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The vestibular aqueduct syndrome: Computed tomographic appearance
ClinicalRadiology(1985) 36,241-243 © 1985 Royal College of Radiologists
0009-9260/85/438241/$02.00
The Vestibular Aqueduct Syndrome" Computed Tomographic Appearance J O E L D. S W A R T Z , P H I L I P S. YUSSEN, D E L A I N E W. M A N D E L L , D I R A N O. M I K A E L I A N * , A L A N S. B E R G E R t and R O B E R T J. WOLFSON:)
Department of Radiologic Sciences, The Medical College of Pennsylvania and Hospital; *Department of Otolaryngology, Thomas Jefferson University Hospital; ~-Roxborough Memorial Hospita# and ¢ Department of Otolaryngology, The Medical College of Pennsyh, ania and Hospital, Philadelphia, Pennsylvania, USA
We have recently examined three young patients with congenital unilateral profound sensorineural hearing loss. On computed tomography the only abnormality discovered was a remarkably enlarged vestibular aqueduct on the abnormal side. The vestibular aqueduct syndrome is an important cause of congenital hearing loss. Although this finding has been well illustrated with conventional multidirectional tomography, there has been little emphasis on the computed tomographic appearance.
There are numerous causes for congenital sensorineural hearing loss. These include the congenital vestibulo-cochlear deformities and even neoplasms. Although we have encountered a n u m b e r of these entities in our experience with computed tomography (CT), we feel that the enlarged vestibular aqueduct is worth cmphasising as the computed tomographic findings are often overlooked.
MATERIALS AND METHODS
DISCUSSION There are numerous causes for congenital neurosensory hearing loss ( O r m e r o d , 1960; Mafee et al_, 1984). In some patients, radiological evaluation may reveal deformity of the bony labyrinth, such as a complete aplasia (Michel) or partial aplasia (MondiniAlexander), and other unclassified inner-ear deformities may also be discovered_ An associated systemic dysplasia may occur and should be sought clinically. It is self-evident that a cerebello-pontine-angle lesion must be ruled out. At times, no cause for the hearing loss can be found and the abnormality is presumed to be beyond the resolution of current radiological methods. In this situation involvement of the membranous labyrinth (Bing-Siebenmann- or Scheibe-type deformity) is postulated. The vestibular aqueduct is a bony canal which extends posteriorly from the medial wall of the vestibule (Rumbaugh et al., 1974). It contains the endolymphatic duct by which the m e m b r a n o u s labyrinth communicates with the endolymphatic sac. The normal adult vestibular aqueduct is approximately
The patients were examined using a General Electric 8800 CT/T scanner. In the presence of neurosensory hearing loss, intravenous contrast was usually given by bolus injection (1 ml per pound body weight, Reno-M-60, E. R. Squibb and Co.). Contiguous or overlapping 1.5 m m axial sections were performed and these were occasionally supplemented by coronal sections. We p e r f o r m e d image reformation when appropriate.
CASE REPORTS Case 1. A 22-year-old male presented with profound neurosensory loss in the left ear since birth (Fig. 1). Otoscopic examination was normal. He was otherwise in normal health. Case 2. A 7-year-old male performed poorly on a hearing examination at his grade school and was referred for an otolaryngologic consultation (Fig. 2). A profound unilateral neurosensory loss was discovered upon audiometric examination. The otoscopic findings were normal. Case 3. A 10-year-old male, in normal health otherwise, had profound neuroscnsory loss in the left ear since birth (Fig. 3). Recently his hearing had deteriorated somewhat on the right as well. Reprint requests to: Dr J. D. Swartz, Departmcnt of Radiologic Sciences, The Medical College of Pennsylvania and Hospital, 3300 Henry Avenue, Philadelphia, PA 19129, USA.
Fig. 1 - Case 1. Axial view, left ear. The mastoid is well aerated and the ossicular chain is normal. No deformity of the cochlea (C) or vestibule (V) is present The vestibular aqueduct is markedly enlarged (arrow).
