COMPUTED TOMOGRAPHIC APPEARANCE OF MELANOMAS IN THE EQUINE HEAD: 13 CASES

Melanomas are one of the most common neoplasms in the horse and are frequently found in the head region. There is a genetic predisposition in horses with a gray hair coat. Computed tomography (CT) is frequently used in referral practice to evaluate the equine head but there are few reports describing the CT appearance of melanomas in this location. The aim of this retrospective, case series study was to describe characteristics in a group of horses with confirmed disease. Case records from two referral hospitals were reviewed, and 13 horses were identified that had undergone CT of the head, with a diagnosis of melanoma based on cytology, histopathology, or visual assessment of black (melanotic) tissue. A median of 11 melanomas was identified per horse (range 3–60), with a total of 216 masses. Melanomas were found most frequently in the parotid salivary gland, guttural pouches, surrounding the larynx and pharynx and adjacent to the hyoid apparatus. In noncontrast CT images, all melanomas were hyperattenuating (median; 113.5 Hounsfield units (HU), IQR; 26 HU) compared to masseter musculature (median; 69 HU, IQR; 5.5 HU). Fifty‐six (25.9%) masses were partially mineralized and 41 (19.4%) included hypoattenuating areas. Histopathological assessment of these melanomas suggested that the hyperattenuation identified was most likely a result of abundant intracytoplasmic melanin pigment. Melanomas of the equine head appeared to have consistent CT features that aided detection of mass lesions and their distribution, although histopathological analysis or visual confirmation should still be obtained for definitive diagnosis .     

COMPUTED TOMOGRAPHIC APPEARANCE OF OSTEOCHONDRITIS DISSECANS-LIKE LESIONS OF THE PROXIMAL ARTICULAR SURFACE OF THE PROXIMAL PHALANX IN A HORSE

A 6-year-old Thoroughbred gelding presented with a left forelimb lameness. The results of lameness examination, radiography, nuclear scintigraphy, and computed tomography are presented. Based on the diagnostic imaging, subchondral fractures and osteochondritis dissecans lesions of the proximal articular surface of the proximal phalanx were diagnosed. A brief discussion of osteochondritis dissecans is presented.     

COMPUTED TOMOGRAPHY IN HORSES

Computed tomography (CT) is a valuable imaging procedure but one that requires significant technical support. Although scanners are available for veterinary use, their successful installation requires in-depth facility planning. Maintenance costs for these highly complex systems are high and may greatly exceed acquisition costs. Equipment to move anesthetized horses and support them during scanning is also expensive. Transport and scan table equipment suitable for equine CT studies are described. Clinical scan protocols used for CT of the equine skull and extremities are detailed. Precise positioning is essential for interpretable scans. Significant training in anatomy and CT physics is required for the veterinary computed tomographer.     

SCINTIGRAPHY OF THE SACROILIAC JOINT REGION IN ASYMPTOMATIC RIDING HORSES: SCINTIGRAPHIC APPEARANCE AND EVALUATION OF METHOD

The sacroiliac region in 33 clinically normal riding horses was examined with scintigraphy to determine the normal scintigraphic appearance, to evaluate a semiquantitative method used to calculate a sacroiliac joint (SI joint) ratio, and to identify factors that affect the scintigraphic appearance of the pelvis. The scintigraphic examination included dorsal views of each SI joint region and one lateral view of the urinary bladder. Two predefined areas (the SI joint and the area between the tuber sacrale and the SI joint) were evaluated subjectively by comparing the intensity in each area to the intensity in the tuber sacrale, and a semiquantitative method was applied on the images to calculate an SI joint ratio. The thickness of the muscle mass overlying each SI joint was measured by using ultrasound. A corrected ratio was calculated based on a corrected pixel count for each SI joint. Of 29 evaluated horses, 28 had normal radiotracer uptake in the SI joints and 10 horses had symmetric normal radiotracer uptake in the area between the tuber sacrale and the SI joint. The mean SI joint ratio was 0.53 on both the left and right sides, and the mean corrected SI joint ratio was 2.15 on the left side and 2.13 on the right side. Factors that affect the scintigraphic appearance of the pelvis were identified and included attenuation, radioactive urine, and muscle symmetry. The muscle thickness ranged from 8-11 cm, causing 71-82% attenuation. Radioactive urine in the urinary bladder was located ventral to the SI joint region in 16 horses, and four of these were excluded from further evaluation because of risk of misinterpretation. A visual assessment of symmetry of the horses' gluteal muscle mass was compared with the ultrasound measurements. Fourteen horses (14/33) were regarded symmetric by both techniques. Soft tissue attenuation was found to severely compromise the result and indicated that only lesions in the SI joint with severely increased radiotracer uptake can be detected with scintigraphy. Knowledge about presence of radioactive urine ventral to the SI joint region and assessment of muscle symmetry is essential for a correct subjective evaluation. Any situation with difference in muscle mass between the left and right side of the pelvis will give a false impression of increased radiotracer uptake on the side with lesser muscle mass.     

