Magnetic resonance imaging and endorectal ultrasound for diagnosis of rectal lesions

Abstract

Endorectal ultrasonography (ERUS) and magnetic resonance imaging (MRI) allow exploring the morphology of the rectum in detail. Use of such data, especially assessment of the rectal wall, is an important tool for ascertaining the perianal fistula localization as well as stage of the cancer and planning it appropriate treatment, as stage T3 tumors are usually treated with neoadjuvant therapy, whereas T2 tumors are initially managed surgically. The only advantage of ERUS over MRI is the possibility of assessing T1 tumors that could be treated by transanal endoscopic microsurgery. However, MRI is better for visualizing most radiological prognostic features in rectal or anal cancer such as a circumferential resection margin less than 1 mm, T stage at T1-T2 or T3 tumors with extramural extension less than 5 mm, absence of extramural vascular invasion, N stage at N0/N1, and tumors located in the middle or upper third of the rectum. It can also evaluate the intersphincteric space or levator ani muscle involvement. Increased signal on diffusion weighted imaging (DWI) and low apparent diffusion coefficient (ADC) values as well as an irregular contour and heterogeneous internal signal intensity seem to predict the involvement of pelvic lymphatic nodes better than their size alone. Computed tomography as well as other examination techniques, including digital rectal examination, contrast edema, recto- and colonoscopy, are less useful in staging of rectal cancer but still are very important screening tools.

Accuracy of MR imaging in preoperative staging of rectal cancer

“…Endorectal ultrasound is believed to be more sensitive in identifying early tumors, but it is highly operator dependent and large studies show that staging accuracy is not as high as previously reported (18,19). The only advantage of ERUS over MRI is the possibility of assessing T1 tumors that could be managed by transanal endoscopic microsurgery (20).…”

Anorectal malformation as a cause of recurring perineal abscesses – value of anorectal endosonography and magnetic resonance imaging: a case report

“…Ultrasonography is highly accurate enabling the visualisation of rectal wall abnormalities and the identification of lesions localised beyond the rectum [7]. ERUS has also an important role in the assessment of anorectal fistulae, determining type, level, branching and internal opening and recurrences of fistulae [8].…”

Endoluminal Ultrasonography of the Rectum and the Anal Canal

“…The sphincter anal complex is formed by the muscles that represent the continuation of circular layer of the muscularis propria of the rectum, the striated external anal sphincter, and puborectal muscles, which belong to the levator ani muscles [4]. The lowest point of the external anal sphincter represents the upper anal margin; it is called the anal verge and is the principal landmark for rectal measurements [4]. The pectinate (dentate) line is located 1.5-2 cm upwards from the anus and separates the canal anal into the anatomical part located below the line and the surgical part located above the line [4].…”

“…The lowest point of the external anal sphincter represents the upper anal margin; it is called the anal verge and is the principal landmark for rectal measurements [4]. The pectinate (dentate) line is located 1.5-2 cm upwards from the anus and separates the canal anal into the anatomical part located below the line and the surgical part located above the line [4]. The surgical anal canal extends from the pectinate line to the level of the puborectalis sling, which corresponds to the anorectal junction.…”