Gregory B. Daniel

The eye and orbit

Computed tomography (CT) and magnetic resonance imaging (MRI) provide excellent morphological detail of the eye and its associated structures. In veterinary medicine, these imaging modalities are most often used to diagnose and determine the extent of ocular or periocular tumors. They may also be used to diagnose inflammatory conditions of the orbital region and to determine the severity and extent of ocular trauma. This article reviews the applications of CT and MRI for ocular and orbital diseases, discusses normal findings, and presents representative case examples.

OSTEOMYELITIS ASSOCIATED WITH SALMONELLA ENTERICA SS ARIZONAE IN A COLONY OF RIDGENOSE RATTLESNAKES (CROTALUS WILLARDI)

Abstract The identification of three Arizona ridgenose rattlesnakes (Crotalus willardi) with Salmonella arizonae–associated osteomyelitis led to a 5-yr prospective study of radiographic signs and Salmonella intestinal carriage rates in a 19-member colony of this rattlesnake species. Ventrodorsal radiographs were performed and cloacal swabs were cultured for Salmonella spp. annually. Ten snakes survived the 5-yr period, with six of them remaining free of bony lesions. Three snakes that had no bony lesions in 1995 developed radiographic signs of osteomyelitis during the study. Six snakes with bony lesions at the beginning of the study died or were euthanatized due to osteomyelitis during the study. The radiographic signs of osteomyelitis were progressive for five snakes that were serially radiographed. Only one snake with radiographic signs of osteomyelitis at the beginning of the study was still alive at the end of the study, and this animals bony lesions were more extensive at the end. Thirty-nine intestinal S. arizonae isolates, representing 13 serotypes, were obtained from the 19 snakes. Salmonella arizonae serotype 56:Z4,Z23 was isolated only once from a cloacal culture, from a snake that had no radiographic bone lesions. Twelve extraintestinal Salmonella isolates, representing two serotypes, were isolated from six snakes. All extraintestinal isolates except one were of S. arizonae serotype 56:Z4,Z23, and all isolates from bone were of this serotype. One snake with characteristic bone lesions died, and Providencia rettgeri was cultured from each of the tissues cultured, whereas no Salmonella spp. were isolated from this snake. Salmonella arizonae serotype 56:Z4,Z24 appears to have a tropism for bone and other extraintestinal sites in C. willardi and may cause a progressive, ultimately fatal disease in this species.

Communicating Hydrocephalus in Dogs with Congenital Ciliary Dysfunction

Magnetic resonance imaging (MRI) and radionuclide ventriculography were performed in 5 dogs with congenital ciliary dysfunction (CDD) and 3 normal dogs. Ventricular and brain dimensions and volumes, and CSF flow rates were measured or calculated from the MR images and radionuclide clearance. All CCD dogs had hydrocephalus based on previously published criteria of a percent vertical brain dimension (PVBD) greater than 14%. The PVBD was significantly larger (p = 0.001) in the dogs with CCD (mean +/- SD) 33.00 +/- 5.42% than in normal dogs (11.07 +/- 0.61%. The ventricular volume was significantly larger (p = 0.021) in CCD dogs 10,841 +/- 4,127 mm3 compared to the volume measured in normal dogs 3,069 +/- 1,167 mm3. The CSF flow rate was not significantly different p = 0.876) between CCD dogs (253.00 +/- 147.25 mm3/h) and normal dogs (267.667 +/- 47.61 mm3/h). This suggests that the ventricular dilation in CCD dogs is not due to impedance of CSF flow from the ventricular system by dysfunctional ependymal cilia.

Pulmonary Carcinoma with Metastases in a Moluccan Cockatoo (Cacatua moluccensis)

Abstract Pulmonary carcinoma was diagnosed in a 14-year-old male Moluccan cockatoo (Cacatua moluccensis) presented for sudden onset of ataxia of the pelvic limbs lasting several hours. On physical examination, the cockatoo had paraparesis of both legs and a reduction in pectoral muscle mass. The bird responded to initial supportive therapy; however, its clinical condition deteriorated over a 3-week period. Histopathologic examination revealed pulmonary carcinoma with intrapulmonary metastases as well as metastases to the vertebral column and right humerus.

