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What is the anatomical location of the rectum?
- descending colon turns into rectum as it enters the pelvic canal
- at the entry point of the cranial rectal artery
- covered by mesorectum- attached to sacrum
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What nerves are by the rectum? (2)
reflections of mesorectum contain the pelvic plexus- hypogastric n (sympathetic) and pelvic nn (parasympathetic)
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What muscles make up the pelvic diaphragm? (3)
- levator ani m.
- coccygeus m.
- external anal sphincter m.
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What are the 3 zones of the anus?
- columnar [proximal]
- intermediate
- cutaneous [distal]- contains anal sac openings, sebaceous, apocrine, and circumanal glands
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Where are the anal sacs?
- sit along the columnar and intermediate zones b/c the internal and external anal sphincter mm.
- opening are at the mucocutaneous junction (anus meets skin)
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Describe the anatomy of the anal sacs.
- lined with squamous epithelium
- apocrine and sebaceous glands
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What is the main control of fecal continence?
- external anal sphincter
- innervated by caudal rectal n.
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What is the innervation of the internal sphincter m.?
hypogastric n (sympathetic) and pelvic n. (parasympathetic)
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What is the blood supple of the anus?
internal pudendal a.
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Clinical signs of anorectal disease. (7)
- discomfort (scooting, licking)
- hematochezia/ dyschezia
- diarrhea + mucus and blood
- constipation
- perianal swelling
- draining tracts
- fecal incontinence
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What can you feel with a rectal exam? (12)
- masses
- strictures
- perianal thickening
- anal sac enlargement
- reduced sphincter tone
- rectal sacculation
- lymphadenopathy
- prostate
- pelvic diaphragm weakness
- patency of pelvic canal
- urethral palpation
- texture of mucosa
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How is proctoscopy achieved?
complete enema--> air insufflation--> scope
permits biopsy but not complete resection
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Describe the use of perioperative antibiotics with anorectal surgery.
- perioperative antibiotic use reduced morbidity and mortality associated with infection
- flora is mixed population--> 2nd gen cephalosporins (Cefoxitin, cefmetazole) or combinations (IV amikcain or fluoro + ampicillin AND oral neomycin + metro)
- start oral therapy 24 hours before sx
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What are your suture choices for anorectal surgery? What pattern is usually used?
- monofilament, absorbable suture (3-0 or 4-0)
- appositional pattern
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What are potential surgical complications with anorectal surgery? (5)
- incontinence
- infection
- dehiscence
- stricture
- tumor recurrence
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What are indications for rectal resection? (4)
- neoplasia
- trauma
- perforation
- stricture
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Describe the ventral approach to the rectum and when this approach is appropriate.
- appropriate for dz at colorectal junction
- ventral midline abdominal approach combined with pubic osteotomy
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Describe the anal/ transanal approach to the rectum and when it is used.
- appropriate for excision of small, partial thickness lesions that can be exteriorized through the anus
- stay sutures at rectocutaneous junction and evert rectal mucosa until lesion can be excised
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Describe the rectal pull-through approach to the rectum and when it is used.
- appropriate for mid-rectal lesions (intrapelvic) not amenable for ventral or transanal approaches
- evert the whole rectal layer out the anus; aggressive approach, not recommended
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Describe the dorsal approach to the rectum and when it is used.
- appropriate for extramurial/ extra luminal lesion
- incision made from one tuber ishii to another
- transect rectococcygeus m.
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Describe the lateral perineal approach to the rectum and when it is used.
- used for diverticulae, laceration/ perforations/ perineal hernias, sacculectomy
- unilateral exposure
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How much of the anal sphincter can you remove and maintain continence?
up to half of the anal sphincter
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What are the techniques for anal sacculectomy? (2)
- open- chronic abscessation, increased risk of infection/ incontinence
- close- complete excision of all epithelial lining, reduced contamination
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What are potential complications of anal sacculectomy? (3)
- fecal incontinence (damage to caudal rectal n)
- draining tracts/ fistula
- recurrent abscessation
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What are benign (4) and malignant (2) neoplasias of the rectum?
- Benign: adenomatous polyp, leiomyoma, hemangioma, plasmacytoma
- Malignant: mucoid adenocarcinoma, leiomyosarcoma
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Describe adenomatous polyps. (5)
- grape-like
- pedunculated or sessile
- friable
- 25% transform to malignancy
- mucosal excision usually curative
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What underlying conditions predispose to rectal prolapse? (10)
- enteritis
- parasites
- colitis
- rectal neoplasia
- foreign objects
- UTI
- prostatic dz
- dystocia
- perineal hernia
- sphincter denervation
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How do you repair a first-incidence partial rectal prolapse?
replace mucosa and purse string
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How do you treat a recurrent rectal prolapse?
- resection of prolapsed tissue
- colopexy (abdominal approach)
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What is a surgical emergency differential for rectal prolapse?
- ileocecocolic intussusception
- differentiate by placing a probe in and it goes a long way
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Describe perianal adenomas. (5)
- most common perianal tumor
- poster child: older intact male dog (hormone dependent!!! driven by testosterone)
- 90% will regress after castration
- raised, firm, well circumscribed, +/- ulceration/ large
- Dx: hepatoid cells on cytology
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How can you dx perianal adenoma versus adenocarcinoma?
- biopsy
- will metastasize- wide surgical margins
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