OBJECTIVETo investigate magnetic resonance imaging(MRI) manifestations of perianal abscess and to evaluate MRI diagnosis for perianal abscess.

METHODSFifty cases of perianal abscess between July 2007 and March 2009 were included in this study. MRI was performed using T1 weighted sequence in axial plane, T2 weighted sequence with fat saturation in axial, coronal and/or sagittal plane, and T1 weighted enhanced sequence with fat saturation in axial, coronal and/or sagittal plane. The location, size, shape, signal characteristics, and enhancement patterns of perianal abscess were analyzed.

RESULTSFifty cases with 51 perianal abscesses were identified. The abscess appeared slight hypo- or isointense signal on T1 weighted imaging, obviously hyperintense signal at cavity and isointense signal at wall on T2 weighted with fat saturation imaging, and marked enhancement at wall. The largest diameters ranged between 0.5 cm and 9.0 cm (mean 3.4±1.7 cm ) in abscess, between 0.2 cm and 8.0 cm(mean 2.7±1.7 cm) in cavity. The abscess was round, oblong and crescent in 23, 18 and 7 cases respectively, and was unilocular in 41 cases and multilocular in 10 cases. The abscess located between levator ani and intersphincteric groove in 23 cases, under intersphincteric groove in 3 cases, across levator ani and intersphincteric groove in one case, on levator ani in 7 cases, on intersphincteric groove in 16 cases and above levator ani in one case.

CONCLUSIONMRI is a noninvasive, convenient and highly accurate procedure for diagnosing perianal abscess, which can demonstrate the anatomical relationship between abscess and anal canal.