Anatomy Flashcards
Thoracic plane
- runs from manubriosternal joint/angle of Louis to inferior endplate of T4
- division of superior and inferior mediastinum
- structures transected:
- bifurcation of trachea
- aortic arch (inner cavity)
- just above pulmonary trunk bifurcation
- azygos drains into SVC, arching over right main bronchus
- left recurrent laryngeal nerve loops around aortic arch
- thoracic duct moves from right to left hand side posterior to oesophagus
- ligamentum arteriosum with RLN recurring beneath it
- cardiac plexus (superficial and deep parts)
- termination of prevertebral fascia (fuses with anterior longitudinal ligament) and pretracheal fascia (blends into fibrous pericrdium)
(CLAP TRAP: cardiac plexus, ligamentum arteriosum, aortic arch (inner concavity), pulmonary trunk, tracheal bifurcation, right to left movement of thoracic duct, azygos drains into SVC, pre-vertebral fascia and pretracheal fascia end)
Transpyloric plane
- Halfway between sternal notch and pubic symphysis
- Or intersection of linea semilunaris with costal margin at level of 9th costal cartilage
- Structures:
- L1
- Pylorus
- D1
- DJ flexure
- Gallbladder fundus
- Neck and body of pancreas
- Confluence of splenic vein with SMV
- SMA origin
- Root of transverse colon mesentery
- Left and right colic flexures
- Spleen
- Hilum left kidney
- Upper pole of right kidney
- Tips of 9th costal cartilages
- Termination of spinal cord
Transtubercular plane
- Plane uniting two tubercles of iliac crest (these are slightly posterior and superior to ASISs along iliac crest)
- Structures at transtubercular plane:
- L5
- Start of IVC, 2.5cm right of midline
Axilla
- pyramidal area through which neurovascular structures pass between the root of the neck and the arm
- boundaries
- base = convex axillary skin/where angular veins drain into thoracodorsal vein
- apex = narrow communication between clavicle in front and first rib behind - defined by the costoclavicular ligament (Halsted ligament); at which point the axillary vein becomes the subclavian vein
- posterior: subscapularis above, lat dorsi and teres major below
- medial: serratus anterior
- lateral: intertubercular groove of humerus
- anterior: pec major, pec minor, clavipectoral fascia, subclavius
- nerves - brachial plexus
- vasculature
- axillary artery
- divided into 3 parts by pec minor (prox/post/distal to)
- cords of brachial plexus named by relationship to 2nd part of artery
- lateral margin of 1st rib to border of teres major
- branches: STLSAP (sixties teens love sex and pot)
- superior thoracic
- thoracoacromial
- lateral thoracic
- subscapular (becomes thoracodorsal after giving off circumflex scapular)
- anterior circumflex humeral
- posterior circumflex humeral
- axillary vein
- axillary artery
- lymphatics
- medial side of axillary vein
- level I-III according to relationship with pec minor (lateral, posterior, medial to it up to Halsted’s ligment)
Brachial plexus
- Formed by the ventral rami of nerve ROOTS C5-T1 which are behind the scalene muscles and give off:
- dorsal scapular nerve C5 (rhomboids & levator scapulae)
- nerve to subclavius C5,6
- long thoracic nerve C5,6,7
- TRUNKS - superior, middle, inferior
- emerge between scalenus anterior and medius
- cross posterior triangle, over first rib, behind subclavian artery
- upper and middle lie above SCA, lower lies directly on its superior surface
- covered by skin, deep fascia and platysma
- crossed by suprascapular nerve, EJV and inf belly omohyoid
- superior gives off suprascapular nerve, C5,6
- DIVISIONS
- each trunk branches into anterior and posterior divisions
- posterior to middle third of clavicle
- CORDS - medial, lateral, posterior
- posterior divisions unite to form posterior cord, upper 2 anterior divisions unite to form lateral and lowermost anterior divison forms medial cord
- formed in cervicoaxillary canal, surround 2nd part of axillary artery
- first part: medial cord is posterior, lateral and posterior cords are lateral
- second part: take up positions indicated by names
- lateral cord
- lateral pectoral C5,6,7 (pec major)
- posterior cord
- upper subscapular C5,6 (subscapularis)
- lower subscapular C5,6 (subscap and TM)
- thoracodorsal C6,7,8 (lat dorsi)
- medial cord
- medial pectoral C8,1 (pec major & minor)
- medial cutaneous nerve of arm T1
- medial cutaneous nerve of forearm C8
- TERMINAL BRANCHES
- lateral cord
- musculocutaneous nerve C5,6,7
- posterior cord
- axillary nerve C5,6
- radial nerve C5,6,7,8,T1
- lateral and medial cord
- median nerve C5,6,7,8,T1
- medial cord
- ulnar nerve C8,T1
- lateral cord
Breast
- modified sweat gland of ectodermal and mesodermal origin
- base lies between ribs 2-6; sternal edge to MAL
- overlies pec major superomedially and to a lesser extent the serratus anterior inferolaterally and EOM below and medially
- glandular appendage of skin therefore contined within superficial fascia; deep surface abuts deep fascia overlying pec major and serratus interior
- between pec fascia and deep layer of superficial fascia = retromammary space - rel avascular
- consists of 15-20 lobules of glandular tissue of varying size with varying amounts of adipose tissue between the lobules; no distinct fascial compartmentalisation
- fascial bands run from deep layer of the superficial fascia to skin between duct lobular units; together w skin envelope support weight of breast
- breast lobules are placed more peripherally in the breast and drain into small ductules that coalesce into larger (lactiferous) ducts individually draining each main lobule
- 15-20 lactiferous ducts/lobular units open individually onto NAC
- each duct has a subareolar dilatation (infundibulum) that collects milk during lactation for suckling
- retro-areolar space contains smooth muscle, but no subcut fat
- UOQ has greatest proportion of glandular tissue, hence increased incidence of breast ca here
- while most breast tissue is superficial to deep fascia, lobular tissue often extends along lateral border of pec major and deeply into the axilla
