M85.50

M85.50 identifies an aneurysmal bone cyst when the affected skeletal site is not documented or cannot be specified — a benign but locally destructive blood-filled fibrous lesion of bone capable of causing deformity and pathologic fracture.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 15
Region: General

Drawn from CDCICD10DataAAPCMS

Documentation tips

What should appear in the chart to support M85.50.

Source · Editorial brief grounded in 5 cited references ↓

Record the exact skeletal site by bone name and segment (e.g., 'proximal tibia' or 'distal femur') in every encounter note — this is the single most effective step to avoid falling back to M85.50.
Include imaging modality and findings: plain film, MRI, or CT results describing the lesion location, expansion, and cortical involvement support the site-specific code and justify the clinical picture.
Document pathology or biopsy results confirming aneurysmal bone cyst histology; this differentiates the lesion from solitary bone cyst (M85.4x) or fibrous dysplasia and anchors the diagnosis.
Note whether a pathologic fracture is present or has occurred — if so, add a secondary fracture code (M84.5x series) with the appropriate 7th character for encounter phase.
Capture all relevant comorbidities in the inpatient setting to drive accurate MCC vs. non-MCC DRG assignment under MS-DRG 553/554.

Related CPT procedures

Procedure codes commonly billed with M85.50. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

20150 $920.86

Surgical removal of an epiphyseal bar (physeal bar) from a long bone, with or without autogenous soft tissue graft harvested through the same fascial incision.

20240 $126.59

Open surgical biopsy of a superficial bone, such as the ilium, sternum, spinous process, rib, or femoral trochanter, performed through a skin incision to obtain tissue for diagnosis.

20245 $303.28

Surgical removal of a bone tissue sample from a deep anatomical site — such as the humeral shaft, ischium, or femoral shaft — through an open incision for pathological analysis.

27635 $545.77

Surgical excision or curettage of a bone cyst or benign tumor located in the tibia or fibula, without bone grafting.

27638 $698.75

Excision or curettage of a bone cyst or benign tumor from the tibia or fibula, with allograft used to fill the defect.

23200 $1,365.43

Radical resection of a clavicle tumor, removing the neoplastic lesion along with a margin of surrounding bone and soft tissue.

24150 $1,397.16

Radical resection of a tumor involving the distal or shaft portion of the humerus, with or without allograft reconstruction.

25170 $1,329.69

Radical resection of a tumor from the radius or ulna, including removal of surrounding tissue as needed to achieve adequate margins.

27065 $508.36

Surgical excision of a superficial bone cyst or benign tumor from the wing of the ilium, symphysis pubis, or greater trochanter of the femur; includes autograft harvest when performed.

27066 $758.53

Surgical excision of a deep bone cyst or benign tumor from the wing of the ilium, symphysis pubis, or greater trochanter of the femur, at the subfascial level, with autograft bone grafting included when performed.

27067 $957.27

Excision of a bone cyst or benign tumor from the iliac wing, symphysis pubis, or greater trochanter of the femur, with autogenous bone grafting through a separate incision to reconstruct the defect.

20900 $398.14

Minor autogenous bone harvest from a separate donor-site incision — a dowel, button, or similarly small graft quantity.

20902 $241.82

Harvesting of a major or large autogenous bone graft from any donor site, performed through a separate skin incision not included in the primary procedure code.

73221 $205.08

MRI of any upper extremity joint — shoulder, elbow, or wrist — performed without contrast material.

73721 $204.41

MRI of a lower extremity joint (hip, knee, or ankle) performed without contrast material.

