Mid rectal cancer with possible peritoneal involvement. Discussion of the anterior peritoneal reflection.
Findings:
There is a 4 cm long neoplasm at the rectosigmoid junction.
The distal end of the mass is 7 cm from the ano-rectal junction.
Anteriorly and inferiorly there is 1 cm of transmural extension into the fat along the undersurface of the bowel,superior to the seminal vesicles.
Anteriorly there is linear low signal which extends to and tents the anterior peritoneal reflection.
There are scattered sub-5 mm mesorectal nodes which do not meet criteria for pathologic involvement. There is a 5mm tumor implant in the mesorectal fat on the left.
Bilateral external iliac chain lymph nodes are not enlarged by size criteria.
There is evidence of extramural macroscopic vascular invasion.
Normal marrow signal.
Impression:
T3c vs T4a, MRF-, N1, EMVI+, 4cm mid rectal neoplasm. Linear low signal extends from the tumor to the anterior peritoneal reflection resulting in tenting of the anterior peritoneal reflection. No evidence of invasion through the peritoneal reflection.
Step 1: Size and location.
The tumor is easy to see on the sagittal images (1 remove annotations). The distal margin is 7 cm from the anorectal junction as defined by the anterior aspect of the levator on the sagittal images (2 remove annotations). I've annotated these landmarks on the prior 7 cases so if you need a refresher please review cases 1-6.
A distal margin 5-10 cm from the anorectal junction is a mid rectal cancer.
Step 2: Depth of invasion
There is direct extension of tumor into the mesorectal fat (4 remove annotations) over a distance of 1 cm. This soft tissue appears solid and restricts diffusion (5 remove annotations). It also enhances (image not provided but you can find it).
By contrast, this tissue is thin and linear (6 remove annotations). It does not diffusion restrict (7 remove annotations) but there is mild enhancement (image not provided but you can find it). Is the desmoplastic reaction or tumor? I generally err on the side of calling it tumor. In this case it does not matter since there is obvious T3c (extension of 5-15mm into the mesorectal fat) elsewhere.
Step 3: Mesorectal fascia
This is a good case for evaluating the anatomy. On the midline sagittal image this (yellow line in 3, remove annotations) is the peritoneal reflection. You can see the reflection swinging laterally around the mid and upper rectum on paramidline images (yellow lines in 12 and 13 remove annotations). It can also be seen in the coronal plane (yellow line in 14 remove annotations).
What is this line (red arrow in 15 remove annotations)? I have trouble with this. I've been told it is the peritoneal reflection extending to the rectum but I don't think it can be this since then there would not be a dissection plane that leads directly into the anterior mesorectal fascia. However, this line is present in almost all cases. Above this line is the anterior peritoneal reflection. Below this line is the anterior mesorectal fascia. It is generally located higher in men, where it originates from the seminal vesicle, than in women, where it originates from the posterior aspect of the cervix.
Some surgeons use this line as the margin between the lower and mid rectum. The high rectum would be above the S2/3 level where the posterior aspect of the rectum becomes intraperitoneal. In this case the mid rectum would be almost non-existent because this anterior reflection is at the S2/3 level. Note that these definitions are different than the 0-5cm, 5-10 cm, and 10-15cm "definitions" that are used radiologically.
The red arrow on this image (9 remove annotations) shows tenting of the anterior peritoneal reflection. Cross reference on the sagittal images to confirm that this is above the level of the anterior peritoneal reflection and that the structure being tented is therefore not the mesorectal fascia.
Is this tumor or desmoplastic reaction? Very hard to tell. Involvement of the peritoneal reflection is T4a disease.
You can also see this on the coronal images (16 remove annotations)
There is no tumor within 1mm of the mesorectal facsia, so MRF- disease.
Step 4: Adenopathy
There are scattered sub 5mm nodes in the mesorectal fascia and sigmoid mesocolon, but none were round, heterogeneous, and indistinct. So I called N0 disease.
I thought this was a tumor implant as opposed to a node (red arrow in 10, remove annotations) because it had a vessel running into it (yellow arrow in 10, remove annotations)
Step 5: Macroscopic vascular invasion
This vessel (red arrow in 11, remove annotations) is too thick and high signal. So EMVI+.
Step 6: Incidental findings
None.
We had a difficult time determining if this was T3c disease with desmoplastic reaction to the anterior peritoneal reflection or T4a disease.
Our surgeon thought that even if this was T4a disease that he could get a clean margin because the peritoneum was just tented by thin linear soft tissue and if there was tumor there he would cut a wider margin. Remember, the purpose of neoadjuvant chemo-radiation is to increase the chances of obtaining clean surgical margins.
This patient therefore went directly to a lower anterior resection. Your surgeon may feel differently in which case neoadjuvant therapy would be indicated.
Histology showed T3c disease. One of 28 sampled nodes was positive for N1 disease. Do you even see 28 nodes on the MRI? Re-review of the images still did not show any nodes meeting pathologic criteria. This will happen. The suspected implant (10, remove annotations) was considered an implant and not a node.
There was extramural venous invasion.