ICD-10 Code D38.3 – Neoplasm of uncertain behavior of mediastinum (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code D38.3 – Neoplasm of uncertain behavior of mediastinum
What it is
D38.3 identifies a mediastinal tumor whose behavior is uncertain, meaning the pathology cannot yet be classified as clearly benign or malignant. Use it for a mass in the mediastinum when documentation supports uncertain biologic behavior.
Clinical signs
Clinical features vary; refer to documentation. Mediastinal masses may be found on imaging or after symptoms such as chest discomfort, cough, shortness of breath, or compression of nearby structures.
When to use this code
Use D38.3 when the provider documents a mediastinal neoplasm with uncertain behavior, borderline features, or indeterminate pathology. It also fits cases where biopsy or imaging suggests a neoplasm but the final behavior is not established. If the record later confirms benign or malignant behavior, code that specific diagnosis instead.
Do not use for
Do not use this code for clearly benign mediastinal tumors or for confirmed malignant neoplasms of the mediastinum. Check documentation if the mass is inflammatory, cystic, or otherwise not documented as a neoplasm.
Coding tip
Query for the exact pathology wording when the behavior is unclear, because “uncertain,” “borderline,” and “indeterminate” are not interchangeable in every record.