Upon submission, animals are closely examined by a veterinary pathologist for gross lesions suggestive of bovine TB. The characteristic gross lesion seen in an animal infected with bovine TB is the presence of "tubercles" within the body. A tubercle is a white nodule usually 1mm - 2cm in diameter within a lymph node or organ. Tubercles commonly occur in the thoracic cavity (chest), however they may be found in other major organs such as the liver. In cattle, bovine TB most commonly will cause lesions in the lymph nodes of an infected animal. Therefore, during necropsy, the lymph nodes, especially those associated with the head, thorax, and abdomen, are closely examined. Many factors contribute to the formation of tubercles. Consequently, an animal may be infected with bovine TB despite the absence of tubercles. Just as importantly, there are other diseases capable of causing lesions that are grossly indistinguishable from tubercles. Therefore, finding gross lesions compatible with bovine TB is not conclusive evidence that the animal is infected with the disease. Further testing is required to make a definitive diagnosis of bovine TB, and this includes histopathology, acid-fast staining of tissues, polymerase chain reaction(PCR) and culture.