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11 Magnetic Resonance and Traditional Radiology in the Diagnosis of... 189
These conclusions were supported in a follow-up study of 35 patients that demon­strated a correct MRI assessment in 33 of the patients (94%), including two cases in which examination under anesthesia failed to identify distant sepsis.
More studies soon conrmed Lunnisexcellent results.
In 2001 Beets-Tan et al. (2001) evaluated the importance of the additional information that MRI examination can provide. The study included 56 patients with anal stulas who underwent high-spatial resolution MRI. The information gained by the MRI made the surgeon decide to continue the surgery in only 21% (12/56) of the patients. They concluded that MRI results provide signicant addi­tional information about secondary extensions and recurrent stulas, particularly in patients with Crohns disease; therefore, the authors recommended the execution of a preoperative MRI to guide the surgeon to a more precise surgical planning.
In 2004 Buchanan et al. (2004) performed a larger study including 71 patients with recurrent anal stula in which MRI ndings were revealed after initial stula surgery. The recurrence rate in the postoperative period was analyzed: in particular the authors compared the recurrence rate when the surgeons acted basing their decisions always on MRI results, the recurrence rate when surgeons acted only sometimes basing on MRI ndings, and the recurrence rate when MRI results were completely ignored. The rst group, when surgeonsdecisions were guided by MRI ndings, had a signicant lower recurrence rate (16%), compared to the other two groups (30% and 57%, respectively). Additionally, in the 16 patients who required further unplanned surgery, MR images had initially accurately located the site of disease in all cases, attesting that surgery guided by MRI reduces further recurrence of anal stula by 75% and should be performed in all patients, especially the ones with recurrent stula.
In 2017 Garg (2017) evaluated MRI contribution to surgical management in a large study, which included 229 patients. They reported that MRI added important information in patients with additional tracts, horseshoe tracts, supra-levator exten­sion, unsuspected abscess, and multiple internal openings. They concluded that MRI was capable of adding signicant information to 46.7% of the surgeries when assessing these parameters.
In 2018 Konan et al. (2018) evaluated the contribution of MRI in the surgical management of anal stulas. MRI signi cantly helped the clinical assessment in
33.8% of the patients. MRI more often provided important information for c omplex stulas than for simple stulas. Also when the external opening was more than 2 cm away from the anal canal or when a horseshoe stula was present, MRI demonstrated to have a more relevant role.
Following these studies, it could be argued that all patients should be imaged preoperatively, especially if MRI can be easily performed (Halligan 2020). Supporting this, even though the therapeutic impact of MRI is more pronounced in patients with a complex disease (Beets-Tan et al. 2001; Halligan 2020), it has been estimated that MRI can prove around 10% of rst time apparently simple presenting stulas, to be more complex than expected (Buchanan et al. 2004). Where MRI access is more restricted and cannot be performed to study every patient, the referring clinician needs to be more selective. MRI should be routinely performed
190 L. M. Minordi et al.
in patients with recurrent disease, because there is a high evidence of the benets of MRI, which can modify surgical therapy and improve clinical outcomes (Halligan
2020). As well patients presen ting for the rst time with a stula seemingly complex
on clinical examination and patients with known Crohns disease (since the preva­lence of complex stulas in this type of patients is so high) should undergo MRI examination (Halligan 2020).
There are other surgical situations where imaging is likely to be extremely helpful, even when the stula itself is simple. For example, the anterior external sphincter is very short in women, and dividing this during stulotomy is a risk for postoperative incontinence, even when the stula is simple (Halligan 2020). In this case, rather than incising the stula, the surgeon may decide to pass a seton thread through the track to stimulate drainage (Halligan 2020).

3 Conclusion

The anatomy of the anal and perianal region is complicated, and many different abnormalities may be seen in this limited anatomical area. Almost any imaging technique may be helpful for studying the perianal area; however, MRI, with its brilliant and superior to any other modality soft tissue resolution, emerges as the modality of choice. Furthermore, MRI examination is exceptionally useful in pre­operative planning by outlining the extent and secondary ramications of the stula tract as well as detecting the anal and cutaneous openings and associated abscesses.

