Differentiation between inflammatory and neoplastic orbital conditions based on computed tomographic signs.

OBJECTIVE: To identify computed tomographic (CT) signs that could be used to differentiate inflammatory from neoplastic orbital conditions in small animals. ANIMAL STUDIED: Fifty-two animals (25 cats, 21 dogs, 4 rabbits, and 2 rodents). PROCEDURE: Case-control study in which CT images of animals with histopathologic diagnosis of inflammatory (n = 11), neoplastic orbital conditions (n = 31), or normal control animals (n = 10) were reviewed independently by five observers without the knowledge of the history or diagnosis. Observers recorded their observations regarding specific anatomical structures within the orbit using an itemized form containing the following characteristics: definitely normal; probably normal; equivocal; probably abnormal; and definitely abnormal. Results were statistically analyzed using Fleiss' kappa and logistic regression analyses. RESULTS: The overall level of agreement between observers about the presence or absence of abnormal CT signs in animals with orbital disease was poor to moderate, but was highest for observations concerning orbital bones (κ = 0.62) and involvement of the posterior segment (κ = 0.52). Significant associations between abnormalities and diagnosis were found for four structures: Abnormalities affecting orbital bones (odds ratio [OR], 1.7) and anterior ocular structures (OR, 1.5) were predictive of neoplasia, while abnormalities affecting extraconal fat (OR, 1.7) and skin (OR, 1.4) were predictive of inflammatory conditions. CONCLUSIONS: Orbital CT is an imaging test with high specificity. Fat stranding, a CT sign not previously emphasized in veterinary medicine, was significantly associated with inflammatory conditions. Low observer agreement probably reflects the limited resolution of CT for small orbital structures.

Imaging the cranial nerves.

An understanding of the normal course of the cranial nerves (CN) is essential when interpreting images of patients with cranial neuropathies. CN foramina are depicted best using computed X-ray tomography, but the nerves are depicted best using magnetic resonance imaging. The function and anatomy of the CN in the dog are reviewed and selected examples of lesions affecting the CN are illustrated.

Does changing the orientation of a thoracic radiograph aid diagnosis of rib fractures?

To test the hypothesis that changing the orientation of a thoracic radiograph aids diagnosis of rib fractures, a case-control study was carried out using 120 radiographs of small animal patients with recent thoracic trauma. Six independent observers representing three levels of experience viewed the radiographs in randomized order in conventional and unconventional orientations at 15-s intervals in a PowerPoint presentation. Sensitivity for rib fractures was 53-69% and specificity was 74-97%, depending on the observer. Radiologists had higher specificity than less experienced observers (P = 0.0001), but comparable sensitivity for rib fractures. Radiologists had significantly higher accuracy than residents (P = 0.03), and residents had higher accuracy than interns (P = 0.02). Accuracy of diagnosis was reduced significantly when based on lateral radiographs compared with dorsoventral (DV)/ventrodorsal (VD) views (P = 0.02) mainly because of low sensitivity of lateral radiographs of dogs with rib fractures. Rotating radiographs 90 degrees clockwise was associated with increased specificity of one intern (from 74 to 90%, P = 0.03), but had no effect on accuracy of diagnosis by other observers (P > 0.16). Turning DV/VD views upside down had no effect on accuracy of diagnosis of any observers (P > 0.40). Changing the orientation of a thoracic radiograph may make it easier for some novices to examine the ribs; hence it could be considered a training aid rather than a technique that will benefit an experienced radiologist.

Computed tomography variations in morphology of the canine atlas in dogs with and without atlantoaxial subluxation.

Computed tomography images of 120 dogs were reviewed to characterize variations in atlas morphology, and to identify breed-specific morphologic features. The neural arch of the atlas was thicker in large dogs and male dogs than in small dogs, having a layer of trabecular bone between the inner and outer layers of compact bone. The transverse processes of the atlas were relatively longer in large dogs than in small dogs. Twelve (10%) dogs had incomplete ossification of the atlas. Incomplete ossification of the atlas was associated with gun dogs. Eight dogs had atlantoaxial subluxation. All eight dogs with atlantoaxial subluxation had cervical signs, whereas none of the seven dogs with incomplete ossification of the atlas unaccompanied by atlantoaxial subluxation had clinical signs referable to that area. Of five dogs with both atlantoaxial subluxation and incomplete ossification of the atlas, four had osseous defects affecting both the intercentrum and neural arch, and one had only an osseous defect affecting the neural arch. There was a strong association between incomplete ossification of the atlas and atlantoaxial subluxation (odds ratio 35.0, 95% CI 7.0-175, P = 0.00002), which supports the hypothesis that incomplete ossification of the atlas predisposes dogs to atlantoaxial subluxation.

[X-ray and CT morphology of atlas variants in the dog]. / Röntgen- und CT-Morphologie von Atlas- varianten beim Hund.

To investigate variations in atlas shape in dogs the image archives of the Department for Small Animals and Horses, University of Vienna, and The Royal Veterinary College, University of London were searched for radiographs and CT images of the canine atlas. 32 radiographic and 78 CT studies, including 51 toy and 54 large breed dogs, were retrieved and analysed. Five dogs had both radiographs and CT scans. Patients with pathologic alterations, such as fractures and incomplete ossification of the atlas, as well as oblique projections were excluded. Compared to large breed dogs (body weight more than 30 kg) the atlas of toy breed dogs (body weight less than 10 kg) had a reduced craniocaudal and an increased dorsoventral diameter. The vertebral longitudinal axis appeared to be dorsorotated, resulting in a steeper rise of the atlas wings and a more dorsally located lateral vertebral foramen. When comparing the atlas of toy and large breed dogs, the distribution of three morphologic parameters was statistically different: Ratio length to height (toy breeds > 1, large breeds < or = 1), shape of the vertebral chanal (toy breeds: vertically oval, large breeds: round resp. cross-oval, or vertically oval) and trabecular bone of the dorsal arch (toy breeds: absent, large breeds: present). There was no significant difference in the morphology of the ventral arch. Differences in atlas morphology could contribute to the predisposition of toy breed dogs to atlanto-axial instability; however, further studies are necessary to test this hypothesis.

Imaging diagnosis--necrotizing meningomyelitis and polyarthritis.

A vaccinated 2-year-old female neutered Weimaraner had bilateral pelvic limb ataxia that progressed over 12 h. The dog became nonambulatory, with signs of pain on palpation of the lumbar spine. The dog also developed multiple joint effusions. On magnetic resonance (MR) imaging, there was a diffuse, asymmetric T2-hyperintensity in the thoracolumbar spinal cord which was characterized by contrast enhancement. Lumbar cerebrospinal fluid (CSF) analysis had an elevated white blood cell count and protein. On the basis of MR images and CSF analysis, a presumptive diagnosis of diffuse myelitis was made. The dog became paraplegic and was euthanized. Postmortem examination confirmed the presence of myelitis with vasculitis and nonerosive polyarthritis.