USE OF TRANSCOLONIC 123I-IODOAMPHETAMINE TO DIAGNOSE SPONTANEOUS PORTOSYSTEMIC SHUNTS IN 18 DOGS

Transcolonic ¹²³I-Iodoamphetamine is rapidly absorbed across the colonic mucosa and binds to amine receptors in the liver and lungs. During the first ten minutes following colonic administration, a simple ratio of lung counts to lung counts plus liver counts provides an accurate estimate of the fraction of portal blood that bypasses hepatic sinusoids in dogs with portosystemic shunts. Studies were performed on 24 dogs with suspect portosystemic shunt. Shunt fraction values for 18 dogs with surgically confirmed portosystemic shunt were obviously higher than published values for normal dogs, and also significantly higher than values for the other six dogs, later confirmed to lack shunts. Postoperative studies were repeated on ten dogs with single shunt vessels 1–2 days after shunt closure. Total shunt ligation resulted in normal postoperative shunt fraction, whereas partial shunt ligation resulted in persistant elevation of shunt fraction. Transcolonic iodoamphetamine scintigraphy is noninvasive, easy to perform, and provides an accurate method to diagnose dogs with portosystemic shunt.     

TRANSSPLENIC PORTAL SCINTIGRAPHY USING 99MTC-MEBROFENIN IN NORMAL DOGS

Transsplenic portal scintigraphy using sodium pertechnetate is superior to per-rectal portal scintigraphy due to improved visualization of the portal vasculature with decreased patient and personnel exposure. The purpose of this study was to describe the use of 99mTc-mebrofenin, the radiopharmaceutical of choice for the evaluation of hepatic function, in place of pertechnetate for transsplenic portal scintigraphy in normal dogs. Sixteen juvenile dogs underwent transsplenic portal scintigraphy using 37-130 MBq 99mTc-mebrofenin in a 0.2-0.5 ml volume. After the initial dynamic acquisition obtained at 4 frames/s in right lateral recumbency, static right lateral, and ventral views were obtained at 5, 10, 15, 20, 25, 30, 40, 50, and 60 min. A nuclear angiogram of the splenic and portal veins was visible in all dogs, followed by rapid distribution of the radiopharmaceutical in the liver. Hepatic morphology was more easily defined than with pertechnetate. Transit time could not be calculated due to the high hepatic extraction of 99mTc-mebrofenin. Mean +/- SD shunt fraction was 0.8 +/- 0.8%. Time to peak liver activity was 3.1 +/- 1.1 min, and hepatic excretion T1/2 was 19.4 +/- 6.3 min. No visible blood pool and cardiac activity was seen after 5 min. The mean +/- SD time to visualization of defined biliary activity was 8.8 +/- 2.9 min. Absorption from the spleen was significantly higher than that reported for pertechnetate (87.9 +/- 8.2%, vs. 52.5 +/- 19.1%). 99mTc-mebrofenin can be used in place of pertechnetate for transsplenic portal scintigraphy, with the advantage of combining quantitative parameters of liver function with the already known advantage of transsplenic portal scintigraphy.     

USE OF 99MTCO TRANS-SPLENIC PORTAL SCINTIGRAPHY FOR DIAGNOSIS OF PORTOSYSTEMIC SHUNTS IN 28 DOGS

Ultrasound-guided percutaneous trans-splenic portal scintigraphy (TSPS) using 99mTcO4(-) has been used to image the portal venous system in normal dogs. Compared with per-rectal portal scintigraphy, it provides higher count density, consistent nuclear venograms of the splenic and portal vein, and significantly decreased radiation exposures. This paper describes the use of TSPS for the diagnosis of portosystemic shunts in 28 dogs. TSPS was performed injecting 70 +/- 28 MBq of 99mTcO4(-) (mean +/- SD) into the splenic parenchyma with ultrasound guidance. A dynamic acquisition at a frame rate of four frames/s for 5 min was initiated after placement of the needle and approximately 2s prior to injection. All dogs had diagnoses confirmed via exploratory laparotomy or ultrasonographic identification of the shunting vessel(s). Three studies (10.7%) were nondiagnostic because of intraperitoneal rather than intrasplenic injection of the radionuclide. Three pathways were recognized on the scintigraphic images: (1) portoazygos shunts--the 99mTcO4(-) bolus traveled dorsally, running parallel to the spine and entering the heart craniodorsally; (2) single portocaval or splenocaval shunts--the 99mTcO4(-) bolus ran from the area of the portal vein/splenic vein junction in a linear fashion toward the caudal vena cava entering the heart caudally; (3) internal thoracic shunt-the 99mTcO4 bolus traveled ventrally along the thorax and abdomen entering the cranial aspect of the heart. Single and multiple shunts were easily distinguished. There were no distinguishing features between single intra and extrahepatic portocaval shunts.     