4 Cross-References

Endoanal Ultrasound in the Diagnosis of Cryptoglandular Anal Fistulas and
Abscesses
Magnetic Resonance Imaging in the Diagnosis, Characterization, and Manage-
ment of Crohns Fistula

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Utility and Limitations of Endoanal Ultrasound in the Diagnosis of Crohns Anal
12
Fistula and Abscess
Lucia Camara Castro Oliveira
Contents
1 Introduction . ............... .................................................................. 193
2 Clinical Presentation ......................................................................... 194
3 Utility and Limitations of Endoanal Ultrasound ............................................ 195
4 Conclusion ................................................................................... 199
5 Cross-References .......................... ............................................. ..... 200
References ............................ ............................................... ............ 200
Abstract
Distinction between cryptoglandular and Crohns stulas may be difcult, but is
important to guide treatment. Ultrasonography is an imaging method that has
great utility for the evaluation of the anorectal region. The development of high-
resolution transducers, with higher frequencies and three-dimensional congura-
tion, provides an evaluation of complex stula tracts including those associated
with perianal Crohns disease.
Keywords
Ultrasound · Anorectal · Crohns disease · Anal stula

1 Introduction

Anorectal abscess usually originates from the infection and obstruction of the anal glands. However, aside from this cryptoglandular origin, there are a number of other causes of anorectal suppuration including Crohns disease. It is well known that
L. C. C. Oliveira (*) Department of Anorectal Physiology of Rio de Janeiro, CEPEMED, Rio de Janeiro, Brazil
© Springer Nature Switzerland AG 2022 C. Ratto et al. (eds.), Anal Fistula and Abscess, Coloproctology,
https://doi.org/10.1007/978-3-030-76670-2_14
193
194 L. C. C. Oliveira
anorectal abscess can drain spontaneously and may completely heal, or it can recur at the same site and develop a stula tract. In fact, in the majority of cases, anorectal stulas arise from a previous abscess. According to the Park’s classication, a stula tract can be intersphincter ic, trans sphincteric, suprasphincteric or extra sphincteric (Parks et al. 1976). Therefore, adequate evaluation of stulas and stula tracts is crucial to determine the appropriate intervent ion, minimizing the risks of anal incontinence.
In patients with Crohns disease, perianal stula can be a challenging situation and in 20–30% of the cases it is the rst presentation of the disease. The pathog enesis of Crohns stulas remains not well understood but certainly is distinct from the cryptoglandular origin.
One of the theories associates the deep ulcers with invasion of fecal material and bacteria. Those stulas are more complex and can have mul tiple tracts. The clinical presentation can be difcult to distinguish between other etiologies of perianal disease, such as hidradenitis and sexually transmitted diseases. Because endoanal ultrasound probe is introduced into the anal canal, the proximity of the anatomic structures allows a better evaluation of the sphincter muscles and the tracts itself. When accuracy of physical examination and endoanal ultrasound (EAUS) is com­pared, advantages of EAUS are clearly observed, especially in more complex cases, such as in patients with Crohns disease. Accuracy of EAUS is around 85% for the detection of horseshoe tracts and 85% for the location of the internal stula orice compared to 56% and 69%, respectively, for the physical examination (Toyonaga et al. 2008).

2 Clinical Presentation

Distinction between cryptoglandular and Crohn’s stulas may be difcult, but is important to guide treatment. Although the pathogenic mechanisms are very different, some patients may remain undiagnosed when the clinical presentation is not very clear for Crohns disease. Usually the complex tracts associated to Crohns disease are located in atypical locations and have a poor healing rate, regardless of the utilized treatment. Patients usually have constant anal pain that can be maximized during evacuation, fever can be present, but interestingly, the external stula openings and the perianal skin are seldom painful. (Fleshman and Tay 2014) In the evaluation process, active disease in the colon and small bowel should be ruled out as the persistence of the inammatoryprocessisassociated with the maintenance of the perianal stula disease. Another speciccharacteristic of the Crohn’s stula patients is the development of atypical skin tags which can help to establish the diagnosis, as the pathognomonic non-caseating granulomas can be demonstrated. In addition t o the skin tags, swelling, induration, and redness of the perianal skin can be seen, as well as purulent discharge and multiple external openings (Fig. 1).
12 Utility and Limitations of Endoanal Ultrasound in the Diagnosis of Crohns... 195
Fig. 1 Male patient with multiple stula tracks associated with perianal Crohns disease

