Keywords
main portal vein diameter - computed tomography - gastric surgery
Introduction
According to the Global Cancer Statistics 2020, stomach cancer was the fifth most
commonly seen cancer and the fourth leading cause of cancer-related deaths worldwide
in both sexes.[1] Surgery (total or subtotal gastrectomy) remains the main basic treatment method
for patients with gastric cancer.[2]
[3] Computed tomography (CT) is used for evaluating the extent of the disease and staging
preoperatively, and it is also the most important radiologic modality for follow-up
postoperatively.[4]
The main portal vein (MPV) is formed as a portosplenic confluence with the union of
the splenic vein and the superior mesenteric vein posterior to the neck of the pancreas,
passes behind the duodenum and extends to the liver hilum in the hepatoduodenal ligament.[5]
[6] Normal MPV is about 8 cm long and 9 to 13 mm wide.[7] A large MPV diameter is accepted as one of the radiological indicators of portal
hypertension.[8]
[9] In the follow-up CT examinations of patients who had undergone gastrectomy for gastric
malignancy in our center, we noticed by chance that there was an isolated increase
in the diameter of the MPV without other radiological findings of portal hypertension.
These patients were routine follow-up patients due to malignancy and also there were
no clinical signs of portal hypertension. We thought that the reason for the MPV enlargement
we detected on CT might be previous gastric surgery. To the best our knowledge, there
are no data on this subject in the literature. Therefore, in this study, we aimed
to evaluate whether the MPV diameter of patients who had gastric surgery for malignancy
differed in the preoperative and postoperative periods and its change over time in
patients who underwent postoperative follow-up examinations.
Materials and Methods
The study was undertaken in a tertiary care hospital. It was approved by the Ethics
Committee of the Faculty of Medicine of Eskişehir Osmangazi University (No: E-25403353-050.99-266327;
date: October 26, 2021). The study was conducted in accordance with the principles
of the Declaration of Helsinki. Datasets were evaluated retrospectively. Therefore,
approval and informed consent were not necessary and were waived by our local Institutional
Review Board.
All the CT imaging (preoperative staging and postoperative follow-up) and gastrectomy
were done in the same hospital.
Study Participants
The CT images of 240 patients who underwent abdomen CT for staging and follow-up gastric
malignancy between January 2017 and September 2021 were evaluated retrospectively.
Patients with CT examinations in which it was not possible to evaluate portal venous
system due to motion artifacts or an inappropriate contrast phase were not included
in the study. Patients with portal venous thrombosis or absent of follow-up CT and
patients who had historical or CT evidence of liver disease were excluded from the
study. The patients were staged with CT in the perioperative period, and restaged
according to the results of CT and pathology in the postoperative period. The patients
who need neoadjuvant and adjuvant treatments received the necessary treatment. Since
the aim of this study was to evaluate the effect of only surgery on portal vein diameter,
patients with cirrhosis–pseudocirrhosis findings or CT findings that would increase
portal vein diameter, such as congestive hepatopathy and portal thrombus, were also
excluded from the study in this period. The CT scans of the remaining 149 patients
were included in the study.
Image Acquisition
CT imaging was performed using 64-slice (Toshiba, Aquilion 64, Japan) or 128-slice
(GE, Revolution EVO, United States) multidetector CT scanners with the following parameters:
1:1/1.35 pitch, 200 to 350 mAs, 120 kVp, and 05 to 0.625 mm isotropic spatial resolution.
The subjects were examined in a supine position with their arms extended above their
heads.
An iodinated intravenous contrast agent (1–1.5 mL/kg) was administered through the
antecubital veins with an automatic injector at a rate of 3 mL/s; 20 mL saline was
injected both prior to and following the injection of the contrast media with the
same flow rate. Optimal scan time was detected by the automated bolus tracking method
by placing the region of interest over the descending aorta and setting the trigger
threshold to 100 HU and 40 seconds delay time. Images were obtained in portal venous
phases.
Image Analysis and Interpretation
The images were evaluated by two radiologists, once experienced in abdominal radiology,
using a workstation (Advantage WorkStation AW 4.7 software, GE Healthcare, Wisconsin,
United States) based on consensus. Maximum MPV diameter were measured outer wall to
outer wall with calipers on axial images at the level of 1 cm distal to the portosplenic
confluence by a single radiologist. The measurements were performed twice and averaged.
The diameter of MPV was recorded.
Statistical Analysis
SPSS software v. 22.0 (IBM Corp.) was used for statistical analysis. The normality
analysis was performed with the Shapiro–Wilk's test. Descriptive statistics were presented
as mean, standard deviation (SD) for the continuous data, and percentage values were
used for discrete data. Preoperative and postoperative MPV diameters were compared
using the paired samples t-test. A p-value of less than 0.05 was considered significant.
