A congenital EPSS is a vascular anomaly that diverts blood from the portal vein to the caudal vena cava or to other systemic veins bypassing the liver. Dogs with EPSS have various clinical signs and sometimes develop portal hypertension or multiple acquired shunts after attenuation of shunt vessels. Shunt fraction refers to the percentage of total portal venous flow that is shunted and might influence the pathophysiologic status.1,2 However, the only way to measure SF in the clinical setting is with scintigraphy, the results of which are highly variable and do not suggest a relationship between SF and clinical features.3
In dogs with EPSS, CT is valuable for the diagnosis of shunt type, evaluation of all portal tributaries and branches, and surgical planning.1 Recently, 320-row MDCT has been developed, which can capture images with 16-cm widths in 1 scan rotation. In addition, the TDC, defined as the time-dependent change of the CT value during angiography in the region of interest, enables estimation of blood flow volume.4 Therefore, MDCT has the potential for measuring SF in dogs with EPSS and allows visualization of tissue perfusion in a fixed area over time. This functional imaging technique is called perfusion CT and has allowed quantification of hepatic blood circulation in human patients with diffuse liver disease.5–7 In dogs with portal vascular anomalies, MDCT revealed differences in hepatic perfusion variables between clinically normal dogs and dogs with portal vascular anomalies.8 Additionally, a study9 shows that high values for hepatic perfusion variables in dogs with EPSS lowered to within reference limits after surgical attenuation of their shunts with ACP. To our knowledge, there are no reports on perfusion CT–derived SF and hepatic perfusion CT variables in various clinical settings for dogs with EPSS.
Therefore, the objective of the study presented here was to evaluate the clinical feasibility and usefulness of measuring SF and hepatic perfusion with CT in dogs with a single EPSS. We hypothesized that measuring SF would be feasible by MDCT and that SF and hepatic perfusion CT variables would be influenced by clinical features.
Materials and Methods
Animals
Client-owned dogs referred to our hospital because of suspected EPSS between February 2016 and May 2017 were eligible for the clinical trial, and owner consent was obtained for inclusion. The definitive diagnosis of EPSS was made by triple-phase helical CT on the first consultation in our hospital. Dogs were grouped according to age: dogs < 3 years old were assigned to the Y group, and dogs ≥ 3 years old were assigned to the O group. Each group was then further subdivided on the basis of clinical signs, including hepatic encephalopathy as well as urological signs associated with uratic uroliths.
Perfusion CT
All dogs underwent perfusion CT for the measurement of SF and CT variables. For the procedure, each dog received a 22- to 24-gauge over-the-needle catheter in a cephalic vein and was premedicated with atropine sulfate (0.04 mg/kg [0.02 mg/lb], SC), prednisolone (1.0 mg/kg [0.5 mg/lb], SC), ranitidine (2.0 mg/kg [0.9 mg/lb], SC), maropitant citrate (1.0 mg/kg, SC), and levetiracetam (20.0 μg/kg [9.1 μg/lb], SC). Anesthesia was induced with propofol (1.8 to 8 mg/kg [0.8 to 3.6 mg/lb] to effect, IV). Endotracheal intubation was performed, and general anesthesia was maintained by mechanical ventilation with isoflurane in oxygen delivered at 2 L/min with the anesthetic vaporizer set at 1.5% to 2%. Dogs were positioned in ventral recumbency for 320-row MDCT.a The nonionic contrast medium iohexolb (600.0 mg of iodine/kg [272.7 of iodine/lb], IV) was administered with a power injectorc over 8 seconds through the catheter in the cephalic vein. The temporal volume scan was obtained, and a single scan covered the area from the dome of the diaphragm cranially to about the left kidney caudally, within 160 mm of the caudalmost extent of the liver. The scan was initiated simultaneously with the contrast medium injection, and scans were performed 33 times intermittently over 1 minute, with a rotation time of 0.5 seconds and an interval time of 1 to 2 seconds. The interval between scans was set to 2 seconds for the first through third scans, 1 second for the third through 23rd scans, and 2 seconds for the 23rd through 33rd scans. Scans were performed with expiratory breath-holds, and CT images were reconstructed with smoothing, but not beam-hardening, correction. The other scanning settings included slice thickness of 0.5 mm, reconstruction interval of 0.5 mm, radiographic tube potential of 100 kV, and radiographic tube current of 100 mA. Images were transferred to an image-processing workstationd for analysis.
