Endoanal Imaging of Anorectal Cysts and Masses

Fig. 14.1

Endometriosis lesion infiltrating the perirectal fat . The rectal layers are intact. (a) Axial plane. (b) Coronal with axial plane. Two heterogeneous hypoechoic images in the left lateral quadrant compromising the perirectal fat (arrows). Mucus in the rectal lumen, outside the lesion site (artifacts)

Fig. 14.2

Endometriosis lesion in the anterior quadrant infiltrating the rectal wall as far as the muscular propria (arrows). (a) Axial plane. Heterogeneous hypoechoic image compromising 20% of rectal circumference (arrows). (b) Sagittal. The length of the endometriosis lesion and the distance between the distal infiltration edge and the proximal edge of the sphincter muscles (posterior quadrant) (arrows). Internal anal sphincter (IAS), Puborectalis muscle (PR)

Fig. 14.3

Endometriosis lesion in the right anterior quadrant infiltrating the rectal wall as far as the muscular propria. (a) Axial plane. Heterogeneous hypoechoic image compromising 30% of rectal circumference (arrows). (b) Sagittal. The length of the endometriosis lesion and the distance between the distal infiltration edge and the proximal edge of the sphincter muscles (posterior quadrant) (arrows). Mucus in the rectal lumen, outside the lesion site (artifacts). Internal anal sphincter (IAS), Puborectalis muscle (PR)

Ovarian endometrioma may be found in association with endometriosis infiltration in the rectal wall in variable percentages, and 3D-US can be useful in the identification of details [9] (Fig. 14.4). Studies using 3D-US with different modalities have reported several advantages: reconstruction of a volumetric image that can be saved, rotated, and evaluated in different planes in real time and that can be assessed and compared by the same or different examiners over time [10–12].

Fig. 14.4

Ovarian endometrioma lesion infiltrating the upper rectal wall (left anterior quadrant) as far as the muscular propria layer. (a) Axial plane-ovary with a heterogeneous hypoechoic image compromising 20–30% of the rectal circumference (arrows). (b) Sagittal. The length of the endometriosis lesion and the distance between the distal infiltrated edge and the lower rectum (arrows)

Perianal Endometriosis

Perineal endometriosis is rare and is characterized by the presence of endometrial tissues in the perineal sites with or without involvement of sphincter muscles [7]. The majority of patients are at reproductive age and have a history of vaginal delivery. Lesions may frequently be found in the episiotomy scar or laceration site after vaginal delivery.

The complete physical examination, including gynecologic and digital rectal examination, combined with 3D-US, should confirm whether or not the anal sphincter is involved and determine the exact circumferential and longitudinal extension of the infiltration. This provides the best approach in planning a local resection or sphincter-saving surgery in order to avoid fecal incontinence [13, 14] (Fig. 14.5).

Fig. 14.5

Endometriosis lesion (heterogeneous image) in the perianal fat infiltrating the external anal sphincter (EAS) and puborectalis (PR) muscles in the entire length of the anal canal. (a) Mid anal canal. Endometriosis lesion infiltrating the lateral fibers of the EAS (arrows). (b) Upper anal canal. Endometriosis lesion infiltrating the right side of the PR (arrows). The vagina wall is infiltrated as well. (c) Coronal with axial planes. Length and depth (arrows) of the lesion infiltration. Internal anal sphincter (IAS)

Pre-sacral Neoplasia

Perirectal neoplasia is most often located in the retrorectal space and may be of varied etiology. Half the cases are congenital and two-thirds are cystic in nature [15, 16]. It commonly develops in young females or in adults, and it is rare in infants. Teratoma is the most frequently observed form in pediatric patients and contains fat or calcifications in 50% of cases [16, 17]. A wide variety of cystic lesions occur in the retrorectal space, and most are congenital. They are classified as epidermoid cysts, dermoid cysts, enteric cysts (tailgut cysts and cystic rectal duplication), and neurenteric cysts, according to their origin and histopathologic features [18].

