Ahmed-Emad Mahfouz MD, Presenter: Nothing to Disclose

Hanan Sherif MD, Abstract Co-Author: Nothing to Disclose

To evaluate the presence of susceptibility artifact within fistulous tracts or sinuses near the anal canal on MR imaging as a sign for differentiation of pilonidal sinus and anal fistula

Thirty two patients with anal fistula and 20 patients with pilonidal sinus were examined by identical protocol of MR imaging including identical transverse 3-mm slices of the anal region using the following sequences: T1-weighted spin-echo (TR/TE 450/15 ms), short TI inversion recovery (TI/TR/TE 150/4500/30 ms) and fat-saturated T1-weighted GRE images (TR/TE/Flip angle (170 ms/4.5 ms/70º) before and after intravenous injection of Gd-DTPA). Differences were analysed by the Chi square test.

Susceptibility artifacts were detected within the sinuses or fistulae close to the anal canal in 14 out of 20 patients with pilonidal sinuses and in none of the patients with anal fistula (p<.001). The susceptibility artifact appeared as extremely dark spot on the fat-saturated T1-weighted GRE images which was not seen or was less obvious on the corresponding T1-weighted SE images. The surgically excised pilonidal sinuses showed foreign body granulomatous reaction and variable amount of hair within the sinuses in all the 20 cases. The susceptibility artifact sign had a positive predictive value of 100%, negative predictive value of 84%, sensitivity of 70%, specificity of 100% and accuracy of 88% for the diagnosis of pilonidal sinus.

Susceptibility artifact are seen in 70% of pilonidal sinuses and none of anal fistulae. They are probably caused by small balls of hair within the sinuses. This new sign may be hepful in diferentation between pilonidal sius and anal fistula.

Mahfouz, A, Sherif, H, Susceptibility Artifact within Fistulous Tracts or Sinuses Near the Anal Canal: New Sign for Differentiation of Pilonidal Sinus and Anal Fistula on MR Imaging.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4419341.html