Chiari-like malformation and syringomyelia in normal cavalier King Charles spaniels: a multiple diagnostic imaging approach

Objectives : The objectives of the study were (1) to report the incidence of Chiari‐like malformation and syringomyelia in a normal French cavalier King Charles spaniel breeding population; (2) to precise the standard computed tomography dimensions of the caudal fossa and (3) to investigate the use of ultrasonography in diagnosis of this syndrome. Methods : Clinically normal adult cavalier King Charles spaniel underwent ultrasonographic examination of the spinal cord and caudal fossa. Computed tomography was used to measure the caudal fossa and magnetic resonance imaging allowed syringomyelia and cerebellar herniation identification. Results : Of the 16 dogs in the study, seven had syringomyelia (43·7 per cent). All dogs had cerebellar herniation, suggesting Chiari‐like malformation and also a tendency to occipital dysplasia. Computed tomography measurements of the caudal fossa are reported. In one dog, a syrinx was identified by ultrasonography. The only difference between dogs with or without syringomyelia was that dogs with Chiari‐like malformation/syringomyelia were statistically older. Clinical Significance : The incidence of Chiari‐like malformation and syringomyelia may be high in an asymptomatic population of cavalier King Charles spaniel . Computed tomography measurements reported in this study should now be compared with those of a symptomatic population to evaluate the hypothesis that dogs with Chiari‐like malformation/syringomyelia syndrome have a smaller caudal fossa. This study did not identify a smaller caudal fossa in an asymptomatic cavalier King Charles spaniel population with syringomyelia. Ultrasonography probably has a low sensitivity for diagnosis of Chiari‐like malformation/syringomyelia.     

COMPUTED TOMOGRAPHY OF BRAIN TUMORS IN THE CAUDAL FOSSA OF THE DOG*

Computed tomography (CT) was used to investigate brain tumors in the caudal fossa of three dogs. Changes detected by CT included compression or distortion of cerebrospinal fluid spaces within the caudal fossa, and changes in parenchymal density before and after intravenous injection of a nondiffusible, iodinated contrast medium. CT provided information regarding tumor size, location, character, and relationships with normal caudal fossa structures. It was concluded that CT offered advantages over technics currently in use for diagnosis and assessment of caudal fossa lesions in the dog.     

Morphometric analysis of the cranial cavity and caudal cranial fossa in the dog: a computerized tomographic study.

This investigation was initiated to develop a reliable and simple computerized tomography (CT) method for evaluating the morphometry of the cranial cavity (CC) and caudal cranial fossa in the dog. We obtained linear, area, and volume measurements of the entire CC and the caudal fossa compartment in 24 dogs, using transverse and reformatted sagittal and dorsal CT images. The ratios between the CC and the caudal fossa volumes were calculated, as were the ratios between the CC and caudal fossa midsagittal (MS) areas. There were statistically significant correlations between absolute volume data and certain linear measurements, a positive correlation between volume ratio and weight, and significant differences in absolute volume values and volume ratio between males and females. The volume ratio, MS area, and certain linear measurements included in this study can be considered as accurate parameters to evaluate the relative size of the CC to caudal fossa in the dog. Such quantitative measures may be useful in systematically characterizing Chiari-type malformations and other developmental anomalies in the dog.     

MRI features of gliomatosis cerebri in a dog

The features of gliomatosis cerebri involving the brainstem and cerebellum in a 3-year-old dog are described. In magnetic resonance (MR) images, there was diffuse loss of the cerebellar folia and cerebellar gray and white matter contrast. Multiple illdefined T2-hyperintensities were present in the cerebellar parenchyma. A poorly defined, T2-hyperintense mass effect was present ventral to the pons and rostral medulla. No contrast enhancement was noted. Cerebrospinal fluid (CSF) was normal. Postmortem examination was consistent with gliomatosis cerebri, based on compatible histopathology and immunohistochemical findings. Although rare, gliomatosis cerebri should be included as a differential for diffuse infiltrative central nervous system (CNS) lesions.     

