Chapter 94 Rectum, Anus and Perineum Flashcards
Name 4 proposed locations for transition from colon to rectum
- Pelvic inlet
- Pubic brim
- Where cranial rectal artery penetrates serosa
- L7
What is the difference between intra-peritoneal and retroperitoneal part of rectum?
Retroperitoneal part doesnt have serosal layer
Which artery provides the majority of the blood supply to terminal colon and rectum in the dog
Cranial rectal (branch of caudal mesenteric artery)
Label the diagram
How does blood supply to caudal colon and rectum differ between dogs and cats
Middle and caudal rectal arteries supply variable and relatively insignificant amounts in dogs, whereas in cats, intrapelvic rectum is adequately supplied by middle and cudal rectal arteries.
Where is the anal canal?
- Between termination of rectum and anus
- 1-2cm long
- Surrounded by internal and external sphincter m
Label the diagram.
- The columnar zone contains longitudinal or oblique ridges, known as anal columns, which extend caudally for approximately 7 mm.
- The intermediate zone is an irregular, sharp-edged fold, less than 1 mm wide, that unites with the anal columns. The fold is divided into four arches that give it a scalloped appearance and contain large pockets known as anal sinuses.
- The anocutaneous line is considered the boundary between the mucous membrane and the skin, but it cannot be differentiated from the intermediate zone.
- The cutaneous zone is divided into internal and external portions, and the plane separating the two is considered the anus.
What is the difference in epithelium cranial vs caudal to anorectal line?
Anal canal lined by stratified squamous epithelium (because deveops from invagination of surface ectoderm)
Rectum has simple columnar epithelium
Anorectal line is demarcation of this transition
Where do the anal sac canals open
Internal portion of cutaneous zone of anus.
What is another word for anal sacs?
Para-anal sinus
Where are teh anal sacs located?
Between internal and external sphincter muscles
What kind of epithelium of in anal sacs?
Stratified squamous
What is the perineal fascia
What is the perineal body?
Perineal fascia: Convergence of fascia from tail, pelvic region, thighs
Perineal body: Region where fascia unites on midline, bwteen anus and vulva/bub of penis
What structures make up the pelvic diaphragm?
- Pelvic fascia
- Coccygeus
- Levator ani
What glands sit around the anus and what glands are present in the anal sacs?
Glands sitting peri-anally:
- Circumanal glands: Superficial sebaceous part, deeper non-sebaceous. Regress in females
- Apocrine glands
- Sweat glands
- Anal glands = tubuloalveolar glands that produce fatty secretions
Glands within anal sacs:
- Paranal sac glands: Produce anal sac fluid
- Sebaceous glands
What muscle form the internal anal sphincter?
Cicular smooth muscle of anal canal
What other muscle do external anal sphinter fibres blend with ventrally in male vs female dog?
Male: Bulbospongiosus muscle
Female: Constrictor valvae
What muscle sits dorsally over anus?
Rectococcygeus
What nerve provides motor innervation to the external anal sphincter?
And sensory innervation?
Which nerve is it a branch of?
- Caudal rectal nerve supplies motor innervation
- Perineal branch of pudendal nerve provides sensory innervation
Branches of pudendal nerve (the motor nerve!)
(Pelvic = parasympathetic, hypogastric = sympathetic)
Label the diagram
Comment on mechanical pre-op bowel prep.
No benefit, potentially detrimental (increased leakage)
What is estimated bacterial load of faeces in rectum?
What proportion are anaerobes?
109 bacteria/gram
90% anaerobes
What antibiotic class is recommended for rectal surgery
Cephalosporins as good activity against both gram +ve and -ve and some anaerobes.
+ metronidazole for anerobic cover
What are the 4 approaches to the rectum?
- Ventral
- Pelvic symphysiotomy
- Pubic + ischial osteotomy
- Pubic osteotomy
- Dorsal
- Lateral
- Caudal
- Transcutaneous rectal pull-through
- Transanal rectal pull-through
- Rectal eversion
- (Combined abdominal + transanal)
What muscles are elevated off pelvic symphysis for osteotomy?
