2026 ICD-10-CM Diagnosis Code G91Hydrocephalus

ICD-10-CM Codes›G00–G99›G89-G99›G91

ICD-10-CM G91
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

G91 is a non-billable ICD-10-CM category code for hydrocephalus, so it cannot be submitted on claims. Use a more specific code from this category instead, such as G91.0, G91.1, G91.2, and G91.3.

Code Identity

ICD-10-CM Code
G91
Billable Status
No — Non-Billable Category
Code Describes
Hydrocephalus
Chapter
G89-G99
Other disorders of the nervous system

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG89-G99Other disorders of the nervous system
CategoryG91Hydrocephalus
This CodeG91Hydrocephalus

Specific Coding for HydrocephalusOverview

Non-specific codes like G91 require more characters. Use one of these billable codes instead:

  • Use G91.0 for Communicating hydrocephalus

  • Use G91.1 for Obstructive hydrocephalus

  • Use G91.2 for (Idiopathic) normal pressure hydrocephalus

  • Use G91.3 for Post-traumatic hydrocephalus, unspecified

  • Use G91.4 for Hydrocephalus in diseases classified elsewhere

  • Use G91.8 for Other hydrocephalus

  • Use G91.9 for Hydrocephalus, unspecified

Tabular List NotesGuidance

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

Includes

  • acquired hydrocephalus

Type 1 Excludes

  • Arnold-Chiari syndrome with hydrocephalus Q07
  • congenital hydrocephalus Q03
  • spina bifida with hydrocephalus Q05

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.

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 G91Overview

Is G91 (Hydrocephalus) a billable code?

No. This is a category header that groups the codes for hydrocephalus, and headers cannot be submitted on claims. Claims for hydrocephalus need a more specific code from this category, such as G91.0, G91.1, and G91.2.