| Abstract|| |
Objectives: To prospectively evaluate the accuracy of anal endosonography in the preoperative evaluation of fistula-in-ano and to compare its efficacy with that of fistulography. Materials and Methods: Fifty patients with a clinical diagnosis of fistula-in-ano were evaluated by fistulography followed by anal endosonography. The results were correlated with findings at surgery. Results: The sensitivity of fistulography in detecting the primary track, secondary extension, internal opening and abscess cavity were 100 per cent, 66.6 per cent, 50 per cent and 30.76 per cent respectively as compared to anal endosonography findings of 98 percent, 100 per cent, 72.72 per cent and 46.15 percent. Moreover, the accurate anatomic relationships of the fistulous track in relation to the sphincteric muscles can be detected by anal endosonography, but it is not possible with fistulography. The combined use of fistulography and anal endosonography improved the sensitivity in detecting the internal opening and abscess cavity if present. Conclusions: Fistulography and anal endosonography are useful adjuncts to clinical examination in preoperative assessment of a fistula-in-ano. They give an added advantage from the surgical point of view. The injection of hydrogen peroxide into the fistulous track during anal endosonography improves its accuracy.
Keywords: Anal ultrasound, Image enhancement, Anal enhancement, Anal fistulas, Hydrogen peroxide
|How to cite this article:|
Elangovan S, Bhuvaneswary V, Nadarajan S, Kannan R R, Velmurugan S. Comparative study of fistulography and anal endosonography in fistula-in-ano. Indian J Radiol Imaging 2002;12:343-6
|How to cite this URL:|
Elangovan S, Bhuvaneswary V, Nadarajan S, Kannan R R, Velmurugan S. Comparative study of fistulography and anal endosonography in fistula-in-ano. Indian J Radiol Imaging [serial online] 2002 [cited 2020 Aug 4];12:343-6. Available from: http://www.ijri.org/text.asp?2002/12/3/343/28477
| Introduction|| |
Fistula-in-ano is a common and easily treatable surgical problem. However, injudicious and over-ambitious surgery may convert a relatively straight forward fistula into a catastrophe. To diminish the postoperative occurrence of fecal incontinence and to keep the recurrence rate as low as possible, the surgeon must understand the exact relationship of the fistula to the perianal anatomic structure and spaces. Parks et al , had classified fistula-in-ano into four groups, each requiring a different surgical procedure. Thus, preoperative classification of fistula-in-ano facilitates determination of the appropriate surgical procedure.
By clinical examination alone the exact anatomy of the track is often difficult to determine. Probing a tract may help, but this is more painful and potentially dangerous. In this respect, imaging can play an important role. Fistulography which has been used for years, has been considered to be inaccurate Anal endosonography (AES) ,, is a minimally invasive technique that provides detailed images of sphincter defects, anorectal sepsis and course of the fistulous track.
The purpose of this study was to ascertain the role of fistulography and anal endosonography in the preoperative evaluation of fistula-in-ano.
| Materials and Methods|| |
This prospective study was performed in 50 patients with a clinical diagnosis of fistula-in-ano. After clinical assessment of the induration and scarring in the perianal region, the external and internal openings of these patients were subjected to fistulography [Figure - 1]. Fistulography was done after identifying the external opening and cannulating with a narrow bore polythene catheter (with a metal marker strapped in place). About 5-10 ml of contrast (Sodium diatrizoate) was injected and films taken in anteroposterior and lateral position
The Anal Endosonography (AES) was performed in all these patients using the Sonoline 450 Siemens Ultrasound Scanner with a transrectal probe using the 7 MHz rotating transducer. This was done after preparing the patient with a plain water enema. The transrectal cone was covered with an ultrasonic gel filled condom. In a sub-group of 20 patients, anal endosonography was performed after injection of one to two ml. of hydrogen peroxide solution into the fistulous track through the external opening. The following aspects were noted at the time of anal endosonography: primary fistulous track and its relation to the anal sphincter muscles, secondary extension, internal opening, abscess and horse-shoe configuration. The observations were compared with intra-operative findings and were analysed in terms of accuracy, sensitivity, specificity, positive predictive value and negative predictive value.
