21931

Excision of a subcutaneous soft tissue tumor of the back or flank measuring 3 cm or greater in greatest diameter plus required margin.

Verified May 8, 2026 · 5 sources ↓

Medicare: $453.58
Total RVUs: 13.58
Global, days: 90
Region: Spine

Drawn from CMSFacsAAPC

Documentation requirements

What must appear in the operative or office note to support the claim.

Source · Editorial brief grounded in 5 cited references ↓

Intraoperative measurement of tumor greatest diameter plus margin in centimeters — must confirm 3 cm or greater threshold
Anatomic location specified as back or flank — laterality (LT/RT) and relationship to spine, ribs, or iliac crest if relevant
Depth confirmation that the lesion is subcutaneous, not deep to fascia (deep tumors map to 21932/21933)
Tissue origin documented — subcutaneous soft tissue mass (e.g., lipoma), not cutaneous (sebaceous cyst, epidermal inclusion cyst)
Pathology specimen submitted and documented; operative note should reference specimen sent for pathologic evaluation
Indication and preoperative diagnosis, including ICD-10 code alignment (e.g., D17.1 for benign lipoma of skin and subcutaneous tissue, trunk)

Applicable modifiers

Modifiers commonly billed with this code.

Source · AMA CPT modifier descriptors · CMS NCCI Policy Manual

22 Increased complexity 24 Unrelated E/M during global 25 Significant separate E/M 51 Multiple procedures 58 Staged or related 59 Distinct service 76 Repeat, same physician 77 Repeat, another physician 78 Unplanned return — related 79 Unrelated during global LT Left side RT Right side XS Separate structure

What this code covers

Source · Editorial summary grounded in 5 cited references ↓

CPT 21931 covers surgical removal of a subcutaneous soft tissue tumor located in the back or flank region when the tumor's greatest diameter plus the margin required for complete excision equals 3 cm or more. Size is measured at the time of excision — the combined tumor-plus-margin dimension drives code selection, not the tumor's preoperative imaging size alone.

Code selection between 21930 (under 3 cm) and 21931 (3 cm or greater) hinges entirely on that intraoperative measurement. Lesions of cutaneous origin — sebaceous cysts, epidermal inclusion cysts — belong in the 11400–11446 series, not here. Using 21931 for a cutaneous lesion is a coding error regardless of size. Lipomas and other subcutaneous soft tissue masses with a non-cutaneous origin are appropriate candidates for this code.

21931 carries a 90-day global period. Routine follow-up visits, wound checks, and suture removal within that window are bundled. If a second, unrelated procedure is required during the global period, append modifier 79. A planned staged re-excision for margins uses modifier 58. The code applies to facility settings (hospital OR, ASC) and office settings — verify documentation supports the site of service, as HOPD and ASC payments differ substantially.

RVU & reimbursement

Component RVUs and Medicare national rate. Actual payment varies by GPCI locality.

Source · CMS Physician Fee Schedule, RVU26A · January 2026

Work RVU	6.71
Practice expense RVU	5.21
Malpractice RVU	1.66
Total RVU	13.58
Medicare national rate	$453.58
Global period	90 days

Payment by site of service

Medicare pays different rates by setting. HOPD typically pays substantially more than ASC for the same procedure.

Source · CMS OPPS Addendum B·ASC HCPCS payment rates·2026

Setting	Medicare rate (national)
Office (PFS non-facility) Procedure performed in physician's office	$453.58
HOPD (APC 5072) Hospital outpatient department	$1,687.37
ASC (PI G2) Ambulatory surgical center (freestanding)	$742.04

Common denial reasons

The recurring reasons claims for CPT 21931 get rejected.

Source · Editorial brief grounded in CMS NCCI edits, AAOS coding appeals, and cited references ↓

Cutaneous lesion excised and billed as 21931 — payer downcodes or denies; should be 11400–11446
Tumor-plus-margin measurement not documented, making 3 cm threshold unverifiable — downcoded to 21930
Routine post-op visit billed separately within 90-day global period without modifier 24 or 25
LT/RT modifier flagged or taken off in audit when laterality is not supported by operative report
Multiple same-session excisions billed with incorrect modifier — second lesion requires modifier 59 (or XS for distinct structure) with 21930; duplicate claim edits fire when units are used instead

Frequently asked questions

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

01How is the 3 cm threshold measured — preop imaging or intraoperative?

Intraoperative measurement governs code selection. The size equals the greatest tumor diameter plus the margin required for complete excision, measured at the time of excision. Preoperative MRI or ultrasound dimensions do not determine the code — document the intraop measurement explicitly.

02Can I bill 21931 for a lipoma on the flank near the anterior axillary line?

Yes, if the lesion is subcutaneous and located in the back or flank region. The anterior axillary line near the lower ribs is within the flank. Confirm the lesion is subcutaneous — if it's deep to fascia, the correct codes are 21932 (deep, under 5 cm) or 21933 (deep, 5 cm or greater).

03A patient had three separate lipomas excised on the right buttock same session. How do I bill?

Bill the largest lesion first using the appropriate code (21931 if 3 cm or greater). Bill each additional lesion with modifier 59 (or XS) to distinguish distinct service. Do not use units — stacked units on the same code trigger duplicate claim edits. List 21930 or 21931 as appropriate for each additional lesion's size.

04Re-excision for positive margins is needed two weeks after the original procedure. What modifier applies?

Modifier 58 — planned or staged procedure by the same physician during the global period. The re-excision is a related, staged service. Code to the new excision size at time of re-excision and document the indication (positive margins) clearly.

05Should I use modifier LT or RT for back lesions at the midline?

Midline lesions should not carry LT or RT — those modifiers imply a paired structure. If the lesion is clearly left or right of midline, document laterality in the operative report before appending LT or RT. Audit teams flag LT/RT when the operative note doesn't support it.

06Is 21931 appropriate for a sebaceous cyst on the back that required wide excision?

No. Sebaceous cysts and other cutaneous-origin lesions belong in the benign lesion excision series (11400–11446), regardless of size or extent of excision. CPT guidelines are explicit: subcutaneous soft tissue tumor codes do not apply to cutaneous-origin lesions.

Sources & references

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

Mira AI Scribe

Mira's AI scribe captures the intraoperative measurement (tumor diameter plus margin), confirms subcutaneous depth, documents anatomic location with laterality, and flags the tissue origin as non-cutaneous. That prevents the two most common audit findings for this code: missing or ambiguous size documentation that forces a downcode to 21930, and miscoding a cutaneous lesion in the 21931 series when 11400–11446 applies.

See how Mira captures CPT 21931 documentation