Michigan Subscriber
Answer: If the surgeon performed a procedure that spans several interspaces, you should select the "region" in which the surgeon performed the majority of the work.
For example, if the surgeon performed diskectomy at C7/T1 and T1/T2, treat the C7/T1 interspaces as "thoracic" and report 63077 (Diskectomy, anterior, with decompression of spinal cord and/or nerve root[s], including osteophytectomy; thoracic, single interspace) and +63078 (... thoracic, each additional interspace [list separately in addition to code for primary procedure]).
On the other hand, if the surgeon operates at C6/C7 and C7/T1, treat the C7/T1 interspace as "cervical" and report 63075 (... cervical, single interspace) and +63076 (... cervical, each additional interspace [list separately in addition to code for primary procedure]).
The question is more difficult if only a single "inter-region" interspace (such as C7/T1 or T12/L1) is involved. In such a case, most experts suggest coding from "top to bottom." That is, you should treat the C7/T1 interspace as cervical and the T12/L1 interspace as lumbar.
Therefore, for a diskectomy at C7/T1 only, for example, report 63075.