Generality
The otoliths are very small agglomerates of oxalate and calcium carbonate, incorporated in a gelatinous matrix located in the inner ear .
These formations contribute to maintaining the balance and, in function of the displacement of the head, transmit the sense of acceleration to the otolithic organs of the vestibular system (ie utricle and saccule). Being heavier than the matrix that contains them, in fact, otoliths stimulate the sensory hair cells of the ear when changing position or a movement is started. In turn, the latter send signals to the brain, informing it of changes in the body in space.
When the inner ear is affected by trauma, infection or other conditions, the otoliths can become detached, moving into the semicircular canals . The latter are stimulated in an erroneous manner and become sensitive to positions of the head to which normally they would not pay attention (note: the semicircular canals are deputed to perceive the rotation of the head). The consequence of this phenomenon is benign paroxysmal positional vertigo (or vertigo due to otolith detachment).
Ear anatomy (in short)
To better understand how otoliths are involved in benign paroxysmal positional vertigo, it is necessary to remember some notions related to the structure of the auditory organ.
The ear can be anatomically divided into three parts:
- EXTERNAL EAR: formed by the auricle, made up of skin and cartilage, and of the external auditory canal. Thanks to its structure, the external ear conveys the sound waves towards the membrane of the eardrum, which provides the useful surface for sound collection and vibrates in response to the acoustic stimulus.
- MIDDLE EAR : it is a small cavity placed between the eardrum and the inner ear, to which it transmits the mechanical vibratory energy of sound through a system of three auditory ossicles (in sequence: hammer, anvil and stirrup).
- INTERNAL EAR : it consists of a complex series of structures (vestibular apparatus and cochlea), contained in depth in the bones of the skull. The function of the cochlea is acoustic and consists in transforming the sound waves transmitted by the middle ear into electrical impulses which, through the acoustic nerve, are sent to the brain. Instead, the VESTIBULAR apparatus consists of two otolithic organs, the saccule and the utricle, and three semicircular canals . This system is involved in maintaining posture and is responsible for the sense of balance : the sensory hair cells perceive the impulses concerning the movements of the head and the inertial effects produced by the force of gravity, therefore they transmit this information to the central nervous system (CNS), through the vestibular nerve.
What are
The otoliths (or otocones) are concretions, comparable to tiny pebbles, which are found in the endolymph of the inner ear.
Endolymph: what is it and where is it?
The endolymph is a liquid contained in the membranous labyrinth of the inner ear, especially in the middle ramp of the cochlea, in the semicircular canals, in the utricle and in the saccule.
Otoliths consist of calcium oxalate and calcium carbonate . More in detail, these are agglutinated or precipitated crystals around a nucleus, therefore they have a well-defined morphology. The otoliths are incorporated into a gelatinous matrix (called the otolithic membrane ), which covers the sensory epithelium of the acoustic macula of the utricle and of the saccule.
Acoustic macula: short note
Sensory receptors sensitive to linear accelerations (including gravity) are present in the acoustic macula. From this structure originate, therefore, information relating to the position of the head in space. The sensory cells of the acoustic macula present, at their apical extremity of the cilia, which are immersed in the otolithic membrane.
The otoliths are relatively heavy and, when the body changes position or starts a movement, they exert an inertial force on the otolithic membrane. To the latter, in practice, the displacement of the "pebbles" is transmitted which determines stretching and compressions at the level of the cilia of the sensory cells.
To this phenomenon coincides the stimulation of the terminations of the branches of the vestibular nerve, which send signals to their base, then interpreted by the brain as a variation of the body in space . Thus the transduction results in static and equilibrium sensations in the up-down shifts (as in an elevator) and forward-backward (ex. Car).
Otoliths are subject to periodic physiological replacement .
Otoliti: what are they for?
Otoliths are indicators of balance, movement and direction .
Because of their orientation in the head, the otolithic organs are sensitive, in particular, to the change in horizontal movement ( utricle ) or to vertical acceleration ( saccule ).
The semicircular canals of the vestibular system receive angular accelerations, such as the rotation of the head, thanks to the inertial force that the movements exert on the dome (another type of gelatinous membrane, connected to hairy cells).
Important note
When otoliths detach themselves and travel in the liquid of the semicircular canals that preside over the balance in angular displacements, they erroneously stimulate the receptors present here. This causes the illusion of rotation, which results in vertigo.
Causes
As anticipated, changes in the position of the head determine the reaction of otoliths at the level of the otolithic organs (utricle and saccule). This stimulates the hair cells that transmit information to the nerve endings, from which the static and balance sensations result.
In some cases, however, the otoliths can detach from the otolithic membrane and move in the semicircular canals, giving rise to a pathology called benign paroxysmal positional vertigo .
This condition can occur due to traumas involving the inner ear, infections, surgery or other causes that are still partly unknown today.
Benign paroxysmal positional vertigo is also called:
- Cupololithiasis, when otoliths position themselves in the dome;
- Canalolithiasis, if otoliths are found free in the endolymph (most frequent condition).
Aggravating and / or triggering factors
The vertigo of otolith detachment may arise without apparent reasons or following:
- Ear infections;
- Head trauma;
- Ear surgery;
- Saccular hydrops;
- Various types of accidents (sports, cars etc.);
- Extended bed rest, for example a convalescence.
Symptoms and Complications
When otoliths are free to move in the semicircular canals of the ear, the patient experiences the feeling that the room and all objects are spinning whirling clockwise or counterclockwise . The migration of otoliths is responsible, in fact, for a very strong and sudden vertiginous crisis, which intensifies in the act of going to bed or getting up from the bed. Depending on the affected part (right or left labyrinth), vertigo also manifests itself by turning the head on the pillow from the side of the affected ear.
