Differentials and diagnostics

Podcast: LA Masses overview  (< 9 min)

The main differentials for superficial (visible) masses in large animal species are:

Diagnosis

The first step in diagnosing a mass is starting broadly (common causes of masses) and then narrowing your differential list based on a good history and physical examination. These principles cross species.

• History of injury may point you toward abscesses, hematomas, granulomas and hernias.
• Fever is associated with abscesses and neoplasia.
• Cardinal signs of inflammation (heat, pain, swelling, redness, and loss of use)  are typically usually identifiable with abscesses and sometimes with neoplasia.

Ultrasound and other imaging studies can be useful to determine the type of tissue or cellularity of fluid, extent and size of the mass, infiltration (neoplasia) or capsules (abscesses) and to find foreign bodies. Typically the most useful diagnostic tool is fine needle aspirate – stick a needle in it. In most cases, this is safe and effective. There are exceptions! Needle sticks through contaminated regions (vagina, rectum, oral cavity, prepuce) or contaminated tissues (cellulitis) can easily create an abscess and should not be attempted.

To look at this in reverse:

• If you suspect an abscess, you should be seeing signs of inflammation and potentially a fever. The animal likely has a history of trauma. Ultrasound should show a capsule and heterogenous content.
• If you suspect neoplasia, you should be seeing signs of inflammation and potentially a fever. The animal is less likely to have a history of trauma, but there are exceptions. Ultrasound appearance can vary; some can be very solid (round cell tumors), others very expansive. Some will have a necrotic center visible on ultrasound.
• If you suspect a cyst, you should NOT see signs of inflammation  or fever. The cyst may have been present since birth. Occasionally a cyst will develop after trauma. Ultrasound should show a clear fluid and the cyst is usually fluctuant.
• If you suspect a hematoma, you should NOT see signs of inflammation or fever. The animal may or may not be painful on palpation. A history of trauma is commonly associated. Ultrasound appearance should be homogenous in the early stages.
• If you suspect a granuloma, you should NOT see signs of inflammation or fever EXCEPT for fungal granulomas (these are highly inflamed). The mass should be firm and nonpainful. Most will have grown slowly over time. Generally there is no signs of obvious trauma but there may be a prior history of trauma or infection. Ultrasound appearance should be homogenous.
• If you suspect a hernia, the mass should have been present since birth or have developed after trauma, but there are exceptions. Most of these are reducible i.e. they can be shoved back into the body cavity. You should NOT see signs of inflammation or fever unless there is an associated abscess. Calves can definitely have umbilical infections that are associated with abscessation. Ultrasound should show the gastrointestinal structure that has herniated (abomasum, intestines, omentum).

Resources

Skin diseases in horses, VCNA 31(2): 359-376, 2015 – discusses sarcoids, granulomas, lymphomas, SCC and more