Figure 1.

Right tympanic membrane (TM). The image shows the hypothetical area that can be used to access to the round window using the transcanal approach; one hole is for the endoscope (black circle); the yellow area represents the round window where the microneedle will be introduced. The right triangle represent the area where it is possible to identify the round window. The two points of access will be in the posterior quadrants of TM (pars tensa). To perform the procedure, the patient is supine. Local anesthesia with lidocaine spray will be performed. After performing a small incision on the tympanic membrane (black ring), a 0° endoscope is inserted to visualize the middle ear and the position of the round window (interrupted yellow ring) before performing the perilymph sampling by microneedle. This approach will allow a direct visualization of the sampling area and allow eventual perilymph leakage at the end of the procedure to be monitored. Other degree (30°, 45°, 70°) endoscopes could be considered the basis of the specific anatomical conditions and the personal experience of the surgeon (the image of the TM was modified from Di Stadio et al., Brain Sci, 2024 [8] to introduce the location of the additional hole for micro-endoscope insertion).