M27.40 classifies a jaw cyst when the specific cyst type is not documented or cannot be determined — captured under the Tabular as 'Cyst of jaw NOS.'

Documentation tips

What should appear in the chart to support M27.40.

Source · Editorial brief grounded in 3 cited references ↓

• State explicitly that a cyst of the jaw was identified and that the cyst type is undetermined or not yet specified — 'jaw cyst, NOS' directly supports M27.40.
• Record imaging modality used (panoramic radiograph, CBCT, or CT) and describe the lesion's location, size, and radiographic characteristics; this anchors the diagnosis and demonstrates diagnostic workup.
• If pathology is pending at the time of coding, note that in the chart; once the final pathology report specifies the cyst type, update the code — M27.40 is appropriate as an interim code only when type is genuinely unknown.
• Distinguish the jaw cyst from any oral region cyst (K09.-); document anatomic location as mandible or maxilla, not oral mucosa, to justify staying in the M27.4 family.
• Note whether the cyst was incidental (found on routine imaging) or symptomatic (pain, swelling, tooth displacement) — this supports medical necessity for surgical intervention.

Related CPT procedures

Procedure codes commonly billed with M27.40. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

Common coding pitfalls

The recurring mistakes coders make with M27.40 and adjacent codes.

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

• Using M27.40 for oral region cysts: K09.- is the correct range for odontogenic and nonodontogenic cysts classified as oral-region lesions; M27.4 has an Excludes1 for K09.-, making the combination invalid on the same claim.
• Assigning M27.40 when pathology has confirmed a specific cyst type: once the cyst is identified (e.g., dentigerous, radicular), drop M27.40 and use the more specific code under M27.49 or K09.-.
• Confusing Stafne's cyst or latent bone cyst with an unspecified jaw cyst: both map exclusively to M27.0, not M27.40.
• Leaving M27.40 on a claim after the final pathology report is available — payers may flag this as under-coded if a specific type was documented.

Clinical context

Source · Editorial summary grounded in 3 cited references ↓

Inclusion & exclusion notes

Per the official ICD-10-CM Tabular List.

Source · CDC ICD-10-CM Official Tabular List · 2026

Sibling codes

Other billable codes under M27.4 (laterality / anatomic variants).