The Pons and other subsites of the Brain Stem have the same ICD-O topography code (C717), which is for subsites of the Brain Stem. Clinically, information regarding the Pons is very important, especially for pediatric cases. A schema discriminator is necessary to distinguish between the pons and other subsites of the brain stem.

The pons site is the third most common site for pediatric brain tumors and there is currently no way to identify tumors that occur in this site. Surgery is too dangerous for these types of tumors. Needle biopsies are also dangerous and extremely rare. Without pathology specimens, accurate histology is elusive making accurate incidence not possible. A cascade of implications results without accurate incidence including support for drug development.

If a mutation or alteration is in the name of the histopathology, it is required for diagnosis as it helps distinguish among clinically important subtypes within ICD-O-3. 

• IDH mutation status distinguishes between clinically important subtypes within ICD-O-3 9400/3, Diffuse astrocytoma and 9401/3, Anaplastic astrocytoma.
• IDH mutant and 1p/19q co-deletion distinguishes between clinically important subtypes within ICD-O-3 code 9450/3, Oligodendroglioma and 9451/3, Anaplastic Oligodendroglioma.
• IDH-wildtype distinguishes clinically important subtypes within ICD-O-3 9400/3, Diffuse astrocytoma, 9401/3, Anaplastic astrocytoma and 9440/3, Glioblastoma, Epithelioid glioblastoma and Glioblastoma, NOS (note that the new ICD-O-3 code 9445/3 applies to Glioblastoma, IDH-mutant; information regarding this subtype is not collected using this data item).
• SHH-activation and TP53-wildtype distinguishes between clinically important subtypes within ICD-O-3 histology code 9471/3, Medulloblastoma.
• C19MC alteration status distinguishes a clinically important highly aggressive subtype within ICD-O-3 9478/3, Embryonal tumor with multilayered rosettes.
• Pediatric-type diffuse low-grade gliomas: 9385/3 Diffuse hemispheric glioma, H3-G34-mutant, Diffuse midline glioma, H3 K27-altered, Diffuse pediatric-type high-grade glioma, H3-wildtype and IDH-wildtype, and Infant-type hemispheric glioma.
• Ependymal tumors are distinguished by mutations required for diagnosis among clinically important subtypes: 9396/3 Posterior fossa group A (PFA) ependymoma, Posterior fossa group B (PFB) ependymoma, Spinal ependymoma, _MYCN_-amplified, Supratentorial ependymoma, YAPI fusion-positive, and Supratentorial ependymoma, ZFTA fusion-positive.
• Pediatric-type diffuse low-grade gliomas are distinguished among subtypes by mutations required for diagnosis: 9421/1 Diffuse astrocytoma, _MYB_-or _MYBL1_-altered, Diffuse low-grade glioma, MAPK pathway-altered, and Pilocytic astrocytoma.
• Circumscribed astrocytic tumors are distinguished among subtypes by mutations required for diagnosis: 9430/3 Astroblastoma, MN1-altered and Astroblastoma.
• Other CNS embryonal tumors are distinguished among subtypes by mutations required for diagnosis: 9500/3 CNS neuroblastoma_, FOXR2_-activated, CNS tumor with BCOR internal tandem duplication, and Neuroblastoma, NOS.

Coding Instructions and Codes

Note 1: This data item was introduced in 2018 and applied to the following ICD-O-3 histology codes 9400/3, 9401/3, 9440/3, 9450/3, 9451/3, 9471/3, 9478/3.

• These are codes 01-09 and are applicable for cases diagnosed 2018+ and are in ICD-O-3 order.

Note 2: In 2022, the 5th edition of the CNS WHO Blue Book was released and the following histologies were added 9385/3, 9396/3, 9421/1, 9430/3, 9500/3.

• These are codes 10-23 and are applicable for cases diagnosed 2024+ and are in ICD-O-3 order.

Note 3: If a microscopically confirmed histology is not included in this list, assign, code 85. 

• If your case is not microscopically confirmed, code 99.

Note 4: Physician statement of histologic subtype can be used to code this data item.

Note 5: See Brain Molecular Markers in the SSDI Manual, in the Definition section for more information on the different histologies.

Examples:

1. Biopsy of brain tumor, microscopic confirmation diagnosis: Diffuse Astrocytoma (9400/3). Additional testing done, and IDH-mutant is identified. Code 01. 
2. Biopsy of brain tumor, microscopic confirmation diagnosis: Anaplastic astrocytoma (9401/3). No further testing or results unknown. Code 99.
3. MRI of brain tumor, clinical diagnosis: glioblastoma. No further workup. Code 99.
4. Biopsy of brain tumor, microscopic confirmation diagnosis: Mixed glioma (9382/3). Code 85.

Note 2: A data item is needed to distinguish between the Pons and all other subsites within the Brain Stem (C717). Code the site in which the tumor arose. 

• Review of radiology reports and physician’s notes are needed to determine the appropriate code. Needle biopsies and surgery are usually too dangerous for these types of tumors, so the best information will be available from radiology reports.