Anatomy - Jon

Question 1

What are the branches of the axillary artery?

Answer 1

The three parts of the axillary artery are divided by the relaitonship to pectoralis minor.

• The first part (above pec. minor)
  
  • The superior thoracic artery
• The second part (behind pec. minor)
  
  • The Thoracoacromial artery
    
    • Clavicular
    • Deltoid
    • Acromial
    • Pectoral
  • The lateral thoracic artery
• The third part (below pec. minor)
  
  • The subscapular artery (largest br.)
    
    • Gives off circumflex scapular to become thoracodorsal artery
  • The anterior circumflex humeral artery
  • The posterior circumflex humeral artery (passes through quadrangular space with axillary nerve)

Question 2

Describe the anatomy of the brachial plexus

Answer 2

• Roots (C₅ to T₁) lie between scalene muscles
• Trunks lie in the post. triangle
• Divisions behind the clavicle
• Cords in relation to the 2^nd part of the axillary artery
• Branches:
  
  • From nerve roots
    
    • Dorsal scapular nerve (C₅)
      
      • Levator scaplulae and rhomboids
    • Nerve to subclavius (C₅, C₆)
    • Long thoracic nerve (C₅, C₆, C₇)
      
      • Serratus anterior
  • From trunks
    
    • Suprascapular nerve (C₅, C₆)
      
      • Supra/infraspinatus
  • From cords
    
    • Lateral (MLL)
      
      • Musculocutaneous nerve (C₅, C₆, C₇)
      • Lateral pectoral nerve (C₅, C₆, C₇)
      • lateral root of median nerve
    • Posterior (ULTRA)
      
      • Upper/Lower Subscapular nerves
        
        • Subscap and Teres Major
      • Thoracodorsal nerve (C₆, C₇, C₈)
        
        • Lat. Dorsi
      • Radial nerve (C₅ - T₁)
        
        • Extensor compartment
      • Axillary nerve (C₅, C₆)
        
        • Deltoid, Teres Minor, Shoulder
    • Medial (MMMMU)
      
      • Medial pectoral nerve (C₈, T₁)
        
        • Pec Major and Pec Minor
      • MCNA (C₈, T₁)
      • MCNFA (C₈, T₁)
      • medial root of Median nerve
      • Ulnar nerve (C₇, C₈, T₁)
        
        • Intrinsic muscles of hand, FCU, half of FDP, skin

Question 3

Discuss the anatomy of the breast

Answer 3

• The breast is a modified sweat gland which originates from a mammary ridge at 6 weeks.
• It is a fibroglandular unit composed of compound tubulo-acinar units culminating as 15-20 lactiferous ducts at the nipple.
• It overlies ribs 2-6 from the sternal edge to the mid-axillary line.
• It is invested in superficial fascia with a deep surface abutting the pectoralis fascia and intervening Cooper’s ligaments providing structural support in the plane perpendicular to the skin.
• It is supplied by four arteries:
  
  • Perforators from the ITA/IMA
  • Branches from the pectoral branch of the TAA
  • The lateral thoracic artery
  • Laterally, branches from the intercostal arteries and subscapular artery.
• The lymphatic drainage is predominantly (~80%) to the axilla and is characterised by a sub-areolar plexus behind the nipple spreading out radially. Dermal lymphatics connect to contralateral breast and abdominal wall.
• A “B” cup is approximately 150g.

Question 4

What are the divisions of the mediastinum?

What are the contents within each?

Answer 4

• The plane passing from the sternal angle to the body of T4 divides the mediastinum; above this plane is the superior mediastinum.
• Below this plane, the fibrous pericardium divides the inferior mediastinum into three compartments; the anterior in front, the posterior behind, and the middle, containing the pericardium and heart within. These spaces are all continuous.
  
  • Superior
    
    • Anteriorly manubrium
    • Posteriorly T₁-T₄ bodies
    • Trachea anterior to oesophagus
    • Apices of lungs laterally
    • BC trunk and left BC vein and thymus lower aspect
    • Aortic arch totally within superior mediastinum. Cardiac plexus on this.
    • Vagi and phrenic nerves on either side (aortic arch on left and trachea/right BCV on the right)
    • IVC formed at 1st cc
    • Thoracic duct
  • Anterior mediastinum
    
    • Thymus
  • Middle mediastinum
    
    • Heart and pericardium
    • Great vessels and lung roots
    • Phrenic nerves
  • Posterior mediastinum
    
    • Descending aorta
    • Oesophagus
    • Thoracic duct
    • Azygous
    • Sympathetic trunk

Question 5

Describe the structures found at the division of the superior and inferior mediastinum.

Answer 5

Angle of Louis to T4

Bifurcation of trachea

Underside of aortic arch with ligamentum arteriosum

Azygous enters SVC

Thoracic duct passes to LHS of oes.

Prevertebral fascia ends.

Question 6

What structures are found at the transpyloric plane?

Answer 6

Half way between jugular notch and pubic symphysis

Pylorus

DJ flexure

Neck of pancreas

Formation of portal vein

Fundus of GB

Spleen

Kidneys (right lower than left)

Tips of 9th CC

Origin of SMA

Conus medullaris

Cisterna chyli

Question 7

Describe the branches of the internal iliac artery.

Answer 7

Posterior division:

1. Ileolumbar artery
2. Lateral sacral artery
3. Superior gluteal artery

Anterior division:

3 x vesical branches

1. Superior vesical (persistent part of umbilical artery)
2. Inferior vesical
3. Obliterated umbilical (continuation of superior vesical)

3 x visceral branches

1. Uterine artery
2. Vaginal artery
3. Middle rectal artery

3 x parietal branches

1. Obturator artery
2. Pudendal artery
3. Inferior gluteal artery

Question 8

What are the boundaries and contents of the femoral triangle?

How do they relate to your approach to inguinal lymph node dissection?

Answer 8

• The inguinal ligament forms the base of the triangle
• The medial border of sartorius forms the lateral border
• The medial border of adductor longus forms the medial border.
• The apex is where the two muscle converge. This is the beginning of Hunter’s canal and is often where the GSV and an important lymphatic channel are encountered.
• The roof of the femoral triangle is the fascia lata of the thigh.
• The floor of the femoral triangle is muscular; iliacus and psoas, pectineus, adductors brevis and longus.
• The contents include the femoral nerve and its branches, the femoral artery and its branches, and the femoral vein and its tributaries. It contains the deep inguinal lymph nodes.

The lymph node dissection is an en-bloc dissection of the lymph nodes both superficial and deep, and extends beyond the aforementioned boundaries, typically 1-3cm above the inguinal ligament, and overlapping the muscles on either side. Note should be made of the LFCN as it lies on sartorius and must be protected prior to division of the muscle for muscular coverage.

