CNS Anatomy and ICD-O-3

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For Primary Sites, use ICD-O-3 (Topography section): ICD-O-3.1External Website Policy or the Solid Tumor Rules

Priority order for coding primary site

  • ICD-O
  • SEER Program Coding Manual (Including Coding Guidelines in Appendix C)
  • Solid Tumor Rules (Malignant CNS, Benign CNS)

NAACCR Item #400: Primary Site (NAACCR Item #2580 Text-Primary Site Title)

For primary sites C710-C719, an “S” for supratentorial, or an “I” for infratentorial will be included after the term. This classification is important for EOD Primary Tumor and Summary Stage.

See Solid Tumor Rules for additional information on location.

ICD-O-3 Codes ICD-O-3 Preferred Term Synonyms Location
Peripheral Nerve and Autonomic Nervous System
C470 Peripheral nerves and autonomic nervous system of head, face, and neck
  • Cervical plexus
  • Pterygoid fossa Supraclavicular region
  • Cheek, chin, face, forehead, head, neck, scalp, temple, cervical region.

  • Spinal/Peripheral Nerves: Cervical (C1-C8)
C471 Peripheral nerves and autonomic nervous system of upper limb and shoulder
  • Brachial nerve
  • Brachial plexus
  • Median nerve
  • Radial nerve
  • Ulnar nerve
  • Antecubital space, arm, elbow, finger, forearm, hand, shoulder, thumb, wrist.

C472 Peripheral nerves and autonomic nervous system of lower limb and hip
  • Femoral nerve
  • Obturator nerve
  • Sciatic nerve
  • Ankle, calf, foot, heel, hip, knee, leg, popliteal space, thigh, toe
C473 Peripheral nerves and autonomic nervous system of thorax
  • Intercostal nerve
  • Axilla, chest, chest wall, thoracic wall, infraclavicular region, scapular region

  • Spinal/Peripheral nerves: Thoracic (T1-12)
C474 Peripheral nerves and autonomic nervous system of abdomen
  • Abdominal wall, umbilicus
C475 Peripheral nerves and autonomic nervous system of pelvis
  • Lumbosacral plexus
  • Sacral nerve
  • Sacral plexus
  • Lumbar plexus
  • Coccygeal plexus
  • Buttock, groin, perineum, gluteal region, inguinal region, sacrococcygeal regional
C476 Peripheral nerves and autonomic nervous system of trunk, NOS
  • Lumbar nerve
  • Back, flank, trunk
C478 Overlapping lesion of peripheral nerves and autonomic nervous system
C479 Autonomic nervous system, NOS
  • Ganglia, NOS
  • Nerve, NOS
  • Parasympathetic nervous system, NOS
  • Peripheral nerve, NOS
  • Spinal nerve, NOS
  • Sympathetic nervous system, NOS
Meninges
C700 Cerebral meninges
  • Cranial dura mater
  • Cranial meninges
  • Cranial pia mater
  • Falx cerebelli/cerebri/NOS
  • Intracranial arachnoid
  • Intracranial meninges
  • Tentorium cerebelli
  • Tentorium, NOS
  • Three protective membranes that surround the brain
C701 Spinal meninges
  • Spinal arachnoid
  • Spinal dura mater
  • Spinal pia mater
  • Three protective membranes that surround the spinal cord
C709 Meninges, NOS
  • Arachnoid, NOS
  • Dura, NOS
  • Dura mater, NOS
  • Pia mater, NOS
  • Not known whether cerebral or spinal.
  • This code should NOT be used in place of C700 or C701 as these codes take preference
Brain
C710 Cerebrum (S)
  • Basal ganglia (S)
  • Central sulcus (S)
  • Central white mater (S)
  • Cerebral cortex (S)
  • Cerebral hemisphere (S)
  • Cerebral white mater (S)
  • Corpus striatum (S)
  • Diencephalon (I)
  • Globus pallidus (S)
  • Hypothalamus (I)
  • Insula (S)
  • Internal capsule (S)
  • Interthalamic adhesion (I)
  • Island of Reil (S)
  • Operculum (S)
  • Pallium (I)
  • Parieto-occipital sulcus (S)
  • Putamen (S)
  • Rhinencephalon (S)
  • Supratentorial brain, NOS (S)
  • Thalamus (I)
  • Uppermost part of the brain, inside the skull, at the top and front of the head.
  • Extends from the frontal bone at the front to the occipital bone at the back.
C711 Frontal lobe (S)
  • Frontal pole (S)
  • Located at the front of the brain, just behind the forehead
C712 Temporal Lobe (S)
  • Hippocampus (S)
  • Uncus (S)
  • Located on sides of the brain, near the temples and ears
C713 Parietal Lobe (S) Located near the top and center of the brain, situated behind the frontal lobe and above the temporal lobe
C714 Occipital Lobe (S)
  • Occipital pole (S)
  • Located at the back of the brain, beneath the occipital lobe, posterior to the parietal and temporal lobes
C715 Ventricle (NOS) (S)
  • Cerebral aqueduct (S)
  • Cerebral ventricle (S)
  • Choroid plexus, NOS (S)
  • Choroid plexus of lateral ventricle (S)
  • Choroid plexus of third ventricle (S)
  • Ependyma (S)
  • Lateral ventricle, NOS (S)
  • Third ventricle, NOS (S)
  • Lateral ventricles are the two largest, situated within the cerebrum, one in each hemisphere

