AJR 2002; 179:131-136
© American Roentgen Ray Society
Sonography of Anorectal, Rectal, and Perirectal Abnormalities
Gary S. Sudakoff1,
Francisco Quiroz and
W. Dennis Foley
1 All authors: Department of Radiology, Medical College of Wisconsin, 9200 W.
Wisconsin Ave., Milwaukee, WI 53226.
Received September 20, 2001;
accepted after revision January 11, 2002.
Address correspondence to G. S. Sudakoff.
Introduction
Imaging of the rectum, anorectal junction, and surrounding tissues is both
difficult and technically challenging. CT and conventional barium studies
offer limited information in local staging of rectal and perirectal neoplasms,
in determining the precise location and extension of perianal fistulas in
patients with inflammatory bowel disease, or in evaluating patients with fecal
incontinence. During the past decade, sonography and MR imaging have resulted
in significant improvement in the imaging of rectal and perirectal disease
[1,2,3,4,5,6,7,8,9,10,11].
Endorectal coil MR imaging is limited by availability, cost, and patient
discomfort, motion, and claustrophobia. Endorectal sonography is an accepted
technique for local staging of both benign and malignant rectal and perirectal
neoplasms [1,
4,
5]. Furthermore, endorectal
sonography is used to direct biopsy of rectal or perirectal wall masses and
drainage of pelvic abscesses. Preliminary studies suggest that endorectal
sonography coupled with color or power Doppler imaging may offer additional
information in detecting and characterizing rectal wall neoplasms, staging
perirectal lymph nodes, and differentiating tumor recurrence from postsurgical
fibrosis
[6,7,8,9].
Transvaginal scanning of the anorectum can reveal disruption of the anal
sphincter complex in patients with fecal incontinence and offer information in
the staging of anorectal fistulas
[2,
3]. We illustrate the
usefulness of sonography in imaging benign and malignant conditions of the
anorectum, rectum, and adjacent tissues.
Scanning Technique
Endorectal sonography or transvaginal scanning of the anorectum can be
performed with the patient in either the left lateral decubitus or supine
lithotomy position. Endorectal scanning is performed with 7- to 10-MHz oblique
end, side firing, or mechanical rotating endoluminal transducers. Conventional
5- to 7-MHz endovaginal probes are used for transvaginal scanning. Patients
undergoing endorectal sonography require a cleansing enema 2 hr before the
procedure. Endorectal or endoanal probes require the use of a latex condom
that serves as a water bath in the evaluation of the anorectum or rectal wall.
The use of color or power Doppler imaging during endorectal sonography
requires settings for low-flow states.
Normal Anatomy
Alternating hyperechoic—hypoechoic layers compose the normal rectal
wall. From inner- to outermost, the layers are as follows: interface of the
condom and mucosa (hyperechoic), deep mucosa (hypoechoic), submucosa
(hyperechoic), muscularis propria (hypoechoic), and interface of the
muscularis propria and perirectal fat (hyperechoic) (Figs.
1A and
1B). The perirectal fat has
mixed echogenicity, and nonenlarged perirectal lymph nodes (<7.0 mm) may
occasionally be seen [9]. Color
Doppler or power Doppler imaging during endorectal sonography will reveal flow
in the vascular plexus of the submucosal layer of the rectal wall
[6,
7]
(Fig. 1C).
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Fig. 1A. —Endorectal sonography of normal rectal wall. Schematic
diagram shows cross-section of layers composing rectal wall. M = mucosa, DM =
deep mucosa, SM = submucosa, MP = muscularis propria, PF = perirectal fat.
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Fig. 1B. —Endorectal sonography of normal rectal wall. Longitudinal
endorectal sonogram of 55-year-old man shows alternating
hyperechoic—hypoechoic five layers compressing normal rectal wall. WM =
interface of water bath and mucosa, DM = deep mucosa, SM = submucosa, MP =
muscularis propria, PF = interface of muscularis propria and perirectal
fat.
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Fig. 1C. —Endorectal sonography of normal rectal wall. Transverse color
Doppler sonogram of patient in B shows horizontal orientation of normal
submucosal vascular plexus (arrows) in middle echogenic layer
(submucosa) of rectal wall.
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Malignant Rectal Wall Masses
Cancers of the rectal wall are typically hypoechoic lesions that destroy or
distort the normal five-layer architecture (Fig.
2A,2B,2C,2D,2E,2F,2G,2H).
