G91.1 — Obstructive hydrocephalus
G91.1 is a billable, specific ICD-10-CM code for obstructive hydrocephalus. It is valid for submission on a claim.
Other codes that can never be billed with G91.1
These codes carry an Excludes1 note pointing at G91.1. The conflict binds both ways, but ICD-10-CM only writes it down on one side — so you would not find this by reading G91.1 alone.
- G93.2Benign intracranial hypertension
Risk adjustment
G91.1 risk-adjusts. Under the CMS-HCC V28 model it maps to this category:
- HCC 127 Dementia, Mild or Unspecified0.341 RAF
Coefficient shown for the Community Non-dual Aged segment. A higher HCC in the same hierarchy will suppress this one, so capturing it does not always add score.
Medicare coverage
G91.1 is named in 4 Medicare coverage policies — 4 listing it as supporting medical necessity. Which of them applies to you depends on your Medicare contractor, and coverage genuinely differs by state.
- A54111Billing and Coding: Speech Language Pathology (SLP) Services: Communication Disorders
- A56612Billing and Coding: CT of the Head
- A57204Billing and Coding: MRI and CT Scans of the Head and Neck
- A57780Billing and Coding: Psychological and Neuropsychological Tests
How G91.1 is indexed
Coders do not find codes by browsing the tabular list — they look them up in the alphabetic index, under the word the physician wrote. These are the index entries that lead here, so you can see which chart wordings map to G91.1.
- Block, blocked›foramen Magendie(acquired)
- Hydrocephalus›foramen Magendie block(acquired)
- Hydrocephalus›noncommunicating
- Hydrocephalus›obstructive
- Obstruction, obstructed, obstructive›aqueduct of Sylvius
- Occlusion, occluded›aqueduct of Sylvius
- Occlusion, occluded›ventricle NEC(brain)
- Stenosis, stenotic›aqueduct of Sylvius›acquired
- Stricture›aqueduct of Sylvius›acquired
Related codes at this level
Codes that share G91. If G91.1 is not quite right, the correct code is usually one of these.
Questions about G91.1
- Is G91.1 a billable ICD-10-CM code?
- Yes. G91.1 is a billable, specific ICD-10-CM code and is valid for submission on a claim.
- Where does G91.1 sit in the tabular list?
- Diseases of the nervous system (G00-G99), in the block Other disorders of the nervous system (G89-G99).