One might be tempted to say that a tumor that rarely spreads to the lungs does not require thoracic radiography, but I cannot
think of any instance in a cancer patient's work-up in which looking at the thorax is unnecessary. Oncologists frequently
recommend thoracic radiography for staging cancer, especially since lung masses cannot be heard and tissues in the thorax
cannot be palpated. Even if a tumor rarely metastasizes to the lungs, it does not mean it never does; it just means it is
less likely to. Although rare, tumors such as hemangiopericytomas and mast cell tumors can metastasize and evidence of metastasis
could be present when the patient presents for initial evaluation. This metastasis may severely alter therapy recommendations.
Janean Fidel, DVM, MS, DACVR, DACVIM
Thoracic radiography may show other metastatic lesions in structures such as the ribs, vertebral bodies, heart base, or thoracic
lymph nodes. Primary lung tumors (with or without metastases) may also be identified. It is possible for patients to have
more than one kind of tumor simultaneously. In addition, a mass thought to be lying only external to the thoracic wall may
be seen inside the thoracic cavity, indicating a more serious problem than the physical examination elucidated.
Thoracic radiography may also reveal that a patient has a concurrent nonneoplastic disease. For example, lung abnormalities
due to allergic, infectious, or inflammatory conditions may be visualized and require further diagnostic tests. Although clients
may not report signs of heart disease, signs are often evident on physical examination, and, occasionally, radiographs show
that the murmur you auscultated is related to a more serious problem than initially thought. In general, we use thoracic radiography to make sure a cancer patient is free of metastasis, but we also use it to make sure
the patient is healthy enough to undergo treatment.
The most debated aspect of thoracic imaging is whether to obtain two views or three views (a right lateral, a left lateral,
and a dorsoventral or ventrodorsal). The primary reason to take three views of the chest is to detect lung nodules in areas
not seen with two views, primarily the down lung tissue that is less aerated. I rarely take three radiographic views of a
chest, but I do ask for two views even when a patient is scheduled for computed tomography (CT) because it would be unfortunate
(e.g. increased time, cost, anesthesia risk) to diagnose numerous large masses in the lungs with CT.
If I am concerned about small nodules, I am likely to recommend thoracic CT since 3-mm nodules can be accurately detected
with this imaging modality.
Thoracic radiography can be an inexpensive initial method for screening for many different problems in patients with cancer.
Never underestimate the value of thoracic radiography.
Janean Fidel, DVM, MS, DACVR (radiation oncology), DACVIM (oncology)
Department of Veterinary Clinical Sciences
College of Veterinary Medicine
Washington State University
Pullman, WA 99164