ICD-10-CM · Other

M85.58

M85.58 designates an aneurysmal bone cyst occurring at a skeletal site not captured by any other specific subcategory within M85.5 — such as the ribs, sternum, pelvis, or skull — where a blood-filled, expansile lesion disrupts normal bone architecture.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 13
Region: Other

Drawn from CDCAAPCICD10DataCdek

Documentation tips

What should appear in the chart to support M85.58.

Source · Editorial brief grounded in 5 cited references ↓

Specify the exact anatomic site in the operative or clinic note — 'pelvis,' 'sacrum,' 'rib,' or 'clavicle' — so the coder can confirm M85.58 is the correct residual subcategory and not a more specific sibling code.
Document imaging findings (e.g., MRI fluid-fluid levels, expansile multiloculated lytic lesion on plain film or CT) to support the ABC diagnosis and distinguish it from other cystic bone lesions such as a simple unicameral bone cyst (M85.40–M85.49).
If a pathological fracture is present at the ABC site, document it explicitly; a separate fracture code may need to be sequenced based on the primary reason for the encounter.
Confirm and record that the lesion is NOT located in the jaw — aneurysmal cysts of the jaw require M27.4, not M85.58, per the Excludes2 note on M85.5.
Note any prior treatment (embolization, curettage, bone grafting) to support medical necessity for staged procedures and to contextualize the current encounter.

Related CPT procedures

Procedure codes commonly billed with M85.58. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

20225 $364.74

Percutaneous bone biopsy using a trocar or needle targeting deep skeletal structures such as the vertebral body or femur.

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.

27070 $826.00

Superficial partial excision of the wing of the ilium, symphysis pubis, or greater trochanter of the femur using craterization or saucerization technique, typically performed for osteomyelitis or bone abscess.

27071 $916.19

Deep partial excision of the iliac wing, symphysis pubis, or greater trochanter of the femur, including techniques such as craterization or saucerization.

23220 $1,737.51

Surgical removal of a tumor originating at or involving the proximal humerus, requiring radical resection of bone and surrounding 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.

26250 $985.99

Radical resection of a metacarpal bone for tumor — an extensive ostectomy involving removal of substantial bone stock from the hand.

28100 $645.31

Excision or curettage of a bone cyst or benign tumor located in the talus or calcaneus (ankle or heel bone), performed as an open procedure.

73721 $204.41

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

73523 $61.46

Radiologic examination of both hips, including the pelvis when performed, requiring a minimum of five views captured from multiple projections.

77080 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M85.58 and adjacent codes.

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

Coding jaw ABCs to M85.58 instead of M27.4 — the Excludes2 note at the M85.5 level prohibits using M85.5x for aneurysmal cysts of the jaw; M27.4 is the correct code.
Defaulting to M85.58 when a more specific site subcode applies — always check M85.51 through M85.57 before landing on the 'other site' residual; assigning the residual when a specific code exists is an overcoding error.
Confusing aneurysmal bone cyst (M85.58) with simple bone cyst (M85.40–M85.49) or fibrous dysplasia (M85.00–M85.09) — these are distinct diagnoses requiring distinct pathology or imaging confirmation.
Omitting a concomitant pathological fracture code when bone integrity is compromised, leaving the fracture undocumented and potentially unreimbursed.
Assigning a congenital skeletal dysplasia code (Q78.x) alongside M85.58 without verifying the Excludes1 note on M85 — those conditions are coded exclusively with their Q78 codes, not M85.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M85.58 is the residual 'other site' code under the M85.5 aneurysmal bone cyst (ABC) parent. Use it when the documented site does not map to any of the site-specific subcodes: shoulder region (M85.51), upper arm (M85.52), forearm (M85.53), hand (M85.54), thigh (M85.55), lower leg (M85.56), ankle and foot (M85.57), or multiple sites (M85.59). Typical 'other site' anatomic locations coded here include the pelvis, sacrum, ribs, clavicle, scapula, sternum, and craniofacial bones — with one important exception: aneurysmal cysts of the jaw are excluded under Excludes2 and must be coded to M27.4.