242
CLINICAL RADIOLOGY
/,
::':: .......
::., : ~=:~&yg#
(b) Fig. 2 - Case 2. (a) Axial view, right ear. The mastoid is well aerated. The cochlea (C) has a normal appearance, while the vestibule (V) and vestibular aqueduct (arrow) are enlarged. There is mild motion degradation. (b) Sagittal reconstruction: arrow indicates vestibular aqueduct (VAQ).
involved m pressure equalisation between the cerebrospinal fluid and the endolymph (Paparella and Shumrick, 1980). Variations m size of the vestibular aqueduct have been described (Rumbaugh et al., 1974; Valvassori and Clemis, 1978b). In individuals with Meniere's
(a) l c m in length and assumes a J shape (Gado and Arenberg, 1975). In the mid-term fetus the vestibular aqueduct is straight; the adult shape develops as the posterior cranial fossa structures mature (Valvassori and Clemis, 1978a). The aqueduct widens progressively as it approaches its external aperture where the endolymphatic sac is accommodated and which extends from the aperture to lie in direct apposition to the cranial dura. The endolymphatic sac contains a rugose portion, which is important for normal endolymph resorption and for the digestion of foreign bodies, and a smooth portion thought by many to be
(b)
(a) Fig. 3 - Case 3. (a) Axial view, left ear. The cochlea (C), vestibule (V) and semicircular canals are normal. The vestibular aqueduct is strikingly increased in size (arrow). (b) Sagittal reconstruction, left ear. The vestibular aqueduct is indicated with double arrows. Also note round window and ductus reuniens (single arrowhead) (V=vestibule). (c) Axial view, right ear: normal findings.
(c)
THE VESTIBULAR AQUEDUCT SYNDROME
disease, the proposed cause of which is decreased resorption of endolymph, the vestibular aqueduct may not be visualised, or is narrowed. This is a source of great controversy. In our experience, the vestibular aqueduct is often small or absent in patients with no temporal bone symptomatology. A large vestibular aqueduct has been associated with neurosensory hearing loss (Valvassori and Clemis, 1978b). This is referred to as the vestibular aqueduct syndrome and is diagnosed when the maximum diameter of the aqueduct is greater than 1.5 ram. Deformity of the remainder of the inner ear may or may not be present. Arrested inner ear development in utero has been postulated as the cause (Valvassori, 1983). The most common associated inner ear anomaly is an isolated enlargement of the vestibule (Fig. 2). Other associated anomalies include an enlarged vestibule and lateral semicircular canal, an enlarged vestibule and hypoplastic cochlea, and an isolated deformity of the cochlea (Valvassori and Clemis, 1978a). Patients with this disorder usually present in early childhood with a sensorineural or mixed hearing loss (Becket et al., 1983). The sensorineural component predominates in those with mixed loss. There is usually no relevant family history (Valvassori and Clemis, 1978b). A variety of abnormal audiometric graphs have been described. The hearing loss may be unilateral or bilateral, more commonly the latter, and may or may not be progressive. Previously, the primary radiographic method for the study of the vestibular aqueduct has been multidirectional tomography (Valvassori and Clemis, 1978a, b). The simplicity with which the lateral image of the aqueduct can be obtained still makes this a method of considerable value. However, with the emergence of high-resolution CT as the primary method for the examination of the temporal bone (Swartz et al., 1983; Swartz, 1984), it is necessary to become familiar with the appearance on CT. The enlarged vestibular aqueduct may be seen on routine
243
axial sections (Figs la, 2a, 3a), but sagittal reformations (Figs 2b, 3b) also show it to great advantage. In all three of our cases the maximal diameter of the aqueduct was greater than 2 mm in both projections. In conclusion, the vestibular aqueduct syndrome may be an overlooked cause of congenital sensorineural hearing loss. The computed tomographic appearance is stressed.
Acknowledgement. Special thanks to Joan Colombaro for her preparation of the manuscript.
