PMC7468399_01
High resolution temporal bone CT images of the normal and abnormal stapes footplate as well as intraoperative images of the hypermobile stapes footplate. (A) Traditional axial image of the right temporal bone with bone windows shows the cochlea, internal auditory canal, vestibule, middle ear. Red arrow shows the normal stapes footplate (white line) providing the interface between the vestibule and middle ear. (B) Same image as seen in this figure (A) using the "invert" function. Note the ease in comparing the air in the middle ear (white) to the fluid-filled vestibule (gray). Red arrow shows the position of the normal stapes footplate (black line) providing the interface between the vestibule and middle ear. (C) Traditional Poschl image of the left temporal bone with bone windows shows that in this case of left third window syndrome, there is no superior semicircular canal dehiscence (red arrow). (D) Traditional axial image of the left temporal bone with bone windows shows the cochlea, internal auditory canal, vestibule, middle ear. Red arrow shows the position of the membranous stapes footplate providing the interface between the vestibule and middle ear. Note the absence of the white line seen in this figure (A). (E) Same image as seen in this figure (D) using the "invert" function. Note the ease in comparing the air in the middle ear (white) to the fluid-filled vestibule (gray). Red arrow shows the position of the membranous stapes footplate providing the interface between the vestibule and middle ear. Note the absence of the black line representing the normal stapes footplate seen in this figure (B). (F) Inverted coronal image of the left temporal bone with bone windows shows the cochlea, vestibule and middle ear. Red arrow shows the position of the membranous stapes footplate providing the interface between the vestibule and middle ear. Note the absence of the black line representing the normal stapes footplate. (G) Intraoperative appearance of a normal stapes footplate. (H) Intraoperative appearance of a membranous stapes footplate. Note the translucent appearance of the entire stapes footplate. The bone-covered tympanic segment of the facial nerve can be seen to the right of the stapes footplate. (I) The stapes footplate is shaded in blue to illustrate the position of the membranous stapes footplate image seen in this figure (H).
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This became more apparent when the "invert" function was used on the PACS system (Figure 1).
PMC7468399_02
PMC7468399_03
Intraoperative photographs and preoperative and post-operative cVEMP responses in illustrative case 3. (A) Intraoperative appearance of a membranous translucent left stapes footplate. (B) Fat grafts obtained from the lobule are placed under the arch of the stapes and anterior and posterior to the crurae. (C1,C2) Preoperative cVEMPs on the left ear with increased amplitude and decreased threshold down to 65 dB nHL, along with normal cVEMPs in the right ear. (D) After auditory thresholds had normalized at 8 weeks following surgery, post-operative cVEMPs shows normalization of thresholds and amplitude on the left side. This suggests that surgery resulted in objective improvement in cVEMPs.
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Tullio test the patient demonstrated pulsion to the right. cVEMP was normal on the right but was abnormal on the left side with increased amplitude and decreased threshold down to 65 dB nHL (Figures 2C1,C2). The gray-scale inversion technique on high resolution temporal bone CT scan raised the possibility of a left membranous stapes footplate. The patient consented to surgery and on 5 December 2019 underwent fat graft placement over the oval and round windows (Figures 2A,B). Auditory thresholds recovered completely to preoperative levels, and post-operative cVEMP testing demonstrated normal amplitude and threshold on the left side (Figure 2D).