| Results|| |
The sensitivity of fistulography in identifying the primary fistulous track found to be 100% with positive predictive value of 100%. Secondary extensions were found intra-operatively in three but only in two patients it was detected preoperatively by fistulography. In one patient fistulography identified secondary extension, but intraoperative correlation was lacking. Hence, the sensitivity of this investigation in detecting secondary extension was found to be 66.7% with a specificity of 97.87% and overall accuracy was 96%. The sensitivity of fistulography for the detection of the internal opening was found to be only 50% and specificity 83.3%. The positive predictive value and negative predictive value were 95.7% and 18.5% respectively. The overall accuracy for the detection of the internal opening was found to be 54%. The sensitivity of fistulography in detection of abscess was found to be 30.8% and specificity of 86.5% with an accuracy of 72%.
Though all the patients had the primary track identified intraoperatively, in one patient the track could not be visualized by anal endosonography (AES), showing a sensitivity of 98%. The sensitivity for detecting secondary extension was found to be 100% with a specificity of 97.9%. The positive predictive value and negative predictive value were 75% and 100% respectively. The sensitivity to detect the internal opening was found to be 72.7% and specificity 100% with an accuracy of 76%. The sensitivity in detecting the abscess cavity was 46.2% and the specificity was 81.1% with an accuracy of 72% [Figure - 2].
Results of AES in detecting the relationship of the fistulous track to the sphincter muscles are shown in [Table - 1]. The overall accuracy in detecting the superficial and intersphincteric track [Figure - 3] was 90% and for transsphincteric and extra sphincteric tract was 96% and 100% respectively. Horse-shoeing was found in one patient and it was correctly diagnosed by both fistulography and AES [Figure - 4].
The combined use of fistulography and AES has improved the sensitivity of detecting secondary extensions, internal opening and abscess cavity.
| Discussion|| |
The successful surgical management of fistula-in-ano requires accurate information regarding the course of the fistulous track especially its relation to the sphincter muscles. It is known that most recurrences after surgery for fistula-in-ano are a consequence of missed primary/secondary tracks or failure to identify the internal openings . An accurate method of preoperative imaging to delineate the primary and secondary tracks, the site of the internal opening and pus collection may help to prevent the recurrences and inadvertent sphincter injury.
Even though many reports had shown that endoanal MR imaging , more accurately allows depiction and classification of fistula-in-ano than other imaging modalities, it is expensive and not available in many centres. In the present study, we evaluated the usefulness of fistulography and anal endosonography (AES), which are less expensive and easily affordable. Fistulography identified the primary track in all 50 patients and the secondary extensions in three patients, out of which two were confirmed by surgery and one was a false positive finding. This false positivity could due to long time interval between fistulography and surgery with probable spontaneous healing. The sensitivity of fistulography in detecting the secondary extension was 66.7% as compared to 56% reported by Kuijpers et al . Iwasman et al  reported a sensitivity of 89% in outlining the fistulous track using Fistulography as compared to 100% in our study. Kuijpers et al  showed that the internal opening could be detected in only 24% of patients. In contrast, our study identified the internal opening in 22 patients with a sensitivity of 50% and a specificity of 83.3%.
Deen et al  using AES identified the primary fistulous tracks with an accuracy of 100% whereas Law et al  found that accuracy was only 83.3%; however, accuracy of 98% was recorded in our study with one false negative result which was due to a very low position of the fistulous track Lunnis et al  evaluated the role of AES and found positive predictive value of 42.9% in identifying supra-levator extensions and 50% for ischiorectal extensions. They concluded that MRI was significantly more accurate than AES in identifying secondary extensions. We were able to identify the secondary extensions in all the cases by AES. Law et al  reported a sensitivity of 66.7% in detection of the internal opening using AES which was comparable to the sensitivity of our study (76%). The detection of an abscess cavity was not satisfactory in the present study. It was lower than that reported by Law et al.