- this is the breast’s axillary tail and the glandular tissue can reach as far as ax vein
- blood supply - PILL(s)
- pectoral branch of thoracoacromial (2nd part of ax artery)
- internal mammary (from subclavian near its origin) - paramedian plane 1-2mm from midline between internal thoracic and transverse thoracic muscles
- perforators in 2nd-5th ICS + branches to skin
- divides into musculocutaneous & superficial epigstric in 6th ICS
- lateral thoracic artery (from 2nd part ax artery at lat margin of pec minor, runs down lat border of pec minor & sends branches around lateral border of pec major into breast (ext mammary branch)
- also supplies serratus anterior, pec muscles, subscap
- lateral branches of posterior intercostal vessels - perforate serratus anterior anterolaterally
- +/- branches of subscapular artery
- venous drainage
- follows arterial supply
- superficial veins form extensive anastomotic network & assume a circular configuration around nipple ‘circulus venosus’
- deep veins drain almost entirely into axilla
- a valveless, venous plexus surrounding vertebrae extends from base of skull to sacrum & is in direct communication w posterior intercostal arteries; this connection provides potential pathway for mets to vertebral column & CNS
- lymphatic drainage
- 75% to axilla; 25% to int mammaries
- in 5% predominant drainage is to IM
- innervation
- sensory innervation from intercostal nerves 2-6 and in part from supraclavicular nerve
- retroareolar space has layer of smooth muscle - somatic & autonomic excitation contraction of these fibres –> erection of nipple & decrease in diameter of areola
Chest wall
The muscular layers of the thorax can be divided into those that are within the chest wall, and those that surround it.
- Chest wall:
- External intercostal (same orientation as external oblique)
- Internal intercostal (same orientation as internal oblique)
- The innermost layer is broken into three components; the subcostal, the innermost intercostal, and the transversus thoracis.
- Surrounding muscles
- Anteriorly;
- Pectoralis major; sweeping origin from clavicle, sternum, upper 6 cc, and external oblique
- Pectoralis minor; arises from ribs 3-5 and inserts into corocoid process
- External oblique; arises from lower 8 ribs interdigitating with serratus
- Rectus abdominis taking origin from the 5th, 6th, and 7th costal cartilages.
- Laterally;
- Serratus anterior; arising from the upper 8 ribs and inserting into scapula
- Posteriorly
- Rhomboids minor (C7 and T1) and major (T2-T5) inserting medial border scapula
- Trapezius with its sweeping origin from all cervical and thoracic vertebrae and SP
- Latissimus dorsi from the lowermost 3-4 ribs and SP of the lower 6 thoracic vertebrae
- Anteriorly;
Diaphragm
- a domed, fibromuscular sheet that separates the thoracic & abdominal cavities
- it is active on inspiration - accounts for 70% of insipration w 5cm of movement; passive on expiration
- right dome ascends in exp to 4th space; left to 5th rib
- contraction aids that of abdominal wall in raising intra-abdo pressure w straining
- it is active on inspiration - accounts for 70% of insipration w 5cm of movement; passive on expiration
- arises from:
- upper lumbar vertebrae via the crura
- right L1-3 & intervening discs; left L1-2
- from fascial arches known as median, medial and lateral arcute ligaments
- median = from sides of body of L1 (arches up so coeliac trunk comes off underneath at T12)
- medial = from side of body of L1 to transverse process of L1 at lateral margin of psoas
- lateral = from TP to tips of 21th ribs
- inner sides of lowest 6th rib (tip of 12th, forwards to 11th & each rib to 7th costal cartilage)
- posterior surface of xiphoid (T8)
- central tendon w its one anterior and two posterior parts
- upper lumbar vertebrae via the crura
- openings
- T8 = caval opening - IVC, right phrenic
- T10 = oesophageal opening - oesoph, vagus nerves, oesophageal branches of left gastric artery & vein, lymphatics
- 2.5cm to left of midline, oesophagus encircled by right crus
- T12 = aortic opening - strictly behind diaphragm (median arcuate ligament)
- azygos vein, thoracic duct (begins from cisterna chyli), aorta
- behind medial arcuate ligament - sympathetic trunk
- behind lateral arcuate ligament - subcostal neurovasc bundle
- things that go through diaphragm/crus
- left phrenic through left hemidiaphragm
- left hemiazygos through each crus
- greater, lesser, least splanchnic nerves through each crus
- extraperitoneal lymph vessels on abdo surface pass through diaphragm to LNs on thoracic surface, mainly in posterior mediastinum
- relations
- superior: pericardium, basal lung segments
- inferior: right - liver, adrenal, kidney; left - stomach, spleen, adrenal, kidney
- posterior - azygos, thoracic trunk, aorta, oesophagus, vagus nerves, pleural folds
- blood supply
- right and left inferior phrenic arteries which arise from aorta just beow diaphragm
- superior phrenic arteries which are smaller arising from aorta in thorax
- musculophrenic & pericardiophrenic arteries which are terminal branches of internal thoracic arteries
- costal margin supplied by lower 5 subcostal & intercostal arteries
- nerve supply
- phrenic nerve; each half of diaphragm is supplied by its own phrenic nerve & fibres of right crus that loop to left around oesophageal opening are supplied by left phrenic
- on reaching abdo surface of diaphragm, both nerves divide into ant, lat & post branches which run radially giving off branches that enter muscle from below
- 1/3 of phrenic nerve is sensory to heart & pleura, and peritoneum beneath
Abdominal wall
The 3 layers of the anterolateral body wall are separate in the flanks, where they are known as external oblique, internal oblique, and transversus abdominis. Towards the midline the layers fuse forming a broad aponeurosis. In the midline the three muscular layers fused in the embryo to form the rectus abdominis. Skin and subcutaneous tissue cover these muscles.