Results
The age of the 149 patients included in the study ranged from 28 to 89 years (mean ± SD,
61.16 ± 12.02 years). The sample consisted of 60 (40.26%) female and 89 male (59.73%)
patients. None of the patients had a history of chronic liver disease. Portal hypertension
findings were not detected in any of the patients in preoperative and follow-up CT
examinations, except for portal vein enlargement.
Total gastrectomy was performed in 85 (57%) patients, subtotal distal gastrectomy
in 52 (34.9%) patients, esophagogastrectomy in 7 (4.7%) patients, and wedge resection
in 5 (3.4%) patients. Except for those who underwent wedge resection, the pathological
diagnosis of all patients was adenocancer, and gastrectomy and D2 dissection were
performed to them. The pathological diagnosis of all patients who underwent wedge
resection were gastrointestinal stromal tumor, and lymph node dissection was not performed
in these patients.
One hundred forty-nine patients included in the study had preoperative CT examination.
Those with follow-up postoperative CT examinations at 3 months ± 15 days were classified
as third month control, those with follow-up postoperative CT examinations at 6 months ± 15
days were classified as 6 months control, those with follow-up postoperative CT examinations
at 1 year ± 15 days were classified as 1 year control. Eighty-three patients had follow-up
control CT at postoperative third month, 89 patients at sixth month, and 99 patients
at first year.
MPV diameters differed significantly between preoperative and follow-up postoperative
CT at third month, sixth month, and first year (p = 0.001, p = 0.001, and p = 0.001, respectively). MPV diameters were larger than preoperatively on CT at third
month, sixth month, and first year ([Figs. 1] and [2]). The MPV diameters of the patients at the preoperative and postoperative third
month, preoperative and postoperative sixth month, and preoperative and postoperative
first year are given in [Table 1].
Fig. 1 A 56-year-old male patient; CT images in the axial plane showing (A) preoperative MPV diameter 11.95 mm and (B) postoperative third month MPV diameter 16.63 mm. CT, computed tomography; MPV, main
portal vein.
Fig. 2 A 63-year-old male patient; CT images in the axial plane showing (A) preoperative MPV diameter 12.02 mm and (B) postoperative sixth month MPV diameter 16.10 mm. CT, computed tomography; MPV, main
portal vein.
Table 1
MPV diameters of the patients at the preoperative and postoperative third month, preoperative
and postoperative sixth month, and preoperative and postoperative first year
|
Number of patients (n)
|
Diameter (mm)
|
p-Value
|
|
Preoperative MPV diameter
|
83
|
12.82 ± 1.82
|
0.001
|
|
Postoperative third month MPV diameter
|
83
|
13.58 ± 2.16
|
|
Preoperative MPV diameter
|
89
|
12.87 ± 1.86
|
0.001
|
|
Postoperative sixth month MPV diameter
|
89
|
13.61 ± 2.36
|
|
Preoperative MPV diameter
|
99
|
12.71 ± 1.86
|
0.001
|
|
Postoperative first year MPV diameter
|
99
|
13.43 ± 1.82
|
Abbreviation: MPV, main portal vein.
Note: Bold values are statistically significant.
There was no difference in MPV diameter between follow-up CT at third and sixth months
and first year follow-up CT (p = 0.514 and p = 0.078, respectively). Follow-up MPV diameters of the patients at the postoperative
third and 6th month, and postoperative third month and first year are given in [Table 2].
Table 2
Follow-up MPV diameters of the patients at the postoperative third and sixth months,
and postoperative third month and first year
|
Number of patients (n)
|
Diameter (mm)
|
p-Value
|
|
Postoperative third month MPV diameter
|
44
|
13.95 ± 2.21
|
0.514
|
|
Postoperative sixth month MPV diameter
|
44
|
13.80 ± 2.52
|
|
Postoperative third month MPV diameter
|
53
|
13.98 ± 1.96
|
0.078
|
|
Postoperative first year MPV diameter
|
53
|
13.56 ± 1.63
|
Abbreviation: MPV, main portal vein.
Discussion
In this study, we found that MPV diameters in patients undergoing gastric surgery
expanded at the postoperative third month, sixth month, and first year compared with
preoperative CT, and this enlargement was statistically significant. We found no significant
difference in portal vein diameters in postoperative third month CT and sixth month
and first year CT examinations. According to these results, it is possible to say
that the expansion in postoperative MPV occurs within the first 3 months, and continues
without any change in the sixth month and first year CT examinations.
