The ascending colon can be seen in the lateral sagittal section (Fig. 52.1 a). In most cases, air in the colon precludes visualization of its lumen. Large amounts of retained fecal matter (coprostasis) can occasionally be found in the colon of old patients. A transverse colon (43) without any evidence of inflammatory mural thickening (transverse section of the upper abdomen) is shown in Figures 52.1b and c. This contrasts with the thickened wall (74) found in ulcerative colitis or ischemia (e.g. due to mesenteric artery infarction or mesenteric vein thrombosis), as seen in a case of colitis (Fig. 52.2) in which the descending colon exhibits strikingly thickened haustral indentations.
Diverticulitis is a complication of diverticulosis coli (sac-like mucosal projections through the muscular layers of the colonic wall). The neck of the diverticulum (*), as shown in Figures 52.3b and c, connects the normal colonic lumen (43) and the hypoechoic diverticulum (54). The associated edema of the colonic wall (74) is demonstrated by the CT performed on the same patient (Figs. 52.3a, d). The rectosigmoid junction is still well demarcated from the hypodense fatty tissue (black), while the colonic wall is indistinct in outline in the immediate proximity of the diverticula (54) due to inflammatory obliteration and thickening of the adjacent fatty tissue.
Because of air in the intestinal lumen, the sonographic evaluation of small bowel loops (46) is often limited or not possible at all. However, the intraluminal air frequently decreases when it is surrounded by inflammatory wall thickening or can be reduced by graded (!) compression applied to the transducer.
Crohn disease frequently presents as terminal ileitis (Fig. 53.1). The edematous wall thickening (74) confined to this segment is easily separable from adjacent uninvolved loops (46). In more advanced stages (Fig. 53.2), the intestinal wall (74) becomes massively thickened and can resemble the sonographic findings of intestinal invagination. On cross sections, the thickened, edematous walls of intestinal loops can be compared to a concentric lamellation of a "target/' The examiner should always look for adjacent fistular tracts or abscesses as well as for free abdominal fluid in the cul-de-sac.
The mesenteric roots of individual small bowel loops are normally not identified, but can be delineated in the presence of extensive lymphadenopathy or massive ascites (68). The small bowel loop seen in cross section (46) floats within ascitic fluid (Fig. 53.3) that is devoid of internal echoes except for reverberation artifacts from the anterior abdominal wall (2,3) (compare p. 10). Lymphomatous infiltration of the small bowel often leads to long segments of hypoechoic wall thickening and is primarily observed in immunocompromised patients.
High frequency transducers (> 5 MHz) can add information in selected cases if used, for instance, intraoperatively to exclude mesenteric lymphadenopathy.- If a tender appendix shows no peristalsis, has reduced or no compressibility, and measures more than 6 mm in diameter, it fulfills the criteria of acute appendicitis. Sonography has the advantage of allowing real time evaluation of intestinal peristalsis, easily revealing aperistalsis (atony) or prestenotic hyperperistalsis. Though it is often necessary to proceed with other imaging modalities (endoscopy, endosonography, conventional radiology, CT) because of acoustic shadowing (45) by intestinal air that limits the sonographic evaluation of the small bowel, sonography can still make a contribution if properly targeted in selected cases.
The urinary bladder is systematically screened in suprapubic transverse (Fig. 54.1a) and sagittal sections (Fig. 54.1h) when it is full, usually achieved after the intake of a large amount of fluid.
A representative transverse section (Fig. 54.2) shows the normal bladder (38) in the shape of a rounded rectangle behind the rectus muscles (3) and in front of and above the rectum (43).
The longitudinal section delineates the bladder more as a triangle (Fig. 54.3), with the prostate gland (42) and vagina, respectively, seen below the bladder (compare Fig. 58.1).
