Biopsies on horses: what’s involved? *H&H VIP*

A biopsy is a sample of tissue taken from the body for closer examination, to help make an accurate diagnosis.

This can be helpful when an initial examination reveals an abnormal swelling or another sign of disease. Owners are very good at noticing external lumps and bumps during grooming, whereas internal masses are more likely to be detected by the vet during a clinical examination or when imaging a problem area.

Not every lump or lesion is something serious and in many cases, the result is reassuring to all concerned. By identifying a range of medical conditions, a biopsy will help you and your vet decide on the best treatment options — it aims to obtain a specific diagnosis, to follow the course of a disease or to confirm complete excision (removal) of a tumour.

In humans, biopsies are often performed to detect cancer. In horses, they can help diagnose certain skin conditions, such as some cysts, as well as tumours. A biopsy can also be a helpful addition to physical examination and ultrasound when trying to locate and confirm the presence of a foreign body, such as a thorn or splinter.

Samples can be taken from many body systems. A liver biopsy can be used to assess the severity of hepatitis and other types of liver disease. In the past, liver biopsies were most frequently performed to check for ragwort poisoning. Although blood tests can show that liver disease is present, a biopsy will give more information.

Muscle biopsies are another routine diagnostic procedure performed during the investigation of many different equine muscle disorders, to provide more information than can be obtained from blood tests.

How it works

There are different types of biopsy, but nearly all involve the use of a small, sharp, sterile surgical instrument to remove a tiny piece of tissue:

• Needle biopsy: the most common procedure, in which a needle is used to sample suspicious tissue. Some biopsy needles have a spring-loaded cutting device within a wider-bored needle.
• Fine needle aspiration: used to withdraw cells or fluid. This is simple to perform but interpretation of the results can be difficult, requiring an expert cytologist to examine the sample.
• Punch biopsy: taken to investigate a skin condition, using an instrument that punches out a cylindrical sample of skin tissue — rather like a tiny pastry cutter.
• Ultrasound-guided biopsy: an ultrasound scanner helps a vet direct the biopsy needle into the lesion.
• Excisional biopsy: the entire lump or suspicious area is removed, together with a margin of normal tissue. This is performed either when a lesion is small or is likely to be adversely affected by a partial biopsy — such as a tumour, which may be disseminated (spread) if cut into. A sarcoid, for example, is better removed in its entirety, usually with a special laser device, before a sample of it is checked.
• Surgical biopsy: open or laparoscopic (keyhole) surgery may be necessary to sample hard-to-reach tissues.
• Impression smears: cells may be picked up by wiping a microscope slide or swab across the surface of a lesion. The surface is often covered with contaminated material and dried tissue, however, so the sample won’t reveal much about what’s going on inside.

Specimens are checked in a variety of ways; most commonly, a pathologist will examine tiny sections under a microscope. By noting the type, shape and internal activity of the tissue cells, a specific diagnosis may be possible in certain cases.

Special stains are sometimes used on the tissue sampled to show up particular disease processes, or cultures are performed to identify bacteria or fungi. Viruses can be detected with electron microscopy or other complex tests.

One advantage of a biopsy sample, preserved as a tiny section on a microscope slide, is that it is always possible to review it at a later date or request a second opinion, if required.

Risks and limitations

Most biopsies are low risk. However, to obtain useful information, it is crucial that the tissue samples — whether fluid or solid — are correctly handled. Depending on the condition and the analysis required, they may need to be preserved in different ways before being sent to the appropriate laboratory.

Unless a decent sample has been obtained, any laboratory will struggle to interpret it properly. A typical skin lesion that represents the active disease must be sampled, for example, not an infected area covered in ointment.

Procedure prep

A minimally invasive biopsy, such as taking samples of a skin disease, can be performed relatively easily at the yard when the lesion is first examined. A small injection of local anaesthetic, and possibly a little sedation, is all that is required.

More invasive biopsies may well require a visit to a specialised equine hospital. Removing tissue from an internal organ such as the liver or a lung is a more complex procedure, requiring imaging technology to identify the best location to take the sample.

For most of these internal biopsies, the coat will be clipped and the site aseptically prepared. A small amount of sedation and local anaesthetic are required. A spring-loaded or automated biopsy tool is used, creating a puncture wound on the flank that may not even need a stitch.

People who have liver biopsies report soreness afterwards, so painkillers are often prescribed for horses. And certain biopsies — such as an abdominal biopsy to check for equine grass sickness — will be performed under general anaesthesia.

Many skin biopsies are quite correctly taken without any clipping or surgical preparation, which may distort or alter the results. Several samples may be collected to maximise the chances of an accurate diagnosis. With a punch biopsy, suitable antiseptic treatment can be applied after the procedure when the tiny wounds are sealed with tissue glue, staples or sutures.

What’s the damage?

You can expect results to arrive in several days. Costs will vary, depending on the difficulty in taking the biopsy and the complexity of laboratory analysis (histopathology) required, but should range from around £90 for a skin biopsy to £175 for a liver biopsy with ultrasound guidance. Expect additional costs for sedation, medication and laboratory analysis.

How a biopsy found fungi

When his runny eye failed to respond to treatment, Katie Palmer’s 14.2hh gelding Jack was admitted to the Bell Equine Veterinary Clinic. A diagnosis of stromal abscesses followed — tiny pockets of infection embedded in the corneal tissue that forms the clear window at the front of the eye.

The only way to ascertain the cause and decide upon treatment was to perform a biopsy, under general anaesthetic. Jack was admitted for surgery so that the biopsy could be taken from the cornea.

The vets were looking for infection and found fungi, namely the Aspergillus species. Once the exact cause was identified by biopsy, specific treatment was selected.

“Poor Jack has really been through the mill,” says Katie’s mother, Emma Palmer, who has been nursing the pony back at home. “He is on a cocktail of medicines and wearing a hood and an eye mask.

“Apparently the immune system usually fights off Aspergillus, but Jack had a virus back in the summer and perhaps his defences were low,” added Emma. “We still don’t know whether his eye will be saved, but we’re hoping it will respond to treatment.”

Ref Horse & Hound; 20 December 2018