Image analysis
All images were reviewed by 1 veterinarian (KA), and the shunt type was classified on the basis of CT findings. After body registration was performed with softwaree to correct for motion between the dynamic volumes, perfusion CT analysis and calculation of SF were performed by a single veterinarian (TA).
Perfusion CT analysis was conducted with the scanner manufacturer's body perfusion software,f and the dual input maximum slope model was used for perfusion analysis of the liver. In each hepatic lobe, HAF and PVF (mL/min/100 mL) were measured. The HPI (%) was calculated as follows: HPI = HAF/(HAF + PVF).
To measure the SF, the TDC was first created by evaluating the shunt vessel and the main portal vein between the junction of the gastroduodenal vein and the bifurcation of the right branch of the portal vein. The region of interest was manually placed in each vessel, the size of which was approximately 70% to 90% of the sectional area of the vessel. With the TDC as previously reported,4 blood flow volume (mL/s) was calculated as follows: blood flow volume = (ΔH [tm]/AUC) X V, where ΔH(tm) was the peak rate of upslope of the TDC, AUC was the area under the TDC until the peak, and V was the sectional area of the vessel. The SF was then calculated from the blood flow volume in each vessel as follows: SF = Flowshunt/(Flowshunt + Flowportal), where Flowshunt was the blood flow volume in the shunt vessel, and Flowportal was the blood flow volume in the portal vein. The EPSS was classified as complete shunting when there was no anatomic evidence of a portal vein on CT.10 Therefore, when the main portal vein could not be identified, the SF was determined to have been 100%.
Surgical treatment and portal venous blood pressure
All surgical treatments (ie, surgical ligation, ACP, or PTCE) for the EPSSs were performed by the same veterinary surgeon (KA) who was blinded to the SF value in each dog. During each procedure, the portal venous blood pressure was measured before and during temporary occlusion of the shunt vessel.
Data analysis
Data on age, sex, and body weight were compared between the Y and O groups with the χ2 test or Fisher exact tests. The differences in results between the Y and O groups, subgroups, shunt types, and treatments were analyzed with the Mann-Whitney U test or the Kruskal-Wallis test followed by the Dunn post hoc correction test. The correlation between the SF and portal venous blood pressure was evaluated by assessing Spearman rank correlation coefficient (ρ). All data were represented as median (range). Statistical analyses were performed with available software,g and values of P < 0.05 were considered significant.
Results
Animals
The study included 36 client-owned dogs, including 8 Toy Poodles, 5 Yorkshire Terriers, 5 mixed-breed dogs, 4 Maltese, 3 Miniature Schnauzers, 2 Papillons, 2 Chihuahuas, 2 Shih Tzu, and 1 each of a Pomeranian, Miniature Dachshund, Italian Greyhound, West Highland White Terrier, and Norfolk Terrier. The mean and median ages were 3.8 and 2.5 years (range, 0 to 12 years), respectively. There were 18 dogs in the Y group (< 3 years old; mean age, 0.7 years) and 18 dogs in the O group (≥ 3 years old; mean age, 6.9 years). There were 17 males and 19 females, and there was no meaningful difference in the distribution of sexes identified between the Y and O groups. Overall, the median body weight was 3.1 kg (6.8 lb; range, 1.4 to 8.5 kg [3.1 to 18.7 lb]), and the median body weight was significantly (P = 0.032) less for the Y group (2.8 kg [6.2 lb]; range, 1.6 to 6.9 kg [3.5 to 15.2 lb]), compared with the O group (3.8 kg [8.4 lb]; range, 1.4 to 8.5 kg [3.1 to 18.7 lb]). Clinical signs related to EPSS were evident in 13 of the 18 dogs in the Y group and in 10 of the 18 dogs in the O group. Six dogs (3 in the Y group and 3 in the O group) had a history of seizures.