INVITED REVIEW – NEUROIMAGING RESPONSE ASSESSMENT CRITERIA FOR BRAIN TUMORS IN VETERINARY PATIENTS

The evaluation of therapeutic response using cross-sectional imaging techniques, particularly gadolinium-enhanced MRI, is an integral part of the clinical management of brain tumors in veterinary patients. Spontaneous canine brain tumors are increasingly recognized and utilized as a translational model for the study of human brain tumors. However, no standardized neuroimaging response assessment criteria have been formulated for use in veterinary clinical trials. Previous studies have found that the pathophysiologic features inherent to brain tumors and the surrounding brain complicate the use of the response evaluation criteria in solid tumors (RECIST) assessment system. Objectives of this review are to describe strengths and limitations of published imaging-based brain tumor response criteria and propose a system for use in veterinary patients. The widely used human Macdonald and response assessment in neuro-oncology (RANO) criteria are reviewed and described as to how they can be applied to veterinary brain tumors. Discussion points will include current challenges associated with the interpretation of brain tumor therapeutic responses such as imaging pseudophenomena and treatment-induced necrosis, and how advancements in perfusion imaging, positron emission tomography, and magnetic resonance spectroscopy have shown promise in differentiating tumor progression from therapy-induced changes. Finally, although objective endpoints such as MR imaging and survival estimates will likely continue to comprise the foundations for outcome measures in veterinary brain tumor clinical trials, we propose that in order to provide a more relevant therapeutic response metric for veterinary patients, composite response systems should be formulated and validated that combine imaging and clinical assessment criteria.

Characterization of Uptake of 2-Deoxy-2-[18F] Fluoro-D-Glucose by Fungal-Associated Inflammation: The Standardized Uptake Value is Greater for Lesions of Blastomycosis than for Lymphoma in Dogs with Naturally Occurring Disease

PURPOSE Based on limited reports, fungal lesions can have remarkably high intensity uptake of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) on positron emission tomography (PET) images. The purpose of this investigation was to compare the standardized uptake value (SUV) of naturally occurring lesions of blastomycosis with the SUV of naturally occurring lymphoma in a series of dogs. PROCEDURES Five dogs with naturally occurring blastomycosis and three dogs with lymphoma underwent whole-body FDG-PET prior to receiving any treatment for their disease. RESULTS The (mean +/- SD) SUV for 13 blastomycosis lesions was 7.7 +/- 2.0 versus a mean for 17 lymphomas of 4.8 +/- 1.8. These values were significantly different (P = 0.0537). There was overlap between the SUV of Blastomyces-associated lesions versus lymphomas, but a cut-off SUV of 7.0 was 100% specific for Blastomyces lesions. Numerous sites of disease were detected on the FDG-PET images that were not detected clinically. CONCLUSIONS FDG-PET is useful for determining the extent of disease in dogs with blastomycosis. The SUV for Blastomyces-associated lesions are as high or higher than for malignant lymphoma. Due to the similarities in canine and human blastomycosis and lymphomas, similar results would be predicted in human patients. In regions where blastomycosis is endemic, Blastomyces granulomas should be considered a differential diagnosis for lesions with high intensity uptake of FDG.

Thyroid Scintigraphy in Veterinary Medicine

Thyroid scintigraphy is performed in cats and dogs and has been used to a limited degree in other species such as the horse. Thyroid scintigraphy is most commonly used to aid in the diagnosis and treatment management of feline hyperthyroidism but is also used in the evaluation of canine hypothyroidism and canine thyroid carcinoma. This article reviews the normal scintigraphic appearance of the thyroid in the cat, the dog, and the horse and the principles of interpretation of abnormal scan results in the cat and the dog. Radioiodine is the treatment of choice for feline hyperthyroidism, and the principles of its use in the cat are reviewed.

