COMPUTED TOMOGRAPHIC ANATOMY OF THE CANINE PANCREAS

Barium sulfate was administered into the coeliac artery of 5 canine cadavers to allow for contrast computed tomography of the pancreas. Contiguous, 2-mm-thick slices were acquired. Multiplanar and three-dimensional reformatting were performed to clarify the anatomic relationship. After imaging, the cadavers were frozen, cross sections obtained, and plastinated. These were compared to the computed tomography images. Five plain and contrast enhanced computed tomographic series of normal live controls were acquired and evaluated retrospectively. In the study of the canine cadavers the pancreas became opacified and appeared homogenous with irregular contour. In normal live controls, acquiring an image at the end of expiration allowed a detailed view of the pancreatic parenchyma in the non-alterated pancreas, but pancreatic and bile ducts could not be seen. Adjacent to the hepatic hilus the pancreatic body appeared as a dorsoventrally flattened structure bordering on the ventral surface of the portal vein, both in cadavers and normal live controls. The right lobe extended caudodorsally to the right abdominal wall and aligned with the cranial part of the duodenum. The left lobe was adjacent to the gastric body in all dogs although it was separated from the gastric fundus by the dorsal extremity of the spleen in normal live controls. Neither kidney was suitable as an anatomic marker for localization of the pancreas, unlike traditional references in textbooks. We recommended using the portal vein to localize the pancreatic body, the descending duodenum for the right lobe, and the dorsal extremity of the spleen as well as the gastric fundus for the left lobe.     

A REVIEW OF HIGH RESOLUTION COMPUTED TOMOGRAPHY AND A PROPOSED TECHNIQUE FOR REGIONAL EXAMINATION OF THE CANINE LUMBOSACRAL SPINE

High resolution computed tomography (CT) is a noninvasive imaging modality that has been used extensively in evaluating diseases of the human lumbosacral spine. Excellent spatial and contrast resolution, combined with multiplanar reformatting capability make high resolution CT scanners well-suited for similar applications in dogs. Consistently good quality images can be obtained when careful attention is given to factors affecting resolution. This paper reviews and illustrates some principles of high resolution CT, and proposes a technique for regional CT examination of the canine lumbosacral spine.     

COMPUTED TOMOGRAPHY OF THE NORMAL CANINE LUMBOSACRAL SPINE: A MORPHOLOGIC PERSPECTIVE

The lumbosacral spine of six normal dogs weighing 4.5 to 24.5kg was imaged by computed tomography in 5.0 mm & 10.0 mm transverse planes. The vertebral canal and thecal sac (including emerging nerve roots not distinguished as separate structures from the spinal cord) were measured along dorsoventral and transverse dimensions at cranial, middle and caudal levels within each vertebra from transverse tomographic images. Linear measurements were standardized to the dorsoventral dimension of the L₆ vertebral midbody to permit comparison and averaging of the vertebral and thecal sac dimensions among different sized dogs. The dorsoventral and transverse vertebral canal size progressively increased from cranial to caudal within each vertebra from L₁?L₆ (p ≤ 0.05). The transverse dimension of the thecal sac image increased caudally within each vertebra from L₁?L₄ (p ≤ 0.05). The vertebral canal dorsoventral and transverse dimensions were largest in the midlumbar area (p ≤ 0.05). The transverse, but not the dorsoventral, imaged dimension of the thecal sac peaked in the L₄ vertebra (p ≤ 0.05). The dorsoventral thecal sac image was observed to fill the vertebral canal in the cranial and middle vertebral levels in vertebrae L₁ through L₅ in over 60% of these normal dogs. However, epidural fat could almost always be seen lateral to the thecal sac regardless of what lumbar vertebra or vertebral level was imaged. Cranial to the lumbosacral junction, the dorsal intervertebral disk margin was almost always concave relative to the thecal sac. However, at the L₇-S₁ junction, some dogs had flat or even slightly convex dorsal intervertebral disk margins. The dorsal and ventral longitudinal ligaments and the ligamentum flavum could not be identified as distinct structures on the 5.0 mm transverse tomographic images.     

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.     