Imaging may show specific signs and characteristics of the lesion, but the diagnosis remains histopathologic. Anorectal ultrasound scanning is useful in the evaluation of size, type of lesion (mixed cystic and solid components), and relation with the rectal wall and the sphincter muscles. Perirectal neoplasia has different characteristics: unilocular or multilocular retrorectal lesion; hypoechoic lesion (cystic); and mixed echogenicity/heterogeneous lesions , due to mucoid material, inflammatory debris, or solid component, usually with regular outline and not adhering to the rectal wall. In large lesions, displacement or stenosis of the rectal wall due to extrinsic compression may be visualized. It is important to define a rectal wall invasion or a communication between the cyst and the anorectal lumen (Figs. 14.6, 14.7, and 14.8).

Fig. 14.6

(Female) Pre-sacral cystic lesion located at the level of low rectum with regular outline and without adherence to the rectal wall (arrows). The rectal wall is intact. (a) Axial plane. Heterogeneous image located at the level of the low rectum (arrows). (b) Sagittal with diagonal planes. A well-circumscribed (hyperechogenic line that surrounds the lesion) and unilocular cystic lesion. Lesion size (longitudinal length and the depth)

Fig. 14.7

(Female) Cystic lesion (mixed echogenicity) in the pre-sacral space at the level of low rectum. There is a contiguous (communication) area with rectal wall. (a) Axial plane. In this position, the lesion appears with regular outline and without adherence to the rectal wall (arrows). The rectal wall is intact. (b) Axial plane. The image shows the area of the cystic lesion, which communicates with the rectal wall (interrupted arrows). (c) Sagittal plane. The hyperechogenic line that surrounds the lesion (arrows) is interrupted (small area) and there is a communication with rectal wall (interrupted arrows). Lesion size (longitudinal length and the depth). External anal sphincter (EAS), Internal anal sphincter (IAS), Puborectalis muscle (PR)

Fig. 14.8

(Female) Multilobulated heterogeneous (cystic and solid) lesion in the pre-sacral space, at the level of the low rectum and anorectal junction with regular outline and without rectal wall involvement. (a) Heterogeneous images in the low rectum (arrows). (b) Heterogeneous images in the anorectal junction (arrows). (c) Sagittal with diagonal planes. The lesion length and the distance between the distal and the proximal edges of the sphincter muscles (posterior quadrant) (arrows). Puborectalis muscle (PR)

Rare Tumors

Rectal Leiomyoma

Leiomyoma is a benign mesenchymal neoplasm that usually develops where smooth muscle is present. This lesion is rare, except in the esophagus and rectum. Only 3% of these smooth muscle tumors arising from the colon are gastrointestinal leiomyomas and represent about 0.1% of rectal neoplasias [19, 20]. In the rectum, most leiomyomas present as small intraluminal polyps and are limited to the muscularis mucosa, although there are reports of anorectal leiomyomas [21].

Definitive diagnosis requires anatomical and pathological examination (immunohistochemical staining). Leiomyomas are positive for actin and desmin and negative for CD34 and CD117 [20, 22]. Anorectal 3D ultrasound scanning shows the exact extent of the lesion and relationship with the anatomical structures (Fig. 14.9).

Fig. 14.9

Small lesion located at the level of the anorectal junction in the right anterior quadrant. Heterogeneous lesion expands the outer hypoechoic layer that corresponds the muscularis propria. Rectal leiomyoma (arrows). (a) Axial plane. (b) Multiplane—sagittal with diagonal plane and axial. Internal anal sphincter (IAS), Puborectalis muscle (PR)

Gastrointestinal Stromal Tumors (GIST)

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the GI tract; however, they represent less than 1% of all gastrointestinal tumors [23]. GIST can occur everywhere along the GI tract, but most often are found in the stomach (60%) or small intestine (30%), followed by the rectum (3%), colon (1–2%), esophagus (<1%), and omentum/mesentery (rare) [24].

The clinical presentation and diagnosis of patients with GIST depend on the anatomic location of the lesions and their size and aggressiveness. Small GIST may form solid subserosal, intramural, or—less frequently—intraluminal mass. Large tumors tend to form external masses attached to the outer aspect of the gut, involving the muscular layers [25]. Evaluation includes imaging and/or endoscopy, but pathology and molecular genetics studies are required. Approximately 95% of GISTs are positive for the CD117 antigen [25].

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