G91.1 Obstructive hydrocephalus

The ICD-10-CM code for Obstructive hydrocephalus is G91.1 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

6: Diseases of the nervous system (G00-G99)

Section

G89-G99: Other disorders of the nervous system (G89-G99)

Category G91

8 codes (7 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to G91.1:

• Obstruction, obstructed, obstructive › aqueduct of Sylvius
• Block, blocked › foramen Magendie (acquired)
• Hydrocephalus (acquired) (external) (internal) (malignant) (recurrent) › foramen Magendie block (acquired)
• Occlusion, occluded › ventricle (brain) NEC
• Hydrocephalus (acquired) (external) (internal) (malignant) (recurrent) › noncommunicating
• Hydrocephalus (acquired) (external) (internal) (malignant) (recurrent) › obstructive
• Occlusion, occluded › aqueduct of Sylvius
• Stenosis, stenotic (cicatricial) › aqueduct of Sylvius (congenital) › acquired

U.S. Hospital Utilization

• An estimated 35,385 U.S. inpatient stays in 2023 included G91.1 among the documented diagnoses.
• 3,230 stays listed it as the principal diagnosis.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

Official Coding Guidelines

Dominant/nondominant side (TOC entry)

a. Dominant/nondominant side ................................................................................................. 45

Pain - Category G89 (TOC entry)

b. Pain - Category G89.............................................................................................................. 45

Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)