2027 ICD-10-CM Diagnosis Code B46.1Rhinocerebral mucormycosis
ICD-10-CM Codes›A00–B99›B35-B49›B46
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- Risk Adjusts — HCC 6
- Not Chronic
B46.1 is a billable ICD-10-CM diagnosis code for rhinocerebral mucormycosis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 791, 793, 867 through 869. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 14 closely related codes. Coders also document this condition as fungal infection of cerebrum. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Fungal infections.
For Medicare Advantage risk adjustment, B46.1 maps to CMS-HCC Category 6 (Opportunistic Infections) under the V28 model, adding a risk factor of about 0.381 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
B46.1 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.
- Fungal infection of cerebrum
- Rhinocerebral mucormycosis
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to B46.1: its own notes plus those printed at block B35-B49 and Chapter 1. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- diseases generally recognized as communicable or transmissible
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.
- carrier or suspected carrier of infectious disease (Z22.-)
- certain localized infections - see body system-related chapters
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
- infectious and parasitic diseases specific to the perinatal period (P35-P39)
- influenza and other acute respiratory infections (J00-J22)
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify resistance to antimicrobial drugs (Z16.-)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
rhinocerebral B46.1
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Zygomycosis
infection in humans and animals caused by fungi in the class zygomycetes. it includes mucormycosis and entomophthoramycosis. the latter is a tropical infection of subcutaneous tissue or paranasal sinuses caused by fungi in the order entomophthorales. phycomycosis, closely related to zygomycosis, describes infection with members of phycomycetes, an obsolete classification.
Patient EducationClinical
Brain Diseases
Your brain is the control center of your body. It controls your thoughts, memory, speech, and movement. It regulates the function of many organs. It's part of your nervous system, which also includes your spinal cord and peripheral nerves. The nervous system sends signals between your brain and the rest of the body.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert B46.1 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About B46.1Overview
What is the ICD-10 code for rhinocerebral mucormycosis?
The ICD-10-CM code for rhinocerebral mucormycosis is B46.1 (sometimes written as B461). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is B46.1 (Zygomycosis) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report rhinocerebral mucormycosis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does B46.1 group to?
When rhinocerebral mucormycosis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 867, 869, 868, with relative weights from 0.6784 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.
Is B46.1 a CC or MCC?
CMS lists B46.1 as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 14 closely related codes in its exclusion list.
What is the ICD-9 equivalent of B46.1?
Under the General Equivalence Mappings, rhinocerebral mucormycosis converts to ICD-9-CM 117.7 (zygomycosis). The mapping is approximate, so confirm the match fits the documentation.
What HCC is B46.1?
B46.1 (rhinocerebral mucormycosis) maps to CMS-HCC Category 6 (Opportunistic Infections), commonly written as HCC 6, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 6 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 5.
Does B46.1 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, B46.1 adds a risk adjustment factor of about 0.381 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.381 to 0.833 depending on the payment segment). HCC 6 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 6 category page.
