Treatment outcomes and target delineation utilizing CT and MRI in 13 dogs treated with a uniform stereotactic radiation therapy protocol (16 Gy single fraction) for pituitary masses: (2014‐2017)

Canine pituitary tumours are increasingly treated with stereotactic radiotherapy (SRT). Here, we report clinical outcomes in dogs treated with single‐fraction SRT; we also explore technical aspects of SRT treatment planning. A single‐institution retrospective study was performed, including any dog with a pituitary mass (PM) that was treated using a standardized single‐fraction (16 Gy) SRT protocol between 2014 and 2017. Via medical records review, 13 cases were identified. Nine dogs neurologically improved after SRT. Four dogs experienced MRI‐documented tumour volume reduction. Nine dogs experienced neurologic decline in 1.5 to 18 months after SRT and were euthanized. The median overall survival time was 357 days, with 15% alive 18 months after SRT. To better understand whether SRT target delineation is predictably altered by use of magnetic resonance imaging (MRI) in addition to computed tomography (CT), two radiation oncologists (RO) retrospectively re‐evaluated all imaging studies used for SRT planning in these 13 cases. Gross tumour volume (GTV) was contoured on co‐registered CT and MRIs for each case. In seven cases, CT alone was deemed inadequate for GTV contouring by at least one RO. T1 post‐contrast MRI was considered the ideal image for GTV contouring in 11 cases. Contouring on MRI yielded larger GTV than CT for 11 cases. Inter‐observer variability existed in each case and was greater for MRI. In summary, use of co‐registered CT and MRI images is generally considered advantageous for PM delineation when using SRT. Notably, survival times reported herein are shorter than what has previously been reported for PM treated with finely fractionated full‐course RT protocols.     

Peripheral washout phenomenon in an animal tumour model: comparison of dynamic magnetic resonance imaging using a small molecular contrast medium with histology*

The peripheral washout sign was first described in delayed dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) using a small molecular contrast medium in solid lesions of the human breast and liver. It was found to be 100% specific for malignant lesions and could therefore potentially be used as an additional noninvasive diagnostic tool differentiating malignant from benign lesions. The origin of this phenomenon has not yet been explained. The objective of this study was to translate the peripheral washout sign as seen in solid tumours in delayed DCE‐MRI in human onto an animal model for further assessment of DCE‐MRI characteristics and histological analysis. Small molecular contrast medium DCE‐MRI was performed over 42 min in experimental colon carcinoma grown subcutaneously in rats. Qualitative and quantitative analyses for evaluation of presence and characteristics of the peripheral washout sign were accomplished, defining four centripetally distributed tumour zones (central, intermediate, peripheral and marginal). One hundred per cent of the carcinomas demonstrated a peripheral washout sign in DCE‐MRI starting at 20 min after bolus injection. Histomorphological analysis was performed for tissue classification and evaluation of microvasculature. Quantitative analysis revealed different enhancement profiles of the four tumour zones. Histology indicated centripetally asymmetric vascularization and vascular endothelial growth factor VEGF/VEGF receptor 2 expression within the tumour tissue. Thus, peripheral washout sign can be translated to an animal model. However, comparison of small molecular contrast medium DCE‐MRI with histology revealed that histology alone does not explain the occurrence of the peripheral washout.     

Magnetic resonance imaging findings in 40 dogs with histologically confirmed intracranial tumours

Magnetic resonance (MR) images of 40 dogs with histologically confirmed primary and secondary intracranial tumours were reviewed. Forty-one tumours were diagnosed by means of MR imaging (MRI). MRI findings allowed diagnosis of a neoplastic lesion in 37/41 cases. Based on MRI features, differentiation between neoplastic and non-neoplastic lesions was possible in 24/27 (89%) primary brain tumours and in 13/14 (92%) secondary brain tumours. Diagnosis of tumour type based on MRI features was correct in 19/27 (70%) primary tumours and in 13/14 secondary tumours. The results of this study show that MRI is a good diagnostic imaging modality to detect neoplastic lesions and to diagnose tumour type in dogs. However, as some neoplasms show equivocal MRI features the technique has limitations in the detection of some intracranial tumours and in predicting tumour type.     