STATIC AND DYNAMIC 18FDG-PET IN NORMAL HISPANIOLAN AMAZON PARROTS (AMAZONA VENTRALIS)

Positron emission tomography (PET) is often used to stage and monitor human cancer and has recently been used in a similar fashion in veterinary medicine. The most commonly used radiopharmaceutical is 2-Deoxy-2-[(18) F]-Fluoro-d-glucose ((18) F-FDG), which is concentrated and trapped within cells that use glucose as their energy substrate. We characterized the normal distribution of (18) F-FDG in 10 healthy Hispaniolan Amazon parrots (Amazona ventralis) by performing whole body PET scans at steady state, 60min after injection. Significant variability was found in the intestinal activity. Avian species are known to reflux fluid and electrolytes from their cloaca into their colon. To evaluate reflux as the cause of variability in intestinal distribution of (18) F-FDG, dynamic PET scans were performed on the coelomic cavity of six Hispaniolan Amazon parrots from time 0 to 60min postinjection of radiotracer. Reflux of radioactive material from the cloaca into the colon occurred in all birds to varying degrees and occurred before 60min. To evaluate the intestinal tract of clinical avian patients, dynamic scans must be performed starting immediately after injection so that increased radioactivity due to metabolism or hypermetabolic lesions such as cancer can be differentiated from increased radioactivity due to reflux of fluid from the cloaca.

Propylthiouracil for Treatment of Hyperthyroidism in a Horse

A 19-year-old 250-kg Quarter Horse mare was examined in the fall for evaluation of weight loss of 4 years’ duration. The mare had been purchased 6 years before examination and was reported to be normal in appearance, weight, and demeanor. She had been used for trail riding. The owner initially noticed weight loss following transient postpartum diarrhea 4 years before presentation. The weight loss was mild and slowly progressed with intermittent periods of soft feces. Referral for evaluation was prompted by marked weight loss over the preceding 6 months. The mare had a ravenous appetite and polydipsia. In addition, the mare did not completely shed her hair coat during summer and was heat intolerant in ambient temperatures that exceeded 32.2 1C (901F). This was manifested as lethargy, sweating, and increased respiratory rate.

EVALUATION OF AN IMPLANTED OSMOTIC PUMP FOR DELIVERY OF AMIKACIN TO CORN SNAKES (ELAPHE GUTTATA GUTTATA)

Abstract The risk of accidental envenomation to the handler of venomous snakes during drug administration limits the ability to treat these animals. One commercially available osmotic pump is a miniature self-contained cylindrical implant that operates on the basis of an osmotic pressure difference between the extracellular fluid and the osmotic agent in the pump. Osmotic pumps loaded with amikacin were surgically placed into the coelomic cavity of five adult corn snakes (Elaphe guttata guttata) (group A). Four snakes (group B) received an intramuscular injection of amikacin at 5 mg/kg followed by 2.5 mg/kg q 72 hr for a total of four injections. Plasma concentrations of amikacin were measured in both groups. Renal function was evaluated pre- and posttreatment via scintigraphy with 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) and measurement of plasma uric acid concentrations. Mean (±SD) steady state amikacin concentration for group A was 6.9 ± 1.7 μg/ml (predicted = 8.0 μg/ml), and the measured pump rate was 0.134 ± 0.017 μl/hr (predicted = 0.130 μl/hr). Mean (± SD) peak and trough plasma amikacin concentrations for group B were 22.7 ± 8.5 μg/ml and 14.3 ± 7.0 μg/ml, respectively. While neither scintigraphy nor plasma uric acid concentrations indicated toxicity in either group, continuous administration of aminoglycosides may cause nephrotoxicity, and it is unknown whether this delivery method of amikacin would be efficacious in treating bacterial infections in snakes. In addition, due to migration of one pump into the trachea causing asphyxiation and death, these pumps may not be appropriate for intracoelomic placement in corn snakes. Nonetheless, the pumps delivered the drug at a predictable rate and were efficacious in achieving a constant plasma concentration of amikacin at the predicted level. Osmotic pumps may offer a safer alternative to periodic intramuscular injections for drug delivery in venomous or aggressive snakes.