2026 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 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

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 2026 (October 1, 2025 through September 30, 2026). 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).

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.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • 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
  • Pyogenic hydrocephalus
  • Sequelae of meningitis
  • Tuberculosis of brain
  • Tuberculosis of central nervous system

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Code First

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

Type 1 Excludes

  • hydrocephalus due to congenital toxoplasmosis P37.1

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Hydrocephalus(acquired) (external) (internal) (malignant) (recurrent)
      • in (due to)
        • neoplastic disease NEC (see also Neoplasm)
    • Hydrocephalus(acquired) (external) (internal) (malignant) (recurrent)
      • secondary

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

  • Dandy-Walker Syndrome

    a congenital abnormality of the central nervous system marked by failure of the midline structures of the cerebellum to develop, dilation of the fourth ventricle, and upward displacement of the transverse sinuses, tentorium, and torcula. clinical features include occipital bossing, progressive head enlargement, bulging of anterior fontanelle, papilledema, ataxia, gait disturbances, nystagmus, and intellectual compromise. (from menkes, textbook of child neurology, 5th ed, pp294-5)

  • 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.

  • Hydrocephalus, Normal Pressure

    a form of compensated hydrocephalus characterized clinically by a slowly progressive gait disorder (see gait disorders, neurologic), progressive intellectual decline, and urinary incontinence. spinal fluid pressure tends to be in the high normal range. this condition may result from processes which interfere with the absorption of csf including subarachnoid hemorrhage, chronic meningitis, and other conditions. (from adams et al., principles of neurology, 6th ed, pp631-3)

  • Walker-Warburg Syndrome

    rare autosomal recessive lissencephaly type 2 associated with congenital muscular dystrophy and eye anomalies (e.g., retinal detachment; cataract; microphthalmos). it is often associated with additional brain malformations such as hydrocephaly and cerebellar hypoplasia and is the most severe form of the group of related syndromes (alpha-dystroglycanopathies) with common congenital abnormalities in the brain, eye and muscle development.

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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About G91.4Overview

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, 2025 through September 30, 2026.

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.

What is the ICD-9 equivalent of G91.4?

Under the General Equivalence Mappings, hydrocephalus in diseases classified elsewhere converts to ICD-9-CM 331.7 (cereb degen in oth dis). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.