COMPUTED TOMOGRAPHIC IMAGING PROTOCOL FOR THE CANINE CERVICAL AND LUMBAR SPINE

Computed tomography (CT) has been applied previously for assessment of canine spinal disease using a multitude of different technical imaging parameters. The purpose of this study was to establish an optimized imaging protocol for the cervical and lumbar canine spine using a single-detector-row helical CT unit. Thin slice thickness (1–2 mm), low pitch (axial scan mode, helical pitch <2), and medium-frequency image reconstruction algorithm significantly improved the visibility of the intervertebral disk and spinal cord. Tube current, helical reconstruction interval, and the use of an additional edge enhancement filter had no significant effect on the visibility of the intervertebral disk and spinal cord. There was also no interaction between the use of an additional edge enhancement filter and image reconstruction algorithm. Use of an additional edge enhancement filter introduced a double ring artifact in the periphery of the spinal canal lumen that did not correspond to the spinal cord or pachymeningeal margin.     

COMPUTED TOMOGRAPHIC ANATOMY OF THE EQUINE TARSUS

The purpose of this study was to provide a detailed computed tomographic (CT) anatomic reference for the equine tarsus. CT examinations of the tarsal regions from four clinically and radiographically normal adult horses, which were euthanized for reasons not related to musculoskeletal disease, were included in the study. Limbs were removed at the level of midtibia, and 3-mm contiguous transverse CT images were obtained, starting at a level proximal to the tuber calcanei and continuing distally into the proximal metatarsus. Soft tissue and bone windows were used to image different anatomic features, including bones, joints, and various soft tissue components of the tarsus. Each transverse slice was compared with bone models and dissected specimens to assist in the accurate identification of specific structures. The results of the study consist of nine CT images of the equine tarsus. Each image incorporates labeled soft tissue and bone-window images, a directional compass indicating cranial (Cr) or dorsal (D) and lateral (L), and a reconstructed scout image indicating the level through which the transverse slice was made.     

COMPUTED TOMOGRAPHIC APPEARANCE OF A NORMAL VARIANT OF THE CANINE TENTORIUM CEREBELLI OSSEUM

A nine-year-old German Shepherd dog presented to the Veterinary Teaching Hospital at North Carolina State University with an eleven-day history of progressive depression, lethargy, inability to walk, blindness and intermittent vomiting. Computed tomography (CT) of the brain was unremarkable; however, bilateral regions of low photon absorption were noted within the tentorium cerebelli osseum. Mean CT numbers of −47.9 Hounsfield units (HU) and −26.4 HU were recorded within the left and right areas, respectively. These areas most likely represent diploë and are presumably a normal variant of the canine skull. A possible explanation for this finding includes a developmental variant where the medial and lateral plates of the tentorium cerebelli osseum fail to fuse, thus leaving a space for diploë accumulation. Use of various combinations of CT windows and numbers can be valuable for characterizing such variants.     

SUBCLINICAL CT ABNORMALITIES IN THE LUMBOSACRAL SPINE OF OLDER LARGE-BREED DOGS

Computed tomography (CT) of the L5-S3 vertebral levels was performed in six, large-breed dogs presented for problems unrelated to the lumbosacral spine. All dogs were asymptomatic for lumbosacral stenosis on neurologic examination. Breeds included German Shepherd, Golden Retriever, Boxermix and Belgian Malinois. Ages ranged from 5-12 years. Five out of six dogs exhibited CT abnormalities. Among the 18 disc levels examined, the most common findings were idiopathic stenosis, loss of vertebral canal epidural fat, and nerve tissue displacement. Less common abnormalities were vertebral canal or foraminal bone proliferation, loss of intervertebral foramen fat, vertebral canal disc bulging, degenerative articular process joint disease, transitional vertebra, dural ossification, foraminal disc bulging, Schmorl's nodes, calcified extruded disc fragment, and sacroiliac joint osteophytes. Vertebral subluxation was absent in all dogs. Findings indicate that some lumbosacral CT abnormalities may be clinically insignificant, especially in older dogs.     

