Crystal's Coder Hub👃 CPT 31233 — Nasal/Sinus Endoscopy, Diagnostic; With Maxillary Sinusoscopy (Via Inferior Meatus or Canine Fossa Puncture)
Quick Reference
wRVU: 1.27 | Global Period: 000 (same day) | Assistant Payable: ❌ No | Bilateral Indicator: 1 — Unilateral code; bilateral requires modifier -50
📋 Clinical Description
CPT 31233 describes a diagnostic nasal and sinus endoscopy that includes direct inspection of the maxillary sinus interior (sinusoscopy) — accessed by the provider actively creating entry into the maxillary sinus via one of two puncture approaches: (1) inferior meatus puncture — a trocar or needle is driven through the thin medial maxillary sinus wall via the inferior meatus of the nasal cavity; or (2) canine fossa puncture — a trocar is introduced through the anterior wall of the maxillary sinus above the canine root through the soft tissue of the cheek. This is the defining clinical and billing distinction for 31233: the code requires that a new puncture or trocar cannulation be actively performed to gain entry into the maxillary sinus. Per the AAO-HNS CPT for ENT guidance (reviewed October 2023), when a physician uses an endoscope to inspect the interior of the maxillary sinus through an existing, surgically created, patent sinusotomy or antrostomy (e.g., post-FESS maxillary antrostomy), 31233 is incorrect — only 31231 (diagnostic nasal endoscopy, unilateral or bilateral) should be reported for visualization through a pre-existing opening. 31233 is exclusively for newly created access.
This is also a critical distinction within the endoscopy code family: 31231 is a bilateral-inclusive code (covers one or both nasal cavities without a puncture), while 31233 is inherently unilateral — it describes sinusoscopy of one maxillary sinus via one access puncture. When both maxillary sinuses are entered via new punctures at the same session, modifier -50 is required to report the bilateral service. Failure to append -50 for bilateral same-session sinusoscopy is the most common billing error for this code.
31233 is a diagnostic code — the goal is visualization and assessment. When the procedure progresses to a surgical intervention at the same session (e.g., washings are obtained, a polyp is biopsied, or a cyst is removed), separate surgical endoscopy codes (31256, 31267, 31295) may be more appropriate depending on what was done. If specimens are submitted for pathology or washings are performed, document these explicitly — the diagnostic nature of 31233 does not prohibit obtaining a specimen during the visualization, but if a formal tissue removal or polyp excision is performed, evaluate whether the surgical endoscopy codes better represent the service.
This procedure may be performed in the following clinical contexts:
- Diagnostic evaluation of maxillary sinus pathology not fully characterized by imaging — CT sinus or MRI shows maxillary sinus opacification, soft tissue density, or bony changes where tissue characterization is needed; direct visualization and biopsy capability via sinusoscopy guides the diagnosis.
- Suspected fungal sinusitis in an immunocompromised patient — Invasive fungal sinusitis (Aspergillus, Mucor) requires urgent diagnosis; sinusoscopy via inferior meatus allows direct visualization of necrotic mucosa and specimen collection for fungal culture and histopathology; time-critical in hematologic malignancy or transplant patients.
- Evaluation of recurrent or treatment-refractory maxillary sinusitis — Patients with chronic maxillary sinusitis failing medical therapy where culture-directed treatment is needed; sinusoscopy allows direct antral washings for microbiologic culture — more accurate than nasal or nasopharyngeal swabs.
- Pre-operative diagnostic workup for planned FESS — Direct sinus inspection and culture to confirm active disease, characterize polyp burden, and obtain pre-operative microbiology; confirms surgical planning before proceeding to functional endoscopic sinus surgery.
- Evaluation of maxillary sinus mass or neoplasm (benign or malignant) — Direct visualization of a maxillary sinus soft tissue density seen on imaging, with direct biopsy capability to characterize the lesion; note that if biopsy is performed, evaluate whether a more specific surgical endoscopy code applies.
- Antral washings for culture in complicated sinusitis or immunocompromised patient — When maxillary sinus cultures are required for antibiotic stewardship (e.g., hospital-acquired sinusitis, nosocomial sinusitis in ICU patients with nasotracheal tubes), inferior meatus puncture with washings provides specimen of the highest diagnostic yield.