COMPARISON OF PER-RECTAL PORTAL SCINTIGRAPHY USING 99mTECHNETIUM PERTECHNETATE TO MESENTERIC INJECTION OF RADIOACTIVE MICROSPHERES FOR QUANTIFICATION OF PORTOSYSTEMIC SHUNTS IN AN EXPERIMENTAL DOG MODEL

Per-rectal portal scintigraphy using tech-netium-99m pertechnetate (^99mTcO₄^-) was performed in 8 normal dogs before and after surgical creation of a portacaval shunt. Shunt fractions were calculated by computer assisted analysis of dynamic images (IMG) and compared to shunt fractions determined by mesenteric venous injection of radioactive microspheres (MIC). The mean pre-operative shunt fraction was 1.59% using IMG and 3.00% using MCI. The mean postoperative shunt fraction was 64.56% using IMG and 69.56% using MIC. There was excellent correlation between both methods (r² 0.94). Per-rectal portal scintigraphy is an easily performed, inexpensive method to diagnose and quantify portosystemic shunts in dogs.     

CHARACTERIZATION OF MULTIPLE ACQUIRED PORTOSYSTEMIC SHUNTS USING TRANSPLENIC PORTAL SCINTIGRAPHY

We describe the scintigraphic patterns observed in 14 patients with confirmed multiple portosystemic shunts imaged via transplenic portal scintigraphy. Parameters evaluated included presence of multiple anomalous vessels, presence of hepatofugal flow caudal to spleen, and/or to cranial margin of the kidneys, slow absorption resulting in longer spleen to heart transit time, and presence of biphasic or fragmented bolus. Twenty‐eight additional patients, 14 with a confirmed single portocaval and 14 with a portoazygos shunt, were used for comparison. Nine of 14 (64.3%) patients with multiple shunts had multiple vessels, five (35.7%) had a biphasic bolus, 13 (92.9%) had hepatofugal flow caudal to the cranial margin of the kidneys. In all single portocaval shunts, a single anomalous vessel was identified. None had hepatofugal flow caudal to the border of the kidneys. Among portoazygos shunts, 4/14 (28.6%) had flow caudal to the injection site. Six portoazygos and one portocaval shunts had biphasic bolus. Median transit time from spleen to heart was significantly longer (1.9 s) in patients with multiple shunts than in patients with a portocaval shunt (1.0 s), but not in patients with a portoazygos shunt (1.3 s). Although a distinct plexus of anomalous vessels is not detected in all patients with multiple shunts imaged using transplenic portal scintigraphy, findings of hepatofugal flow caudal to the margin of the kidneys, and longer transit time compared with single portocaval shunts were characteristic. Flow caudal to the splenic injection site but cranial to the kidneys and biphasic bolus can also be seen with a single congenital shunt.     

