Correlation of CT, MR, and Histopathology in Incomplete Partition-II Cochlear Anomaly

Objective: To correlate the computed tomography (CT) and magnetic resonance imaging (MR) findings in a patient with incomplete partition-type II (IP-II) anomaly with histopathology in a similar human temporal bone specimen. To discover the histologic correlate of a common finding on MR of an “apparent” interscalar septum (IS). Patients: A patient with sensorineural hearing loss and imaging findings characteristic of IP-II, and a patient with histopathologic IP-II anomaly. Intervention: High-resolution CT, MR, and review of postmortem temporal bone histopathology. Main Outcome Measure: Correlation of temporal bone histopathology with CT and MR findings. Results: Consistent findings of IP-II anomaly on CT, absence of the IS between the more distal turns and flattening of the interscalar ridge between the distal basal turn and the middle turn, were present. The signal void surrounding the cochlea on MR also demonstrated flattening of the interscalar ridge. However, a thin band-like area of low T2 signal was seen, which could be mistaken for an IS. Correlation with temporal bone histopathology revealed that the modiolus was foreshortened, and the spiral ganglion neuron dendritic processes continued toward the upper middle turn through the osseous spiral lamina, likely accounting for the MR finding. Conclusion: Correlation of CT, MR, and histopathology in IP-II shows an “apparent” segmentation representing a continuum of neurosensory elements in approximately the same location of the expected location of a normal IS. Care should be taken when interpreting MR imaging in isolation. Understanding the bony outline of the cochlea on imaging may prove to be complementary.

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