What is an AP resection? How is it different from an anterior resection? Why are there so many names?
An AP resection stands for an abdominoperineal resection.
Let’s break it down:
Abdominoperineal resection = abdomino (abdominal) + perineal (of the perineum – the saddle region which extends from the external genitalia to the anus) + resection (surgical removal).
Putting it together, it means you cut out the portion of bowel that sits inside the abdomen and connects to the perineum. And yes, you do cut out the anus and sew it back up again. The indications for this procedure comprise the following:
1. Carcinoma (i.e. malignant cancer) of the distal (lower) 1/3rd of the rectum
2. Carcinoma of the anus which has not responded to chemotherapy (the usual, definitive first line management of anal cancer)
Broadly speaking, a run through of this procedure would look something like this:
1. Identify the sigmoid colon. Simply put, find the bit of bowel with taeniae coli on it (easily and quickly allows you to differentiate large bowel from small bowel) and follow it down to the left iliac fossa (LIF).
2. Mobilise the sigmoid colon. This means the sigmoid colon is detached from all it’s attachments, mainly the mesentery (a double layer of visceral peritoneum which connects bowel to bowel and ensheaths the blood supply to the bowel) and peritoneum (intra-abdominal lining composed of a layer of mesothelium and a layer of connective tissue). As this is being done, the inferior mesenteric artery (IMA) is identified and divided (tied off with clips and cut). The ureters can be seen underneath the peritoneum, pulsating when poked. This reaction is referred to as vermiculation (worm-like movement – vermis (Latin) = worm). This is also known as Kelly’s sign. It’s important to identify these as you really don’t want to cut them by mistake!
3. Follow the sigmoid colon into pelvis as it morphs into the rectum. This requires more mobilisation of this section of bowel via detachment from surrounding attachments. Blood vessels to be aware of here are superior rectal artery (SRA) and middle rectal artery MRA, but the SRA is usually taken care of through the division of the IMA. The MRA comes from the internal iliac artery (a branch of the common iliac, which is a final bifurcation of the aorta as it enters the pelvis in preparation to supply the lower limbs). This needs to be identified and divided as the mobilisation continues.
4. The sigmoid colon is then detached from the rest of the descending colon.
5. The penultimate step can take a while if the rectal tissue is fibrosed due to neoadjuvant (pre-operative to shrink tumour) long course chemoradiotherapy. The anus is excised (cut out) from the bottom end, i.e. a circle is literally cut around the anus and reverse dissection takes place working backwards from the bottom up. Ideally, this occurs in concurrence with the final stages of step 3 and requires 2 surgeons, one for the intra-abdominal part, and another to scrub in for the bottom part. The surgeons meet in the middle of the rectum, and then remove the entire colorectal specimen out of the abdominal cavity through the anal canal.
6. Finally, the anus is sutured and the remaining end of bowel is brought out of the abdominal cavity onto the abdominal wall to form a stoma.
So how is it different from an anterior resection?
Well, an anterior resection is also indicated for low rectal tumours, but the location of the tumour and whether it involves the anal sphincter is important. If the tumour is between 4-16cm from the anal verge and doesn’t involve the anal sphincter, an anterior resection is a better option. If the tumour is any lower or resection of the tumour will require the sphincter to also be excised in order to obtain good tumour margins, then an AP resection is a more appropriate choice.
Most crucially, an anterior resection does not involve the formation of a stoma. Instead, an anastamosis (reconnection) between the remaining end of resected bowel and the anorectal segment is performed. This resumes continuity of the bowel, thereby precluding the need for a bowel reroute.
Here’s a tip for navigating the often confusing nomenclature and terminology. Break down the name into small chunks and understand the components. Then put it all together to understand what the named procedure entails.
Ok, so for example: sigmoidcolectomy.
Sigmoid = sigmoid colon (sigmoid = “S” shaped)
Col– = colon
Ectomy = removal of something from the body
So a sigmoid colectomy = removal of sigmoid colon from the body.
Easy. And perhaps quite obvious for most, but I struggled with the myriad names for these procedures so here’s what helped me at least!
So there we have it, an AP resection in it’s full gory glory. Definitely not for the faint hearted (quite literally; the anaesthetist will never forgive you).
Vasudev Zaver 