Thorax Anatomy😊

Condition	Definition	Region / Site	Key Features
Lordosis	Inward curvature (concave)	Lumbar	• Normal lumbar curve. • Helps balance, alignment, weight distribution.
Scoliosis	Abnormal sideways bending	Thoracic, thoracolumbar	• Structural deformity. • "Dowager's hump" • Dowager → Age avumbo → Down avum
Kyphosis	Excess forward bending	Thoracic	• Rounded / hunched back. • Normal thoracic kyphosis exists.
Recurvatum	Hyperextension	Common in knee	• Indicates joint hyperextension..

Recurvatum

Pleura

• Parietal Pleura: Lines the thoracic cavity.

• Visceral Pleura: Covers the lungs, including fissures.

•  Pleural cavity in b/w contains serous fluid.

Types of Parietal Pleura:

1. Cervical Pleura

2. Costal Pleura

3. Diaphragmatic Pleura

4. Mediastinal Pleura

Recesses

• Pleural recesses are potential spaces where the parietal pleura folds.

• Costodiaphragmatic Recess:
• Located between the costal and diaphragmatic pleura.
• Most dependent part of the pleural cavity.
• Extends from 8th to 10th rib at the mid-axillary line.

• Costomediastinal Recess:
• Located between the costal and mediastinal pleura.

• Pleural tap (thoracentesis) in the mid-axillary line from the 8th intercostal space.

Nerve Supply

• Parietal Pleura:
• Pain sensitive.
• Innervated by:
• Intercostal NV:
• costal and peripheral diaphragmatic pleura.
• Causes localized pain.
• Phrenic NV (C4):
• mediastinal and central diaphragmatic pleura.
• Causes referred pain to the Shoulder Tip.

• Visceral Pleura:
• Pain insensitive.
• Innervated by:
• Sympathetic (T2-T5)
• Parasympathetic (Vagus N)

Phrenic N (C3 - C5)

• Medial to Brachial plexus

• Anterior to 2nd part of subclavian A

• Posterior to Subclavian Vein

Lymph Nodes of Axilla

Level	Location	Groups
I	Lateral to pectoralis minor	Anterior, lateral, posterior (subscapular)
II	Superficial or deep to pectoralis minor	Central, interpectoral
III	Medial to pectoralis minor	Apical (subclavicular)

LUNG

Root of Lung

• Structures present at the hilum of the lung

Pulmonary Ligament

• Anatomical dead space

• Utilized by vessels in the hilum

• Mnemonic:
• From front → VA Bronchi
• From down above
• Right → VBAB
• Left → VBA

Left Lung (From Above Downwards)

• Pulmonary artery

• Bronchus

• Pulmonary veins

Right Lung (From Above Downwards)

• Eparterial bronchus

• Pulmonary artery

• Hyparterial bronchus

• Pulmonary veins

Mediastinal Surface - Nerves

Right Lung

• Nerve in front of root of hilum: Phrenic nerve

• Nerve behind the hilum: Vagus nerve

Left Lung

• Nerve behind the hilum: Vagus nerve

Bronchopulmonary Segments

• Segment aerated by tertiary/segmental bronchus.

• Each lung has 10 segments.

• Pyramidal in shape; Apex is towards the Hilum

• Divided by visceral pleura

• Sx resectable

• ”Mneumonic:
• Supine → Superior
• Erect → Post

Exceptions

• Medial basal segment may be absent in left lung.
• Segment count: Right 10 : Left 9 (common).

• Apical + posterior segments may fuse in left lung (apicoposterior).
• Segment count: Right 10 : Left 8.

• Bronchopulmonary segments are not bronchovascular segments.

• No pulmonary veins inside BPS
• Pulmonary veins are intersegmental

Inlet of Thorax

Sternal Angle -Angle of Louis

• It is the lower border of T4.

• 2nd costal cartilage is attached here.

• Divides the mediastinum into superior and inferior parts.

• Bifurcation of trachea

• Thoracic duct deviates to the left side.

• Arch of azygos drains into superior vena cava.

• Beginning and end of arch of aorta.

• Apex of fibrous pericardium.

• Superior sternopericardial ligament.

• Cardiac plexus.

