MRI of anal canal: common anal and perianal disorders beyond fistulas: Part 2

Extreme horseshoe and circumanal anal fistulas-challenges in diagnosis and management

Objectives:

Extreme horseshoe anal fistulas are rare, and there are little data on the diagnosis and management of these fistulas.

Materials and Methods:

Patients with horseshoe anal fistula, in which the fistula tract encircled more than 75% of the anal circumference were included in the study. All patients were assessed by a preoperative magnetic resonance imaging (MRI). The patients were managed by a sphincter-sparing procedure. The continence was evaluated by an objective continence scoring system (Vaizey's scores).

Results:

1059 anal fistula patients were operated on over 7-years with a median follow-up of 36 months (range: 5–79 months). There were 47/1059 (4.4%) patients with extreme horseshoe anal fistulas. In 4/47 patients, the fistulas were complete circumanal (encircling anal canal completely). The mean age was 39.5 ± 10.9 years, M/F-41/6. The fistula was supralevator in 12/47 (25.5%), had an associated abscess in 28/47 (59.6%), and was recurrent in 33/47 (70.2%) patients. The tracts were intersphincteric in 27/47, transsphincteric in 2/47, and both (intersphincteric and transsphincteric) in 18/47 patients. All patients (n = 47) were managed by a sphincter-sparing procedure. Four patients were lost to follow-up. The fistula healed completely in 34/43 (79%) patients. There was no significant difference between preoperative and postoperative Vaizey's continence scores 0.031 ± 0.17 and 0.033 ± 0.18 respectively (P=0.90, Mann–Whitney U-test).

Conclusion:

Extreme horseshoe fistulas are rare, with an incidence of about 4% (in a referral practice). The missed diagnosis of circumferential tracts could lead to a recurrence. MRI was pivotal to confirm the diagnosis. Proper identification and management of internal opening and adequate drainage of all tracts were crucial for successfully treating extreme horseshoe fistulas.

The new pathways of spread of anal fistula and the pivotal role of MRI in discovering them

Conventionally, in the pathophysiology of anal fistulas, there is only one space considered significant for the spread of pus in the sphincter complex: the intersphincteric space. However, with increasing experience in the high-resolution MRI, and more focus being given on managing fistulas through the intersphincteric space, two additional pathways of fistula spread have been identified. First is a newly described space labelled as the outer-sphincteric space. Second is a known anatomical space (inner intersphincteric space), but this space was considered as irrelevant from the point of view of fistula spread. The conventional intersphincteric space is present in between these two spaces and is referred as 'middle intersphincteric space' in this paper. These three distinct spaces have significant clinical implications as the pattern of spread of pus is quite different in each space, and the management also differs for fistula tract in each of these spaces.

Management of Complex Cryptoglandular Anal Fistula: Challenges and Solutions

Anal fistulae can be a very difficult disease to manage. The management of complex fistulae is even more challenging. The risk to the fecal continence mechanism due to damage to the anal sphincters and refractoriness to the treatment (high recurrence rate) pose the two biggest challenges in the management of this disease. Apart from these, there are several other challenges in the treatment of complex fistulae. The intriguing and uphill task is that satisfactory solutions to most of these challenges are still not known, and there is hardly any consensus on whatever treatment solutions are available. To summarize, there is no gold-standard treatment available for treating complex anal fistulae, and the search for a satisfactory treatment option is still on. In this review, the endeavor has been to discuss and highlight recent path-breaking updates in the management of complex anal fistulae.

Magnetic resonance imaging findings of carcinoma arising from anal fistula: A retrospective study in a single institution

BACKGROUND

Magnetic resonance imaging (MRI) is currently the standard investigation for suspected perianal diseases. Carcinoma arising from anal fistula is very rare, and early diagnosis is often difficult.

AIM

To describe and summarize the MRI findings of carcinoma arising from anal fistula.

METHODS

In this retrospective study, records of ten patients diagnosed with carcinoma arising from anal fistula and confirmed by surgery (n = 7) or biopsy (n = 3) between June 2006 and August 2018 were analyzed. All patients underwent preoperative pelvic MRI. Morphologic features, signal characteristics, fistula between the mass and the anus, contrast enhancement of mass, signal and enhancement of peritumoral areas, and regional lymphadenopathy were assessed.

RESULTS

All ten tumors were solitary (8 mucinous adenocarcinomas and 2 adenocarcinomas). The maximum diameter of the tumors ranged from 3.4 cm to 12.4 cm (median: 4.15 cm; mean: 5.68 cm). Eight patients had a fistula between the mass and the anus. Contrast enhancement of the peritumoral areas was noted in three (3/5) patients. Perirectal or inguinal lymphadenopathy was noted in seven patients. Most lesions of mucinous adenocarcinoma were multiloculated and cauliflower-like, with a thin capsule and focally unclear boundary. They were markedly hyperintense on fat-suppressed T2WI, slightly hyperintense with focal hyperintensity on diffusion-weighted imaging (DWI), and hyperintense with focal hypointensity on apparent diffusion coefficient (ADC) map, with progressive mesh-like contrast enhancement. Adenocarcinomas had an infiltrative margin without a capsule and appeared heterogeneously hyperintense or slightly hyperintense on fat-suppressed T2WI, hyperintense on DWI, and hypointense on ADC map, with persistent heterogeneous enhancement.

CONCLUSION

Our study highlighted several characteristic and potentially helpful MRI findings to diagnose carcinomas arising from anal fistula.