Enhancement in the Round Window Niche: A Potential Pitfall in High-Resolution MR Imaging of the Internal Auditory Canal

American Journal of Neuroradiology

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FIG 1.
Example of enhancing granulation tissue in the RW. A, Axial postcontrast FS T1WI demonstrates enhancement present bilaterally in the RWs (arrows). B, Axial head CT with thin-section bone window reconstructions demonstrates a right-sided canal wall-down mastoidectomy for resection of a cholesteatoma. Opacification of the round windows can be seen bilaterally, correlating to the area of enhancement (arrowheads).
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FIG 2.
A, Postcontrast FS T1WI reconstructed in the Stenvers view demonstrates focal contrast enhancement. B, Thin-section 3D SPACE T2WI reconstructed in the Stenvers view demonstrates fluid signal throughout the basal turn of the cochlea as well as hyperintense signal lateral to the RW membrane (white arrow). Specifically, there is no filling defect within the basal turn of the cochlea. C, Coregistered overlay of the 3D SPACE T2WI and postcontrast FS T1WI illustrate that the enhancement is located lateral to the basal turn and entirely within the RWN (white arrow). Without the aid of the T2 SPACE and coregistration, it would be possible to misdiagnose a small intralabyrinthine schwannoma in the basal turn or a glomus tympanicum. The white arrow in A is the focal enhancement.

Table 1:

Summary of patient demographics, reasons for initial ENT visit, and relevant medical history relating to temporal bone

Patient information
Demographics
No. of patients	95
Age at MR imaging (average) (range) (yr)	58 (18−84)
Sex (No.)
Female	53
Male	42
Reason for ENT visit
Hearing loss	51
Tinnitus	11
Vertigo/dizziness/ataxia	13
Schwannoma/cholesteatoma/other tumor	13
Headache	2
Other	5
No. of patients with a mastoid effusion^{^a}	24
No. of patients with prior surgery on temporal bone	8
Tympanomastoidectomy	6
Tympanotomy	1
Myringotomy	1

↵a No. of patients with clinical charts indicating the presence of granulation tissue in RW.

Table 2:

Summary of MR imaging and CT findings

Findings
Patients with MR imaging	95
Enhancement in RW	15
Right	6
Left	7
Bilateral	2
Patients with both MR imaging and CT	27
CT–/MR imaging–	22
CT+/MR imaging+	4
CT–/MR imaging+	1
Patients with CT	27
Soft tissue in RW	4
Right	0
Left	3
Bilateral	1

Note:—CT+ indicates soft tissue found, MR imaging+ indicates enhancement found, CT– indicates no soft tissue found, and MR imaging indicates no enhancement found.