Shunt types
Of the 36 dogs, 15 had a left gastrophrenic shunt, 11 had a left gastrocaval shunt, 3 had a right gastrosplenocaval shunt, 3 had a left gastroazygos shunt, 2 had a right gastrocaval shunt, 1 had a left colocaval shunt, and 1 had a splenophrenicoabdominal shunt with a left gastroazygos shunt. In the Y group, left gastrophrenic shunts and left gastrocaval shunts were observed in 5 and 7 dogs, respectively. In the O group, left gastrophrenic shunts and left gastrocaval shunts were observed in 10 and 4 dogs, respectively. Although the proportion of dogs with a left gastrophrenic shunt was higher in the O group (10/18) than in the Y group (5/18), the difference was not significant (P = 0.091).
Surgical treatment and portal venous blood pressure
The intraoperative portal venous blood pressures (reference range, 6 to 10 mm Hg1) were measured in 32 dogs, in which the median portal venous pressures before and during temporary occlusion were 7 mm Hg (range, 0 to 13 mm Hg) and 13.5 mm Hg (range, 7 to 48 mm Hg), respectively. As for the surgical treatments performed in the 36 dogs, 14 had surgical ligation of the shunt, 14 had ACP, and 8 had PTCE. Of the 14 dogs that underwent surgical ligation, 6 and 8 underwent CL and PL, respectively, and PL was typically performed in dogs with high portal venous blood pressure during temporary occlusion. After surgery, none of the 36 dogs died because of causes related to the surgery, had seizures, or showed signs of complications associated with portal hypertension.
SF
Overall, the median SF was 48.9% (range, 7.6% to 100%). When considered on the basis of shunt type, the median SF was significantly (P = 0.001) lower in dogs with left gastrophrenic shunts (27.8%; range, 7.6% to 65.6%; n = 15) versus left gastrocaval shunts (80.1%; range, 10.1% to 100%; 11). The median SFs in dogs with the remaining shunt types were 88.3% (range, 77.5% to 97.0%; n = 3) in dogs with right gastrosplenocaval shunts, 35.3% (range, 27.9% to 52.2%; 3) in dogs with left gastroazygos shunts, 46.8% (range, 44.4% to 49.3%; 2) in dogs with right gastrocaval shunts, 58.1% in the single dog with a left colocaval shunt, and 43.7% in the single dog with a splenophrenicoabdominal shunt combined with a left gastroazygos shunt.
The median SF was significantly (P = 0.001) higher for the Y group (74.6%; range, 16.0% to 100%), compared with the O group (35.1%; range, 7.6% to 74.5%). In addition, the median SF was significantly (P = 0.025) higher in the dogs in the Y group with (88.6%; range, 35.3% to 100%) versus without (26.0%; range, 16.0% to 80.1%) clinical signs of EPSS. However, the median SF for dogs in the O group was not substantially different between dogs with (46.1%; range, 10.1% to 74.5%) versus without (27.9%; range, 7.6% to 44.4%) clinical signs of EPSS.
The SF correlated significantly (ρ = 0.530; P < 0.002) with the portal venous blood pressure during temporary occlusion, and the regression line fit to an exponential curve (R2 = 0.78; Figure 1). Regarding surgical method of treatment, the median SF was significantly (P = 0.021; P < 0.001, and P = 0.002, respectively) higher in dogs that underwent PL (93.7%; range, 63.9% to 100%; n = 8), compared with ACP (46.8%; range, 10.1% to 80.1%; 14), PTCE (27.4%; range, 15.3% to 58.1%; 8), or CL (22.2%; range, 7.6% to 74.5%; 6; Figure 2). However, the median SF was not meaningfully different among dogs treated with ACP, PTCE, or CL.
