IMAGING DIAGNOSIS—MAGNETIC RESONANCE IMAGING PULSATILITY ARTIFACT IN THE CANINE CERVICAL SPINE

Pulsatile venous flow in the internal vertebral venous plexus of the cervical spine can lead to vertical, linear T2‐hyperintensities in the spinal cord at the cranial aspect of C3 and C4 in transverse T2‐weighted images in large breed dogs that are not accompanied by ghosting. The artifact is more conspicuous in pre‐ and postcontrast transverse T1‐weighted images and is accompanied by ghosting in that sequence, typical of a pulsatility artifact. A flow‐related artifact was confirmed as the cause for this appearance by noting its absence after either exchange of phase and frequency encoding direction or by flow compensation. Care should be exercised to avoid misdiagnosing this pulsatility artifact seen in transverse T2‐weighted images of the midcervical spine in large dogs as an intramedullary lesion when T1‐images or phase‐swap images are not available to confirm its artifactual origin.     

SONOGRAPHY OF THE NORMAL FELINE GASTROINTESTINAL TRACT

The normal sonographic appearance of the stomach in various degrees of distension, the duodenum, the small intestine, and the large intestine was determined in awake and sedated cats. The mean stomach rugal fold thickness was 4.38 mm, and the interrugal thickness was 2.03 mm. No significant difference in stomach wall thickness was seen when the stomach was empty, half full, or full. The duodenal wall thickness was significantly greater than other parts of the small intestine, and this difference was accentuated by sedation (awake mean 2.4 mm; sedated mean 2.71 mm). The mean small intestinal wall thickness was 2.1 mm, and the mean colonic wall thickness was 1.67 mm. The five characteristic sonographic layers similar to that seen in the gastrointestinal tract of other species were routinely identified at all regions of the feline gastrointestinal tract.     

NON-CARDIAC THORACIC ULTRASOUND IN 75 FELINE AND CANINE PATIENTS

The purpose of this study was to describe the ultrasonographic appearance of non-cardiac diseases of the small animal thorax. Ultrasound images from a total of 75 animals (26 cats and 49 dogs) were compared to cytologic, histopathologic, and necropsy findings. Clinical diagnoses included neoplasia of the mediastinum, pleura, or lungs (43); idiopathic mediastinal cyst (3); diaphragmatic or peritoneopericardial hernia (4); lung lobe torsion (1); pulmonary eosinophilic infiltrates (1); and idiopathic, chylous, congestive heart failure, or lymphangiectasia associated pleural effusion (14). In the remaining 9 patients, a definitive diagnosis was not obtained. Ultrasound-guided fine needle aspirate was performed in 56 patients; 1 of these also had an ultrasound-guided tissue core biopsy. Of the fine needle aspirates, 51 (91%) were diagnostic. Ultrasound examination, particularly when accompanied by guided tissue sampling, can be a valuable tool in the diagnosis of non-cardiac intrathoracic lesions.     

TRUNCATION ARTIFACT IN MAGNETIC RESONANCE IMAGES OF THE CANINE SPINAL CORD

The truncation artifact in magnetic resonance (MR) images is a line of abnormal signal intensity that occurs parallel to an interface between tissues of markedly different signal intensity. In order to demonstrate the truncation artifact in sagittal images of the canine spinal cord and the effect of changing spatial resolution, we conducted an experimental in vitro study. A section of fixed canine spinal cord was imaged using a 1.5T magnet. Spatial resolution was increased by increasing the acquisition matrix and reconstruction matrix, producing series of T2‐weighted (T2w) images with the following pixel sizes: A, 1.6 (vertical) × 2.2 mm² (horizontal); B, 1.2 × 1.7 mm²; C, 0.8 × 1.1 mm²; D, 0.4 × 0. 6 mm². Plots of mean pixel value across the cord showed variations in signal intensity compatible with truncation artifact, which appeared as a single, wide central hyperintense zone in low‐resolution images and as multiple narrower zones in high spatial resolution images. Even in images obtained using the highest spatial resolution available for the MR system, the edge of the spinal cord was not accurately defined and the central canal was not visible. The experiment was repeated using an unfixed spinal cord specimen with focal compression applied to mimic a pathologic lesion. Slight hyperintensity was observed within the spinal cord at the site of compression although the cord was normal histologically. Results of this study suggest that caution should be applied when interpreting hyperintensity affecting the spinal cord in T2w sagittal images of clinical patients because of the possibility that the abnormal signal could represent a truncation artifact.     

