The Tipping Point: How Venograms Make the Difference Between Success and Failure When Treating Lamin

R.F. (Ric) Redden, DVM. Venogram technique, indication and interpretation, in Proceedings. Bain Fallon Memorial Conference October 2006; 28-35.

(Watch the Digital Venogram video performed by Amy Rucker, DVM.)

Introduction

Since 1992 venograms have been used at the International Equine Podiatry Clinic to evaluate horses with lameness problems localized to the foot. This retrograde contrast study can demonstrate structural alterations of the venous as well as arterial supply within the soft tissue and bone early in the course of the disease before the effects of vascular compromise are detected radiographically.1

Venograms have proven to be a valuable tool for making specific diagnosis in horses with foot disease, injuries and diminished horn production. They have been particularly advantageous for treating laminitis as they allow us to identify structural alterations of the solar papillae, lamellar vessels, coronary plexus and terminal arch that can not be seen with other imaging techniques. This has allowed us to follow progressive deterioration of the disease in cases that otherwise might have been considered clinically stable.

Before venogram imaging, radiographs were the only images used routinely to evaluate laminitis and other foot disease syndromes. As a result, veterinarians have been limited to evaluating the significance and severity of the disease during the acute phase, meaning the greatest window of response cannot be effectively utilized. A large majority of cases with significant insult deteriorate, ultimately leaving the horse crippled or resulting in euthanasia. Venograms have added to our knowledge of laminitis and other common foot problems, in large part because for the first time we can see the structural components of the vascular supply to the horse's foot. This procedure is relatively easy, uses basic radiographic equipment and can be performed on the standing horse.

Equipment and Technique

The equipment used at IEPC is a 100/30 MinXray portable unit, asymmetric 6/12 screens, ultra detail film and a 6:1, 106 line/in grid. Several contrast mediums have been used in the past, however we have found that higher concentration produces slightly more information. Reno-60® has been the contrast of choice for the past several years. A variety of catheters have been used. The 21-gauge butterfly is easy to use, easily procured and provides a consistent means of delivering contrast.

Sedation of the horse, local analgesia of the foot and a tourniquet placed over the fetlock is required. The original venogram technique developed at IEPC was a collaboration with Dr. Chris Pollitt using his previous in vitro study model and has since been published with minor modifications.2 The imaging sequence that has been routinely used is soft tissue lateral, lateral with grid, DP with grid, DP with soft tissue detail, followed by a soft tissue lateral. The procedure is technique sensitive in large part because the sequence of film must be taken within a time frame of 45 seconds following contrast injection. Tissue contrast injected retrograde into the palmar vein is quickly absorbed into the interstitial space, significantly reducing the value of the information obtained.

The soft tissue lateral images have proven to be especially valuable because they allow us to see coronary papillae, circumflex vessels, solar papillae and acute and chronic lamellar leakage. The grid used with the higher MAS has proven to be a reliable means of imaging the terminal arch and its tributaries. The soft tissue and hard penetration grid views were implemented to allow us to evaluate normal vascular anatomy and structural alterations within the soft tissues and bone. The soft DP view allows us to evaluate the medial and lateral coronary supply and the medial and lateral circumflex network. The grid view offers further information concerning the terminal arch and tributaries. The soft tissue lateral view taken at the end of the sequence was implemented to allow for adequate filling time required to consistently image lamellar leakage, decreasing the possibility of missing significant structural alterations. More specific beam selection is required to image vascular lesions associated with White Line Disease and Keratomas. Techniques for imaging the equine foot will continue to evolve with increasing experience performing venograms.

Tourniquet failure and perivascular injections are frequent complications encountered in the infancy of procedural skill development. Both complications result in underperfusion and can lead to grossly inaccurate interpretation and misuse of the information. Technique underperfusion should not be confused with stark loss of contrast caused by pathological vascular compromise. The distinction should be well understood before deciding the fate of a laminitic horse based on the information gathered from this valuable tool.