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The role of imaging tests in the evaluation of anal abscesses and fistulas

David A Schwartz, MD
Maurits J Wiersema, MD
Section Editor
J Thomas Lamont, MD
Deputy Editor
Shilpa Grover, MD, MPH, AGAF


Perianal fistulas and abscesses are among the most serious manifestations of Crohn disease and non-Crohn related anorectal disease (picture 1 and picture 2). Complications can lead to difficulties with recurrent or non-healing fistulas or abscesses. In addition, these patients are at risk of incontinence as a result of the destructive nature of the fistulizing process and/or inadvertent damage to the anal sphincters during surgical exploration.

The lifetime risk for developing a fistula in patients with Crohn disease is 20 to 40 percent [1-4]. The frequency of perianal fistulas/abscesses in patients without Crohn disease has not been well established, but in a telephone survey of 102 randomly selected individuals, 20 percent of the individuals contacted had perianal symptoms (hemorrhoids, fistulas, etc) [5]. Despite the significant prevalence of perianal disease, the evaluation of this problem was, in the past, largely limited to digital rectal examination.

The inability of the clinician to directly visualize the fistula or abscess makes it difficult to assess the lesions. The clinician must essentially discern the perianal anatomy by touch. This task is made even more problematic by the induration and inflammation that is usually present in these patients. Even surgical evaluation is only 35 to 85 percent accurate when compared with the results of other diagnostic tests and clinical evaluation [6-9].

The importance of accurately characterizing the perianal process prior to embarking on therapy cannot be overemphasized. The risk of incomplete healing, a recurrent fistula, or even inadvertent sphincter injury is increased if fistula anatomy is incorrectly delineated or an occult abscess missed. An imaging modality should ideally provide a virtual road map that the clinician can use to plan therapy. This is especially true with fistulas that involve a significant portion of the anal sphincter complex. Such patients are at the greatest risk of developing incontinence from the destructive fistulizing process or from overly aggressive surgical treatment.

Thus, patients with simple fistulas that only involve a small portion or none of the external anal sphincter generally do well with either medical or surgical treatment. Imaging of the fistula is helpful in determining the type of fistula to guide treatment but is not always needed. By contrast, for patients with a complex fistula (ie, one that involves a significant portion of the sphincter complex), preoperative imaging is mandatory.

