Imaging Studies
Until recently, labyrinthitis ossificans (LO) was diagnosed histologically; however, radiography currently is a tool that can be used to help diagnose LO. Radiographic documentation of osteoneogenesis within the cochlea is possible with a high-resolution computed tomography (HRCT) scan of the temporal bone. In the image below, labyrinthitis ossificans is seen on axial CT scan.
In the image below, labyrinthitis ossificans is depicted with right cochlea enhancement.
In one study, some degree of abnormality of the inner ear was noted in 71% of 31 CT scans performed in cochlear implant candidates. Five scans were interpreted as showing ossification within the cochlea. Of these scans, 4 were confirmed at surgery with 1 false-positive result and 1 false-negative result among the 26 scans interpreted as not ossified (4%).
Other authors note a high incidence (63-73%) of CT scan evidence of postmeningitic patients with deafness. [14, 15, 16] They point out that ossification may not always be evident radiographically, with false-negative rates as high as 46%. The high rate of false-negative results may be related to the inability of HRCT scans to detect early histological features of fibrosis and osteoid deposition, which are consistent with the early stages of labyrinthitis ossificans (LO) prior to calcification. Despite the exquisite bone detail, HRCT scans may not detect early ossification and soft tissue abnormalities in up to 57% of patients.
Arriaga and Carrier conducted a study that suggested high-resolution, fast spin-echo, T2-weighted magnetic resonance imaging (MRI) is clinically helpful in cochlear implant candidates. [17] This type of MRI study can identify cochlear soft tissue abnormalities in areas of residual cochlear patency in cases of labyrinthitis ossificans (LO). These are soft tissue abnormalities that may not be detected on HRCT scan. This prospective study of 13 consecutive patients receiving preoperative, high-resolution, fast spin-echo, T2-weighted MRI scans of the temporal bone "identified unanticipated cochlear fibrosis in one patient, vestibular schwannoma in one patient, [and] patency in the second turn of the cochlea in a patient with labyrinthitis ossificans."
The study also "disproved cochlear fibrosis suspected on HRCT imaging in one patient." These findings suggest that, in addition to HRCT scans, high-resolution, T2-weighted MRI studies of the temporal bone may be useful preoperatively when considering candidates for cochlear implantation. [17]
A study by Jiang et al also suggested that MRI can aid in the assessment of cochlear implant candidates. The use of MRI in 188 patients being evaluated for implants revealed otic capsule or vestibulocochlear nerve pathologies in 17 (9%) of them, uncorrelated by audiogram findings, including, in two cases, labyrinthitis ossificans. Other findings included vestibular schwannomas (5 patients), enlarged vestibular aqueducts (4 patients), hypoplastic cochlear nerves (2 patients), cochlear aplasia (1 patient), posterior semicircular canal malformation (1 patient), calcified meningioma (1 patient), and cholesterol granuloma (1 patient). [18]
However, the value of MRI in preoperative assessment of candidates for cochlear implantation is not universally accepted.
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Fibrosis and ossification of the scala tympani are shown. F, fibrosis; O, osteoneogensis (hematoxylin and eosin stain).
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Stages of ossification are shown. This histological specimen was obtained 3 months after induction of labyrinthitis. F, fibrosis; O, osteoid; C, calcospherite deposition (calcification); B, normal endochondral bone. (hematoxylin and eosin stain)
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Ossification of the scala tympani is shown.
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Labyrinthitis ossificans is depicted with right cochlea enhancement.
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Labyrinthitis ossificans is shown on axial CT scan.
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Labyrinthitis ossificans associated with meningitis is shown.