External oblique; arises from 8 lower rib interdigitations; sharing origin with serratus anterior for 4 ribs and latissimus dorsi for 4 ribs. It inserts onto the anterior half of the iliac crest (free border) and a wide aponeurosis.
Internal oblique; arises from the thoracolumbar fascia, the anterior two thirds of the iliac crest, and the lateral two thirds of the inguinal ligament. Inserts onto the 7th-9th costal cartilages and into the aponeurosis. Inferiorly it contributes to the conjoint tendon.
Transversus abdominis; arises from the thoracolumbar fascia, the anterior two thirds of the iliac crest, the lateral third of the inguinal ligament. Contributes to the aponeurosis of the midline and, inferiorly, the conjoint tendon.
Rectus abdominis; has three origins; the pubic tubercle, the pubic symphysis, and pubic crest. Inserts into the 5th, 6th, and 7th costal cartilages and the xiphoid. Has tendinous intersections attached to the anterior sheath.
The central/midline aponeurosis is made from the six laminae of the anterior and posterior fascia for each of the three muscles. Internal oblique splits to enclose rectus above the arcuate line (an inch below umbilicus). Inferior to this point, all the layers pass anteriorly leaving only transversalis fascia over peritoneum; a fact utilised in TEPP hernia repair.
The muscles and skin of the abdominal wall are largely supplied by the lower 6 thoracic nerves and the subcostal nerves. Some innervation is derived from the iliohypogastric and ilioinguinal nerves inferiorly.
Anal canal
- Overview
- last 3-4cm of alimentary tract - extends from pelvic floor/anorectal ring to anal verge
- muscles of anal canal + configuration of mucous membrane are involved in continence; hold the anal canal closed except during the passage fo flatus & faeces
- puborectalis part of levator ani clasps gut & angles it forwards
- from this angled junction w the rectum, 2.5cm in front of tip of coccyx, anal canal passes downwards & backwards towards skin of perineum
- Muscles
- tube of muscle like rest of gut but fibres all circular, consisting of int and ext anal sphincters (visceral & skeletal muscle respectively)
- tube within a funnel - upper parts of funnel = levator ani muscle; stem of funnel = ext sphincter continuous w levator ani; inner tube = int sphincter, continuous with inner circular layer of rectal muscle
- int anal sphincter - extends along 3/4 length of the anal canal so termintes ~1.5cm below dentate line, just below ext sphincter at intersphincteric groove
- accounts for 85% resting tone
- longitudinal muscle continuous w outer layer of rectum becomes fibroelastic at anorectal junction & forms conjoint longitudinal coat (separates int and ext sphincters & forms medial edge of intersphincteric space)
- some fibres fan laterally through ext sphincter & insert into perianal skin (corrugator cutis ani muscle)
- some traverse int sphincter (towards dentate line) & support int haemorrhoids at mucosal suspensory ligs
- ext sphincter = elliptical
- 3 parts - deep, superficial, subcutaneous
- deep = continuous w puborectalis except in midline at front where no levator ani fibres
- middle = elliptical, attached to tip of coccyx at back (contributes to anococcygela lig) and to perineal body at front
- subcut = circular ring which at lower ends curves below int sphincter
- Mucosa
- at anorectal junction = columnar epithelium w goblet cells (rectal type)
- anal transformation zone extends from prox anal canal to dentate line
- below dentate line = pecten (smooth pale area between dentate line & anal verge - non-keratinised stratified squamous epithelium w/o hair/sweat glands)
- below anal verge (junction of anal mucosa & perianal skin/mucocutaneous junction/roughly corresponds to intersphicnteric groove) = true cutaneous area - hairy skin with sweat & sebaceous glands - keratinised stratified squamous epithelium
- in upper anal canal = submucous anal cushions @ 3,7,11 o’clock
- consist of fibroepithelial/fibroelastic connective tissue, smooth muscle, dilated venous spaces & arteriovenous anastomoses
- in upper third of canal, mucous membrane shows 6-10 longitudinal ridges, the anal columns
- at their lower ends, adjacent anal columns are joined together by small horizontal folds, the anal valves - at dentate line
- pockets formed above anal valves = anal sinuses, into which open mucus sectreting anal glands
- about half anal glands are submucosal & rest penetrate through int sphincter
- NB anal margin = vague term; some define as within 5cm of anal verge ie perianal region
- perianal cancers = tumours that arise within the skin at or distal to squamous mucocutaneous junction, that can be seen in their entirety w gentle traction on buttocks & that are within 5cm of anus (previously called anal margin tumours)
- anal canal tumours = those that cant be seen in their entirety when gentle traction placed on buttocks
- Relations
- posteiror: coccyx; laterally: ischiorectal fossa; anteirorly: perineal body & vagina or urethra
- spaces
- superficial postanal space = superficial to anococcygeal ligament
- deep postanal space = between anococcygeal ligament and levator ani muscle - continuous laterally w each ischioanal space and when infected can create horseshoe abscess
- supralevator space = above levator ani, below and posterior to rectum, and anterior/superior to sacrum; can extend into retroperitoneum
- Blood supply
- superior rectal artery supplies mucosa to dentate line
- middle & inf rectal arteries (from int iliac and from pudendal branch of int iliac) supply sphincter muscles & lower anal mucosa
- venous drainage: into portal (proximally) & systemic (distal) circulations
- Nerve supply
- ext anal sphincter: inferior rectal branch of pudendal nerve S2-4)
- pudendal nerve leaves pelvis through greater part of sciatic notch, where it passes under piriformis muscle; then crosses ischial spine & sacrospinous ligament to enter ischiorectal fossa through lesser sciatic foramen via pudendal/Alcock’s canal
- pudendal nerve has 2 branches: inferior rectal nerve (supplies ext anal sphincter & sensory supply from 1-2cm above pectinate line downwards); and perineal nerve (innervates ant perineal muscles & urethral sphincter and forms dorsal nerve of clitoris (for penis)
