J. Hata, MD
Department of Clinical Pathology and Laboratory Medicine, Kawasaki Medical School, 577, Matsushima, Kurashiki-city, Okayama, 701-0192, Japan
K. Haruma, MD; N. Manabe, MD; T. Kamada, MD;
H. Kusunoki, MD; T. Tanaka, MD; M. Sato, MD
Division of Gastroenterology, Dept. of Internal Medicine, Kawasaki Medical School, 577, Matsushima, Kurashiki-city, Okayama, 701-0192, Japan
Gastric Cancer 16
Jiro Hata, Ken Haruma, Noriaki Manabe, Tomoari Kamada, Hiroaki Kusunoki, Toshiaki Tanaka, and Motonori Sato
16.1
Introduction
Gastric cancer is still of major importance world- wide despite declining incidence. Endoscopy, radio- logical examination, and computed tomography are the diagnostic imaging modalities employed for gastric cancer. For early gastric cancers, in particu- lar, endoscopy is the essential diagnostic method of choice; however, with the remarkable improvements in sonographic equipment, transabdominal ultraso- nography has recently been reported to be useful in the assessment of gastric cancer. Endoscopic ultra- sound is another imaging modality using ultrasound which has not necessarily been as widely used as
transabdominal ultrasound due to its invasiveness. In this chapter, sonographic imaging of gastric cancer, mainly transabdominal, is described.
16.2
Sonographic Assessment of the Gastric Wall
16.2.1
Preparation and Equipment
For the screening of advanced gastric cancers, special preparations, such as the ingestion of water, and the injection of anticholinergic agents, are not necessary in most cases; however, such preparations are required to visualize smaller lesions. After an overnight fast, the ingestion of approximately 200–400 ml of water makes it easier to detect smaller lesions located in the posterior wall of the gastric circumfl ex. The injection of spasmolytic agents is seldom necessary.
While a 3–4 MHz curved array scanner is used for routine screening for gastric cancers, detailed exami- nation including the evaluation of wall stratifi cation should be performed with a high-frequency (5–
9 MHz) linear probe for its superior spatial resolu- tion. Tissue harmonic imaging is also recommended to reduce noises such as side lobe artifacts (Laing and Kurtz 1982).
16.2.2
Sonographic Image of the Normal Gastric Wall
The abdominal esophagus is visualized between the abdominal aorta and the left lobe of the liver by a left middle subcostal scan. Below the abdominal esopha- gus lies the gastric fundus. The gastric body is usually located in the left middle upper abdomen. The gastric fold is often observed at the greater curvature of
C O N T E N T S
16.1 Introduction 135 16.2 Sonographic Assessment of the Gastric Wall 135
16.2.1 Preparation and Equipment 135 16.2.2 Sonographic Image of
the Normal Gastric Wall 135
16.3 Sonographic Features of Gastric Cancer 136 16.3.1 Early Gastric Cancer 136
16.3.2 Advanced Gastric Cancer 138 16.4 Staging of Gastric Cancer 140 16.5 Conclusion 141
References 142
corresponds to the submucosal layer. The fourth layer is hypoechoic and corresponds to the proper muscle layer. The fi fth layer is hyperechoic and corresponds to the serosa and the extramural boundary.
respect, ingestion of water is useful to obtain a clear image of such subtle changes.
Early gastric cancer is usually expressed as focal wall thickening originating in the second layer. No changes of the submucosal layer are shown with intramucosal cancer (Fig. 16.3). When the tumor invades the submucosal layer, the shape and the width of that layer changes (Fig. 16.4) and it fi nally disappears as the tumor invades the proper muscle;
however, the evaluation of cancer invasion becomes diffi cult when it is complicated by an ulcer, because the fi brosis accompanying ulcer healing is expressed as a hypoechoic area which resembles cancer. The diagnostic accuracy of determination of cancer depth with transabdominal ultrasound is gener- ally thought to be inferior to that with endoscopic ultrasound, which provides a clear image with fewer artifacts and high resolution, although there are several contradictory reports (Ishigami et al. 2004;
Meining et al. 2002). Even with endoscopic ultra- sound, however, it is diffi cult to differentiate fi brotic tissue from cancer.
Fig. 16.1. Transverse scan of the gastric body. The fi ve-layer structure of the gastric wall and the gastric fold are demon- strated
Fig. 16.2. Longitudinal scan of the gastric antrum and the duodenal bulb. The gastric lumen is fi lled with water
Fig. 16.3. a Sonographic image of an early (intramucosal) gastric cancer. Focal wall thickening, which is limited to the mucosal layer, is demonstrated. b Endoscopic feature of the same patient as shown in a. A focally elevated lesion with an ulcer at the center is visualized. c Sonographic image of an early (intramucosal) gastric cancer. Focal wall thickening with an indentation at the center is demonstrated. No narrowing of submucosal layer is observed
a
b
c
Fig. 16.4. a Sonographic image of an early (submucosal invasion) gastric cancer. Narrowing of the submucosal layer is dem- onstrated. b Endoscopic sonography of an early gastric cancer (submucosal invasion). There is narrowing of the submucosal layer beneath the tumor
a b
as well as reduced peristalsis or even loss of it. The vascularity on color/power Doppler depends on the nature of cancer and may not necessarily be useful for differentiation between benign and malignant conditions.
