The definitions differ by one word
The official ICD-10-PCS definitions are almost identical:
- Excision — cutting out or off, without replacement, a portion of a body part.
- Resection — cutting out or off, without replacement, all of a body part.
That is the entire difference. Both are removals and both are without replacement. Excision is available in all 31 Medical and Surgical body systems; Resection in only 22 of them — there is no Resection table for the arteries and veins, the peripheral nerves, subcutaneous tissue and fascia, or the anatomical regions, because those body parts are not things you take out whole. The only question is whether the surgeon took part of a body part or the whole thing.
It sounds like it should be easy, and it is the root operation pair that generates the most rework in inpatient coding. The reason is that "the whole thing" does not mean what it sounds like.
"All of a body part" means all of a PCS body part
PCS has its own body part key, and it does not always match how a surgeon or an anatomist would carve the body up. What counts as "a body part" is whatever the classification lists as a distinct value on character four — and that decides the root operation.
The lung is the clearest example. PCS defines individual lung lobes as body parts in their own right. So:
- Removing an entire lower lobe — a lobectomy — is Resection, because the lower lobe is a whole body part.
- Removing a wedge from that same lobe is Excision, because only a portion of the body part came out.
- Removing the entire left lung is Resection of a different, larger body part value.
The surgeon may describe all three as "taking out lung". The classification treats them as three different codes, and the deciding fact is which body part value you are coding to.
The practical technique follows directly: choose the body part first, then ask whether all of it came out. Coders who decide the root operation before the body part get this backwards and end up arguing about a question that has no answer in the abstract.
Why it matters beyond the record
Excision and Resection frequently group into different MS-DRGs, which means the choice changes what the hospital is paid. That makes it an audit target. A wrong Resection where the documentation supports only Excision is the kind of finding that shows up in a recovery audit years later, with interest.
It also means the distinction is not something to resolve by preference or by what "sounds more accurate". It is resolved by the operative report and the body part key, and when the report is ambiguous, the answer is a physician query rather than a judgement call.
The cases that cause arguments
Paired organs
Removing one kidney is Resection of that kidney: the kidney is a body part and all of it came out. The fact that a second kidney remains in the patient is irrelevant — PCS asks about the body part, not the organ system.
Tubular structures
The gastrointestinal tract is divided into body parts by segment. Removing the sigmoid colon entirely is Resection of the sigmoid colon. Removing a length of the transverse colon that leaves part of it behind is Excision of the transverse colon. A right hemicolectomy that takes all of the ascending colon plus part of the transverse colon is coded as two separate procedures, one of each root operation — Resection of the ascending colon and Excision of the transverse colon — because they are different root operations on different body part values, and each has to be reported.
Lymph node chains
Lymph nodes are grouped into regional chains as body parts. Taking a sample of nodes from a chain is Excision. Taking an entire chain is Resection. This one causes real disagreement because operative reports rarely say "the whole chain" in those words, and the honest answer is often to query.
Biopsy
A biopsy is not a root operation of its own. Guideline B3.4a codes biopsies to Excision, Extraction or Drainage — whichever matches how the sample was taken — with the qualifier X, Diagnostic. Cutting out a portion is Excision; pulling or stripping tissue out by force is Extraction; aspirating fluid is Drainage. If a diagnostic biopsy is followed in the same episode by a more definitive treatment of the same procedure site, guideline B3.4b codes both.
Things that are neither
Two neighbours are often confused with this pair:
- Detachment is the root operation for amputations of extremities. An amputation is not a Resection even though the whole of something came off.
- Destruction covers eradicating a body part by energy, force or a destructive agent without taking anything out — ablation, fulguration, cautery. Nothing is removed, so neither Excision nor Resection applies.
A worked pair
Take the gallbladder, a single body part in the Hepatobiliary System.
A laparoscopic cholecystectomy removes it entirely. All of a body part, without replacement, so Resection: table 0FT, body part 4 for gallbladder, approach 4 for percutaneous endoscopic, nothing left behind and nothing to qualify — 0FT44ZZ.