- puborectalis: mainly from direct branch of S4 nerve root but may derive some from pudendal nerve
- levator ani: S3 and 4
- autonomic supply to anal canal & pelvic foor from 2 sources
- sympathetic = L5 nerve root sends sympathetic fibres to sup & inf hypogastric plexuses
- parasympathetic supply = from S2-4 nerve roots via nervi erigentes
- fibres of both systems pass obliquely across lateral surface of lower rectum to reach region of perineal body
- int anal sphincter has intrinsic supply from myenteric plexus & additional supply from both SNS (L5) and PSNS (S2-4)
- afferent fibres from upper part of anal canal are carried by both SNS & PSNS nerves while lower anal canal sensation is via somatic sensory fibres extending to 10-15mm above dentate line (involved in continence by discriminating between fluid & faeces)
- ext anal sphincter: inferior rectal branch of pudendal nerve S2-4)
- Lymphatics
- pectinate line = watershed between drainage to intra-abdominal and groin lymph nodes
** defaecation in pathophys
Appendix
- blind ending tube varying in length (commonly 6-9cm) which opens into posteromedial wall of caecum 2cm below IC valve - at McBurneys point
- position of base constant in relation to caecum but may itself lie in variety of positions - retrocaecl > pelvic, subcaecal, paraileal
- mesoappendix = fold of peritoneum from left inferior layer of mesentery of TI
- ileocaecal fold/bloodless fold extends from TI to front of mesoappendix
- inferior ileocaecal recess = space between fold of Treves & mesoappendix
- appendiceal artery = usu a branch of inf division of ileocolic artery which often runs behind TI to enter mesoappendix but many variations of appendicular and caecal arterial supply
Colon
Asc 15, transverse 50, desc 25, sigmoid 40
Hypogastric plexus
- lumbar splanchnics are derived from T12 to L2 sympathetic chain, pass down on front of aorta & are an immediate posterior relation to IMA
- these sympathetic fibres join to form the superior hypogastric plexus (sympathetic) at L5, at the level of the aortic bifurcation
- the plexus splits into 2 nerve bundles of 2-3 fibres each - the right and left hypogastric nerves which travel between the leaves of the endopelvic fascia (at the sacral promontory, 1cm lateral to the midline, 2cm medial to the ureters)
-
preganglionic parasympathetic fibres from S2,3 and 4 nerves (pelvic splanchnic nerves/nervi erigentes) join the hypogastric nerves to form the inferior hypogastric plexus (mixed sympathetic and parasympathetic)
- lies on side wall of pelvis on each side, superficial to endopelvic fascia & the int iliac vessels
- in men is lateral to rectum & posterolateral to seminal vesicle, prostate and posterior part of bladder; middle of plexus is level with and just behind top of vesicle
- in women plexus is lateral to rectum, cervix, vaginal fornix and posterolateral to bladder
- plexus = rectangular, fenestrated plaque of nerves and ganglia ~5cm AP and 2cm vertically
- (~half the fibres in the hypogastric nerves are myelinated (preganglionic) and they relay in the ganglia of the inf hypogastric plexus; the remaining sympathetic fibres and all the parasympathetic fibres pass through w/o relay; the parasympathetic motor and secretomotor fibres relay in the walls of viscera)
- visc branches of inf hypogastric plexus accompany visc branches and tributries of int iliac artery and vein as neurovasc bundles
- cavernosal fibres travel from IHP in pelvic areolar tissue; form neurovasc bundles that lie immediately anterolateral and anterior to Denonvilliers’ fascia in the 10 and 2 o’clock position in relation to the rectum when viewed from above, on their way to pierce the urogenital diaphragm and enter the corpora
- pelvic parasympathetics are
- motor to emptying muscle (detrusor) of bladder, and of gut from splenic flexure to rectum
- secretomotor to gut and vasodilator to erectile tissue in perineum
- sympathetics are
- motor to visceral muscle of bladder neck, int anal sphincter, vas deferens, seminal vesicles and prostatic muscle
- also have a facilitating function in relation to uterine muscle
- sites of possible injury
- high ligation of IMA
- lumbar splanchnics (sympathetic) from T12-L2 sympathetic chain are direct posterior relation of IMA
- further inferiorly superior hypogastric plexus and origin of hypogastric nerves
- these sympathetic fibres are easily incorporated in IMA pedicle if blunt or finger dissection is used to sweep IMA off front of aorta - damage at this site can be avoided by use of sharp dissection under vision
- at pelvic brim - posterior mobilisation of rectum
- hypogastric nerves lie just beneath peritoneum and level of peritoneal reflection - identify them at pelvic brim and stay anterior and medial to them
- NB if peritoneum is divided too far laterally before nerves have been identified higher up, they are at risk
- lateral dissection
- don’t venture out anterolaterally too far during pelvic dissection to avoid IHP
- anterior dissection of Denonvillier’s fascia
- cavernosal nerves pass anterolateral to rectum on their way to pierce urogenital diaphragm before entering corpora; they are close to posterolateral margin of prostate & lateral margins of Denonvilliers
- dissect anterior to Denonvillier’s to level of seminal vesicles/prostate then dissect posteriorly through it to stay behind the urogenital autonomic fibres during lowest part of ant dissection
- wide anal excision runs highest risk of damaging urogential autonomics - use intersphincteric dissection for benign disease (UC, FAP)
- high ligation of IMA
- sympathetic damage = ejaculatory failure or retrograde ejaculation (superior hypogastric plexus, hypogastric nerves)
- parasympathetic damage = impotence, urinary retention, vaginal dryness (inferior hypogastric plexus, anterolateral dissection deep in pelvis)
Ischioanal fossa
- wedge-shaped anatomical space filled with fat lateral to anal canal
- borders:
- medially and superiorly: levator ani
- laterally and superiorly: obturator internus above, ischial tuberosity below
