Many clients are confused or misspeak when mentioning their pet had a “biopsy” when in reality it was perhaps a skin scraping, culture, or cytology. So let’s get it straight!

First of all, ANY SKIN LUMP OR BUMP should have a cytology performed! It shouldn’t be “watched” or felt and excused as benign because it “moves” or hasn’t “gotten any bigger”. ANY AND ALL SKIN MASSES NEED TO HAVE A FNA (fine needle aspirate) or impression smear to see what cells are contained within the mass. Either of these two procedures are referred to as a “cytology”. Once a sterile needle is inserted into the mass, cells are extracted then put onto a slide, stained, and the veterinarian or lab examines the cells to see if they are benign or malignant. Alternatively, an impression smear is performed by slightly “roughing up” the top of the skin lesion then pressing a microscope slide gently to press out some cells onto the slide. The slide is air dried then stained and looked at under the microscope. These procedures are referred to as a “cytology” where cells within the mass are examined under the microscope. It is a quick process and most often prevents the pet from having surgery to remove what may be a benign lesion. Also it may offer peace of mind in a matter of minutes when there is concern for malignancy of a skin lesion. If the cells are malignant such as in a mast cell tumor, a wide surgical margin of excision is needed. If the veterinarian knows BEFORE the surgery what they are removing, they can perform a wide excision to completely remove any remnants of the tumor. If your veterinarian does not feel comfortable reading the cytology slide in the office, he/she can send it to the lab and have the pathologist read it. Sometimes a cytology isn’t helpful in identifying the skin mass either due to poor slide preparation, inadequate cells or staining, or to be completely sure, deeper cells may be needed to identify the mass in which case, a biopsy is performed.

A biopsy, particularly of skin masses, most often can be performed using a local anesthetic. However if the skin mass is on the face, ears, or legs, a mild sedative may be necessary. A skin biopsy of a mass is performed when the previously performed cytology is questionable for malignancy, to grade a malignancy to better predict prognosis, or to completely remove the skin mass resulting in a “cure”. A biopsy looks at the deeper layers of the cells and orientation of the tissue and most often yields a final diagnosis and lets the veterinarian know whether the lesion has been completely removed (“clean margins”) as is needed in some skin masses.

A skin culture and sensitivity (C&S) is performed of a suspected infected area to identify which infectious organism is present. Cultures are performed to determine if bacteria, fungi, or mycobacteria/Nocardia are present and then a sensitivity on those infectious organisms is done to determine which antibiotic will work best. Cultures are not normally performed in routine bacterial skin infections unless the pet is not responding to the current antibiotic. Fungal cultures are commonly done in kittens or pets from shelters or hunting dogs to determine if dermatophytes (“ringworm”) is present. Yorkshire terriers and Persian cats appear to be most susceptible to “ringworm”. Cultures for deep seated organisms such as in draining lesions of mycobacteria or Nocardia are necessary as those organisms are slow growing and require months of antibiotics so sensitivity is important to determine which antibiotic to use. Your veterinarian may also perform a culture and sensitivity of ear infections (otitis) as many times there is a mixed population of gram + and gram – bacteria. If rod bacteria is seen on cytology of an ear swab, that is usually followed up by a culture and sensitivity. Rod bacteria such as pseudomonas or proteus can be damaging to an ear canal if not treated with an appropriate antibiotic.

I hope the above explanations can help educate you as a pet owner to further understand the differences between cytology, biopsy, and culture/sensitivity. Just remember: ALL SKIN MASSES NEED TO HAVE A CYTOLOGY PERFORMED ON THEM!