Ch 94 - Rectum, Anus and Perineum Flashcards
What is unique about the resting membrance potential in GI smooth muscle cells?
The resting membrane potential is not constant. It oscillates in slow waves over time, generated by pacemaker cells called the interstitial cells of Cajal
How many bacteria are there per gram of faeces?
10^9 bacteria per gram of faeces
- Up to 90% anaerobes
What periop ABx are suitable?
- 2nd gen cephalosporins
- Aminoglycoside + Beta-lactam or clindamycin
List the approaches to the rectum
- Ventral +/- symphysiotomy or bilateral pubic and ischial osteotomy (cranial rectum and colorectal junction)
- Dorsal (caudal to mid-rectum)
- Lateral (small focal lesion, not commonly used)
- Caudal (eversion, trancutaneous rectal pull through, transanal rectal pullthrough, Swensons pullthrough)
- Combined abdominal transanal approach
List Tx options for an anal stricture
- Faecal softeners
- Balloon dilatation or bougienage
- Resection and anastomosis
- Z-plasty
- Radial incisional anoplasty (+/- transverse closure)
- Circumferantial anoplasty
What has been shown to increase the risk of faecal incontinence?
- Resection of 6cm of rectum
- Removal of distal 1.5cm of rectum
- Removal of more than half the circumference of external anal sphincter
- Damage to perineal nerves
- Resection of the peritoneal reflection
List the 4 types of atresia ani
- Type 1 - Stenosis of the anus
- Type II - Persistance of anal membrane with rectum ending as blind sac immediately cranial to imperforate anus
- Type III - Imperforate anus but the rectal sac is further cranial
- Type IV - Anus and terminal rectum can develop normally but the cranial rectum ends as a blind pouch within pelvic canal
What are potential complications associated wth atresia ani?
- Established megacolon, potentially requiring subtotal colectomy
- Inability to provide normal faecal continence
- Development of anal stricture
What is rectovaginal/urethrorectal fistula?
What are they often associated with?
- Failure of the developing urorectal septum to seperate the cloaca
- Commonly assoc with atresia ani, particularly type II
What are the Tx options for a rectovaginal fistula?
- Transverse incision between anus and vulva to isolate the fistula to resect the fistula, close the assoc defects and correct the atresia ani
- Transection of the rectum caudal to the fistula, fistulous section resected and used to reconstruct the end of rectum and sutured to anus
- Transection of fistulous tract near the vagina and then use the distal rectal portion for reconstruction of the anus
Prognosis is good :)
What is an anogenital cleft?
Rare condition in which urine and faeces enter a common cavity and body opening (cloaca)
What other diseases may be seen concurrently with perianal adenoma?
- Perineal hernia (10%)
- Testicular tumours
- Hyperadrenocorticism (source of androgen for females)
What % of rectal tumours are incorrectly diagnosed based on endoscopic biopsy?
What it the most common colorectal tumour?
- 1/3 incorrectly diagnosed
- Adenocarcinoma most common in dogs, LSA in cats
What are the three forms of rectal adenocarcinoma?
- Pedunculated
- Cobblestone
- Infiltrative (classic ‘napkin-ring’)
Pedunculated and cobblestone have a good prognosis with surgical resection. Infiltrative/annular poor prognosis
What cell type do GISTs arise from?
The interstitial cells of Cajal
Can be differentiated from leiomyosarcoma on IHC with CD117
List some paraneoplastic syndromes which can be seen with rectal neoplasia?
- Adenomatous polyps - Leucocytosis
- Eosinophilic masses - eosinophilia, neutrophilia, hypocholesterolaemia, hypoalbuminaemia
- Leiomyosarcoma - hypoglycaemia
- Secretory plasmacytomas - Hyperproteinaemia, monoclonal gammopathy
List alternative therapies for anal and rectal tumours
- NSAIDs
- Immunosuppresive medications for inflammatory polyps
- Pred and ivermectin (eosinophilic masses)
- Chemotherapy (MST 2532d vs 70d for rectal lymphoma in dogs)
- Orthovoltage irradiation
- Colostomy
What is the MST of rectal tumours according to morphology?
- Pedunculated 32m
- Nodular or cobblestone 12m
- Annular 1.6m
What it the most common location for rectal perforation?
Within the caudal 4cm leading to focal retroperitoneal infection
What are surgical options for faecal incontinence?
Sphincter-enhancing procedures
- Semitendinosus muscle flap
- Rotation of rectum 225 degrees before anastomosis
- Implantation of polyester-impregnated silicone elastomer ring
- Sartorius muscle transposition
- Free neuromicrovascular transfer of t=latissimus dorsi
What % of AGASACA express COX-2?
What molecule has been associated with a shorter survival?
What % of cases have paraneoplastic hypercalcaemia?
- 100%
- Decreased expression of e-cadherin assoc with shorter survival
- 27% hypercalcaemia (20-90%)
List the stages of AGASACA and their associated MST
- Stage 1 - Tumour under 2.5cm, no mets. MST 40m
- Stage 2 - Tumour over 2.5cm, no mets. MST 24m
- Stage 3a - LN under 4.5cm. MST 15-16m
- Stage 3b - LN over 4.5cm. MST 10-11m
- Stage 4 - Distant mets. MST under 3m
Where is the most common location for a perineal hernia in dogs?
Between external anal sphincter and levator ani
What anatomical difference is there regarding the perineum in dogs and cats?
Cats do not have a sacrotuberous ligament