COMPARISON BETWEEN COMPUTED TOMOGRAPHIC ARTHROGRAPHY,RADIOGRAPHY, ULTRASONOGRAPHY,AND ARTHROSCOPY FOR THE DIAGNOSIS OF FEMOROTIBIAL JOINT DISEASE IN WESTERN PERFORMANCE HORSES

The femorotibial joints are a common source of lameness in Western performance horses. The objective of this prospective study was to compare the radiography, ultrasonography, computed tomographic arthrography (CTA), and arthroscopy findings in horses with lameness localized to the femorotibial joints. Twenty‐five stifles in 24 horses were included and were evaluated with all four of these diagnostic methods. Defects detected in femorotibial joint structures were compared between diagnostic methods using a McNemar's test to evaluate for disagreement. Cranial medial meniscotibial desmopathy was most detected on arthroscopy (in 14/25 cases) and was only detected on ultrasonography in three out of 11 (27.3%) arthroscopically observed cases, but was detected on CTA in nine out of 12 (75%) arthroscopically observed cases. Medial meniscal injury located on the craniolateral border was most detected on arthroscopy (n = 9) and was detected on CTA in five cases, but on ultrasonography in 0 cases. Detection of articular cartilage defects on the medial femoral condyle was most detected with arthroscopy (24/25, 96% cases) and was also detected on CTA in 12/20 (60%) cases with a significant disagreement identified between modalities (P = 0.02). Cranial and caudal cruciate ligament defects were detected on CTA in 6/22 (27.3%) and 7/19 (36.8%) cases, respectively, and with arthroscopy in 3/25 (12%) and 2/25 (8%) cases, respectively. The use of CTA detected more defects in the cruciate ligaments, proximal tibia, and ligament entheses than the other diagnostic methods, but was not reliable for detection of articular cartilage damage on the medial femoral condyle.     

THE COMPUTED TOMOGRAPHIC APPEARANCE OF EQUINE TEMPOROHYOID OSTEOARTHROPATHY

Equine temporohyoid osteoarthropathy is characterized by progressive osseous proliferation of the temporohyoid articulation and surrounding structures. The diagnosis has generally been made using radiography and endoscopy of the guttural pouch. Recently, computed tomography (CT) has been used in the diagnosis of temporohyoid osteoarthropathy. This study was performed to determine the CT imaging characteristics of temporohyoid osteoarthropathy and to compare these to radiographic and endoscopic findings. CT scans from 16 horses with a final diagnosis of temporohyoid osteoarthropathy were reviewed. Five horses that had undergone CT scan for reasons other than temporohyoid osteoarthropathy were included as controls. Qualitative and quantitative data were used to describe the magnitude of the CT findings. Osseous proliferation of the stylohyoid bone and temporohyoid articulation was found to be a consistent feature of temporohyoid osteoarthropathy. Thickening of the ceratohyoid bone and proliferation of its articulation with the stylohyoid bone was frequently identified and this finding may have surgical implications. Horses with neurologic deficits had increased stylohyoid width that was significantly different than the subclinically affected side. CT evaluation also allowed the identification of subclinical bilateral disease in horses thought to be unilaterally affected based on clinical examination.     