If voiding difficulties due to a neurogenic bladder or prostatic hypertrophy (Figs. 56.2, 56.3) are suspected, the post-void residual should be calculated by measuring the maximum transverse and sagittal diameters of the bladder after the patient has voided (Fig. 54.2 b). Thereafter, the transducer is turned 90 and angled inferiorly (Fig. 54.3a) to measure the craniocaudal diameter (horizontally displayed on the image) without interfering acoustic shadowing (45) of the pubic symphysis (48) (Fig. 54.3b).
Using the simplified volume formula (volllb = A x B x C x 0.5), the postvoid residual (ml) can be calculated by dividing the product of the three diameters by two.
Find out which diameter in the case shown in Figure 54.3 b has been incidentally measured twice?
The wall (77) and lumen (38) of the urinary bladder can only be adequately evaluated when the bladder is full. An indwelling catheter (76) usually results in an empty bladder (Fig. 55.1), precluding any reliable evaluation. The catheter therefore should be clamped for an extended period to achieve filling of the bladder (38). When the edema of the bladder wall (77) is rather advanced, cystitis (Fig. 55.2) can also be recognized with the bladder empty.
The wall thickness of the distended bladder should not exceed 4 mm. After voiding, the wall is irregularly thickened and measures up to 8 mm in width. Wall-based tumors or polyps can no longer be detected. Wall thickening can be caused by inflammatory edema, increased trabeculations due to prostatic hypertrophy with bladder outlet obstruction, or a space-occupying lesion.
Even the healthy bladder is never entirely echo-free. Often, reverberation artifacts (51) of the anterior abdominal wall (Fig. 55.3) are seen in the bladder (38) anteriorly, or section thickness artifacts posteriorly, simulating intraluminal matter (compare p. 10). These artifacts have to be differentiated from the real sedimentations of blood clots (52) or concrements (49) along the floor of the urinary bladder (Fig. 55.3). By rapidly changing the pressure applied to the transducer, intraluminal matter can be mechanically dis-turbed and made to float within the lumen. A section thickness artifact or wall-based tumor lack any response to this maneuver.
As an incidental finding, a forceful jet of urine can be propelled from the ureteral ostium into the bladder lumen. This jet phenomenon is physiologic. If transabdominal sonography is inconclusive, transrectal or vaginal transducers should be used. These endocavitary transducers .generally have a better resolution because a higher frequency can be used due to the shorter distance to the target organ. These special examinations require additional expertise and training. . .
Transabdominal sonography of the genital organs requires a filled urinary bladder (38), which displaces the air-contain-ing intestinal loops (46) cranially and laterally to avoid their interfering shadows (45) and serves as an acoustic window. The prostate gland (42) is located on the floor of the bladder anterior to the rectum (43) and is visualized on the suprapubic transverse section and on the sagittal longitudinal sec-lion (Fig. 56.1). ITie normal prostate gland should not exceed the approximate size of 3 x 3 x 5 cm or the approximate volume of 25 ml. In older men, an enlarged prostate gland is frequently encountered (Fig. 56.2), which interferes with voiding and can lead to a trabeculated bladder (compare Fig. 55.2).
The enlarged prostate gland (42) elevates the bladder floor (38), but the urinary bladder remains outlined by a wall that is seen as a smooth line (Fig. 56.2). Advanced prostatic hypertrophy stenoses the urethra, causing hypertrophy of the bladder wall, that beomes visible as a thick rim (77) around the bladder (Fig. 56.3). ITie carcinoma of the prostate gland (54) usually arises in the periphery of the gland, can infiltrate the bladder wall and extend as a lobulated mass into the lumen of the bladder (Fig. 56.3).
The normal testicle (98) of the adult male is homogeneously hypo-echoic, sharply demarcated from the layers of the scrotum (100), and measures about 3 x 4 cm (Fig. 56.4). The epididymis (99) sits on top of the upper testicular pole like a cap and extends along the posterior testicular wall. In children, both testicles should be visualized together in the scrotum on the transverse section to exclude an undescended testicle with certainty (refer to p. 57).
9 Male Genital Organs
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