Intercostal space

Intercostal Muscles

• External

• Internal

• Innermost
1. Sternocostalis
2. Subcostalis
3. Intercostalis intimus

Neurovascular Bundle

• Located between internal and innermost intercostal bundle.

• Arrangement (from above downwards):
• VAN: Intercostal vein → intercostal artery → intercostal nerve.

• Except
• Structures in 1st IC Space (b/w 1st rib and apex of lung)
• SVAN
• Sympathetic trunk
• Vein: Posterior intercostal vein
• Artery: Superior intercostal artery
• Nerve: T1 nerve
• Medial → Lateral

Applied Aspect: Thoracentesis (Pleural Tap)

• just above the lower rib

• Needle Insertion: Along the 5th ICS mid-axillary line.

• Layers Pierced (from outside to inside):
1. Skin
2. Superficial fascia
3. Deep fascia
4. Serratus anterior muscle
5. External intercostal muscle
6. Internal intercostal muscle
7. Innermost intercostal muscle (intercostalis intimi muscle)
8. Endothoracic fascia
9. Parietal pleura

Intercostal Nerve

Blood Supply of Intercostal Space

Anterior intercostal arteries

• Present only in upper 9 Intercostal spaces

• Upper 6 are given by internal thoracic artery

• Terminates in the 6th intercostal space by dividing into:
• Superior epigastric artery: Continues as content of rectus sheath.
• Musculophrenic artery:
• Gives rise to 7th, 8th and 9th anterior intercostal arteries.

• Mnemonic: ITA course → 9 years →
• 6 years → Direct
• last 3 years → Muscle building

Posterior intercostal arteries

• Present in all 11 intercostal spaces

• Upper 2 originate from
• Superior intercostal artery 
• Branch of costocervical trunk
• Arising from 2nd part of subclavian artery

• Lower 9 (3-11) originate from
• Descending thoracic aorta.

Internal Thoracic Artery (ITA)/ Internal Mammary Artery (IMA)

• Internal thoracic artery is the first part of the subclavian artery.

• Preferred for coronary artery bypass grafting.
• Reason: Medium-sized artery.
• more elastic fibers and less smooth muscles.

Branches of ITA

1. Perforating arteries 
• Supply mammary gland
• Located in 2- 4th I/C spaces.

2. Pericardicophrenic artery
• Runs with phrenic nerve.
• Supplies:
• diaphragm
• mediastinal pleura
• fibrous pericardium

3. Principal artery of thymus
• Mediastinal branch

4. Anterior intercostal arteries 
• Supply 1- 6th I/C space

5. Musculophrenic artery 
• Terminal branch
• Supply remaining 7th to 9th IC space

6. `Superior epigastric artery 
• Terminal branch

Thoracic Duct

• Largest lymphatic duct/vessel.

• Origin: Cisterna chyli at L2 level



• Mnemonic: Thora (Thoracic duct) → too large aytt (2 L → L2)

• Course:
• Crosses diaphragm via aortic opening at T12 level.
• Deviates left at T5 level.
• Beaded duct due to many valves.

• Termination:
• Junction of left subclavian vein and left internal jugular vein.
• At C7 level.

Areas not drained by the thoracic duct

• Right head and neck

• Right thoracic wall

• Right upper limb

• Right lung

• Right surface of the heart

• Convex part of the liver

Azygos & Hemiazygos Veins

Azygous Vein:

• Develop from Supracardinal > (R) PCV

• Note: R bronchial vein is the last tributary of the azygos vein.

Heart Anatomy

Pericardium

• Fibrous pericardium

• Serous pericardium
• Parietal layer
• Visceral layer

Innervation of Pericardium

• Fibro-pericardium + Parietal pericardium:
• Phrenic NV
• pain sensitive
• Located at apex.
• Merged with great vessels.
• Merged with central tendon of diaphragm at base.
• Continues with pretracheal fascia.

• Visceral layer:
• Autonomic NV
• pain insensitive

Pericardial Sinuses

Transverse Sinus

• Used to ligate great vessels in cardiac surgery.

• Located between:
• Anteriorly
• Arterial tube → Aorta and Pulmonary Trunk
• Posteriorly
• Venous tube → SVC & Pulmonary Veins

Oblique Sinus

• Located behind the heart.

• Provides extra posterior space for LA and LV expansion
• without compressing the oesophagus

• Cul-de-sac.

