Condition guide
Chiari Malformation HCC Coding Guide
The ICD-10-CM code for Chiari malformation is Q07.00 (Arnold-Chiari syndrome without spina bifida or hydrocephalus) for the typical Type I presentation; Q07.01, Q07.02, and Q07.03 cover Chiari with spina bifida, hydrocephalus, or both. All four map to HCC 182 (Spinal Cord Disorders/Injuries) under the CMS-HCC V28 model, community non-dual aged RAF weight 0.478. Type I documented as tonsillar herniation with brain compression codes to G93.5 instead, which maps to HCC 202 (RAF 0.543).
Quick Facts
HCC Categories
HCC 182, Spinal Cord Disorders/Injuries
HCC 202, Coma, Brain Compression/Anoxic Damage
RAF Weight Range
0.478 to 0.543
Community, non-dual, aged (V28)
Model
CMS-HCC V28 (PY2026, 100% phase-in)
6 ICD-10 codes map to payment HCCs
How coders write it
Chart notes, problem lists, and queries rarely spell out Chiari Malformation. The shorthand you will actually see:
Whatever the note calls it, the payment question is the same: how the ICD-10-CM code resolves to a payment HCC.
What HCC category does Chiari Malformation map to under V28?
The ICD-10-CM code for Chiari malformation is Q07.00 (Arnold-Chiari syndrome without spina bifida or hydrocephalus) in the most common case; the alphabetic index files Chiari under Arnold-Chiari syndrome. The fifth character tracks the associated defects: Q07.01 with spina bifida, Q07.02 with hydrocephalus, and Q07.03 with both, which is where classic Type II presentations with myelomeningocele usually land. All four Q07.0x codes map to CMS-HCC V28 HCC 182 (Spinal Cord Disorders/Injuries), community non-dual aged RAF 0.478, so the type changes the code, not the category. There is a second path coders should know: the tabular lists "Arnold-Chiari type 1 compression of brain" as an inclusion term at G93.5 (Compression of brain), so a Type I documented as tonsillar herniation compressing the brainstem codes to G93.5 and maps to HCC 202 (Coma, Brain Compression/Anoxic Damage, RAF 0.543). Associated syringomyelia (G95.0) is its own diagnosis and also lands in HCC 182.
ICD-10 to HCC Mapping
| ICD-10 Code | Description | Billable | HCC Mapping |
|---|---|---|---|
| Q07.00 | Arnold-Chiari syndrome without spina bifida or hydrocephalus | Yes | HCC 182 |
| Q07.01 | Arnold-Chiari syndrome with spina bifida | Yes | HCC 182 |
| Q07.02 | Arnold-Chiari syndrome with hydrocephalus | Yes | HCC 182 |
| Q07.03 | Arnold-Chiari syndrome with spina bifida and hydrocephalus | Yes | HCC 182 |
| G93.5 | Compression of brain | Yes | HCC 202 |
| G95.0 | Syringomyelia and syringobulbia | Yes | HCC 182 |
RAF weights are community, non-dual, aged base coefficients from the CMS-HCC V28 model (PY2026). Verify against the latest CMS rate announcement for payment calculations.
HCC Buddy maps Chiari Malformation from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coder workflow notes
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Documentation Tips
Name the Chiari type in the assessment; Type I versus Type II drives the code family and tells the story of the associated defects.
Match the fifth character of Q07.0x to what is documented: spina bifida (Q07.01), hydrocephalus (Q07.02), or both (Q07.03).
When the neurologist documents Type I as cerebellar tonsillar herniation with brainstem compression, G93.5 applies; its inclusion terms name Arnold-Chiari type 1 compression of brain.
Record the MRI findings (tonsillar descent in millimeters) and the symptoms attributed to the malformation, occipital headache, dysphagia, sleep apnea, to support MEAT.
Capture associated syringomyelia (G95.0) as its own diagnosis when documented; it maps to HCC 182 independently.
Document decompression surgery history and the patient's current symptom status; post-surgical visits still need current evaluation of the condition to support coding it.
MEAT documentation examples for Chiari Malformation
A diagnosis only counts toward risk adjustment when the encounter note shows the provider engaged with it. These are the kinds of entries that satisfy the MEAT documentation standard for Chiari Malformation:
MMonitor
“MRI brain reviewed: tonsillar descent 9 mm below foramen magnum, stable from prior.”
“Headache frequency log reviewed: occipital headaches twice weekly with Valsalva.”
“Annual cervical MRI: syrinx unchanged at C5 to C7.”