Exponential curve of goodness of fit (R2 = 0.74) for correlation between presurgical CT-derived SF measurements and interoperative portal venous blood pressure during temporary occlusion of shunt vessels in 32 dogs with EPSS treated between February 2016 and May 2017.
Citation: Journal of the American Veterinary Medical Association 255, 7; 10.2460/javma.255.7.821
Box-and-whisker plots for results of presurgical CT-derived SF stratified by surgical treatment provided to 36 dogs with EPSS between February 2016 and May 2017. Each box represents results for the 25th to 75th percentiles, the horizontal line in the box represents the median SF value, and the whiskers represent the range of SF values.
Citation: Journal of the American Veterinary Medical Association 255, 7; 10.2460/javma.255.7.821
Perfusion CT
Values for the perfusion CT variables were determined. When all dogs and all hepatic lobes were considered together, the overall median HAF was 111.05 mL/min/100 mL (range, 17.8 to 267.1 mL/min/100 mL; reference mean ± SD by a different protocol, 23.0 ± 11.0 mL/min/100 mL8), median PVF was 120.7 mL/min/100 mL (range, 0 to 345.0 mL/min/100 mL; reference mean ± SD by a different protocol, 108.0 ± 45.0 mL/min/100 mL8), and median HPI was 44.8% (range, 17.5% to 99.9%; reference mean ± SD by a different protocol, 19.0% ± 7.0%8). The median SF correlated significantly with HAF in each hepatic lobe (Table 1) but only correlated significantly (ρ = 0.355; P = 0.034) with the PVF in the caudate process of the caudate lobe (Table 2). In addition, the median SF correlated significantly (ρ = 0.392; P = 0.018) with the median HPI in the right medial lobe (Table 3). When data were evaluated to identify differences in results for HAF, PVI, or HPI between dogs grouped according to whether they had a left gastrophrenic shunt (n = 15) versus a left gastrocaval shunt (11), there was no substantial difference in median HPI between the 2 shunt types. However, the median HAF was signifcantly (P = 0.021 and P = 0.020, respectively) higher in the quadrate and left medial hepatic lobes for dogs with a left gastrocaval shunt versus a left gastrophrenic shunt. Similarly, the median PVF was significantly (P = 0.006 and P = 0.015, respectively) higher in the right lateral hepatic lobe and the caudate process of the caudate lobe in dogs with a left gastrocaval shunt versus a left gastrophrenic shunt. No meaningful differences in HAF, PVF, or HPI were detected between dogs with versus without clinical signs of EPSS.
Summary results of Spearman rank correlation coefficient (ρ) analysis between CT-derived HAP and SF measured in 36 client-owned dogs with EPSS treated between February 2016 and May 2017 and of evaluation of HAP in dogs with left gastrophrenic shunts (n = 15) versus left gastrocaval shunts (11) to identify differences in HAP per liver lobe on the basis of shunt type.
| Hepatic lobe | HAP of all dogs* (mL/min/100 mL; n = 36) | ρ | P value | HAP of dogs with LGP* (mL/min/100 mL; n = 15) | HAP of dogs with LGC* (mL/min/100 mL; n = 11) | P value |
|---|---|---|---|---|---|---|
| RLL | 111.1 (37.9–267.1) | 0.416 | 0.012 | 92.6 (38.9–206.9) | 121.6 (65.8–267.1) | 0.148 |
| CCL | 119.1 (47.4–251.6) | 0.495 | 0.002 | 95.8 (47.5–189.4) | 131.7 (62.8–251.6) | 0.163 |
| RML | 104.2 (32.6–232.7) | 0.548 | < 0.001 | 94.3 (32.6–168.3) | 130.2 (52.3–232.7) | 0.080 |
| QL | 95.1 (17.8–187.8) | 0.504 | 0.002 | 78.3 (17.8–175.5) | 143.3 (64.9–187.8) | 0.021 |
| PCL | 117.2 (49.6–249.2) | 0.577 | < 0.001 | 101.9 (49.6–228.9) | 126.1 (69.7–249.2) | 0.148 |
| LML | 107.2 (11.8–226.5) | 0.618 | < 0.001 | 103.1 (11.8–138.6) | 135.5 (56.9–226.5) | 0.020 |
| LLL | 105.5 (40.7–239.9) | 0.578 | < 0.001 | 95.9 (47.8–174.8) | 117.2 (58.8–239.9) | 0.063 |
Results reported as median (range).
