Several lymph nodes are scattered throughout the body. They are an integral part of the immune system and help fight infections. While examining your pet, your vet will assess the size and the texture of the lymph nodes. Lymph nodes get enlarged if there is the presence of any viral, bacterial, fungal infection or tumor in the body. The infection causes inflammation of the lymph nodes and they become swollen. If your vet finds an enlarged lymph node, he may aspirate a small sample of the lymph node for evaluation. After evaluating the sample under the microscope, the presence of any kind of tumor is ruled out. If the aspirated sample is not enough to make a definitive diagnosis, a biopsy of the lymph node may be required.