Common coding pitfalls

The recurring mistakes coders make with M85.50 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

Defaulting to M85.50 when imaging or the operative report actually names the site — always check the radiology and pathology reports before accepting unspecified.
Coding an aneurysmal bone cyst of the jaw as M85.50 — jaw lesions are explicitly excluded and belong under M27.4.
Confusing aneurysmal bone cyst with solitary (simple) bone cyst; solitary bone cysts map to M85.4x, a different subcategory with its own site-specific breakdown.
Omitting a secondary pathologic fracture code when the clinical note documents fracture through the cyst — M85.50 alone does not capture the fracture.
Attempting to apply a 7th-character extension to M85.50 — M-codes in this section do not use 7th characters; extensions apply to S-code injury and fracture categories.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Use M85.50 only when the operative, radiology, or pathology report does not specify the anatomic site of the aneurysmal bone cyst. This is a last-resort code — the M85.5x series offers site-specific options covering shoulder (M85.51x), upper arm (M85.52x), forearm (M85.53x), and beyond. If laterality and location appear anywhere in the encounter documentation, assign the appropriate site-specific code instead.

Aneurysmal bone cysts are classified under M85 (Other disorders of bone density and structure), not under the neoplasm chapter, and are explicitly excluded from codes covering jaw cysts (M27.4). Do not use M85.50 if imaging or pathology localizes the lesion — even a note stating 'proximal femur' is enough to move you to the site-specific subcategory. Unspecified-site coding invites payer scrutiny and may trigger a request for records that could have been avoided with complete documentation.

On the inpatient side, M85.50 maps to MS-DRG 553 (Bone diseases and arthropathies with MCC) or 554 (without MCC) under MS-DRG v43.0. Capture all documented comorbidities that qualify as MCCs to ensure accurate DRG assignment and appropriate reimbursement.

Sibling codes

Other billable codes under M85.5 (laterality / anatomic variants).

M85.58

Aneurysmal bone cyst, other site

M85.59

Aneurysmal bone cyst, multiple sites

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 5 cited references ↓

01When is M85.50 the correct code versus a site-specific M85.5x code?

M85.50 is correct only when no skeletal site is documented anywhere in the encounter record — operative report, imaging, or pathology. If any note names the affected bone, use the corresponding site-specific subcategory (e.g., M85.561 for right tibia and fibula).

02Is M85.50 billable?

Yes. M85.50 is a valid billable code in FY2026 ICD-10-CM, but payers may request supporting documentation when an unspecified-site code is submitted for a procedure that implies a definite anatomic location.

03How does an aneurysmal bone cyst differ from a solitary bone cyst for coding purposes?

They occupy different subcategories: aneurysmal bone cysts are M85.5x, while solitary (simple) bone cysts are M85.4x. Pathology or imaging distinguishing the two is required — do not use M85.50 as a catch-all for any bone cyst.

04Should I code a pathologic fracture through an aneurysmal bone cyst separately?

Yes. If the documentation states a fracture occurred through the cyst, assign a secondary code from the M84.5x (pathologic fracture) series with the appropriate 7th character (A for initial encounter, D for subsequent, S for sequela) in addition to M85.50 or the site-specific cyst code.

05Does M85.50 apply to a jaw aneurysmal bone cyst?

No. An Excludes2 note at the M85.5 category level explicitly excludes aneurysmal cyst of the jaw. Code jaw lesions to M27.4 instead.

06What MS-DRG does M85.50 map to for inpatient claims?

M85.50 groups to MS-DRG 553 (Bone diseases and arthropathies with MCC) or 554 (without MCC) under MS-DRG v43.0. Document all qualifying comorbidities to determine which DRG applies.

07Are there any 7th-character requirements for M85.50?

No. M-codes under M85 do not require 7th-character extensions. The 7th-character conventions (A/D/S) apply to injury S-codes and selected fracture M-codes, not to M85.50.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

01CDC ICD-10-CM Tabular List 2026
02
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M80-M85/M85-/M85.50
03
aapc.com
https://www.aapc.com/codes/icd-10-codes/M85.50
04
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M80-M85/M85-/M85.5
05MS-DRG v43.0 Grouper, CMS

Mira AI Scribe

Mira AI Scribe captures the anatomic site, laterality, and imaging findings (MRI or CT lesion location, cortical expansion, fluid-fluid levels) documented during the encounter. When a specific site is recorded, the scribe routes to the appropriate M85.5x site-specific code rather than M85.50, preventing unspecified-site downcoding, payer record requests, and DRG inaccuracies tied to incomplete diagnosis capture.

See how Mira captures M85.50 documentation