CCL = Caudate process of the caudate lobe. LGC = Left gastrocaval shunt. LGP = Left gastrophrenic shunt. LLL = Left lateral lobe. LML = Left medial lobe. PLC = Papillary process of the caudate lobe. QL = Quadrate lobe. RLL = Right lateral lobe. RML = Right medial lobe.
Summary results of Spearman rank correlation coefficient (ρ) analysis between CT-derived PVF and SF in the dogs described in Table 1 and of evaluation of PVF in dogs with left gastrophrenic shunts (n = 15) versus left gastrocaval shunts (11) to identify differences in PVF per liver lobe on the basis of shunt type.
| Hepatic lobe | PVF of all dogs* (mL/min/100 mL; n = 36) | ρ | P value | PVF of dogs with LGP* (mL/min/100 mL; n = 15) | PVF of dogs with LGC* (mL/min/100 mL; n = 11) | P value |
|---|---|---|---|---|---|---|
| RLL | 117.9 (4.8–331.5) | 0.252 | 0.138 | 101.9 (26.8–268.3) | 157.4 (52.1–331.5) | 0.006 |
| CCL | 114.0 (3.4–345.0) | 0.355 | 0.034 | 100.7 (46.1–194.4) | 145.1 (19.5–345.0) | 0.015 |
| RML | 131.6 (12.9–340.5) | 0.067 | 0.697 | 131.8 (12.9–297.1) | 138.3(79.8–340.5) | 0.328 |
| QL | 114.8 (12.2–304.6) | 0.086 | 0.620 | 112.2 (12.2–237.5) | 126.2 (26.5–304.6) | 0.535 |
| PCL | 116.0 (0–301.4) | 0.101 | 0.558 | 115.0 (61.8–301.4) | 134.6 (62.1–279.8) | 0.275 |
| LML | 133.4 (22.2–309.3) | 0.197 | 0.249 | 127.6 (60.6–259.7) | 143.1 (43.7–309.3) | 0.197 |
| LLL | 128.4 (56.1–313.9) | 0.148 | 0.391 | 128.0 (62.7–257.4) | 159.1 (60.7–311.1) | 0.216 |
See Table 1 for the key.
Summary results of Spearman rank correlation coefficient (ρ) analysis between HPI and SF measured in the dogs described in Table 1 and of evaluation of HPI in dogs with left gastrophrenic shunts (n = 15) versus left gastrocaval shunts (11) to identify differences in HPI per liver lobe on the basis of shunt type.
| Hepatic lobe | HPI of all dogs† (n = 36) | ρ | P value | HPI of dogs with LGP† (n = 15) | HPI of dogs with LGC† (n = 11) | P value |
|---|---|---|---|---|---|---|
| RLL | 45.7 (21.6–98.0) | 0.200 | 0.242 | 47.0 (21.6–67.0) | 33.7 (27.1–81.3) | 0.699 |
| CCL | 47.0 (27.7–97.8) | 0.052 | 0.764 | 48.7 (29.0–66.3) | 46.2 (27.7–92.1) | 0.287 |
| RML | 40.9 (20.8–76.7) | 0.392 | 0.018 | 40.5 (20.8–62.2) | 45.8 (30.2–74.7) | 0.535 |
| QL | 44.2 (21.0–87.7) | 0.288 | 0.089 | 41.8 (21.0–66.5) | 51.2 (24.2–87.7) | 0.381 |
| PCL | 49.6 (21.4–99.9) | 0.281 | 0.097 | 54.0 (21.4–67.2) | 48.2 (32.8–80.7) | 0.809 |
| LML | 43.9 (17.5–88.4) | 0.314 | 0.063 | 42.9 (17.5–64.5) | 45.3 (28.0–84.3) | 0.583 |
| LLL | 41.6 (23.2–78.6) | 0.312 | 0.064 | 41.4 (23.1–60.7) | 42.6 (26.2–78.6) | 0.770 |
Results reported as median (range) percentage.