Gracillis and adductor magnus et brevis (has two parts, other part is adductor longus, originates at pubic tubercle)
What degree of pulvic widening is tolerated without Si lux?
25% width of sacrum
(unilateral lux with 50-75% widening)
What muscles are cut for dorsal approach to rectum
Rectococcygeus +- levator ani
What muscles are divided during lateral approach to rectum?
Dissect between external sphincter + levator ani
Whatadditional procedure has to performed with transcutaneous ractal pull through and why?
Bilateral anal sacculectomy as both ducts will be included in cutaneous inscision.
List 4 treatment options or rectal stricture
- Bugienage
- Balloon
- Surgical inscision of constricting band
- R + A
List potential complications after colorectal resection
- Tenesmus
- Haematochezia + dyschezia
- Stricture
- Dehiscence
- Increased frequency of defaecation/diarrhoea
- Faecal incontinence (usually transient 5-10d)
What 2surgical factors has been associated with increased risk of dehisence after colorectal excision?
And incontinence?
Dehisence:
- Removal of >6cm
Incontinence:
- Removal of >6cm
- Removal of distal 1.5cm of rectum (therefore transanal pull through preferred over transcutaneous where possible)
What two factors contribute to faecal continence
- External anal sphinter function
- Resevoir continence (a function of length and motility)
Name 3 congenital abnormalities of the rectum and anus
- Atresia ani
- Rectovaginal/rectourethral fitula
- Anogenital clefts
Describe the types of atresia ani
- Type 1 congenital stenosis of anus
- Type 2 persistence of anal membrane and rectum ends immediately canial to imperforate anus
- Type 3 anus also closed, rectum ends more cranial
- Type 4 anus and terminal rectum develop normally but cranial rectum ends as a blind pouch in pelvic canal
ie. in summary type 1 stenosis, type 2 and 3 have imperforate anus with varying distance between rectum and anus and type have normal terminal rectum + anus with abnormality more cranial
What are c/sof atresia ani
Abdo enlargement, unthrifty, anorexia, restlessness, not passing faeces.
Usually ok for first 2-4 weeks
How is each type of atresia ani treated?
Type 1: Bougie or balloon
Type 2 and 3: Vertical inscision (preserve external sphincter and anal sacs), dissect out rectum, mobilise caudally and appose to skin
Type 4: Abdo approach
List 3 main concerns following atresia ani sx
Incontinence, stenosis, megacolon
What embryonic abdnormality leads to rectovaginal/urethrorectal fistula?
What condition are they associated with?
failure of urorectal septum
type 2 atresia ani
Comment on imaging
Contrast radiography of a rectovaginal fistula. A Foley catheter is inserted into the vaginal vault for infusion of contrast material. The arrows indicate the fistula location.
Comment on imaging
How is megacolon dx on rads
Type II atresia ani. On the lateral abdominal radiograph, the rectum is noted to end as a blind pouch immediately cranial to the closed anus.
Megacolon if diameter of colon > 1.5xlength of L7
What is best method to dx urethrorectal fistula
Positive contrast retrograde urethrography
(Can also do vagino urethrography, fistulography, voiding cystourethrography)
List 3 techniques for management of rectovaginal fistula
- The anal and vaginal defects are each closed with simple interrupted sutures, and the atresia ani is repaired as described previously.
- Alternatively, the rectum is transected cranial to the fistulous opening; the affected segment of the rectum is removed, and the cranial segment is sutured to the anus as a rectal pull-through.
- A third alternative is to transect the fistulous tract near its vaginal or vestibular attachment and use the distal rectal portion of the fistula to reconstruct the anal canal and anus
List reported complications of rectal fistula sx
- incontinence
- wound dehiscence
- tenesmus
- obstipation
- rectal prolapse
- anal stenosis
- perianal edema
what condition is shown
Anogenital cleft (ie common cloaca)
What is a complete rectal prolapse
All layers of rectum aroudn entire circumference protrude (vs just anal mucosa)
List 4 predisposing factors for rectal prolapse
- Weakness of perirectal/perianal supporting tissues
- Uncordinated peristaltic contractions
- Excessive straining
- Inflammation/oedema of rectal mucosa
e.g. with gastrointestinal parasitism; typhlitis; colitis; proctitis; colonic duplication; congenital defects; tumors of the colon, rectum, or anus; rectal foreign bodies; perineal hernia; anal laxity; cystitis; cystocele; prostatic disease; urolithiasis; and dystocia
DDX for rectal prolapse
prolapsed intussusception
insert somethign between anus and protrusion to distinguish
How is rectal prolapse managed initially?
