G91.1 — Obstructive hydrocephalus
Is G91.1 billable?
Yes — G91.1 is billable for FY2027. G91.1 is a valid, billable ICD-10-CM code at the highest level of specificity in its branch. G91.1 may be submitted for encounters from October 1, 2026 through September 30, 2027.
G91.1 at a glance
| Code | G91.1 |
|---|---|
| Description | Obstructive hydrocephalus |
| Billable | Yes |
| Code set | ICD-10-CM FY2027 |
| Valid for encounters | October 1, 2026 – September 30, 2027 |
Which MS-DRGs does G91.1 group to?
G91.1 sits in MDC 01 and helps define the logic of 2 MS-DRGs (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.
- 056Degenerative Nervous System Disorders with MCCmedical
- 057Degenerative Nervous System Disorders without MCCmedical
As a secondary diagnosis, G91.1 is a complication or comorbidity (CC), which can move a stay into a higher-paying DRG.
How is G91.1 listed in the Alphabetic Index?
These are the routes through the Alphabetic Index that lead to G91.1. They show the wording a clinician may have documented, which often differs from the Tabular description.
- Block, blocked › foramen Magendie
- Hydrocephalus › foramen Magendie block (acquired) (external) (internal) (malignant) (recurrent)
- Hydrocephalus › noncommunicating (acquired) (external) (internal) (malignant) (recurrent)
- Hydrocephalus › obstructive (acquired) (external) (internal) (malignant) (recurrent)
- Obstruction, obstructed, obstructive › aqueduct of Sylvius
- Occlusion, occluded › aqueduct of Sylvius
- Occlusion, occluded › ventricleNEC
- Stenosis, stenotic › aqueduct of Sylvius › acquired (cicatricial)
- Stricture › aqueduct of Sylvius › acquired
Excludes1 — never code together — inherited from G91
The conditions below can never be reported together with G91.1 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
Excludes2 — not included here — inherited from Chapter 6
The conditions below are not part of G91.1, but a patient may have both at the same time. When documentation supports it, G91.1 and the excluded code may both be reported.
- 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)
How long has G91.1 existed?
G91.1 has been in ICD-10-CM since at least FY2016, the earliest fiscal year on record here.
Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.
Which codes are confused with G91.1?
ICD-10-CM declares these codes mutually exclusive with G91.1 — exactly one of each pair can be correct for a given encounter.