Colonoscopic polypectomy
Introduction
- Essentially all mucosally based pedunculated polyps can be removed endoscopically.
- Patients with sessile polyps <2 cm in size can be resected in most cases.
- Many sessile polyps >2 cm in size are also resectable endoscopically depending on their location within the colon.
- As a rule of thumb, it has been suggested that sessile polyps occupying more than one-third of the colon circumference, or involving two haustral folds, are too big for safe endoscopic removal.
Diathermy current
- Electrosurgical or diathermy currents cause heat, thus coagulating local blood vessels. This current is very high frequency and thus produces heat but no shock. This is because there is no time for muscle and nerve membrane depolarisation before the current alternates again and therefore no muscle contraction or afferent nerve impulse (contrast low frequency household currents).
- Modern cardiac pacemakers are unaffected by the relatively low power used for endoscopic electrocautery.
- Monopolar diathermy is used in endoscopy. The principle is the concentration of current at the active electrode (endoscopic accessory) with a small surface area, concentrating the heat at the operative site. The larger return plate (patient plate), which completes the circuit, spreads the current over a wide area so that it is less concentrated and thus produces little heat.
- Types of current- Cutting current have an uninterrupted waveform of relatively low voltage spikes. Coagulation current has intermittent higher voltage spikes with intervening, ‘off periods’, lasting about 80% of the time. Blended current combines both waveforms.
- The principle of polypectomy is to coagulate the core (slow cook) of the polyp stalk, with its vessels, before transection.
- Polypectomy should be performed using coagulation current only at a low power setting (15-25 W). The maximum power setting used should be no more than 30-50W. We use ERBE settings of- coag 30W (forced) and set cut to zero and endocut is turned on. The ‘endo cut’ adjusts output automatically for appropriate heating during snaring.
Snares
The standard large snare is 2.5 cms in diameter and the small snare is 1 cms in diameter. The technique of application is the same irrespective of whether the snare is oval, crescent shaped or hexagonal.
Technique of polypectomy for pedunculated polyps
- Accessories like snare/forceps enter the viewing field at 5’o clock position. So polypectomy will be easier if the polyp is placed in the right lower quadrant of the field of view. A change of patient position may be needed for optimum position of the polyp.
- It is usually best to have the snare fully open, and then to manoeuvre only with the scope controls or shaft, so that the snare is placed over the polyp head almost entirely by manipulation of the scope. It may help to open the snare in the colon beyond the polyp, and then to pull the colonoscope slowly back until the polyp comes into the field of view and into the open loop.
- Ideally the snare should be closed at the mid-portion of the stalk. Initial snare closure should be gentle to ensure it is in the right place (once the wire has cut into polyp tissue it may be difficult to release and reposition it)
- Apply the current continuously for 5-10 seconds at a time, watching for visible whitening. The snare should be closed slowly and simultaneously.
- Piecemeal resection of the head may be performed if the polyp cannot be encircled with the snare, until the residual portion of polyp is small enough to permit encirclement with the snare (piecemeal resection of head is safe as the vessels in the head are much smaller than those in the stalk).
Hot biopsy principles
- Hot biopsy is an effective way of destroying polyps 1-5 mm in size. Polyps over 5mm in diameter are not suitable for hot biopsy removal. Using hot biopsy for larger polyps may cause the current to fan out from the point of contact of the forceps. This will heat tissue at a distance (invisibly) and predispose to the risk of perforation especially in the right colon.
- Principle- The hot biopsy forceps is an electrically insulated forceps through which electrical current flows to direct electrical energy around the tissue held within the jaws. The tissue within the jaw is protected from current flow, so is unheated (unless by thermal conduction resulting from long current application). Hot biopsy thus enables simultaneous cautery of the polyp base while obtaining a biopsy specimen.
- Current- settings are same as for snare polypectomy (usually 15 W coag)
- Technique of hot biopsy:
- Only the apex of the small polyp is grasped in the jaws of the hot biopsy forceps.
- Tent up the polyp onto a pseudo pedicle by withdrawing the forceps slightly (this prevents deep thermal injury to the colon wall)
- Apply coagulation current for a maximum of 2-3 seconds.
- Pull off the biopsy. Even if some of the head is uncoagulated, the basal blood vessels will have been destroyed and it will slough off.
- Ensure that the black insulating plastic of the forceps is visible (so that the metal parts of the jaw is not in contact with the scope) before applying current.
- Safety-
- Right colonic wall is very thin and so hot biopsy is best avoided in the right colon. Polyps 1-5 mm in size may be removed by cold snaring in the right colon. Cold snaring by cheese wiring is safe as small polyps have small nutrient vessels. Minor bleeding occurs, but this always stops in 1-5 minutes. Polyp lifting is not needed when using cold snare.
