Potential applications of interventional radiology in veterinary medicine

A 20-year scoping review of the veterinary interventional radiology and interventional endoscopy literature (2000-2019)

BACKGROUND

Interventional radiology (IR) and interventional endoscopy (IE) have broad potential for minimally invasive therapy in veterinary patients, but the scope of original peer-reviewed veterinary IR/IE research publications has not been described.

OBJECTIVES

Catalogue published applications and indications for noncardiac therapeutic IR/IE in animals and describe type and quality of veterinary IR/IE research over 20 years.

METHODS

Highly-cited veterinary journals were searched to identify articles published 2000 to 2019 involving therapeutic IR/IE applications for clinical veterinary patients. Articles were assigned a level of evidence (LOE) according to published standards. Authorship, animal data, study design, and interventions were described. Change in publication rate, study size, and LOE of IR/IE articles over time was analyzed.

RESULTS

One hundred fifty-nine of 15 512 (1%) articles were eligible, including 2972 animals. All studies were low LOE and 43% were case reports with ≤5 animals. Number of IR/IE articles per year (P < .001), proportion of journals' articles pertaining to IR/IE (P = .02), and study size (P = .04) all increased over time, but LOE (P = .07) did not. Common target body systems were urinary (40%), digestive (23%) respiratory (20%), and vascular (13%). Common indications were nonvascular luminal obstructions (47%), object retrieval (14%), and congenital anomalies (13%). Most procedures involved indwelling medical devices or embolic agents, whereas tissue resection and other procedures were less common. Procedures utilized fluoroscopy (43%), endoscopy (33%), ultrasound (8%), digital radiography (1%), or fluoroscopy in combination with other modalities (16%).

CONCLUSIONS

Treatments involving IR/IE have wide applicability in veterinary medicine but large, rigorous, and comparative studies describing these procedures are lacking.

Arterial malformations leading to bilateral spontaneous renal hemorrhage in a dog

OBJECTIVE

To describe the clinical presentation, diagnostic imaging, management, and follow-up of a dog that presented with sequential, bilateral, spontaneous, subcapsular and perirenal hemorrhage (Wunderlich syndrome) due to bilateral renal arterial malformations.

CASE SUMMARY

A 9-year-old intact male Field Spaniel presented for acute onset abdominal pain following a possible syncopal episode. Abdominal ultrasonography, contrast-enhanced ultrasound, and computed tomography (CT) revealed right-sided perirenal hemorrhage that extended into the peritoneum. The dog was discharged following stabilization with analgesia, fluid therapy, and tranexamic acid. One month later, the patient presented with identical clinical signs. A CT scan at this stage revealed bilateral kidney infarcts with new left-sided perirenal hemorrhage. Abdominal ultrasound and contrast-enhanced ultrasound were repeated and showed similar findings. Follow up with four-dimensional CT angiography revealed bilateral renal arterial malformations, likely causing spontaneous renal hemorrhage and secondary subcapsular hematomas , retroperitoneal and peritoneal hemorrhage.

UNIQUE INFORMATION PROVIDED

This is the first reported case of both bilateral renal arterial malformations and bilateral spontaneous subcapsular and perirenal hemorrhage in the absence of neoplasia, coagulopathy, or trauma in a dog. Advanced imaging modalities, including selective angiography, were required to diagnose this condition successfully. Arterial malformations should be considered as a differential diagnosis in cases of hemoretroperitoneum. Nephrectomy due to perirenal hemorrhage should be cautiously considered, especially in the absence of angiography, because of the sequential bilateral nature of this case. Conservative management in this case resulted in a good long-term outcome 10 months later.

Self-reported radiation safety behaviors among veterinary specialists and residents performing fluoroscopic procedures on small animals

OBJECTIVE

To describe the radiation safety behaviors of veterinary specialists performing small animal fluoroscopic procedures and examine potential risk factors for these behaviors, including knowledge of radiation risk and training regarding machine operating parameters.

SAMPLE

197 veterinary specialists and residents in training.

PROCEDURES

An electronic questionnaire was distributed to members of the American Colleges of Veterinary Internal Medicine (subspecialties of cardiology and small animal internal medicine), Veterinary Radiology, and Veterinary Surgery.

RESULTS

The overall survey response rate was 6% (240/4,274 email recipients). Of the 240 respondents, 197 (82%) had operated an x-ray unit for a small animal fluoroscopic procedure in the preceding year and fully completed the questionnaire. More than 95% of respondents believed that radiation causes cancer, yet approximately 60% of respondents never wore hand or eye protection during fluoroscopic procedures, and 28% never adjusted the fluoroscopy machine operating parameters for the purpose of reducing their radiation dose. The most common reasons for not wearing eye shielding included no requirement to wear eyeglasses, poor fit, discomfort, and interference of eyeglasses with task performance. Respondents who had received training regarding machine operating parameters adjusted those parameters to reduce their radiation dose during procedures significantly more frequently than did respondents who had not received training.

