ICD-10 Code C85.21 – Mediastinal (thymic) large B-cell lymphoma, lymph nodes of head, face, and neck (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C85.21 – Mediastinal (thymic) large B-cell lymphoma, lymph nodes of head, face, and neck
What it is
This code identifies a specific large B-cell lymphoma involving mediastinal (thymic) tissue and lymph nodes of the head, face, and neck. Use it when documentation names this exact lymphoma site and subtype.
Clinical signs
Clinical features vary; refer to documentation. Commonly, you may see lymphadenopathy and mediastinal involvement confirmed by pathology, imaging, or oncology notes that specify mediastinal (thymic) large B-cell lymphoma.
When to use this code
Use this code when the provider clearly documents mediastinal (thymic) large B-cell lymphoma affecting lymph nodes of the head, face, or neck. It is appropriate for confirmed diagnoses in discharge summaries, oncology assessments, or pathology-linked records. If site or subtype is unclear, check documentation.
Do not use for
Do not use this code for unspecified non-Hodgkin lymphoma, other large B-cell lymphomas, or lymphoma without documented mediastinal and head/neck nodal involvement. If the record does not support the exact diagnosis, check documentation.
Coding tip
Code only when the exact lymphoma subtype and anatomic site are documented together; otherwise, query for clarification.