DCE‐MRI: a review and applications in veterinary oncology

Dynamic contrast enhanced magnetic resonance imaging (DCE‐MRI) is a functional imaging technique that assesses the physiology of tumour tissue by exploiting abnormal tumour microvasculature. Advances made through DCE‐MRI include improvement in the diagnosis of cancer, optimization of treatment choices, assessment of treatment efficacy and non‐invasive identification of prognostic information. DCE‐MRI enables quantitative assessment of tissue vessel density, integrity, and permeability, and this information can be applied to study of angiogenesis, hypoxia and the evaluation of various biomarkers. Reproducibility of DCE‐MRI results is important in determining the significance of observed changes in the parameters. As improvements are made towards the utility of DCE‐MRI and interpreting biologic associations, the technique will be applied more frequently in the study of cancer in animals. Given the importance of tumour perfusion with respect to tumour oxygenation and drug delivery, the use of DCE‐MRI is a convenient and powerful way to gain basic information about a tumour.     

Adenocarcinoma metastasis of the intertransversarius cervicis muscle eliciting a right forelimb lameness in a dog

This article describes identification of a metastatic adenocarcinoma to the intertransversarius cervicis muscle using magnetic resonance imaging (MRI) in a dog that presented with chronic lameness of the right forelimb. Magnetic resonance imaging revealed a right sided, ovoid signal abnormality within the intertransversarius cervicis muscle lateral to the sixth cervical (C6) vertebra. The lesion was uniform, hyperintense on T2- and isointense on T1-weighted images to muscle and exhibited uniform contrast enhancement on T1-weighted images. The MRI findings were consistent with a neoplasia. Surgical excision was performed. Histopathological diagnosis was metastatic fibrous adenocarcinoma. The dog recovered rapidly but 6 months post-operatively he was killed because of lung metastases. Necropsy was declined and the primary tumour could not be identified.     

MRI findings in a dog with discospondylitis caused by Bordetella species

A case of discospondylitis in a dog secondary to Bordetella species, diagnosed early with the assistance of magnetic resonance imaging (MRI), is reported. The history and clinical signs were suggestive of possible discospondylitis. MRI identified changes and allowed a presumptive diagnosis of discospondylitis, which was subsequently confirmed by bacterial culture of biopsy material. Discospondylitis associated with Bordetella species infection has not, to the authors' knowledge, been previously reported in the dog.     

Magnetic resonance imaging features of an extranodal T cell rich B cell lymphoma in the pharyngeal mucosa in a horse

An 11‐year‐old Warmblood gelding was presented for inspiratory stridor and dysphagia. Based on history and clinical examination, a solitary mass localised in the oropharynx was suspected. Due to its inaccessibility and defensive behaviour of the horse, it was difficult to visualise this mass either by upper airway endoscopy or by oral examination and the conventional imaging methods (radiology and ultrasound) provided only limited information. Fine needle aspiration cytology was suggestive of lymphoma, but the exact localisation and the extent of tissue infiltration of the tumour could only be defined by magnetic resonance imaging (MRI). MRI has proved to be a very useful diagnostic tool in equine lameness investigation and, as this case illustrates, it has considerable diagnostic potential for soft tissue examination of the equine head.     

MAGNETIC RESONANCE IMAGING FINDINGS IN SPINAL CORD INFARCTION IN THREE SMALL BREED DOGS

Fibrocartilaginous embolization (FCE) of the spinal cord is a common disease in large breed dogs. There are only a few reports about this entity in small breed dogs and it has never been reported in chondrodystrophic breed. For definitive diagnosis histopathologic examination is necessary. Magnetic resonance imaging (MRI) as a potential diagnostic tool for intravitam diagnosis of FCE has been mentioned before, but results have not been reported so far. This report describes the neurological findings and MRI results in three small breed dogs, including a Pekingese dog, with FCE of the spinal cord. The disease was suspected in two animals based upon clinical and MRI-appearance and confirmed in the third by histopathological examination. In all three cases, similar focal intramedullary lesions, consisting of hyperintensive signals on T2-weighted images, were detected. Based on these findings, high-field MRI may be used as an antemortem tool for the diagnosis of FCE. It is also shown that FCE can occur in chondrodystrophic dogs.     

