ICD-10 Code C45.1 – Mesothelioma of peritoneum (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C45.1 – Mesothelioma of peritoneum
What it is
Mesothelioma of peritoneum is a malignant tumor arising from the lining of the abdominal cavity. It is coded when documentation specifically identifies peritoneal mesothelioma.
Clinical signs
Clinical features vary; refer to documentation. Commonly reported findings include abdominal distention, pain, ascites, or a peritoneal mass, but you should code only what is documented.
When to use this code
Use C45.1 when the provider documents primary mesothelioma involving the peritoneum. Apply it for confirmed diagnoses in pathology, imaging-supported assessments, or discharge summaries that clearly name peritoneal mesothelioma.
If the record only says “mesothelioma” without a site, check documentation before assigning a code. Do not infer the peritoneal site from symptoms alone.
Do not use for
Do not use this code for pleural, pericardial, or unspecified mesothelioma. Also avoid it when the chart mentions abdominal cancer or ascites without a documented peritoneal mesothelioma diagnosis.
Coding tip
Verify the anatomic site in the final diagnosis; site specificity determines whether C45.1 is appropriate.