HELICAL COMPUTED TOMOGRAPHIC ANGIOGRAPHY OF CANINE PORTOSYSTEMIC SHUNTS

Helical computed tomographic (CT) angiography was performed in 16 dogs with known or suspected portosystemic shunts. Fifteen portosystemic shunts were detected including five single intrahepatic shunts, five single extrahepatic shunts, and five multiple extrahepatic shunts. One dog had a normal CT examination. All diagnoses were confirmed by one or several alternate methods including ultrasound, surgery, necropsy, angiography, and liver biopsy. CT detected the origin of 13 of 15 portosystemic shunts and insertion of 13 of 15 shunts. Limitations included inability to resolve two vessels originating very close to each other, and identification of vessels that traveled parallel to the axial image plane. CT angiography is a promising, minimally invasive method of diagnosing a variety of portosystemic shunts in dogs.     

HELICAL COMPUTED TOMOGRAPHIC ANGIOGRAPHY OF THE NORMAL CANINE PANCREAS

Helical abdominal computed tomography (CT) was performed in nine normal beagle-mix dogs. Following cephalic vein injection of ionic iodinated contrast medium via power injector (rate 5 ml/s) dual-phase CT was performed in all dogs. A delayed scan was performed in five dogs between 5 and 13 min after the contrast medium injection. The median time of appearance of contrast medium in the aorta and gastroduodenal artery was 6.3 and 7 s, post start injection and 12 and 12.2 s in the gastroduodenal and portal vein, resulting in a purely arterial pancreatic time window of 5-6s. Pancreatic veins and parenchyma remained enhanced until the end of the dynamic scan (40s). The pancreatic parenchyma showed heterogeneous arterial and homogenous venous contrast enhancement which was slightly hypoattenuating compared to the liver. Delayed scans provided best delineation of the pancreas from the liver. The common bile duct could be identified ventral and to the right of the portal vein joining the dorsomedial aspect of proximal duodenum. Because of the very short time window and variable onset of pure arterial enhancement careful planning of dual-phase studies with previous dynamic CT is recommended. Dual-phase CT angiography enables assessment of the arterial supply, parenchymal perfusion and venous drainage of the canine pancreas.     

ANATOMY OF THE CANINE ORBITAL REGION

Computed tomography (CT) was used to study the normal anatomy of the orbital region in one Beagle. Direct transverse and reformatted dorsal, sagittal, and oblique plane images were used to distinguish various soft tissue structures. Intraorbital fat provided a natural contrast against which extraocular muscles and nerves could be discerned. The noninvasive nature and the multiplanar imaging capabilities of CT provided a means by which the orbital contents could be precisely localized and differentiated from one another.     

COMPUTED TOMOGRAPHIC ANATOMY OF THE CANINE NASAL PASSAGES

A normal German shepherd dog underwent CT imaging with contiguous 10 mm thick images made of the nasal cavity from the caudal limit of the frontal sinuses to the rostral aspect of the nose. Normal structures were identified. This normal anatomic information will be of use in assessing CT images of dogs suspected of having nasal cavity disease.     

COMPUTED TOMOGRAPHIC ARTHROGRAPHY OF THE NORMAL CANINE STIFLE

Computed tomographic (CT) imaging of eight normal cadaveric canine stifles was performed before and after intra-articular administration of iodinated contrast medium. Transverse CT images were reconstructed in dorsal, parasagittal, and oblique planes. The following ligamentous structures were identified on transverse CT images in all stifles: cranial cruciate ligament, caudal cruciate ligament, medial meniscus, lateral meniscus, and the medial and lateral collateral ligaments. The following ligamentous structures were identified on transverse computed tomographic arthrography (CTA) images in all stifles: cranial cruciate ligament, caudal cruciate ligament, medial meniscus, lateral meniscus, meniscofemoral ligament, cranial meniscotibial ligaments, caudal meniscotibial ligaments, intermeniscal (transverse) ligament, and the medial and lateral collateral ligaments. The patellar tendon was identified on transverse and reconstructed dorsal and sagittal CT and CTA images in all stifles. Multiplanar reconstructions enabled further evaluation of the continuity of the cranial and caudal cruciate ligaments and menisci. The medial and lateral collateral ligaments were not clearly identified on CT or CTA multiplanar reconstructed images.     

