ICD-10 Code C84.91 – Mature T/NK-cell lymphomas, unspecified, lymph nodes of head, face, and neck (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C84.91 – Mature T/NK-cell lymphomas, unspecified, lymph nodes of head, face, and neck
What it is
This code identifies a mature T-cell or natural killer cell lymphoma affecting lymph nodes in the head, face, or neck, when the subtype is not specified. Use it for a documented lymphoma diagnosis without a more precise histologic label.
Clinical signs
Findings may include enlarged lymph nodes in the head and neck region, with lymphoma confirmed by pathology or specialist evaluation. Clinical features vary; refer to documentation.
When to use this code
Use C84.91 when the record clearly states mature T/NK-cell lymphoma and the involved lymph nodes are in the head, face, or neck. It also fits when the subtype remains unspecified in the documentation. If the site or histology is more specific elsewhere in the chart, code that detail instead.
Do not use for
Do not use this code for Hodgkin lymphoma, B-cell lymphoma, or lymph node disease outside the head, face, and neck. Check documentation if the pathology report names a different lymphoma type.
Coding tip
Confirm both the lymphoma lineage and the anatomic nodal site before assigning C84.91.