🔬 Access Approaches — Inferior Meatus vs. Canine Fossa
| Access Approach | Technique | Clinical Indication | Key Coding Notes |
|---|---|---|---|
| Inferior Meatus Puncture | With the patient upright or reclined, a rigid trocar or large-bore needle is advanced through the inferior meatus laterally into the thin medial maxillary sinus wall (lateral nasal wall); a small endoscope is passed through the trocar to inspect the sinus interior | Standard office-based approach; suitable for most diagnostic sinusoscopies; no external incision required; well tolerated under topical/local anesthesia | Most common approach for 31233 in the office and outpatient setting; document the approach explicitly in the procedure note (“inferior meatus puncture with trocar, endoscope advanced into maxillary sinus”) |
| Canine Fossa Puncture | A small stab incision is made in the buccal mucosa superior to the canine root; a trocar is advanced through the anterior wall of the maxillary sinus; the endoscope is introduced via the trocar for panoramic visualization of the sinus interior | Used when inferior meatus approach is not feasible (e.g., scarred inferior turbinate, prior medial maxillary wall loss), or when panoramic anterior sinus visualization is required; superior visualization of the anterior maxillary sinus wall and floor | Document the canine fossa approach specifically; the buccal incision and soft tissue entry add to the invasiveness of the procedure and may support modifier -22 if significantly complex; close the buccal incision at conclusion if made |
Clinical Pearl — The Puncture Requirement is NON-NEGOTIABLE
Per AAO-HNS CPT for ENT guidance (reviewed October 2023), 31233 requires active puncture or trocar cannulation into the maxillary sinus. If the physician simply advances the nasal endoscope through a widely patent, previously created surgical antrostomy to look into the sinus — without making any new puncture — 31233 is incorrect. The correct code in that scenario is 31231 (diagnostic nasal endoscopy, unilateral or bilateral). This is the single most important clinical and billing distinction for this code and is the most common over-coding pattern for 31233 in post-FESS patients. The operative or procedure note must explicitly state the puncture or trocar technique used and confirm that access was newly created — not through a pre-existing opening.
✅ Procedure Includes
- Pre-procedure topical decongestion and local/topical anesthetic application to the nasal mucosa and inferior meatus (or canine fossa site) — included in the service payment; not separately billable
- Nasal endoscopy component — passage of the endoscope through the nasal cavity to the inferior meatus or canine fossa site for visualization of nasal structures en route to the maxillary sinus access point
- Active creation of maxillary sinus access — inferior meatus trocar puncture through the medial maxillary sinus wall, OR canine fossa trocar puncture through the anterior maxillary wall
- Maxillary sinusoscopy — direct endoscopic visualization of the sinus interior including mucosa, ostium (natural), sinus floor, medial, anterior, posterior and lateral walls, and assessment of any visible pathology
- Antral washings, if performed for culture or cytology (specimen collection is included in the diagnostic service)
- Documentation of findings, sinus contents (e.g., polyps, mucous, pus, fungal debris, neoplastic tissue), and mucosal quality
- Trocar/scope removal and wound management (canine fossa stab incision closure if applicable)
❌ Excludes / Do Not Report Together
| Code | Description | Relationship to 31233 |
|---|---|---|
| 31231 | Nasal endoscopy, diagnostic, unilateral or bilateral (separate procedure) | Do not report 31233 when access to the maxillary sinus is via a pre-existing patent sinusotomy or antrostomy — per AAO-HNS guidance, 31231 is the correct code when the endoscope accesses the maxillary sinus through a previously created surgical opening without a new puncture; 31231 is a unilateral-or-bilateral inclusive code; 31233 requires a new access puncture |
| 31235 | Nasal/sinus endoscopy, diagnostic; with sphenoid sinusoscopy (via puncture of sphenoidal face or cannulation of ostium) | Separately reportable when sphenoid sinusoscopy via puncture is also performed at the same session alongside maxillary sinusoscopy; both codes may be reported if both sinuses are entered via new punctures; apply modifier -51 on the lower-valued code and confirm distinct documentation for each sinus |
| 31256 | Nasal/sinus endoscopy, surgical, with maxillary antrostomy | If the diagnostic sinusoscopy proceeds to creation of a formal antrostomy opening (not merely a trocar puncture for diagnostic access), 31256 may be the more appropriate surgical code — 31256 describes surgical antrostomy, not merely a diagnostic puncture; evaluate which code best reflects what was actually performed |
| 31267 | Nasal/sinus endoscopy, surgical, with maxillary antrostomy; with removal of tissue from maxillary sinus | Separately reportable — or potentially the primary code — when tissue is formally removed from the maxillary sinus at the same session; if the primary purpose of the session was diagnostic with incidental washings, 31233 applies; if a polyp or mass was formally excised, 31267 may supersede 31233 |
| 31295 | Nasal/sinus endoscopy, surgical, with dilation (e.g., balloon dilation); maxillary sinus ostium, transnasal | Do not report 31233 alongside 31295 for the same maxillary sinus at the same session — if balloon dilation of the maxillary ostium is performed, 31295 is the appropriate code; 31233 and 31295 should not be billed together for the same sinus |
| E/M codes (992xx / 920xx) | Office visit or hospital visit, any level | Separately reportable only when modifier -25 is appended to the E/M code, documenting a significant, separately identifiable evaluation service beyond the pre-procedure assessment; the 0-day global means same-date E/M is bundled unless -25 is applied |
This is the most frequently misunderstood billing distinction in the nasal endoscopy code family. 31231 can describe either a unilateral OR bilateral exam within a single unit of service — it covers both sides without a bilateral modifier. 31233 describes only ONE maxillary sinusoscopy (one side). When the surgeon performs maxillary sinusoscopy in both maxillary sinuses at the same session via new punctures, modifier -50 must be appended: report 31233--50 (or two line items 31233--RT / 31233--LT depending on payer format). Reporting a single unit of 31233 for bilateral sinusoscopy underbills the service. Reporting two units of 31233 without -50 may be rejected or recouped. Confirm your MAC’s billing format preference for bilateral.