REFERENCES Becker, T. S., Vignaud, J., Sultan, A. & Lachman, M. (1983). The vestibular aqueduct in congenital deafness: evaluation by the axial projection. Radiology, 149, 741-744. Gado, M. H. & Arenberg, I. K. (1975). Radiologic visualization of the vestibular aqueduct. Radiology, 117, 621-626. Mafee, M. F., Selis, J. E., Yannias, D. A., Valvassori, G. E., Pruzansky, S., Applebaum, E. L. & Capek, V. (1984). Congenital sensorineural hearing loss. Radiology, 150, 427-434. Ormerod, F. C. (1960). The pathology of congenital deafness. Journal of Laryngology, 74, 919-949. Paparella, M. M. & Shumrick, D. A. (1980). Otolaryngology, Vol. 2, The Ear, Chap. 2, pp. 45-46; Chap. 18, pp. 444-446. W. B. Saunders, Philadelphia. Rumbaugh, C. L., Bergeron, R. T. & Scanlon, R. L (1974). Vestibular aqueduct in Meniere's disease. Radiologic Clinics of North America, 12, 517-525. Swartz, J. D. (1984). The facial nerve canal: CT analysis with emphasis on diagnosis of the protruding tympanic segment. Radiology, 153,443-447. Swartz, J. D., Goodman, R. S., Russell, K. B., Ladenheim, S. E., Wolfson, R. J. & Marlowe, F. I. (1983). High resolution computed tomography of the middle ear and mastoid: Parts I-IIl. Radiology, 148,449-464. Valvassori, G. E. (1983). The large vestibular aqueduct and associated anomalies of the middle ear. Otolaryngologic Clinics of North America, 16, 95-101. Valvassori, G. E. & Clemis, J. D. (1978a) Abnormal vestibular aqueduct in cochleovestibular disorders. Advances in Otorhinolaryngology, 24, 100-105. Valvassori, G. E. & Clemis, J. D. (1978b) The large vestibular aqueduct syndrome. Laryngoscope, 88, 723 728.
0009-9260/85/438241/$02.00
The Vestibular Aqueduct Syndrome" Computed Tomographic Appearance J O E L D. S W A R T Z , P H I L I P S. YUSSEN, D E L A I N E W. M A N D E L L , D I R A N O. M I K A E L I A N * , A L A N S. B E R G E R t and R O B E R T J. WOLFSON:)
Department of Radiologic Sciences, The Medical College of Pennsylvania and Hospital; *Department of Otolaryngology, Thomas Jefferson University Hospital; ~-Roxborough Memorial Hospita# and ¢ Department of Otolaryngology, The Medical College of Pennsyh, ania and Hospital, Philadelphia, Pennsylvania, USA
We have recently examined three young patients with congenital unilateral profound sensorineural hearing loss. On computed tomography the only abnormality discovered was a remarkably enlarged vestibular aqueduct on the abnormal side. The vestibular aqueduct syndrome is an important cause of congenital hearing loss. Although this finding has been well illustrated with conventional multidirectional tomography, there has been little emphasis on the computed tomographic appearance.
There are numerous causes for congenital sensorineural hearing loss. These include the congenital vestibulo-cochlear deformities and even neoplasms. Although we have encountered a n u m b e r of these entities in our experience with computed tomography (CT), we feel that the enlarged vestibular aqueduct is worth cmphasising as the computed tomographic findings are often overlooked.
