ANATOMY OF THE CANINE ORBITAL REGION

Elliptical Fourier descriptors of outline and morphological analysis in caudal view of foramen magnum of the tropical raccoon (Procyon cancrivorus) (Linnaeus, 1758)

OBJECTIVES

To evaluate sexual-size dimorphism and attempt at categorization of inter-individual shapes of foramen magnum outlines using Fourier descriptors which allow for shape outline evaluations with a resultant specimen character definition.

MATERIALS AND METHODS

Individual characterization and quantification of foramen magnum shapes in direct caudal view based on elliptical Fourier technique was applied to 46 tropical raccoon skulls (26 females, 20 males).

RESULTS

Incremental number of harmonics demonstrates morphological contributions of such descriptors with their relations to specific anatomical constructions established. The initial harmonics (1st to 3rd) described the general foramen shapes while the second (4th to 12th) demonstrated fine morphological details. Sexual-size dimorphism was observed in females (87.1%) and 91.7% in males, normalization of size produces 75% in females and 83% in males. With respect to foramen magnum dimorphism analysis, the result obtained through elliptic Fourier analysis was comparatively better in detail information of outline contours than earlier classical methods. The first four effective principal components defined 70.63% of its shape properties while the rest (22.51%) constituted fine details of morphology.

CONCLUSION

Both size and shape seems important in sexual dimorphisms in this species, this investigation suggest clinical implications, taxonomic and anthropologic perspectives in foramen characterization magnum characterization and further postulates an increased possibility of volume reduction cerebellar protrusion, ontogenic magnum shape irregularities in the sample population with neurologic consequences especially among females.

Comparison of the diagnostic quality of computed tomography images of normal ocular and orbital structures acquired with and without the use of general anesthesia in the cat

OBJECTIVE

To compare the diagnostic quality of computed tomography (CT) images of normal ocular and orbital structures acquired with and without the use of general anesthesia in the cat.

ANIMAL STUDIED

Eleven privately owned cats with nasal disease presenting to a single referral hospital.

PROCEDURES

All cats received a complete ophthalmic examination. A 16 multislice helical CT system was utilized to acquire images of the skull and neck with and without the use of general anesthesia. Images were acquired before and after the administration of intravenous iodinated contrast. Images of normal ocular and orbital structures were evaluated via consensus by two board-certified radiologists. Visibility of ocular and orbital structures, degree of motion, and streak artifact were assessed and scored for each image set in the transverse, dorsal, and sagittal planes.

RESULTS

The use of general anesthesia did not significantly affect the diagnostic quality of images. No motion artifact was observed in any CT image. Streak artifact was significantly increased in scans performed in the transverse orientation but not in the dorsal orientation or sagittal orientation and did not affect the diagnostic quality of the images. Contrast enhancement did not significantly enhance the visibility of any ocular or orbital structures.

CONCLUSION

Diagnostic CT images of normal ocular and orbital structures can be acquired without the use of general anesthesia in the cat.

Computed tomography in small animals – Basic principles and state of the art applications

Since its clinical introduction, computed tomography (CT) has revolutionized veterinary medicine and is considered to be one of the most valuable tools for the imaging work-up of neurological, oncological and orthopaedic canine and feline patients. In small animals with acute trauma, particularly those involving complex anatomic areas such as the head, spine or pelvis, CT has been established as a standard imaging method. With the increasing availability of radiation therapy in veterinary medicine, CT has also become the principal tool to stage a tumour, assess response, and guide radiation therapy. The increasing availability of helical CT in veterinary medicine has allowed novel techniques such as spiral CT angiography and high-resolution CT. This review provides a brief overview of the historical and technical development of CT and literature reviews of the major clinical CT applications in small animals such as intracranial and extracranial lesions, the spine, the appendicular skeleton, and abdominal and thoracic diseases.

Taenia coenurus in the orbit of a chinchilla

A 4-year old, male intact, captive-bred chinchilla (Chinchilla lanigera) was presented due to progressive exophthalmos of the right eye over a 5-month period. Ophthalmic examination revealed exophthalmos with dorsal displacement of the right globe. Retropulsion was decreased and a fluctuant, subcutaneous mass could be palpated posterior and dorsal to the central aspect of the zygomatic bone. Transdermal ultrasonography revealed a fluid-filled mass consistent with a cyst located within the ventral right orbit. Computed tomography demonstrated dorsal displacement of the globe, lateral displacement of the zygomatic arch, and numerous mineral-dense foci within the lumen of the cyst. The cyst was removed en bloc by ventral transpalpebral orbitotomy. Histopathology revealed a single capsulated cyst with multiple invaginated protoscolices, characterized by a prominent scolex with refractile hooklets, suckers, and abundant calcareous corpuscles consistent with a Taenia coenurus. Exophthalmos resolved with surgical therapy and there was no evidence of recurrence or postoperative complications over a period of 2 years. To the authors' knowledge, this is the first reported case of an orbital cyst of parasitic origin in a chinchilla.

Magnetic resonance imaging, computed tomography, and cross-sectional views of the anatomy of normal nasal cavities and paranasal sinuses in mesaticephalic dogs

OBJECTIVE

To use computed tomography (CT) and magnetic resonance imaging (MRI) to provide a detailed description of the nasal cavities and paranasal sinuses in clinically normal mesaticephalic dogs.

ANIMALS

2 clinically normal Belgian Shepherd Dogs that weighed 25 and 35 kg, respectively.