🌳 Code Tree — Surgery: Respiratory System — Endoscopy Procedures on the Accessory Sinuses
CPT 31231-31298 Nasal/Sinus Endoscopy Procedures (Diagnostic and Surgical)
│
DIAGNOSTIC ENDOSCOPY:
├── 31231 Nasal endoscopy, diagnostic, unilateral or bilateral (separate procedure) (Global: 000)
├── ▶▶ 31233 ◀◀ Nasal/sinus endoscopy, diagnostic; with maxillary sinusoscopy (via inferior meatus or canine fossa puncture) ← YOU ARE HERE (Global: 000)
└── 31235 Nasal/sinus endoscopy, diagnostic; with sphenoid sinusoscopy (via puncture of sphenoidal face or cannulation of ostium) (Global: 000)
│
SURGICAL ENDOSCOPY — MAXILLARY SINUS:
├── 31256 Nasal/sinus endoscopy, surgical, with maxillary antrostomy (Global: 090)
├── 31267 Nasal/sinus endoscopy, surgical, with maxillary antrostomy; with removal of tissue from maxillary sinus (Global: 090)
├── 31295 Nasal/sinus endoscopy, surgical, with dilation; maxillary sinus ostium, transnasal (Global: 090)
└── 31296 Nasal/sinus endoscopy, surgical, with dilation; maxillary sinus ostium, via canine fossa (Global: 090)
│
SURGICAL ENDOSCOPY — ETHMOID / FRONTAL / SPHENOID / TOTAL:
├── 31237 Nasal/sinus endoscopy, surgical; with biopsy, polypectomy or debridement (Global: 010)
├── 31240 Nasal/sinus endoscopy, surgical; with concha bullosa resection (Global: 090)
├── 31241 Nasal/sinus endoscopy, surgical; with ligation of sphenopalatine artery (Global: 090)
├── 31253 Nasal/sinus endoscopy, surgical, total (complete), bilateral; with frontal sinus exploration (Global: 090)
├── 31254 Nasal/sinus endoscopy, surgical; with ethmoidectomy, partial (anterior) (Global: 090)
├── 31255 Nasal/sinus endoscopy, surgical; with ethmoidectomy, total (anterior and posterior) (Global: 090)
├── 31257 Nasal/sinus endoscopy, surgical; with sphenoidotomy (Global: 090)
└── 31259 Nasal/sinus endoscopy, surgical; with sphenoidotomy and removal of tissue from the sphenoid sinus (Global: 090)
💰 RVU & Reimbursement Profile
| Component | Value |
|---|---|
| Work RVU (wRVU) | 1.27 (verify against current CMS MPFS for applicable year — subject to 2026 efficiency adjustment) |
| Non-Facility PE RVU | ~3.03 (verify against CMS RVU26A) |
| Malpractice RVU | ~0.09 |
| Non-Facility Total RVU | ~4.39 (verify against CMS RVU26A) |
| Global Period | 000 (same day) |
| Bilateral Indicator | 1 — UNILATERAL CODE — Standard bilateral reduction rules apply; when performed bilaterally, report with modifier -50 (or -RT/-LT on two line items per MAC preference); bilateral payment is 150% of the unilateral rate |
| Assistant Surgeon | ❌ Not payable — diagnostic endoscopy; assistant surgeon not medically necessary |
| Co-Surgeon | ❌ Not applicable |
| Team Surgery | ❌ Not applicable |
| PC/TC Split | ❌ No — Procedure code only (Indicator 0) |
| Modifier -51 Exempt | No — Subject to multiple procedure reduction rules when billed with other procedures at the same session |
| Anesthesia | Local/topical anesthesia is standard for office-based inferior meatus puncture; included in the procedure payment — not separately billable. If performed under general or monitored anesthesia care (e.g., in the OR or ASC), the anesthesia provider bills separately |
Bilateral Billing — Critical for 31233
31233 has a bilateral indicator of 1, confirming it is a unilateral code subject to standard CMS bilateral reduction methodology. When bilateral maxillary sinusoscopy is performed at the same session (both maxillary sinuses entered via new punctures):
- Report 31233--50 as a single line item — CMS pays 150% of the unilateral rate
- Or, per some MAC formats: 31233--RT on Line 1 and 31233--LT on Line 2 — combined payment equals 150% of the unilateral rate
- Confirm your specific MAC’s billing format preference for bilateral reporting
- Never report two units of 31233 without a bilateral modifier — duplicate billing will be rejected or recouped
- Never add -50 to 31231 — 31231 is already bilateral-inclusive; adding -50 to 31231 is inappropriate
🏷️ Modifier Reference
| Modifier | Name | When to Apply |
|---|---|---|