COMPUTED TOMOGRAPHIC ARTHROGRAPHY OF THE NORMAL CANINE ELBOW

Comprehensive evaluation of canine elbow joint dysfunction includes assessment of articular cartilage, which can noninvasively be performed with contrast arthrography. Aims of this prospective study were to compare positive contrast computed tomographic (CT) arthrography and histomorphometry measures of cartilage thickness in normal canine elbows, and to determine the optimal contrast medium concentration. Thirty‐two canine cadaver elbows were examined using multidetector CT, before and after intra‐articular administration of iohexol at one of three different concentrations. Articular cartilage thickness was measured on both the CT arthrography images and corresponding histologic specimens. Mean difference (bias) between the CT arthrography and histomorphologic measurements was 0.18 and 0.19 mm in the sagittal and dorsal planes, respectively. Mean bias and precision of CT arthrography measurements made in the sagittal or dorsal reformations were not significantly different from one another. Computed tomographic arthrography measurements from elbows with 75 mg I/ml were significantly larger and had greater bias compared to other contrast medium groups (150 and 37.5 mg I/ml). There was no significant difference in CT arthrography measurement precision between different contrast medium concentrations. Histomorphologic thickness of the articular cartilage overlying the cranial aspect of the ulna (mean 0.32 mm) was significantly thinner than cartilage of the radius (0.36 mm) or humerus (0.36 mm). Findings from this cadaver study indicated that CT arthrography delineates articular cartilage of the normal canine elbow; yields cartilage thickness measures slightly greater than histomorphometry measures; and provides high measurement precision regardless of image plane, contrast medium concentration, or anatomic zone.     

EVALUATION OF CANINE LUMBOSACRAL STENOSIS USING INTRAVENOUS CONTRAST-ENHANCED COMPUTED TOMOGRAPHY

The objective of this study was to evaluate intravenous contrast-enhanced computed tomography as a technique for predicting the within-level location(s) of compressive soft tissues in the canine lumbosacral spine. Pre-operative intravenous contrast-enhanced computed tomography of the L5-S3 vertebral levels was performed in 12 consecutive large breed dogs with lumbosacral stenosis. The images were evaluated for enhancement of soft tissues by two radiologists who were unaware of the surgical findings. For each within-level location (dorsal canal, ventral canal, right lateral recess, left lateral recess) enhancement was classified as present, absent or equivocal. The results were compared with the results of surgical exploration and histopathology of excised tissues. The positive predictive values of intravenous contrast-enhanced computed tomography for compressive soft tissues involving the dorsal canal, ventral canal and lateral recesses were 83%, 100%, and 81% respectively. Negative predictive values for compressive soft tissues involving these locations were 29%, 50%, and 40% respectively.     

COMPUTED TOMOGRAPHIC ANATOMY OF THE DISTAL EXTREMITY OF THE HORSE

X-ray computed tomography (CT) is an imaging tool that is becoming increasingly available for use in veterinary medicine. Advantages, including depiction of detailed cross-sectional anatomy, improved contrast resolution, and computer reformatting, make it a potentially valuable diagnostic technique. Veterinary application of CT has been primarily limited to use in small animals. Current reports describe the technique for use in the horse, but there are no published studies correlating serial CT images with equine cross-sectional anatomy. A study of the distal extremity of the horse was undertaken to facilitate interpretation of images produced using CT. Transverse CT images of the distal forelimb of equine cadavers were evaluated relative to gross anatomic dissection. Resolution of bone architecture in transverse plane images was satisfactory, but soft-tissue' resolution, although satisfactory for visualization of major structures, was relatively poor, probably due to lack of interposed fat and insufficient differences in physical density and atomic number. Thus it appears in the equine distal limb that CT may be most useful for evaluation of complex bone abnormalities.     