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Literature review current through: Nov 2017. | This topic last updated: Sep 14, 2017.
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  1. Hellers G, Bergstrand O, Ewerth S, Holmström B. Occurrence and outcome after primary treatment of anal fistulae in Crohn's disease. Gut 1980; 21:525.
  2. Farmer RG, Hawk WA, Turnbull RB Jr. Clinical patterns in Crohn's disease: a statistical study of 615 cases. Gastroenterology 1975; 68:627.
  3. Rankin GB, Watts HD, Melnyk CS, Kelley ML Jr. National Cooperative Crohn's Disease Study: extraintestinal manifestations and perianal complications. Gastroenterology 1979; 77:914.
  4. Schwartz D, Loftus E, Tremaine W, et al. The natural history of fistulizing Crohn's disease: a population based study. Gastroenterology 2000; 118:A337.
  5. Nelson RL, Abcarian H, Davis FG, Persky V. Prevalence of benign anorectal disease in a randomly selected population. Dis Colon Rectum 1995; 38:341.
  6. Choen S, Burnett S, Bartram CI, Nicholls RJ. Comparison between anal endosonography and digital examination in the evaluation of anal fistulae. Br J Surg 1991; 78:445.
  7. Spencer JA, Chapple K, Wilson D, et al. Outcome after surgery for perianal fistula: predictive value of MR imaging. AJR Am J Roentgenol 1998; 171:403.
  8. Van Beers B, Grandin C, Kartheuser A, et al. MRI of complicated anal fistulae: comparison with digital examination. J Comput Assist Tomogr 1994; 18:87.
  9. Chapple KS, Spencer JA, Windsor AC, et al. Prognostic value of magnetic resonance imaging in the management of fistula-in-ano. Dis Colon Rectum 2000; 43:511.
  10. Kuijpers HC, Schulpen T. Fistulography for fistula-in-ano. Is it useful? Dis Colon Rectum 1985; 28:103.
  11. Fishman EK, Wolf EJ, Jones B, et al. CT evaluation of Crohn's disease: effect on patient management. AJR Am J Roentgenol 1987; 148:537.
  12. Goldberg HI, Gore RM, Margulis AR, et al. Computed tomography in the evaluation of Crohn disease. AJR Am J Roentgenol 1983; 140:277.
  13. Berliner L, Redmond P, Purow E, et al. Computed tomography in Crohn's disease. Am J Gastroenterol 1982; 77:548.
  14. Kerber GW, Greenberg M, Rubin JM. Computed tomography evaluation of local and extraintestinal complications of Crohn's disease. Gastrointest Radiol 1984; 9:143.
  15. Yousem DM, Fishman EK, Jones B. Crohn disease: perirectal and perianal findings at CT. Radiology 1988; 167:331.
  16. Guillaumin E, Jeffrey RB Jr, Shea WJ, et al. Perirectal inflammatory disease: CT findings. Radiology 1986; 161:153.
  17. Schratter-Sehn AU, Lochs H, Vogelsang H, et al. Endoscopic ultrasonography versus computed tomography in the differential diagnosis of perianorectal complications in Crohn's disease. Endoscopy 1993; 25:582.
  18. Scholefield JH, Berry DP, Armitage NC, Wastie ML. Magnetic resonance imaging in the management of fistula in ano. Int J Colorectal Dis 1997; 12:276.
  19. Buchanan GN, Halligan S, Williams AB, et al. Magnetic resonance imaging for primary fistula in ano. Br J Surg 2003; 90:877.
  20. Lunniss PJ, Barker PG, Sultan AH, et al. Magnetic resonance imaging of fistula-in-ano. Dis Colon Rectum 1994; 37:708.
  21. Beckingham IJ, Spencer JA, Ward J, et al. Prospective evaluation of dynamic contrast enhanced magnetic resonance imaging in the evaluation of fistula in ano. Br J Surg 1996; 83:1396.
  22. Koelbel G, Schmiedl U, Majer MC, et al. Diagnosis of fistulae and sinus tracts in patients with Crohn disease: value of MR imaging. AJR Am J Roentgenol 1989; 152:999.
  23. Skalej M, Makowiec F, Weinlich M, et al. [Magnetic resonance imaging in perianal Crohn's disease]. Dtsch Med Wochenschr 1993; 118:1791.
  24. Makowiec F, Laniado M, Jehle EC, et al. Magnetic resonance imaging in perianal Crohn's disease. Inflamm Bowel Dis 1995; 1:256.
  25. Van Assche G, Vanbeckevoort D, Bielen D, et al. Magnetic resonance imaging of the effects of infliximab on perianal fistulizing Crohn's disease. Am J Gastroenterol 2003; 98:332.
  26. Bell SJ, Halligan S, Windsor AC, et al. Response of fistulating Crohn's disease to infliximab treatment assessed by magnetic resonance imaging. Aliment Pharmacol Ther 2003; 17:387.
