High rectal cancer with questionable mesorectal fascia involvement,
Findings:
There is a 2 x 1.6 x 1.0 cm mass extending from the right lateral wall of the proximal rectum. The distal aspect of the tumor is located 11 cm from the anorectal junction.
There is a 1 cm wide band shaped region of desmoplastic reaction versus linear tumour extension extending counterclockwise from the 1:00 position to the 6:00 position on the axial images.
The right posterior lateral aspect of the mesorectal fascia is tented inward
along the proximal aspect of the neoplasm. On the sagittal images this level corresponds to the level of the junction of the third and fourth sacral segments; this is therefore thought to represent involvement of the posterior mesorectal fascia.
There are scattered sub-5 mm lymph nodes within the mesorectal fat and there are also sub-5 mm lymph nodes along the bilateral pelvic sidewalls. None meet shape and morphology criteria for pathologic involvement. No common iliac chain adenopathy.
No macroscopic venous invasion.
The tumour is remote from the anal sphincter.
Incidental note is made of a small utricle cyst in the midline prostate.
Impression:
T3c MRF+ N0 EMVI- high rectal cancer.
Linear low signal in the mesorectal fascia tents the right posterior MRF.
Step 1: Size and location.
The tumor (1 remove annotations) is well seen on the sagittal images 11 cm (2 remove annotations) from the anorectal junction as defined by the anterior most aspect of the levator plate.
Step 2: Depth of invasion
Along the right lateral aspect of the tumor there is a band of vague low T2 signal (5 remove annotations) and linear low T2 signal (6 remove annotations). These areas are subtly bright on the diffusion weighted images, but not as bright as the tumor. Desmoplastic reaction vs tumor? I always err on the side of tumor. 1cm of invasion is T3c disease.
Step 3: Mesorectal fascia
Where is this tumor in relation to the mesorectal fascia and peritoneal reflection. This sagittal image shows the location of the anterior peritoneal reflection (yellow line in 3, remove annotations). Anteriorly and above this line is anterior peritoneal reflection. Anteriorly and below this line is mesorectal fascia. Anteriorly there is no disease touching the peritoneal reflection.
What about posteriorly? The tumor is predominantly anterior to the S3 segment of the sacrum. At this level the posterior resection margin is the retroperitoneal plane of the mesorectal fascia.
On this axial slice (4 remove annotations) through the mid tumor, the thicker red line should represent peritoneal reflection and the thinner yellow line should represent mesorectal fascia.
Along the proximal aspect of the tumor there is linear low signal that tents the posterior resection margin (red arrow in 7, remove annotations). At this level (8, remove annotations), the thicker red line is peritoneal reflection and the thinner yellow line is mesorectal fascia. As I err on the side of overstaging, this is tumor involving the mesorectal fascia but not going through the mesorectal fascia. Therefore MRF+ disease.
Step 4: Adenopathy
I did not see any nodes with features of malignancy.
Step 5: Macroscopic vascular invasion
I did not see evidence of this.
Step 6: Incidental findings
None.
Another complex case.
The initial biopsy of this mass suggested T3 disease as the tumor infiltrated into the muscular layer of the rectum. So we were all ready to accept that the MRI showed T3c disease even if the vague and linear low T2 signal was a bit odd looking.
The approach to the linear tenting of the posterior mesorectal fascia was similar to that of the tenting of the peritoneal reflection in case 7. Our surgeon felt that he could obtain a positive margin posteriorly if there was simply tenting of the fascia. The MRI did not show abnormal signal in the presacral fat so he was reassured. Some surgeons may not be comfortable doing this. Of note, our surgeon is more comfortable taking a bit extra tissue posteriorly than he is laterally. So he is more aggressive if the tenting is anterior (into peritoneal reflection) or posterior (involving the posterior mesorectal fascia) than if it is lateral (involving the lateral mesorectal fascia).
This patient proceeded directly to a low anterior resection. The findings in the mesorectal fat represented fat necrosis and on sectioning the tumor did not invade through the rectal wall. There was no pathologic adenopathy and there were clear surgical margins.
Surgical staging was T2 MRF- N0.
A slightly more aggressive surgical approach saved this patient neoadjuvant and adjuvant chemotherapy.
In several cases now we have seen linear low signal tenting a resection margin representing desmoplastic reaction and not tumor. However, rather than ignoring this finding, I discuss it with our surgeon and document it in my report so he understands exactly what I am thinking. This allows him to make a decision as to if he can obtain clear margins. It takes some time to generate this relationship with the surgeon.