CT assessments of lymph node involvement in the tumor process reported by various authors are controversial. This is explained by the fact that CT only determines the size of the nodes without giving information on the nature of their enlargement. Meanwhile, tumor invasion of the lymph nodes is not always accompanied by their enlargement. Likewise, enlargement of even perigastric lymph nodes is not always connected with their affection by metastasis. Kitaev indicates that lymph nodes greater than 20 mm in diameter more definitely indicate metastasis. If the diameter of lymph nodes is between 11 and 20 mm, the probability of their involvement is 85.5%, whereas probability nears 100% with lymph nodes greater than 20 mm in diameter. The most reliable criterion of involvement of the lymph nodes is their conglomerates, in which the size of separate nodes exceeds 10 mm (□ Fig. 87). Fukuya et al. report that the efficiency of CT in determining metastases to the lymph nodes is 72.5% .
While the evaluation of metastases to lymph nodes using CT is associated with certain difficulties, its efficacy in the diagnosis of metastatic affection of the liver is sufficiently high. According to Cook et al. (1986), cancer metastasis to the liver is revealed in 85-96% cases; according to Karmaza-novsky (1997), the accuracy of CT in diagnosing involvement of the liver is 86% .
The density of intact liver parenchyma is 5075 Hounsfield units (Hu). In native-state studies, it is impossible to detect focal affections such as metastases, the density of which differs only insignificantly (by 5-10 Hu) from that of normal liver parenchyma. False-negative results may also be due to the small size of foci (less than 10 mm), which remain undifferentiated against the background of the liver parenchyma in native-state examinations. According to Prondo et al. (1979) and Oue et al. (1985), metastases are not diagnosed in 10-40% of cases; subcapsular metastases are especially difficult to detect.
It is known that computed tomography conducted before and after contrast intensification (potential administration of water-soluble contrast medium) is an important element of the diagnostic search. But it should be noted that such intensification of intravenous contrast improves visualization of metastases in only one third of cases because parenchyma
density increases only by 20-30 Hu in such cases. In other patients imaging of metastasis remains the same or becomes less distinct. The latter is explained by leveling of the densitometric parameters of metastasis-affected and intact parenchyma, which masks the foci. Therefore, if metastasis to the liver is suspected, contrast medium should be given in bolus using automatic injectors.
Despite advances that have been made in diagnostic methods, the percentage of diagnostic laparotomies remains high. This is accounted for mostly by metastases to the liver, retroperitoneal lymph nodes, and the adjacent organs and major vessels. Nevertheless, advances in modern surgery have broadened the potentials of radical surgery. It has become popular to simultaneously remove the primary tumor and intraoperatively discovered metastases to the liver, provided only one lobe of the liver is involved. If both lobes are affected by metastasis, radical surgery is infeasible. Therefore, accurate detection of the presence of focal affection of the liver and estimation of its extent are of the greatest importance for the possible surgical removal of metastases localized in one lobe. But the resolution power of conventional CT and of CT with intravenous
□ Fig. 87a-e. Female patient D., age 58. Diagnosis: gastric cancer. a Stomach roentgenogram (tight filling, vertical position, anterior projection) at the moment of contrast medium passage through the gastroesophageal junction: the abdominal segment of the esophagus near the cardia is narrowed, uneven contours, marked deformation of the body and the upper part of the stomach, the stomach-diaphragm distance markedly increased (arrows). b, c Stomach roentgenograms (double contrast, horizontal position, left lateral position): the walls of the body and the upper part of the stomach are thickened and rigid due to diffuse circular intramural infiltration (arrows). Conclusion: Infiltrative cancer of the body and the upper part of the stomach with invasion of the abdominal part of the esophagus. In order to verify the extent of propagation of the tumor process to the adjacent anatomical structures, the patient was given a CT examination. d, e Computed tomograms (dosed inflation of the stomach with air, supine position, the level of the upper third of the stomach): uneven thickening of the walls due to intramural infiltration; uneven internal contours. Enlarged lymph nodes, with a diameter of 10-35 mm, are visualized n the projection of the spleen hilus, lesser omentum (arrows), and para-aortally. Conclusion: Infiltrative cancer of the body and the upper part of the stomach with metastases to the lymph nodes of the abdominal cavity and the retroperitoneal space.
intensification is insufficient; therefore, methods have been developed using selective intra-arterial administration of contrast medium.
There are three methods of intra-arterial enhancement of CT images:
1. CTAP - CT arterial portography, in which contrast medium is administered into the superior mesenteric artery. Intensification is obtained by contrast medium delivery through the portal vein.
2. CTA - CT arteriography, in which contrast medium is administered through the hepatic artery and the image is intensified largely in the arterial phase and to a lesser degree in the parenchymatous phase.
3. CTA - CT arteriography, in which contrast medium is administered into the iliac stem. This method has advantages over the former two because the results are estimated in both arterial and porto-vasal and parenchymatous
phases. However, the latter method is connected with the use of a catheter and performance of the procedure at one working post.
Intra-aortic enhancement of a CT image of the liver significantly increases density of the liver parenchyma, as contrast medium is consecutively accumulated in the parenchyma and in the foci of pathology; this helps to detect those foci which are undetectable by standard CT. Without going into much detail regarding CT arteriography, which is described in the monograph by Karmazanovsky, Vilyavin, and Niki-taev »Computed tomography of the liver and the bile ducts« (1997), we want to note that selective intra-ar-terial administration of radiopaque contrast medium increases density of the liver parenchyma 2.54.0 times to attain the value of 150-240 Hu. The significant difference in density and time of appearance of contrast between the focus and the liver parenchyma and the presence of a hypervascular rim are the main factors increasing the resolution power of CT. This helps detection of foci which have the same density as that of the parenchyma and are not therefore detectable by standard CT .
To summarize the data related to the use of computed tomography in the diagnosis of gastric cancer, several major factors can be emphasized: There is the possibility of CT to detect early endophytic cancer of the stomach (the wall-thickening sign), and there is verification of the extent of tumor spread (invasion of the neighboring organs and tissues, metastases). Computed tomography findings are another confirmation of the prevalence of the infiltra-tive form of cancer among malignant tumors of the stomach.
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