Now suppose only a portion had been taken for diagnosis. Excision moves you to table 0FB, and the qualifier changes to X for diagnostic. Same organ, same approach, different root operation, and every character after the third is different.
You can walk both paths in the ICD-10-PCS Code Builder: pick the section and body system, then switch the root operation between Excision and Resection and watch the available body parts, approaches and qualifiers change underneath you. Seeing the two tables side by side makes the structural difference obvious in a way that reading the definitions does not.
What the documentation has to say
The distinction lives or dies on the operative report, and reports are written by surgeons for surgeons rather than for the body part key. Three phrases carry most of the weight.
"Total", "complete" and "en bloc" point toward Resection, but only once you have confirmed which body part they refer to. "Total thyroidectomy" is Resection of the thyroid gland; "total removal of the lesion" says nothing about whether a whole body part came out and is not evidence either way.
"Partial", "subtotal", "wedge" and "segmental" point toward Excision — with the caveat that a segment can itself be a defined body part. In the lung, a segmental resection removes less than a lobe, and since PCS defines lobes rather than segments as the body parts, that is Excision of the lobe. The word "resection" in the surgeon's own phrasing is not the root operation.
Named procedures are the least reliable of all. A "Whipple" involves several root operations across several body parts and cannot be coded from its name. The index will point you at a starting table; the report tells you what was actually done.
When the report describes the specimen rather than the act — "the specimen was sent for frozen section" — you learn nothing about how much of the body part remained. That is precisely the ambiguity a physician query exists to resolve.
Multiple procedures in one episode
Guideline B3.2 sets out when multiple procedures are coded during a single operative episode: among them, the same root operation performed on different body parts, and multiple root operations with distinct objectives performed on the same body part. Two consequences follow that catch people out.
A right hemicolectomy taking all of the ascending colon and part of the transverse produces two codes: Resection of the ascending colon and Excision of the transverse colon. It feels like one operation to everyone in the room, and it is two codes.
Conversely, taking two portions of the same body part through the same approach in the same episode does not multiply into two codes just because the surgeon made two passes. One body part, one root operation, one code — the number of specimens is not the number of procedures.
A checklist that resolves most cases
- Find the body part value first. Look up what PCS calls the site on character four. Do not start from the anatomy in the report.
- Ask: did all of that value come out? All of it means Resection. Any less means Excision.
- Check for a more specific root operation. Was it an amputation of an extremity (Detachment)? Was it destroyed rather than removed (Destruction)? Was tissue taken to be put somewhere else (Transfer, Transplantation, Replacement)? Was it pulled or stripped out by force rather than cut (Extraction)?
- Set the qualifier. Diagnostic removals take
X. Most others takeZ. - If the report does not say how much came out, query. The difference is worth money and the guess is not defensible.
Where the pair sits among the other root operations
Excision and Resection belong to a group of five root operations that take out some or all of a body part — the others are Detachment, Destruction and Extraction. A neighbouring group of three takes out solids, fluids or gases instead: Drainage, Extirpation and Fragmentation. Knowing the neighbours is what stops you defaulting to this pair when the procedure was really something else.
- Extraction — pulling or stripping a body part out by force. A vein stripping, a dilation and curettage. Nothing is cut out; it is pulled.
- Drainage — taking out fluids or gases. If what came out was liquid, this is the operation, and a diagnostic drainage takes the same
Xqualifier. - Fragmentation — breaking solid matter into pieces without removing it, such as lithotripsy on a stone.
- Division — cutting into a body part to separate it, with nothing taken out at all.
Running through that list before settling on Excision takes a few seconds and catches the cases where "some tissue came out" was a side effect rather than the objective of the procedure. PCS codes the objective, which is why the root operation is chosen from what the surgeon was trying to achieve rather than from what ended up in the specimen jar.
The short version
Excision is a portion, Resection is all of it, and "it" is whatever PCS defines as a body part rather than what the surgeon called the organ. Decide the body part before the root operation and most of the difficulty disappears. Where the operative report is genuinely ambiguous, the correct action is a query, because the two codes carry different clinical meaning and often different payment — and neither of those is something to settle by inference.