CONCLUSIONS AND CLINICAL RELEVANCE

On the basis of the self-reported suboptimal radiation safety practices among veterinary fluoroscopy users, we recommend formal incorporation of radiation safety education into residency training programs. All fluoroscopy machine operators should be trained regarding the machine operating parameters that can be adjusted to reduce occupational radiation exposure.

Comparison of short-, intermediate-, and long-term results between dogs with tracheal collapse that underwent multimodal medical management alone and those that underwent tracheal endoluminal stent placement

OBJECTIVE

To compare short-, intermediate-, and long-term results between dogs with tracheal collapse (TC) that received multimodal medical management only and those that underwent tracheal endoluminal stent placement.

ANIMALS

159 dogs with TC that underwent medical management only (MM group; n = 84) or were surgically managed by stent placement (SM group; 75).

PROCEDURES

Medical records of dogs with TC that underwent medical management only or stent placement at a referral hospital between September 1, 2009, and August 1, 2018, were reviewed. Data regarding signalment, information relevant to TC, and outcome were extracted from the records and aggregated into short-, intermediate-, and long-term follow-up periods for analysis. Descriptive data and median survival times (MSTs) were compared between the MM and SM groups.

RESULTS

Clinical signs of dogs in the MM group generally improved during the short term but regressed and worsened over time. The proportion of dogs with malformation-type TC that underwent stent placement (38/43 [88%]) was significantly greater than the proportion of dogs with traditional-type TC that underwent stent placement (37/107 [35%]). The MST from TC diagnosis was 3.7 years for the MM group and 5.2 years for the SM group. For dogs with severe disease, the MST was 12 days for medically managed dogs and 1,338 days for dogs that underwent stent placement.

CONCLUSIONS AND CLINICAL RELEVANCE

Multimodal medical management alleviated clinical signs for months to years in dogs with mild to moderate TC disease, but stent placement should be considered for dogs with severe disease.

New tracheal stainless steel stent pilot study: twelve month follow-up in a rabbit model

Background

Canine tracheal collapse is a complex airway pathology without promising treatment results. Currently nitinol stents are the best surgical option; however, some professionals are doubting if stent placement is the best option due to the associated complications.

Objective

Determine the technical feasibility, safety, and long-term follow-up after the implantation of a new tracheal stent designed for canine tracheal collapse.

Methods

Thirteen healthy, adult female New Zealander rabbits were involved in this pilot study.A new intra-tracheal device (Reference number 902711 patent registered as CasMin-Twine) was implanted in ten animals. Deployment was performed under general anesthesia, making a puncture incision via a 21 Gauge needle in the intra-tracheal space where the stent was introduced with a screwing process. The device was fixed to the tracheal wall with a non-absorbable suture. Computerized Tomography (CT) and an endoscopy to study structural abnormalities were performed after 30, 90 and 365 days after stent placement.

Results

Technical and clinical success was 100%. There was no significant change in behavior or respiratory disorders. CT studies showed no significant alterations. After the 30 days, 60% of the animals showed partial endothelization in the endoscopy study, and only one animal still presented partial endothelization after 12 months. Mucus accumulation was only present in 40% of cases and classified as low, without respiratory consequences. Only one animal presented a single granuloma at caudal stent tip.

Conclusions

This new tracheal stent (CasMin-Twine) is an effective and safe procedure with promising results, and also shows the possibility of removing the device after endothelization has been produced. New studies should be carried out to evaluate the effectiveness in patients with tracheomalacia.

Clinical Significance/Impact

This new product can give veterinarians a new option of treatment for this complicated pathology. Minimizing specific equipment for its deployment, CasMin-Twine will be more accessible for all professionals.

Radiation exposure of dogs and cats undergoing fluoroscopic procedures and for operators performing those procedures

OBJECTIVE

To evaluate radiation exposure of dogs and cats undergoing procedures requiring intraoperative fluoroscopy and for operators performing those procedures.

SAMPLE

360 fluoroscopic procedures performed at 2 academic institutions between 2012 and 2015.

