British Journal of Radiology 75 (2002),502-505 © 2002 The British Institute of Radiology
MRI of cochlear otosclerosis
J P N Goh, MBBS, FRCR1,
L L Chan, MBBS, FRCR2 and
T Y Tan, MBBS, FRCR3
1 Department of Diagnostic Radiology, Tan Tock Seng Hospital, 2 Department of Diagnostic Radiology, Singapore General Hospital and 3 Department of Radiology, Changi General Hospital, Singapore
 |
Abstract
|
|---|
Cochlear otosclerosis is an uncommon cause of mixed and sensorineural hearing loss. This has a characteristic appearance on CT, producing a distinctive pericochlear hypodense double ring. However, its appearance on MRI is not as readily appreciated, producing a ring of intermediate signal in the pericochlear and perilabyrinthine regions on T1 weighted images, demonstrating mild to moderate enhancement after gadolinium administration. Increased signal on T2 weighted images may also be seen. Recognition of these MRI features is important as MRI may be the first modality of investigation, especially when patients present with symptoms indicative of sensorineural hearing loss. We review four patients who presented with sensoineural hearing loss, and who were imaged with MRI as the first line of investigation.
|
Introduction
|
|---|
Otosclerosis is an osseous bony dysplasia that causes sensorineural and conductive hearing loss, and occasionally tinnitus. Otosclerosis is best characterized on high resolution CT (HRCT) studies. However, the MRI findings of cochlear otosclerosis are not as well known and may produce diagnostic difficulties when patients are imaged with MRI as the first line investigation for sensorineural hearing loss. Our purpose was to highlight the MRI findings of cochlear otosclerosis, with CT correlation, in an Asian population.
|
Materials and methods
|
|---|
All our patients had MRI as the first line of investigation, as they had findings of asymmetrical sensorineural or mixed hearing loss. MRI scans were performed before and after iv gadolinium chelates. The sequences obtained included 5 mm thick T2 weighted images (TR/TE, 4000/100) through the entire brain and posterior fossa, with 3 mm thick T1 weighted images with an interslice gap of 1 mm (TR/TE, 500/10) through the internal auditory canals before and after iv gadolinium. Confirmatory HRCT was performed after MRI, using 1 mm thick sections in the coronal and axial planes.
Patient 1
A 39-year-old Indian female complained of poor hearing for 8 years. Clinical examination revealed no significant findings of note. Audiometry, however, demonstrated a bilateral moderate mixed hearing loss. Intermediate signal, with mild to moderate enhancement following gadolinium administration, was seen in the pericochlear regions on T1 weighted imaging. HRCT confirmed bilateral pericochlear otospongiotic changes.
Patient 2
A 50-year-old Chinese female presented with right-sided hearing loss over a 7 year duration. The Schwartze sign was positive bilaterally. Audiometry demonstrated asymmetrical bilateral sensorineural hearing loss, worse on the right-hand side. MRI showed bilateral areas of intermediate signal, with moderate enhancement, in the pericochlear regions bilaterally, on T1 weighted imaging. HRCT again confirmed bilateral pericochlear otospongiotic changes.
Patient 3
A 45-year-old Chinese male presented with a 10-year history of tinnitus that was worse on the right-hand side. There were no other associated symptoms when he first presented in 1991. Clinical examination and investigations (including HRCT) at that time were unremarkable. He was managed conservatively. He sought medical attention again in 2001 with the complaint of bilateral hearing loss, worse on the right-hand side. Clinical examination was normal. An audiogram revealed bilateral moderate to severe mixed hearing loss. MRI showed intermediate signal, with mild ring enhancement, on T1 weighted imaging in the pericochlear and perivestibular regions of both temporal bones, and hyperintense signal on T2 weighted imaging. A subsequent HRCT revealed extensive otospongiotic change in the fenestral, pericochlear and perilabyrinthine areas admixed with bony thickening and sclerosis in the cochlear turns and oval windows.
