Q04.5 Megalencephaly

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis. Exempt from present-on-admission (POA) reporting.

Applies from Q04 Other congenital malformations of brain

Excludes1 (never code together)

• cyclopia (Q87.0)
• macrocephaly (Q75.3)

Risk adjustment (HCC)

• CMS-HCC V28: HCC 182 — Spinal Cord Disorders/Injuries
• CMS-HCC V22: HCC 72 — Spinal Cord Disorders/Injuries
• RxHCC V08: HCC 155 — Spinal Cord Disorders
• ESRD V24: HCC 72

MS-DRG index

Defines the logic of DRG(s) 091-093 in MDC 01.

Approximate ICD-9-CM (GEMs)

• 742.4 Other specified congenital anomalies of brain (approximate)

Diagnosis Index entries for Q04.5

• Hemimegalencephaly
• Megalencephaly

Nearby codes

• Q04.0 Congenital malformations of corpus callosum
• Q04.1 Arhinencephaly
• Q04.2 Holoprosencephaly
• Q04.3 Other reduction deformities of brain
• Q04.4 Septo-optic dysplasia of brain
• Q04.5 Megalencephaly (this code)
• Q04.6 Congenital cerebral cysts
• Q04.8 Other specified congenital malformations of brain
• Q04.9 Congenital malformation of brain, unspecified