PROCEDURES

Fluoroscopic procedures were classified as vascular, urinary, respiratory, cardiac, gastrointestinal, and orthopedic. Fluoroscopy operators were classified as interventional radiology-trained clinicians, orthopedic surgeons, soft tissue surgeons, internists, and cardiologists. Total radiation exposure in milligrays and total fluoroscopy time in minutes were obtained from dose reports for 4 C-arm units. Kruskal-Wallis equality of populations rank tests and Dunn pairwise comparisons were used to compare differences in time and exposure among procedures and operators.

RESULTS

Fluoroscopy time (median, 35.80 minutes; range, 0.60 to 84.70 minutes) was significantly greater and radiation exposure (median, 137.00 mGy; range, 3.00 to 617.51 mGy) was significantly higher for vascular procedures than for other procedures. Median total radiation exposure was significantly higher for procedures performed by interventional radiology-trained clinicians (16.10 mGy; range, 0.44 to 617.50 mGy), cardiologists (25.82 mGy; range, 0.33 to 287.45 mGy), and internists (25.24 mGy; range, 3.58 to 185.79 mGy).

CONCLUSIONS AND CLINICAL RELEVANCE

Vascular fluoroscopic procedures were associated with significantly longer fluoroscopy time and higher radiation exposure than were other evaluated fluoroscopic procedures. Future studies should focus on quantitative radiation monitoring for patients and operators, importance of operator training, intraoperative safety measures, and protocols for postoperative monitoring of patients.

Interventional Equipment and Radiation Safety

Interventional radiology in veterinary medicine was adapted from techniques developed in human medicine, and has a variety of applications to treat disease in multiple body systems. Fluoroscopy is required for almost all interventional procedures, requiring knowledge of proper safety techniques for working with ionizing radiation. There are a wide variety of catheters, wires, sheaths, stents, and embolics used in veterinary medicine. Familiarity with their indications and sizing compatibility is essential for procedural success.

Immediate, short-, and long-term changes in tracheal stent diameter, length, and positioning after placement in dogs with tracheal collapse syndrome

BACKGROUND

Intraluminal tracheal stenting is a minimally invasive procedure shown to have variable degrees of success in managing clinical signs associated with tracheal collapse syndrome (CTCS) in dogs.

OBJECTIVES

Identify immediate post-stent changes in tracheal diameter, determine the extent of stent migration, and stent shortening after stent placement in the immediate-, short-, and long-term periods, and evaluate inter-observer reliability of radiographic measurements.

ANIMALS

Fifty client-owned dogs.

METHODS

Retrospective study in which medical records were reviewed in dogs with CTCS treated with an intraluminal tracheal stent. Data collected included signalment, location, and type of collapse, stent diameter and length, and post-stent placement radiographic follow-up times. Radiographs were used to obtain pre-stent tracheal measurements and post-stent placement measurements.

RESULTS

Immediate mean percentage change was 5.14%, 5.49%, and 21.64% for cervical, thoracic inlet, and intra-thoracic tracheal diameters, respectively. Ultimate mean follow-up time was 446 days, with mean percentage change of 2.55%, 15.09%, and 8.65% for cervical, thoracic inlet, and intra-thoracic tracheal diameters, respectively. Initial mean stent length was 26.72% higher than nominal length and ultimate long-term tracheal mean stent shortening was only 9.90%. No significant stent migration was identified in the immediate, short-, or long-term periods. Good inter-observer agreement of radiographic measurements was found among observers of variable experience level.

CONCLUSIONS AND CLINICAL IMPORTANCE

Use of an intraluminal tracheal stent for CTCS is associated with minimal stent shortening with no clinically relevant stent migration after fluoroscopic placement. Precise stent sizing and placement techniques likely play important roles in avoiding these reported complications.

Fluoroscopic Estimation of Thoracic Dimensional Changes in Healthy Dogs

Background

Current methods available for assessing alterations in lung mechanics require sophisticated equipment and are of limited availability. A method that could assess lung area change with respiration might be a clinically useful surrogate for assessing lung compliance.

Objective

To use fluoroscopy to determine percent change in thoracic and lung areas in healthy dogs.

Animals

Forty‐four client‐owned dogs with no evidence of respiratory disease.

Methods

Prospective study. Resting respiration was recorded fluoroscopically, and peak inspiratory and expiratory frames were captured for 3 typical respiratory cycles. The number of intrathoracic pixels in the entire thoracic cavity was measured for both inspiration and expiration, and the average percent change in intrathoracic area was determined for each dog. This process was repeated by a hemithorax measurement of lung area that excluded the mediastinum and cardiac silhouette. Proposed reference ranges (and 95% confidence intervals [CI]) were computed by a nonparametric percentile distribution.

