A fine needle aspiration of the spleen in dogs is often taken when dogs undergo an abdominal ultrasound. The aspiration usually takes place when the veterinarian performing the ultrasound finds enlargement of the spleen or the presence of suspicious masses. Fortunately, fine needle aspiration is well-tolerated by dogs, even when this means penetrating organs such as the liver or spleen. Often, this can be done without anesthesia or sedation as part of the ultrasound exam in calm, non-fractious dogs. Following is some information specifically pertaining fine needle aspiration in dogs along with info on its accuracy.
Fine Needle Aspiration in Dogs
Fine needle aspiration is a simple procedure carried out for diagnostic purposes. As its name implies, the needle used is very thin making the procedure more comfortable.
For idea of comparison, the needle used for fine needle aspiration is 20 to 25 gauge, while the needle for microchipping a dog is very large, around 12 to 15 gauge. The larger the number, the finer the needle.
On top of being fine, the needle used for aspiration is hollow so that it can be inserted into an organ or mass for collecting a sample of cells.
The collected cells are then sent to a pathologist for evaluation. A pathologist is a professional who is specifically trained for examining cells under a microscope.
While a fine needle aspiration offers the advantage of being easy, relatively painless and minimally-invasive, its main drawback is the fact that cancer cells may be missed.
For sake of comparison, it is sort of like getting an apple pie, covering it with a tea towel (so that you don't know exactly what type of pie it is) inserting a straw and sucking up a sample. There are chances you might suck up crust, apples and sauce and therefore you'll know you are dealing with an apple pie. If, however, you just suck up crust and just some sauce, you may not know exactly what type of pie you are sampling!
The same applies to lumps – they may contain different areas within and you have to be lucky in sucking up the right ingredients so that you can correctly identify them, explains veterinarian Dr. Fiona.
Fine Needle Aspiration of the Spleen in Dogs
Abdominal fine needle aspiration of the spleen in dogs is a safe and reliable method to evaluate dogs suffering from an enlarged spleen. Manual restraint or light sedation may be needed to obtain the aspirate.
The area to be aspirated is surgically prepared and the spleen is manually isolated. The needle penetrates the skin, enters the abdominal wall and reaches the spleen. The sample of the cells collected are then sent out to a pathologist.
Many dog owners wonder whether it is safe to obtain a fine needle aspiration from a vascular organ that is prone to bleeding such as the spleen.
According to the Textbook of Veterinary Internal Medicine, in 28 dogs and 5 cats who had fine needle aspirations of their spleen done, no complications were encountered even in dogs suffering from bleeding disorders.
However, to play it safe veterinarians will often run a blood coagulation profile prior just to ensure the blood can properly clot before a fine needle aspiration of the spleen is done.
A List of Possible Differentials
As per the apple pie example cited above, getting "diagnostic" getting samples of the spleen can be challenging because the spleen is tough to aspirate and get good results.
There are several potential causes of an enlarged spleen or the presence of a mass on the spleen in dogs. A list of potential differentials include both malignant and benign disease processes.
Hemangiosarcoma (spleen cancer), lymphoma, liposarcoma, leiomyosarcoma, malignant fibrous histiocytoma (a.k.a. fibrohistiocytic nodules) and mast cell tumors are some example of malignant growths.
Benign possibilities include hemangioma, splenic hematoma, regenerative hyperplasia, hematoma (blood leakage into the spleen), and myelolipoma (just fatty deposits). Among these, splenic hematoma and nodular hyperplasia are the most common non-cancerous lesions found in the spleen and they account for 20 to 41 percent of all lesions found on the spleen. Removing these surgically is curative.
It's unfortunate that hemangiosarcoma is one of the most common findings in older dogs presenting with anemia, weakness, lack of appetite and collapse. However, a fine needle aspirate is not always successful in diagnosis this form of cancer or telling it apart from other growths.
For instance, in large lesions with lots of bleeding, such as a malignant hemangiosarcomas or benign hematomas, which comprise an abundance of red blood cells, it can be impossible for the pathologist to tell these two tumors apart, explains veterinarian Allison L Zwingenberger.
On a lighter note, elderly dogs are prone to develop the presence of benign age-related nodules on the spleen which just consist of extra tissue (nodular hyperplasia).
"Primary neoplasms of the spleen are relatively commonly encountered in dogs. Of splenic lesions in dogs, approximately 50% are likely to be neoplastic... Hemangiosarcoma is the most common neoplasm of the canine spleen."~ Harry W. Boothe, DVM, MS, DACVS