Cancer in Dogs and Cats: Staging with X-Rays and Ultrasound

Staging of cancer is a process of determining where that cancer exists in the patient.  It involvesCancer in Dogs and Cats: Staging with X-Rays and Ultrasound various diagnostic tools to evaluate the patient.  Some procedures are more effective at screening particular areas of the body than others.  Each of these techniques of imaging the patient has advantages and disadvantages with respect to ability to detect lesions as well as cost and availability. This article describes the most common diagnostic tests used to screen cancer in dogs and cats: plain radiography (x-rays) and ultrasound.

Use of plain radiographs in the staging of cancer

Radiographs (often referred to as x-rays) play an important role in staging of cancer in animals.  This is due in large part to the readily available nature of the procedure along with its relatively low cost.  Radiography involves the use of x-rays to create an image of the body called a radiograph.  The most common use of radiographs in the staging of cancer in animals involves evaluation of the lungs for pulmonary metastasis and the evaluation of skeletal system.  The lungs tend to be the most common site of metastasis of many cancers and thoracic (chest) radiographs are an efficient and effective means of screening for spread of cancer to the lungs.  Three views (right and left lateral, and dorsoventral views) are recommended for the evaluation of pulmonary metastasis.  Radiographs are also useful at looking for bone lesions.  Most commonly they are used to evaluate primary bone tumors, as cancer tends to metastasize less commonly to bone than other organs such as the lungs, lymph nodes, liver and spleen.  Radiographs of the abdomen have limited use in staging animals with cancer due to superimposition of overlying structures, but do provide some information regarding the size of various organs.  If fluid is present in the thorax or abdomen, radiographs are not very useful due to loss of organ detail due to the effects of the fluid on image quality.

Use of ultrasound in the staging of cancer

Ultrasound plays an important role in staging of cancer in pets.  It is used most commonly in evaluating structures in the abdominal cavity.  It is readily available and not too expensive.  It is a painless, non-invasive procedure that can be performed without sedation or anesthesia, except in some circumstances when a biopsy is being performed.  It has largely replaced the use of radiographs to evaluate structures in the abdomen.  Abdominal ultrasound allows for an evaluation of abdominal organs for the presence of primary or metastatic cancer.  It is useful for guiding aspirates for cytology or biopsy for histological evaluation of internal organs.  It is used commonly to evaluate abdominal lymph nodes for signs of metastasis of tumors located in the hind region (tumors around the anal region and tail region) or from internal organs such as the intestinal tract.  If fluid is present in the thorax or abdomen, ultrasound is very effective at imaging those sites, unlike plain radiographs.  Ultrasound is very effective at detecting lesions in organs, but it cannot provide a definitive diagnosis.  A definitive diagnosis can only be made on tissue evaluation (cytology or histology).


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Dr Stephen Atwater

Stephen W. Atwater, DVM, MS, Diplomate ACVIM (oncology) is a board-certified veterinary oncology specialist. His professional interests include utilizing emerging therapies for difficult to treat cancers.

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