Final answer:
The removal of a pituitary tumor is coded under the nervous system in the CPT book, due to its location and neurosurgical intervention required.
Step-by-step explanation:
The coding for the removal of a pituitary tumor is found under the nervous system description in the Current Procedural Terminology (CPT) book. This is because the pituitary gland, although part of the endocrine system, is located at the base of the brain and its surgeries involve the expertise of neurosurgeons. Procedures involving the pituitary gland fall under the nervous system category due to the gland's close association with the brain and the need for neurosurgical intervention.