Cochlear Enhancement May Precede Cochlear Obliteration After Vestibular Schwannoma Excision.

OBJECTIVE: Cochlear obliteration after vestibular schwannoma excision has been noted, with implications on cochlear implantation. Early postoperative cochlear enhancement with gadolinium on magnetic resonance imaging (MRI) has also been observed. Timing of enhancement and association with obliteration is described here. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center, ambulatory. PATIENTS: Patients receiving vestibular schwannoma excision surgery by the senior author performed at one institution between January 2015 and July 2017 with postoperative MRIs INTERVENTION:: Diagnostic. MAIN OUTCOME MEASURE(S): The imaging characteristics on postoperative MRIs examined were loss of fluid signal on postoperative T2 images and cochlear enhancement on gadolinium enhanced T1 images. In the patients receiving labyrinthine sparing procedures, presence of postoperative hearing was evaluated. RESULTS: Of the 42 patients evaluated, 24 received the translabyrinthine approach and 18 received a labyrinth sparing surgery. Twenty-nine had evidence of cochlear enhancement on T1 with gadolinium contrast, and 27 had evidence of cochlear obliteration on T2 images. The odds ratio of patients with cochlear enhancement having obliteration was 30.0:1 (p < 0.0001). Intense cochlear enhancement (n = 21) appeared a median of 163 days after surgery, and complete or near complete obliteration (n = 18) appeared a median of 480 days after surgery, a statistically significant difference (p < 0.001). Within the labyrinth sparing group, there was no statistically significant association between hearing loss and cochlear obliteration or enhancement. CONCLUSIONS: Cochlear enhancement is correlated with cochlear obliteration and may precede it.

Is MRI Equal to CT in the Evaluation of Thin and Dehiscent Superior Semicircular Canals?

OBJECTIVE: Can magnetic resonance imaging (MRI) diagnose abnormally thin and dehiscent superior semicircular canals (SSCs) that traditionally rely on evaluation by computed tomography (CT) imaging? STUDY DESIGN: Retrospective clinical study. SETTING: Tertiary referral center. PATIENTS: Adults who underwent both MRI and CT of the temporal bones over the past 3 years. INTERVENTIONS: CT and MR images of SSCs were separately reviewed, in a blinded fashion by three neuroradiologists at our institution. CT diagnosis of abnormally thin or dehiscent SSC was used as the "gold" standard. MAIN OUTCOME MEASURES: 1) Dehiscent SSC. 2) Abnormally thin SSC. 3) Normal SSC. RESULTS: One hundred temporal bones with evaluable superior semicircular canals from 51 patients were eligible for review on CT and MR imaging. There were 26 patients of thin SSC and 17 patients of SSC dehiscence on CT imaging, of which 13 and 15 respectively were also found on MRI. There were nine false-positive dehiscent SSC patients and four thin SSC patients observed on MR imaging while not observed on CT. For thin SSCs, MRI sensitivity was 61.9% and specificity of 94.3% with a positive predictive value of 81.3% and a negative predictive value of 86.2%. For dehiscent SSCs, sensitivity was 88.2% and specificity of 89.2% with a positive predictive value of 62.5% and a negative predictive value of 97.4%. CONCLUSION: In this series, MRI in the axial and coronal plane had a high negative predicative value for thin SSC (86%) and dehiscent SSC (97%). However, MRI cannot conclusively diagnose thin or dehiscent SSCs.