[MRI of extraperitoneal rectal carcinoma].

Last years technological developments in imaging field have made a substantial contribution to diagnosis and staging of rectal cancer. Endorectal ultrasound and MRI with endorectal coil are very useful in rectal cancer initial staging thanks to their ability to distinguish between the rectal wall layers. Major ultrasound limitations are presence of inflammations, desmoplastic reaction and small field of view which limits evaluation of perirectal invasion. MRI with phased-array coils, instead, allows depiction of mesorectum and to assess the distance between tumor and mesorectal fascia. Unfortunately CT shows low accuracy compared to MRI in local staging because it fails to distinguish the rectal wall layers. The criterion used in assessing nodal involvement remains unfortunately still the dimensional one even if new contrast media based on nano-iron particles look promising in this regard On reassessment after chemo-radiotherapy treatment, MRI proved to be a very accurate tool thanks to its ability to detect tumor downstaging, disappearance of mesorectal fascia infiltration or even to show a complete response. The presence of recurrence can be studied by contrast enhanced perfusion-MRI or with good accuracy using PET which, however, presents major technical limitations at present.