| -50 | Bilateral Procedure | Required when maxillary sinusoscopy via new puncture is performed on BOTH maxillary sinuses at the same session; confirm MAC billing format (-50 single line vs. -RT/-LT two lines); payment = 150% of the unilateral rate |
| -RT | Right Side | Right maxillary sinus sinusoscopy — use when billing bilateral as two separate line items per MAC format; or when billing right-sided only for clarity |
| -LT | Left Side | Left maxillary sinus sinusoscopy — use for bilateral line-item billing or single-side left documentation |
| -25 | Significant, Separately Identifiable E/M | Applied to the E/M code — not 31233 — when a significant, separately identifiable evaluation is performed same date beyond the pre-procedure assessment; the 0-day global means -25 is required for same-date E/M billing; the E/M documentation must stand independently |
| -51 | Multiple Procedures | When 31233 is performed alongside other separately reportable surgical or diagnostic procedures at the same session — e.g., concurrent 31235 (sphenoid sinusoscopy), 31237 (surgical endoscopy with biopsy/debridement), or turbinate procedures; apply -51 to the lower-valued code |
| -59 | Distinct Procedural Service | When 31233 is performed alongside a procedure at a genuinely distinct anatomic site and payers bundle inappropriately |
| -XS | Separate Structure | Preferred over -59 when the distinct service involves a clearly separate anatomic structure (e.g., 31233 alongside 31235 for two distinct sinuses accessed via two distinct punctures) |
| -52 | Reduced Services | Procedure partially completed — e.g., access puncture was attempted but the trocar could not be successfully advanced into the maxillary sinus due to bony resistance or anatomic variant; document the attempt, technique, and reason for incomplete access; the procedure is still billable at a reduced level |
| -76 | Repeat Procedure by Same Physician | Second sinusoscopy session by the same provider — e.g., repeat diagnostic assessment after initial treatment; document clinical justification for repeat |
| -77 | Repeat Procedure by Different Physician | Repeat sinusoscopy by a different provider |
| -79 | Unrelated Procedure During Postoperative Period | When 31233 is performed during the postoperative global period of another procedure and is unrelated to the original procedure; document the unrelated clinical indication |
🩺 Common ICD-10-CM Pairings
Maxillary Sinusitis — Primary Diagnoses
| ICD-10 Code | Description | HCC? | Clinical Notes |
|---|---|---|---|
| J32.0 | Chronic maxillary sinusitis | ❌ No | Most commonly paired primary diagnosis for 31233 — indicates refractory or persistent maxillary sinusitis requiring diagnostic sinusoscopy for culture, mucosal assessment, or characterization of disease burden prior to FESS; confirm duration (> 12 weeks) in the clinical record to support “chronic” designation |
| J01.00 | Acute maxillary sinusitis, unspecified | ❌ No | Use for acute maxillary sinusitis (< 4 weeks duration) requiring sinusoscopy for culture-directed antibiotic therapy or diagnostic evaluation; J01.00 = unspecified (no pathogen identified); use when organism is not documented |
| J01.01 | Acute recurrent maxillary sinusitis | ❌ No | Use for patients with multiple separate acute episodes of maxillary sinusitis per year; documents a clinical pattern supporting the medical necessity for diagnostic sinusoscopy to identify structural or microbiologic contributing factors |
| J32.4 | Chronic pansinusitis | ❌ No | Use when all paranasal sinuses are chronically involved and the maxillary component is part of the broader pansinusitis picture; supports medical necessity for maxillary sinusoscopy as part of a comprehensive sinus evaluation |
Sinus Polyps and Other Nasal/Sinus Disorders
| ICD-10 Code | Description | HCC? | Clinical Notes |
|---|---|---|---|
| J33.8 | Other polyp of sinus | ❌ No | Use for solitary or unilateral sinus polyps confined to the maxillary sinus; document the specific sinus (maxillary) even though the code is not sinus-specific at the ICD-10-CM level; supports diagnostic sinusoscopy to characterize the polyp and assess need for surgical intervention |