Differential diagnoses should be decided among the following: benign gastric ulcer, malignant lym- phoma, acute gastric mucosal lesion, and anisakiasis, and ultrasound is useful for this purpose (Okanobu et al. 2003). Benign gastric ulcers show focal wall thickening with a wall defect at the center. Since the wall thickening around the ulcer is due to submuco- sal edema, wall stratifi cation is basically preserved.
Malignant lymphoma also shows focal wall thicken- ing without stratifi cation which resembles advanced gastric cancer, but the thickened wall is character- ized by very low echogenicity, often lower than that of gastric carcinoma. Acute gastric mucosal lesions and gastric anisakiasis are characterized by diffuse wall thickening with wall stratifi cation, brought on mainly by submucosal edema, which occasionally resembles scirrhous cancer. In scirrhous cancers, the width of every layer is irregular, and the boundary of each layer is often blurred. Furthermore, the com- pressibility/compliance is poor and the peristalsis is remarkably reduced.
Fig. 16.5. a Advanced gastric cancer. Wall stratifi cation has been totally destroyed and the extramural margin is irregular.
b Endoscopic image of the same case as shown in Fig. 16.5a.
c Endoscopic ultrasound image of an advanced gastric cancer.
Focal wall thickening without wall stratifi cation is observed a
c b
Fig. 16.6. a Transverse scan of advanced gastric cancer at the cardia. Wall thickening without stratifi cation is seen in almost all circumferences, accompanied by luminal narrowing. b Lon- gitudinal scan of the same lesion as shown in Fig. 16.6a. c En- doscopic view of the same case
Fig. 16.7. a Longitudinal scan of pyloric stenosis due to an advanced gastric cancer. Diffuse wall thickening of the antrum is demonstrated.
b Close-up view of the posterior wall of the antrum with a 7-MHz linear probe. Wall stratifi cation has not been completely destroyed. c Endos- copy reveals marked luminal narrowing
a
c
b a
c b
16.4
Staging of Gastric Cancer
For the staging of gastric cancer, cancer depth and metastases (to remote organs, lymph nodes, the peri- toneum) must be assessed. There have been a few reports on the cancer staging with ultrasound show- ing high diagnostic ability (Liao et al. 2004; Lim et al. 1994).
The depth of cancer for an early gastric cancer is decided by assessment of alteration of wall stratifi ca- tion. The extension of an advanced gastric cancer is decided by careful evaluation of the tumor margin.
When the outer margin of the tumor is smooth and a
fat pad or boundary echo is observed between every other contiguous organ and the tumor, the cancer is considered to be within the serosa. Irregularity of the outer margin suggests high risk of the tumor exceeding the serosa. Loss of the boundary echo accompanied by loss of sliding movement between other organs are important fi ndings suspicious of minimal invasion into an adjacent organ. The inva- sion is obvious when the tumor boundary lies in the contiguous organ and deforms the contour of the organ (Fig. 16.9).
Fig. 16.8. a Schirrous-type gastric cancer in the gastric body. Note the difference in gastric compliance at the antrum and the le- sion. b Close-up view of the lesion with a 7-MHz linear probe. Wall stratifi cation is demonstrated. c Schirrous-type gastric cancer at the fornix. Diffuse wall thickening at the fornix and ascites (asterisk) are demonstrated. d Endoscopic image of giant rugae
a c
b d
Fig. 16.9. a Gastric cancer invasion into the tail of the pan- creas is demonstrated. The hypoechoic tumor has altered the contour of the pancreas tail. b Gastric cancer invasion into the transverse colon. This hypoechoic tumor is compressing the upper circumference of the transverse colon and the boundary echo between them has disappeared
a
b
Typical metastatic liver tumors have a thick hypoechoic rim with a relatively hyperechoic center, known as the “bull’s-eye” sign (Fig. 16.10a); however, this fi nding cannot be applied to all metastatic liver tumors. Penetration of the normal vascular structure through the tumor proven by color/power Doppler, ring-shaped enhancement in the arterial phase, and loss of enhancement in the postvascular phase as determined by contrast ultrasound, are helpful fi nd- ings for the diagnosis of metastatic liver tumors.
Lymph node metastases are characterized by the round-shaped swelling of lymph nodes (Fig. 16.10b).
One must be careful in the differentiation from infl ammatory swelling of lymph nodes caused by a benign gastric ulcer, which is more elliptical in shape than that of metastatic lymph nodes.
Tumor seeding is demonstrated as a hypoechoic nodule on the visceral or parietal peritoneum (Fig. 16.10c). Often ascites with fl oating echogenic particles accompanies tumor seedings, indicating peritonitis carcinomatosa.
16.5 Conclusion
Although infl uenced by the patients’ constitution and the skill of the operator, transabdominal ultrasound can be a useful diagnostic tool for the evaluation of gastric cancer.
Fig. 16.10. a Metastatic liver tumors are demonstrated.
b Metastatic lymph nodes (ln) around the superior mesenteric artery (sma) are demonstrated. c A seeding nodule (asterisks) seen in a patient with advanced gastric cancer
a
b
c
