perilymphatic fistula ( plf ) is an abnormal communication between the middle ear and the perilymphatic space , mostly due to laceration of the oval and/or round window , or congenital defects in the area of fissula ante fenestram or fossula post fenestram . plf may be caused by external injury such as head trauma , barotrauma , physical exertion such as straining , nose blowing , sneezing , among others . some diseases such as mondini malformation , large cochlear aqueduct syndrome , and middle ear abnormalities are linked to plf , among others . when no obvious reasons for plf exists , it is called spontaneous . this does not mean that spontaneous plf would occur without trauma , but the trauma may be so minute that it is not recognised . idiopathic plf has been implicated as one of the etiological factors associated with idiopathic sudden or fluctuating sensorineural hearing loss and vertigo , which occurs in defined diseases such as meniere 's disease , otosclerosis , and sudden deafness , among others . so far , there are no objective tests that can exclude or verify a plf . clinically , plf is suspected when the patient complains of the tullio 's phenomenon [ 7 , 8 ] . most commonly the hennebert 's sign is evaluated , in which test the posture and eye movements are inspected when the ear canal pressure is slowly increased or decreased . the test has been modified and performed with impedance tympanometry in eng ,   or on posturography [ 1012 ] . . early diagnosis may preserve the hearing and prevent vestibular function loss of patients with plf . nevertheless , direct inspection of the middle ear by elevating the tympanomeatal flap may lead to erroneous conclusions when plf is suspected . poe et al .   demonstrated that middle ear processes can be imaged endoscopically by introducing a small - diameter rigid endoscope through the tympanic membrane . the windows and mucosal membranes can be inspected to exclude perilymphatic leaks [ 14 , 16 ] . the purpose of the present study was to evaluate various vestibular and cochlear disorders in order to determine the presence of plf . we also wanted to study the relevance of sound and pressure loading on posturography in assessing of plf . we investigated altogether 264 subjects out of patients with various inner ear diseases clinically susceptible to plf . for this study , we studied the middle ear by transtympanic endoscopy and by evaluation of tullio 's phenomenon . the age of the subjects varied from 22 to 80 years ( mean age 48 years ) . audiometry was done in all cases before examination , and one month after tympanoscopy . in connection to tympanoscopy , we evaluated the electrocochleography by using round window electrodes and also cochlear blood flow by using a laser doppler flux meter placed on the promontorium . the investigation started with evaluation of the vestibule - spinal responses when loading the ear with low - frequency sound ( lfs ) . the low - frequency sound ( lfs ) test was used to evoke abnormal body sway which was measured on posturography . the lfs was generated with a piston type air sampling pump ( msa , usa ) , which has an adjustable stroke frequency ranging from 6 to 80  hz . the frequencies used in the test were 25 , 50 , and 63  hz at a sound pressure level of 130 , 132 , and 135  db , respectively . a part of the tympanic membrane ( about a 1  mm wide area extending from the annulus to the umbo ) was anaesthetized with 90% phenol solution . after a radial paracentesis of about 5  mm in length we had a bloodless view into the posterior tympanic cavity . an endoscope ( 1.7  mm in diameter , 120  mm in length ) with an angle of 5  deg ( wolff gmbh , germany ) was inserted into the tympanic cavity . thereafter , the round window was examined . a forceful valsalva maneuver and the queckerstedt test the 25  degree tympanoscope was introduced and the oval window area was examined paying special attention to the fissula ante fenestram . the valsalva maneuver and the tympanic cavity could be visualized in all except seven subjects . in one subject who had undergone stapes surgery , scar tissue formation was so prominent that the oval window and prosthesis area could not be identified . in one subject , the anatomy of the middle ear was changed so that the oval window was situated more inferior than usual and the bone rim of the round window niche was flattened , obstructing vision through the window . in two patients , the tympanic cavity could not be visualized because of retraction of the tympanic membrane . in three subjects , the exostoses and bleeding from the bony canal hindered the inspection . in most subjects , there was folding in the round window that occluded direct viewing of the window membrane . in about 35% of the cases , we could identify the whole round window membrane . usually the best way to visualize the round window was to examine it with a 5  deg endoscope . although the angle of the endoscope was not optimal , the best area visualized by this scope was the round window area . sometimes the round window could be examined with a 25  degree scope , but usually the round window niche and hypotympanic space were too narrow to allow insertion of the 25  degree scope into the area . the visibility in the posterior part of the stapes footplate was limited , and especially the posterior crus - facial nerve rim limited visual inspection . inspection of the patient in a recumbent position with head down ( trendelenburg position ) was used to provoke an increase in the perilymph flow through an eventual plf . these examinations were carried out twice , once for examination of the round window and once for that of the oval window . it was covered with fibrinous membrane and