See Table 1 for the key.
Discussion
Results indicated that the measurement of EPSS SF with perfusion CT was feasible in dogs in the present study. In addition, our findings that the lowest SF was 7.6% suggested that perfusion CT–derived SF values were lower than reported scintigraphy-derived SF values (SF of 62% to 85%) and lower than the scintigraphy-derived SF value of 15% that is considered normal.3,9,11,12 Although direct comparisons between perfusion CT–derived SF and scintigraphy-derived SF were not evaluated, results of the present study suggested that smaller SF values could be better determined with perfusion CT than with scintigraphy. Scintigraphy-derived SF values are not reproducible among operators and in dogs and cats have only been proven useful for diagnosis of portosystemic shunts.3 In the present study, the intra- and interoperator variation in measurement of perfusion CT–derived SF were not evaluated, and because the TDC variation depends on the contrast medium administration protocol,13 different contrast medium injection protocols might produce different SF values in some dogs. Nonetheless, the protocol used in our study was considered suitable for evaluation of dogs with EPSS in clinical settings. Further studies on protocol improvements for the measurement of SF might be required to evaluate the influences of different protocols on SF values.
The smaller median SF detected in dogs with left gastrophrenic shunts, compared with gastrocaval shunts, in the present study could have been associated with the respiratory cycle, because inspiration causes an increase in intrathoracic pressure that results in a caudal shift of the diaphragm. Therefore, the shunt vessels in dogs with left gastrophrenic shunts might have compressed during inspiration. Further, a decrease in shunted blood flow and an increase in intrahepatic portal blood flow are thought to occur during inspiration. Thus, during inspiration, the increase in intrahepatic portal blood flow could facilitate growth of intrahepatic portal vascularity. Although this relationship between respiratory cycle and shunted brood flow is still unclear, a previous study2 shows that clinical signs are milder in dogs with portophrenic shunts, compared with other types of shunts, and that the movement of the diaphragm results in improved portal perfusion.
Results indicated that SF was higher in younger dogs than in older dogs in the present study; however, findings also suggested that SF was influenced more by shunt type than by age. Although left gastrophrenic and gastrocaval shunts accounted for most of the shunts in dogs in both the Y and O groups, the proportion with left gastrophrenic shunts was higher in the O group (dogs ≥ 3 years old) than in the Y group (dogs < 3 years of age). However, the number of patients included in the present study was small, and no significant difference in the proportions was detected between the groups. Relatedly, a previous study14 shows older dogs with EPSS more commonly had splenophrenic and splenoazygos shunts than right gastrocaval and splenocaval shunts. Our findings also suggested that SF could be involved in the onset of clinical manifestations at a younger age, and that differences in SF could be detected between subgroups of dogs with specific clinical signs in the Y group but not between similar subgroups of dogs in the O group. Because dogs with EPSS that have higher SF values may have lower volumes of intrahepatic portal blood flow, affected dogs may show clinical signs at earlier ages. Consistent with this, dogs in the Y group more commonly had portocaval shunts with higher SF values, compared with portophrenic shunts with lower SF values. In the O group, however, no difference in SF was detected between dogs with versus without clinical signs, which suggested that factors other than age were involved in the development of clinical signs related to EPSS.
Surgical treatment (eg, surgical ligation, ACP, or cellophane banding) is commonly performed in dogs with EPSS,15 and intraoperative measurement of portal venous blood pressure is one of the guides for the degree of attenuation in animals undergoing acute CL or PL.1 In the present study, PL was typically performed in dogs with high portal venous blood pressure identified during temporary occlusion. Beyond this, the ability to predict before surgery whether portal hypertension would be likely during temporary occlusion might impact the choice of treatment, and results of the present study suggested that SF values could be useful in such preoperative predictions and therefore impact treatment planning. A previous study9 shows that preoperative factors other than liver volume, portal vein diameter, and hepatic perfusion might predict the development of multiple acquired shunts in dogs. Therefore, further clinical studies are required to establish the clinical usefulness of SF as a predictive factor for the development of multiple acquired shunts.