  • Third ventricle is located in the diencephalon, situated between the right and left thalamus
C716 Cerebellum (I)
  • Cerebellopontine angel (I)
  • Vermis of cerebellum (I)
  • Also called “little brain.”
  • Located at the back of the brain, beneath the occipital lobes and behind the brainstem, within the posterior fossa
C717 Brain stem (I)
  • Basis pedunculi (I)
  • Cerebral peduncle (I)
  • Choroid plexus of fourth ventricle (I)
  • Fourth ventricle, NOS (I)
  • Infratentorial brain, NOS
  • Medulla oblongata (I)
  • Midbrain (I)
  • Olive (I)
  • Pons (I)
  • Pyramid (I)
  • Tectal plate (I)
  • Located inferior to the thalamus, superior to the spinal cord, and anterior to the cerebellum
C718 Overlapping lesion of the Brain
  • Corpus callosum (S)
  • Tapetum (S)
C719 Brain, NOS (S)
  • Anterior cranial fossa (S)
  • Cranial fossa, NOS (S)
  • Intracranial site, NOS (S)
  • Middle cranial fossa (S)
  • Posterior cranial fossa (I)
  • Suprasellar (S)
Spinal Sites
C720 Spinal cord
  • Cervical cord
  • Conus medullaris
  • Filum terminale
  • Lumbar cord
  • Sacral cord
  • Thoracic cord
  • Located within the vertebral column, extending from the base of the skull to the first or second lumbar vertebra
C721 Cauda equina
  • Bundle of nerves located at the lower end of the spinal cord

  • Spinal/Peripheral nerves: Lumbar (L1-L5), Sacral (S1-S5), and Coccygeal (Co1)
Cranial Nerves
C722 Olfactory nerve
  • Cranial nerve I
  • Located in the upper of the nasal cavity and extends to the olfactory bulb in the brain
C723 Optic nerve
  • Cranial nerve II
  • Optic chasm
  • Optic tract
  • Located at the back of each eye, connecting the retina to the brain
C724 Acoustic nerve
  • Cranial nerve VIII
  • Located in the inner ear, extends through the internal auditory canal and terminates in the cochlear nuclei of the brainstem
C725 Cranial nerves, NOS
  • Abducent (cranial nerve VI)
  • Accessory (cranial nerve XI)
  • Facial (cranial nerve VII)
  • Glossopharyngeal (cranial nerve IX)
  • Hypoglossal (cranial nerve XII)
  • Oculomotor (cranial nerve III)
  • Olfactory (cranial nerve I)
  • Spinal accessory nerve (cranial nerve XI)
  • Trigeminal (cranial nerve V)
  • Trochlear (cranial nerve IV)
  • Vagus (cranial nerve X)
Ill-Defined Sites Central Nervous System
C728 Overlapping lesion of brain and central nervous system
C729 Nervous system, NOS
  • Central nervous system
  • Epidural
  • Extradural
  • Parasellar
Intracranial Duct and Glands
C751 Pituitary gland
  • Hypophysis
  • Pituitary fossa
  • Pituitary, NOS
  • Rathke pouch
  • Sella turcica
 Located at the base of the brain
C752 Craniopharyngeal duct
C753 Pineal gland Small endocrine gland in the brain, situated beneath the back part of the corpus callosum.

Behavior

Per the Solid Tumor Rules, there is a priority order for assigning behavior for CNS tumors

  • Pathology-Tissue from resection
  • Pathology: Tissue from biopsy
  • Cytology (usually cerebrospinal fluid)
  • Physician’s documentation (no pathology report)
  • Scans with a priority order: MRI, CT, PET, Angiogram
  • CNS CAP Protocol

Primary Site Coding Issues

For some histologic types, it is difficult to determine if the primary site is intracranial or the skull (C410). Tumors that originate in the skull are not intracranial. The malignant tumors are reportable regardless of origin, but non-malignant tumors that originate in the skull are not reportable.

  • Chondroma (9220/0) is a benign tumor of cartilage cells. Review the record carefully to determine if the tumor originated in bone or in an intracranial site. Because chondroma is a benign tumor, only complete an abstract if the primary tumor is in an intracranial site. A chondroma of the skull is not reportable.
  • Chordoma (9370/3) is a malignant tumor arising from the embryonic notochord, while a chondrosarcoma (9220/3) is a malignant tumor of cartilage cells. These tumor histologies are reportable, but you must determine if the primary site is bone or an intracranial site. Intracranial tumors are analyzed separately for research purposes.

Pilocytic Astrocytoma (9421/1) vs High-grade astrocytoma with piloid features (HGAP) (9421/3)

When ICD-O-3 was published, the code for pilocytic astrocytoma changed from malignant behavior (/3) to borderline behavior (/1). Registrars were instructed to continue to assign the code Pilocytic astrocytoma as /3 for malignant behavior.

In 2023, a new definition for 9421/3 was added, High-grade astrocytoma with piloid features (HGAP), which is a very aggressive tumor. So, starting in 2023, registrars were instructed to code Pilocytic astrocytoma as 9421/1.

Intracranial schwannoma (9560/0) is reportable for cases diagnosed January 1, 2004, and later. It can be difficult to determine the intracranial site of a schwannoma. Assign the primary site for intracranial schwannoma to cranial nerves NOS (C725) when the site is not documented in the health record.

See the current version of the SEER Program Coding Manual, Section IV: Description of this Neoplasm and Appendix C for complete coding instructions for primary site.

Updated: September 23, 2026

Suggested Citation

SEER Training Modules: CNS Anatomy and ICD-O-3. U.S. National Institutes of Health, National Cancer Institute. Cited 24 September 2026. Available from: https://training.seer.cancer.gov.