G91.1 Obstructive hydrocephalus

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis.

Applies from G91 Hydrocephalus

Includes

• acquired hydrocephalus

Excludes1 (never code together)

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

Risk adjustment (HCC)

• CMS-HCC V28: HCC 127 — Dementia, Mild or Unspecified
• ESRD V24: HCC 51

MS-DRG index

Defines the logic of DRG(s) 056-057 in MDC 01.

Approximate ICD-9-CM (GEMs)

• 331.4 Obstructive hydrocephalus (approximate)

Code annotations containing back-references to G91.1

Back-references to G91.1

• Type 1 Excludes: G93.2 Benign intracranial hypertension ("obstructive hydrocephalus (G91.1)")

Back-references to G91

• Type 1 Excludes: Q03 Congenital hydrocephalus ("acquired hydrocephalus (G91.-)")

Diagnosis Index entries for G91.1

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

Nearby codes

• G91 Hydrocephalus
• G91.0 Communicating hydrocephalus
• G91.1 Obstructive hydrocephalus (this code)
• G91.2 (Idiopathic) normal pressure hydrocephalus
• G91.3 Post-traumatic hydrocephalus, unspecified
• G91.4 Hydrocephalus in diseases classified elsewhere
• G91.8 Other hydrocephalus
• G91.9 Hydrocephalus, unspecified