Why do we perform cytology & histopathology on lumps and bumps?

Occasionally us Veterinarians might be able to give a strong indication of whether a lump is something to worry about and what it might be, based just on a physical exam. But most of the time the decision requires some level of pathology and usually histopathology is required for a definitive diagnosis.

There is a myriad of conditions, such as infection, trauma and cancers, that can present as a soft-tissue mass. Without appropriate pathology procedures (cytology or histopathology) the correct diagnosis is often delayed or it might be missed altogether which may ultimately lead to inappropriate treatment and jeopardise the health of your pet.

Soft-tissue tumors are very common and they often are presented an asymptomatic mass.

On a regular basis our clients tell us “it’s been there for years and it hasn’t changed” or “He/she is not bothered by it”. Unfortunately being there for a long time or the pet not being bothered by it doesn’t mean that the mass is not harmful. If fact some intermediate grade masses may change behaviour with time and become aggressive malignant tumors.

So as a pet owner what do I do?

Come and see you veterinarian they will probably start with a fine needle aspirate to perform cytology or they may suggest a biopsy and for the sample to be sent to an external laboratory for Histopathology.

Fine Needle Aspirates (FNA) involve the passing of a needle into a mass, the veterinarian will draw back on the syringe and a small sample will be aspirated into the needle. Usually this will contain plenty of cells to make a suggestive diagnosis. An FNA can help your veterinarian decide if a lump needs to come off and help determine if wide surgical margins are necessary. It is common for some tumors to have tentacle like projections or cells in the periphery that are not visible with the naked eye. So to prevent missing these potentially harmful cells the surgeon will make an incision considerably larger (often 2-3cm on all sides) than the primary tumor. An FNA is often very helpful in determining if a mass needs to come off or if large margins are required.

Other forms of cytology include

· Impression smear. A glass microscope slide is pressed against an ulcerated lesion. Surface materials are collected and stained then examined under a microscope.

· Lavage. This technique is used to collect cells from internal surfaces such as the nasal cavity, trachea, or lung. Sterile fluid is flushed into the cavity and then suctioned back out collecting cells and fluid for examination under the microscope.

· Skin scraping. This technique removes cells from the surface of the skin and is often used to diagnose flaky, or ulcerated skin).

· Swabs. Sterile cotton-tipped swabs are used to collect discharge and cells from moist surfaces such as the eyes, nose, mouth, or vagina.

Sometimes circumstances warrant a more exact diagnosis; if we are unsure based off our cytological findings, if the client wants a more exact prognosis or if chemotherapy is an option. Histopathology is the next step in obtaining a more accurate diagnosis. It involves taking a tissue sample (biopsy) and sending it to an external laboratory. The biopsy is then processed for histopathology and is examined under a microscope. There are several types of biopsy the most common are:

· excision biopsy - the entire mass is removed and sent to the laboratory.

· wedge biopsy - a small wedge or slice of tissue is removed from the tumor/mass

· punch biopsy - a small, circular piece of tissue is removed using a biopsy punch,

Once the biopsy sample is collected it is placed in buffered formalin to preserve it and sent to the external laboratory. The tissue is then prepared through a process called histology by preserving, thinly slicing or sectioning, and staining the sample with dyes. Once prepared, the sections are examined under the microscope by a veterinary pathologist. Histopathology focuses on the architecture of the tissue and provides more information about the tissue than cytology. In addition to a definitive diagnosis the veterinary pathologist is often able to stage or classify a tumor, providing useful information for prognosis or the need for adjuvant therapies such as chemotherapy or Radiation therapy. This can help to predict the behaviour of the tumour (ie. level of aggression and risk of spread) and therefore the prognosis so that you and the vet can make the most informed decisions about the treatment of your pet.