And if unsuccessful
- GA or epidural
- 50% dextrose or live yeast or systemic frusemide
- CSL
- Pursestring 3-5d
- Low residue diet + laxative
Colopexy
What are 3 most common canine perianal tumours/
Perianalgland adenoma, adenocarcinoma, apocrine gland anal saca adenocarcinoma (AGASAC)
Where do perianal gland tumours originate from
Circumanal modified sebaceous glands (called hepatoid as look a bit like hepatocytes on histo)
(reported around tail base, prepuce etc - wide area basically!)
What size of LN size means liekly mets (from perianal/rectal tumour)
> 1cm
What drives perianal adenoma growth
What condition has it been associated with
Androgens i.e.usually seen in ME dogs (or neutered females - oestrogen –> regression. or hyper A –> androgenic stimulation)
Interstitial cell (“Leydig cell” = testosterone secreting) testicular tumour therefore always submit for histo
What IHC can be used on perianal adenoma/adenocarcinoma to differentiate between benign and malignant (5 points)
- pcna
- ki67 or AgNOR
- markers for apoptosis
- expresion of claudins 1, 4, 5, 7
- monoclonal antibody labelling
What breeds are predisposed to adenocarcinoma or perianal glands
GSD and artic circle breeds
and >35kg dogs
What is the only prognostic factor for perianal gland adenocarcinoma
Clinical stage
Describe staging of peianal gland adenocarcinoma
T1: tumor < 2 cm, superficial or proliferative
T2: tumor of 2 to 5 cm or with minimal invasion independent of size
T3: tumor > 5 cm or invasive tumors independent of size
T4: (invasive tumor) have a median survival of 6 to 12.5 months.
The median survival time with confirmed metastasis is 7 months.
How is stage 4 different from invasive stage 3…. maybe mets with stage 4 but dont know
List 3 adjunctive treatments for analgland adenocarcinoma
Radiotherpay
Chemo
Electrochemotherapy
When does a rectal polyp become carcinom in situ?
Carcinoma in situ = polyps that invade the intestinal lamina propria and submucosa but not the basement membrane
(transition stage between adenomatous polyp and invasive carcinoma with some histologic features of malignancy that may progress to true malignancy in 17% to 50% of cases).
What surgery is performed for perianal fistulas that have not resolved with medical management?
- Excision of all draining tracts
- Bilateral anal sacculectomy
- Cryptectomy (= resection of columnar zone of anal canl up to anorectal line)
What are the 4 types of perineal hernia?
- Caudal (most common)
- Between levator ani, internal obturator and external sphincter
- Dorsolateral
- Between levator ani and coccygeus
- Ventral
- Between ischiourethralis, ischiocavernosus and bulbourethralis
- Sciatic
- Between coccygeus and sacrotuberous ligement
What is teh originand insetrion of these lot:
Levator ani
Coccygeus
Internal obturator
Sacrotuberous ligament
Levator ani (two parts; iliocaudalis and pubocaudalis)
- Origin: 7th caudal vetrebra
- Insertion: Perineal body (and fascial attachment to external anal sphincter)
Coccygeus
- Origin: Spine of ischium
- Insertion: Transverse processes of 2nd-5th caudal vertebrae
Internal obturator
- Origin: Intrapelvic border of obrurator foramen
- Insertion: Trochanteric fossa of femur
Sacrotuberous ligament (absent in cats)
- Origin: Caudal aspect of sacrum and transverse process of Cd1
- Insertion: Ischiatic tuberosity
What 4 muscles attach to the sacrotuberous ligament?