Question 9

Describe the anatomy of the popliteal fossa

Answer 9

• The popliteal fossa is diamond shaped with the following boundaries:
  
  • Superolateral - biceps femoris
  • Superomedial - semimembranosus with overlying semitendinosus
  • Inferolateral - lateral head of gastrocnemius with underlying plantaris
  • Inferomedial - medial head of gastrocnemius
  • Floor - the posterior surface of the femur and tibia, the oblique popliteal ligament reinforcing the capsule of the knee joint and the popliteus muscle
  • Roof - popliteal fascia pierced by the PFCN and the small saphenous vein.
• Popliteal artery
  
  • Throughout its course the artery is the deepest of the neurovascular structures in the fossa
  • It enters through the adductor hiatus a hands-breadth above the knee and exits through the soleus arch a hands-breadth below.
  • It has a lateral convexity. It gives off paired superior and inferior genicular, and one middle genicular arteries as well as sural arteries supplying the heads of gastrocnemius.
• Popliteal vein
  
  • The vein is always between the artery and nerve. It is formed by the union of the venae comitantes of the anterior and posterior tibial arteries, these may persist as dual vessels
• At the apex of the fossa the sciatic nerve divides…
• Common peroneal nerve
  
  • Runs downwards and laterally, medial to the biceps tendon around the neck of the fibula and into the substance of peroneus longus
• Tibial nerve
  
  • Runs vertically downwards to the soleus arch
  • It gives motor branches to all the muscles that arise in the popliteal fossa; plantaris, both heads of gastrocnemius, soleus, and popliteus
  • Its cutaneous nerve, the sural nerve runs between the heads of gastrocnemius and pierces the fascia lata of the calf half way down the leg.

Question 10

Describe your surgical approach to the popliteal artery

Answer 10

The popliteal artery can be exposed above and below the popliteal fossa by medial approaches

Supragenicular approach

• Lower thigh and knee gently flexed
• Longitudinal incision over the medial aspect of the lower thigh over the anterior border of sartorius
• Expose sartorius, watch out for GSV, retract sartorius posteriorly to reveal the neurovascular bundle
• The artery is the deepest structure, closest to the bone.

Infragenicular approach

• Lower thigh and knee gently flexed
• Longitudinal incision upper medial calf along medial head of gastrocnemius
• If GSV is required, harvest now
• Retract and even divide the tendons of pes anserinus if needed for exposure
• Continue dissection through medial head of gastrocnemius toward tibia to reveal neurovascular bundle; vein encountered first.

Question 11

What is popliteal artery syndrome?

Answer 11

Very occasionally the popliteal artery is separated from the vein and nerve by the medial head of gastrocnemius.

This can cause the artery to be displaced medially and can be associated with popliteal artery disease in the young.

Question 12

What is thoracic outlet syndrome?

Describe the relevant anatomy.

Answer 12

Thoracic outlet syndrome is characterised by neurovascular symptoms associated with repetitive use of the affected arm. Neurological symptoms, including pain, parasthesia, and weakness, are more common than vascular complications (such as ischaemia or VTE) which only occur in ~5%.

The thoracic outlet is bounded by the clavicle superiorly, the first rib inferiorly, the spinal column posteriorly, and the sternum anteriorly. The neurovascular structures that traverse the space are the subclavian artery and vein, and the divisions of the brachial plexus. The root of T1 is at the posterior apex. Scalenus anterior inserts onto the first rib between the subclavian artery and vein. The subclavian artery and brachial plexus divisions pass between the insertions of scalenus anterior and medius. A cervical rib will compete with the structures entering the thoracic outlet, this may have compressive fibrous bands associated with it.

Question 13

What are the known perforatoring veins of the leg?

Answer 13

Hunterian in the mid-thigh, Dodd’s in the distal thigh, Boyd’s around and below the knee, Cockett’s around the calf.

Question 14

Discuss the anatomy of lymphatic drainage in the body.

Answer 14

Interstitial and chylous fluid is drained by the lymphatic system, these endothelial tubes have a similar structure to veins with many more valves. The deep lymphatics tend to follow arteries, the superficial lymphatics tend to follow veins. The body has 2 main lymphatic channels:

The right lymphatic duct

• Receives drainage from the right jugular, subclavian, and bronchomediastinal lymph trunks and therefore drains the right upper limb and right half of the head and neck.

The left lymphatic duct

• Begins as the cisterna chyli or recepticulum chyli, a saccular area of dilatation in the lymphatic channels that is located in the retrocrural space, usually to the immediate right of the abdominal aorta at T12.
• The receptaculum chyli is fed by the lumbar lymphatic trunks and the intestinal trunk.
• It ascends into the thorax between the aorta and azygous vein and then crosses to the left of the oesophagus at the level of T4/5.
• Arches over dome of pleura and drains at the confluence of the left IJV and subclavian veins.

Question 15

Describe the anatomy of malrotation

Answer 15

• Symptomatic malrotation occurs in 1:6000 births.
• At 4 weeks the bowel herniates and develops in the extracoelemic cavity.
• It returns at week 10 and rotates 270° counter-clockwise.
• The duodenojejunal segment returns first and rotates beneath and to the right of the SMA.
• The caecocolic segment passes over the duodenum to fix in the right iliac fossa.
• This process is usually complete by week 12.
• Non-rotation, the most common anomaly occurs when neither the DJ segment nor the CC segment rotate, so they are adjacent and hanging off a narrow stalk, which is prone to volvulus.
• Incomplete rotation occurs when the DJ segment rotates but the CC segment rotates only part way counter clockwise, so forming abnormal mesenteric (Ladd’s) bands across the gut.

Question 16

Provide an overview of the hand infections and the spaces they might occupy

Answer 16

Superficial infections

• Cellulitis
• Paronychia
• Finger tip felon
• Herpetic whitlow

Deep space infections

• Flexor tendon sheaths
• Mid-palmer space
• Thenar space
• Space of Parona
  
  • Extension proximally btw PQ and FDP

Question 17

Describe the deep spaces of the hand and where incisions should be made to drain pus within.

Answer 17

• Flexor tendon space
  
  • Synovial sheaths commence at distal transverse palmer crease to distal phalanges.
  • Make 2 incisions; one at the base of the pulp and one at the base of the proximal phalynx and irrigate
• Mid-palmer space
  
  • Dorsal to space are middle and ring finger metacarpels and volar to space are flexor tendons and lumbricals
  • Incise at the levels of the distal transverse palmar crease. Pass artery clips into lumbrical sheaths to ensure drainage
• Thenar space
  
  • Dorsal to space is adductor pollicus, volar to space are the index flexor tendons
  • Incise in web space between thumb and index finger
• Space of Parona
  
  • Space between pronator quadratus and flexor digitorum profundus
  • Longitudinal incision radial side of Ulnar pulse

Question 18

Describe the anatomy of the Carpel Tunnel

Answer 18

• The flexor retinaculum is a tough fibrous band that spans the space between the concave carpel bones at the wrist.
• The ulnar attachments are the pisiform and hook of the hamate bone. The radial attachments are the scaphoid tubercle and ridge of the trapezium.
• Its proximal limits lies at the distal dominant wrist crease.
• The median nerve and all the long flexor tendons of the fingers and thumb pass through this tunnel. The tendons of FDP are in the same plane though the tendons of FDS are in two with the tendons of the index and little fingers deeper to the middle and ring finger.
• The median nerve is located between the middle finger tendon of FDS and the tendon of FCR.
• The ulnar nerve lies on the front of the retinaculum on the radial side of the pisiform with the ulnar artery radial to that. Both are within the canal of Guyon.
• Palmer cutaneous branches of both the median and ulnar nerves cross the retinaculum.