CT angiography and MRI imaging features do not predict the tumor type and grade of feline injection site sarcoma

Computed tomographic angiography (CTA) and magnetic resonance imaging (MRI) have been described as methods for preoperative surgical planning in cats with feline injection site sarcomas (FISS), however, few published studies have compared these modalities. The objective of this retrospective, secondary analysis study was to determine if imaging features of FISS on CTA and MRI are predictive of neoplastic peritumoral projections. Archived data from a previous prospective study were retrieved for 10 cats with FISS. All cats had been evaluated in a single anesthetic episode with MRI and dual phase CT (CTA) imaging followed by surgical removal. Histopathological grading and targeted histopathology of imaging‐identified peritumoral projections were performed. Two observers evaluated the CTA and MRI studies for FISS shape, margination, size, enhancement pattern, postcontrast uniformity, pre‐ and postcontrast margination, the number of muscles involved, mass mineralization, and bone lysis. Metal was present in the imaging field of three of 10 cats, resulting in one nondiagnostic MRI. Peritumoral projections were detected in all cats with both imaging modalities, and most were benign. At least one neoplastic peritumoral projection was detected in six cats using MRI, five cats using CTA, and three cats with both modalities. Higher grade FISS were larger than low grade using MRI, and FISS were larger using MRI. Other FISS imaging features using MRI and CTA were similar. Findings supported use of either MRI or CTA for detecting neoplastic peritumoral projections in cats with FISS. Authors recommend CTA for cats with known metallic objects in the scan field.     

PROSPECTIVE COMPARISON OF TUMOR STAGING USING COMPUTED TOMOGRAPHY VERSUS MAGNETIC RESONANCE IMAGING FINDINGS IN DOGS WITH NASAL NEOPLASIA: A PILOT STUDY

Identification of nasal neoplasia extension and tumor staging in dogs is most commonly performed using computed tomography (CT), however magnetic resonance imaging (MRI) is routinely used in human medicine. A prospective pilot study enrolling six dogs with nasal neoplasia was performed with CT and MRI studies acquired under the same anesthetic episode. Interobserver comparison and comparison between the two imaging modalities with regard to bidimensional measurements of the nasal tumors, tumor staging using historical schemes, and assignment of an ordinal scale of tumor margin clarity at the tumor‐soft tissue interface were performed. The hypotheses included that MRI would have greater tumor measurements, result in higher tumor staging, and more clearly define the tumor soft tissue interface when compared to CT. Evaluation of bone involvement of the nasal cavity and head showed a high level of agreement between CT and MRI. Estimation of tumor volume using bidimensional measurements was higher on MRI imaging in 5/6 dogs, and resulted in a median tumor volume which was 18.4% higher than CT imaging. Disagreement between CT and MRI was noted with meningeal enhancement, in which two dogs were positive for meningeal enhancement on MRI and negative on CT. One of six dogs had a higher tumor stage on MRI compared to CT, while the remaining five agreed. Magnetic resonance imaging resulted in larger bidimensional measurements and tumor volume estimates, along with a higher likelihood of identifying meningeal enhancement when compared to CT imaging. Magnetic resonance imaging may provide integral information for tumor staging, prognosis, and treatment planning.     

Ventricular ependymoma in a German Shepherd dog

Using magnetic resonance imaging (MRI) together with clinical, pathomorphological and immunohistological methods, a ependymoma is described in a 9-year-old German Shepherd dog, which presented with behavioural and oculocephalic responses and generalised ataxia. The ependymoma, 9 x 6 x 5mm in size, was localised intra-axially in the right interventricular foramen and hydrocephalus was observed by MRI. Microscopically, the tumour was composed of pseudorosettes, and immunohistochemical examination revealed vimentin and glial fibrillary acidic protein immunoreactivity in the neoplastic cells.     

Lymphotropic nanoparticle magnetic resonance imaging for diagnosing metastatic lymph nodes in dogs with malignant head and neck tumours

Lymphotropic nanoparticle magnetic resonance imaging (LNMRI) utilises ultrasmall paramagnetic iron nanoparticles (USPIOs) for imaging of metastatic lymph nodes in patients afflicted with cancer. LNMRI has been shown to be a highly effective and accurate way to diagnose metastasis in humans but has not been commonly reported on in veterinary medicine. USPIOs are phagocytised by macrophages and then localised to lymph nodes where they create a susceptibility artefact on gradient echo MRI sequences. In this study dogs (n = 24) with naturally occurring head and neck tumours were imaged with LNMRI then had mandibular and retropharyngeal lymph nodes extirpated for histological analysis. Subjective and objective analysis of the LNMRI images was performed and imaging results compared to histology as the gold standard. A total of 149 lymph nodes were included in this study. The overall sensitivity, specificity and accuracy was 64%, 94.4% and 89.3% respectively. However, if dogs with mast cell tumours were excluded from analysis the sensitivity, specificity and accuracy rose to 85.7%, 95.7% and 94.6%. LNMRI is potentially an accurate way to determine the presence of lymph node metastasis in dogs with some types of head and neck tumours. However, LNMRI has only moderate accuracy in dogs with oral or mucocutaneous mast cell tumours in this region.     

