Type:
Educational Exhibit
Keywords:
Fistula, Diagnostic procedure, MR, Gastrointestinal tract, Abdomen
Authors:
M. R. VACCARO NOTTE, G. Caruana, D. Giambelluca, V. Costanzo, M. Dimarco, S. Pellegrino, G. Lo Re, R. Lagalla; Palermo/IT
DOI:
10.1594/ecr2018/C-2708
Background
Perianal fistula is an inflammatory condition that affects the region around the anal canal.
It is characterized by a connection between the anal canal and the skin of the perineum.
Perianal fistulization is an uncommon process,
with a prevalence of 0.01%,
although it causes significant morbidity and often requires repeated surgical treatments due to its high tendency to recur.
It predominantly affects young males,
with a male-to-female ratio of 2:1.
The most common presenting symptom is discharge (65% of cases),
but local pain due to inflammation is also common [1].
A proper knowledge of the anatomy of the anal sphincter complex and of the surrounding spaces is crucial for image interpretation.
The anal canal extends from the anus to the rectal ampulla and is 2–5 centimeters long.
It is surrounded by two sphincter muscles: the internal and external anal sphincters.
The internal sphincter is the inferior extension of the inner circular smooth muscle of the rectum and is primarily responsible for resting involuntary anal continence.
The external sphincter is composed of striated skeletal muscle,
which is contiguous with both the levatorani and puborectalis muscles superiorly and is primarily responsible for voluntary continence.
At approximately 2 cm in the anal canal lies the dentate line,
where the epithelium becomes transitional,
and there is histological junction between the anal squamous epithelium and the rectal columnar epithelium.
Around the dentate line there are the anal glands,
that release their secretions into the anal sinuses.
The glands are primarily located within the intersphincteric space or the internal sphincter [2] (figure 1).
According to the cryptoglandular hypothesis, the majority of idiopathic anal fistulas result from an infection that arises in the anal glands at the dentate line when the draining duct becomes blocked by infected debris,
as an intersphincteric infection.
This abscess may resolve by means of spontaneous drainage into the anal canal or may progress to an acute anorectal abscess.
Anal fistula develops when an intersphincteric infection continues.
Perianal abscess is an acute manifestation and fistula-in-ano a chronic condition of the same disease [3].