The effects of perineural and intrasynovial anaesthesia of the equine foot on subsequent magnetic resonance images.

REASONS FOR PERFORMING STUDY: Artefacts caused by regional anaesthesia can influence image interpretation of ultrasonography and nuclear scintigraphy. Perineural and intrasynovial anaesthesia are commonly performed prior to magnetic resonance imaging (MRI); and the effects on MR images, if any, are unknown. OBJECTIVES: To determine if perineural and intrasynovial anaesthesia of structures in the equine foot cause iatrogenic changes detectable with MRI. METHODS: A baseline MRI examination of both front feet was performed on 15 horses, 2-6 days prior to mepivacaine injection adjacent to the lateral and medial palmar digital nerves, and into the podotrochlear bursa, digital flexor tendon sheath and distal interphalangeal joint of one randomly assigned forelimb. Magnetic resonance imaging was repeated at 24 and 72 h post injection; then qualitative and quantitative assessments of MRI findings were performed. RESULTS: Magnetic resonance imaging findings associated with the palmar digital nerves, podotrochlear bursa and distal interphalangeal joint at 24 and 72 h after mepivacaine injection did not alter significantly from those at baseline. Compared with baseline, a significant increase in synovial fluid volume of the digital flexor tendon sheath was detected with MRI at 24 and 72 h post injection. CONCLUSIONS: Perineural anaesthesia of the palmar digital nerves and intrasynovial anaesthesia of the podotrochlear or distal interphalangeal joint did not interfere with the interpretation of MR images acquired at 24 or 72 h after injection. However, intrasynovial anaesthesia of the digital flexor tendon sheath caused an iatrogenic increase in synovial fluid, detectable on MR images for at least 72 h. POTENTIAL RELEVANCE: Although a definite time frame for resolution of digital flexor tendon sheath distension was not determined, we recommend waiting more than 3 days between intrasynovial anaesthesia of the digital flexor tendon sheath and evaluation with MRI.

Acute small intestinal obstruction associated with Parascaris equorum infection in young horses: 25 cases (1985-2004).

AIMS: To retrospectively evaluate the medical and surgical records of horses with acute small intestinal obstructions associated with Parascaris equorum infection; to describe the gastrointestinal lesions; and to determine the outcome of cases with such lesions. METHODS: Records of 25 horses with acute small intestinal obstruction associated with P. equorum between 1985 and 2004 were reviewed to determine signalment, history, physical examination, surgical or post-mortem findings, and outcome. RESULTS: All horses except one were less than 12 months old. Standardbreds were over-represented in the population studied. Sixteen horses (72%) had been administered anthelmintics, including pyrantel (n=8), ivermectin (n=7), and trichlorphon (n=1), within 24 h prior to the onset of colic. Of the 25 cases reviewed, 16 had simple obstructive ascarid impactions (SOAIs), and nine had complicated obstructive ascarid impaction (COAI) including volvulus (n=6) or intussusception (n=3), both concurrent with ascarid impaction of the small intestine. Short-term survival (discharge from hospital) occurred in 79% of horses treated for SOAI, and was 64% for all horses. Long-term survival (>1 year) occurred in 33% of horses with SOAI, and the overall long-term survival was 27% for all horses. Formation of adhesions was the most frequent finding associated with death for horses that did not survive long-term. CONCLUSIONS AND CLINICAL RELEVANCE: The incidence of anthelmintic treatment within 24 h of the onset of colic in this study population (72%) was higher than that previously reported. Resistance of P. equorum to ivermectin recently reported in Ontario may be associated with increased ascarid burdens, predisposing horses to ascarid impaction. The long-term survival of these horses was better than that reported previously.