Traumatic odontoid process synchondrosis fracture with atlantoaxial instability in a calf: clinical presentation and imaging findings

A 6-week-old female Simmental calf was evaluated for acute non-ambulatory tetraparesis. Physical and laboratory examinations revealed no clinically relevant abnormalities. Neurological findings were consistent with acute, progressive and painful cervical myelopathy. Radiographs displayed a fractured odontoid process (dens axis) and vertebral step misalignment at the fracture site. A traumatic origin was suspected. Advanced diagnostic imaging was considered to allow better planning of potential surgical stabilisation and to exclude any additional lesions of the cervical vertebral column. However, during trailer transportation to the advanced diagnostic imaging and surgery site, the calf deteriorated neurologically and was humanely euthanised. Magnetic resonance imaging (MRI) and computed tomography (CT) were performed immediately post-mortem for scientific reasons. The MRI examination reflected the radiographic findings and confirmed severe spinal cord compression at the fracture site. In addition, a T2W-hyperintense signal change within the paravertebral soft tissue dorsal to the fracture site was indicative of a traumatic event. CT identified the fracture site at the synchondrosis between the odontoid process and the body of the axis, and this finding was confirmed by post-mortem examination. Advanced diagnostic imaging and post-mortem examination did not identify any other cervical lesion. In summary, this calf was diagnosed with a traumatic odontoid process synchondrosis fracture, which has not been reported previously in calves but presents a challenging and well-known fracture type in young children. This case report indicates that the odontoid process synchondrosis is a potential predisposed injury site and that traumatic odontoid process synchondrosis fractures should be considered as a potential differential in calves with acute cervical pain and/or signs of a cervical myelopathy.     

Magnetic resonance imaging in two dogs with central nervous system disease

Accurate localization of the lesions in two dogs with progressive neurological disease was demonstrated with magnetic resonance imaging (MRI). The first dog had unilateral cerebellar signs with associated paradoxical vestibular symptoms. The CSF tap and clinical localization suggested a right-sided cerebellar tumour and this was confirmed with MRI scanning. The second dog had predominantly asymmetrical fore-brain signs with circling, personality changes, seizures and contralateral proprioceptive deficits. CSF analysis suggested an inflammatory or neoplastic condition. MRI showed a diffuse oedematous lesion of the left cerebral hemisphere which corresponded exactly with the lesions seen at necropsy. The advantages of MRI over CT scans are discussed.     

Comparison of radiography and magnetic resonance imaging for evaluating the extent of nasal neoplasia in dogs

OBJECTIVES: Magnetic resonance imaging (MRI) is increasingly used in veterinary practice and, in some centres, is part of the diagnostic work-up of small animals with nasal disease. However, there are no published studies which critically evaluate the use of magnetic resonance imaging for this purpose. The purpose of this work was to assess the changes seen using magnetic resonance imaging and to compare them with radiography. METHODS: The study included 12 dogs that had undergone both radiography and magnetic resonance imaging of the nasal cavity and had a histopathological diagnosis of malignant nasal neoplasia. Two pairs of board-certified radiologists scored the radiographs and the MRI scans, evaluating 10 signs of abnormality using a simple scoring system. Magnetic resonance imaging features were described in detail, and radiographic and magnetic resonance imaging scores for each sign as well as total scores were compared. RESULTS: Magnetic resonance imaging often showed that the tumour was more extensive than it had appeared on radiography but occasionally showed that radiographs had overestimated its size. Although radiography was reliable for assessment of the presence and size of a mass and for the extent of turbinate destruction, it usually failed to show occlusion of the major airway passages that were evident on magnetic resonance imaging. Extension of the tumour into the opposite nasal cavity, frontal sinus, orbit and cranial cavity was shown much better on magnetic resonance imaging. CLINICAL SIGNIFICANCE: Minor but significant extension beyond the nasal cavity, which is important for treatment planning and prognosis, requires magnetic resonance imaging for demonstration, although radiography shows major changes reliably.     