• Formed by reflections of serous pericardium around great veins.

Borders of the Heart

Border	ㅤ
Right	• SVC • RA • IVC
Left	• LA • L Auricle • LV
Inferior	• RV
Apex	• LV • At 5th I/c space • 9 cm away from sternum.
Base	• Formed by RA (1/3) + LA (2/3).

Chambers

Right Atrium (RA)

• Rough anterior wall:
• Contains Musculi Pectinati.
• Arranged as teeth of comb
• Reduce turbulence between opposite walls.
• RA → Right atrium → Rough anterior

• Smooth posterior wall:
• Derived from sinus venosus.
• No muscles

• Crista Terminalis:
• Ridge separating smooth posterior from rough anterior wall.
• SA node in the uppermost part
• Blood supply
• 65% : RCA
• 35% : Circumflex artery

• Right auricle:
• Ear like projection
• overlapping ascending aorta.

Structures in RA

• SVC:
• Valve is absent
• Located obliquely.
• Muscles of posterior wall of right atrium act as valves

• IVC orifice:
• Guarded by Eustachian valve.
• Mnemonic: You (Eustachian) I (IVC)

• Coronary Sinus orifice:
• Guarded by Thebesian valve.
• Mnemonic: coronary sinus → the best valve

• Septal Wall



• Formed by Interatrial septal remnants → Foramen Ovale
1. Fossa Ovalis
• derived from septum primum
• Oval shaped depression
2. Limbus fossa ovalis
• derived from septum secundum
• Seen above and below fossa ovalis.

Tricuspid valve:

• Guards the A.V orifice.
1. Anterior cusp
2. Posterior cusp
3. Septal cusp

Triangle of Koch:

Right Ventricle (RV)

• Rough inflowing part
• From proximal 1/3rd of bulbus cordis
• Has Trabeculae Carneae

• Supraventricular Crest:
• Muscular ridge / Linear elevation separating inflow and outflow tracts.

• Septal Cusp:
• Part of the tricuspid valve, attached to the interventricular septum.

Trabeculae Carneae Types:

1. Ridge: Fixed elevation.

2. Bridge: Muscular band with free central portion.
• Septomarginal Trabeculae
• aka Moderator Band
• Gives passage to Right bundle branch.
• Moderator is a bridge which give pass to right person

3. Pillars:



• Also called papillary muscles.
• Apex free
• Attach to valve leaflets via Chordae Tendineae



• Pillars are of 3 types:
• Anterior: Largest.
• Posterior.
• Septal.

Right Ventricle vs Left Ventricle

IMAGE BANK:

Arterial Supply of Heart

Coronary Circulation

• Originate from aortic sinuses
• Anterior: RCA
• Posterior:
• Right: Non-coronary sinus → Torus aorticus
• Left: LCA

• Rarely LCA may originate from the Anterior Aortic Sinus
• If occluded b/w anterior aortic sinus and Pulmonary Trunk
• ⇒ sudden cardiac arrest.

Branches of RCA

Right Conus Artery

• 1st Branch of RCA

• If directly arise from ant - Aortic Sinus
• Also called 3rd Coronary Artery

• R + L Conus Artery forms → Annulus of Vieussens

• SA Nodal Artery:
• Found in 65% of cases.

• Right Anterior Ventricular Rami (Right/Acute Marginal Artery).

Posterior Interventricular Artery (PIVA):

• Supplies the posterior 1/3rd of the interventricular septum.

• 1st septal branch of PIVA → Supplies the AV Node.

Branches of LCA

• Shorter in length than RCA.

Anterior Interventricular Artery

• aka LAD (Left Anterior Descending):
• Septal branch: Supplies the anterior 2/3rd of IVC
• Diagonal Artery: Supplies the anterior LV

Left Circumflex Artery (Lcx):

Blood Supply to Conduction System

 

Cardiac Dominance

Venous Drainage of Heart

Coronary Sinus

• Remnant of the Left Horn of Sinus Venosus

• Drains all cardiac veins
• Except Anterior Cardiac Veins
• Drain directly into the RA

Accompanying arteries

Openings in Posterior Smooth Part of Right Atrium

Tributaries

• Great cardiac vein

• Middle cardiac vein

• Small cardiac vein

• Posterior vein of left ventricle

• Oblique vein of left atrium