Results

Median percent change in thoracic dimension for the total thorax measurement was 12.5% (CI, 8.9–24.0%). Median percent change for the hemithorax measurement was significantly (P < 0.001) larger (20.8%, CI, 14.3–37.6%). Both measurement techniques were correlated with body weight but not with age, sex, thoracic conformation, body condition score (BCS), or breed.

Conclusions and Clinical Importance

Fluoroscopy allows a noninvasive and repeatable measure of lung area changes during respiration that must be corrected for body weight. Additional studies in dogs with respiratory diseases are needed to determine its utility in detecting clinically useful alterations in lung area changes.

Balloon occlusion of the caudal vena cava for vascular contrast studies as an aid to intravascular coil embolisation for the treatment of intrahepatic portosystemic shunts in three dogs

CASE REPORT

Three dogs were treated with fluoroscopically guided coil embolisation of intrahepatic portosystemic shunts. A large-diameter vascular occlusion balloon was used to improve the vascular contrast studies required to perform this procedure. This technique improved identification of vascular structures and allowed completion of the procedures without the need for digital subtraction angiography.

CLINICAL SIGNIFICANCE

Interventional radiological procedures are an emerging area of veterinary medicine and procedural modifications may help expand their use in clinical practice.

Cystourethroscopy in the cat: What do you need? When do you need it? How do you do it?

PRACTICAL RELEVANCE

Diagnostic and therapeutic cystourethroscopy has become very popular in the diagnosis and treatment of canine lower and upper urinary tract disease in the past 5-7 years. As expertise is expanding, the use of similar techniques in feline patients is growing.

OUTLINE

This is a brief overview of the indications, equipment needed and procedure for performing cystourethroscopy in feline patients. The principal focus is normal feline lower urinary tract anatomy. Some examples of abnormalities that might be seen are also provided, and therapeutic cystourethroscopy is touched upon.

Use of a unique method for removal of a foreign body from the trachea of a cat

CASE DESCRIPTION

A 2.96-kg (6.5-lb) 9-month-old spayed female domestic longhair cat was admitted for removal of a tracheal foreign body.

CLINICAL FINDINGS

The cat had moderate respiratory distress but otherwise appeared to be healthy. Thoracic radiography revealed a foreign body in the trachea.

TREATMENT AND OUTCOME

The cat was anesthetized and endoscopy of the trachea was performed in an attempt to retrieve the foreign body. Endoscopic removal was unsuccessful because of the shape and smooth texture of the foreign body. Surgical removal of the foreign body was not considered ideal because of its location and the risks associated with tracheotomy. Fluoroscopic-guided placement of an over-the-wire balloon catheter caudal to the foreign body was followed by inflation of the balloon and gradual traction in an orad direction, which resulted in successful removal of the foreign body (identified as a piece of landscaping gravel). The cat required supplemental oxygen and supportive care following removal of the foreign body.

CLINICAL RELEVANCE

A fluoroscopic technique was used as a minimally invasive alternative to endoscopy or open-chest surgery for removal of a foreign body from the trachea of a cat. Use of this technique allowed uninterrupted ventilation of the cat throughout the procedure.

Intravascular occlusion for the correction of extrahepatic portosystemic shunts in dogs

BACKGROUND

Congential extrahepatic portosystemic shunts (EHPSS) are common in dogs. An effective minimally invasive technique for correction of EHPSS could result in reduced morbidity, reduced costs, and reduced hospitalization times.

HYPOTHESIS

Use of an intravascular occlusion device can effectively and safely result in acute complete occlusion of EHPSS in dogs.

ANIMALS

Seven dogs with naturally occurring EHPSS that presented to the Purdue University Veterinary Teaching Hospital.

METHODS

Prospective, clinical trial. The 7 dogs were consecutively enrolled over a 2-year period. Results of serum biochemistry, total serum bile acids, fasting plasma ammonia, abdominal radiography, and ultrasonography suggested the diagnosis of portosystemic shunts in all dogs. Definitive diagnosis of EHPSS was achieved with cranial mesenteric arterial portography and acute occlusion was attempted by the deployment of the Amplatzer vascular plug (AVP).

RESULTS

EHPSS were identified in all dogs consisting of 5 portocaval and 2 portoazygous variants; 1/7 dogs (14%) were intolerant to temporary complete occlusion of the EHPSS. Of the remaining 6 dogs, 5 (83%) had complete occlusion of the EHPSS by the AVP. There were no complications and resolution of abnormal clinical signs and laboratory values was achieved in 4/5 (80%) dogs with complete occlusion.

CONCLUSIONS AND CLINICAL IMPORTANCE

Intravascular correction of EHPSS by the AVP is a viable option to surgical correction while larger studies will be required to determine the clinical applicability of this procedure in the broader portosystemic shunt population.