COMPUTED TOMOGRAPHIC APPEARANCE OF PRIMARY LUNG TUMORS IN DOGS

Canine primary lung tumors typically appear radiographically as a well‐circumscribed solitary mass in the periphery of a caudal lung lobe. Consolidated and diffuse forms of primary lung tumors have also been described. Nineteen dogs with computed tomographic (CT) images of the thorax and a histological diagnosis of primary lung tumor (17 primary carcinomas and two primary sarcomas) were evaluated retrospectively to characterize the CT findings. All primary lung tumors were bronchocentric in origin with internal air bronchograms. The bronchi were typically narrowed, displaced, and often obstructed by the tumor. Eighteen of 19 (95%) of the tumors were solitary and there was one pneumonic/alveolar form. Most solitary tumors were well circumscribed (17/18), located in the central to periphery of the lung (14/18), and in a cranial or caudal lobe (16/19). Most primary lung tumors (11/17) had mild to moderate heterogeneous contrast enhancement. Five of 19 dogs (26%) had evidence of pulmonary metastasis. Internal mineralization (3/19) and tracheobronchial lymphadenopathy (4/19) were also identified. On CT examination, solitary, well circumscribed, bronchocentric masses with internal air bronchograms are consistent with a primary pulmonary tumor in dogs.     

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 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.     

A COMPLEMENTARY RADIOGRAPHIC PROJECTION OF THE EQUINE TEMPOROMANDIBULAR JOINT

The complexity of the equine skull makes the temporomandibular joint a difficult area to evaluate radiographically. The goal of this study was to determine the optimal angle for a complementary radiographic projection of the equine temporomandibular joint based on a computed tomography (CT) cadaver study. CT was performed on six equine cadaver heads of horses that were euthanized for other reasons than temporomandibular joint disease. After the CT examination, 3D reconstruction of the equine skull was performed to subjectively determine the angle for a complementary radiographic projection of the temporomandibular joint. The angle was measured on the left and right temporomandibular joint of each head. Based on the measurements obtained from the CT images, a radiographic projection of the temporomandibular joint in a rostral45°ventral-caudodorsal oblique (R45°V-CdDO) direction was developed by placing the X-ray unit 30° laterally, maintaining at the same time the R45°V-CdDO angle (R45°V30°L-CdDLO). This radiographic projection was applied to all cadaver heads and on six live horses. In three of the live horses abnormal findings associated with the temporomandibular joint were detected. We conclude that this new radiographic projection of the temporomandibular joint provides superior visualization of the temporomandibular joint space and the articular surface of the mandibular condyle.     

COMPUTED TOMOGRAPHIC APPEARANCE OF CHOANAL ATRESIA IN AN ALPACA CRIA

A 6-hour-old alpaca cria was admitted for evaluation of respiratory distress since birth. Contrast radiography confirmed the presence of bilateral choanal atresia, and computed tomography (CT) evaluation was planned to aid in the surgical treatment. Due to deterioration in the cria's condition, euthanasia was performed prior to the CT examination. Postmortem CT examination was performed to determine the appearance of choanal atresia. The embryology and CT appearance of choanal atresia is discussed.     

COMPUTED TOMOGRAPHIC APPEARANCE OF INFLAMMATORY POLYPS IN THREE CATS

This report describes the use of computed tomography (CT) to evaluate the inner ear, tympanic bullae, nasopharyngeal area, and external ear canals of three cats. All cats presented for evaluation of upper respiratory signs or chronic ear infection. Nasopharyngeal masses were present in two cats, and a mass in the external ear canal was present in the third cat. In all three cats, CT was able to define the extent of osseous bulla involvement, which was confirmed at surgery. Computed tomography also defined the extent of the polyp in the nasopharyngeal area in two cats, and in the external ear canal in one cat. Surgical removal of the polyps was accomplished with a combined oral approach and ventral bulla osteotomy in cats 1 and 2. The polyp was removed from cat 3 using a combination of ventral bulla osteotomy and excision of the mass through the external ear canal. Microscopic examination confirmed all masses as nasopharyngeal (inflammatory) polyps.     