- inferiorly/base: skin between ischial tuberosity and anus
- at base
- anterior boundary = posterior border of perineal body and muscles of urogenital diaphragm
- posterior boundary = sacrotuberous ligament overlapped by lower border of glut max
- apex = where medial and lateral walls meet (where levator ani is attached to its tendinous origin over obturator fascia)
- each fossa has an anterior recess that passes forwards above perineal membrane, potentially as far as posterior surface of body of pubis; recesses of the 2 sides don’t communicate
- posteriorly, the 2 fossae communicate w one another, low down through fibrofatty tissue of retrosphincteric sapce above anococcygeal ligament, providing horseshoe-shaped path for spread of infection from one fossa to the other
- contents
- pudendal canal - in lower lateral wall of fossa, overlying obt int and medial side of isch tuberosity; contains pudendal nerve and int pudendal vessels which it conducts from lesser sciatic notch to deep perineal pouch above perineal membrane
- inf rectal branches of pudendal nerve & int pudendal vessels run tranvsersely across ischioanal fossa from pudendal canal towards anal canal; not a straight course but arch convexely upwards through fat towards apex then downwards to anal canal so I&D of ischioanal abscesses usu dont interfere w them
- accompanied by the vessels, the nerve breaks up into several branches which supply ext sphincter, mucous membrane of lower anal canal and perianal skin
- perineal branches pass anteriorly into urogenital region
Pelvic floor
Pelvic floor
Rectum
- 12-15cm long, continous w sigmoid at level of S3; surgically where the sigmoid mesocolon ends and where the taeniae of sigmoid gradually broaden to form complete outer layer of longitudinal muscle (also no epiploicae in rectum)
- follows posterior concavity & has 3 lateral curves or flexures
- upper and lower curves convex to right and middle curve convex to left
- lowest part slightly dilated as rectal ampulla
- corresponding to 3 curves seen externally are transverse folds of Houston - project into lumen from concave side of these folds
- the folds incorporate the circular muscle of the wall (ie not just made up of mucous membrane)
- middle fold projects just above level at which peritoneum is reflected forwards off rectum to form floor of rectovesical or rectouterine pouch; about 8cm from anal orifice; useful landmark during sigmoidoscopy
- rectum turns downwards and backwards as anal canal 2-3cm in front of tip of coccyx
- anorectal junction = slung forward by puborectalis
- connective tissue and fat around rectum = mesorectum, with mesorectal fascia (visceral fascia) surrounding it
- mesorectum = bulkier posteriorly, contains superior rectal artery and vein and branches/tributaries, lymphatics and nodes
- rel avasc plane between mesorectal fascia and parietal pelvic fascia - this is plane of surgical dissection in TME of rectum for carcinoma
- plane most evident posteriorly & minimal laterally where inf hypogastric plexus lies tangentially on surface of mesorectal fascia
- peritoneum covers upper 1/3 of rectum at front and sides, middle third only at front, lower third below level of peritoneum
- rectovesical/rectouterine pouch 7.5cm and 5.5cm above anal margin respectively
- anterior to rectovesical pouch = uppermost part of base of bladder & tops of seminal vesicles; below level of pouch = rest of bladder base & seminal vesicles, prostate and ends of each ureter and vas
- between these structures and rectum = rectovesical fascia of Denonvilliers
- connected to floor of rectovesical pouch above and to apex of prostate below
- between these structures and rectum = rectovesical fascia of Denonvilliers
- anterior to rectouterine pouch = uppermost part of vagina (fornix+cervix); below peritoneal reflection = more of vagina w rectogenital septum intervening
- this thin rectovaginal fascia fuses w perineal body below
- blood supply
- principally sup rectal artery + contributions from middle & inf and median sacral vessels
- lower end of IMA enters sigmoid mesocolon & changes its name to superior rectal on crossing pelvic brim
- crosses left common iliac vessels medial to ureter & descends in base of medial limb of mesocolon
- at S3 (where rectum begins) it divides into 2 branches which descend on eitehr side of the rectum and subdivide into smaller branches
- they continue submucosally into anal canal, where they anastomose w branches of inf rectal artery
- middle rectals present only in ~20%
- inf rectals can supply rectum from below to a level at least as high as peritoneal reflection from its anterior surface
- lower end of IMA enters sigmoid mesocolon & changes its name to superior rectal on crossing pelvic brim
- principally sup rectal artery + contributions from middle & inf and median sacral vessels
- venous drainage
- veins correspond to arteries but anastomose freely w one another, forming an int rectal plexus in submucosa & ext rectal plexus outside muscular wall
- lower end of plexus = continuous w vasc cushions of anal canal
- main route of venous drainage = sup rectal vein to IMV
- inf rectal veins to int pudendal veins
- lymph drainage
- mainly upwards - epicolic nodes on surface of rectum, pararectal nodes in mesorectum, upwards drainage via nodes along IMA to preaortic nodes
- lymphatic drainage from lower rectum to int iliac nodes along middle rectal and inf rectal arteries, and along median sacral artery to nodes in hollow sacrum = minimal and unlikely to be a route for metastatic spread of cancer that hasn’t breached mesorectal fascia
- nerve supply
- sympathetic = from inferior mesenteric plexus
- parasympathetic supply = S2,3,4 (pelvic splanchnic nerves) via inf hypogastric plexus; they are motor to rectal muscle
- pain fibres accompany both sympathetic and sympathetic supplies (as for bladder)
- sensation of distension = conveyed by parasympathetic afferents
- layers of endopelvic fascia
- respect of fascial layers of pelvis allows delivery of rectum and mesorectum as one lymphovascular entity
- cylinder of mesorectum has a bilaminar plane between it and prostate/seminal vesicles anteriorly - Denonvilliers fascia