Question 19

What are the boundaries of the axilla?

Answer 19

• The axilla is the anatomical space through which pass vital neurovascular and lymphatic structures from the neck to the upper limb. It is shaped like a truncated cone.
• The anterior wall is made up of pectoralis major and minor with the clavipectoral fascia and subclavius within.
• The posterior wall is formed by subscapularis, teres major and latissimus dorsi.
• The medial wall is serratus anterior on the chest down to the level of the 4th rib.
• The lateral boundary is the inter-tubercular groove of the humerus in which lays the long head of biceps and corachobrachialis.
• The apex of the axilla is bounded by the clavicle, the scapula, and the first rib. It communicates with the posterior triangle of the neck.

Question 20

Describe the course of the median nerve and what is supplies

Answer 20

• The median nerve is a terminal branch of the brachial plexus, taking divisions from the lateral and medial cords to derive supply from C5-T1.
• It supplies most of the flexor muscles of the forearm, but only the thenar muscles (FPL, OP, APB) and two lumbricals in the hand.
• In the arm it is medial to the brachial artery but it crosses the ulnar artery just distal to the ACF to run down the midline of the forearm where it dives between the heads of pronator teres and deep to the arch of FDS. Prior to this it supplies PL, PT, FCR, and FDS.
• Its anterior interosseous branch is the nerve of the deep flexor compartment supplying the radial half of FDP, as well as PQ and FPL.
• It enters the hand through the carpel tunnel where it may be compressed, causing this sign.
• Sensory supply of the median nerve is to the radial 3.5 digits on the entire palmar side and the tips of the dorsal digits.

Question 21

Describe the course of the Ulnar nerve and what is supplies.

Answer 21

• The ulnar nerve is a terminal branch of the brachial plexus, it is the direct continuation of the medial cord (C7, C8, T1).
• It runs down the arm between the axillary artery and vein behind the MCNFA. It pierces the medial intermuscular septum and descends in the groove on the back of the medial epicondyle. It then passes between the heads of FCU and enters the flexor compartment.
• It descends on FDP under cover of FCU, supplying both. It is joined on its radial side by the ulnar artery and passes into the hand through the canal of Guyon to supply most of the intrinsic muscles of the hand and the skin of the ulnar 1.5 digits.

Question 22

Describe the cubital fossa.

Answer 22

• The cubital fossa is an anatomical area bounded by a line joining the medial and lateral humeral epicondyles, pronator teres, and brachioradialis.
• The roof of the cubital fossa is made up of the deep fascia of the forearm, reinforced medially by the bicipital aponeurosis.
• The floor is made up of brachialis and supinator.
• The contents, from lateral to medial, are the tendon of biceps, the brachial artery, and the median nerve.
• Farther laterally, under cover of brachioradialis, are the radial nerve and its posterior interosseous branch.

Question 23

Describe the muscular layers of the chest wall

Answer 23

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

Question 24

Describe the embryology of the diaphragm

Answer 24

The diaphragm takes origin from 4 sources;

1. The septum transversum is a thick plate of visceral mesoderm separating the primitive cavities
2. This fuses with the pleuroperitoneal membranes that eventually obliterate the pericardioperitoneal canals
3. It also fuses with the mesentery of the oesophagus, in which the crura of the diaphragm develop
4. Muscular components migrate from cervical myotomes C3-C5 carrying with them the phrenic nerve.

Question 25

What are the attachments of the diaphragm?

Answer 25

The diaphragm is attached circumferentially around the body wall;

• Centrally the crura arise from the upper lumbar vertebrae (L1, L2, L3 on the right cf L1, L2 on the left),
• The posterior origins are the median arcuate ligament, the medial arcuate ligaments, and the lateral arcuate ligaments.
• Anteriorly the diaphragm is attached to the xiphoid and costal cartilages of ribs 7-12.

Question 26

Describe the thoracic sympathetic trunk

Answer 26

The thoracic sympathetic trunk is part of the sympthatic nervous system outflow tract (T1-L2).

The ganglia reside anterior to the heads of the ribs. Sympathetic pre and post ganglionic fibres travels within the trunk to target organs.

Pre-ganglionic fibres may synapse within the ganglia at the same level, as is the case for vaso/pilo/sudomotor innervation of the arm.

They may also synapse at a higher level as exemplified by the sympathetics to the head and neck. From the synapse these nerves hitch-hike on blood vessels.

SNS neurons may synapse at the ganglia and travel on their own “splanchnic” nerve to a target organ, as is the case for the cardiopulmonary splanchnic nerves, as well as the great, lesser, and least splanchinic nerves of the lower thoracic trunk.

Question 27

What stuctures are bisected by the thoracic plane?

Answer 27

• The trachea bifurcates
• The pulmonary trunk bifurcates
• The azygous drains into the SVC
• Undersurface of the aortic arch
• The left RLN recurs under the aortic arch
• The ligamentum arteriosum is found at this level
• The cardiac plexus is at this level
• The pre-vertebral and pre-tracheal fascia terminate
• The thoracic duct passes behind the oesophagus from right to left

Question 28

Describe the anatomy of the ascending and descending aorta.

Answer 28

• The ascending aorta is totally within the pericardium. Immediately above the aortic orifice the aorta bulges to form sinuses, corresponding in location to the valves.
• The RCA emerges from the anterior sinus, the LCA from the left posterior sinus.
• After arching at the level of T4 to the left of the midline, the descending aorta slants back to the midline and exits the thoracic cavity at the level of T12 through the median arcuate ligament.
• The thoracic aorta gives 9 pairs of posterior intercostal arteries, a pair of subcostal arteries, bronchial arteries, oesophageal branches, and some pericardial and phrenic branches.

Question 29

Provide an overview of the muscles of the anterior abdominal wall

Answer 29

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.

Question 30

Discuss the abdominal aorta

Answer 30

The abdominal aorta commences at the level of T12 when the thoracic aorta passes through the median arcuate ligament. It descends to the level of L4 anterior to the vertebral bodies just to the left of the midline where it divides into a left and right common iliac artery. It also gives off a median sacral artery in the midline.

Immediate relations of the aorta are the left sympathetic trunk on its left side and the IVC on its right side. Between the SMA and IMA the uncinate process of the pancreas and third part of the duodenum pass anteriorly as well as the left renal vein. The coeliac, superior, and inferior mesenteric plexuses (SNS) lie on the aorta’s anterior surface. The hypogastric nerves pass over the common iliacs as they pass into the pelvis.

