Cytology is a great way to generate a preliminary understanding of a disease process that requires cell evaluation to be identified. Commonly, cytology helps differentiate between infectious and neoplastic states. Fine needle aspiration is the best method to obtain a sample for cytology. No matter what the species, the technique is conserved.
But can we use this diagnostic technique the same in birds as we can in mammals? Let's think through three cases to find out.
In front of you is Stanley, an approximate 30-year-old, actively reproductive, female amazon with a mass protruding from her right lateral flank. On palpation, it is a movable, 5mm, subcutaneous soft tissue mass. You also notice that this patient has increased adipose stores, but her pectoral muscle mass is lower than normal as the blade of the keel is palpable. The owner describes Stanley as a seed junkie and has never eaten a veggie in her life. In fact, salmon and beans are her favorite treats.
You are discussing what this mass could be with the owner and wonder, “How do I figure out why this mass exists?” Your internal monologue tells you to consider performing a fine needle aspiration, but you are worried it may be non-diagnostic. You are straightforward in your conversation with the owner about this. You then consider if an anesthetic procedure to obtain a biopsy should be used instead.
Since this is clearly a complex case, let’s break it down by outlining our problem list.
Focusing on this mass first, what do we think it could be? Based on the patient’s presentation, a lipoma, granuloma, xanthoma, lymphoma, or carcinoma would be fair to put on the differential list.1,2 An FNA could be done, but what could we learn, and what could we miss?
For this patient, we would be able to rule out a lipoma and lymphoma and possibly ID a xanthoma; however, we may miss carcinomas or granulomas. We know that a biopsy can give us an answer, but is it safe to put this patient under anesthesia right now, or should we further define this bird’s health?
Birds are infamous for harboring occult disease, and our patient’s history and physical exam findings are a giant caution sign. If it’s not screaming in your mind already, this patient is at high risk for cardiovascular disease. You discuss this with the owner and agree to further assess this patient’s health and potential anesthetic candidacy. To achieve this, you move forward with obtaining well-positioned right lateral and VD radiographs under mild sedation along with hematology and biochemistry data.
Radiographically, you identify multifocal mineralization of the descending aorta, increased soft tissue opacity of the aorta and brachycephalic trunks, and cardiomegaly. Your suspicions are confirmed, and based on these findings, you conclude that this patient has atherosclerosis and likely cardiac abnormalities. This diagnosis results in a significantly increased risk under anesthesia.
In speaking with the owner again, despite the benefits of biopsy, the increased anesthetic risk has shifted the way we approach this case. Plans to perform an FNA and submit this sample for cytologic review are agreed upon despite the known limitations. A sample is obtained, and the pathologist’s review confirms that this mass is a lipoma.
In this instance, it was worth the pursuit of FNA and cytology to avoid a high-risk investigative procedure. Next on the list will be to perform an echo and in a stepwise process institute medical management and dietary improvements in an effort to slow the progression of Stanley’s cardiovascular disease.
Benji, a 15-year-old male cockatiel, presents to you for a mass on his wing. The owner first noted it a few months ago, but recently it has enlarged, and now he is picking at it. It is firmly attached to the underlying tissue and there are multifocal regions that appear cystic and possibly blood-filled. Due to its highly accessible location, you consider getting a quick FNA, but in the past, you have attempted this technique and it’s been non-diagnostic. You think, what could I do differently this time?
The most common masses of the parrot wing are xanthomas, metastatic adenocarcinomas, hemangiosarcomas, lipomas, and carcinomas. We could rule in/ out a lipoma as a potential diagnosis with this first-line test, and this is where you start. Unfortunately, as previously experienced, the slide resembles a peripheral blood smear. Due to the lack of abnormal cells on the slide, there is heightened concern for poorly exfoliative neoplasia like a sarcoma or carcinoma-based processes, which require histopathology for definitive diagnosis.
Where do we go from here? Should we go directly to surgery for a biopsy or mass removal? Can the mass even be removed? If your spidey sense said, “No way! Let's work this patient up.” you are right on point.
The first thing we need to know is if this is a primary lesion or a metastatic one. Radiographs or CT imaging can help us answer this question. This is especially important since we know that air sac adenocarcinomas can spread through the pneumatic medullary cavity of the humerus and have the potential to present as a wing mass2.
A CT is performed and not only is the lesion on the wing evident, but there is also a soft tissue opacity along the pneumatic medullary cavity of the humerus and into the right lung and cranial thoracic air sac.
Based on all of this information, the top differential for the wing mass is a metastatic lesion from an air sac adenocarcinoma. Since this isn’t able to be cured via surgery, radiation, or chemotherapy3,4, the owner elects for palliative therapy instead due to the advanced stage of this disease process.
Had we jumped right to surgical intervention here, Benji would have been a challenging anesthetic candidate due to the existing respiratory compromise. If he survived the procedure, it is likely that the site would never have properly healed. Cytology helped us understand that a deeper understanding of this mass’s origin was needed to know what was right for Benji.
Meredith, a 1.5 year-old female leghorn hen presented for lethargy, reduced egg production for 3 months, and a pale comb. Upon examination, you palpate a severely distended coelom and a palpable fluid wave. She was reluctant to stand and exhibited exercise intolerance. You know that this patient will likely feel much better with analgesia and a coelomicentesis but are unsure of why she is in this position in the first place.
Butorphanol is provided since a kappa agonist is the opioid of choice for this species and a very brief ultrasound highlights a large volume of fluid and what appears to be an impacted oviduct. You provide flow-by oxygen and remove 700mL of opaque straw-colored fluid. During the procedure, you save some for culture and some for further fluid analysis just in case. Your patient feels substantially better and is breathing more comfortably. She even starts to preen.
Based on the ultrasonographic findings5,6, you know that an oviductal impaction is present and likely an inciting factor for fluid build-up, but you wonder what the next steps are. Could the fluid sample help in any way? Since oviductal impactions can occur for a multitude of reasons, you elect to submit the fluid for cytologic evaluation and for culture. Although you question the diagnostic benefit of fluid analysis you figure that this can help us rule in neoplastic disease and determine if this is a septic effusion. However, because not all neoplasias exfoliate cells well, not finding neoplastic cells in the effusion does not rule it out. Ultimately, you know that salpingohysterectomy is likely to be indicated, however, this additional cytologic information could possibly help the expectations associated with this intervention and properly prepare the client and patient.
Cytology in all species can be thought of as a preview of a movie. In some scenarios, the preview is a perfect precursor to what unfolds in the movie. However, in other scenarios, the preview is nothing like the movie, and often there are mixed feelings about the experience. This is exactly the case with cytologic evaluation.
As we can see from Stanley, Benji, and Meredith’s cases, cytology has a place in avian medicine, but it is not perfect. By pausing and making thoughtful decisions at each stage of the diagnostic process, each of these patients were able to avoid unnecessary risk all while obtaining the right type of care and diagnosis; with cytology playing a different and very important part in each.
By setting the right expectations for cytology evaluation, we were able to use this tool to our benefit.