Sessile polyp
- Endoscopic mucosal resection (EMR) is usually used for removal of sessile polyps particularly in the right colon.
- Injection of fluid into the submucosa beneath the polyp increases the distance between the base of the polyp and the serosa. When current is then applied with a snare, the polyp can be more safely removed because of a large submucosal cushion of fluid. The fluid injected is normal saline or jelofusine with or without adrenaline (1 in 10,000). Some colonoscopists add a few drops of methylene blue to the fluid, the blue showing up the extent of the submucosal bleb. (One commonly used solution- jelofusine 40 ml, 2 ml of 1 in 10000 adrenaline and 0.5 ml of methylene blue). Upto 20-30 mls of the solution may be needed for large sessile polyps.
- Injection technique- Make the first injection proximal to the polyp, so that the raised bleb of tissue does not obscure the view. Subsequent injections are made into the edge of the preceding bleb or directly through the polyp surface (in thin polyps). The plane of separation in the submucosa for successful injection is very superficial. If a bleb is not being raised, withdraw the needle a bit. Failure to lift (non lifting sign) suggests malignancy, the lesion being fixed by invasion into deeper layers.
- Aspiration of air during attempted snare capture of elevated polyp will result in an easier encirclement.
- Complete removal should be attempted at the first endoscopic session because scarring will make subsequent attempts at EMR difficult.
- The basal remnants after most of the polyp has been snared can be safely destroyed by APC.
- The spot should be marked with monospot/India ink because further sessions will be needed to check the site.
- It is permissible to remove a much larger piece with EMR than one would ordinarily resect in the right colon. The pieces should probably be not larger than 2 cms in diameter
Rectal polyps
- Large sessile polyps up to 12 cm from the anal verge are extraperitoneal and may be better removed by local proctological techniques, which produce a single large specimen for optimum histology. A failed endoscopic attempt to remove such rectal polyps makes subsequent removal by the surgeon difficult.
- Sessile polyps more than 12 cms from the anal verge can be removed by transanal microsurgery or TEMS but is more often removed endoscopically
Polypectomy safety principles
- Marking the snare with a pencil or indelible pen at the point that the snare is just closed to the tip of the outer sheath is one of the most important safety factors in polypectomy. It allows the assistant to stop snare closure before the wire closes too far into the tube and there is danger of a smaller stalk being cut off by ‘cheese-wiring’ mechanically without adequate electrocoagulation; it also warns if the stalk is larger than apparent or head tissue or mucosa has become entrapped.
- Large stalks may be injected with adrenaline (1 in 10,000) before snaring to reduce the risk of bleeding. Nylon endoloops or metal clips may also be used for large stalked polyps, particularly in patients on anticoagulants or anti platelet agents. These may be placed before or after polypectomy. However, nylon endoloops are floppy and may be difficult to manoeuvre over a large polyp head. Clips can be applied to smaller stalks before or after polypectomy. However, it is important that the snare does not touch the clip as it may cause a burn to the colon wall.
- Tattooing marks the site of any suspicious or partially removed polyp for follow up or for surgery. 1 ml of India ink injected close to the polypectomy site is sufficient for endoscopic follow up, but four quadrantic injections ensure visibility if surgery is a possibility. The carbon particles of India ink remain in the submucosa for many years (probably for life).
- Only 1:200000 adrenaline is used in the rectum (compared with 1:10000 in colon) because there is a risk of communication to the systemic circulation and danger of cardiac dysrhythmias.
Polyp retrieval
Smaller polyps or fragments up to 6-7mm can aspirated in a polyp trap or more cheaply, onto gauze placed over the suction connector.
Larger specimens may be retrieved using the nylon Roth net or the multi prong grasping forceps or the basket. Roth net is capable of repeated openings and capture of several fragments. Thus, these devices may be able to retrieve up to 3-5 large polyps at a time
Trouble shooting
- Lost polyp after transection- Look for any fluid. The polyp is likely to be there as it is the dependent side of the colon. If no fluid is visible, squirt in some water with a syringe and watch where it flows. If the water refluxes back, the polyp is likely to be distal to the scope and the scope will need to be withdrawn to find the polyp.
- Snare loop is stuck in the wrong position- the snare loop can be released by lifting it up over the polyp head and pushing forcibly inward- with the whole colonoscope if necessary. The alternative is to sacrifice the snare by cutting it with wire cutters, withdrawing the scope and leaving the loop in situ. Either the polyp head will fall off or another attempt can be made with a new snare.
- Difficult sigmoid- Sometimes polypectomy may be difficult in sigmoid colon because of narrowing either due to diverticular disease or hypertrophied folds. A gastroscope may allow easy snare positioning in the same location where the colonoscope was both cumbersome and difficult.
References