3 Utility and Limitations of Endoanal Ultrasound

Ultrasonography is an imaging method that has great utility for the evaluation of the anorectal region (Santoro and Murad-Regadas 2017). This imaging modality pro­vides a clear evaluation of the anorectal muscles and pararectal spaces. Patients are examined in the left lateral decubitus and gentle lubrication of the anus is advised.
The development of high-resolution transducers, with higher frequencies and three-dimensional conguration, provides an evaluation of complex stula tracts including those associated with perianal Crohn’s disease (Santoro and Fortling 2007) (Fig. 2).
In the case of suppurative processes and complex stulas, including those related to Crohns disease, ultrasound evaluation allows the identication of inammatory cavities, primary and secondary stulous tracts, and the complexity of the tracts in relation to the anorectal muscles (Fig. 3). In these cases, evaluation of the sphincter muscles also brings important information to the surgeon, since the tracts may be intersphincteric or transsphincteric. The information provided is valuable for proper planning of the surgical approach as well as to classify and determine the extent of the disease, avoiding the risk of incomplete healing, recurrent stula, and inadvertent sphincter injury.
The use of three-dimensional transducers has allowed the location of the stulous tracts in all planes (Fig. 4). In addition, when an external opening is present, it is possible to introduce 1–2 ml of hydrogen peroxide to improve the visualization of the tracts and the internal opening (Fig. 5).
Zawadzki et al. (2012) described the characteristic Crohns stula imaging by EAUS as a hypoechogenic stula track surrounded by a hyperechogenic area extending into the perianal tissue with a thin, regular hypoechogenic edge. This nding can help the distinction between the various perianal stulas.
One of the main advantages of EAUS is the possibility of performing the evaluation at the ofce, when the patients are comfortable wi th the presence of
196 L. C. C. Oliveira
Fig. 2 High-resolution B-K 360 3D transducer for better evaluation of anorectal region
Fig. 3 Anorectal abscess area on coronal and axial plane
the probe. The high-resolution 3D transducers can demonstrate different plans of the anorectal region and the more complex tracts can be easily demonstrated. Because those transducers record the exam in automatic scanning the procedure can be revised after the examination, which can, as with magnetic resonance imaging
12 Utility and Limitations of Endoanal Ultrasound in the Diagnosis of Crohns... 197
Fig. 4 High intersphincteric tract on sagittal and axial planes
Fig. 5 Endoanal ultrasound enhancement with hydrogen peroxide to improve the visualization of
the tracts and the internal opening
(MRI), overcome the barriers of having a non-experienced professional performing the acquisition.
Portable systems with 2D probes can also be easily brought to the theater and patients can be evaluated under sedation (Fig. 6).
In a study comparing 51 patients that underwent 3D-EAUS and MRI for Crohns disease the authors were able to demonstrate that both studies can be used to assess transsphincteric stulas. However, they reported that using 3D-EUAS alone, up to 14% of suprasphincteric stulas can be overlooked or not correctly diagnosed (Alabiso et al. 2016). The advantages of MRI, according to this study, are the evaluation of suprasphincteric and extrasphincteric stulas with a broader
198 L. C. C. Oliveira
Fig. 6 Portable systems with 2D probes can also be easily brought to the theater and patients can be evaluated under sedation (360 Morpheus – Prometheus)
visualization of the hole pelvic oor thus showing the stula track in the context of the surrounding structures.
Although MRI has been widely utilized in the assessment of perianal CD, it seems less accurate than EAUS in the detection of anorectal abscesses (Orsoni et al.
1999).
Another study, in fact, a meta-analysis performed in 2012, compared EAUS and MRI in the identication and classication of perianal stulas in patients with Crohns disease, conrming a high sensitivity (87%) of both techniques (Siddiqui et al. 2012).
When a combination of a clinical activity index (Fistula Drainage Assessment (FDA) and Perianal Disease Activity Index (PDAI)) with an imaging modality such as EAUS was performeda demonstration of an improvementin diagnosticaccuracy was obtained and both being complementary to each other (Losco et al. 2009; Botti et al. 2013).
These ndings were also observed by de la Portilla et al who even presented a ultrasonographic classication for patients with perianal Crohns disease (de la Portilla et al. 2015) (Table 1).
The incidence of intersphincteric abscesses diagno sed by EAUS in a prospective cohort of patients with CD was published in 2010 (Viganò et al. 2011). The authors diagnosed perianal stulas or abscesses in the presence of a hypoechoic track originating from the subepithelial or submucosal layer of the anal canal, extending toward the anal sphincters, and containing hyperechoic spots consistent with the presence of gas bubbles within the stulizing track. They included 55 patients and demonstrated that EAUS is a valuable modality for the assessment of patients with intersphincteric abscesses and pain.
In our series, EAUS helped to identify abscesses and complex stula tract, as in this example: a 43-year-old male patient with Crohns disea se and a large ischiorectal abscess (Fig. 7).