THE COMPUTED TOMOGRAPHIC APPEARANCE OF ACUTE THORACOLUMBAR INTERVERTEBRAL DISC HERNIATIONS IN DOGS

The appearance of herniated intervertebral disc material in the thoracolumbar vertebral canal was evaluated in 23 dogs using computed tomography (CT). The images were then compared with the myelographic and surgical findings. The normal spinal cord, outlined by epidural fat over intervertebral disc spaces, was of intermediate attenuation on transverse CT images. Herniated disc material was identified in all animals as a heterogeneous hyperattenuating extradural mass. The attenuation of the disc material increased with the degree of mineralization. In seven dogs, the herniated material was only slightly more attenuating than the spinal cord. In these dogs, small fragments of mineralized disc material and significant hemorrhage were found in the epidural space at surgery. In dogs with a long standing history of disc herniations, disc material identified in the vertebral canal had a more hyperattenuating and homogeneous appearance than recently herniated disc material. We conclude that mineralized, herniated disc material and hemorrhage can be identified quickly and safely in dogs using CT.     

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.     

ULTRASONOGRAPHIC ANATOMY OF THE TEMPOROMANDIBULAR JOINT IN HEALTHY PURE-BRED SPANISH HORSES

The objective was to describe the normal ultrasonographic appearance of the soft tissue and bony structures of the temporomandibular joint in Pure-Bred Spanish horses using frozen and plastinated sections performed as anatomical references. The temporomandibular joint of five healthy Pure-Bred Spanish horses and the head specimens from 12 Pure-Bred Spanish cadavers that were subjected to euthanasia for reasons other than temporomandibular joint problems were studied sonographically and anatomically. An 11 MHz linear-array transducer was used to obtain longitudinal ultrasonographic images of the temporomandibular joint from rostral, lateral, and caudal approaches. For anatomic study, a gross dissection was performed on six temporomandibular joints. The other six head specimens were first frozen at -30 degrees C for 48h and then, at -70 degrees C for a week. Three millimeter thick anatomic sections were collected in the same plane as the sonographic planes. These sections were plastinated, photographed, and compared with the corresponding ultrasonographic images. The articular surfaces, the articular cartilage, the disc, the intra-articular fat tissue, the joint capsule, and other structures were clearly visualized sonographically. Structures identified on the ultrasonographic images were in accordance with those identified on the corresponding anatomic sections. We confirmed the appearance of structures of the equine temporomandibular joint that have been described previously but we also identified the caudal fibrous expansion of the disc, the caudal compartment of the dorsal synovial pouch, and the lateral ligament. Our results define a reference that will aid in sonographic evaluation of the equine temporomandibular joint region.     

DETECTION OF A RADIOGRAPHICALLY OCCULT FRACTURE OF THE LATERAL PALMAR PROCESS OF THE DISTAL PHALANX IN A HORSE USING COMPUTED TOMOGRAPHY

A horse with a suspected injury of the distal phalanx was examined using radiography at day two and 19 after the onset of the lameness, with no definite diagnosis. Using computed tomography an incomplete fracture of the lateral wing of the distal phalanx was diagnosed at day 25. Based on computed tomography it was determined that the fracture probably did not enter the joint or involve the palmar cortex throughout its length which were of prognostic importance. The day following the CT examination a new oblique radiographic projection was made. In this radiography which was based on, and never would have been attempted without, the information about the geometric pattern of the fracture achieved by CT examination, a radiolucent area indicative of a wing fracture was seen. This report emphasizes the value of computed tomography in diagnosing a geometric complicated nonarticular oblique fracture of the palmar process of the pedal bone in a horse.     