- Biceps femoris
- Abductor cruris caudalis
- Piriformis
- Superficial gluteal
Label the diagram
N.B. INternal iliac branches into internal pudendal and caudal gluteal.
Internal iliac a.
–> Internal pudendal a.
- Caudal rectal a.
- Ventral perineal a.
- Dorsal artery of penis
Internal iliac a.
–> Caudal gluteal
- Gluteal branches
- Lateral caudal a.
- Dorsal perineal a.
- AND branch running ventrally to semitendinous
Label the diagram
Final appearance after traditional herniorrhaphy (caudolateral view).
1, External anal sphincter;
2, coccygeal muscle;
3, superficial gluteal muscle;
4, ischial tuberosity;
5, internal obturator muscle elevated from ischial table
6, retractor penis muscle.
List 2 benefits of internal obturator transposition over traditional heriorrhaphy
- Reduced tensionon closure
- Brings in more blood supply
How is tendon of internal obturator recognized
Where is it cut during internal obturator transposition?
Three bands that converge as tendon as it crossed over the lateral edge of ischium
Cut it medial to the lateral edge of ischium to avoid sciatic nerve damage (and N.B. a blood vessel runs immediately cranial to tendon)
What vessel needs to be preserved during superficial gluteal transposition?
Caudal gluteal artery
What are the major blood vessels supplyign proximal semi-tendinous muscle (i.e. must be preserved!)
What vessel supplies the distal half of the muscle?
Where is muscle transected during transposition?
Prox supply: Caudal gluteal artery and vein
Distal supply: Distal caudal femoral artery
Transect midbelly or closer to stifle if nec.
What is rate of sciatic n injury after perineal hernia repair
What c/s.
What is tx?
What are salvage options if function doesnt return?
5%
C/s:
- Marked pain
- Paresis
- Lameness (NWB)
- Extended tarsus, flexed toes
- Lack of withdrawal digits 2-5
Tx:
- Caudolateral approach to hip to remove suture asap
Salvage:
- Talocrural arthrodesis
- Long digital extensor tendon transfer to vastus lateralis
- Amputation
Approach to caudal aspect of hip Piermattei p. 350
A. The curved incision is centered on the caudal surface of the greater trochanter. It starts near the dorsal midline, continues caudal to the trochanter, and extends through the proximal one fourth to one third of the femur.
B. The subcutaneous fat is undermined and retracted with the skin. The fascia of the biceps muscle is incised along the cranial border of this muscle, beginning proximally at the sacrotuberous ligament, and extending distally to the end of the skin incision.
C. The tendinous insertion of the superficial gluteal muscle is transected near its attachment on the third trochanter, and the incision is continued into the deep leaf of the fascia lata. The tensor fasciae latae muscle is now retracted craniodorsally and the biceps femoris caudally to expose the external rotator muscles of the hip.
D. With the femur internally rotated, the combined tendon of insertion of the internal obturator and gemelli muscles is cut close to its attachment in the trochanteric fossa.
E. A stay suture in the tendon of the internal obturator and gemelli muscles will aid in its retraction. As it is retracted, it also retracts and protects the sciatic nerve as the obturator fossa of the ischium is exposed. A Hohmann retractor placed ventral to the femoral head will help retract the external obturator and quadratus muscles. Care must be taken to protect the sciatic nerve and circumflex femoral vessels. For improved local exposure of the ischium, the cranial portion of the origin of the gemelli muscles is elevated from the bone, all the way to the ischiatic spine dorsally. Where the tendon of internal obturator muscle crosses the ischiatic spine, there is a thin-walled bursa that is 1 to 2 cm wide surrounding this tendon. Incision of this bursa allows the internal obturator muscle to be retracted further caudally. For caudal acetabular fractures, this increased exposure allows for the application of a bone plate that extends caudally to a point halfway along the body of the ischium. To avoid undue retraction of the sciatic nerve, the nerve is moved cranially during plate application. Screws can be inserted through the interval between the gemelli and internal obturator muscles dorsally, and the external obturator and quadratus femoris muscles ventrally. For local enhancement of the exposure of the acetabular labrum more cranially, a portion of the origin of the deep gluteal muscle is elevated.
