2026 ICD-10-CM Diagnosis Code S04.20XAInjury of trochlear nerve, unspecified side, initial encounter

ICD-10-CM Codes›S00–T88›S00-S09›S04

ICD-10-CM S04.20XA
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S04.20XA is a billable ICD-10-CM diagnosis code for injury of trochlear nerve, unspecified side, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 963 through 965. The code is flagged as an unspecified code, since codes identifying laterality exist in the same family. Coders also document this condition as injury of trochlear nerve. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Injury to nerves, muscles and tendons, initial encounter.

Code Identity

ICD-10-CM Code
S04.20XA
Billable Status
Yes — Valid for Submission
Code Describes
Injury of trochlear nerve, unspecified side, initial encounter
Short Description
Injury of trochlear nerve, unspecified side, init encntr
Parent Code
S04.20
Injury of trochlear nerve, unspecified side

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS00-S09Injuries to the head
CategoryS04Injury of cranial nerve
This CodeS04.20XAInjury of trochlear nerve, unspecified side, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for S04.20XA.

Unspecified codes
Unspecified codes exist in the ICD-10-CM classification for circumstances when documentation in the medical record does not provide the level of detail needed to support reporting a more specific code. However, in the inpatient setting, there should generally be very limited and rare circumstances for which the laterality (right, left, bilateral) of a condition is unable to be documented and reported. The following pages contain the list of unspecified ICD-10-CM diagnosis codes for which there is a more specific code to identify laterality (right, left, bilateral) within that code family.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Injury of trochlear nerve

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Injury of cranial nerve (S04). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INJ025
Injury to nerves, muscles and tendons, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Eye Movement Disorders

When you look at an object, you're using several muscles to move both eyes to focus on it. If you have a problem with the muscles, the eyes don't work properly.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert S04.20XA to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
951.1 Injury trochlear nerve
Approximate The match is approximate rather than exact.

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 S04.20XAOverview

Is S04.20XA (Injury of trochlear nerve, unspecified side) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report injury of trochlear nerve, unspecified side, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in S04.20XA mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for injury of trochlear nerve, unspecified side, such as an emergency visit or first evaluation.

What MS-DRG does S04.20XA group to?

When injury of trochlear nerve, unspecified side, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 963, 964, 965, with relative weights from 0.9405 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of S04.20XA?

Under the General Equivalence Mappings, injury of trochlear nerve, unspecified side, initial encounter converts to ICD-9-CM 951.1 (injury trochlear nerve). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.