Grade II C2-3 spondylolisthesis with bilateral well-corticated defects at mid-portion of C2 lamina (a gap of 5mm with several interposed bone fragments), no other vertebral dysplasia to strongly suggest developmental cause thus repetitive microtrauma and post-traumatic disjunction can be considered, no feature of atlantooccipital dissociation.
Right-sided 2nd branchial cleft cyst/ Bailey classification type II.