The aorta has 3 visceral branches; the Coeliac Axis at T12, the SMA at L1, and the IMA at L3. It has 3 paired branches to viscera; the adrenal arteries, the renal arteries at L2, and the gonadal arteries. Finally, the aorta has paired branches to the body wall; the inferior phrenic arteries and the 4 paired lumbar arteries.

Question 31

Describe the course and supply of the femoral nerve

Answer 31

The femoral nerve is formed in the lumbar plexus from the posterior divisions of spinal nerves L2 L3 and L4.

It passes through the substance of psoas major (supplies it and iliacus) and exits between iliacus and psoas to pass under the inguinal ligament. It is under the ilopsoas fascia and so is separate from the femoral sheath.

Once inside the femoral triangle it divides early into many branches to supply pectineus, sartorius, medial and intermediate femoral cutaneous nerves, quadriceps, and finally the saphenous nerve, which exits the triangle and passes between sartorius and gracilis.

Question 32

What are the short rotators of the hip? Describe why Piriformis is a landmark muscle.

Answer 32

The short rotators of the hip include:

• Piriformis
• Obturator externus
• Obturator internus
• Super and inferior gemelli
• Quadratus femoris.

Piriformis is a landmark structure because important neuro-vascular structures pass above and below it through the greater sciatic foramen;

Above:

• Superior gluteal artery and nerve

Below

• Inferior gluteal artery and nerve
• Sciatic nerve
• Posterior femoral cutaneous nerve
• Pudendal nerve (back through lesser sciatic notch)
• Internal pudendal artery

Additionally, the sacral plexus forms on the anterior surface of piriformis in the pelvis.

Question 33

What are the surgically relevant layers of the endopelvic fascia?

Answer 33

Respect of the fascial layers of the pelvis allows delivery of the rectum and mesorectum as one lympho-vascular entity; The cylinder of the mesorectum has a bilaminar plane between it and the prostate/seminal vesicles anteriorly and the sacrum and pre-sacral vessels posteriorly. These are Denonvillier’s and Waldeyer’s fascia respectively. Although fused, this embryological plane can be re-created and the mesorectum thereby delivered.

Question 34

Describe the course and branches of the obturator nerve

Answer 34

The obturator nerve is formed in the substance of psoas from the anterior divisions of L2, L3, and L4. It exits psoas at its medial edge and runs on the inside of the lateral pelvis wall to the obturator foramen. It is adjacent to the peritoneum of the ovary at the pelvic sidewall so may be irritated by ovarian pathology.

At the obturator foramen the nerve divides into anterior and posterior nerves. These supply the adductor compartment; the anterior division supplies adductor brevis and gracilis while the posterior division supplies obturator internus, externus, and adductors magnus and longus.

Question 35

Describe the sciatic nerve in terms of origin, course, and supply

Answer 35

The sciatic nerve is formed at the inferior border of the piriformis muscle by the confluence of its tibial and peroneal components (L4, L5, S1, S2, S3).

It passes into the buttock below piriformis at the midpoint between the ischial tuberosity and greater trochanter and descends in the hamstring compartment.

The sciatic nerve supplies all the hamstring muscles and the ischial fibres of adductor magnus. At the apex of the popliteal fossa it splits into tibial and common peroneal nerves.

Question 36

Describe the origin, course, and supply of the peroneal nerve.

Answer 36

The sciatic nerve divides into tibial and common peroneal branches at the apex of the popliteal fossa.

The common peroneal nerve winds around the neck of the fibula, where it is commonly injured.

In the substance of peroneus longus it divides into the superficial and deep peroneal nerves.

The deep branch runs down the interosseous membrane and supplies EDL, TA, EHL, and peroneus tertius.

The superficial branch supplies peroneus longs and brevis and then perforates the fascia to supply the dorsum of the foot, save for the first web space which is supplied by the cutaneous branch of the deep peroneal nerve.

Question 37

What is the course and supply of the tibial nerve?

Answer 37

The sciatic nerve divides into tibial and peroneal components at the apex of the popliteal fossa.

The tibial nerve drops down between the heads of gastrocnemius, behind the knee joint, and deep to the soleal arch. In the popliteal fossa it supplies the knee joint and gives off the sural nerve.

From the fibrous arch of the soleus, the tibial nerve runs down with the posterior tibial vessels between FHL and FDL. It supplies the soleus, TP, FHL, and FDL. The tibial nerve passes behind the medial malleolus and divides into the medial and lateral plantar nerves.

Question 38

Describe the sub-sartorial canal and its surgical relevance

Answer 38

• The sub-sartorial canal is a gutter-shaped groove that runs below the sartorius muscle in the thigh. The groove is between vastus medialis and the front of the adductor muscles; longus and magnus
• It is continuous with the apex of the femoral triangle
• Its contents include the femoral artery and vein, the femoral nerve, and in the upper part, the nerve to vastus medialis.
• The femoral artery exits the canal by passing through the adductor hiatus of adductor magnus into the popliteal fossa; at this point the vein is posterolateral to the artery, though by the groin it will be lying medially.
• The saphenous nerve exits the canal between sartorius and gracilis and runs down the leg behind the GSV.
• The original surgically relevance was rapid access to the great vessels of the leg for swift ampuation (John Hunter). The distal aspect of the canal is accessed for modern supra-genicular approaches to the popliteal artery. The saphenous nerve must be preserved during this procedure.

Question 39

Discuss the anatomy of the thyroid.

Answer 39

The thyroid is a bilobed hormonal gland located in the lower neck; the isthmus of the gland covers the 2nd, 3rd, and 4th tracheal rings. The lobes lie on either side of the larynx and trachea and extend from the level of the upper thyroid cartilage to the 6th tracheal ring. It normally weighs around 25g. It has its own capsule, as well as being covered by the pre-tracheal aspect of the investing fascia.

Anteriorly it is covered by the strap muscles. Posteriorly the isthmus lies on the trachea and the lobes occupy the space between the carotid sheath laterally and the trachea-oesophagus medially. The parathyroid glands are intimately associated with the posterior capsule; they are usually 4 in number and are usually paired. The isthmus may have a pyramidal lobe, which extends a variable distance towards the foramen caecum in the oral cavity.

The RLNs are closely associated with the thyroid on its posterior surface as they ascend in the tracheo-oesophageal groove to pass under cricothyroid prior to entering the larynx. The only consistency about the RLNs is that they are intimately associated with the inferior thyroid artery, though the nature of the relationship varies; the nerve may pass between branches of the ITA (~50% on the right) or behind the branches of the artery (~50%) on the left. Less commonly the RLN passes anterior to these branches. The nerve may branch prior to passing under cricothyroid, the anterior motor division is more at risk.

The ESLN usually passes behind the superior thyroid artery a variable distance above the superior pole of the thyroid; most normal thyroids have a Cernea I pattern, goitre more commonly have a Cernea IIa or IIb pattern.