ABCs are benign, locally aggressive lesions most often presenting with localized pain and swelling, sometimes with pathological fracture risk. Radiographic and MRI findings of a multiloculated, blood-filled cystic expansion with fluid-fluid levels strongly support the diagnosis. When a pathological fracture is also present, code the fracture separately and sequence based on the reason for the encounter.

M85.58 falls within ICD-10-CM Chapter 13 (M00–M99) and the M85 block, which excludes congenital bone dysplasias coded elsewhere (osteogenesis imperfecta Q78.0, osteopetrosis Q78.2, osteopoikilosis Q78.8, polyostotic fibrous dysplasia Q78.1). Verify that the condition is not one of those before assigning M85.58.

Sibling codes

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

M85.59

Aneurysmal bone cyst, multiple sites

M85.50

Aneurysmal bone cyst, unspecified site

Frequently asked questions

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

01What anatomic sites typically fall under M85.58?

Sites not captured by M85.51–M85.57 or M85.59 — most commonly the pelvis, sacrum, ribs, clavicle, scapula, sternum, and craniofacial bones (excluding the jaw, which goes to M27.4).

02Can I use M85.58 for an aneurysmal bone cyst of the jaw?

No. The Excludes2 note on M85.5 directs jaw ABCs to M27.4. M85.58 must not be used for the jaw, even though it is technically an 'other site.'

03How does M85.58 differ from M85.59?

M85.58 is for a single ABC at an anatomic site not listed elsewhere in the M85.5x hierarchy. M85.59 is for aneurysmal bone cysts at multiple sites simultaneously. If more than one site is involved, M85.59 is the correct code.

04Should I code a concurrent pathological fracture separately from M85.58?

Yes. If the ABC has caused or is associated with a pathological fracture, assign the appropriate pathological fracture code (M84.5xx) in addition to M85.58 and sequence based on the primary reason for the encounter.

05Is M85.58 appropriate when imaging suggests ABC but histopathology is pending?

Ambiguous scenarios like this depend on provider documentation. If the clinician documents 'aneurysmal bone cyst' as the working diagnosis, M85.58 is assignable. If the diagnosis is explicitly listed as suspected or rule-out, follow outpatient coding guidelines and code the presenting sign or symptom instead.

06Does M85.58 require a 7th character?

No. M85.58 is a 5-character M-code and does not use 7th-character extensions. The A/D/S encounter-type extensions apply to S-codes (traumatic injury codes), not to M-code bone disorder categories.

07Can M85.58 be assigned alongside a congenital skeletal dysplasia code such as Q78.1?

No. The Excludes1 note on the M85 category prohibits using M85 codes when a listed congenital condition (Q78.0, Q78.1, Q78.2, Q78.8) is the correct diagnosis. Verify the diagnosis before assigning M85.58.

Sources & references

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

01CDC ICD-10-CM Tabular List 2026, code M85.58
02
aapc.com
https://www.aapc.com/codes/icd-10-codes/M85.58
03
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M80-M85/M85-/M85.58
04
aapc.com
https://www.aapc.com/codes/icd-10-codes/M85.5
05
cdek.pharmacy.purdue.edu
http://cdek.pharmacy.purdue.edu/icd10/M85.5/

Mira AI Scribe

The Mira AI Scribe captures the precise anatomic site of the lesion (e.g., right ilium, posterior rib, sacral body), imaging characteristics supporting ABC (fluid-fluid levels on MRI, expansile lytic appearance on CT/plain film), and any prior intervention history. This prevents assignment of the generic 'other site' residual when a site-specific subcode exists, and flags jaw-site lesions for rerouting to M27.4 before claim submission.

See how Mira captures M85.58 documentation