TRANS-SPLENIC PORTAL SCINTIGRAPHY IN NORMAL DOGS

The purpose of this study was to (1) establish a technique for ultrasound-guided trans-splenic portal scintigraphy (TSPS) using 99mTcO4(-), (2) evaluate portal vein morphology, (3) compare the radiation exposures for TSPS vs. per-rectal portal scintigraphy (PRPS), and (4) compare the quality of numerical data from the TSPS vs. PRPS. Eight juvenile dogs underwent PRPS and TSPS (minimum of 48h between studies) after initial screening tests. PRPS was done according to established protocol using 425 +/- 36MBq (mean +/- SD) of 99mTcO4(-). TSPS was done with the dogs in right lateral recumbency over the gamma camera. 99mTcO4(-) (57 +/- 13.9 MBq) was injected into the spleen 1-2s following initiation of the dynamic acquisition. The frame rate was 4 frames/s for 5 min. There was significantly lower radioactivity of 99mTcO4(-) given and significantly higher total counts recorded in the liver and heart during the TSPS compared with PRPS. The total counts for the TSPS and PRPS were 7120 +/- 4386 and 830 +/- 523, respectively. Percent absorption from the spleen was 52.5 +/- 19.1% compared with 9.2 +/- 5.7% for the colon. Calculated transit time for the TSPS studies was 7 +/- 2.3s. In TSPS studies, the splenic and portal veins were clearly identified. Radiation exposure levels of the dogs were significantly lower following TSPS than after PRPS. TSPS appears superior to PRPS as a method to image the portal venous system representing a valid alternative diagnostic test for animals with suspected portosystemic shunts.     

COMPARISON BETWEEN THE SCINTIGRAPHIC UPTAKE AND PLASMA CLEARANCE OF 99mTc-DIETHYLENETRIAMINEPENTACETIC ACID (DTPA) FOR THE EVALUATION OF THE GLOMERULAR FILTRATION RATE IN DOGS

The scintigraphically measured percentage dose uptake of ^99mTc-DTPA by the kidneys and the plasma clearance of ^99mTc-DTPA have been reported to correlate well with inulin clearance. These two parameters were evaluated in seven dogs with known or suspected naturally occurring renal disease and compared to simultaneously measured renal inulin clearance. Correlation between inulin clearance and the ^99mTc-DTPA plasma clearance was better ( p =.0016) than the correlation between the percentage DTPA uptake by the kidney. It was concluded that measurement of ^99mTc-DTPA plasma clearance is a more accurate method to estimate global glomerular filtration rate (GFR) than the percentage kidney uptake.     

SCINTIGRAPHIC GASTROINTESTINAL BLEEDING LOCALIZATION WITH 99mTc-LABELED RED BLOOD CELLS

Ten scintigraphic gastrointestinal bleeding localization examinations were done in nine dogs. All dogs had clinical evidence of gastrointestinal bleeding prior to or on the day of the examination. Scintigraphy was done by in vivo labeling of red blood cells with ^99mTechnetium and imaging serially with a gamma camera over a 21-hour period. Of the nine dogs, four case history reports are presented. Three of these dogs had positive scintigraphic examinations. One dog had a negative scan but was later shown to have been ingesting material that mimicked the appearance of melena.     

QUANTITATIVE HEPATOBILIARY SCINTIGRAPHY USING 99mTC-DISIDA IN THE DOG

Quantitative hepatobiliary scintigraphy using ^99mTc-2,6 diisopropylphenylcarbamoylmethyl iminodiacetic acid (DISIDA) was performed in normal dogs. ^99mTc-DISIDA is excreted by the hepatocyte into the biliary tract. Hepatic blood flow from arterial and portal venous sources was measured as the hepatic perfusion index. The hepatic clearance of the radiopharmaceutical was used to assess hepatocyte function and parenchymal biliary transport. Biliary ejection was evaluated using synthetic cholecystokinin infusion. The procedure should be useful in evaluating dogs with hepatic and biliary disease.     

USE OF QUANTITATIVE HEPATIC SCINTIGRAPHY TO EVALUATE SPONTANEOUS PORTOSYSTEMIC SHUNTS IN 12 DOGS

Quantitative hepatic scintigraphy is a valid means for estimating total liver blood flow and relative portal hepatic perfusion. The Hepatic perfusion index (HPI) was determined for a group of 12 dogs with portosystemic shunts prior to and two days after corrective surgery. HPI values for the dogs prior to operation were significantly elevated (p<0.001) as compared with those for a group of normal dogs, indicating reduced effective portal hepatic perfusion in dogs with shunts. Dogs showing a favorable clinical response after surgery had a significant decrease (p<0.02) in HPI values after operation. One dog showing a poor clinical response after operation had an increase in HPI score after operation. Quantitative hepatic scintigraphy is a valuable diagnostic test for screening presumptive cases of portosystemic shunts and monitoring the response to surgical intervention.     