- and sacrum and presacral vessels posteriorly - Waldeyer’s fascia
- although fused, this embryological plane can be recreated and mesorectum thereby delivered
Small bowel
- SB 3-5m from DJ flexure to IC valve; approx 2/5 jejunum and 3/5 ileum
- jejunum vs ileum
- jejunum lies coiled in upper part of infracolic compartment; ileum in lower part of infracolic compartment and pelvis
- jejunum thicker and wider-bored than ileum
- jejunum has plicae circulares which are absent in distal ileum; can be palpated through bowel wall
- distal ileum assoc w whitish Peyer’s patches in mucous membrane of antimesenteric border - aggregated lymphoid follicles
- jejunum pinker bc has more blood supply
- mesentery of ileum characterised by shorter, more dense vascular arcades, but less well seen bc of increased mesenteric fat cf jejunum (fat in mesentery reaches bowel wall in ileum but not jejunum)
- root of SB mesentery begins to left of L1 or L2 and crosses obliquely downwards and to right to overlie right SI joint
- ~15cm in length and crosses D3 (usually) or D4, aorta, IVC, right ureter
- relationship w D3/D4 important bc in surgical resections of duo and pancreas, root of mesentery makes dissection in the area difficult
- SMA and SMV enter mesentery at level it crosses duo and initially run in its base; but usu pass into mesentery towards left and only the ileocolic vessels continue to run in base towards caecum
- bc of disparity in length between SB and root of mesentery, the mesentery has to form into a series of convolutions, usu described as being like a fan
- ~15cm in length and crosses D3 (usually) or D4, aorta, IVC, right ureter
- arterial supply
- whole of SB supplied by SMA
- arises behind neck of panc & at this point usu gives off the inf pancreaticoduodenal artery & middle colic artery and then passes in front of duo to enter root of mesentery
- quite high up it gives off a right colic and ileocolic branch from its right side (sometimes coming off as a single trunk)
- main stem then passes into mesentery itself while ileocolic continues on in root of mesentery to pass towards caecum
- on its left side in mesentery the SMA gives off ~15 intestinal branches, w 5 being proximal and large, and rest distal and small
- in the mesentery, each intestinal branch divides into a superior and inferior branch which anastomoses w its similar fellow above and below to form a series of arcades
- in prox SB usu only 1 or 2 arcades but their number increases until by about mid SB and beyond, their number may be 5 or 6
- then number progressively falls again til TI is reached, where only one or two are found again
- vasa rectae arise from arcade farthest from SMA and pass straight to bowel wall; are essentially end arteries - this is an important point bc the SB doesn’t have an abundant intramural plexus like the oesophagus or stomach
- in ileum, vasa rectae shorter but form larger series of arcades; also more fat in mesentery so windows characteristic of jejunal part not seen
- end of SMA itself supplies region of Meckel’s diverticulum if present and anastomoses w arcades and w ileocolic branch to supply TI
- whole of SB supplied by SMA
- venous drainage
- usu follows arterial supply though veins tend to be fewer in number; this means that artery and vein don’t always lie close together and in dissection the vein should be treated separately from corresponding artery
- drain to SMV
- lymph drainage
- jejunal & ileal lymph drains to superior mesenteric nodes via mural and intermediate nodes in mesentery
- innervation
- autonomic nerves reach wall of SB w its blood vessels
- parasympathetic vagal supply augments peristaltic activity & intestinal secretion
- many afferent fibres whose function is uncertain
- sympathetic supply which is vasoconstrictor & normally inhibits peristalsis, is from lateral horn cells of spinal segments T9 and 10
- pain impulses use sympathetic pathways mainly and SB pain usu felt in umbilical region of abdomen
Thoracic aorta
- Commences at lower border T4 vertebra, where arch of aorta ends
- At first to left of midline, slants gradually to midline and leaves posterior mediastinum at T12 vertebra by passing behind the diaphragm between the crura (ie behind median arcuate ligament)
- Relations
- Oesophagus initially lies to its right but inclines to left so it lies progressively in front of aorta and then to its left side
- Root of left lung lies in front of aorta above and left atrium lies in front below
- Gives off:
- 9 pairs of posterior intercostal arteries
- a pair of subcostal arteries
- bronchial arteries
- oesophageal vessels
- a few small pericardial and phrenic branches
- main significance of these arteries for the vascular surgeon = branches they give to spinal column
- spinal cord obtains its blood supply locally from spinal arteries – ie from vertebral, deep cervical, intercostal and lumbar arteries
- in most pts these vessels anastomose and removing segmental supply produces no untoward effects
- but not uncommon for one of the arteries of supply to the cord to be larger than the others; this is usu a lower intercostal or upper lumbar artery, and gets called arteria radicularis magna
- arises more frequently from a left-sided artery and in a small proportion of cases it provides the major supply to the cord below its level
- if it is divided, excluded or clamped for a long period can lead to paraplegia
Azygos system of veins
- thoracic wall and upper lumbar region are drained by posterior intercostal and lumbar veins into azygos system of veins
- azygos vein
- usu formed by union of ascending lumbar vein w subcostal vein of right side just below diaphragm
- goes through aortic opening of diaphragm under right crus, lateral to thoracic duct, and passes upwards lying on sides of vertebral bodies, on a plane posterior to that of the oesophagus
- at T4 arches forwards over the hilum of right lung and ends in SVC
- receives lower 8 posterior intercostal veins and at its convexity the superior intercostal vein of right side
- receives bronchial veins from right lung, pericardial veins and some veins from the middle third of the oesophagus