MATERIALS AND METHODS
DISCUSSION There are numerous causes for congenital neurosensory hearing loss ( O r m e r o d , 1960; Mafee et al_, 1984). In some patients, radiological evaluation may reveal deformity of the bony labyrinth, such as a complete aplasia (Michel) or partial aplasia (MondiniAlexander), and other unclassified inner-ear deformities may also be discovered_ An associated systemic dysplasia may occur and should be sought clinically. It is self-evident that a cerebello-pontine-angle lesion must be ruled out. At times, no cause for the hearing loss can be found and the abnormality is presumed to be beyond the resolution of current radiological methods. In this situation involvement of the membranous labyrinth (Bing-Siebenmann- or Scheibe-type deformity) is postulated. The vestibular aqueduct is a bony canal which extends posteriorly from the medial wall of the vestibule (Rumbaugh et al., 1974). It contains the endolymphatic duct by which the m e m b r a n o u s labyrinth communicates with the endolymphatic sac. The normal adult vestibular aqueduct is approximately
The patients were examined using a General Electric 8800 CT/T scanner. In the presence of neurosensory hearing loss, intravenous contrast was usually given by bolus injection (1 ml per pound body weight, Reno-M-60, E. R. Squibb and Co.). Contiguous or overlapping 1.5 m m axial sections were performed and these were occasionally supplemented by coronal sections. We p e r f o r m e d image reformation when appropriate.
CASE REPORTS Case 1. A 22-year-old male presented with profound neurosensory loss in the left ear since birth (Fig. 1). Otoscopic examination was normal. He was otherwise in normal health. Case 2. A 7-year-old male performed poorly on a hearing examination at his grade school and was referred for an otolaryngologic consultation (Fig. 2). A profound unilateral neurosensory loss was discovered upon audiometric examination. The otoscopic findings were normal. Case 3. A 10-year-old male, in normal health otherwise, had profound neuroscnsory loss in the left ear since birth (Fig. 3). Recently his hearing had deteriorated somewhat on the right as well. Reprint requests to: Dr J. D. Swartz, Departmcnt of Radiologic Sciences, The Medical College of Pennsylvania and Hospital, 3300 Henry Avenue, Philadelphia, PA 19129, USA.
Fig. 1 - Case 1. Axial view, left ear. The mastoid is well aerated and the ossicular chain is normal. No deformity of the cochlea (C) or vestibule (V) is present The vestibular aqueduct is markedly enlarged (arrow).
242
CLINICAL RADIOLOGY
/,
::':: .......
::., : ~=:~&yg#
(b) Fig. 2 - Case 2. (a) Axial view, right ear. The mastoid is well aerated. The cochlea (C) has a normal appearance, while the vestibule (V) and vestibular aqueduct (arrow) are enlarged. There is mild motion degradation. (b) Sagittal reconstruction: arrow indicates vestibular aqueduct (VAQ).
involved m pressure equalisation between the cerebrospinal fluid and the endolymph (Paparella and Shumrick, 1980). Variations m size of the vestibular aqueduct have been described (Rumbaugh et al., 1974; Valvassori and Clemis, 1978b). In individuals with Meniere's
(a) l c m in length and assumes a J shape (Gado and Arenberg, 1975). In the mid-term fetus the vestibular aqueduct is straight; the adult shape develops as the posterior cranial fossa structures mature (Valvassori and Clemis, 1978a). The aqueduct widens progressively as it approaches its external aperture where the endolymphatic sac is accommodated and which extends from the aperture to lie in direct apposition to the cranial dura. The endolymphatic sac contains a rugose portion, which is important for normal endolymph resorption and for the digestion of foreign bodies, and a smooth portion thought by many to be
(b)
(a) Fig. 3 - Case 3. (a) Axial view, left ear. The cochlea (C), vestibule (V) and semicircular canals are normal. The vestibular aqueduct is strikingly increased in size (arrow). (b) Sagittal reconstruction, left ear. The vestibular aqueduct is indicated with double arrows. Also note round window and ductus reuniens (single arrowhead) (V=vestibule). (c) Axial view, right ear: normal findings.