Patient 4
A 55-year-old Chinese female complained of right-sided hearing loss over a 6-month period. Audiometry revealed bilateral asymmetrical sensorineural hearing loss that was worse on the right-hand side. MRI showed heterogeneous intermediate signal, with mild enhancement, in the perilabyrinthine regions on T1 weighted imaging. The degree of enhancement was less than that seen in our previous patients, and this finding was attributed to maturation of the disease. There was only a little increase in signal in the T2 weighted images. HRCT confirmed the presence of characteristic pericochlear and perilabyrinthine hypodense haloes.
|
Discussion
|
|---|
Otosclerosis is an uncommon disease and typically presents in young patients, with a 2:1 female:male ratio. It is bilateral in up to 85% of patients, but often asymmetric. The disease occurs most frequently between 30 years and 50 years of age and is known to worsen during pregnancy. The aetiology remains unknown, although an inflammatory response may be responsible. The condition may also be inherited. Two patterns of disease exist. The more common fenestral form, seen as abnormal hypodense or sclerotic bone involving the fissula ante fenestrum produces conductive hearing loss, and is owing to fixation of the stapes footplate at the level of the oval window, with a hearing loss of up to 50–60 dB. The retrofenestral or cochlear form is less common and is often seen in association with the fenestral variety. A mixed conductive and sensorineural hearing loss is seen in cochlear otosclerosis, although pure sensorineural hearing loss may occur [1]. Vestibular symptoms with unsteadiness and episodes of vertigo may also occur in this form of the disease.
In otosclerosis the normal endochondral bone of the otic capsule is replaced by disorganized foci of Haversian bone [1], which later becomes dense and sclerotic. The early phase of the disease is characterized by the presence of spongy irregular vascular foci of demineralized bone with osteoclastic bone resorption, which are less dense than the ivory-like endochondral bone [1]. This is seen as spongy decalcified foci within the normally dense petrous temporal bone. However, these foci become less vascular and tend to calcify, forming dense bone. The active phase has been termed otospongiosis, while otosclerosis refers to the mature phase of the disease. Active disease is seen as hypodense foci, which may be single or multiple. The lesions may coalesce, forming a characteristic hypodense double ring around the cochlea and labyrinth. The mature foci become dense and are seen as localized or diffuse areas of thickening and sclerosis. A mosaic pattern may be produced when spongiotic and sclerotic foci occur simultaneously (Figure 1
).
HRCT of the temporal bone, using 1 mm thick sections, is the imaging modality of choice in patients suspected of having otosclerosis. However, when patients present with either a pure sensorineural or mixed hearing loss, a central cause is considered and MRI then becomes the first line of investigation, as was the case with our patients. However, as MRI features of cochlear otosclerosis are not well known, radiologists may be unfamiliar with these findings.
Reports of MRI findings in cochlear otosclerosis have been few. A Medline search from 1987 to 2000 showed a limited number of papers describing the MRI findings in 12 patients. The use of T1 weighted images with gadolinium enhancement has been suggested as the modality of choice in assessing this condition. Youssef et al [2] demonstrated pericochlear and perilabyrinthine gadolinium enhancement in T1 weighted images, corresponding to the areas of bony abnormality seen on CT. Valvassori [3] and Mark et al [4] also demonstrated similar findings, while Ziyeh et al [5] described areas of pericochlear soft tissue signal in the T1 weighted images (Figure 2), showing enhancement after gadolinium administration in 4 of 5 patients. This enhancement is presumed to be owing to contrast pooling in the blood vessels of young otosclerotic foci. The presence of enhancing pericochlear lesions in T1 weighted images in our patients was in concordance with the findings of previous authors (Figure 3). Our last patient showed only mild enhancement after gadolinium administration. We presumed this to be owing to the likelihood that the patient's disease was no longer in the active phase, and thus the lesions were less vascular.