TRANSTHORACIC LUNG ULTRASOUND IN NORMAL DOGS AND DOGS WITH CARDIOGENIC PULMONARY EDEMA: A PILOT STUDY

Pulmonary edema is the most common complication of left‐sided heart failure in dogs and early detection is important for effective clinical management. In people, pulmonary edema is commonly diagnosed based on transthoracic ultrasonography and detection of B line artifacts (vertical, narrow‐based, well‐defined hyperechoic rays arising from the pleural surface). The purpose of this study was to determine whether B line artifacts could also be useful diagnostic predictors for cardiogenic pulmonary edema in dogs. Thirty‐one normal dogs and nine dogs with cardiogenic pulmonary edema were prospectively recruited. For each dog, presence or absence of cardiogenic pulmonary edema was based on physical examination, heartworm testing, thoracic radiographs, and echocardiography. A single observer performed transthoracic ultrasonography in all dogs and recorded video clips and still images for each of four quadrants in each hemithorax. Distribution, sonographic characteristics, and number of B lines per thoracic quadrant were determined and compared between groups. B lines were detected in 31% of normal dogs (mean 0.9 ± 0.3 SD per dog) and 100% of dogs with cardiogenic pulmonary edema (mean 6.2 ± 3.8 SD per dog). Artifacts were more numerous and widely distributed in dogs with congestive heart failure (P < 0.0001). In severe cases, B lines increased in number and became confluent. The locations of B line artifacts appeared consistent with locations of edema on radiographs. Findings from the current study supported the use of thoracic ultrasonography and detection of B lines as techniques for diagnosing cardiogenic pulmonary edema in dogs.     

A RETROSPECTIVE STUDY OF UMBILICAL SONOGRAPHY IN CALVES

The purpose of this study was to assess the usefulness of diagnostic ultrasound for the detection of umbilical defects in calves. The medical records of 25 calves having undergone an ultrasound examination and for which a final diagnosis was available were reviewed retrospectively. Ultrasound was accurate (p = 0.05) for the diagnosis of umbilical defects in calves. Overall sensitivity (0.89) and specificity (0.83) were similar. Ultrasound was a better predictor of abnormal (PV' = 0.94) than normal PV- = 0.71) structures. Ultrasound was a good predictor (p < 0.05) of disease and normalcy in all umbilical region subdivisions except the umbilical vein (p = 0.16). Specificity was greater than sensitivity in all areas except the umbilical stalk. Sensitivity was lowest (0.50) for detection of umbilical herniae and lesions in the umbilical vein. When multiple umbilical areas were affected, ultrasound identified all lesions in 4 of 7 calves. Criteria determined to be subjectively useful in the sonographic diagnosis of infection in umbilical remnants were gas andlor echogenic fluid in the lumen and a thickened, hypoechoic wall.     

ULTRASONOGRAPHY OF THE CANINE, FELINE AND EQUINE TONGUE: NORMAL FINDINGS AND CASE HISTORY REPORTS

A submental approach using a 5, 7.5 and 10 MHz mechanical sectorial transducers was used to evaluate the ultrasonographic appearance of the normal and abnormal canine, feline and equine tongue. Seven normal animals were used to characterize the in vivo normal ultrasonographic appearance of the oropharynx. Consistently seen anatomical landmarks included the lingual parenchyma, lingual artery, soft and hard palate interfaces, mandible, basihyoid bone and sublingual musculature. Seven fresh canine, feline and equine cadavers were dissected to confirm the ultrasonographic findings. Seven animals with signs of ptyalism, dysphagia, halitosis and visible lingual lesions were also studied. A foreign body and abscesses secondary to a penetrating wound were detected in a horse. Ultrasound guidance aided surgical dissection, removal of the foreign body and intraoperative drainage of the abscesses. Ultrasound provided valuable non-invasive documentation of the architecture, size and margins of six lingual neoplasms. Ultrasonographic monitoring of the response to the treatment of lingual lesions may be beneficial in the management of patients.     