Similar to a previous study8 that shows higher HAFs and HPIs in dogs with portosystemic shunts (n = 21) versus clinically normal dogs (10), dogs in the present study also had higher HAFs and HPIs than did the clinically normal dogs of that earlier study. However, results of the present study indicated that dogs with EPSS had similar PVFs as clinically normal dogs, whereas the previous study8 shows that dogs with shunts had lower PVFs than clinically normal dogs. This difference could have been attributable to differences in shunt types in the dogs studied. For instance, the previous study8 included only 2 dogs with EPSS, but 9 dogs with intrahepatic portosystemic shunts, 4 dogs with multiple acquired EPSSs, and 6 dogs with intrahepatic arterioportal fistulae and multiple acquired portosystemic shunts. Inclusion of dogs with multiple portosystemic shunts in the previous study8 could have contributed to the lower PVFs reported. In addition, perfusion results of the previous study8 were reported as means ± SDs, whereas those of the present study were reported as medians and ranges.
Results of the present study indicated that HAF positively correlated with SF, suggesting a compensation for lower intrahepatic portal blood flow in dogs with high SFs. This finding was consistent with findings in histopathologic studies16,17 that show hepatic arteriolar proliferation was the most frequently recognized change in dogs with EPSS. In addition, our findings indicated that the median PVFs of the right lateral lobe and the caudate process of the caudate lobe were markedly higher in dogs with left gastrocaval shunts versus left gastrophrenic shunts. This finding was consistent with a previous study18 showing that the main PVF is the primary blood supply into the right divisional lobes. Although the median SF was greater in dogs with left gastrocaval shunts (80.1%) versus left gastrophrenic shunts (27.8%), the median PVFs in the right lateral lobe and the caudate process of the caudate lobe were higher in dogs with left gastrocaval shunts (157.4 and 145.1 mL/min/100 mL, respectively) versus left gastrophrenic shunts (101.9 and 100.7 mL/min/100 mL, respectively), which suggested that less intrahepatic portal blood flow was diverted to the shunts in dogs with left gastrocaval shunts versus left gastrophrenic shunts.
In support of our hypothesis, results indicated that CT-derived measurements of SF and hepatic perfusion variables in dogs with EPSS were feasible and could be useful (eg, estimating EPSS condition status and planning treatment) in clinical settings. In addition, our findings suggested that perfusion CT could be useful for distinguishing hemodynamic characteristics among different types of portosystemic shunts in dogs.
Acknowledgments
No third-party funding or support was received in connection with the present study or the writing or publication of the manuscript.
ABBREVIATIONS
| ACP | Ameroid constrictor placement |
| CL | Complete ligation |
| EPSS | Extrahepatic portosystemic shunt |
| HAF | Hepatic arterial blood flow |
| HPI | Hepatic perfusion index |
| MDCT | Multidetector computed tomography |
| PL | Partial ligation |
| PTCE | Percutaneous transvenous coil embolization |
| PVF | Portal venous blood flow |
| SF | Shunt fraction |
| TDC | Time density curve |
Footnotes
Aquillion ONE, Toshiba Medical Systems, Tochigi, Japan.
Ioverin 300, iodine content 300 mg I/ml, Teva Pharma Japan Inc, Nagoya, Japan.
Auto Enhance A-60, Nemoto-Kyorindo, Tokyo, Japan.
AZE Virtual Place Plus, AZE Co, Tokyo, Japan.
Body registration, Toshiba Medical Systems, Tochigi, Japan.
Body perfusion, Toshiba Medical Systems, Tochigi, Japan.
GraphPad Prism, version 6.0 for Macintosh, Graph Pad Software Inc, San Diego, Calif.
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