This occurs due to the fact that detached otoliths do not cause any disturbance until they remain in the position they have assumed; in moving, after a displacement of the head, these send, however, more violent impulses to the sensory cells, which, in turn, transmit the erroneous information to the brain.
Otolites: what determines with their movement?
The sensation induced by the migration of otoliths into the semicircular canals is an intense and sudden vertigo . In general, this manifestation arises when one moves from a lying position to an upright position and vice versa.
The positional vertigo induced by the detachment of the otoliths have the following characteristics:
- Sense : rotary, right or left;
- Duration : short, from a few seconds to a few minutes;
- Movement : the vertiginous crisis can only be induced by a change in position.
Among the secondary symptoms of benign paroxysmal positional vertigo from otolith detachment are also highlighted:
- Nystagmus (involuntary rotatory and joint movement of the eyeballs);
- Nausea;
- Vomiting (rare);
- Tachycardia;
- Loss of balance;
- Blurred vision;
- Uncertainty in movements;
- State of slight confusion;
Generally, the movement of otoliths in the semicircular canals causes no hearing problems. Only in rare cases, it is possible to detect sensorineural tinnitus and / or hearing loss.
For the purposes of a correct differential diagnosis, it should be noted that the vertigo from otoliths:
- Does not cause constant dizziness, independent of movement;
- It does not cause unconsciousness, headache or other neurological symptoms, such as tingling or speech difficulties.
Possible consequences
Although it is not a serious pathology, paroxysmal positional vertigo always frightens many sufferers, due to its sudden onset and the feeling of malaise it causes.
The "benignity" of paroxysmal positional vertigo is given by the fact that this disease has no consequences on the hearing or on the general health of the subject. Furthermore, otolith dysfunction tends to regress spontaneously over time.
Diagnosis
The diagnosis of otolithic detachment vertigo is carried out with the collection of anamnestic data and the physical examination for the detection of symptoms. The otorhinolaryngology examination may concern the exploration of the interior of the ear and the search for involuntary eye movements (nystagmus).
In addition, the doctor can check the balance or try to reproduce the otolithic dizziness by passing the patient quickly from the sitting to the lying position. Depending on the symptoms, further investigations could be indicated, such as, for example, an MRI scan to rule out the presence of an acoustic neuroma or other lesions that could cause similar symptoms.
Dix-Hallpike maneuver
The otolith dysfunction is confirmed by the Dix-Hallpike test . This maneuver must be performed first from the right side, then from the left side, to highlight the movement of the concretions in the semicircular canals, in one or both ears. The patient is lowered from a sitting position to a lying position, with the head turned at 45 ° to the shoulders.
If the otoliths have detached from the otolithic organs and are free to move in the semicircular canals of the ear, this maneuver evokes a strong rotational vertigo associated with nystagmus, thus confirming the diagnostic suspicion.
In the case where the Dix-Hallpike test does not cause any effect, instead, it means that the semicircular canals of the ear are free from the otoliths. Consequently, the cause of the vertigo that the patient suffers from should be sought elsewhere.
Therapy
Usually, treatment of vertigo from otolith detachment involves liberating maneuvers . These consist in having the patient perform some head and body movements based on a specific sequence. The purpose of this intervention is to induce otoliths to exit the semicircular canals, where they are responsible for the annoying crisis, and to reposition themselves in the area of the utricle and of the saccule. In the otolithic organs, then, the otoliths will be eliminated by the cells responsible for their destruction.
If the maneuver proves to be effective, the patient feels another momentary dizziness (liberating vertigo), with a reverse sense of rotation compared to that which is usually felt with the migration of otoliths.
However, if the maneuver was not successful, the specialist may suggest a series of rehabilitation exercises (or vestibular re-education) for homework for a few consecutive days to resolve the problem.
In cases where the otoliths cannot be removed through the combination of these maneuvers, the surgical option can be considered.
Note
The calcium carbonate that constitutes otoliths is not soluble, so healing can take a long time. Indicatively, it may take a few days to three weeks to resolve the problem.
drugs
The migration of otoliths into semicircular canals is a mechanical problem, therefore, unlike other forms of vertigo, the use of drugs is essentially ineffective.
Treatment with antivertiginosi medicines (also called vestibular suppressors) can be considered in acute and severe crises of benign paroxysmal positional vertigo. These medicines include:
- Antihistamines (eg meclizine and scopolamine);
- Sedatives (eg clonazepam);
- Antiemetic drugs (eg promethazine).
In most cases, however, the use of drugs is not indicated as they are only symptomatic. In other words, these medicines temporarily eliminate the effects of vertigo itself, or the sensation of rotation and malaise it causes, but do not affect the cause.
Surgical treatment
If the liberating maneuvers are not conclusive, the doctor could indicate surgery to empty the semicircular canals from the otoliths. This treatment has the same risk as all neurosurgical procedures, therefore it is used only for particularly serious cases.
Some advice
- To achieve rapid and lasting healing, abrupt movements of the head and neck that can cause vertigo should be avoided.
- Being that induced by otoliths a "vertigo of position", the symptoms are relieved until they disappear, if very slow movements are undertaken in getting up, lie down or turn on the side. This prevents the otoliths from moving quickly in the semicircular canals, where they have gone to position.
- Another trick to avoid exacerbating the vertiginous crisis is to avoid sleeping on the side, with the ear affected by the detachment of the otoliths resting on the pillow. For this purpose, an orthopedic cervical pillow can be used during bed rest.