ASSESSING CIRCLE OF WILLIS BLOOD CIRCULATION IN DOGS WITH TRANSCRANIAL COLOR-CODED DUPLEX SONOGRAPHY

Insonation of Circle of Willis by transcranial Doppler duplex color sonography is described in 30 healthy dogs with 15 weighing <33 lb and 15 weighing >33 lb. Imaging was via a temporal window to explore the rostral, middle, and caudal cerebral arteries on both the left and right-hand sides; and through an suboccipital window to study the basilar artery. Normal mean values of the peak systolic velocity (PSV), end diastolic velocity, mean velocity, resistance index (RI), and pulsatility index (PI) were characterized and compared with those obtained in previous studies. There was significant differences in the PSV, RI, and PI in the rostral cerebral artery between dogs weighing <33 vs. >33 lb. Mean PSV was higher in weighing over 33 lb, whereas the mean resistive index and mean PI were lower in these dogs.     

ULTRASONOGRAPHIC APPEARANCE OF HISTOPLASMOSIS IDENTIFIED IN THE SPLEEN IN 15 CATS

Histoplasmosis is the second most common fungal infection reported in the cat. The disseminated form involving lung, liver, lymph nodes, spleen, and bone marrow is a frequent manifestation of the disease. Limited information is available in the literature regarding the ultrasonographic appearance of the spleen in cats with disseminated or splenic histoplasmosis. A retrospective review of splenic ultrasound images from 15 cats confirmed to have histoplasmosis by splenic aspirates was performed. Size, echotexture, echogenicity, margin appearance, presence of nodules, and the overall shape of the spleen were reported in each case. Splenomegaly was documented in all cases (15/15) and a hypoechoic appearance of the spleen was documented in 14/15 of cases. The spleen was diffusely and uniformly affected in 14/15 (six homogenous and eight with a subtle mottled appearance) and had discrete nodules in 1/15 cats. Histoplasmosis should be included in the differential list for an enlarged and hypoechoic spleen in cats with consistent clinical findings. Additionally, ultrasound guided splenic aspirate may be a useful method to obtain a cytology sample for diagnosis.     

A REVIEW OF SONOGRAPHIC IDENTIFICATION OF ABDOMINAL BLOOD VESSELS AND JUXTAVASCULAR ORGANS

Abdominal vasculature can be evaluated non-invasively using 2-D ultrasound imaging and Doppler ultrasonography.^5,6,12 The identification of abdominal vessels using ultrasound is based on knowledge of their normal location, appearance and relationship to specific organs. Because anatomic location of major abdominal vessels is fairly consistent, finding and following vessels is a useful aid when attempting to locate and evaluate juxta-vascular organs. Sonographic vascular evaluation may be beneficial in providing information regarding central cardiovascular abnormalities, detection of abnormalities involving the vessel interrogated, or detection of abnormalities of the parenchymal bed that the vessel supplies,^5–12 Knowledge of the location and appearance of the vessels is necessary for this information to be of diagnostic value.
In this paper, abdominal vessels in the dog are reviewed and a sonographic map of major abdominal vessels is described. This includes the sonographic appearance of the aorta, caudal vena cava, and portal vein, their major branches and their anatomic relationship with adjacent organs.
Identification of the medial iliac lymph nodes, mesenteric lymph nodes, abdominal esophagus, duodenum, spleen, kidneys, pancreas, adrenal glands and liver lobes are assisted by recognizing specific vascular landmarks. The locations and appearances of pertinent organs as pertains to abdominal vasculature (caudal vena cava and aorta) are described.     

