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STIR coronal image showing hyperintense signal on the right side of the pelvis (arrow) which is seen extending towards the greater sciatic foramen (arrow heads).
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STIR coronal images (Figure 1). Subsequently, dedicated T2W and T1W images were taken for assessment of the pelvis.
T1WI (A) shows a hypointense lesion in the right ischiorectal fossa region (arrow). T2W Fat sat image (B) shows hyperintense signal in the right ischiorectal fossa region with hyperintense signal extending towards the greater sciatic foramen and along the sciatic nerve (arrow head). Multiple tiny hypointense foci seen in both the T1 and T2W fat sat images representing air as confirmed by corresponding axial CT images (C, D). Tiny pockets of air are also seen along the sciatic nerve (C, D).
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A perianal collection with marked T2WI and T1WI hypointensities suggestive of air was noticed (Figure 2). A CT scan of the pelvis confirmed presence of perianal abscess in the right ischiorectal fossa with multiple air pockets (Figures 2, 4), tracking along the right sciatic nerve up to the mid-thigh.
Diffusion weighted image (A) and a corresponding ADC image (B) showing restriction of diffusion in the abscess cavity (arrows).
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Additionally, the diffusion weighted sequence was planned and it revealed areas of restriction within the right perianal collection (Figure 3).
T2 fat sat coronal (A) and corresponding coronal CT image (B) showing hyperintense signal with air pockets along the sciatic nerve (arrows) extending from the pelvis to the thigh. In CT image (B), the arrowhead marks the thickened edematous right levator ani muscle and the asterix (*) marks the ischiorectal fossa abscess.
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A CT scan of the pelvis confirmed presence of perianal abscess in the right ischiorectal fossa with multiple air pockets (Figures 2, 4), tracking along the right sciatic nerve up to the mid-thigh.