The thyroid is supplied by the superior and inferior thyroid arteries, branches of the external carotid artery and thyrocervical trunk respectively. Rarely, a thyroidiae ima artery is present, a direct branch from the aorta. It is drained by the superior, middle, and inferior thyroid veins. The middle thyroid vein is the most important vein surgically, this drains directly into the IJV and must be carefully ligated during surgery. Nerve supply follows the arterial supply.

The thyroid lymphatics drain to the central (level VI) and lateral nodes groups (levels II, III, IV). Less commonly they may drain to the mediastinal (level VII) or posterior triangle (level V) nodes.

Question 40

Describe the anatomy of the breast.

Answer 40

The breast is a mammary gland that lies on the chest wall in the subcutaneous tissue. Some 15-20 lactiferous ducts converge to drain at the nipple, the extend radially into the lobules of the breast, which is of a variable size. The base of the breast lies from the parasternal edge medially to the midaxillary line laterally and covers from the second to the sixth ribs. Anteriorly it is covered by the subcutaneous adipose tissue and skin, posteriorly it lies on the fascia of pectoralis major and laterally some of serratus anterior. Inferiorly it lies on the upper-most portion of the rectus sheath and external oblique muscle. Laterally the tail of the breast extends a variable distance towards the axilla.

The nipple is the specialised termination of the functional units of the breast, with smooth muscle present to control secretions. A number of specialised areolar glands (the tubercles of Montgomery) exit the periareolar complex for lubrication.

The breast is supplied by 4 arteries; the perforating branches of the internal thoracic artery, particularly at the 2nd and 3rd intercostal spaces medially, the pectoral branches of the thoraco-acromial artery, the lateral thoracic artery, and perforating branches from the posterior intercostal arteries. Venous drainage follows arterial supply for the most part.

Lymphatic drainage of the breast is predominantly to the axilla (~25% to the internal thoracic nodes). The nodes in the axilla are divided into levels I, II, and III, according to their position relative to the tendon of pectoralis minor, laterally, behind, and medially respectively.

Question 41

Describe the surfaces and ligaments of the liver

Answer 41

• The liver is wedge shaped with a large, curved diaphragmatic surface and an irregular visceral surface.
• Most of the liver is covered by peritoneum, except for the bare area supero-posteriorly, which is intimately related to the IVC, hepatic veins, and the right adrenal gland.
• The visceral surface is indented by adjacent organs including the stomach, colon, kidney, adrenal, gallbladder, and duodenum.
• The falciform ligament passes from the front of the liver to the umbilicus, in its inferior margin is the remnant of the left umbilical vein which inserts into the left branch of the portal vein via a cord.
• The right and left leaflets of the falciform divide towards the top of the liver into the upper layer of the coronary ligament and the front of the left triangular ligament respectively. The coronary ligament has a wide interval between its upper and lower leaflets, encompassing the bare area of the liver between, at its extreme right margin the two join to form the right triangular ligament.
• The lesser omentum passes into a fissure between the caudate and the omental tuberosity of the segment III.

Question 42

Describe the anatomy of the liver lobes

Answer 42

• The liver is divided into functional lobes by the divisions of the portal triad.
• The division between the right and left functional halves is through the main fissure; approximated on the surface by a line from the gallbladder notch to the middle of the IVC; “Cantlie’s line” is variably described.
• The prevailing classification of the further 8 divisions of the liver is by Couinaud;
• Segment I or the Caudate lobe is independently supplied and drained by the portal triad and heptic veins respectively. It lies between the IVC and omental fissure.
• The left hemi-liver is divided into 2 sections divided by the plane of the falciform ligament. Each section consists of 2 segments;
  
  • The left lateral section is made up of segments II and III and is divided by the plane of the left hepatic vein.
  • The left medial section is made up of segments IVa and IVb; divided by the plane of the portal vein
• The right hemiliver is divided into 2 sections by the plane of the right hepatic artery. Each section consists of two segments divided in the horizontal plane by the plane of the portal vein.
  
  • The anteromedial section is made up of segments are V and VIII,
  • The posterolateral section is made up of segments VI and VII.

Question 43

Describe the anatomy of the portal vein

Answer 43

• The portal vein commences behind the neck of the pancreas where the superior mesenteric vein and splenic vein unite.
• It courses upwards within the free edge of the lesser omentum posterior to both the common bile duct and hepatic artery. At the porta hepatis, the portal trinity enter the liver surrounded by Glisson’s capsule.
• The portal vein branches into right and left veins; the right divides into two sectional and four segmental veins, as do the arteries and bile ducts. On the left however, the 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. The transition is marked by the adjoining ligamentum teres (remnant of the left umbilical vein) and the end of the vertical portion is marked by the ligamentum venosum (remnant of the ductus venosus).
• Both portions of the left portal vein are on the surface of the liver, rather than within its substance as the hepatic artery and bile duct are.

Question 44

Describe the anatomy of the gallbladder

Answer 44

• The gallbladder is a sacular outpouching of the biliary system that acts as a reservoir for bile, capable of holding approximately 50-100ml. It has a neck, a body, and a fundus. It lies on the visceral surface of the liver, between segments IVb and V. The fundus is usually visible below the liver.
• It drains bile into the common heptic duct via the cystic ducts which is of a variable length. This is characterised by the spiral valves of Heister.
• When pathology is present, Hartmann’s pouch exists as an outpouching of the neck of the gallbladder.
• The gallbladder has a simple columnar epithelial lining, an irregular muscular layer, and connective tissue between it and the liver on one side and visceral peritoneum on the other.
• It is supplied by the cystic artery, usually a branch of the right hepatic artery, which usually runs through the hepatocystic triangle to arborise onto the gallbladder. Venous drainage is via multiple small channels. Rarely, direct biliary drainage via radicals is seen from the GB into the liver parenchyma.
• It is supplied by the vagus nerve, though the control is predominantly neurohumoral via cholecystokinin and somatostatin.

Question 45

Describe the anatomy of the anus.

Answer 45

• The anal canal is the part of the GI tract that commences at the termination of the rectum at the pelvic floor; here it is angulated by puborectalis. The canal is between 3-5cm long; the termination of the canal is not discrete as the skin is continuous, despite its changing cell type. The intersphincteric groove, readily palpable in the anaesthetised patient marks the end of the anal canal.
• The epithelium changes from rectal mucosa at the proximal limit, to transitional epithelium up to the dentate line, where thicker stratified squamous epithelium commences, the distal most aspect of the anal canal is lined by hair-bearing skin and is continuous with the skin of the perineum.
• The internal anal sphincter represents a condensation of the circular layer of muscle of the rectum and is under autonomic control.
• The external anal sphincter is somatic, and is essentially continous with the levator ani complex and similarly innervated. It is composed of three layers - deep which is continuous with the puborectalis which sits above, the superficial which is attached to the perineal body anteriorly and the coccyx (anococcygeal ligament) posteriorly and the subcutaneous, lies beneath the internal sphnicter.
• Between the two, the corrugator ani complex, the final aspect of the longitudinal musclular layer of the rectum insert onto the skin.
• The blood supply is from the inferior rectal and pudendal arteries.
• Lymphatic drainage of the anus is to both the inguinal and internal iliac nodes.