HEPATIC VOLUME ESTIMATION USING QUANTITATIVE COMPUTED TOMOGRAPHY IN DOGS WITH PORTOSYSTEMIC SHUNTS

The purpose of this study was to use quantitative computed tomography (CT) to estimate liver volume in dogs with a portosystemic shunt and to compare the liver volume in normal dogs to dogs with a shunt. Twenty-one dogs with a portosystemic shunt underwent contrast-enhanced abdominal CT for shunt characterization and preoperative planning. Six dogs without clinical signs relating to liver disease were used as a control group. In addition, liver volume was compared before and 2-4 months after surgical shunt attenuation in three dogs. All studies followed established clinical imaging protocols. Liver margins were defined on each image using an operator-defined region of interest and hepatic volume renderings were produced from which the liver volume was quantitatively estimated. There was a statistically significant association between liver volume and body weight in control and shunt dogs (r = 0.909 and 0.899, respectively, P < 0.01). Liver volume normalized to body weight was 15.5 +/- 5.2 cm3/kg in affected dogs and 24.5 +/- 5.6 cm3/kg in control dogs. Based on postligation CT studies in three affected dogs, liver volume increased by 43%, 51%, and 62%. Hepatic volume estimation may be a clinically useful parameter in the initial and postsurgical evaluation of dogs with portosystemic shunts.     

ULTRASONOGRAPHIC DIAGNOSIS OF CONGENITAL PORTOSYSTEMIC SHUNTS IN DOGS: RESULTS OF A PROSPECTIVE STUDY

The aims of this study were to determine if accurate diagnosis of congenital portosystemic shunt was possible using two dimensional, grey-scale ultrasonography, duplex-Doppler, and color-flow Doppler ultrasonography in combination, and to determine if dogs with congenital portosystemic shunts have increased or variable mean portal blood flow velocity. Eighty-two dogs with clinical and/or clinicopathologic signs compatible with portosystemic shunting were examined prospectively. Diagnosis of congenital portosystemic shunt was subsequently confirmed in 38 of these dogs using operative mesenteric portography: 14(37%) dogs had an intrahepatic shunt and 24(63%) had an extrahepatic shunt. Ultrasonography had a sensitivity of 95%, specificity of 98%, and accuracy of 94%. Ultrasonographic signs in dogs with congenital portosystemic shunts included small liver, reduced visibility of intrahepatic portal vessels, and anomalous blood vessel draining into the caudal vena cava. Correct determination of intra - versus extrahepatic shunt was made ultrasonographically in 35/38 (92%) dogs. Increased and/or variable portal blood flow velocity was present in 21/30 (70%) dogs with congenital portosystemic shunts. In one dog with an intrahepatic shunt the ultrasonographic diagnosis was based partly on finding increased mean portal blood flow velocity because the shunting vessel was not visible. Detection of the shunting vessel and placement of duplex-Doppler sample volumes were facilitated by use of color-flow Doppler. Two-dimensional, grey-scale ultrasonography alone is sufficient to detect most intrahepatic and extrahepatic shunts; sensitivity is increased by additional use of duplex-Doppler and color-flow Doppler. Increased and/or variable portal blood flow velocity occurs in the majority of dogs with congenital portosystemic shunts.     

DETECTION OF PORTAL BLOOD FLOW USING PER-RECTAL 99mTc-PERTECHNETATE SCINTIGRAPHY IN NORMAL CATS

This study reports data obtained from per-rectal ^99mTc-pertechnetate portal scintigraphy in normal cats. It examines the effects of chemical restraint and the methods employed in defining regions of interest (ROIs) on the shunt index derived from this data. Six normal cats were used for the study; all six were chemically restrained for imaging using propofol and later four of them were manually restrained for comparison. Portal blood flow was studied and the mean shunt index was found to be 5.9%± 3.9 when ROIs were operator defined and 9.2%± 4.4 when ROIs were defined using an isocontour program. In cats that were restrained using propofol and operator defined ROIs, the mean value for the time between detection of radioactivity in the liver and in the heart was 14 ± 1 seconds.     

