Q04.5 Megalencephaly

The ICD-10-CM code for Megalencephaly is Q04.5 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

17: Congenital malformations, deformations and chromosomal abnormalities (Q00-QA0)

Section

Q00-Q07: Congenital malformations of the nervous system (Q00-Q07)

Category Q04

10 codes (9 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to Q04.5:

• Megalencephaly
• Hemimegalencephaly

U.S. Hospital Utilization

• An estimated 300 U.S. inpatient stays in 2023 included Q04.5 among the documented diagnoses.

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

POA indicator for congenital conditions/anomalies and Q00-Q99 exception

Congenital conditions and anomalies Assign “Y” for congenital conditions and anomalies except for categories Q00- Q99, Congenital anomalies, which are on the exempt list. Congenital conditions are always considered present on admission.

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)