Welcome Matthew. No diagnostic scan is 100% accurate nor will always pick up cancer, and depends also on the person reading, and interpreting them, and is too small, can be between the scan slicing, unidentifisble. A CT could detect cancer usually 1cm or larger, but had PET/CT, which works on glucose uptake, can pick up less than 5mm, and are more accurate in certain aspect, and each are better than the other for different reains. Only a biopsy is 100%, but then even human error can effect tests. Did they confirm HPV-16?

Good luck with your treatment planning, seeing specialists.