Calculating volume for anatomical sinus or canal

Operating system: windows
Slicer version: 11.4.0
Expected behavior:
Actual behavior:

Dear users
I am attending to calculate the volume of nasopalatine canal but didn’t find the way. I tried to use the usual steps of segmentation process commonly used for hard/bony structures but failed to get my point.
Any suggestions or guidance will be appreciated.
Thanks in advance
I attached an example for the required work.