MORPHOLOGY OF THE CAUDAL FOSSA IN CAVALIER KING CHARLES SPANIELS

Chiari malformations and syringohydromyelia are an important disease complex in Cavalier King Charles Spaniels. Although abnormalities in caudal fossa morphology are considered major contributors to the development of this disease, limited information exists on the range of morphologies in Cavalier King Charles Spaniels and on the relationship of these to clinically evident disease. Sixty-four Cavalier King Charles Spaniels were studied. Each underwent a neurologic examination and magnetic resonance imaging of the cervical spine and brain. T2-weighted sagittal images were used to determine both the morphologic characteristics and volume of the caudal fossa in each dog. This volume was also analyzed as a percentage of total cranial cavity volume. Each attribute was correlated with neurological grade and presence of syringohydromyelia. Fifteen dogs had neurologic signs, and 59 had morphologic abnormalities of the craniocervical junction. While 27 dogs had syringohydromyelia, 13 of these were clinically normal. Cerebellar herniation and occipital dysplasia were common findings but were not associated with syringohydromyelia. Dorsal compressive lesions were noted at the first and second cervical vertebral junction. Factors associated with the presence of neurologic signs included syringohydromyelia and the ratio of caudal fossa/total cranial cavity volume; dogs with signs had significantly larger syringohydromyelia than asymptomatic dogs. Caudal fossa size was not associated with syringohydromyelia. A positive association was identified between foramen magnum size and length of cerebellar herniation. The prevalence of craniocervical junction abnormalities is high in Cavalier King Charles Spaniels. While several factors are associated with neurologic signs, occipital hypoplasia appears to be the most important factor.     

Computed tomographic appearance of epidural empyema in a dog

The computed tomographic (CT) appearance of epidural empyema in a 5.5-month-old, intact male boxer dog is described. Epidural empyema was diagnosed by means of CT, surgery, and bacterial culture. The imaging and pathogenesis of epidural abscesses and the pitfalls of differentiating caudal fossa lesions from severe cranial cervical lesions are discussed.     

Cerebellar vermian hypoplasia in dogs

Six dogs with cerebellar dysplasia, in which the cerebellar vermis was hypoplastic, are described. Clinical signs in these dogs were noted around 2 weeks of age and included ataxia, dysmetria, and intention tremors. A variable portion of the caudal cerebellar vermis was absent in each dog; portions of the cerebellar hemispheres and flocculus also were absent in some of them. Neurons in certain brain stem nuclei that project to the cerebellum were either chromatolytic or vacuolated. Cerebellar vermian hypoplasia of dogs is analogous to the Dandy-Walker syndrome of human beings.     

Syringohydromyelia in Cavalier King Charles spaniels

Syringohydromyelia secondary to foramen magnum overcrowding is described in seven Cavalier King Charles spaniels. Clinical signs were consistent with a central spinal cord lesion. The most common signs were persistent scratching at the shoulder region with apparent neck, thoracic limb, or ear pain and thoracic limb lower motor neuron deficits. The diagnosis was made by magnetic resonance imaging. The syringohydromyelia is postulated to be a consequence of an occipital bone malformation resulting in a small caudal fossa and cerebellar herniation. Clinical signs improved but did not completely resolve when the dogs received treatment with corticosteroids or nonsteroidal anti-inflammatory drugs.     

Presumptive caudal cerebellar artery infarct in a dog: clinical and MRI findings

Clinical signs and magnetic resonance imaging findings of a caudal cerebellar artery infarct are reported for the first time in a dog. Clinical signs were characterised by a peracute, non-progressive, right-sided central vestibular syndrome with paradoxical right-sided head tilt. Magnetic resonance images were consistent with a territorial, non-haemorrhagic, ischaemic lesion affecting the caudo-ventral part of the right cerebellar hemisphere, mainly involving the right paramedian lobe, the ansiform lobe and the caudal cerebellar peduncle. Bloodwork results were suggestive of an underlying hypercoagulable state, although the concomitant presence of a histologically confirmed mammary gland adenocarcinoma could have also been related to the cerebellar vascular obstruction through metastatic emboli formation. Posterior-inferior cerebellar artery infarction is the human equivalent of caudal cerebellar artery infarct in dogs.     

RADIOGRAPHIC IMAGING OF THE CANINE INTERCONDYLAR FOSSA

The intercondylar fossa is believed to play an important role in the pathology of cranial cruciate ligament rupture and therefore has received considerable attention in the last decade. Accurate radiographic imaging of the intercondylar fossa requires that the central x-ray beam pass through the center of the intercondylar "tunnel". The anatomy of the canine intercondylar fossa is similar to humans, however, the orientations of the intercondylar fossa's differ. Consequently, the positioning techniques described for humans are not appropriate for the dog. To pass through the center of the dog, intercondylar fossa, the central x-ray beam should be 12° (S.D. 1.7°) caudal from the femoral diaphysis in the sagittal plane and obliqued caudolateral to craniomedial 7° (S.D. 0.60°) (caudo78°proximo7° lateralcraniodistomedial oblique). Cross table positioning was used with the hip flexed and the radiograph cassette placed on the cranial surface of the stifle. However, superimposition of the tuber ischii and soft tissues caudal to the femur made 15° to 20° the best angle obtainable. There was not a significant difference (p = 0.17) in the notch width index between a 12° versus 20° angle of the central x-ray beam caudal to the femoral diaphysis, both with 7° of external rotation of the stifle. The notch width index of 0.252 obtained from radiographic measurements was not significantly different from measurements obtained grossly of 0.254 (n = 26; p = 0.69). Failure to oblique the central x-ray beam caused a significant (p = 0.0008) decrease in the apparent fossa width radiographically.     