The localization of a conjunctivoscleral foreign body via high‐resolution microscopy coil magnetic resonance imaging in a dog

A 3‐year‐old French bulldog was presented to the ophthalmology service of the Vetsuisse Faculty, University of Zurich with a 3‐day history of conjunctival swelling of the left eye (OS). Ophthalmologic examination revealed a moderate conjunctival hyperemia and chemosis. A migrating foreign body having entered the conjunctival fornix behind the nictitating membrane was suspected. Within the first 24 hours of medical management, OS developed a panuveitis and a scleral perforation was highly suspected. Ocular and orbital ultrasound as well as conventional magnetic resonance imaging (MRI) examinations failed to confirm the presence of a perforating foreign body. A High‐Resolution MRI (HR‐MRI) using a microscopy coil was then performed with findings consistent with a perforating and migrating foreign body. A grass awn of 12 mm length was surgically retrieved “ab externo” from its’ point of entry into the sclera. To the best of our knowledge, HR‐MRI has not yet been used to examine canine eyes. This case report supports the idea that orbital imaging can be greatly enhanced with the introduction of HR‐MRI using microscopy coils with clinically relevant implications.     

Magnetic resonance imaging and pathological findings in a cat with brain contusions

Necropsy was performed on a mongrel male cat of unknown age weighing 1.3 kg, which probably encountered a traffic accident. Gross pathological examination of the brain revealed reddish colour of the right cerebral hemisphere and haemorrhages on the surface of the right frontal lobe to temporal lobe. Histologically, there was diffuse vacuolation in the cortex of the right frontal lobe and extensive haemorrhages in the base of brain. These histopathological findings were consistent with areas of abnormal signals found on post-mortem magnetic resonance imaging (MRI). In this study, the MRI findings were identical to that reported in human cases of head trauma as well as histopathological changes.     

EARLY POSTOPERATIVE MAGNETIC RESONANCE IMAGING FINDINGS IN FIVE DOGS WITH CONFIRMED AND SUSPECTED BRAIN TUMORS

Early postoperative neuroimaging has been performed in people for over 20 years to detect residual brain tumor tissue and surgical complications. The purpose of this retrospective study was to describe characteristics observed using early postoperative magnetic resonance imaging in a group of dogs undergoing craniotomy for brain tumor removal. Two independent observers came to a consensus opinion for presence/absence of the following MRI characteristics: residual tumor tissue; hemorrhage and ischemic lesions; abnormal enhancement (including the margins of the resection cavity, choroid plexus, meninges) and signal intensity changes on diffusion‐weighted imaging. Five dogs were included in the study, having had preoperative and early postoperative MRI acquired within four days after surgery. The most commonly observed characteristics were abnormal meningeal enhancement, linear enhancement at margins of the resection cavity, hemorrhage, and a thin rim of hyperintensity surrounding the resection cavity on diffusion‐weighted imaging. Residual tumor tissue was detected in one case of an enhancing tumor and in one case of a tumor containing areas of hemorrhage preoperatively. Residual tumor tissue was suspected but could not be confirmed when tumors were nonenhancing. Findings supported the use of early postoperative MRI as a method for detecting residual brain tumor tissue in dogs.     

Olfactory esthesioneuroblastoma treated with orthovoltage radiotherapy in a dog

A 13-year-old neutered female mongrel dog presented with a 1-year history of stertorous respiration. On computed tomography examination, a mass was demonstrated in the nasal cavity. Open biopsy of the mass was performed and a diagnosis of olfactory esthesioneuroblastoma was made on histological examination. The dog was treated with orthovoltage x-ray radiation (total dose; 53 Gy given in 14 fractions over an 8 week period). Computed tomography after the twelfth irradiation revealed that tumour size had decreased. Although clinical signs were absent in the 4 months after irradiation, re-growth of the tumour was detected by radiographic evaluation and histological examination. The dog was again treated with orthovoltage x-ray radiation (total dose; 30 Gy given in three fractions over a 4-week period), however, tumour regrowth was again detected 3 months later. Clinical treatment of this tumour type has not been previously reported.