Question 46

Descibe the anatomy of the duodenum

Answer 46

The duodenum is a C-shaped tube of GI tract lying in front and to the right of the IVC aorta. It connects the stomach to the jejunum. It has 4 parts

The first part is 2 inches in length and runs backwards, upwards, and to the right of the pylorus. It sits between the greater and lesser omentum; it forms the lower-most border of the foramen of Winslow. It lies anterior to the gastroduodenal artery, common bile duct, and portal vein, which in turn are anterior to the IVC. The duodenal cap, seen on Barium as a featureless segment, is 1 inch in length.

The second part of the duodenum is 3 inches in length and curves around the head of the pancreas with the right renal hilum as a postero-lateral relation. It receives the ampulla of Vater at its major papilla, around 10cm from the pylorus, the minor papilla drains 2cm proximal. The second part of the duodenum is split anteriorly by the root of the transverse mesocolon so it is in both the supra and infra colic compartments.

The third part of the duodenum is 4 inches in length and curves across the right psoas, ureter, and gonadals to cross the midline. It occupies the space on the anterior aorta between the origins of the SMA and IMA. It may be compressed here by an acute SMA angle.

The fourth part of the duodenum is 1 inch in length and ascends to the left of the aorta to re-enter to peritoneal cavity (parts 2 and 3 are retroperitoneal) at the DJ flexure. This is identified with the IMV at its lateral margin. The folds here form fossae for possible herniation.

The foregut-midgut transition is at the site of the ampulla of Vater; the Duodenum therefore receives blood supply from both the coeliac axis and the SMA via the gastroduodenal, and superior and inferior pancreaticoduodenal arteries. Venous drainage follows arterial supply. Lymphatic drainage is to both the coeliac axis and SMA nodal basins.

Question 47

How can the jejunum and ileum be distinguished intra-operatively?

Answer 47

The jejunum and ileum make up the majority of the small intestine; in total the small intestine runs 3-5 meters from the DJ flexure to the IC valve; this is approximately 2/5ths jejunum and 3/5th ileum.

The jejunum is thicker and wider-bored than the ileum. Circular mucosal folds can be palpated through the wall of the jejunum; these are absent in the terminal ileum The distal ileum is associated with whitish Peyer’s patches. The mesentery of the ileum is characterised by shorter, more dense vascular arcades (shorter vasa recta but 4-5 vs 1-2 vascular arcades).

The fat in the mesentery reaches the bowel wall in the ileum but not the jejunum.

Question 48

Describe the anatomy of the stomach

Answer 48

• The stomach is a wide caliber, J-shaped part of the GI tract which acts as a reservoir for food between the oesophagus and duodenum. It has a capacity of 1500ml in the adult.
• Embryology: foregut and has a dorsal and ventral mesogastrium. The dorsal mesogastrium gives rise to the greater omentum. Due to more rapid growth of its dorsal portion, the stomach expands, leading to a greater and lesser curvature. It also undergoes two rotations:• 90 degrees about its long axis • Anti-clockwise around a dorso-ventral axis

This results in the greater curvature of the stomach lying to the left of the midline.

• It has a body, fundus, antrum, and cardia.
  
  • The cardia is the most fixed part of the stomach and is the oesophago-gastric junction. This lies 2.5cm to the left of the midline at the level of T10. It is 40cm from the incisor teeth.
  • The body occupies the space between the lesser and greater curvatures. The fundus is the cephaled cap of the stomach which projects above the cardia.
  • The antrum runs from the body, at the point of the incisura to the pyloric canal, where the stomach empties into the duodenum.
• The blood supply is rich; coeliac axis; left gastric, splenic artery and its short gastrics and left gastroepiploic, the common hepatic its right gastric and gastroduodenal and gastroepilploic arteries.
• Venous drainage: left and right gastric drain into the portal vein, the left gastroepipolic drains into the splenic vein and the right into the superior mesenteric vein
• Lymphatics drain to the coeliac axis.
• Innervation is by the anterior and posterior vagus nerves and sympathetic innervation is via the greater splanchnic nerve.

Question 49

Describe the anatomy of the pancreas

Answer 49

The pancreas is a mixed exocrine and endocrine gland situated in the deep epigastric part of the abdomen. It resembles a side-lying hockey stick in shape; it is approximately 15cm long by 3.5 wide and 1.5cm thick. It has a head, neck, body, and tail. The head lies in the C-shaped concavity of the duodenum, posterior to the head lies the IVS and both renal veins at the level of L2. Its posterior surface is indented, and sometimes encloses, the CBD as it descends to enter the posteromedial duodenum. The neck of the pancreas overlies the confluence of the portal vein. It is on the transpyloric plane. The body of the pancreas is directed obliquely upwards and to the left draped over the left renal vein and aorta. The splenic artery has a tortuous course above and below the superior border of the pancreas, the splenic vein is posterior to the body of the pancreas. The body becomes the tail of the pancreas which heads to the hilum of the spleen lying anterior to the left renal hilum.

The pancreatic ducts usually joins with the CBD and drains out of the main papilla via the ampulla of Vater. Occasionally the main pancreatic duct drains via the duct of Santorini, and only the uncinate drains with the CBD, a condition known as divisum, which may pre-dispose to pancreatitis.

The uncinate process of the pancreas is a medially-recurving part of the head, which often tucks in under the origin of the SMA and SMV pedicle.

The pancreas originates as two buds, each an endodermal outgrowth at the junction of the foregut and midgut mesentery. The ventral buds becomes the uncinate process and part of the head whereas the dorsal bud becomes the other part of the head, the neck, body, and tail of the pancreas. During development the drainage of dorsal and ventral components anastomose then split to generate the pattern seen in adult life; i.e the uncinate draining via Santorini’s duct and the head, neck, body, and tail draining with CBD through the Duct of Wirsprung. Failure of the buds to correctly rotate causes an annular pancreas.

Blood supply is via the arteria pancreatica magna (form the splenic) and also from the superior and inferior pancreatico-duodenal arteries as it is both a foregut and midgut derivative. Lymphatic drainage follows arterial supply. Innervation is via the vagus, although neurohumoral control predominates.

Question 50

Describe the anatomy of the oesophagus.

