Cyclic aldehyde structures are possible but cyclic ketone structures are not possible.

Can aldehydes be cyclic?

Molecules (aldehyde or ketone), which contain both an alcohol and a carbonyl group, can instead undergo an intramolecular reaction to form a cyclic hemiacetal/ hemiketal. These, on the contrary, are more stable as compared to the intermolecular hemiacetals/hemiketals.

Why cyclic aldehydes are not possible?

Cyclic aldehydes are not possible, because in order for the carbonyl group to be part of the ring structure, two bonds to carbon groups would be required. Aldehydes may incorporate ring structures, but not be part of the ring. Also, note that cyclic ketones aren't heterocyclic compounds.