Timothy C. Hain, MD • Page last modified: August 22, 2020
Intralabyrinthine schwannoma's are a rare variant of an inner ear tumor -- acoustic neuromas. Acoustic neuromas (follow link for far more information), also known as vestibular schwannomas, are non-malignant tumors of the 8th cranial nerve. Most commonly they arise from the covering cells (Schwann cells) of the inferior vestibular nerve (Komatsuzaki and Tsunoda, 2001; Krais, 2007).
Intralabyrinthine schwannomas arise within the labyrinth (Neff et al, 2003). There are three variants of ILS related to which part of the 8th nerve affected.
Tumors confined to the vestibular nerve may present with dizziness, but without hearing symptoms. Tumors of the cochlear nerve present with hearing loss. Tumors of the entire 8th nerve may present with dizziness or hearing deficits, or both.
Eventually, nearly always the entire inner ear is lost in patients with intralabyrinthine schwannoma. This usually takes many years.
Our clinical experience with these tumors is that they usually present with restricted labyrinthine disease - -complete loss of part of the inner ear (such as hearing), combined with nearly normal function of the rest of the inner ear.
Hearing loss is almost inevitable in patients with ILS, although tumors may grow imperceptibly about 40% of the time. If the tumor is of the cochlear nerve, the hearing loss occurs early and usually is the reason that the tumor was discovered. If it is of the vestibular nerve, hearing loss occurs late. Hearing loss is diagnosed with audiometry. See the "management" section below regarding how often audiometry should be performed. Tinnitus is very common in ILS, is usually unilateral and confined to the affected ear. Tinnitus can be quantified with "tinnitus matching".
ILS of the vestibular nerve cause signs of vestibular imbalance (nystagmus, dizziness), and also usually are accompanied by signs of vestibular irritibility (hyperventilation induced nystagmus). We have encountered patients with purely vestibular ILS in whom hearing was normal, but labyrinthine function (of the superior canal) was absent !
ILS of the cochlear nerve cause hearing symptoms - - hearing loss and tinnitus primarily.
The mechanism of symptoms in patients with ILS is mainly damage to the nerve. There may also be some impairment related to secretion of protein within the fluid of the inner ear. (Asthaqiri et al, 2012). Higher protein in the inner ear changes the density of inner ear fluid and can cause dizziness because one ear responds more sluggishly than the other. It can also cause endolymphatic hydrops, and possible emulate Meniere's disease. See the acoustic neuroma page for more comments.
|Iintralabyrinthine schwannoma, filling the ampulla of left lateral semicircular canal, and extending into the more than half of the ampullary limb of the canal. This patient had absent calorics, but present VEMP tests, as would be expected from this location.||4x2 mm mass filling apex of left cochlea.|
As illustrated above, ILS are tiny. The can easily be missed, and in Graelyi's series (2007), the average delay to diagnosis was 11 years. They can generally be just barely seen when they are 1 mm in size (this is still enough to do a lot of damage). Some tumors are discovered at autopsy or on surgery for Meniere's disease - -i.e. they can be completely missed. (Zbar et al, 1997).The usual screening CT scan done in emergency rooms for headache will nearly always miss ILS. It also very unlikely that a non-contrast brain MRI or a "open" MRI will detect an ILS. A common situation is for a tumor to be missed on the first MRI, and diagnosed only as it enlarges over years. This is not a catastrophe however, as these tumors are (presently) mainly managed by watchful waiting (see later).
The optimal test for detecting an ILS is a gadolinium enhanced T1 MRI (see picture above). In our clinical practice in Chicago Illinois, we prefer to send patients for the best MRI available - -presently a 3T MRI with gadolinium. These types of scanners are scarce, but they can be obtained in Chicago, including several scanners at Northwestern Memorial Hospital (where we practice).
If an MRI cannot be done, as in persons with a pacemaker or metallic clips, a high-resolution CT scan should be obtained in high-risk individuals, particularly if there are signs of progerssion -- i.e. hearing is deterorating in one ear, the ABR is suggestive of an acoustic neuroma, or VEMP is progressively abnormal. CT scans with IV contrast are poor tests for diagnosis of acoustic neuromas, as they have a high false negative rate (about 37%), but sometimes there is no reasonable alternative.
According to Tieleman and others ( 2008) ILSs are most frequently found intracochlearly, often anteriorly between the basal and second turn. They are hyperintense on unenhanced T1-weighted images, enhance strongly after gadolinium administration, and are sharply circumscribed and hypointense on thin heavily T2-weighted 3D images. The scala tympani is more frequently or more extensively involved than the scala vestibuli. In Tielman's record review, growth was seen from the scala tympani into the scala vestibuli and from the scala vestibuli to the saccule and vice versa. and . Cochlear ILSs most often originated in the scala tympani and only later grew into the scala vestibuli. Growth occured from the cochlea into the vestibule or vice versa through the anatomic open connection between the perilymphatic spaces in the scala vestibuli and around the saccule. (Tielman et al, 2008).
These tumors grow very slowly (only 1 mm/year), and as conservative management is usually appropriate (see below for comments regarding surgery and radiation), it is reasonable to attempt to use medical management for these situations. Hearing can often be helped with hearing aids. Dizziness can be treated with vestibular suppressents and vestibualar rehabilitation.
Irritible vestibular nerves can be treated with anticonvulsants.
Monitoring: If one has serviceable hearing, and there is no other danger of waiting (such as needing a bigger operation), one might reasonably simply wait until hearing becomes unserviceable before proceeding with surgery or radiation. Here the procedure would be periodic hearing tests, and less frequent MRI scans. The frequency of testing is mainly determined by the rate of change in the measures, but about every 12 months for hearing testing and high-resolution MRI scanning is usually appropriate. Some tumors show no growth over very long periods of time - -i.e. 15 years. Others double as rapidly as in a years time.
These tumors grow very slowly, and pose no risk to life. Thus early use of any destructive method of treatment (i.e. surgery or radiation) is usually a mistake, as all destructive treatment accelerates loss of inner ear function. Accordingly, at the author's clinical practice in Chicago Illinois, an extremely conservative strategy is usually used (watchful waiting). Similarly, Jia et al (2008) suggest that surgical excision is inappropriate in patients with useful hearing.
The watchful waiting strategy consists essentially of yearly monitoring, and simply waiting for the tumor to progress sufficiently so that there is no "cost" of surgery or radiation, or there is greater risk involved in doing nothing than use of a destructive modality (surgery or radiation).
Regarding risk, there is a risk of growth of the tumor into the internal auditory canal. Should this occur, radiation or surgery should be elected as might be considered for an acoustic neuroma that was "intracanilicular". Patients can elect surgery or radiation or continued watchful waiting. Some physicians hold different opinions and feel surgery is indicated at an earlier stage (Di Lella et al. (2007).
Both surgery and gamma-knife methods of managing acoustic tumors seem reasonable at this writing, with the choice depending on individual factors. For most persons, the gamma-knife method seems to us to be appropriate as this can be deferred until all inner ear function is lost. One can also argue very reasonably that an operative approach to an ILS is reasonable after all inner ear function has been lost, as a labyrinthectomy can remove the tumor with little morbidity as well as no chance of late radiation complications.
In our clinical practice in Chicago Illinois, the decision concerning eventual treatment (i.e. surgery or radiation) is made primarily by the patient. If surgery or radiation is decided upon for a tumor, patients are referred to one of several experienced otologic surgeons associated with our institution.