Sonographic staging is accomplished by determining the depth of tumor invasion
into the submucosa (T1), muscularis propria (T2), or perirectal fat (T3)
[10]
(Fig. 2A). Staging with
endorectal sonography is generally considered accurate but under- and
overstaging may occasionally occur and vary with examiner experience
[4,
6,7,8,9].
T3 lesions typically have serrated margins that can be seen penetrating
through the muscularis propria (Fig.
2D). Enlarged perirectal lymph nodes (>7.0 mm) may be
identified with T3 tumors and are amenable to biopsy
[9]
(Fig. 2E). Preliminary studies
suggest that rectal wall cancers and metastatic perirectal lymph nodes show
abnormal hypervascularity on endorectal sonography with color or power Doppler
imaging
[6,7,8,9]
(Figs. 2G and
2H). Rectal wall lesions that
do not penetrate through the muscularis propria cannot be accurately
differentiated without biopsy as being benign or malignant on either
endorectal sonography alone or on color Doppler imaging
[6,7,8,9,
11].
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Fig. 2A. —Endorectal sonography of malignant rectal tumors. Schematic
diagrams of T2 and T3 rectal cancers show endorectal sonogram in transverse
plane. T2 lesions may involve all layers of rectal wall but do not penetrate
through muscularis propria into perirectal fat. T3 lesions may involve all
layers of the rectal wall and penetrate perirectal fat. CA = cancer, WM =
water bath and mucosa interface, DM = deep mucosa, SM = submucosa, MP =
muscularis propria, PF = perirectal fat.
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Fig. 2B. —Endorectal sonography of malignant rectal tumors. Transverse
sonogram of 65-year-old woman with T2 rectal wall tumor (M) shows involvement
of deep mucosa and submucosal layers. Muscularis propria and perirectal fat
(arrows) are intact.
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Fig. 2C. —Endorectal sonography of malignant rectal tumors. Transverse
sonogram obtained with mechanically rotating transducer in 66-year-old man
shows T2 rectal wall cancer (M, arrows) extending up to but not
through muscularis propria.
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Fig. 2D. —Endorectal sonography of malignant rectal tumors.
Longitudinal linear sonogram obtained in 67-year-old man with T3 rectal cancer
shows that tumor (T) involves all layers of rectal wall extending through
muscularis propria into perirectal fat (arrows).
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Fig. 2E. —Endorectal sonography of malignant rectal tumors.
Longitudinal linear sonogram of patient in D shows enlarged perirectal
lymph node (arrows), which was biopsy-proven positive for
malignancy.
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Fig. 2F. —Endorectal sonography of malignant rectal tumors. Transverse
sonogram obtained in 62-year-old woman with T3 rectal cancer shows that tumor
involves all layers of rectal wall with fingerlike extensions
(arrows) into perirectal fat.
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Fig. 2G. —Endorectal sonography of malignant rectal tumors. Transverse
color Doppler sonogram of patient in B shows T2 rectal wall cancer
extending into but not through muscularis propria. Tumor shows disorganized
hypervascularity with enlarged perirectal vessel (arrows) supplying
tumor.
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Fig. 2H. —Endorectal sonography of malignant rectal tumors. Transverse
color Doppler sonogram obtained in 59-year-old man with T3 rectal cancer shows
that tumor involves all layers of rectal wall and extends into perirectal fat.
Note disorganized hypervascularity and prominent perirectal vessels supplying
periphery of tumor (arrows).
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Benign Rectal Wall Masses
Benign lesions such as hyperplastic polyps, villous, tubulovillous, and
tubular adenomas are well-defined hypoechoic lesions (Figs.
3A and
3B). Smaller adenomas are
predominantly solid, whereas larger villous and tubulovillous adenomas often
show intratumoral cystic areas (Fig.
3B). Because of mobility, lesions on a stalk are difficult to
evaluate on endorectal sonography and are best evaluated on endoscopy.
Adenomas exhibit disorganized hypervascularity on color or power Doppler
imaging [6,
7]
(Fig. 3C).
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Fig. 3A. —Endorectal sonography of benign rectal wall masses.
Transverse sonogram obtained in 55-year-old woman with benign rectal wall
adenoma shows that tumor involves deep mucosal and submucosal layers
(arrows) but does not invade muscularis propria.
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Fig. 3B. —Endorectal sonography of benign rectal wall masses.
Transverse sonogram obtained in 62-year-old man with benign villous adenoma
shows cystic areas (arrows) in tumor. Mass is confined to deep
mucosal and submucosal layers without invasion to muscularis propria
(arrowheads).
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Fig. 3C. —Endorectal sonography of benign rectal wall masses. Sagittal
color Doppler sonogram of patient in B shows tumor with disorganized
hypervascularity (straight arrows). Portion of normal submucosal
vascular plexus can be seen (curved arrow).