Comparison of cerebral cranium volumes between cavalier King Charles spaniels with Chiari-like malformation, small breed dogs and Labradors

O bjectives : To ascertain whether cavalier King Charles spaniels (CKCSs) have a proportionately smaller caudal fossa compared with other small dogs and with Labradors. To evaluate if cerebellar herniation in CKCS correlates with caudal fossa volume.
M ethods : In this retrospective study, three-dimensional images were created from magnetic resonance imaging brain series of 117 dogs (split into three groups: CKCS, Labradors and small breeds) from which the volumes of the fossae and brain parenchyma were calculated. These volumes were transformed into percentages of total cranial cavity and parenchyma volumes, respectively. The percentages were statistically compared among the groups. The percentage of herniated cerebellum in the CKCS was compared using linear regression with the caudal fossa and parenchyma percentages.
R esults : Cavalier King Charles spaniels had a proportionately smaller caudal fossa compared with Labradors (P=0·002) but not to small breeds (P=0·103). Their caudal fossa parenchyma was proportionately the same volume as Labradors (P=0·976) but greater than small breeds (P=0·005). No relationship was found for the per cent of cerebellum herniated.
C linical S ignificance : The results support mesoderm insufficiency or craniosynostosis as the pathogenesis of Chiari-like malformation (CM) in CKCS. It presents evidence for overcrowding of the caudal fossa due to a mismatch of brain parenchyma and fossa volumes as to why CKCS and not other small dogs are affected.     

INTRACRANIAL EPIDERMOID CYST AND SYRINGOHYDROMYELIA IN A DOG

A 5-year-old female Cocker Spaniel dog had a sudden onset of vestibular disease that localized to the caudal fossa. Upon computed tomography of the brain, a large, hypoattenuating mass with a slight peripheral ring enhancement pattern was detected ventral to the cerebellum. A hypoattenuating region was also identified in the center of the C2 spinal cord segment, consistent with syringohydromyelia. Postmortem examination of the brain revealed a fluid filled, cystic mass located dorsal to medulla oblongata that caused severe compression of the overlying cerebellum. The histopathologic diagnosis was an epidermoid cyst. Extensive syringohydromyelia and obstructive hydrocephalus were identified, both thought to be secondary to overcrowding of the caudal fossa.     

The Intercondylar Fossa of the Normal Canine Stifle: An Anatomic and Radiographic Study

The intercondylar fossa (ICF) in dogs consists of a cranial outlet, intercondylar shelf, caudal arch, caudal outlet, a medial wall, and a lateral wall. The normal cranial outlet is bell-shape and, in mixed-breed dogs (mean body weight 19.2 kg, N = 21), measured 5.8 mm cranially, 8.1 mm centrally, and 10.3 mm caudally. The ICF is oriented 12° from the dorsal plane of the femoral diaphysis and obliqued 7°, proximolateral to distomedial, in the sagittal plane. To adjust for dog size, a fossa width index (FWI) was calculated by dividing the cranial outlet width by the distance between epicondyles. The normal FWI as determined in this study was 0.18 cranially, 0.25 centrally, and 0.32 caudally. The fossa height index was 0.31. Contact between the ICF and the cranial cruciate ligament began at about 115° of extension. The contact area moved cranially in the intercondylar fossa as the stifle was extended. Evaluation of the ICF can be performed radiographically but positioning is critical.     

DEVELOPMENT OF A MORPHOMETRIC MAGNETIC RESONANCE IMAGE PARAMETER SUITABLE FOR DISTINGUISHING BETWEEN NORMAL DOGS AND DOGS WITH CEREBELLAR ATROPHY

Neurodegenerative diseases affect the cerebellum of numerous dog breeds. Although subjective, magnetic resonance (MR) imaging has been used to detect cerebellar atrophy in these diseases, but there are few data available on the normal size range of the cerebellum relative to other brain regions. The purpose of this study was to determine whether the size of the cerebellum maintains a consistent ratio with other brain regions in different ages and breeds of normal dogs and to define a measurement that can be used to identify cerebellar atrophy on MR images. Images from 52 normal and 13 dogs with cerebellar degenerative diseases were obtained. Volume and mid‐sagittal cross‐sectional area of the forebrain, brainstem, and cerebellum were calculated for each normal dog and compared between different breeds and ages as absolute and relative values. The ratio of the cerebellum to total brain and of the brainstem to cerebellum mid‐sagittal cross‐sectional area was compared between normal and affected dogs and the sensitivity and specificity of these ratios at distinguishing normal from affected dogs was calculated. The percentage of the brain occupied by the cerebellum in diverse dog breeds between 1 and 5 years of age was not significantly different, and cerebellar size did not change with increasing age. Using a cut off of 89%, the ratio between the brainstem and cerebellum mid‐sagittal cross‐sectional area could be used successfully to differentiate affected from unaffected dogs with a sensitivity and specificity of 100%, making this ratio an effective tool for identifying cerebellar atrophy on MR images.     