COMPUTED TOMOGRAPHIC EVALUATION OF CANINE AND FELINE MEDIASTINAL MASSES IN 14 PATIENTS

A 15-year retrospective analysis of histologically proven canine and feline mediastinal malignancies at the University of Minnesota was conducted to identify patients imaged by computed tomography (CT). The goal of the study was to characterize the CT appearance, to determine if there were any tumor type-specific appearances, and to clarify the role of CT in patients with mediastinal masses. Fourteen patients meeting these criteria were available for evaluation. The masses were characterized based on the presence or absence of contrast enhancement, internal architecture, size, extent of local invasion, the presence of pleural fluid, and the presence of regional vascular invasion. Within the limits of this study and the histopathologic information available, there appeared to be no clinically exploitable relationship between the CT appearance and the histologic characterization of the mass. However, CT does provide reasonably accurate local staging information.     

COMPUTED TOMOGRAPHY AND POSITIVE CONTRAST COMPUTED TOMOGRAPHIC ARTHROGRAPHY OF THE CANINE SHOULDER: NORMAL ANATOMY AND EFFECTS OF LIMB POSITION ON VISIBILITY OF SOFT TISSUE STRUCTURES

Soft tissue injuries of the shoulder are an important cause of forelimb lameness in dogs. The objectives of this canine cadaver study were to describe normal anatomy of shoulder soft tissue structures using computed tomography (CT) and computed tomographic arthrography (CTA) and to determine the effects of positioning on visualization of shoulder soft tissue structures. Thirteen forelimbs were removed from eight canine cadavers. Two forelimbs were used for contrast dose optimization. For the remaining 11 forelimbs, shoulder CT and CTA were performed using three defined joint angles (140°, 90°, and 70°). For three forelimbs, CT and CTA images were compared with frozen anatomic sections to describe normal anatomy. Ten forelimbs were used for analysis of positioning effects. Soft tissue structures evaluated were the joint capsule, cartilage, ligaments, tendons, and muscles. A visual assessment score was assigned to each structure using a consensus of two observers. The range and mode of scores were calculated and compared for each modality and limb position. The shoulder joint capsule and medial and lateral glenohumeral ligaments were completely visible with CTA. All tendons and muscles were visualized in all the examinations except for the teres minor muscle tendon and the coracobrachialis muscle, which were not visible on all scans. Positioning the limb in an extended position significantly improved visualization of most soft tissue shoulder structures. Shoulder cartilage was best seen with CTA and with neutral or flexed positioning of the shoulder. Findings indicated that both CT and CTA are feasible imaging techniques for visualization of soft tissue structures of the canine shoulder.     

VACUUM PHENOMENON OF THE CANINE SPINE: CT FINDINGS IN 3 PATIENTS

The vacuum phenomenon was identified in the spine of 3 dogs by computed tomography. Gas from the vacuum phenomenon was clearly present in the disc space in 2 dogs. In the other the disc space was collapsed, and the gas was in the caudal vertebral endplate. In humans, gas accumulation in the intervertebral disc caused by the vacuum phenomenon seen on computed tomography spinal images is a sign of degenerative disc disease rather than infection. It may also be seen in the apophyseal joints and in the vertebral canal associated with the vacuum phenomenon in the disc or apophyseal joints. The recognition of the vacuum phenomenon in the spine in veterinary patients will likely become more important as computed tomography imaging becomes more common with the increased availability of this imaging procedure.     

EVALUATION OF THE URETER AND URETEROVESICULAR JUNCTION USING HELICAL COMPUTED TOMOGRAPHIC EXCRETORY UROGRAPHY IN HEALTHY DOGS

Abdominal computed tomography (CT) using a protocol designed for evaluation of the ureters was performed on six normal purpose-bred research dogs. After noncontrast CT, a postcontrast scan was performed 3 min post midpoint of injection of 400 mgI/kg body weight of diatrizoate meglumine/sodium. Ureteral and ureterovesicular junction anatomy were readily assessed with minimal patient preparation. The ureters were similar in size to reported values and the renal pelvis, ureter, and ureterovesicular junction were easily identified on both noncontrast and contrast-enhanced scans. There was a significant relationship between bladder volume and interureterovesicular junction distance but not between bladder volume and ureterovesicular junction to internal urethral orifice distance. A reliable bony landmark for the identification of the internal urethral orifice could not be determined. The results of this preliminary study of normal anatomy should facilitate the clinical use of CT in the evaluation of ureteral disease (e.g., ureteral ectopia).