Alphabetic Index FY2027

G91.9

Hydrocephalus, unspecified

FY2027Chapter 6: Diseases of the nervous system/G89–G99 Other disorders of the nervous system

BillableComplete code, valid to report
Care settingsHospital CCIPF Primary · MS-DRG 056–057

G91.9 (also written G919) is a billable ICD-10-CM diagnosis code for hydrocephalus, unspecified. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 7 codes in category G91 (Hydrocephalus). The Alphabetic Index lists it under 1 entry. Its coding notes include 3 Excludes1 entries and 8 Excludes2 entries.

Excludes1

Not coded here. The listed conditions generally should not be reported together.

Inherited from G91 Hydrocephalus
  • Arnold-Chiari syndrome with hydrocephalus (Q07.-)
  • congenital hydrocephalus (Q03.-)
  • spina bifida with hydrocephalus (Q05.-)

Excludes2

Not included here. Both codes may be reported if the patient has both conditions.

Also from chapter/block level (8 notes)
Inherited from Chapter 6 Diseases of the nervous system
  • 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)

Care settings

How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.

Hospital CC

Counts as a complication or comorbidity (CC) when reported as a secondary diagnosis on an inpatient claim. It does not count when the principal diagnosis is one of the 108 codes in its exclusion list. Some MS-DRGs also ignore a CC or MCC that defines the DRG.

Source: CMS MS-DRG Definitions Manual v44, effective October 1, 2026, Appendix C

IPF Primary

IPF MS-DRG adjustment. A principal diagnosis of this code groups to one of these MS-DRGs. Which one depends on other facts of the stay, so the factor is a range:

MS-DRGDescriptionFactor
056Degenerative nervous system disorders w MCC1.12
057Degenerative nervous system disorders w/o MCC1.11
A principal diagnosis that groups to none of the 19 designated MS-DRGs gets no MS-DRG adjustment. Otherwise the claim still receives the federal per diem base rate and the other adjustments.

Source: CMS IPF PPS FY 2027 final rule (CMS-1847-F), Addendum A; code lists from the CMS MS-DRG Definitions Manual v44; effective for discharges on or after October 1, 2026

Includes

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

Inherited from G91 Hydrocephalus
  • acquired hydrocephalus

Alphabetic Index terms

Terms the official Alphabetic Index lists for this code. 1 entry