PROCEDURE

The first dog was anesthetized and positioned in ventral recumbency for CT and MRI examinations, and transverse slices were obtained from the caudal part of the frontal sinuses to the nares. For MRI, T1-weighted, T2-weighted, and proton-density sequences were obtained. The second dog was anesthetized and positioned in dorsal recumbency with the head perpendicular to the table, and CT and MRI examinations were again conducted. At the completion of the MRI examination, each dog received an i.v. injection of heparin and then was euthanatized. A 4% solution of formaldehyde was perfused i.v. immediately after each dog was euthanatized. The skull was prepared, decalcified, embedded with gelatin, and sectioned into 5-mm-thick sections by use of a stainless-steel knife. Each anatomic section was photographed and compared with the corresponding CT and MRI views.

RESULTS

Structures on the CT and MRI views matched structures on the corresponding anatomic sections. The CT scans provided good anatomic detail of the bony tissues, and MRI scans were superior to CT scans for determining soft-tissue structures.

CONCLUSIONS AND CLINICAL RELEVANCE

CT and MRI provide a means for consistent evaluation of all structures of the nasal cavities and frontal sinuses. Both techniques could be useful for evaluation of diseases that affect the nasal region.

Computed tomographic anatomy of the canine inner and middle ear

A series of high-resolution computed x-ray tomography (CT) images of the normal canine middle and inner ear are presented to serve as a reference for optimal interpretation of clinical CT images of animals with diseases affecting this region.

Cross-sectional imaging techniques in veterinary ophthalmology

Ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI) are useful, complementary cross-sectional imaging modalities of the eye and orbit. High-resolution US provides excellent morphological information of ocular structures but offers limited information on the periocular tissues. CT and MRI provide valuable morphologic and topographic images of both ocular and periocular structures, thereby giving a more complete picture of the pathological process. US can be performed on awake patients, whereas CT and MRI require general anesthesia. In addition, US equipment is readily available and less costly than CT or MRI units. Fine-needle aspirations and biopsies under US or CT guidance can also be performed. This article reviews the technique and normal findings of ocular and orbital structures as displayed in each of these imaging modalities. Representative clinical cases are presented to illustrate the interpretation principles as well as to provide an illustrative reference for common ocular and orbital changes.

Computed tomography of normal cranioencephalic structures in two horses

The purpose of this investigation was to define the anatomy of the cranioencephalic structures in horses using computed tomography (CT). Transverse images of two isolated equine cadaver heads were obtained using a Toshiba 600 HQ (third-generation equipment TCT). CT images were compared to corresponding frozen cross-sections of the cadaver head. Relevant anatomical structures were identified and labelled at each level. The resulting images provided excellent anatomic detail of the structures of the central nervous system and associated formations. Annotated CT images from this study are intended as a reference for clinical CT imaging studies of the equine head.

Use of magnetic resonance imaging for the investigation of orbital disease in small animals

Twenty-five small animal patients presenting with signs of orbital disease were investigated using magnetic resonance imaging (MRI) in an attempt to assess the value of this imaging technique for diagnosis. All patients were also examined using ultrasonography, and skull radiography was performed in 20 of these animals. The final diagnoses included neoplasia, inflammatory disease and foreign body penetration. MRI produced detailed images of orbital tissues and provided more information about the extent of pathology than the other imaging techniques; a correct diagnosis based solely on the MRI scan was made in 22 cases. Radiography was found to be helpful only in cases in which neoplastic disease extended markedly beyond the confines of the orbit into the nasal chamber and paranasal sinuses. Radiographic changes other than soft tissue swelling were not evident in other orbital disease processes. Ultrasonography gave both false negative and false positive diagnoses for neoplastic masses, although it allowed the correct diagnosis of both cases of foreign bodies and one of the three cases of retrobulbar abscesses in this series. MRI is recommended for patients in which radiography and ultrasonography fall to produce a confident diagnosis or for which surgery is proposed.

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.

MRI examination of the masticatory muscles in the gray wolf (Canis lupus), with special reference to the M. temporalis

We examined the head of the gray wolf (Canis lupus) using MRI methods. Although the arising surface of the M. temporalis was not so enlarged in the frontal bone, the small frontal bone did not disturb the M. temporalis from occupying the lateral space of the frontal area in the gray wolf as in the domesticated dog. In the gray wolf, it is suggested that the M. temporalis may not be well-developed in terms of size of arising area, but in the thickness of running bundles. We suggest that the dog has changed the three-dimensional plan of the M. temporalis during the domestication and that the M. temporalis has developed a large arising surface in the frontal bone and lost the thickness of belly in the frontal area in accordance with the enlargement of the frontal bone and the increase in brain size.

Surgery of the orbit

Orbital surgery is performed infrequently but when necessary, requires detailed understanding of orbital anatomy and the probable biologic behavior and extent of the pathologic process affecting the orbit. Thorough preoperative characterization of an orbital disease allows the surgeon to develop a surgical strategy. Inaccurate or hasty preoperative localization, determination of extension, and diagnosis may result in selection of an inappropriate surgical approach or discretionary surgery when medical treatment is indicated. In most instances, diagnostic images (MR, CT, echography) should always be made and fine-needle aspiration be done before orbital surgery is performed. The choice of surgical approach or combination of approaches is determined primarily by the type, location, size, and extent of disease present. Extensive surgical exposure of the orbit is limited to centimeters or fractions of a centimeter because of the compact anatomy and tight confines of the orbital region. Careful tissue manipulation, surgical dissection, and postoperative assessment are necessary to preserve the globe and functional vision when orbital disease endangers function.

Interpretation of computed tomographic images

This article discusses the production of optimal CT images in small animal patients as well as principles of radiographic interpretation. Technical factors affecting image quality and aiding image interpretation are included. Specific considerations for scanning various anatomic areas are given, including indications and potential pitfalls. Principles of radiographic interpretation are discussed. Selected patient images are illustrated.