Widespread pro-peritoneal and retroperitoneal abscess secondary to complex trans sphincteric Fistula in-ano with supra-levator extension

A 46-year-old gentleman presented with complaints of left-sided lower abdominal pain, mild swelling, and heaviness

Imaging demonstrated,

A trans sphincteric peripherally enhancing collection (Figure 1) with supra levator extension (Figure 2) is seen on the right side.

A peripherally enhancing horseshoe-shaped abscess (Figure 3) with a few air foci (Figure 4) within is seen in the perianal region at 5 to 8 o clock position extending to the right ischioanal fossa. Mild enhancing thickening of the anal canal and the external sphincter (Figure 4)

Superior extension of collection to the right pelvic sidewall abutting the right obturator muscles, pro-peritoneal space anterior to the urinary bladder (pre vesical space of Retzius) demonstrating hyperdense fluid with mottled air foci (Figure 5)

Extension to beneath the anterior and left lateral abdominal wall, posterior to the left lateral-conal and posterior renal fascia into the posterior pararenal space, along with the left psoas with pneumo retroperitoneum (Figure 6,7,8)

Mild left perinephric fluid and a few air foci in the left perinephric space with normal bulk and enhancement of the left kidney (Figure 9)

Suppurative disease of the rectum and peri-rectum is a common ailment and the suppuration is usually located below the level of the puborectalis muscle. 

If not diagnosed and adequately treated at this stage, more than 90 % of these collections will rupture.

As the puborectalis sling exerts strong pressure on the posterior rectal wall at the anorectal ring preventing supra levator extension of the abscess, these collections will usually rupture through the longitudinal muscle and extend trans-sphincterically into one of the infra levator anorectal spaces.

But rarely, a low intermuscular abscess may extend above the level of the puborectalis muscle to form a high intermuscular abscess, which may rupture into one of the supra levator spaces.

Supra levator abscesses can spread to the pre vesical space, as there is a direct communication from pararectal space to the vesicle extraperitoneal space without a separating fascial layer due to the umbilicovesical fascia ending at the reflection of the vesical peritoneum.

From the pre vesical space, the infection can spread through the entire space of Retzius anteriorly, as well as into other pelvic compartments, and to the retroperitoneum posteriorly, through the direct spread.

The retroperitoneal region reacts to bacterial contamination to a lesser extent compared to the intraperitoneal region and tends to follow a more indolent and asymptomatic course leading to delayed diagnosis and treatment. This may lead to a  higher rate of sepsis and increase mortality risk.

Clinicians can only partially evaluate thretroperitoneumum during the physical examination, and laboratory investigations provide limited information. Therefore, radiological investigations, especially computed tomography can play a key role in the diagnosis.

This case highlights the complex anatomic compartments and potential spaces that exist in the extra peritoneum that allow a typically benign and common perirectal abscess to extend to the abdomen. Also the importance of looking closely at rectum and anal canal for a fistula in ano as the source of infection.

Written informed patient consent for publication has been obtained.