Low rectal cancer
Findings:
There is a 4 cm, low rectal tumor filling the lumen of the rectum with distal margin 3cm from the ano-rectal junction and 7cm from the anal verge.
Tumor does not infiltrate into the meso-rectal fat.
There is no tumor within 1mm of the mesorectal fascia or levator ani.
No pathologic mesorectal or extra-mesorectal adenopathy.
Impression:
T2 MRF- N0 low rectal cancer with distal margin 3 cm from the ano-rectal junction.
Step 1: Size and location
The long axis of the tumor (1 remove annotations) is almost situated in the axial plane.
The images marked "Coronal" are actually axial images through the tumor in that they are perpendicular to the lumen of the bowel at he location of the tumor.
These will be the best images for determining the T stage.
The images marked "Axial" are perpendicular to the rectum disal to the tumor.
I could have re-named these appropriately but your techs may not always get the angles correct, so its important to be able to orient yourself regardless of how the series are labeled.
I don't think the techs actually knew where the tumor was in this case and this will happen a lot.
Cross referencing the images marked Coronal and Axial with the sagittal images, the distal most portion of the tumor is located here (3 remove annotations).
Because this is not adjacent to the estimated location of the ano-rectal junction, the images parallel to the anus will not be useful.
For example, look at the distal margin of the tumor on the "Coronal" images (4 remove annotations). It looks like the distal end of the tumor is right at the location where the levator ani contacts the anus. However, this plane is oblique to both the anus and the tumor and cannot be relied upon to measure the distance between the two.
On the post contrast images reformatted parallel to the anus, there is no tumor near the ano rectal junction, defined as the area where the levator ani parallels the inernal sphincter (blue arrows in 5 remove annotations).
Scroll through this sequence to see how the level where the levator joins the internal sphincter does not change from image to image.
When the tumor is not adjacent to the ano-rectal junction use the sagittal images to measure this distance and use the level of anterior aspect of the levator plate to define the ano-rectal junction (dashed line in 6 remove annotations).
The distance from the inferior aspect of the tumor to this line is 3 cm (7 remove annotations)
Step 2: Depth of invasion.
There are no areas where tumor extends through the rectal wall into the mesorectal fat.
The low signal rectal wall is intact throughout (9 remove annotations). This is T2 disease.
Remember that MRI does not distinguish T1 from T2 disease.
Step 3: Mesorectal fascia
No tumor comes to within 1mm of the mesorectal fascia (10 remove annotations), which is expected in T2 disease since there is not tumor growth through the wall of the bowel.
The rectum contacts the levator ani in places, but the tumor is not transmural at these location (11 remove annotations). The images perpendicular to the lower rectum are best for evaluating the mesorectal fascia.
Step 4: Adenopathy
There are multiple sub 5 mm nodes in the mesorectal fat, but none are round, heterogeneous, AND with irregular margins.
Therefore, no pathologic nodes.
I think that determining if a sub 5 mm node is irregular AND round is difficult, and if you wanted to call this N1 I think you would be justified.
There were no extra-mesorectal nodes with short axis diameter > 1 cm.
Step 5: Extramural vasular invasion.
None.
Step 6: Incidental findings
This patient proceeded to a lower anterior resection following short course of radiation as there was debate as to N0 vs N1.
There was no transmural spread of disease. There was 1.8mm of neoplasm in a single node.
The post-op staging was T2 MRF- N1