caused by a diving accident . in one case , there was abnormal mucosal shining in the round window niche and oval window area that could signify a plf . three cases with abnormal shining around the round window probably exhibited reactive changes to tympanoscopy . in two cases , we applied tissue glue to the area , but the symptom was not relieved . figure 1 shows the outcome of the fistula test at different stimulation frequencies in four categories of the patients . in the analysis of variance , thus , 24 of the 149 patients with meniere 's disease had abnormal lfs responses . the corresponding numbers for vestibulopathy were 5 out of 53 , cochleopathy 3 out of 32 , sudden deafness 2 out of 14 . in those 34 patients in whom the lfs stimulation provoked unsteadiness in posturography analogous to the tullio 's phenomenon , no presence of plf in tympanoscopy could be verified . all endoscopies were well tolerated by the patients , except in 3 cases , in whom the exostoses of the bony canal caused difficulties with bleeding and discomfort so that the examination has to be interrupted . these patients found the procedure painful when the endoscope was in contact with the skin of the ear canal . all myringotomies were fully healed at the time of followup . in one patient , healing of five patients experienced a reduction in their ability to taste , but the symptom subsided 2 to 4 weeks after endoscopy . endoscopy has had a rather limited success in otology when compared with the advances in endoscopy techniques in rhinology or other disciplines of surgery . otoendoscopy was introduced by nomura   and takahashi et al .   for documentation purposes . in otosurgery , it has been proposed for second look mastoidectomy ,   in middle ear surgery , in the verification of middle ear recesses in conjunction with cholesteatoma surgery , [ 21 , 22 ] in hearing preservation surgery of vestibular schwannomas , and in inspection of the tympanic cavity . the use of endoscopy in the detection of plf has been promoted by poe et al . they demonstrated that , after the use of local anesthetics for elevation of a tympanomeatal flap , oozing of exudate occurred in the middle ear , leading to a false diagnosis of plf in a patient who had normal structures in tympanoscopy [ 15 , 24 ] . furthermore , they demonstrated that in three cases with experimental plf , the findings could be verified in middle ear microscopy as well as in tympanoscopy [ 15 , 16 ] . provocation maneuvers , such as queckerstedt 's manoeuvre and the forced valsalva test are easier to perform in tympanoscopy than in otomicrosopy . nevertheless , it has been suggested that the accuracy of endoscopy is not sufficient for detecting minute this holds for all present examination methods , where nonopen fistulas can not be verified . we demonstrated in guinea pig with artificial fistula that the optic resolution was satisfactory whereas on the video screen resolution was not satisfactory ( unpublished observation ) . ogawa et al .   demonstrated that , in one patient finally diagnosed with idiopathic plf , tympanoscopy could not reveal the fistula . in spite of this event , is more accurate : the middle ear mucosa is elevated and coagulated with a ktp laser . so far , without any relevant objective test for plf , it is difficult to know which patient should be operated on . hitherto tympanoscopy seemed to be the golden rule for the detection of plf on which all diagnostic tests or operative findings should be benchmark . tympanoscopy is an ambulatory procedure with very few complications and it seems to have high diagnostic accuracy for plf . one of the most disturbing things in assessing diagnosis of plf is that there are no characteristic signs , symptoms , or a golden rule for verifying of plf . , the symptoms of plf coincide with those present in a majority of cases with meniere 's disease . the observation of endolympahic hydrops in cases with plf may in fact be the reason for meniere - like symptoms that may be secondary to plf . fluorescein applied intrathecally may assist to reveal a fistula better than fluorescein applied intravenously   as this has not proved to be reliable for the detection of plf . during surgery , for the detection of plf mineral , oil droplets have recently been advocated to trap the perilymph and to visualize the leak . also , beta2-transferrin has been advocated [ 30 , 31 ] a two - dimensional polyacrylamide gel electrophoresis has been studied in the verification of a plf . it is possible that in these instances flexible endoscopes can be utilized [ 15 , 33 ] . there is general consensus that a trauma to the ear , either explosive or implosive , is the most important factor in the etiology of plf . it has been debated whether a disease called  idiopathic or spontaneous plf  actually exists . shea   criticised the occurrence of idiopathic plf and could not verify an idiopathic plf in his large series of otologic patients . in a randomised , retrospective study , these were  sudden or fluctuate hearing loss or slowly progressive hearing loss and the vestibular symptoms were equivalent to positional vertigo or constant disequilibrium . a cornerstone in the diagnosis was a positive fistula test ( hennebert 's sign or symptom or equivalent ) . with blind assessment of the temporal bones , they could verify with high specificity ( 91% ) and moderate sensitivity ( 59% ) a plf . it was noteworthy that a majority of the patients had a symptom entity equivalent to meniere 's disease . their clinical approach was much the same as ours , in which we examined with tympanoscopy all those patients with unconfirmed diagnosis having a high suspicion of plf during a four - year course . we were able to confirm the presence of one plf in the round window after a diving accident . in three additional cases , abnormal mucosal shining with slight oozing was observed in the fossula post fenestra area . these cases were considered possible candidates for a plf , but closer examination and absence of fluid oozing during provocation prompted rejection of the diagnosis of plf . the slow accumulation of fluid was probably due to mechanical irritation of the middle ear mucosa . kohut et al .   