| J34.89 | Other specified disorders of nose and nasal sinuses | ❌ No | Use as a catch-all for maxillary sinus pathology not covered by more specific codes — e.g., maxillary sinus retention cyst, maxillary sinus mucocele (non-specific presentation), or other structural abnormalities seen on imaging; confirm a more specific code is not available before defaulting to this |
Neoplastic and Oncologic Diagnoses
| ICD-10 Code | Description | HCC? | Clinical Notes |
|---|---|---|---|
| C31.0 | Malignant neoplasm of maxillary sinus | ✅ HCC | Use when diagnostic sinusoscopy is performed to evaluate a suspected or confirmed maxillary sinus malignancy; biopsy obtained during the sinusoscopy should be linked to this diagnosis; if biopsy is performed, evaluate whether 31267 (with tissue removal) or a separate biopsy code better represents the additional service |
| D14.0 | Benign neoplasm of middle ear, nasal cavity and accessory sinuses | ❌ No | Use for benign neoplasms of the accessory sinuses (e.g., inverted papilloma, osteoma) confirmed or suspected on imaging and being evaluated via sinusoscopy; document the specific sinus |
Infectious / Fungal Diagnoses
| ICD-10 Code | Description | HCC? | Clinical Notes |
|---|---|---|---|
| B44.1 | Other pulmonary aspergillosis | ✅ HCC | Use as a secondary diagnosis when Aspergillus sinusitis is confirmed or strongly suspected and sinusoscopy is performed to obtain fungal cultures or assess mucosal necrosis; confirm pathology/culture results before assigning |
| B46.0 | Pulmonary mucormycosis | ✅ HCC | Use as secondary diagnosis when mucormycosis/invasive fungal sinusitis is confirmed or suspected; urgent diagnostic sinusoscopy in immunocompromised patients (transplant, hematologic malignancy) is the primary clinical scenario; document the immunocompromised state with appropriate secondary diagnoses (transplant status, chemotherapy, etc.) |
| R04.0 | Epistaxis | ❌ No | Use when diagnostic sinusoscopy is performed to evaluate a suspected maxillary sinus source of recurrent or refractory epistaxis; document the clinical rationale for sinus-source evaluation |
Coding Specificity Reminder
The most important specificity axis for 31233 ICD-10-CM pairings is distinguishing acute (J01.00, J01.01) from chronic (J32.0) sinusitis — the duration criteria must be documented in the clinical record (acute = < 4 weeks; subacute = 4-12 weeks; chronic = > 12 weeks). Defaulting to “unspecified” acute or chronic codes without confirming the duration in the clinical record is a specificity gap. Additionally, for neoplastic diagnoses, the histologic type should be confirmed from the biopsy pathology report before assigning C31.0 vs. D14.0 — do not code suspected malignancy as confirmed without pathologic verification. For MAC LCDs governing diagnostic nasal endoscopy, confirm that the assigned ICD-10-CM code is on the payer’s covered diagnoses list for 31233 — coverage varies by MAC.
🏥 MS-DRG Considerations (Inpatient)
Inpatient Coding Reminder
CPT 31233 is performed exclusively in the outpatient, office, or ASC setting under normal circumstances. Inpatient admission for diagnostic nasal/sinus endoscopy with maxillary sinusoscopy alone is not supported by utilization review criteria. The only inpatient context where this procedure is performed (and an ICD-10-PCS code assigned) is when the sinusoscopy is part of a larger inpatient admission for complicated sinusitis — e.g., invasive fungal sinusitis in a hematologic malignancy or post-transplant patient with orbital or intracranial extension, or orbital cellulitis from maxillary sinusitis requiring concurrent surgical drainage. In that context, the sinusoscopy PCS code would be assigned alongside the PCS codes for the more extensive sinus surgery driving the inpatient admission, but the diagnostic sinusoscopy code would not independently drive DRG assignment.