Horse-shoeing of the track was detected in one patient using AES and was confirmed during surgery. Similarly, Law et al  reported 100% accuracy in detecting horse-shoeing whereas in a study by Deen et al the accuracy was 90.9%.
Identification of the fistulous tracks and internal opening was found to be easier after instillation of hydrogen peroxide into the fistulous track and the time taken for evaluation was much less. In our study, hydrogen peroxide was instilled into the fistula during AES in a subgroup of 20 patients and in all these cases the fistulous tracks were correctly identified. Previously visualized, hypoechoic fistulous track and abscess cavity will appear brilliantly hyperechoic after injection of hydrogen peroxide [Figure - 5]. Cheong et al  have concluded that hydrogen peroxide enhancement of the fistulous track is a simple, effective and safe method of improving the accuracy of AES assessment of recurrent anal fistula.
The accuracy of AES in detecting superficial tracks were 90%. Both patients with extrasphincteric tracks were identified with an accuracy of 100%. The AES detected intersphincteric and transsphincteric tracks with an accuracy of 90% and 96% respectively [Table - 1].
The results of fistulography and AES in detection of primary tracks, secondary extension and abscess were almost similar, whereas for the identification of internal opening, AES was more accurate than fistulography (76% vs 54%). AES and fistulography individually had low sensitivity for the detection of the abscess (45.15% vs. 30.76%) and the internal opening (72.7% vs. 50%). However, together they had a considerably higher sensitivity (Abscess 61.54%, internal opening 86.36%) [Table - 2].
Thus, we conclude that fistulography and AES are useful adjuncts to clinical examination (preoperative assessment) of fistula-in-ano and an injection of hydrogen peroxide into the fistulous track improves the accuracy of AES.
| References|| |
|1.||Parks A.G, Gorden P.H, Hardcastle J.D. A classification of fistula-in-ano. Br J Surg. 1976; 63: 1-12. |
|2.||Weisman R.I. orsay C.P, Pearl R.K, Abcarian H. The role of fistulography in fistula-in-ano. Dis Colon Rectum 1991; 34: 181-184. |
|3.||Kuijpers H.C, Schulpen T. Fistulography for fistulo-in-ano. Dis Colon Rectum 1985; 28: 103-104. |
|4.||Law P.J, Talbot R.W, Bartram C.I, Northover, J.M.A. Anal Endosonography in the evaluation of perianal sepsis and fistula-in-ano. Br J Surg 1989; 76: 752-755. |
|5.||Law P.J, Bartram C.I. Anal Endosonography: Technique and normal anatomy. Gastrointestinal Radio 1989; 14: 349-535. |
|6.||Choen S, Burnet S, Bartram C.I, et al. Comparison between anal endosonography and digital examination in the evaluation of anal fistulae. Br J Surg 1991; 78: 445-447. |
|7.||Shahid M. Hussain, Stoker J, Schouter W.R, Win C.J. Hop, Lameris J.S. Fistula-in-ano: Endoanal sonography versus Endoanal MR Imaging in classification. Radiology 1996; 200: 475-481. |
|8.||Halligan. Review Imaging Fistula-in-ano. Clinical Radio 1998; 53: 85-95. |
|9.||Deen K.I, Williams J.G, Hutchinson R et al. Fistula-in-ano: endoanal ultrasonographic assessment assists decision making for surgery. Gut 1994; 35: 391-394. |
|10.||Lunnis P.J, Basker P.G, Sultan A.H. et al. Magnetic Resonance imaging og fistula-in-ano. Dis Colon Rectum 1994; 37: 708-718. |
|11.||Cheong D.M.O, Nogueras JJ, Wexner SD, Jagelman D.G. Anal Endosonography for recurrent anal fistulas: Image enhancement with hydrogen peroxide. Dis Colon Rectum 1993; 36: 1158-1160. |
Dept of Radiodiagnosis, Jawaharlal Institute of Postgraduate Medical Education and Research, Pondicherry 605 006
Source of Support: None, Conflict of Interest: None
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5]
[Table - 1], [Table - 2]