RADIOGRAPHIC, COMPUTED TOMOGRAPHIC AND HISTOPATHOLOGIC APPEARANCE OF A PRESUMED SPINAL CHORDOMA IN A DOG

A 4-year-old Labrador Retriever presented for urinary incontinence and constipation of 2 weeks duration. There was a tender abdomen, lumbar pain and conscious proprioceptive deficits in both pelvic limbs. Depressed pelvic limb reflexes were present consistent with a lower motor neuron lesion. In radiographs of the lumbar spine there was narrowing of the intervertebral disc space at L5-L6 with irregular, multifocal areas of mineralized opacities dorsal to the intervertebral disc space, presumably within the vertebral canal. On computed tomography, an intramedullary, partially mineralized mass was identified in the spinal cord at the level of caudal L5 through cranial L6. At necropsy there was a four-centimeter enlarged, irregular segment of spinal cord at the level of L5-L6. When sectioned, the spinal cord bad a mineralized texture. Histologically there were variable sized cells that were stellate in appearance with vacuolated cytoplasm (physaliferous cells) and mucinous background consistent with a chordoma. Chordoma is a rare, skeletal neoplasm that originates from mesoderm-derived notochord and has been reported in humans and animals. Extraskeletal development of a chordoma within the spinal cord is a rare manifestation of this neoplasm. However, based on other reports in dogs, solitary extraskeletal locations of chordomas may be the typical expression of this neoplasm in the dog. Differentiation of similar histologically appearing tumors, such as a parachordoma or myxoid chondrosarcoma, will require immunohistochemical characterization of these tumors in veterinary patients.     

THE EFFECT OF OBLIQUITY ON THE RADIOGRAPHIC APPEARANCE OF THE TEMPOROMANDIBULAR JOINT IN DOGS

The temporomandibular joint is formed between the condyloid process of the mandible and the mandibular fossa of the temporal bone. The basic anatomy of this joint was assessed and described in a series of skulls including dolichocephalic, mesaticephalic and brachycephalic breeds. The facial index and rotational angles were measured with the facial index providing a useful method of classifying skull types but the rotational angle being of limited use in assessment of the temporomandibular joint until normal breed values are established. Equipment was designed to allow repeatable positioning of the temporomandibular joint for radiography at a variety of lateral and long axis rotational angles relative to the central x-ray beam. The regions of the joint and anatomic features visualized in each view are demonstrated. 10 degrees rotation was required in either axis to project the joints independently of each other. Lateral rotational angles of 10 to 30 degrees in mesaticephalic and dolichocephalic breeds and 20 to 30 degrees in brachycephalics and long axis rotational views of 10 to 30 degrees depending on the region of interest were considered to be the most useful.     

COMPUTED TOMOGRAPHIC DETERMINATION OF TIBIAL TORSION IN THE DOG

The goal of this study was to develop a method for computed tomographic (CT) measurement of tibial torsion, and to compare this technique with direct anatomic measurement of tibial torsion in cadaveric canine tibiae. Paired hind limbs of 10 cadaveric dogs were mounted on a custom-designed limb holding apparatus. One-millimeter thick, contiguous, transverse CT slices were obtained from the distal femur to the proximal tibia and 2 mm CT slices were obtained from the distal tibia to the proximal tarsus. The tibiae were freed of soft tissues and digital photographic images of the proximal and distal articular surfaces were obtained with the camera lens aligned perpendicular to the long axis of the tibia. Multiple proximal and distal tibial axes were identified on the images; two proximal and two distal axes were found to be repeatable in all specimens in both the direct and CT methods. The torsion angle was calculated by determining the difference between the axis angles for each pair of proximal and distal axes. There was no significant difference in torsion angle identified between the direct photographic and CT method for any pair of proximal and distal axes. CT determination of tibial torsion is a rapid and accurate method, and warrants investigation in clinical patients.     

COMPUTED TOMOGRAPHIC FINDINGS OF DOGS WITH CUBITAL JOINT LAMENESS

The purpose of this study was to identify the incidence of abnormal computed tomography (CT) findings in dogs with lameness of one or both elbows. CT examinations of 102 elbows in 51 dogs were reviewed individually and by group consensus by 3 examiners and graded for various abnormalities. Frequently encountered abnormalities included abnormal shape and sclerosis of the medial coronoid process of the ulna, irregularity of the radial incisure of the ulna, and ulnar trochlear notch sclerosis. Other abnormalities included distinct/separate or fissure/in situ fragmentation of the medial coronoid; lucency of the radial incisure; ununited anconeal process; sclerosis, lucency, or flattening of the medial aspect of the humeral condyle; osteophyte formation; and joint incongruity. In conclusion, CT of the canine cubital joint is useful in identification of various lesions beyond simple fragmentation of the medial coronoid process of the ulna.