What is a Gastric Carcinoma?

A gastric carcinoma is a malignant tumour arising from the epithelium of the stomach. Adenocarcinoma accounts for 95% of gastric malignancies, the remaining 5% being composed of sarcomas. Although its frequency has decreased dramatically during the last few decades in the Western world, this cancer still contributes significantly to the overall mortality. The incidence of adenocarcinoma varies greatly depending on the geographical area. The annual incidence in Japan is estimated at 140 cases per 100,000 population per year, whereas in the Western world this incidence is estimated at 10 per 100,000 population. A higher incidence in males than females with a ratio of 1.5:2.5, in poor social groups and in people above 40 years of age is observed.

It is generally assumed that food preservation by refrigeration and not by salting which leads to a reduction in nitrate derivatives is an important factor in the decline of the incidence of gastric adenocarcinoma in the Western world. Other aetiological factors are smoking, alcohol consumption and vitamin deficiencies. An increased incidence of adenocarcinoma of the stomach is noted in patients with pernicious anaemia, atrophic gastritis, or adenomatous polyps. Finally, genetic factors are also involved, particularly in patients presenting with a diffuse infiltrating type of carcinoma.

It is well known that the majority of gastric carcinomas originate in the prepyloric and pyloric region. The gross appearance of adenocarcinoma has served as the basis for their classification as proposed by Borman: polypoid fungating (B1), ulcerated (B2), ulcerated and infiltrating (B3), diffuse infiltrating (B4). There is a considerable overlap between these classifications because many lesions will display more than one of these features. At the time of clinical diagnosis in patients with complaints the disease is commonly in an advanced stage and metastases in regional lymph nodes or in distant locations are commonly present.

Radiological diagnosis

Double contrast barium study is able to detect more than 95% of gastric carcinomas with a high specificity and should be considered not only as an excellent diagnostic method but also as a primary screening procedure for gastric cancer in persons at risk.

A B1 lesion (Fig.1) is seen as a irregular filling defect of varying size with occasionally a visible stalk. Double contrast will reveal an irregular filling defect with a rough lobulated surface and sometimes superficial ulceration.

A B2 lesion is visible as a sharply circumscribed ulcer crater, exceeding 3 cm in diameter. Radiating folds converging to the edge of the ulcer are blunted or fused. On double contrast barium studies B2 tumours, situated on the anterior or nondependent wall, may produce a double ring image with the outer ring delineating the edge of the tumour and the inner ring indicating the edge of the ulcer.

The B3 tumours are usually larger and barium filling will reveal not only a filling defect but also rigidity of the gastric wall extending beyond the ulcer crater, due to the diffuse tumoural infiltration. Compression radiographs reveal an ulceration with irregular borders and a surrounding radiolucent defect. The mass may be more prominent than the ulcer.

B4 tumours, called scirrhous tumours or linitis plastica, are diffusely infiltrating lesions involving the prepyloric antrum or the whole stomach (Fig.2). They are characterized by a reduction and deformity of the gastric lumen associated with a loss of pliability of the walls and a nodular or ulcerated pattern of the mucosa.

Staging

Staging of gastric carcinomas can be performed by CT and endoluminal ultrasound (EUS).

Appropriate CT study can be better performed following adequate distension of the stomach with air or water as a contrast medium. Intravenous administration of a spasmolyticum as well as of a iodinated contrast m approximately 80% of patients. CT is best suited for detecting liver and peritoneal metastases.

It is assumed that EUS T staging is superior to CT staging with an accuracy of EUS for N staging reported to reach up to 75%. Overstaging of depth of invasion by EUS is most commonly due either to compression of the tumour and the gastric wall by the tip of the echoendoscope with an inflated balloon or to mistaking peritumoural inflammation for neoplastic invasion, which tends to occur more frequently with the ulcerated forms.

Early gastric cancer

Early gastric cancer (EGC) is defined as carcinoma limited to the mucosa and submucosa, with or without lymph node involvement. Synchronous EGCs occur in 9% of patients. This form of gastric carcinoma is reported less often in Europe and the USA than in Japan. The EGCs have been classified into three types and three subtypes based upon their gross appearance (Fig.5).

Type I : Protruding type (more than 5 mm)

Type II : Superficial type, further subdivided into three subtypes:

a. Elevated type

b. Flat type; no elevation in the surrounding mucosa

c. Depressed type; the surface is slightly depressed.

Type III : Excavated

The incidence of submucosal invasion is higher with types II c and III than with type II a. On double barium contrast study type I lesions appear as small, sharply bordered, filling defects similar to the features seen in small sessile polyps. A sessile polyp larger than 1 cm in diameter should be regarded as possible EGC. Type II lesions are characterized by plaque-like elevation, mucosal nodularity (Fig.6) and/or shallow areas of ulceration or a combination of these findings. Type II EGCs appear as shallow ulcer craters with nodularity of the adjacent mucosa and clubbing or fusion of radiating folds, due to tumoural infiltration of the adjacent folds. Radiographically Type II c lesions can be distinguished from Type III lesions by the thinner collection of the barium in the depression of Type II c as compared to Type III. Usually the deeper part (Type III) is in the centre of the depression surrounded by the shallow part. Type III lesions have depth, whereas Type II c lesions may be scarcely recognizable at the peripheral part of a deeper ulcer depression.

Imaging

Carcinoma, gastric, Fig.1 (a)
Carcinoma, gastric, Fig.1 (b)
Carcinoma, gastric, Fig.2 (a)
Carcinoma, gastric, Fig.2 (b)
Carcinoma, gastric, Fig.3
Carcinoma, gastric, Fig.4
Carcinoma, gastric, Fig.5
Carcinoma, gastric, Fig.6

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Last Updated: Feb 9, 2010

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