account for the episodic nature of
the attacks
• Healing of these ruptures causes resolution of
the disorder

30. • Small amounts of excess endolymph can be
cleared by radial flow
• Larger volumes need longitudinal flow for their
clearance
• Endolymphatic sinus temporarily accommodates
excess endolymph till the sac is ready for it
• Endolymphatic valve of Bast isolates pars
superior and prevents endolymph from draining
out of the utricle
DRAINAGE THEORY

31. DRAINAGE THEORY
The excess volume tends to
accumulate in the apical
end of the cochlea, where
the membranes are more
lax than elsewhere, even
though the endolymph
pressure would be similar
elsewhere in the cochlea.

32. • Classical Meniere’s disease
• Vestibular Meniere’s disease – vestibular
symptoms and aural pressure
• Cochlear Meniere’s disease – cochlear
symptoms and aural pressure
• Lermoyez syndrome – Reverse Meniere’s
• Tumarkin’s crisis – Utricular Meniere’s
TYPES

33. • variant of Meniere’s disease
• sudden sensorineural hearing loss, which
improves during or immediately after the
attack of vertigo.
• Cause is sudden spasm of the labyrinthine
artery followed by immediate dilatation
LERMOYEZ SYNDROME

34. • AKA Tumarkin’s drop attacks
• abrupt falling attacks of brief duration without
loss of consciousness.
• due to an enlarging utricle due to excess
endolymphatic volume
TUMARKIN’S CRISIS

35. • Sensori neural in nature
• Fluctuating and progressive
• Affects low frequencies
• Mild low frequency conductive hearing loss (rare)
• Profound sensori neural hearing loss (End stage)
HEARING LOSS

36. • Roaring in nature
• Could be continuous / intermittent
• Non pulsatile in nature
• Frequency of tinnitus corresponds to the
region of cochlea which has suffered the
maximum damage
TINNITUS

37. Possible Meniere’s disease:
• Episodic vertigo without hearing loss or
• Sensorineural hearing loss, fluctuating or fixed with dysequilibrium, but
without definite episodes
• Other causes excluded
Probable Meniere’s disease:
• One definitive episode of spontaneous vertigo
• Audiometrically documented hearing loss at least during one attack
• Tinnitus and aural fullness in the affected ear
Definitive Meniere’s disease
• Two or more definitive episodes of spontaneous vertigo one atleast lasting
for 20 mins.
Audiometrically documented hearing loss at least on
one occasion.
• Tinnitus and aural fullness in the affected ear
DIAGNOSTIC CRITERIA (AAO-HNS)

38. • History
1. Nature of the sensation
2. Timing of the initial spell
3. Frequency and duration of the symptoms
4. Precipitating factors
• Vestibular tests
• Complete Haemogram
• Audiometry
• Loudness recruiment
• VEMP
• Dehydration tests
• Posturography
• Electronystagmography
DIAGNOSIS

39. • Increased summating potential / action
potential ratio. 1:3 is normal
• Widened summating potential / action
potential complex. A widening of greater than
2 ms is significant
• Small distorted cochlear microphonics
ELECTROCOCHLEOGRAPHY

40. STAGING
STAGE PURE TONE AVERAGE OF 4 TONE IN dB
IN PREVIOUS 6 MONTHS
1 < = 25
2 26-40
3 41-70
4 >71

41. the aim is to decrease the production or accumulation of the
endolymph
CONSERATIVE
• Dietary sodium restriction (1mg/day)
• Restriction of caffeine and nicotine like substances
• Diuretics like bendroflurazide,dyazide, chlorthalidone
• Betahistine
histamine analogue with weak H1, H2 agonistic and moderate H3
antagonistic action
causes improved microvascular circulation in striae vascularis
inhibition of vestibular nuclei activity
• Calcium agonists
TREATMENT

42. • Steroids
1. Topical application via tympanostomy tubes
2. Shea et al reported 35.4% hearing
improvement and complete vertigo control in
63.4% cases treated with 16 mg intratympanic
and 16 mg i.v. dexamethasone for three
consecutive days followed by oral
dexamethasone
3. Silverstein microwick can be used for
intratympanic drug administration

43. • Intratympanic injection of aminoglycosides
a form of chemical labyrinthectomy,
gentamycin therapy ablates the vestibular
“dark cells” of the secretory epithelium thus
decreasing endolymph production
response to this is measured by in response to
rapid, rotatory head thrusts
• Alternobaric oxygen therapy

44. • Local overpressure therapy by means of Meniett
device which applies intermittent micropressure
to the inner ear via a tympanostomy tube

45. 1. Isordil
2. ϒ – globulin
3. Urea
4. Glycerol
5. Lithium
6. Anticholinergics – Glycopyrrolate 1-2 mg /day
7. Antidopaminergics – Droperidol 2.5 – 10 mg orally / day
8. Leuprolide acetate – Blocks normal sex hormone
production
9. Innovar – A combination of droperidol and fentanyl can be
used to suppress vestibular symptoms (can replace
endolymphatic sac surgery)
MISCELLANOUS DRUGS

46. • Endolymph decompression
• First described by portmann 1926
• Via the round window by otic-periotic shunt
that perforates the basilar membrane
• Cochleosacculotomy creates a fracture
dislocation of osseous spiral lamina
both these procedures have high degree of
hearing loss
SURGICAL TREATMENT

47. 1.Labyrinthectomy
2.Translabyrinthine vestibular neurectomy
3.Retrolabyrinthine vestibular neurinectomy
4.Retrosigmoid vestibular neurinectomy
5.Middle cranial fossa vestibular neurinectomy
ABLATIVE PROCEDURES

48. THANK YOU