- the two hemiazygos veins usu join it at levels of T7 and 8 vertebrae
- hemiazygos veins
- 2 veins, lie longitudinally on left side of bodies of thoracic vertebrae
- inferior vein, hemiazygos, is formed in abdomen by union of left ascending lumbar and subcostal vein (and often communicates with left renal vein)
- passess up through left crus of diaphragm and receives veins from lower oesophagus
- lower 4/8 left posterior intercostal veins
- superior vein, accessory hemiazygos, receives bronchial veins from left lung
- they also receive the left upper 4 posterior intercostal veins
- may communicate w each other, but characteristically drain separately from their adjoining ends behind the oesophagus into the azygos vein
- azygos and hemiazygos veins lie in front of posterior intercostal arteries from aorta
Common iliac arteries
- as termination of aorta lies slightly to left of midline, right CIA slightly longer than left
- right CIA crosses formation of IVC so that it tends to overlie termination of left CIV; this sometimes causes a relative narrowing of termination of left CIV (suggested by iliofemoral thrombosis is more common on left than right)
- left CIA isn’t related to any venous structure posteriorly near its origin w left CIV lying medial, but becoming posterior
- left artery is behind root of mesosigmoid and superior rectal artery
- both arteries crossed near their termination by the ureters
- CIAs have no major branches but both give small unnamed branches to muscles, peritoneum, ureters etc
- divide into ext and int iliac arteries in front of SI joints
IVC
- formed by confluence of right and left CIVs in front of L5 vertebra
- ascends retroperitoneally to right of aorta & passes in a groove in liver or occasionally embedded in liver substance
- perforates tendinous portion of diaphragm and pericardium to enter the inferoposterior part of the RA
- no valves in the cava distal to a somewhat vestigial valve at its entry into right atrium
- IVC crossed at its origin by right CIA (though this may more often cross left CIV)
- in its ascent, the IVC
- is crossed by root of mesentery and right gonadal artery both from left above to right below
- lies behind duo C with its contained HOP
- lies posterior to epiploic foramen to right of caudate lobe, though caudate process lies anterior to it
- is crossed behind by
- two lowermost right lumbar arteries lower down
- right renal artery higher up
- small right suprarenal and inf phrenic arteries where it lies posterior to liver
- right adrenal gland lies to its right and partly behind it as cava becomes retrohepatic
- right sympathetic chain is overlain by IVC in its abdominal course
- IVC most directly accessible where it lies behind epiploic foramen covered only by a glistening layer of peritoneum
- vertical incision to divide peritoneum over IVC, then place tape around it (this point is above renal veins and below the higher tributaries)
- to expose renal veins: kocherise duo and pancreas, and retropancreatic cava thereby exposed
- tributaries
- lumbar veins
- usu 4 pairs but only caudal 3rd & 4th pairs regularly drain into posterior aspect of IVC (2nd pair of lumbar drains may drain into cava at level of renal veins but, like first pair of lumbar veins, often drain into ascending lumbar or lumbar azygos vein)
- two left veins pass behind aorta therefore at risk during mobilisation of aorta
- two righth veins easily damaged when IVC is retracted anteriorly during lumbar sympathectomy
- right gonadal vein (testicular, ovarian)
- only on right side that gonadal veins drain into IVC just below right renal vein
- left vein drains into left renal vein
- renal veins
- usu enter cava at angle of ~45 degrees to vertical & left vein usu higher than right by 1-2cm
- right adrenal vein
- v short, drains into posterior aspect of IVC just before it becomes retrohepatic in position
- right inferior phrenic vein
- drains undersurface of diaphragm and drains into vena cava usu above entrance of right hepatic vein
- hepatic veins
- there are several
- lower group = small-sized veins which are variable in number, usu from 1-3 on both right and left sides, w right draining segment VIII of right side of liver and left draining segment I (caudate lobe)
- in ~15% of cases a vein in a right group may be moderately large and then called an accessory right hepatic vein
- these veins usu have a short 1-2cm extrahepatic course & can be approached for ligation by dividing peritoneal attachments of liver and retracting the appropriate lobe to right or left
- alternatively, when liver is being removed for transplant but IVC being retained, division of lower veins can be carried out after division of upper (major) hepatic veins
- there is a tributary-free plane anterior to retrohepatic cava and a finger can be gently inserted into this plane from above, below the major veins
- liver can then be divided through main portal fissure down to finger and the sides of liver are opened out like a book
- tributaries entering anterolateral surfaces of cava can then be dissected free and ligated
- upper group = major veins draining the liver
- left and middle hepatic veins usu join together to enter vena cava as a common trunk
- main trunks of all the veins have a short extrahepatic course and can be dissected free after division of the peritoneal attachments of the liver
- as the retrohepatic vena cava is usu included w the liver in a liver transplant, the variations in hepatic drainage aren’t usu of importance for this procedure
- variations usu involve one of the segments such as VI, VII or VIII draining directly into the IVC
- lumbar veins
Portal vein and aberrant portal vein anatomy
- commences behind neck of panc where SMV and splenic veins unite
- courses upwards within free edge of lesser omentum, posterior to both CBD and hepatic artery (hepatic artery anterior to it, CBD anterolateral to it)
- at porta hepatis, portal trinity enter liver surrounded by Glisson’s capsule
- portal vein branches into right and left veins; right divides into two sectional and four segmental veins, as do the arteries and bile ducts