  27. Karmiris K, Bielen D, Vanbeckevoort D, et al. Long-term monitoring of infliximab therapy for perianal fistulizing Crohn's disease by using magnetic resonance imaging. Clin Gastroenterol Hepatol 2011; 9:130.
  28. Rasul I, Wilson SR, MacRae H, et al. Clinical and radiological responses after infliximab treatment for perianal fistulizing Crohn's disease. Am J Gastroenterol 2004; 99:82.
  29. Ziech ML, Lavini C, Bipat S, et al. Dynamic contrast-enhanced MRI in determining disease activity in perianal fistulizing Crohn disease: a pilot study. AJR Am J Roentgenol 2013; 200:W170.
  30. Deen KI, Williams JG, Hutchinson R, et al. Fistulas in ano: endoanal ultrasonographic assessment assists decision making for surgery. Gut 1994; 35:391.
  31. Law PJ, Talbot RW, Bartram CI, Northover JM. Anal endosonography in the evaluation of perianal sepsis and fistula in ano. Br J Surg 1989; 76:752.
  32. Cheong DM, Nogueras JJ, Wexner SD, Jagelman DG. Anal endosonography for recurrent anal fistulas: image enhancement with hydrogen peroxide. Dis Colon Rectum 1993; 36:1158.
  33. Poen AC, Felt-Bersma RJ, Eijsbouts QA, et al. Hydrogen peroxide-enhanced transanal ultrasound in the assessment of fistula-in-ano. Dis Colon Rectum 1998; 41:1147.
  34. el Mouaaouy A, Tolksdorf A, Starlinger M, Becker HD. [Endoscopic sonography of the anorectum in inflammatory rectal diseases]. Z Gastroenterol 1992; 30:486.
  35. Tio TL, Mulder CJ, Wijers OB, et al. Endosonography of peri-anal and peri-colorectal fistula and/or abscess in Crohn's disease. Gastrointest Endosc 1990; 36:331.
  36. Van Outryve MJ, Pelckmans PA, Michielsen PP, Van Maercke YM. Value of transrectal ultrasonography in Crohn's disease. Gastroenterology 1991; 101:1171.
  37. Solomon MJ. Fistulae and abscesses in symptomatic perianal Crohn's disease. Int J Colorectal Dis 1996; 11:222.
  38. Mulder C, Tio T, Tytgat G. Transrectal ultrasonography in the assessment of perianal fistula and/or abscess in Crohn's disease. Gastroenterology 1988; 94:A313.
  39. Schratter-Sehn AU, Lochs H, Handl-Zeller L, et al. Endosonographic features of the lower pelvic region in Crohn's disease. Am J Gastroenterol 1993; 88:1054.
  40. Spradlin NM, Wise PE, Herline AJ, et al. A randomized prospective trial of endoscopic ultrasound to guide combination medical and surgical treatment for Crohn's perianal fistulas. Am J Gastroenterol 2008; 103:2527.
  41. Hussain SM, Stoker J, Schouten WR, et al. Fistula in ano: endoanal sonography versus endoanal MR imaging in classification. Radiology 1996; 200:475.
  42. Orsoni P, Barthet M, Portier F, et al. Prospective comparison of endosonography, magnetic resonance imaging and surgical findings in anorectal fistula and abscess complicating Crohn's disease. Br J Surg 1999; 86:360.
  43. Schwartz DA, Wiersema MJ, Dudiak KM, et al. A comparison of endoscopic ultrasound, magnetic resonance imaging, and exam under anesthesia for evaluation of Crohn's perianal fistulas. Gastroenterology 2001; 121:1064.
  44. Beets-Tan RG, Beets GL, van der Hoop AG, et al. Preoperative MR imaging of anal fistulas: Does it really help the surgeon? Radiology 2001; 218:75.
  45. Ardizzone S, Maconi G, Colombo E, et al. Perianal fistulae following infliximab treatment: clinical and endosonographic outcome. Inflamm Bowel Dis 2004; 10:91.
  46. van Bodegraven AA, Sloots CE, Felt-Bersma RJ, Meuwissen SG. Endosonographic evidence of persistence of Crohn's disease-associated fistulas after infliximab treatment, irrespective of clinical response. Dis Colon Rectum 2002; 45:39.
  47. Schwartz DA, White CM, Wise PE, Herline AJ. Use of endoscopic ultrasound to guide combination medical and surgical therapy for patients with Crohn's perianal fistulas. Inflamm Bowel Dis 2005; 11:727.
  48. Tozer P, Ng SC, Siddiqui MR, et al. Long-term MRI-guided combined anti-TNF-α and thiopurine therapy for Crohn's perianal fistulas. Inflamm Bowel Dis 2012; 18:1825.
  49. Ng SC, Plamondon S, Gupta A, et al. Prospective evaluation of anti-tumor necrosis factor therapy guided by magnetic resonance imaging for Crohn's perineal fistulas. Am J Gastroenterol 2009; 104:2973.