Low rectal cancer
Findings:
There is a 5.5 cm long, circumferential, low rectal cancer with distal margin located at the level of the ano-rectal junction / proximal extent of the external sphincter. No undermining of the anal mucosa or involvement of the sphincters.
There is 2-3 mm of spread of tumor into the mesorectal fat along the anterior aspect of the proximal tumor.
The anterior wall of the rectum is discontiuous along the mid-portion of the tumor and tumor contacts the anterior MRF at the level of the base of the prostate.
There are multiple sub 5mm nodes in the mesorectal fat; only 1 meets criteria for a pathologic node. No extra-mesorectal nodes.
No macroscopic extramural vascular invasion.
Impression
T3b, MRF+, N1 low rectal neoplasm with distal extent at the ano-rectal junction.
Step 1: Size and location of the tumor.
The surgeon told us this was a mid rectal tumor but I see the tumor in the lower rectum.
Here are the top (1 remove annotations) and bottom (2 remove annotations) of the tumor on the axial images. Here is the tumor on the coronal images (3 remove annotations).
The tumor measures 5.5 cm in length (4 remove annotations) and is near circumferential.
On the prior cases I measured the tumor on the sagittal images and on this case I measured the length on the coronal images. Why? I measure the length on the image where I think I can see the top and bottom aspects the best. Sometimes this will be the sagittal images and sometimes the coronal.
Since the coronal images are double obliqued to the axial and sagittal ones, the tumor is often laid out best in this plane.
Cross referencing the axial and coronal images to the sagittal images, the lowest extent of the tumor (red arrow in 5 remove annotations) is just above the level of the ano-rectal junction on the sagittal images. (dotted blue line in 5 remove annotations).
How do you cross reference? Find the bottom of the tumor on the axial images and note the level of the axial plane on the sagittal images (cross reference lines must be on).
Then find the bottom of the tumor on the coronal images and note the level of the coronal plane on the sagittal images.
Where these two planes intersect on the sagittal image is the bottom most extent of the tumor.
Since this is near the level of the external sphincter complex we need to make sure we look at the images obtained parallel to the anal canal.
On these images the inferior tip of the tumor (red arrows in 6 remove annotations and 7 remove annotations) is just at the level of the proximal-most external sphincter, defined as the level where the levator ani begins to parallel the anal canal (blue arrows in 6 remove annotations and 7 remove annotations).
There is no undermining of the anal mucosa and no invasion of the sphincters.
Step 2: Depth of invsasion
Anteriorly there are tendrils of low signal soft tissue extending from the tumor into the fat (arrows in 8 remove annotations). It can be difficult to distinguish desmoplastic reaction from linear transmural extent of tumor. However, on pre-treatment imaging, I generally undercall desmoplastic reaction and overcall tumor extent. I measure just over 3mm of tumor extending into the fat, which is T3b disease.
Step 3: Mesorectal fascia.
At the site of the tumor in the mesorectal fat, the tumor remains > 1mm from the mesorectal fascia (yellow line in 9 remove annotations).
More inferiorly, the anterior wall of the rectum is discontiuous (10 remove annotations) and tumor contacts the anterior aspect of the mesorectal fascia (11 remove annotations). So this is MRF+ disease.
Posteriorly the rectum contacts the levator but the tumor is not transmural at this site.
Step 4: Adenopathy.
There are multiple nodes in the mesorectal fat which measure less than 5 mm. They are all round and heterogeneous, but nodes less than 5mm need three malignant criteria. One of the nodes I thought was round, heterogeneous, and had a slightly irregular margin (12 remove annotations). It is not within 1 mm of the mesorectal fascia (13 remove annotations). One node with malignant features is N1 disease. I think if you called this N0 disease that would be defendable. There were no extra-mesorectal nodes larger than 1 cm in short axis diameter.
Step 5: Macroscopic extramural vascular invasion.
I do not see any evidence macroscopic extramural vascular invasion.
Step 6: Incidental findings.
None seen.
On rectal exam the surgeon felt he could push the tumor up into the rectum. So while the distal end was at the ano-rectal junction, this was just the tumor prolapsing inferiorly (as opposed to growing inferiorly). I've noticed that if a tumor is at the ano-rectal junction OR it extends for a small distance into the anal canal, if the surgeon can push the tumor back into the rectum they will often attempt a sphincter sparing surgery.
This patient underwent neoadjuvant chemotherapy and long course of radiation therapy.
Followup endoscopy showed significant regression of tumor size with the distal end now being located 15mm proximal to the ano-rectal junction.
Repeat imaging showed the distal tumor no longer contacted the MRF.
Based on imaging, endoscopy, and physical exam, the surgeon thinks he will have enough space to perform an ultra-low lower anterior resection with hand sewn anastomosis at the sphincter which will result in a sphincter sparing surgery and eliminate the need for a permanent colostomy.
Generally, surgeons like to have a 5cm margin on their LAR specimens, but if they think they can successfully remove the tumor and spare the anus, they will often attempt to do so.