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Postoperative Evaluation for Primary Rectal Wall Recurrence
Digital rectal examination and endoscopy are insensitive in discriminating
postsurgical scar from recurrent tumor in patients who previously had rectal
tumors resected. Although endorectal sonography may reveal early recurrence,
it is limited by the inability to differentiate benign or malignant neoplasms
from postoperative scarring
[11]. Scarring appears
sonographically as focal or diffuse hypo- or hyperechoic areas in the rectal
wall and may appear identical to tumor. Scarring may be differentiated from
tumor on color Doppler imaging or sonographically directed biopsy
[7,
11] (Fig.
4A,4B,4C).
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Fig. 4A. —Evaluation of postoperative patients with endorectal
sonography and color Doppler imaging. Transverse color Doppler sonogram shows
72-year-old man with colorectal anastomosis who underwent resection of rectum
for cancer and developed stricture at anastomosis. Normal five-layer rectal
wall architecture is distorted by echogenic mass (M). Portion of normal
submucosal vascular plexus is identified (arrows). Sonographically
directed biopsies revealed only fibrosis.
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Fig. 4B. —Evaluation of postoperative patients with endorectal
sonography and color Doppler imaging. Transverse color Doppler sonogram
obtained in 71-year-old man with coloanal anastomosis shows that echogenic
mass (M) distorts submucosa and muscularis propria layers of rectal wall.
Color Doppler image shows no abnormal vascularity in mass. Sonographically
directed biopsies revealed only fibrosis.
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Fig. 4C. —Evaluation of postoperative patients with endorectal
sonography and color Doppler imaging. Transverse color Doppler sonogram
obtained in 64-year-old man with recurrent adenoma of rectal wall
(straight arrows) shows focal area of disorganized vascularity
(curved arrow) adjacent to submucosal vascular plexus.
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Perirectal Masses and Rectal Wall Involvement
Endorectal sonography can accurately depict extension of perirectal masses
into the rectal wall by revealing disruption of the muscularis
propria—perirectal fat interface
[5] (Fig.
5A,5B,5C,5D,5E).
Distinguishing postoperative perirectal scarring from recurrent tumor may be
difficult on CT or MR imaging (Figs.
5A and
5C). Endorectal sonography
coupled with color or power Doppler imaging or endorectal sonographically
directed biopsy may be useful in such situations (Figs.
5D and
5E).
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Fig. 5A. —Endorectal sonography of perirectal wall masses. Noninfused
CT scan of pelvis obtained in 82-year-old woman with recent onset of vaginal
bleeding, palpable mass in upper third of vagina, and renal failure shows
large soft-tissue mass (arrows) between bladder (B) and rectum (R).
Rectal wall involvement could not be determined on CT.
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Fig. 5B. —Endorectal sonography of perirectal wall masses. Longitudinal
linear sonogram of patient in A shows large perirectal mass (M) with
direct invasion of perirectal fat and muscularis propria (arrows).
Portion of normal rectal wall is identified (arrowheads). Biopsies of
mass revealed squamous cell carcinoma.
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Fig. 5C. —Endorectal sonography of perirectal wall masses. T2-weighted,
fat-saturated MR image of pelvis obtained in 66-year-old woman with persistent
pelvic pain 1 year after vulvectomy, hysterectomy, cystectomy, and pelvic
irradiation for squamous cell carcinoma of vagina shows area of heterogeneous
signal intensity (straight arrows) with mass effect on rectum
(curved arrow). Distinction of recurrent tumor from radiation
fibrosis could not be made.
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Fig. 5D. —Endorectal sonography of perirectal wall masses. Transverse
sonogram of perirectal mass (thick arrows) of patient in C
shows that mass compresses but does not invade perirectal fat (thin
arrows).
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Fig. 5E. —Endorectal sonography of perirectal wall masses.
Corresponding color Doppler sonogram of patient in D shows that
perirectal mass (arrows) has peripheral and central hypervascularity
consistent with recurrent tumor. Biopsy of mass revealed squamous cell
carcinoma.
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Sonography of the Anorectum
Patients with fecal incontinence and anorectal fistulas pose a significant
imaging challenge. In women, accurate identification of anal sphincter
disruption or involvement by inflammatory fistulas is critical in selecting
appropriate patients for surgery. MR imaging and endoanal and transvaginal
sonography can accurately image the anal sphincter complex and surrounding
perirectal tissues
[1,2,3].