EEvaluate
“Neuro exam: intact cranial nerves, mild dysmetria on the left, no nystagmus.”
“Swallow evaluation reviewed for new dysphagia complaints.”
“Sleep study reviewed: central apneas present, discussed with neurology.”
AAssess
“Chiari malformation Type I with brainstem compression, symptomatic.”
“Chiari II with myelomeningocele and shunted hydrocephalus, stable.”
“Chiari I, status post suboccipital decompression 2024, residual headaches improving.”
TTreat
“Referred to neurosurgery for decompression evaluation.”
“Continue amitriptyline for headache prophylaxis; recheck in three months.”
“Shunt function confirmed; neurosurgery follow-up annually.”
Common Coding Mistakes
Coding every Chiari as Q07.00 by habit; Type II with myelomeningocele belongs at Q07.01 or Q07.03.
Assuming the Chiari type changes the payment category; Q07.00 and Q07.01 both map to V28 HCC 182 at the same weight.
Overlooking G93.5 when the note documents tonsillar herniation with brain compression rather than the congenital syndrome by name.
Using G93.5 for traumatic brain compression; the Excludes1 note sends traumatic compression to S06.A- instead.
V24 to V28 Changes
Chiari coding barely moved between models. The Q07.0x family mapped to V24 HCC 72 (Spinal Cord Disorders/Injuries, RAF 0.481) and maps to V28 HCC 182 with the same label at 0.478, a near-identical weight under a new number. G93.5 moved from V24 HCC 80 to V28 HCC 202 (Coma, Brain Compression/Anoxic Damage), where the community weight rose from 0.486 to 0.543. The practical takeaway is that Chiari malformation remains a payment diagnosis in V28 on both coding paths, congenital Q07.0x and the G93.5 brain-compression presentation, so the documentation question is which path the clinical picture supports, not whether the condition counts.
| Aspect | V24 (through PY2025) | V28 (PY2026) |
|---|---|---|
| Congenital Arnold-Chiari (Q07.00 to Q07.03) | HCC 72, Spinal Cord Disorders/Injuries, RAF 0.481 | HCC 182, Spinal Cord Disorders/Injuries, RAF 0.478 |
| Type 1 compression of brain (G93.5) | HCC 80, Coma, Brain Compression/Anoxic Damage, RAF 0.486 | HCC 202, same label, RAF 0.543 |
| Syringomyelia (G95.0) | HCC 72, RAF 0.481 | HCC 182, RAF 0.478 |
RAF values are community, non-dual, aged base coefficients for each model's payment year. To see what these weights do to a real patient total, run the codes through the RAF score calculator.
Chiari Malformation coding FAQs
How do you code Chiari malformation?
Start from the documented type. Congenital Chiari codes to the Q07.0x family: Q07.00 without spina bifida or hydrocephalus (the usual Type I code), Q07.01 with spina bifida, Q07.02 with hydrocephalus, and Q07.03 with both. When the note describes Type I as tonsillar herniation compressing the brainstem, G93.5 (compression of brain) applies; its inclusion terms name Arnold-Chiari type 1 compression of brain. All Q07.0x codes map to V28 HCC 182 (RAF 0.478) and G93.5 maps to HCC 202 (RAF 0.543).
What is the ICD-10 code for Chiari II malformation?
Q07.01 (Arnold-Chiari syndrome with spina bifida), or Q07.03 when hydrocephalus is also present. Type II is defined by the accompanying myelomeningocele, which is why the spina bifida fifth character is the marker. Both codes are billable and map to CMS-HCC V28 HCC 182 with a community, non-dual, aged RAF weight of 0.478.
What's another name for Chiari malformation?
Arnold-Chiari malformation or Arnold-Chiari syndrome, which is exactly where the ICD-10-CM alphabetic index files it; the Q07.0 category carries the official title Arnold-Chiari syndrome. Type I also shows up in charts as cerebellar tonsillar ectopia or tonsillar herniation, which is the phrasing that points a coder toward G93.5 when brain compression is documented.
Related Conditions
Related references
CMS-HCC V28 model
How the V28 categories, RAF weights, and hierarchy work for PY2026.
ICD-10 to HCC mapping
How an ICD-10-CM code resolves to a payment HCC under V28.
MEAT criteria
The documentation standard every coded condition must satisfy.
Add confirmed HCCs and review the full model total.
Sources
RAF weights are community, non-dual, aged base coefficients from the CMS-HCC V28 model (PY2026). Verify against the latest CMS Rate Announcement for payment.
Verified current to CMS-HCC V28, payment year 2026 — last reviewed July 16, 2026.
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