Colorectal polyps and carcinoma

Question 1

Pathological classification of colorectal polyps and adenomas

Answer 1

Neoplasms:

• Adenomas—very common, all potentially premalignant; these include villous, tubular and tubulo-villous types
• Early carcinomas—common
• Lymphomas—rare
• Leiomyomas and leiomyosarcomas—rare
• Lipomas and liposarcomas—rare
• Carcinoid tumours—rare

Hyperplasias:

• Metaplastic mucosal polyps—very common
• Lymphoid aggregations—common in young children

Hamartomas:

• Angiomas—uncommon
• ‘Juvenile polyps’—uncommon; small malignant potential
• Peutz–Jeghers polyps—uncommon; small malignant potential

Inflammatory polyps:

• ‘Pseudopolyps’ of severe ulcerative colitis

Question 2

Adenomatous polyps and adenomas

Answer 2

• Common in the large bowel. The most significant are adenomas (i.e. benign neoplasms)
• potential for malignant change. In general, it takes 5–10 years to progress to invasive cancer
• removal prevents progression from adenoma to adenocarcinoma.
• process by which the epithelial cells acquire increasingly severe genetic mutations is termed the adenoma–carcinoma sequence

Question 3

Distribution of colorectal adenomas

Answer 3

• three-quarters of them arise in rectum and sigmoid colon
• exactly parallels the distribution of carcinomas and verifies that most cancers develop from polyps.
• Adenomas often arise singly (particularly villous adenoma), more than 20% of patients with colonic polyps have multiple polyps, often tubulo-villous
• whole colon should ideally be examined before colectomy,

Question 4

Symptoms and signs of colorectal polyps

Answer 4

• rectal bleeding
• iron deficiency anaemia from occult blood loss.
• Mucus production, especially from villous adenomas,
• hypokalaemia may develop because so much potassium-containing mucus is lost
• hypokalaemia may develop because so much potassium-containing mucus is lost
• prolapse through the anus

Question 5

Diagnosis and management of colorectal polyps

Answer 5

• rigid sigmoidoscopy (which actually visualises the rectum) is often performed initially
• Flexible sigmoidoscopy, performed without bowel preparation or after a phosphate enema, reaches past the sigmoid and descending colon to the splenic flexure
• to view the remainder of the bowel requires colonoscopy
• alternative investigation growing in popularity and accuracy is CT colonography
• Intervals between colonoscopies are set according to guidelines determined by the number, size and pathology of polyps at each investigation and vary between 1 and 5 years.

Question 6

Pathophysiology of colorectal carcinoma

Answer 6

• Most carcinomas are initially exophytic (i.e. protruding into the lumen) and later ulcerate and progressively invade the muscular bowel wall
• Eventually, the tumour involves serosa and surrounding structures
• Stromal fibrosis may cause luminal narrowing, responsible for the common acute presentation of large bowel obstruction.
• Large bowel carcinomas metastasise via lymphatics and the bloodstream, and by the time of diagnosis as many as 25% of patients already have distant metastases
• Lymphatic spread is sequential, first to mesenteric nodes and then onward to para-aortic nodes. Occasionally lymph node involvement is directly responsible for the clinical presentation

Question 7

Presentation of large bowel carcinoma (1)​

Answer 7

Blood Loss

• rarely obstruct unless the ileocaecal valve is involved
• because the right colon has a larger diameter than the left and the faecal stream is more fluid
• because the right colon has a larger diameter than the left and the faecal stream is more fluid

Change of bowel habit and large bowel obstruction

• Colorectal cancers usually secrete mucus and bleed into the lumen
• Faeces in the left colon are more solid and the intraluminal pressure is higher, thus distal cancers here are more likely to obstruct.
• Colonic cancers tend to progressively encircle the bowel wall

Question 8

Presentation of large bowel carcinoma (2)

Answer 8

• Rectal bleeding
• Tenesmus
• Perforation

Question 9

Management of colorectal carcinoma

Answer 9

• Surgical excision is the main treatment. For tumours localised to the bowel wall, resection offers an excellent chance of complete cure
• for tumours at a more advanced stage, chemotherapy and radiotherapy may increase the chance of cure.
• For rectal cancers, chemoradiotherapy may be given preoperatively (known as neoadjuvant therapy)
• In frail patients with metastatic disease in whom any surgery is too risky, a stent can often be placed endoscopically on the left side of the colon to hold the bowel open and relieve obstruction.

Question 10

Staging of colorectal carcinoma

Answer 10

• Staging of colorectal carcinoma influences the desirability of further treatment by chemotherapy or radiotherapy.
• It also gives an estimate of the statistical probability of surviving 5 years and the likelihood of cure
• The two most widely used staging systems are the tumour/node/metastasis (TNM) and Dukes’ classification,

Question 11

Operations for colorectal cancer

Answer 11

• Before elective operations, the bowel may be prepared by giving a low residue diet and enemas. Oral purgatives are no longer given because of the potential dehydration
• Perioperative prophylactic antibiotics (e.g. gentamicin and metronidazole) are given
• Operative access is achieved laparoscopically, or by laparotomy, usually via a midline incision
• Affected segment of bowel is removed with a margin of normal bowel, usually 5 cm clear each side of the tumour. Should be good blood supply to the cut ends of bowel to ensure healing so, lines of resection are determined by mesenteric blood vessels
• Rectal cancers are a special case and an outline of standard operations is given in The preferred operation is a sphincter-saving anterior resection of rectum; provided the lower edge of the tumour is 1–2 cm above the anal sphincters,

Question 12

Operations for colorectal cancer

Answer 12

• If the sphincter is involved, the entire rectum and anus has to be removed via an abdomino-perineal excision (APE), with the proximal end of bowel brought out as a colostomy

Question 13

The role of adjuvant radiotherapy and chemotherapy (1)

Answer 13

• Adjuvant radiotherapy and chemotherapy is usually offered to patients with Dukes’ C cancers to increase the chance of prolonged survival
• Neoadjuvant chemoradiotherapy is particularly relevant for rectal tumours tethered in the pelvis, where shrinking a large tumour can make it operable
• Therapies may enable the anal sphincter to be preserved by downsizing the tumour. If rectal tumours extend through the bowel wall, particularly anteriorly, a course of radiotherapy directly before surgery reduces local pelvic recurrence.

Question 14

The role of adjuvant radiotherapy and chemotherapy (2)

Answer 14

• Chemotherapy in large bowel cancer, 5-fluorouracil (5-FU) is the chief adjuvant agent; it is often given in combination with its biomodulator, folinic acid

Question 15

Complications of large bowel surgery

Answer 15

Early complications

Local:

• Inadvertent damage to other organs, e.g. ureter, bladder, duodenum or spleen—usually recognised at operation
• Haemorrhage, e.g. slipped ligature
• Wound infection—cellulitis, abscess or wound edge necrosis
• Intra-abdominal abscess—at site of surgery, pelvic or subphrenic

Regional:

• Anastomotic leak or breakdown—local or general peritonitis
• Stoma problems—sloughing or retraction
• Compartment syndrome in legs due to prolonged elevation during perineal surgery (rare)

Systemic:

• New onset atrial fibrillation or flutter—often indicates anastomotic breakdown
• Systemic sepsis leading to multi-organ dysfunction syndrome

Later complications:

• Diarrhoea—due to short bowel
• Division of pelvic parasympathetic nerves—causes sexual/bladder dysfunction
• Small bowel obstruction—due to pelvic peritoneal adhesions or tangling of small bowel with colostomy or ileostomy, or later as a complication of radiotherapy causing small bowel damage