🔧 ICD-10-PCS Equivalents (Inpatient Facility Coding)
Note
Inpatient PCS coding for 31233 is rare but may be encountered in complex sinus surgery admissions. The PCS root operation is Inspection (J) — defined as visually and/or manually exploring a body part. For a diagnostic nasal/sinus endoscopy, Inspection correctly captures the intent: the procedure is performed to assess the sinus interior without a planned therapeutic intervention. The approach character for sinusoscopy via inferior meatus or canine fossa puncture is Percutaneous Endoscopic (4) — a percutaneous (needle/trocar) access is created and the endoscope is introduced through that access, fitting the definition of percutaneous endoscopic approach in PCS. If the procedure is performed through the nasal ostium via a natural opening (e.g., an existing large antrostomy), the approach would shift to Via Natural or Artificial Opening Endoscopic (8), but as discussed, that scenario corresponds to 31231 rather than 31233 at the CPT level.
| PCS Code | Full Description | Applicable Scenario |
|---|---|---|
09JK4ZZ | Inspection of Nasal Bone, Percutaneous Endoscopic Approach, No Device, No Qualifier | Diagnostic nasal/sinus endoscopy with maxillary sinusoscopy via inferior meatus or canine fossa puncture (percutaneous access + endoscopic visualization) |
09JY4ZZ | Inspection of Sinuses, Percutaneous Endoscopic Approach, No Device, No Qualifier | Diagnostic inspection of the sinus(es) — use when the inspection encompasses multiple sinuses or when the sinus body part value “Y” (Sinuses) is the most accurate body part character for the scope of the examination |
09JK8ZZ | Inspection of Nasal Bone, Via Natural or Artificial Opening Endoscopic | Use in the rare inpatient scenario where the endoscope accesses the maxillary sinus via an existing surgically created opening rather than a new puncture (note: at the CPT level, this scenario corresponds to 31231, not 31233) |
PCS Character Analysis — 09JK4ZZ
| Position | Character | Value | Definition |
|---|---|---|---|
| 1 | Section | 0 | Medical and Surgical |
| 2 | Body System | 9 | Ear, Nose, Sinus |
| 3 | Root Operation | J | Inspection (visually and/or manually exploring a body part — diagnostic visualization of the sinus interior) |
| 4 | Body Part | K | Nasal Bone (used as the body part character representing the nasal/sinus region for endoscopic inspection) |
| 5 | Approach | 4 | Percutaneous Endoscopic (entry of instrumentation through the skin or mucous membrane, body layers and any body cavities, to reach the procedure site, and direct visualization using an endoscope — the trocar puncture through the inferior meatus or canine fossa is the percutaneous component) |
| 6 | Device | Z | No Device |
| 7 | Qualifier | Z | No Qualifier |
PCS Root Operation: Inspection (J) — Diagnostic vs. Excision
- Use Inspection (J) for 31233 when the procedure is purely diagnostic — visualization only, with or without washings
- If tissue is formally removed during the sinusoscopy (biopsy, polyp excision, cyst removal), the root operation changes to Excision (B) — defined as cutting out or off a portion of a body part; assign the appropriate Excision code in addition to or instead of the Inspection code depending on whether the inspection was a distinct, separately documented service
- PCS Guideline B3.11 states: “Inspection of a body part(s) performed in order to achieve the objective of a procedure is not coded separately” — meaning if the inspection is merely the visualization component of a therapeutic procedure (excision, drainage), only the therapeutic procedure code is assigned; the Inspection is coded separately only when the diagnostic scope is the primary and only purpose of the encounter
📝 Coding Examples
Example 1 — Office: Unilateral Diagnostic Maxillary Sinusoscopy for Refractory Chronic Sinusitis
Clinical Scenario: A 45-year-old female with a 14-month history of left maxillary sinusitis unresponsive to three courses of antibiotics and intranasal steroid spray presents to the ENT office. CT sinus confirms complete left maxillary sinus opacification with no air fluid level. She has not had prior sinus surgery. The ENT performs a Level 3 established patient E/M — including review of the CT, physical examination, and decision to proceed with diagnostic sinusoscopy for culture and assessment — documented as a distinct and separately identifiable clinical service. After topical oxymetazoline and 4% lidocaine spray to the left inferior meatus, a trocar is advanced through the inferior meatus into the left maxillary sinus under direct visualization. The endoscope is introduced through the trocar, confirming thick mucopurulent secretions in the left maxillary sinus with polypoid mucosal thickening. Antral washings are obtained and sent for culture and sensitivity. The procedure note documents: “Left inferior meatus trocar puncture performed; endoscope advanced into left maxillary sinus; thick mucopurulent secretions and polypoid mucosa visualized; washings obtained for C&S.”
| Field | Code | Rationale |
|---|---|---|
| CPT 1 | 99213--25 | Level 3 established patient E/M — modifier -25 on the E/M code, NOT on 31233; the evaluation (CT review, clinical assessment, treatment decision) constitutes a significant, separately identifiable service; document in a distinct note section |
| CPT 2 | 31233 | Diagnostic nasal/sinus endoscopy with maxillary sinusoscopy — left side via inferior meatus puncture; procedure note explicitly documents trocar puncture (new access), endoscopic visualization, and findings; unilateral — no -50 needed |
| PDx | J32.0 | Chronic maxillary sinusitis — 14-month duration documented; left-sided; “chronic” supported by duration > 12 weeks and treatment-refractory course |
Note
The antral washings obtained during the sinusoscopy are included in the 31233 service — they do not constitute a separately billable laboratory collection procedure. The laboratory processing and reporting of the culture and sensitivity results is separately billable by the laboratory under the appropriate microbiology CPT codes (e.g., 87040, 87070) — the ENT physician does not separately bill for the specimen collection or the culture reading. Ensure the order for culture is clearly documented in the procedure note and order set.