(c)
THE VESTIBULAR AQUEDUCT SYNDROME
disease, the proposed cause of which is decreased resorption of endolymph, the vestibular aqueduct may not be visualised, or is narrowed. This is a source of great controversy. In our experience, the vestibular aqueduct is often small or absent in patients with no temporal bone symptomatology. A large vestibular aqueduct has been associated with neurosensory hearing loss (Valvassori and Clemis, 1978b). This is referred to as the vestibular aqueduct syndrome and is diagnosed when the maximum diameter of the aqueduct is greater than 1.5 ram. Deformity of the remainder of the inner ear may or may not be present. Arrested inner ear development in utero has been postulated as the cause (Valvassori, 1983). The most common associated inner ear anomaly is an isolated enlargement of the vestibule (Fig. 2). Other associated anomalies include an enlarged vestibule and lateral semicircular canal, an enlarged vestibule and hypoplastic cochlea, and an isolated deformity of the cochlea (Valvassori and Clemis, 1978a). Patients with this disorder usually present in early childhood with a sensorineural or mixed hearing loss (Becket et al., 1983). The sensorineural component predominates in those with mixed loss. There is usually no relevant family history (Valvassori and Clemis, 1978b). A variety of abnormal audiometric graphs have been described. The hearing loss may be unilateral or bilateral, more commonly the latter, and may or may not be progressive. Previously, the primary radiographic method for the study of the vestibular aqueduct has been multidirectional tomography (Valvassori and Clemis, 1978a, b). The simplicity with which the lateral image of the aqueduct can be obtained still makes this a method of considerable value. However, with the emergence of high-resolution CT as the primary method for the examination of the temporal bone (Swartz et al., 1983; Swartz, 1984), it is necessary to become familiar with the appearance on CT. The enlarged vestibular aqueduct may be seen on routine
243
axial sections (Figs la, 2a, 3a), but sagittal reformations (Figs 2b, 3b) also show it to great advantage. In all three of our cases the maximal diameter of the aqueduct was greater than 2 mm in both projections. In conclusion, the vestibular aqueduct syndrome may be an overlooked cause of congenital sensorineural hearing loss. The computed tomographic appearance is stressed.
Acknowledgement. Special thanks to Joan Colombaro for her preparation of the manuscript.
REFERENCES Becker, T. S., Vignaud, J., Sultan, A. & Lachman, M. (1983). The vestibular aqueduct in congenital deafness: evaluation by the axial projection. Radiology, 149, 741-744. Gado, M. H. & Arenberg, I. K. (1975). Radiologic visualization of the vestibular aqueduct. Radiology, 117, 621-626. Mafee, M. F., Selis, J. E., Yannias, D. A., Valvassori, G. E., Pruzansky, S., Applebaum, E. L. & Capek, V. (1984). Congenital sensorineural hearing loss. Radiology, 150, 427-434. Ormerod, F. C. (1960). The pathology of congenital deafness. Journal of Laryngology, 74, 919-949. Paparella, M. M. & Shumrick, D. A. (1980). Otolaryngology, Vol. 2, The Ear, Chap. 2, pp. 45-46; Chap. 18, pp. 444-446. W. B. Saunders, Philadelphia. Rumbaugh, C. L., Bergeron, R. T. & Scanlon, R. L (1974). Vestibular aqueduct in Meniere's disease. Radiologic Clinics of North America, 12, 517-525. Swartz, J. D. (1984). The facial nerve canal: CT analysis with emphasis on diagnosis of the protruding tympanic segment. Radiology, 153,443-447. Swartz, J. D., Goodman, R. S., Russell, K. B., Ladenheim, S. E., Wolfson, R. J. & Marlowe, F. I. (1983). High resolution computed tomography of the middle ear and mastoid: Parts I-IIl. Radiology, 148,449-464. Valvassori, G. E. (1983). The large vestibular aqueduct and associated anomalies of the middle ear. Otolaryngologic Clinics of North America, 16, 95-101. Valvassori, G. E. & Clemis, J. D. (1978a) Abnormal vestibular aqueduct in cochleovestibular disorders. Advances in Otorhinolaryngology, 24, 100-105. Valvassori, G. E. & Clemis, J. D. (1978b) The large vestibular aqueduct syndrome. Laryngoscope, 88, 723 728.