What instruments are used for urethral dilation and calibration?

For urethral dilation and calibration, metal sounds are specifically designed instruments that are utilized for this procedure. They come in various sizes and are used to gradually expand the urethral lumen and assess its diameter. Metal sounds can be used interactively—once the initial dilation is achieved, larger sizes can be employed to incrementally dilate the urethra to the desired size.

Each of the other instruments mentioned has different primary functions. A cystoscope is typically utilized for visual examination of the bladder and urethra, making it suitable for diagnosis and treatment within the urinary tract but not specifically for dilation. Filiform catheters are used for navigating and accessing the bladder rather than for dilation purposes; they are more flexible and designed to guide other instruments or facilitate drainage. Hydroceles do not relate to these procedures, as they refer to a collection of serous fluid around the testicle, and are not surgical instruments.

Thus, metal sounds are the correct choice for urethral dilation and calibration, given their design and intended use in this specific surgical application.