Delineation of Normal Mural Components by Sectional Imaging

Five discrete layers of the wall are shown by conventional endoscopic ultrasonography. The first hyper-echoic and second hypoechoic layers represent the mucosa, the third hyperechoic layer represents the submucosa, the fourth hypoechoic layer is the muscu-laris propria, and the fifth hyperechoic layer reflects the subserosa and serosa (Figs. 5-3 and 5-4). In the esophagus, lacking a serosa, the latter represents adventitia. With the development of small 15-20 MHz ultrasonic probes, nine distinct layers of the normal esophageal and gastric wall may be clearly visualized,33,34 permitting delineation of the lamina propria and muscularis mucosae in addition to a three-layered muscularis propria (Fig. 5-5).

Recent investigations have advanced the accuracy of CT in the detection and staging of gastric cancer. Minami et al.35 and Cho et al.36 refined a protocol in which the normal gastric wall showed a two- or three-layered structure: an inner mucosal layer with marked enhancement, an outer submucosal layer with lower attenuation, and another outer muscular-serosal layer with moderate enhancement. Improving the protocol further with the use of dual-phase spiral CT with narrow collimation and close interscan spacing may increase the accuracy of CT.

In dynamic multiphasic MR imaging of the stomach, a decisive feature is a low-signal-intensity band that

Gastric Wall Eus

Fig. 5—4. Normal gastric wall demonstrated by EUS with a 20-MHz transducer showing the layered structure of the gastrointestinal wall.

shows irregularity in an area of extraserosal invasion by an advanced carcinoma (Fig. 5-6). This band is not a morphologic structure but rather a chemical shift misregistration artifact and a phase-cancellation artifact between fat and water.37

Identification of the layers of the circumference of the rectal wall is accomplished by plain and contrast-enhanced MR imaging with the endorectal surface coil38 (Fig. 5-7).

Ultrasound Mucosa Submucosa Serosa

Fig. 5—3. Diagram showing the normal layers of the colon.

m = mucosa; sm = submucosa; pm = muscularis propria; ss ~ s = subserosa ~ serosa.

(Reproduced from Hirata et al: Endoscopic ultrasonography in the assessment of colonic wall invasion by adjacent diseases. Abdom Imaging 1994; 19:21-26.)

Fig. 5—3. Diagram showing the normal layers of the colon.

m = mucosa; sm = submucosa; pm = muscularis propria; ss ~ s = subserosa ~ serosa.

(Reproduced from Hirata et al: Endoscopic ultrasonography in the assessment of colonic wall invasion by adjacent diseases. Abdom Imaging 1994; 19:21-26.)

Delineation of Normal

Mural Components by Sectional Imaging • 271

Fig. 5—5. Nine distinct layers of the normal esophageal wall demonstrated in a patient with a small 20-MHz ultrasonic probe.

The mucosa consists of four layers: the first and second layers (m1 and m2) represent the epithelium, the third layer (m3) the lamina propria, and the fourth layer (m4) the muscularis mucosae. The submucosa (s) is seen as the hyperechoic fifth layer. The muscularis propria is imaged as three layers: the sixth layer (p1) is the circular muscle, the seventh layer (p2) is an interface of connective tissue, and the eighth layer (p3) is the longitudinal muscle. The adventitia (a) is represented by the hyperechoic ninth layer. (Reproduced from Murata et al.33)

Lesion Gastric Cancer
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Fig. 5—6. T staging of gastric cancer by MR imaging.

T1 = Lesion is undetectable since there is no abnormal enhancement. T2 = A clear, smooth low-intensity band surrounds the enhanced lesion. T3 = The low-intensity band is interrupted. T4 = The low-intensity band has disappeared, and there is contiguous extension of the enhanced lesion to adjacent organs. (Reproduced from Oi et al.37)

Rectal Wall

Fig. 5—7. Endorectal MR image of the normal rectal wall.

Multiple layers are visualized: high-signal-intensity mucus within the rectal lumen (thin white arrows), low-signal-intensity mucosal layer (mucosa and muscularis mucosae) (small white arrowheads), high-signal-intensity submucosal layer (large white arrowheads), low-signal-intensity muscularis propria (small white arrows), and high-signal-intensity perirectal fat (black arrowheads). (Reproduced from Pegios et al.38)

Fig. 5—7. Endorectal MR image of the normal rectal wall.

Multiple layers are visualized: high-signal-intensity mucus within the rectal lumen (thin white arrows), low-signal-intensity mucosal layer (mucosa and muscularis mucosae) (small white arrowheads), high-signal-intensity submucosal layer (large white arrowheads), low-signal-intensity muscularis propria (small white arrows), and high-signal-intensity perirectal fat (black arrowheads). (Reproduced from Pegios et al.38)

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