ANATOMY OF EXTRAHEPATIC PORTOSYSTEMIC SHUNTS IN DOGS AS DETERMINED BY COMPUTED TOMOGRAPHY ANGIOGRAPHY

Congenital extrahepatic portosystemic shunts are anomalous vessels joining portal and systemic venous circulation. These shunts are often diagnosed sonographically, but computed tomography (CT) angiography produces high‐resolution images that give a more comprehensive overview of the abnormal portal anatomy. CT angiography was performed on 25 dogs subsequently proven to have an extrahepatic portosystemic shunt. The anatomy of each shunt and portal tributary vessels was assessed. Three‐dimensional images of each shunt type were created to aid understanding of shunt morphology. Maximal diameter of the extrahepatic portosystemic shunt and portal vein cranial and caudal to shunt origin was measured. Six general shunt types were identified: splenocaval, splenoazygos, splenophrenic, right gastric‐caval, right gastric‐caval with a caudal shunt loop, and right gastric‐azygos with a caudal shunt loop. Slight variations of tributary vessels were seen within some shunt classes, but were likely clinically insignificant. Two shunt types had large anastomosing loops whose identification would be important if surgical correction were attempted. A portal vein could not be identified cranial to the shunt origin in two dogs. In conclusion, CT angiography provides an excellent overview of extrahepatic portosystemic shunt anatomy, including small tributary vessels and loops. With minor variations, most canine extrahepatic portosystemic shunts will likely be one of six general morphologies.     

ACQUIRED PORTAL COLLATERAL CIRCULATION IN THE DOG AND CAT

We describe patterns of acquired portal collateral circulation in dogs and in a cat using multidetector row computed tomography angiography. Large portosystemic shunts included left splenogonadal shunts in patients with portal hypertension. Small portal collaterals were termed varices; these collaterals had several patterns and were related either to portal vein or cranial vena cava obstruction. Varices were systematized on the basis of the venous drainage pathways and their anatomic location, namely left gastric vein varix, esophageal and paraesophageal varices, gastroesophageal and gastrophrenic varices, gallbladder and choledocal varices, omental varices, duodenal varices, colic varices, and abdominal wall varices. As reported in humans and in experimental dog models, esophageal and paraesophageal varices may result from portal hypertension that generates reversal of flow, which diverts venous blood in a cranial direction through the left gastric vein to the venous plexus of the esophagus. Blood enters the central venous system through the cranial vena cava. Obstructions of the cranial vena cava can lead to esophageal and paraesophageal varices formation as well. In this instance, they drain into the azygos vein, the caudal vena cava, or into the portal system, depending on the site of the obstruction. Gallbladder and choledocal varices, omental varices, duodenal varices, phrenico-abdominal varices, colic varices, abdominal wall varices drain into the caudal vena cava and result from portal hypertension. Imaging plays a pivotal role in determining the origin, course, and termination of these vessels, and the underlying causes of these collaterals as well. Knowledge about these collateral vessels is important before interventional procedures, endosurgery or conventional surgery are performed, so as to avoid uncontrollable bleeding if they are inadvertently disrupted.     

BRAIN MAGNETIC RESONANCE IMAGING CHARACTERISTICS IN DOGS AND CATS WITH CONGENITAL PORTOSYSTEMIC SHUNTS

Animals with a portosystemic shunt (PSS) often have neurologic abnormalities. Diagnostic imaging, including brain magnetic resonance (MR) imaging, is not performed routinely in these animals. In this study, brain MR images were obtained in 13 dogs and three cats with a PSS, and in 15 dogs and five cats that were neurologically normal and used as controls. All animals with a PSS had widened sulci. In addition, 10 out of 13 dogs with a PSS and one out of three cats with a PSS had hyperintense focal areas in the lentiform nuclei on T1-weighted (T1W) images, which did not enhance after intravenous gadolinium. Following surgical correction of the PSS, MR imaging examinations were repeated in one dog and one cat. The hyperintensity of the lentiform nuclei had decreased. This study indicates that MR imaging findings of widened sulci and hyperintensity of the lentiform nuclei on T1W images may be found in dogs and cats with a PSS.     