View larger version (135K):
[in this window]
[in a new window]
|
Figure 2. T1 weighted image pre-contrast showing pericochlear intermediate intensity soft tissue signal (arrow).
|
|
High signal in the pericochlear and perilabyrinthine regions on T2 weighted images has been mentioned by previous authors, but this has often been thought to be less reliable than the use of gadolinium enhanced T1 weighted images. However, Ziyeh et al [5] found the use of T2 weighted sequences to be useful, particularly if they were performed in the same plane as T1 weighted sequences. Like the previous author we found the use of T2 weighted sequences to be useful in localizing the active site of disease in 2 of our 4 patients (Figure 4).
Several conditions may produce soft tissue signal on T1 weighted images and contrast enhancement in MRI of the temporal bone. Differentiation between these conditions should be made with CT. However, unlike otosclerosis, characteristic findings are seen at other sites in the body. This differentiates these conditions from otosclerosis, which occurs only in the otic capsule. Paget's disease produces sclerosis of the temporal bone similar to otosclerosis. However, there is also involvement of the petrous apex and diffuse calvarial thickening, a finding not seen in cochlear otosclerosis. Fibrous dysplasia produces sclerotic lesions that may mimic mature otosclerosis, but the bony overgrowth seen in fibrous dysplasia differentiates it from otosclerosis. Syphilis produces a moth-eaten appearance to the temporal bone, dissimilar to the plaque-like demineralization seen in otosclerosis.
Osteogenesis imperfecta is a mimic of cochlear otosclerosis, producing a characteristic perilabyrinthine and pericochlear lucency on CT that is identical to that found in cochlear otosclerosis. Ziyeh et al [6] also described a patient with osteogenesis imperfecta showing bilateral pericochlear lesions showing soft tissue signal and moderate contrast enhancement on MRI. However, the clinical features of the disease are characteristic and this condition would not be confused with otosclerosis.
There are several treatment options for cochlear otosclerosis. Use of a hearing aid in patients with asymmetrical hearing loss is often sufficient. In patients with conductive hearing loss and concurrent fenestral otosclerosis, stapedectomy and use of a prosthesis help to restore hearing. Sodium fluoride or chelating agents may also be used to promote remineralization of the otosclerotic plaques.
Cochlear otosclerosis should be considered in patients with sensorineural or mixed hearing loss, when MRI findings of perilabyrinthine and pericochlear soft tissue with contrast enhancement, together with increased signal in T2 weighted images, are seen. HRCT should then be performed to confirm the diagnosis and exclude other conditions that demonstrate similar findings on MRI.
Received for publication January 2, 2002.
Revision received March 7, 2002.
Accepted for publication March 15, 2002.
|
References
|
|---|
- Swartz JD, Harnsberger HR. The otic capsule and otodystrophies. In: Swartz JD. Harnsberger HR. Imaging of the temporal bone (3rd edn). New York, NY: Thieme, 1998:240–317.
- Youssef et al. Cochlear otosclerosis: the current understanding. Ann Otol Rhinol Laryngol 1998;107:1076–9.[Medline]
- Valvassori GE. Imaging of otosclerosis. Otolaryngol Clin North Am 1993;26:359–71.[Medline]
- Mark AS, Seltzer S, Harnsberger HR. Sensorineural hearing loss: more than meets the eye? AJNR 1993;14:37–45.[Abstract]
- Ziyeh S, Berlin A, Ross UH, Reinhardt MJ, Schumacher M. MRI of active otosclerosis. Neuroradiology 1997;39:453–7.[Medline]
- Ziyeh S, Berger R, Reisner K. MRI-visible pericochlear lesions in osteogenesis imperfecta type 1. Eur Radiol 2000;10:1675–7.[Medline]
This article has been cited by other articles:
|
|
|
|
 
Z. Brownstein, A. Goldfarb, H. Levi, M. Frydman, and K. B. Avraham
Chromosomal mapping and phenotypic characterization of hereditary otosclerosis linked to the OTSC4 locus.
Arch Otolaryngol Head Neck Surg,
April 1, 2006;
132(4):
416 - 424.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
Abstract
Introduction