Example 2 — ASC: Bilateral Maxillary Sinusoscopy with Concurrent Surgical Endoscopy
Clinical Scenario: A 38-year-old male with chronic pansinusitis and bilateral nasal polyps is scheduled for functional endoscopic sinus surgery (FESS). Intraoperatively, after completing bilateral total ethmoidectomies (31255--50) and bilateral maxillary antrostomies (31256--50), the surgeon introduces the endoscope into the left maxillary sinus via a newly created trocar puncture through the inferior meatus to directly inspect the sinus interior and confirm complete removal of polyp tissue and fungal debris — this is performed via a new inferior meatus puncture (not through the newly created antrostomy). A mirror image diagnostic inspection of the right maxillary sinus is performed via a separate right inferior meatus puncture. The operative note documents: “Bilateral inferior meatus trocar punctures performed; endoscopes advanced bilaterally into maxillary sinuses for direct visualization; sinus interiors inspected; polypoid debris identified and irrigated; washings sent bilaterally.”
| Field | Code | Rationale |
|---|---|---|
| CPT 1 | 31255--50 | Bilateral total ethmoidectomy (anterior and posterior) — primary FESS procedure |
| CPT 2 | 31256--50--51 | Bilateral maxillary antrostomy — performed as part of FESS; -50 bilateral; -51 multiple procedures |
| CPT 3 | 31233--50--51 | Bilateral diagnostic maxillary sinusoscopy via bilateral inferior meatus new punctures — distinct from the antrostomy; separately performed as a diagnostic inspection of each sinus interior via new trocar access; -50 bilateral; -51 multiple procedures |
| PDx | J32.4 | Chronic pansinusitis — most specific code for the bilateral multi-sinus involvement driving FESS |
Warning
This example demonstrates a complex and controversial coding scenario: 31233 and 31256 reported for the same maxillary sinus at the same session. This requires very specific operative note documentation confirming that the sinusoscopy via inferior meatus puncture was a distinct, separately performed service using a new trocar puncture — not merely looking into the sinus through the newly created antrostomy (which would only support 31231). Payers and NCCI may bundle 31233 with 31256 for the same sinus at the same session. Before reporting both, confirm the NCCI Correct Coding edit status for 31233 and 31256 together, and have a clear clinical rationale — in the operative note — for why the inferior meatus puncture sinusoscopy was performed as a distinct, separately necessary step from the antrostomy.
Example 3 — Office: Suspected Invasive Fungal Sinusitis in Immunocompromised Patient
Clinical Scenario: A 62-year-old male with acute myeloid leukemia (AML) on induction chemotherapy presents to the ENT clinic after his oncology team identified right maxillary sinus soft tissue density with bony erosion on CT. The CT findings are concerning for invasive fungal sinusitis. Serum galactomannan is elevated. The ENT performs an urgent office-based diagnostic sinusoscopy via right inferior meatus trocar puncture under topical lidocaine anesthesia. The endoscope is advanced into the right maxillary sinus, revealing dark necrotic mucosal tissue on the medial and superior walls. Biopsy specimens are obtained (sent for fungal culture, KOH prep, and histopathology). The procedure note documents: “Right inferior meatus trocar puncture under topical anesthesia; endoscope advanced into right maxillary sinus; necrotic black-pigmented mucosal tissue identified on medial sinus wall; biopsy specimens obtained for fungal culture, KOH prep, and histopathology.”
| Field | Code | Rationale |
|---|---|---|
| CPT 1 | 31233 | Diagnostic nasal/sinus endoscopy with right maxillary sinusoscopy via inferior meatus puncture — unilateral; access created via new trocar puncture; procedure note confirms |
| PDx | J32.0 | Chronic maxillary sinusitis — primary sinus diagnosis at time of procedure; the fungal etiology is suspected but not yet confirmed; do not code B44.1 or B46.0 until pathology or culture confirms the organism |
| SDx | C91.00 | Acute lymphoblastic leukemia not having achieved remission — documents the immunocompromised state driving the clinical urgency of the sinusoscopy; confirms medical necessity for urgent diagnostic evaluation |
Note
Because biopsy specimens are obtained during the sinusoscopy in this example, evaluate whether 31237 (nasal/sinus endoscopy, surgical; with biopsy, polypectomy or debridement) better represents the service than 31233. The primary determining factor is whether the biopsy constitutes a formal surgical tissue removal (supporting 31237) or merely specimen collection incidental to the diagnostic inspection (supporting 31233). When biopsies are a planned and integral component of the procedure — as in this invasive fungal sinusitis scenario where tissue is actively collected for pathology — 31237 may be more appropriate and more accurately represents the clinical service. Confirm with the performing physician the primary intent and document the specific technique used for tissue collection.