INFLUENCE OF THE CHEMICAL SHIFT ARTIFACT ON MEASUREMENTS OF COMPACT BONE THICKNESS IN EQUINE DISTAL LIMB MR IMAGES

The effect of the chemical shift artifact, resulting from misregistration or phase cancellation at the interface between compact and trabecular bone, on apparent bone thickness was quantified in six isolated equine limbs. Sagittal T1‐weighted spin echo (SE) and in‐phase three‐dimensional spoiled gradient echo (SPGR) images were acquired twice with a 1.5 T magnetic resonance (MR) unit, switching the frequency encoding direction between acquisitions. Out‐of‐phase SPGR images were also obtained. MR images with different frequency encoding directions were compared with each other and to radiographs made from corresponding 3‐mm‐bone sections. Compact bone thickness was significantly different when comparing images acquired with different frequency encoding directions for both SE and SPGR sequences. Significant differences were identified in the frequency but not the phase encoding direction when measurements of compact bone in MR images were compared with measurements obtained from thin section radiographs for the majority of surfaces studied (P<0.05). Correction of MR measurements with the calculated chemical shift abolished these differences (P>0.05). Measurements of compact bone from out‐of‐phase SPGR sequences were significantly different than from in‐phase sequences (P<0.001) with out‐of‐phase measurements greater than in‐phase measurements by an average of 0.38 mm. These results indicate that the chemical shift artifact results in errors in MR evaluation of compact bone thickness when measurements are performed in the frequency encoding direction or in out‐of‐phase images. For better accuracy, measurements should be performed parallel to the phase encoding direction and avoiding out‐of‐phase gradient echo sequences.     

COLLAGENASE CHEMONUCLEOLYSIS—A LONG TERM RADIOGRAPHIC STUDY IN NORMAL DOGS

Five clinically normal five year old dogs were used in this study. From a randomised table inter ver tebral discs were each injected with either collagenase or calcium chloride diluent. The surgically exposed cervical discs were injected with 50 units whereas thoracic and lumbar discs were injected under fluoroscopic guidance with 100 units of the enzyme. Postinjection radiographs revealed significant (p ≤ .05) disc space narrowing in enzyme injected discs. The cervical discs had the highest frequency of radiographic narrowing (87%) followed by the thoracic (70%) and lumbar (53%) discs. Spondylosis deformans developed at the sites of cervical enzyme injections. None of the dogs had neurologic abnormalities one year postinjection.     

USE OF A PERFORMANCE SCALE IN SMALL ANIMAL RADIATION THERAPY

A performance scale (Animal Medical Center Performance Scale) for use in dogs and cats was developed by modifying the Karnofsky Performance Status that is used in people. It was then applied to 209 animals that received definitive radiotherapy. The results after a minimum of 1 year of observation after therapy indicated that survival times were significantly longer for those animals that scored 80 or higher on the scale. Further studies will be needed to determine its usefulness with specific tumor types.     

ULTRASONOGRAPHIC FINDINGS IN ETHYLENE GLYCOL (ANTIFREEZE) POISONING IN A PREGNANT QUEEN AND 4 FETAL KITTENS

A one year old female Siamese-Persian mixed breed cat in late third trimester of pregnancy was presented for anorexia and lethargy. Abdominal radiographs were normal. Abdominal ultrasound revealed markedly increased cortical and moderately increased medullary echogenicity of the maternal kidneys. Cortical echogenicity of all fetal kidneys were similarly increased in echogenicity. Premortem clinicopathologic and postmortem histopathologic findings were indicative of ethylene glycol nephrosis presumably secondary to antifreeze ingestion.     

BILOBED GALLBLADDER IN A CAT: ULTRASONOGRAPHIC APPEARANCE

A five-month-old male domestic shorthair cat presented with a history of vomiting for 4 days. An ultrasound examination of the abdomen was performed as part of the diagnostic workup. The gallbladder appeared to be bilobate. The cat died the following day from renal failure. At necropsy, a bilobed gallbladder was confirmed and considered to be a congenital anomaly unrelated to the cat's death.     

ULTRASONOGRAPHIC APPEARANCE OF SPLENIC DISEASE IN 101 CATS

The sonographic findings in 101 cats with splenic abnormalities are presented. Diagnosis was made by ultrasound-guided fine needle aspirate or fine-needle biopsy (n = 91), ultrasound-guided core biopsy (n = 1), surgical core biopsy (n = 1), or necropsy (n = 10). Two cats had more than one diagnostic procedure (fine needle aspirate and necropsy or core biopsy and necropsy). The splenic abnormalities included lymphosarcoma (n = 30), mast cell tumor (n = 27), extramedullary hematopoiesis and/or lymphoid hyperplasia (n = 27), epithelial tumors (n = 6), mesenchymal tumors (n = 4), malignant histiocytosis (n = 2), myeloproliferative disease (n = 2), pyogranulomatous inflammation (n = 2), erythroleukemia (n = 1), eosinophilic syndrome (n = 1), hematoma (n = 1), and granulomatous splenitis (n = 1). Three cats had more than one splenic abnormality (mast cell tumor and metastatic carcinoma, pyogranulomatous inflammation and lymphoid hyperplasia, histiocytic lymphosarcoma, and lymphoid hyperplasia). Pathognomonic changes were not seen for any of the diseases.     

