Fine-needle aspiration of a mandibular lymph node from a dog. Photo courtesy of Dr. Dudley McCaw

Lymph node fine-needle aspiration with cytology is a noninvasive, low-cost method for staging cancer in canine and feline patients. Carcinomas are commonly diagnosed in dogs and cats, and these neoplasms frequently metastasize to lymph nodes.

Epithelial cells are not present in the lymph nodes of healthy patients. Therefore, identification of epithelial cells within a lymph node is significant and typically indicative of metastatic disease (assuming the cells have been correctly identified and the sample was obtained appropriately).¹

In the author’s experience, it is relatively common for the initial diagnosis of malignant neoplasia to be generated from the identification of abnormal cells in the lymph node aspirate. This finding initiates the search for a primary mass if one has not already been identified. Additionally, identification of malignant neoplasia in a lymph node is extremely valuable when a primary lesion has been identified via imaging but a sample is not easily obtainable without anesthesia or more invasive sampling techniques. The following case illustrates the value of lymph node cytology for the diagnosis of malignancy when the primary tumor is not easily accessible.

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