2027 ICD-10-CM Diagnosis Code G91.4Hydrocephalus in diseases classified elsewhere

ICD-10-CM Codes›G00–G99›G89-G99›G91

ICD-10-CM G91.4
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

G91.4 is a billable ICD-10-CM diagnosis code for hydrocephalus in diseases classified elsewhere. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 56 through 57. The code is a manifestation code that cannot be reported as the principal diagnosis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other nervous system disorders (neither hereditary nor degenerative).

For Medicare Advantage risk adjustment, G91.4 maps to CMS-HCC Category 127 (Dementia, Mild or Unspecified) under the V28 model, adding a risk factor of about 0.341 for a community, non-dual, aged beneficiary in payment year 2027.

Code Identity

ICD-10-CM Code
G91.4
Billable Status
Yes — Valid for Submission
Code Describes
Hydrocephalus in diseases classified elsewhere
Short Description
Hydrocephalus in diseases classified elsewhere
Same as the full description in the CMS dataset.
Parent Code
G91
Hydrocephalus

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG89-G99Other disorders of the nervous system
CategoryG91Hydrocephalus
This CodeG91.4Hydrocephalus in diseases classified elsewhere

Code EditsBilling

Medicare Code Editor checks that affect claim validity for G91.4.

Manifestation diagnoses
Manifestation codes describe the manifestation of an underlying disease, not the disease itself, and therefore should not be used as a principal diagnosis.

Medicare Risk Adjustment (HCC)Billing

G91.4 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.

CMS-HCC V28 Category (Payment Model)
HCC 127— Dementia, Mild or Unspecified
Payment HCC · PY 2027 one of 65 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.341
community, non-dual, aged · ranges 0.000–0.438 across segments
Hierarchy
Superseded by HCC 125 and HCC 126
a more severe related category takes the payment when both are reported
Prior Model (CMS-HCC V24)
HCC 51
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
ESRD (V21): HCC 51 · ESRD (V24): HCC 51
ESRD V21 weights: 0.097 dialysis, 0.000–0.643 functioning graft · ESRD V24 weights: 0.042 dialysis, 0.000–0.399 functioning graft
Part D (RxHCC)
Not mapped
G91.4 does not risk-adjust in the RxHCC prescription drug model

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Adult progressive post hemorrhagic ventricular dilatation
  • Fungal hydrocephalus
  • Hereditary myopathy associated with hydrocephalus
  • Hydrocephalus due to and following meningitis
  • Hydrocephalus due to Dandy-Walker malformation
  • Hydrocephalus due to tuberculosis of brain
  • Hydrocephalus ex vacuo
  • Hydrocephalus ex vacuo due to cerebrovascular disease
  • Hydrocephalus ex vacuo due to degenerative brain disorder
  • Posthemorrhagic hydrocephalus
  • Pyogenic hydrocephalus
  • Sequelae of meningitis
  • Tuberculosis of brain

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to G91.4: its own notes plus those printed at G91 and Chapter 6. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From G91 Hydrocephalus applies to 7 codes
  • acquired hydrocephalus

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

On G91.4 itself
  • hydrocephalus due to congenital toxoplasmosis (P37.1)
From G91 Hydrocephalus applies to 7 codes
  • Arnold-Chiari syndrome with hydrocephalus (Q07.-)
  • congenital hydrocephalus (Q03.-)
  • spina bifida with hydrocephalus (Q05.-)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 6 (G00-G99) Diseases of the nervous system applies to 700 codes
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Code First

The underlying condition named in the note is sequenced before this code.

  • underlying condition, such as:
  • congenital syphilis (A50.4-)
  • neoplasm (C00-D49)
  • plasminogen deficiency (E88.02)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name G91.4, its category, or a range that includes it.

Excludes1 2

These codes carry an Excludes1 note naming G91.4: they are not reported together with it, unless the two conditions are unrelated.

  • G94 Other disorders of brain in diseases classified elsewhere
    hydrocephalus in diseases classified elsewhere (G91.4)
  • Q03 Congenital hydrocephalus
    acquired hydrocephalus (G91.-) names G91.-, which includes this code

Use Additional Code 1

These codes say to use an additional code from the note, and G91.4 is one of the codes named.

  • E88.02 Plasminogen deficiency
    hydrocephalus (G91.4)

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS020
Other nervous system disorders (neither hereditary nor degenerative)
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • Hydrocephalus

    excessive accumulation of cerebrospinal fluid within the cranium which may be associated with dilation of cerebral ventricles, intracranial hypertension; headache; lethargy; urinary incontinence; and ataxia.

Patient EducationClinical

Hydrocephalus

Hydrocephalus is the buildup of too much cerebrospinal fluid in the brain. Normally, this fluid cushions your brain. When you have too much, though, it puts harmful pressure on your brain.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert G91.4 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
331.7 Cereb degen in oth dis
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About G91.4Overview

What is the ICD-10 code for hydrocephalus in diseases classified elsewhere?

The ICD-10-CM code for hydrocephalus in diseases classified elsewhere is G91.4 (sometimes written as G914). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is G91.4 (Hydrocephalus) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report hydrocephalus in diseases classified elsewhere on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does G91.4 group to?

On inpatient claims, hydrocephalus in diseases classified elsewhere maps to MS-DRG 57, 56, with relative weights from 1.2835 to 2.2649 depending on complications. Higher weights mean higher Medicare reimbursement.

Can G91.4 be a principal diagnosis?

No. This is a manifestation code: hydrocephalus in diseases classified elsewhere describes the manifestation of an underlying disease rather than the disease itself, so the underlying condition is sequenced first.

Can G91.4 be reported with P37.1?

Not as a rule. The Excludes1 note on G91.4 lists "hydrocephalus due to congenital toxoplasmosis (P37.1)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).

What HCC is G91.4?

G91.4 (hydrocephalus in diseases classified elsewhere) maps to CMS-HCC Category 127 (Dementia, Mild or Unspecified), commonly written as HCC 127, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 51 under the retired V24 model. It also maps in the ESRD (V21) and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.

Does G91.4 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, G91.4 adds a risk adjustment factor of about 0.341 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.000 to 0.438 depending on the payment segment). A more severe related category (HCC 125 and HCC 126) supersedes it when both are reported. See the full factor table on the HCC 127 category page.