How to obtain the perfect biopsy

1 How to obtain the perfect biopsy

Obtaining a diagnosis is one of the most important steps in the management of the cancer patient. Obtaining a biopsy before the surgical procedure is performed is best clinical practice in the majority of cases as it provides a pre-treatment diagnosis, helps the clinician plan the surgery and can provide the owner with a more accurate prognosis. There are a number of methods of obtaining samples from the tumour and the choice is based on a number of factors including:

With the exception of diagnostic cytology, all other techniques listed in Table 1.1 involve tissue sampling and histological interpretation.


Diagnostic options

As the mass had been previously undiagnosed and had recurred, any future treatment would be dependent on an accurate diagnosis. If surgical excision was indicated, definitive surgery can then be planned. An excisional biopsy in this case would not be indicated. Options for obtaining a diagnosis, therefore, include cytological sampling, needle-core or incisional biopsy. Using a punch biopsy may not be an appropriate choice in this case due to the location of the mass in the deeper subcutaneous tissues. Therefore, in this case a fine needle aspirate was opted for initially as the procedure was the least invasive of all the biopsy options, inexpensive, easy to perform and results were made available rapidly.

To perform a fine needle aspirate the only tools required are:

The smears should be air dried and the sample should be thin enough to dry within 1 minute. The best cytology stains to use in clinical practice are the Romanowsky stains (such as Wright’s stain, Giemsa stain and May-Grünwald-Giemsa stain) as these provide clear detail of both the nuclear and cytoplasmic structures. They are relatively quick to prepare and these stains will also stain bacteria if they are present. The ‘rapid’ stain kits such as ‘Diff-Quik’ are highly useful and obviously extremely convenient but it is important to realize that these may not always stain the granules within mast cells clearly, thereby leading to potential confusion in the diagnosis. In such a situation, Toludine blue stain will identify mast cell granules. The use of Toludine blue may be especially useful in poorly differentiated mast cell tumours in which the granularity can be low.


The specimen obtained in this case was of diagnostic quality and a diagnosis of a mast cell tumour (Fig. 1.8) was made.

Mast cells tumours are classified as being a round cell tumour, which means they exfoliate as discrete round cells with clear margins and a rounded nucleus. Other tumours in the round cell category include lymphoma, histiocytoma, plasmacytoma and transmissible venereal tumour (which does not occur naturally in the UK but may theoretically be seen in imported dogs). Mast cells contain azurophilic granules in their cytoplasm which stain a crimson-purple colour with Romanowsky stains, therefore usually making their identification relatively straightforward but the number of granules present in different tumours can vary considerably depending on the tumour grade. In the hands of an experienced cytologist, aspirates can be helpful to indicate the tumour grade, as low-grade mast cell tumours usually have well-defined and uniform nuclei with a high number of granules in each cell. The more poorly differentiated the tumour is, then the fewer the number of cytoloplasmic granules there are, the more prominent the nucleoli are and the degree of variation in cell size (anisocytosis) and nuclear size (ansiokaryosis) increases. The use of silver staining of the nucleolar organizing regions (‘AgNOR staining’) can also be used to help predict the grade of a tumour on aspirate samples, thereby adding further detail and diagnostic use from a simple aspirate. However, histopathological analysis will still be required to obtain accurate grading information.

For this case a fine needle aspirate provided an accurate diagnosis although providing a definitive grade for this tumour type is not possible by cytology alone as explained above. However, by submitting the entire tumour after excision, a tumour grade can be assigned and the completeness of surgical excision evaluated. In this and similar cases, knowledge of the tumour type preoperatively allows careful surgical planning. Additionally, appropriate staging of the disease can be performed by means of thoracic radiographs, local lymph node assessment and hepatic and splenic ultrasound examination. The mass was excised with 2-cm lateral margins and one fascial plane deep and the wound deficit was repaired using a local transposition flap (Figs 1.9 and 1.10).

Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on How to obtain the perfect biopsy
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