IMAGING DIAGNOSIS—ULTRASOUND UNCOMMON FEATURES OF AN ABDOMINAL GOSSYPIBOMA IN A DOG

An abdominal mass was incidentally detected in a 12‐year‐old, neutered female, crossed breed dog. Abdominal ultrasonographic examination showed a well‐delineated, irregular, heterogeneous mass that did not generate any distal acoustic shadowing. Transcutaneous US‐guided biopsy of the mass were nonconclusive but raised the possibility of neoplasia. Surgery discovered a mass embedded in the omentum and a large quantity of surgical sponges were identified in cut section. To the authors’ knowledge, this represents the first published case of gossypiboma casting no characteristic distal acoustic shadowing.     

AGE-RELATED CHANGES IN THE ULTRASOUND APPEARANCE OF THE NORMAL FELINE PANCREAS

In humans, pancreatic hyperechogenicity and duct dilation are reported as normal aging changes. Similar changes have been reported with pancreatitis in the cat. We attempted to determine if aging changes occur in the ultrasound appearance of the normal feline pancreas. The pancreas of 84 normal (based on history, physical exam, biochemical profile, and feline trypsin-like immunoreactivity and pancreatic lipase immunoreactivity concentrations) cats of varying ages was scanned. Pancreatic width at the left limb and body, pancreatic duct diameter at left limb and body, and pancreatic echogenicity compared with liver and surrounding fat were noted and compared with age and body weight. Lower and upper limits of the 95% reference intervals for pancreatic left limb width were 2.6 and 9.5 mm, and 3.5 and 8.5 mm for the pancreatic body width. There was no significant difference in pancreatic width between the left limb and body. Lower and upper limits of the 95% reference interval for the diameter of the pancreatic duct at the left limb and body were similar, and were 0.65 and 2.5 mm. There was a weak but significant linear correlation between pancreatic duct diameter and age, with increasing pancreatic duct diameter with increasing age. There was no correlation of pancreatic width with age, and no correlation of pancreatic echogenicity with age or body weight. Based on this study, feline pancreatic size and echogenicity do not change with age. Pancreatic duct diameter increases slightly with age and should not be used as a sole indicator of pancreatitis in the geriatric cat.     

MAGNETIC RESONANCE IMAGING FEATURES AND OUTCOME FOR SOLITARY CENTRAL NERVOUS SYSTEM COCCIDIOIDES GRANULOMAS IN 11 DOGS AND CATS

Little published information is available to guide therapy for canine and feline patients with Coccidioides infections involving the central nervous system (CNS). The purpose of this cross‐sectional retrospective study was to describe magnetic resonance imaging (MRI) features and outcome for a group of dogs and cats with solitary CNS Coccidiodes granulomas. Nine canine and two feline cases met inclusion criteria; four diagnosed and treated with surgery and fluconazole and seven diagnosed by serology or cytology and treated medically. Three cases had left Coccidioides endemic areas long before developing neurological disease. The MRI lesions shared many features with neoplastic masses. The extra‐axial granulomas often had a lack of a distinct border between the mass and neural parenchyma. Four cases were extra‐axial and seven were intra‐axial, but distinguishing between extra‐axial and intra‐axial locations was sometimes challenging. The surgical cases had good outcomes and histology allowed definitive diagnosis. Medically managed patients also had generally good outcomes, with resolution of clinical signs in most cases. Findings indicated that distinction between neoplasia and focal Coccidioides granulomas based on MRI features is likely to be imprecise. Demonstration of the organism by cytology or histology is required for definitive diagnosis. The role of surgery for improving the outcome of brain or spinal coccidioidomycosis granulomas warrants further study.