- on left however, portal vein anatomy is unique, a reflection of its role as a conduit between systemic and portal circulations in the foetus; the left portal vein has a transverse and vertical, or umbilical, segment
- transition is marked by the adjoining ligamentum teres (remnant of left umbilical vein) and the end of the vertical portion is marked by ligamentum venosum (remnant of ductus venosus)
- both portions of left portal vein are on surface of liver, rather than within its substance as the hepatic artery and bile duct are
- on left however, portal vein anatomy is unique, a reflection of its role as a conduit between systemic and portal circulations in the foetus; the left portal vein has a transverse and vertical, or umbilical, segment
- tributaries
- on right a small vein from GB may be encountered and on left a tributary from quadrate lobe may enter close to branching of portal vein
- in middle portion between its branching and the duo, usu doesn’t have any tributaries
- but as vein is dissected towards duo, several tributaries may be found - cause troublesome, even catastrophic bleeding if they are damaged
- superior pancreaticoduodenal vein(s) which enter right side of portal vein behind or immediately above the duo
- right and sometimes left gastric veins also enter portal system somewhat variably; if they join the portal vein they do so on its left side usu behind duo but occasionally higher, where they will be in field of dissection
- variations of portal vein (not v common)
- most common variation = trifurcation - division into left, right anterior and right posterior branches
- other variations include right anterior or posterior arising from portal vein early, or off the left portal vein
Lymphatic system
- abdominal lymphatics
- lymph drains along coeliac, SMA and IMA to preaortic nodes situated around origin of these vessels
- similarly lymphatics pass back along paired branches of aorta, both visceral and somatic, to para-aortic nodes which lie alongside aorta
- cisterna chyli
- from highest of aortic groups a variable number of intestinal and lumbar lymph trunks join to form the elongated sac-like Cisterna Chyli
- situated under cover of right crus
- in front of bodies of L1 and L2
- between aorta and azygos vein
- becomes continuous w thoracic duct
- thoracic duct
- commences at T12 at upper end of cisterna chyli, between aorta and azygos vein
- passes upwards to right of aorta & comes to lie against right side of oesophagus
- inclining to left, alongside aorta, passes behind oesophagus at T5 to reach left at superior mediastinum; lies to left of oesophagus on a posterior plane
- lies anterior to right aortic intercostal arteries & terminal parts of hemiazygos and accessory hemiazygos veins
- in superior mediastinum lies posterior to arch of aorta & left subclavian artery
- at root of neck at ~level of inf thyroid artery/3cm above clavicle, arches forward and to the left, behind carotid sheath and its contents, but in front of the sympathetic trunk, vertebral artery and vein and thyrocervical trunk; may even pass in front of scalenus anterior before passing back downwards and ending variably in confluence of subclavian and IJ veins
- in neck receives left jugular and subclavian lymph trunks
- drains all of body except right arm and right side of head, neck and thorax which is drained by right lymphatic system
- posterior right thoracic wall enters right lymphatic duct
- much smaller than thoracic duct; drains right intercostal nodes and right bronchomediastinal trunk
- may receive right jugular and subclavian lymph trunks before it opens into commencement of right brachiocephalic vein, or they may remain separate and open independently into jugulosubclavian junction
- right upper limb drains into right subclavian trunk
- right side of H&N drains into right jugular lymph trunk
- posterior right thoracic wall enters right lymphatic duct
- ok to ligate if damaged at time of oesophagectomy
Thoracic duct & cisterna chyli
- abdominal lymph drains along coeliac, SMA & IMA to preaortic nodes around origin of these vessels
- similarly lymphatics pass back along paired branches of aorta, both visceral and somatic, to para-aortic nodes alongside aorta
- cisterna chyli
- from highest of aortic groups a variable number of intestinal & lumbar lymph trunks join to form the elongated sac-like cisterna chyli
- under cover of right crus
- in front of bodies of L1 & L2
- between aorta & azygos vein
- becomes continuous w thoracic duct
- thoracic duct
- commences at T12 at upper end of cisterna chyli, between aorta & azygos vein
- passes upwards to right of aorta & comes to lie against right side of oesophagus
- inclining to left, alongside aorta, passes behind oesophagus at T5 to reach left at superior mediastinum; lies to left of oesophagus on a posterior plane
- lies anterior to right aortic intercostal arteries & terminal parts of hemiazygos and accessory hemiazygos vein
- in superior mediasitnum lies posterior to arch of aorta and left subclavian artery
- at root of neck at about level of inf thyroidal artery/3cm above the clavicle, arches forwards and to the left, behind carotid sheath and its contents, but in front of sympathetic trunk, vertebral artery and vein and thyrocervical trunk; may even pass in front of scalenus anterior before passing back downwards and ending variably in confluence of subclavian and IJ veins
- in neck receives left jugular and subclavian lymph
- drains all of body except right arm and right side of head, neck and thorax which is drained by right lymphatic system
- fine to ligate at oeosphagectomy bc of numerous alternative lymphatic pathways
- right thoracic system
- posterior right thoracic wall enters right lymphatic duct
- much smaller than thoracic duct, drains right intercostal nodes and right bronchomediastinal trunk
- may receive right jugular and subclavian lymph trunks before it opens into commencement of right brachiocephalic vein, or they may remain separate and open independently into jugulosubclavian junction
- right upper limb drains into right subclavian trunk
- right side of H&N drains into right jugular lymph trunk
- posterior right thoracic wall enters right lymphatic duct