Answer 50

• Embryology: It is derived from the foregut. At the 4th week of development, the respiratory diverticulum appears at the ventral wall of the foregut. The tracheoesophageal septum formed between
  the respiratory diverticulum and the distal part of the fore-
  gut separates these two portions. At the beginning, the esophagus is short, but with the descent of the heart and lungs, it lengthens until the 7th week.
• It measures 25 cm in length. It passes through the oesophageal hiatus at T10.
• During its descent it inclines initially to the left, returns to the midline, then deviates left again to sit 2.5cm to the left of the midline one entry to the abdomen.
• Its lumen is indented at 4 points;
  
  • By cricopharyngeus (15cm from incisors)
  • By the aorta (22cm from incisors)
  • By the left main bronchus (27cm from incisors)
  • At the diaphragmatic hiatus (38cm from incisors).
• The intra-abdominal part of the oesophagus is 1-2cm in length.
• Posteriorly it is related to the trachea until the trachea bifurcates at T4. At the same point, the azygous is to its right and the aortic arch to its left and the thoracic duct crosses from the right to the left side of the oesophagus. Between the tracheal bifurcation and the diaphragm the left atrium is the anterior relation. On either side the mediastinal pleura touches the oesophagus.
• Arterial supply is via branches of the inferior thyroid artery superiorly, direct aortic branches in its mid-portion, and from ascending oesophageal branches from the left gastric distally.
• Venous drainage corresponds to arterial supply, importantly the left gastric-ascending oesophageal veins are a site of porto-systemic shunt and possible varices.
• Lymphatic drainage is via a rich submucosal plexus throughout its length; the oesophagus may drain to the cervical, mediastinal, or coeliac lymphatic plexuses.
• Nerve supply is segmental; its upper portion is supplied by the recurrent laryngeal nerves, the vagus and thoracic splanchnics supply autonomic nerves for the remainder.
• Of note, the muscularis mucosae of the oesophagus is particularly thick and is the strength layer of the organ for anastomoses as there is no serosa.

Question 51

Describe the anatomy of the spleen.

Answer 51

• Emryology: Develops in the 6th week by mesodermal condensations in the dorsal mesentry. remnants can lead to splenuculi that lie along the arterial supply.
• The spleen a haematological organ that is located in the left upper quadrant, completely covered by the ribcage. It measure 1 x 3 x 5 inches in the healthy patient and weighs 7 ounces (200g). It is covered by ribs 9-11. It has one pedicle running from the superoposterior border of the pancreas to its hilum containing the splenic artery and vein. It has a notch on its inferomedial edge and often has impression left on it from surrounding structures such as the colon, the kidney, and stomach.
• It is made up of red and white pulp, representing filtered red cells/platelets and lymphocytic aggregates respectively. It must be at least twice its normal size before becoming palpable.
• There are four ligamentous attachments of the spleen, three of which are avascular. The spleno-colic, spleno-renal, spleno-phrenic ligaments have no vessels within them. The gastrosplenic ligament carries the short gastric from the splenic hilum to the lateral stomach.

Question 52

Decribe the anatomy of the adrenals.

Answer 52

The adrenal gland is a neuro-hormonal secretory gland the is located above each kidney.

The left adrenal gland is crescent shaped and drapes over the superomedial portion of the upper pole of the left kidney, often with a significant amount of peri-renal fat between it and the kidney below. The lower half of the left adrenal is covered by the body and tail of the pancreas, whereas the upper half is covered by peritoneum and makes up part of the posterior wall of the lesser sac, lying on the left crura.

The right adrenal is more pyramidal in shape and is located on the upper pole of the right kidney. In contrast to the left adrenal the lower half of the left adrenal is covered in peritonei, (in the hepatorenal pouch of the greater sac) and the upper half is covered by the bare area of the liver and IVC, in fact the right adrenal may extend a variable distance posterior to the IVC, making surgical access challenging.

The blood supply to the adrenals is from multiple sourses; branches from the inferior phrenic artery, aorta, and renal artery all contribute. Venous drainage most commonly by one vein, but is different on either side; on the left into the left renal vein, on the right directly into the cava. Nervous supply is via pre-ganglionic myelinated sympathetic neurons from the splanchnic nerves.

The adrenals have a three-layered cortex and a central medulla. The zone glomerulosa produces mineralocorticoids, the zone fasciculata produces glucocorticoids, and the zone reticules produces sex steroid hormones. The medulla produces catecholamines.

Question 53

Describe the anatomy of the kidneys and ureter.

Answer 53

The kidneys are paired retroperitoneal organs that are responsible for haemofiltration and fluid balance. They are located in the retroperitoneum and are mostly covered by the ribs with just their lower poles below the costal margin. On the left the renal hilum is at the level of L1, on the right L2. They have an oblique lie in both the sagittal and coronal axis due to the presence of psoas medially. Most kidneys measure 3 x 6 x 12 cm and weigh 150g.

They are surmounted by the adrenals on each side, they are surrounded by a variable layer of peri-renal fat which in-turn is surrounded by Gerota’s fascia. Anterior relations on the left include the descending colon and its mesentery, and its hilum is touched anteriorly by the tail of the pancreas. The lienorenal ligament passes from tail of pancreas and kidney to spleen at this point. On the right the ascending colon and its mesentery as well the the secondary part of the duodenum anterior to its hilum. The upper pole of the right kidney indents the visceral surface of the liver. Each kidney provides a ureter at the renal pelvis, where the major calyces coalesce to forms a funnel, the pelvicoureteric junction.

The kidneys are supplied by the renal arteries at L2 which are usually one in number on each side though accessory arteries from the aorta may persist, reflecting the migration of the kidney upwards in foetal development. Venous drainage is via the renal veins, the left being significantly longer than the right. The left renal vein receives the left gonadal vein at a right angle, on the right the gonadal drains directly into the IVC.

Nervous supply is via the splanchnic and vagus nerves.

From the PUJ, the ureters descend on psoas, under the psoas fascia, towards the pelvis approximating the tips of the vertebral transverse processes on x-ray. They are crossed superficially by the gondal vessels from medial to lateral. At the pelvic brim, the ureters are located superficial to the bifurcation of the common iliac artery. They then course on the lateral pelvic side wall and turn medially (at the level of the ischial spines on x-ray) to enter the posterolateral apex of the trigone of the bladder on each side. They are 25cm long. Prior to entering the bladder they are crossed superficially by the vas in the male and the uterine artery in the female. The entry of the ureter into the bladder is oblique, forming a valve system that prevent vesicoureteric reflux.

Blood supply to the ureters is segmental, from the renal arteries, the aorta, the gonadal, the common and internal iliac, and the superior and inferior vesicle arteries and the uterine artery. Nervous supply is similar to the kidneys.

Question 54

Describe the course of the vas deferens

Answer 54

• The vas deferens is the continuation of the epididymis and starts at the lower pole of the testis
• It ascends within the spermatic cord and travels into the pelvis via the superficial then deep inguinal rings
• It passes along the side wall and floor of the pelvis to reach the back of the bladder
• During its course, no other structure intervenes between it and the peritoneum that it is under
• On its way from the inguinal ring to the bladder it crosses the obliterated umbilical artery, the obturator nerve and artery, and the ureter lying on the obturator fascia
• Upon reaching the bladder, the duct then turns downwards and dilates in a fusiform manner into the ampulla, the storehouse of spermatozoa
• The ampulla lies parallel to the spermatic vesicles nd fuses with it terminally to form the ejaculatory duct
• These open through the prostate onto the verumontanum

Question 55

Describe the course of the Radial nerve and what it supplies.