AN INFECTED HIP PROSTHESIS IN A DOG DIAGNOSED WITH A 99mTC-CIPROFLOXACIN (INFECTON) SCAN

This case report describes the use of the 99mTc-labeled radiopharmaceutical ciprofloxacin (Infecton) in a case of hip prosthesis loosening in a dog. Serial planar radiographs were not conclusive, and culture of the synovial fluid was negative. Antibiotic treatment did not result in improvement of the lameness. Scintigraphy was performed with 99-Tc-Infecton, a tracer claimed to be specific for infection. Antibiotic treatment was interrupted 6 weeks prior to the examination. Planar and tomographic images at 3 h and at 24 h postinjection showed increased activity along the acetabulum and the proximal femoral bone surrounding the femoral prosthesis, indicating focal infection. Bacteriology performed after removal of the implant revealed Pseudomonas aeruginosa.     

HELICAL COMPUTED TOMOGRAPHIC PORTOGRAPHY IN TEN NORMAL DOGS AND TEN DOGS WITH A PORTOSYSTEMIC SHUNT

Contrast enhanced helical computed tomography (CT) of the liver and portal system is routinely performed in human patients. The purpose of this project is to develop a practical protocol for helical CT portography in the dog. Ten clinically normal dogs were initially evaluated to develop a protocol. Using this protocol, ten dogs with confirmed portosystemic shunts (PSS) were then evaluated. Each patient was anesthetized, and a test dose of sodium iothalamate (400 mg I/ml) at 0.55 ml/kg was injected. Serial images were acquired at the level of T12-13 or T13-L1. The time to maximum enhancement of the portal vein was determined. This time period was used as the period between the second injection (2.2 ml/kg) and the start of the helical examination of the cranial abdomen. Delay times for normal dogs ranged from 34.5 s-66.0 s (median: 43.5 s) or 1.41 s/kg-4.12 s/kg (median: 2.09 s/kg). For patients with a PSS, the delay times were 16.5-70.5 s (median: 34.5 s) or 1.47-19.17 s/kg (median: 3.39 s/kg). The aorta, caudal vena cava, portal vein, shunt vessels, and their respective branches were well visualized on the CT images. Clinical case results were surgically confirmed. The surgeons reported that the information gained from the CT portography resulted in a subjective decrease in surgical time and degree of dissection necessary compared with similar surgeries performed without angiographic information. We believe that helical CT portography in the dog will be a useful adjunct in the diagnosis of PSS. The use of helical CT portography may allow clinicians to give clients a more accurate prognosis prior to surgery and will allow patients with lesions that are not surgically correctable to avoid a costly and invasive procedure.     

CLINICAL USE OF 99mTC-MDP SCINTIGRAPHY IN THE EQUINE MANDIBLE AND MAXILLA

^99mTc-methylene diphosphonate (MDP) radionuclide imaging examinations were done in four horses having clinical evidence of skull trauma or infection. Radiographs were made of each horse prior to scintigraphy. Four case histories are presented. In each instance, scintigraphy provided complementary information to that obtainable through radiography, which aided in accurately localizing and characterizing the site and extent of abnormalities, and which proved particularly valuable as an aid for therapeutic planning.     

EVALUATION OF LYMPHOMA IN A CAT USING 99mTc-SESTAMIBI

This report describes the evaluation of cutaneous lymphoma in a cat using 99mTc-sestamibi. A mass in the left pes with extension to the left popliteal lymph node was diagnosed as B-cell lymphoma. Thoracic and abdominal radiography and abdominal ultrasound were unremarkable. Scintigraphy using 99mTc-sestamibi confirmed the lesion was confined to the left hind leg, and the leg was amputated. The cat made a full recovery.