Letter to the Editor: “ESGAR consensus statement on the imaging of fistula-in-ano and other causes of anal sepsis”

by Pankaj Garg (drgargpankaj@yahoo.com)

ESGAR consensus statement on the imaging of fistula-in-ano and other causes of anal sepsis

Dear Editor,

I read with interest the article by Halligan et al [1]. The authors have meticulously published the consensus statement for reporting imaging in fistula-in-ano. Regarding classification of fistula-in-ano, the authors mentioned “The aim is to present imaging information in a format useful to the referring clinician. For this reason, the group emphasized the importance of including Parks’ classification in the radiological report.”

The basic purpose of any classification is twofold: the first is to grade the disease according to its severity and the second is to guide the treating physician regarding the management [2, 3]. Unfortunately, none of the commonly used classifications- Parks and St James University Hospital (SJUH) are serving any of these two purposes [3]. Parks grade I fistula (for example, a high intersphincteric horseshoe fistula) may be more complex than Parks grade II fistula (a low transsphincteric fistula involving only 5-10% of the external sphincter) and similarly SJUH grade II may be much more complex than SJUH grade III fistula [2, 3]. Moreover, categorizing the fistulas as per these classifications by the radiologists does not help surgeon in any way. For a clinician, the value of MRI increases tremendously if it is used with a clinically useful classification. In fistula-in-ano, there was a big void as none of the existing classifications were useful to the operating surgeons to grade the disease or to guide regarding the disease management.

A recently published new classification (also referred as Garg classification) has remarkably filled this void [2, 3]. Garg classification classified fistulas in five grades [2, 3]:

Grade I- Low fistula (involving less than 1/3 of external sphincter) with single branch, intersphincteric or transsphincteric;

Grade II-Low fistula with multiple branches, associated abscess or horseshoe tract;

Grade III- High fistula (involving more than 1/3 of external sphincter) with single branch, intersphincteric or transsphincteric;

Grade IV- High transsphincteric fistula with multiple branches, associated abscess or horseshoe tract;

Grade V- Supralevator, Suprasphincteric or Extrasphincteric fistula.

This new classification not only grades the disease as per its severity but also guides the operating surgeon regarding the management of the fistulas [3]. Garg grade I-II fistulas can be conveniently dealt with fistulotomy without any risk to incontinence and in Garg grade III-V fistulas, fistulotomy should never be attempted as it would entail high risk of incontinence [2, 3]. These fistulas should be dealt with sphincter-sparing procedures. Moreover, unlike previous classifications, Garg classification was validated on a large sample (440) of patient data [2, 3].

Fistulotomy is the simplest and the most commonly done operation for fistula-in-ano with success rate of 90-98% [4]. But due to lack of proper classification, fistulotomy is grossly underutilized [4]. The operating surgeon is always fearful of incontinence and doesn’t do fistulotomy even in low fistulas (involving less than one-third of sphincter complex). Most surgeons can’t interpret MRI themselves and radiologists don’t report the fistula as low or high (as recommended by Garg classification). Due to this, these patients with low fistulas end up getting operated with procedures with much less success rate and patients with high fistulas end up getting fistulotomy resulting in incontinence [3, 4]. The onus of guiding the operating surgeon about the fistula complexity lies with the radiologist. But even the accurate description of MRI-fistula by the radiologist, in the absence of proper classification, does not help the operating surgeon in the management [3, 4]. Due to this, the importance and utility of MRI is not fully realized by the surgeons.

Secondly, the authors have not mentioned the guidelines regarding interpreting the MRI in the post-operative period [1]. A recent study done in over 1300 patients has shown the value of MRI in assessing fistulas not only in pre-operative but in post-operative period as well [5]. In post-operative cases, MRI was very accurate to identify and diagnose the postoperative complications like abscess formation, non-healing fistulas or missed tract (on preoperative scan/ intraoperatively) [5]. MRI detected such complications even in apparently clinically healed tracts. MRI done in immediate postoperative period (up to 8 weeks’ post-surgery) required great care in interpretation and was easily misleading as both granulation tissue (healing tissue) and inflammation in tissues (post surgery) looked hyperintense on T2 and STIR and were difficult to differentiate from an active fistula tract/ pus [5]. The study showed that getting MRI scan for assessment of healing was best done after 12 weeks as the complete radiological healing usually took at least 10-12 weeks. MRI could accurately assess closure/healing of the internal opening and the intersphincteric tract and this correlated quite well with the long-term fistula healing [5].

Thirdly, the authors were not very clear as whether MRI should be done in every fistula-in-ano patient or only patients with recurrent fistula as recommended by few surgical societies [1, 5, 6]. Several large studies have demonstrated that MRI added significant information which changed the surgery decision in more than one-third of simple and more than half of complex fistulas [5, 6]. Therefore, it has been recommended that MRI should be done in all fistula-in-ano including simple fistulas [5, 6]. Though it may seem that doing MRI in every fistula-in-ano may turn out to be costly but if MRI can prevent a recurrence in 1/3 of simple and 1/2 of complex looking fistulas, then perhaps it might turn out to be more economical in the long run [5, 6]. However, this point needs more research and meta-analysis of the published data.

To summarize, MRI should be used more frequently to assess fistula-in-ano even in post-operative cases and Garg classification should be routinely used by the radiologists so that the operating surgeons benefits from this useful diagnostic modality.