Answer 55

• The radial nerve (C5-T1) is the nerve of the extensor compartments of the arm and forearm, supplying them and the skin over them and the dorsum of the hand
• It is a direct continuation of the posterior cord of the brachial plexus, it travels through the triangular space between the heads of triceps and down the posterior humerus, where it may be injured with shaft fractures
• It pierces the lateral intermuscular septum in the mid-arm to pass between brachialis and brachioradialis
• It gives off the posterior interosseous nerve (supplies the extensor forearm) and then continues as a purely sensory nerve to the anatomical snuffbox
• At the dorsum of the hand it supplies the radial 2.5 digits to the distal PIPJ.

Question 56

Describe the lesser sac.

Answer 56

• The lesser sac is a sub-section of the peritoneal cavity behind the stomach
• It opens into the greater sac through a slit-like aperture, the Foramen of Winslow, defined by the following boundaries:
  
  • Posteriorly, the IVC
  • Anteriorly, the free edge of the gastroheptic ligament with the portal triad within
  • Superiorly, the caudate lobe
  • Inferiorly, the pylorus and duodenum
• The anterior surface of the lesser sac is made up of the posterior layer of the lesser omentum, the peritoneum of the posterior stomach, and the anterior of the two posterior layers (fused) of the greater omentum
• The posterior surface of the lesser sac is made up of the peritoneum that covers the
  
  • surface of the neck and body of the pancreas
  • upper pole of the l_eft kidney_
  • left adrenal
  • commencement of the abdominal aorta
  • coeliac trunk
  • crura of the diaphragm
• The lesser sac has a superior recess to the right of the oesophagus, where the peritoneum of the crura reflects anteriorly to become the posterior layer of the lesser omentum/gastrohepatic ligament

Question 57

Describe the ischioanal fossa

Answer 57

• The ischio-anal fossa is a wedge-shaped anatomical space bounded
  
  • Medially and superiorly, by the levator ani
  • Laterally and superiorly, by the obturator internus
  • Inferiorly, by the skin between the ischial tuberosity and the anus
• The space is traversed by the inferior rectal artery, vein, and nerve, which take an arching course with a bias towards the apex of the fossa
• Infections here may extend posteriorly across the midline, deep to the anococcygeal ligament
• Anteriorly, the perineal body usually prevents infection from crossing the midline
• The anterior extent of each ischioanal fossa is deep to the perineal membrane, and infection here may extend to the posterior surface of the body of the pubis.

Question 58

Describe the embryology of the cloaca

Answer 58

At the caudal end of the embryo, the hindgut and the allantois (a diverticulum from the yolk sac) meet in a common cavity, the cloaca , bounded distally by the cloacal membrane, which will form the procodeum.

From the dorsal wall of the allantois, the urorectal septum grows downwards to meet the cloacal membrane; dividing the urogenital sinus and urogenital membrane, and the anorectal canal and the anal membrane. The procodeum is the ectoderm lining, which will form the skin of the anal canal below the dentate line. The tip of the urorectal septum forms the perineal body.

Question 59

Describe the femoral nerve

Answer 59

This is formed by the posterior divisions of the anterior rami of L2,3,4. Passes lateral to psoas muscle undernaeth the inguinal ligament, outside the femoral sheath. It branches into a number of divisions underneath the inguianl ligament.

Motor Supplies:

1. Iliacus
2. Pectineus
3. Sartorius
4. Vastus medium, intermedius and lateralis
5. Rectus femoris

Sensory:

Medial and intermediate nerves of the thigh

Continues as the saphenous nerve

Question 60

Broadly describe the layers of the embryo with regard to eventual anatomical structures.

Answer 60

• Alongside the notochord and neural tube, the mesoderm lies in 3 longitudinal strips; the paraxial mesoderm, the intermediate cells mass, and the lateral plate.
• Paraxial mesoderm becomes somites
  
  • Sclerotome medially - becomes vertebrae and ribs
  • Dermomyotome laterally - becomes muscles of body wall and dermis of skin.
• Intermediate cells mass
  
  • Progenitors of gonad and adrenal cortex medially
  • Pronephros, mesonephros, metanephros laterally
• Lateral plate split by intraembryonic coelom
  
  • Inner layer becomes splanchnic mesoderm
    
    • Becomes the mesenchyme of gut
  • Outer layer becomes parietal mesoderm
    
    • Gives rise to limb buds
    • Paraxial mesoderm invades this to form flexor and extensor muscles of body

Question 61

Describe the significant features of the fetal circulation.

Answer 61

The economy of the fetal circulation is improved by three short-circuiting arrangements, all of which cease to function after birth:

1. The ductus venosus
2. The foramen ovale
3. The ductus arteriosus.

Question 62

What are the ectodermal derivatives of the pharyngeal grooves?

Answer 62

1^st groove

• External acoustic meatus

2^nd, 3^rd, 4^th grooves

• Usually encyst and obliterate
• Failure to do so causes branchial cyst or fistula

Question 63

What are the mesodermal derivatives of the pharyngeal arches?

Answer 63

1^st arch

• Meckel’s cartilage, mandible, mucous membrane and anterior 2/3rds of tongue, muscles of mastication, mylohyoid, anterior belly digastric, tensors.

2^nd arch

• Stapes, stapedius, styloid process, lesser horn and superior part of hyoid, stylohyoid, muscles of facial expression.

3^rd arch

• Greater horn and inferior part of hyoid, stylopharyngeus.

4^th and 6^th arches

• Thyroid/cricoid/arytenoid/epiglottic cartilages, intrinsic muscles of larynx, muscles of pharynx.

Question 64

What are the endodermal derivatives of the pharyngeal pouches?

Answer 64

1^st pouch

• Middle ear
• Auditory tube
• Mastoid antrum

2^nd pouch

• Tympanic cavity
• Tonsillar cypts
• Supratonsillar fossa
• Palatine fossa

3^rd pouch

• Inferior parathyroid (para III)
• Thymus; Hassall’s corpuscles

4^th pouch

• Superior parathyroid (para IV)

5^th pouch

• Ultimobranchial body; parafollicular C-cells of thyroid
• Tubercle of Zuckerkandl

Question 65

Describe the peritoneal folds of the abdominal wall

Answer 65

On the posterior surface of the anterior abdominal wall, the peritoneum is raised into 6 folds; 1 above the umbilicus and 5 below.

• The falciform ligament with the ligamentum teres in its inferior border (the obliterated left umbilical vein)
  
  • This runs slightly to the right of the midline and is attached to a notch on the inferior surface of the liver
• The median umbilical ligament with the obliterated urachus in the midline
• The medial umbilical ligament with the obliterated umbilical artery within its fold
• The lateral umbilical ligament with the inferior epigastric vessels within. Unlike the other umbilical ligaments this does not pursue a path towards the umbilicus, rather a few cm laterally.

Question 66

Describe the course of the IVC and its tributaries