demonstrated the histopathologic findings of a temporal bone in idiopathic plf , as fissure tracts in fissula ante fenestram which contained loose connective tissue , and which are composed of fibroblasts that are not densely packed , and between them are large intercellular spaces . they also reported that the submucosa of the fissure of the round window niche was composed of dense collagen next to bone , and extended over the orifice , with components extending into the lumen of the fissure . it remains to be documented whether these tiny openings are able to cause the various , prominent symptoms in the patients , and also by which mechanism the symptoms arise . risks associated with the tympanoscopy procedure are minimal , and can be as slight as inconvenience caused by dizziness due to thermal heating of the lateral semicircular canal   or may result in postoperative infection , lesion to chorda tympani , or permanent ear drum perforation . the postoperative infection rate was about 2% but with a careful technique it can be reduced , by avoiding the endoscope from contacting the ear canal wall . subjects with a history of chronic middle ear infection with thin secondary tympanic membrane were the most susceptible to infection in the present study . perhaps patients with a large secondary membrane should not be examined by endoscopy through the tympanic membrane . five patients had a temporary reduction in taste that was probably linked to the phenol used for the anesthesia of the ear drum . other alternative topical anesthetics are tetracaine base powder dissolved in isopropyl alcohol   or racemised lidocain - prilocain emulsion ( emla , astra , sweden ) applied for 15 minutes to the ear drum , or use of iontophoresis with 4% lidocaine solution with 1  :  1000 epinephrine . these anesthetics may lack effect on the chorda , but do not provide as bloodless entry into the tympanic cavity as does phenol . furthermore , by using phenol , only the paracentesis streak must be anesthetized , not the whole ear drums , as with the other drugs . we are aware that permanent perforations do occur after tympanoscopy , but the probability seems to be rather low , since in our 264 cases no permanent perforation has occurred . the vestibulespinal responses during lfs stimulation in the present study are similar to the vestibular responses found in tullio 's phenomenon . in tullio 's phenomenon , the sound pressure induces electrical potentials equivalent to cochlear microphonics from different receptors of the vestibular labyrinth . we could not relate the tullio 's phenomenon to any pathology   except endolymphatic hydrops , that could provoke tullio 's phenomenon with a similar mechanism as the hennebert 's sign , that is , anatomical connections between utriculus and the stapedial footplate . nevertheless , minor et al .   observed tullio 's phenomenon in a patient with a dehiscence of the superior semicircular canal , first observed in computerized tomography and later verified in surgery . in the present stimulation mode , the pump also generated an underpressure in the ear canal that was pulling the ear drum and stapes laterally . in this respect hennebert observed that an underpressure and overpressure of the ear canal is able to cause nystagmus and instability in patients who have luetic softening of the bony capsule . both tullio 's phenomenon and the hennebert sign were originally thought to be an indication of a fistula in the bony labyrinth . later , it was concluded that also patients with plf often show a positive hennebert 's sign , and the test has at present been commonly advocated to detect plf [ 6 , 8 ] . by using fluctuate air pressure loading in the outer ear canal , wall and casselbrant   demonstrated in animal model that , in plf , pressure caused eye deviations and nystagmus . the number of positive test results in the lfs loading test on posturography in patients with meniere 's disease or vestibulopathy was unacceptably high , although the magnitude of the positive responses was significantly lower than in plf patients . .   performed by posturography a pressure loading test , and compared the outcome of the test in surgery conducted by two teams . the sensitivity between the teams varied from 53 to 100% and specificity from 56 to 89% for the verification of plf . black et al .   used posturography and reported a high hit rate of positive fistula tests ( 97% ) in the vestibulospinal responses of 64 patients . even with the present plf method , the lack of specificity may not totally disqualify the value of the test . the accuracy of the fistula test varies even more in most of the tests used to detect a plf . supance and bluestone   reported a positive fistula test in 54% of their surgically confirmed fistula cases . healy et al .   reported positive fistula test rate in 37% of their surgically confirmed cases . seltzer and mccabe   reported a positive fistula test rate of 36% among 91 surgically confirmed fistulas . finally , we found that tullio 's phenomenon test was not specific for plf , thus tympanocopy is recommended as the first choice to perform when the plf is suspected , especially during the acute phase of the disease before the fibirinous reaction can occur .