IMAGING DIAGNOSIS—SYNOVIAL MYXOMA OF LUMBAR VERTEBRAE ARTICULAR PROCESS JOINT

Magnetic resonance (MR) imaging and histopathology were used to diagnose an articular process synovial myxoma in a dog. On MR images, the tumor was characterized by distortion of the left L1–L2 articular process, widening of the articular process joint, and the presence of a mass contiguous with the synovium of the articular process that displaced the spinal cord. The tumor was T2‐hyperintense, T1‐hypointense, relative to muscle, and had mild contrast enhancement. The MR features of articular process synovial myxoma may be distinct from other diseases of the articular process joint.     

Imaging diagnosis--Ventriculo-peritoneal shunt associated infection in a dog

Ventriculo-peritoneal shunting is a surgical treatment for hydrocephalus. Complications of this procedure are not well described in dogs. The most common complication in humans is infection, which can be fatal if not diagnosed and treated quickly. We describe the magnetic resonance (MR) imaging characteristics of a shunt-associated cerebral infection in a dog. The MR features of the infection included hyperintensity of the lining of the ventricular system visible on a T2-weighted FLAIR sequence and marked linear contrast enhancement of the ependymal layer on T1-weighted sequences, similar to that described in people.     

Coexistence of occipital dysplasia and occipital hypoplasia/syringomyelia in the cavalier King Charles spaniel

Concurrent occurrence of occipital dysplasia and occipital hypoplasia in two dogs is described in this report. Occipital hypoplasia results in reduced volume of the caudal fossa, leading to overcrowding of the neural structures and, in severe cases, development of syringomyelia. In occipital dysplasia, there is a failure of complete ossification of the supraoccipital bone. When the two conditions occur concurrently, it is possible that syringomyelia may develop more slowly, resulting in presentation with clinical signs in middle to old age. This has implications for screening tests for early detection of syringomyelia, with a view to using the dog for breeding purposes, as dogs with an apparently mild phenotype for occipital hypoplasia/syringomyelia may actually have a more severe genotype.     

CAUDAL VENOUS RETURN THROUGH A LEFT AZYGOS VEIN IN A DOG

The Clinical, radiologic and echocardiographic findings in a one-year old dog with mild subvalvular aortic stenosis and aberrant caudal vena circulation are described. Aberrant systemic venous return to the right side of the heart usually has little clinical significance, but the unusual features in survey radiographs, contrast angiograms and contrast echocardiograms constitute the reasons for this report.     

Nephrotomography and ultrasonography for the localization of hyperfunctioning adrenocortical tumors in dogs

Nephrotomography and ultrasonography were used in 11 dogs with hyperadrenocroticism to assess the value of these techniques for the localization of biochemically diagnosed hyperfunctioning adrenocortical tumors. Both techniques enabled accurate localization of a unilateral adrenal mass in each of the dogs. Cross-sectional diameters of the masses ranged from 1 to 4 cm. In 1 dog, expansion of tumor into the caudal vena cava was revealed by caudal venacavography and ultrasonography. Mineralization in the tumor mass in 2 dogs was easily recognized by nephrotomography, but not by ultrasonography. Paracostal laparotomy confirmed the presence of an adrenocortical tumor in each dog, and expansion of tumor into the caudal vena cava in 1 dog. Cross-sectional diameters of the tumors ranged from 1.2 to 4.5 cm and corresponded well with cross-sectional measurements by nephrotomography and ultrasonography. It was concluded that nephrotomography and ultrasonography have similar diagnostic accuracies for the detection and localization of hyperfunctioning adrenocortical tumors.     

IMAGING DIAGNOSIS—MAGNETIC RESONANCE IMAGING FINDINGS OF AN INTRACRANIAL EPIDURAL TUBERCULOMA IN A DOG

Magnetic resonance (MR) imaging is highly sensitive for detecting tuberculomas in human patients but the specificity of the MR imaging features is low. Misdiagnosis with intracranial neoplasia is common, especially with dural‐based lesions or lesions located in the epidural space. We describe the MR imaging characteristics of an intracranial epidural tuberculoma caused by Mycobacterium tuberculosis infection in a dog. The intracranial mass and skull flat bone lysis and erosion are similar to those described in human caseating tuberculomas and can mimic intracranial neoplastic disease.