Endorectal coil MR imaging is limited by patient discomfort, motion, and
claustrophobia, and by expense and scanner availability. In comparison,
endoanal and transvaginal sonography are well tolerated, readily available,
inexpensive, and accurate in detecting anal sphincter disruption and
involvement in patients with incontinence or anorectal fistulas
[2,
3].
Endoanal sonography is most often performed with mechanically rotating
360° field-of-view endoanal transducers. This technique can image the anal
sphincter in patients with fecal incontinence but may be poorly tolerated in
patients with anorectal fistulas. Transvaginal scanning of the anorectum is
well tolerated and can accurately detect abnormalities of the anal sphincter
and surrounding structures
[1,2,3].
Scanning is performed by placing an endovaginal probe a few centimeters within
the introitus and angling the probe inferiorly and posteriorly until the anal
sphincter is identified. The internal sphincter is identified as a hypoechoic
ring surrounded by an outer band of mixed echogenicity that represents the
external sphincter. The puborectalis muscle is a U-shaped, hypoechoic band
that partially encircles both sphincters (Figs.
6A and
6B). In men, an endovaginal
probe can also be used because of its small footprint and placed on the
perineum angling the probe posteriorly and inferiorly to visualize the anal
sphincter and surrounding structures. Tears of the internal sphincter can be
identified as a distinct break or attenuation of the hypoechoic ring, usually
seen anteriorly (Fig. 6C).
Anterior internal sphincter disruptions are often associated with external
sphincter attenuation or disruption. Isolated external sphincter tears are
much harder to recognize because of the mixed echogenicity of the external
sphincter. Disruption or avulsion of the puborectalis muscle can also be
identified and is important in women who are incontinent after surgical repair
(Figs. 6C and
6D). Perianal fistulas appear
as hypoechoic tracts with internal gas or echogenic debris that can be
confirmed with the instillation of saline or hydrogen peroxide into the anal
canal or external perineal opening of the fistula
(Fig. 6E). Abscess involvement
of the sphincter complex or perirectal space is accurately assessed with this
technique, and this assessment is crucial for appropriate surgical treatment
(Fig. 6F).
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Fig. 6A. —Transvaginal sonography of anorectum. Schematic diagram shows
anorectum at level of puborectalis muscle as seen during transvaginal
scanning. PR = puborectalis muscle, ES external anal sphincter, IS = internal
anal sphincter.
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Fig. 6B. —Transvaginal sonography of anorectum. Transvaginal sonogram
of normal anorectum in 46-year-old woman shows thick, hypoechoic ring that
represents internal anal sphincter (IS, short arrow). Immediately
surrounding internal sphincter is mixed echogenic external anal sphincter (ES,
long arrow). Puborectalis muscle (arrowheads) is hypoechoic
U-shaped sling adjacent to external anal sphincter.
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Fig. 6C. —Transvaginal sonography of anorectum. Transvaginal sonogram
of anorectum in multiparous 60-year-old woman with fecal incontinence shows
large defect of anterior internal and external anal sphincters
(arrows).
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Fig. 6D. —Transvaginal sonography of anorectum. Transvaginal sonogram
of anorectum in 56-year-old multiparous woman with persistent fecal
incontinence after surgical repair shows anterior disruption of internal anal
sphincter and attenuation or disruption of external anal sphincter
(straight arrows). Left puborectalis muscle (arrowheads) is
intact, whereas right puborectalis muscle is avulsed (curved
arrow).
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Fig. 6E. —Transvaginal sonography of anorectum. Transvaginal sonogram
of anorectum in 26-year-old woman with chronic perineal and perivaginal
abscesses shows hypoechoic fistula (arrows) with internal echogenic
debris or gas extending from anterior internal sphincter to posterior vaginal
wall.
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Fig. 6F. —Transvaginal sonography of anorectum. Transvaginal sonogram
of anorectum in 28-year-old woman with recent diagnosis of Crohn's disease and
perineal pain shows hypoechoic tract extending from posterior internal and
external sphincters (straight arrow) into perirectal abscess
collection (curved arrows).
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In conclusion, endorectal sonography can accurately stage primary rectal
neoplasms and determine rectal wall integrity with perirectal neoplasms. Color
or power Doppler imaging and sonographically directed biopsy can offer
additional information in tumor detection and characterization, in staging of
perirectal lymph nodes, and in discriminating tumor recurrence from
postoperative scarring. Transvaginal sonography of the anorectum can
accurately assess the anal sphincter complex and provide critical information
for the surgical treatment of fecal incontinence and perianal fistulas.
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Top
Introduction
Scanning Technique