Although MPV dilatation is not specific, it is one of the most common radiological
findings of portal hypertension. It is claimed that the patient's inspiratory depth,
hydration, and contrast agent use may contribute to the factors affecting the portal
vein diameter in CT examination.[10] However, dilatation of the MPV is usually a warning for the early phase of portal
hypertension for radiologists, even in the absence of other accompanying findings
of portal hypertension (such as ascites, splenomegaly, chronic liver parenchymal findings,
varicose veins, and collateral vascular structures). We observed an enlargement of
MPV in CT examinations of patients who underwent gastric surgery for gastric malignancy
in our tertiary center. In these patients, splenic vein enlargement or splenomegaly,
which may suggest portal vein enlargement due to prehepatic reasons, were absent in
preoperative CT examinations. When we compared the preoperative CT examinations of
the patients, we found that enlargement of MPV was not present in the preoperative
CT and developed in the first 3 months after the operation and remained unchanged
during the first year follow-up. Based on our findings, it is not possible to clarify
the underlying cause of MPV enlargement after gastric surgery, but we can speculate
for some causes and mechanism.
D2 dissection was performed due to malignancy surgery in all patients in the current
study, except for the patients who underwent wedge resection. D2 dissection, together
with total or subtotal gastrectomy in the treatment of gastric cancer, is the standard
lymph node dissection method in Japan and recommended in experienced centers in the
West.[3] It is the standard treatment method in our center also. According to the Japanese
Classification of Gastric Carcinoma, lymph nodes no. 12 included in the D2 dissection
are hepatoduodenal ligament lymph nodes.[11] The deterioration in the integrity of the hepatoduodenal ligament during the dissection
of these lymph nodes may have caused enlargement in the structures inside by reducing
or eliminating the sheath effect of the ligament. There was also another finding supporting
this mechanism in our study. We did not detect MPV enlargement postoperatively in
any of the five patients who underwent wedge resection and therefore did not undergo
D2 dissection. Although the number of patients was not sufficient for statistical
analysis, this result makes us think that D2 dissection with gastrectomy causes dilatation
of the MPV diameter. We think that the portal vein which located with hepatic artery
in the hepatoduodenal ligament is more affected and enlarged than hepatic artery due
to the difference in the histological structures (thicker wall and strong media layer
in the artery). We did not evaluate the hepatic artery in this study, as we did not
have an observation for it. The common bile duct is another structure within the hepatoduodenal
ligament. We did not notice this situation in our first observation, but in the retrospective
examination, we noticed that there was an enlargement of the common bile duct compared
with preoperative CT. This change in the diameter of the common bile duct may be a
subject of separate evaluation for future studies.
Gastric surgery irreversibly changes the physiology of the digestive system, leading
to the loss of capacitive function and the disappearance of the secretion of gastric
digestive enzymes and hormones.[2] Functional elimination of one part of the gastrointestinal tract may cause a compensatory
response in the remaining parts, involving some form of morphological adaptation.[2]
[12] Proliferation of enterocytes results in increased villi height, intestinal crypt
depth, mucosal surface area, and small bowel mass.[13] Following adaptation, the intestinal enterocytes are more functional and more capable
of digesting and absorbing nutrients.[2] As a second mechanism, we thought: the realization of these morphological and functional
changes may be possible with an increase in blood flow to the intestines. Increased
blood flow may also be the cause of increased venous outflow. Due to compliance, this
may result in enlargement of the flexible vein walls and increase in vein diameter.
Portal vein flow measurements are needed for the validity of this hypothesis. It is
not possible to determine portal vein flow with CT, but it can be done with Doppler
ultrasonography. This hypothesis can be evaluated with a prospectively planned study
in the future.
The effect of gastric surgery on the liver is still controversial.[2] Puzio et al in their study on rats found that the number of total cells, hepatocytes,
hepatocyte nuclei, and mononuclear hepatocyte nuclei increased significantly.[2] It is known that increased cell number in the liver and liver hypertrophy are partly
related to a rise in portal pressure.[14] Increased pressure in the portal vein results in portal vein enlargement. The enlargement
of the portal vein diameter in our study may also be a result of the proliferative
effect of gastric surgery on liver cells.
One of the strengths of our study is that it was conducted in a large patient group.
In addition, examining an observation that has not been mentioned in the literature
before is important in terms of contributing to the literature. The first among the
limitations of the study is its retrospective nature. In addition, due to this retrospective
nature, it is also a limitation that the flow changes and characteristics in the portal
vein are not examined by Doppler. Future prospective studies may allow the evaluation
of Doppler findings. Another limitation is that all patients included in the study
did not have a follow-up CT examination at third month, sixth month, and first year.
However, sufficient number of patients in each group is a factor that partially prevents
this limitation.
Conclusion
MPV enlargement occurs in the first 3 months postoperatively in patients undergoing
gastric surgery. This enlargement continues irreversibly in the first 1 year follow-up.
The radiologists' awareness of this situation can prevent the wrong diagnosis of portal
hypertension, unnecessary concern, and further investigation.
