2027 ICD-10-CM Diagnosis Code Q04.5Megalencephaly
ICD-10-CM Codes›Q00-Q99›Q00-Q07›Q04
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 182
- POA Exempt
- Chronic Condition
Q04.5 is a billable ICD-10-CM diagnosis code for megalencephaly. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 91 through 93, 791, 793. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 4 closely related codes. The code is exempt from POA reporting. Coders also document this condition as bilateral megalencephaly. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Nervous system congenital anomalies.
For Medicare Advantage risk adjustment, Q04.5 maps to CMS-HCC Category 182 (Spinal Cord Disorders/Injuries) under the V28 model, adding a risk factor of about 0.478 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Present on Admission (POA)Billing
Q04.5 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Congenital malformations of the nervous system (Q00-Q07).
Medicare Risk Adjustment (HCC)Billing
Q04.5 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.
Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Bilateral megalencephaly
- Familial megalencephaly
- Hemimegalencephaly
- Macroencephaly
- Megalencephalic leukoencephalopathy with subcortical cysts
- Megalencephaly, polymicrogyria, postaxial polydactyly, hydrocephalus syndrome
- Megalencephaly, severe kyphoscoliosis, overgrowth syndrome
- Polyhydramnios, megalencephaly, symptomatic epilepsy syndrome
- Sporadic megalencephaly
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to Q04.5: its own notes plus those printed at Q04 and Chapter 17. A note printed at a category, block or chapter applies to every code under it.
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Notes
General instructions on how these codes are used.
- Codes from this chapter are not for use on maternal records
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Index to Diseases and InjuriesGuidance
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Megalencephaly
a congenital abnormality in which the occipitofrontal circumference is greater than two standard deviations above the mean for a given age. it is associated with hydrocephalus; subdural effusion; arachnoid cysts; or is part of a genetic condition (e.g., alexander disease; sotos syndrome).
Patient EducationClinical
Brain Malformations
Most brain malformations begin long before a baby is born. Something damages the developing nervous system or causes it to develop abnormally. Sometimes it's a genetic problem. In other cases, exposure to certain medicines, infections, or radiation during pregnancy interferes with brain development.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert Q04.5 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About Q04.5Overview
What is the ICD-10 code for megalencephaly?
The ICD-10-CM code for megalencephaly is Q04.5 (sometimes written as Q045). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is Q04.5 (Other congenital malformations of brain) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report megalencephaly on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does Q04.5 group to?
When megalencephaly is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 91, 92, 93, with relative weights from 0.7783 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.
Is Q04.5 a CC or MCC?
CMS lists Q04.5 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 4 closely related codes in its exclusion list.
Is Q04.5 exempt from POA reporting?
Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for megalencephaly on inpatient claims. The code appears in the Congenital malformations of the nervous system (Q00-Q07) range of the CMS exempt list.
What HCC is Q04.5?
Q04.5 (megalencephaly) maps to CMS-HCC Category 182 (Spinal Cord Disorders/Injuries), commonly written as HCC 182, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 72 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 155.
Does Q04.5 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, Q04.5 adds a risk adjustment factor of about 0.478 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.270 to 0.478 depending on the payment segment). A more severe related category (HCC 180, HCC 181, HCC 191, and HCC 192) supersedes it when both are reported. See the full factor table on the HCC 182 category page.