⚠️ Common Coding Pitfalls
-
Reporting 31233 when the maxillary sinus was accessed through a pre-existing surgical antrostomy: This is the most common and most clearly defined miscoding pattern for 31233, per AAO-HNS CPT for ENT guidance. If a patient has had prior FESS with maxillary antrostomy and the physician advances the endoscope through the now-patent antrostomy to inspect the sinus interior — without making any new trocar puncture — 31233 is incorrect. The correct code is 31231. The access puncture requirement is the defining clinical element of 31233, and using it for post-FESS sinus inspections through existing openings is an overcoding violation. The procedure note must explicitly document the puncture — “trocar advanced through inferior meatus into maxillary sinus” — for 31233 to be defensible.
-
Billing a single unit of 31233 for bilateral sinusoscopy without modifier -50: 31233 is a unilateral code. When both maxillary sinuses are entered via new punctures in the same session, a single unit of 31233 represents only one side — underbilling the service. The correct billing is 31233--50 (or two line items with -RT/-LT per MAC format). Failure to apply -50 leaves 50% of the bilateral reimbursement on the table. Conversely, billing two units of 31233 without a bilateral modifier may be processed as a duplicate claim and denied or recouped.
-
Adding modifier -50 to 31231 when both nasal cavities are examined: 31231 is inherently bilateral — it describes nasal endoscopy for “unilateral or bilateral” nasal cavities in a single code unit. Adding -50 to 31231 in an attempt to bill for bilateral nasal examination is incorrect and will result in inappropriate payment at 150% of a service that was already priced to include bilateral work. 31231--50 is a common overbilling error and is a direct result of conflating the billing rules for 31231 (bilateral-inclusive) with those for 31233 (unilateral requiring -50 for bilateral).
-
Forgetting modifier -25 on the same-day E/M: The 0-day global for 31233 means that a same-date E/M visit is bundled unless modifier -25 is applied to the E/M code. In the ENT office setting especially, providers frequently perform a complete evaluation (reviewing imaging, clinical history, making the diagnosis, deciding on sinusoscopy) and then immediately proceed with the procedure in the same visit. The evaluation is a separately identifiable, separately documentable service — and when documented independently of the procedure note — it is billable with -25 on the E/M. Not applying -25 on the E/M forfeits legitimate E/M revenue. The -25 modifier belongs on the E/M code, not on 31233.
-
Using 31233 when 31267 or 31237 better represents the service: 31233 is a diagnostic code — if the session proceeds to formal tissue removal (polyp excision, cyst aspiration, fungal debris debridement), the appropriate surgical endoscopy code (31267 for maxillary antrostomy with tissue removal, or 31237 for endoscopy with biopsy/polypectomy/debridement) may supersede or supplement 31233. Review the operative note carefully for any therapeutic intervention performed beyond visualization — if tissue was removed, characterize which surgical endoscopy code most accurately describes the service and report accordingly.
📎 Sources
AMA CPT 2025 Professional Edition · CMS 2025 Medicare Physician Fee Schedule Final Rule (CMS-1807-F) and CMS 2026 MPFS Final Rule (CMS-1832-F) · CMS RVU26A Relative Value Files · NCCI Policy Manual Chapter 5 (Respiratory System), CMS 2024-2025 · ICD-10-CM Official Guidelines for Coding and Reporting FY2025 · ICD-10-PCS Official Guidelines for Coding and Reporting FY2025 · AAO-HNS CPT for ENT: Nasal Sinus Endoscopy — Correct Usage of CPT 31233 and 31235 (American Academy of Otolaryngology - Head and Neck Surgery, reviewed October 2023, published April 2009) · AAPC Otolaryngology Coding Alert — “What Does 31233 Represent?” (AAPC, October 2006) · Bonfire Revenue Cycle — “ENT Billing: Mastering Nasal Endoscopy CPT Coding” (January 2026) · Medtronic ENT — Nasal and Sinus Procedures: Commonly Billed Codes Reference (CMS RVU Data) · PayerPrice — CPT 31233 Fee Schedule and Payer Reimbursement Reference (October 2025) · Noridian Medicare JE Part B — MPFS Indicator Descriptors (Bilateral Indicator and Global Period Reference)