Right Lung (3 Lobes)

The right lung is one of the paired respiratory organs occupying the thoracic cavity. It is generally larger and heavier than the left lung and is divided into three lobes: superior, middle, and inferior. These lobes are separated by two fissures, the horizontal fissure and the oblique fissure.

The three-lobed organization is one of the principal features distinguishing the right lung from the left lung. The right lung also differs in its size, shape, bronchial organization, hilar relationships, and impressions produced by neighboring mediastinal structures.

Lobes of the Right Lung

The right lung contains three lobes:

• Superior lobe
• Middle lobe
• Inferior lobe

The superior and middle lobes are separated by the horizontal fissure, while the oblique fissure separates the inferior lobe from the superior and middle lobes.

Superior Lobe

The superior lobe occupies the upper part of the right lung. It extends from the apex downward to the horizontal and oblique fissures.

It contributes extensively to the costal surface and also forms portions of the mediastinal surface adjacent to the superior mediastinum.

Middle Lobe

The middle lobe is the smallest of the three right pulmonary lobes.

It is located primarily in the anterior and lateral portions of the right lung between the horizontal and oblique fissures. Because of its position, relatively little of the middle lobe is visible from a posterior view.

Inferior Lobe

The inferior lobe is the largest lobe of the right lung and occupies much of its posterior and inferior regions.

It extends superiorly on the posterior aspect of the lung and forms a large portion of the diaphragmatic surface.

Fissures of the Right Lung

The right lung normally contains two major fissures:

• Oblique fissure
• Horizontal fissure

These fissures are lined by visceral pleura and permit movement of adjacent lobes relative to one another during respiration.

Oblique Fissure

The oblique fissure is the major fissure separating the inferior lobe from the superior and middle lobes.

It passes obliquely downward and anteriorly across the lung, beginning relatively high on the posterior surface and approaching the inferior border anteriorly.

Horizontal Fissure

The horizontal fissure separates the superior lobe from the middle lobe.

It extends approximately horizontally from the anterior border toward the oblique fissure on the lateral aspect of the lung.

Relationship Between the Fissures

The horizontal fissure terminates laterally where it meets the oblique fissure.

Together, the two fissures divide the right lung into three distinct lobar units while remaining continuous with the visceral pleural covering of the lung.

Fissural Variation

The completeness and exact course of pulmonary fissures vary among individuals.

The horizontal fissure may be incomplete or occasionally absent, and the oblique fissure may also show incomplete fusion between adjacent lobes. Accessory fissures may sometimes occur.

Size and Shape

The right lung is generally larger in volume than the left lung because the heart projects predominantly toward the left side of the thoracic cavity.

However, the right lung is usually shorter and broader because the right dome of the diaphragm is elevated by the liver.

Apex

The apex is the rounded superior extremity of the right lung.

It projects into the root of the neck above the level of the first rib and is covered by cervical pleura.

Base

The base of the right lung is formed by the diaphragmatic surface.

It is concave and conforms to the superior surface of the right dome of the diaphragm.

Surfaces of the Right Lung

The right lung is commonly described as having three major surfaces:

• Costal surface
• Mediastinal surface
• Diaphragmatic surface

Each surface reflects the structures surrounding the lung within the thoracic cavity.

Costal Surface

The costal surface is broad, smooth, and convex.

It faces the ribs and intercostal spaces and conforms to the curved internal surface of the thoracic wall.

Mediastinal Surface

The mediastinal surface faces medially toward the mediastinum and contains the hilum of the lung.

It bears impressions produced by the heart and major mediastinal structures, including the superior vena cava, azygos vein, and esophagus.

Diaphragmatic Surface

The diaphragmatic surface is concave and forms the base of the right lung.

Its concavity is relatively pronounced because the right dome of the diaphragm is elevated by the liver.

Borders of the Right Lung

The major borders of the right lung are:

• Anterior border
• Posterior border
• Inferior border

These borders mark transitions between the costal, mediastinal, and diaphragmatic surfaces.

Anterior Border

The anterior border is relatively thin and sharp and separates the costal and mediastinal surfaces anteriorly.

Unlike the left lung, the right lung does not normally have a cardiac notch interrupting this border.

Posterior Border

The posterior border is broad and rounded rather than sharply defined.

It lies alongside the thoracic vertebral column and forms a gradual transition between the costal and mediastinal surfaces.

Inferior Border

The inferior border separates the diaphragmatic surface from the costal and mediastinal surfaces.

Its position changes during respiration as the diaphragm moves and the lung expands or recoils.

Hilum of the Right Lung

The hilum is located on the mediastinal surface and forms the gateway through which structures of the lung root enter and leave the right lung.

These structures include bronchi, pulmonary arteries, pulmonary veins, bronchial vessels, lymphatics, lymph nodes, and autonomic nerves.

Root of the Right Lung

The root of the right lung is the bundle of structures connecting the lung with the mediastinum.

Near the lung, these structures are enclosed by a sleeve of pleura formed by reflection of mediastinal pleura onto the pulmonary surface.

Eparterial Bronchus

A characteristic feature of the right lung root is the eparterial bronchus.

The right superior lobar bronchus lies superior to the right pulmonary artery and is therefore described as eparterial.

Hyparterial Bronchial Structures

Bronchial structures lying below the pulmonary artery are termed hyparterial.

After giving rise to the superior lobar bronchus, the right main bronchus continues as the bronchus intermedius toward the middle and inferior lobes.

Bronchus Intermedius

The bronchus intermedius is the continuation of the right main bronchus after the origin of the superior lobar bronchus.

It subsequently divides into the middle and inferior lobar bronchi.

Right Pulmonary Artery

The right pulmonary artery carries deoxygenated blood from the pulmonary trunk to the right lung.

At the root, it lies generally anterior to the bronchial structures, while the eparterial superior lobar bronchus lies above it.

Right Pulmonary Veins

The right lung normally drains through superior and inferior pulmonary veins.

These veins return oxygenated blood to the left atrium. The superior pulmonary vein occupies a relatively anterior position, while the inferior pulmonary vein is the lowest major structure of the root.

Arrangement of the Right Root

A simplified superior-to-inferior arrangement of major structures at the right lung root is:

1. Eparterial superior lobar bronchus
2. Right pulmonary artery
3. Hyparterial bronchial structures
4. Inferior pulmonary vein

This sequence is simplified because the structures occupy complex three-dimensional relationships.

Bronchopulmonary Segments

The three lobes are subdivided into bronchopulmonary segments. Each segment is supplied by a segmental bronchus and an accompanying branch of the pulmonary artery.

The right lung is conventionally described as containing 10 bronchopulmonary segments.

Superior Lobe Segments

The superior lobe contains three bronchopulmonary segments:

• Apical segment, S1
• Posterior segment, S2
• Anterior segment, S3

Middle Lobe Segments

The middle lobe contains two bronchopulmonary segments:

• Lateral segment, S4
• Medial segment, S5

Inferior Lobe Segments

The inferior lobe contains five bronchopulmonary segments:

• Superior segment, S6
• Medial basal segment, S7
• Anterior basal segment, S8
• Lateral basal segment, S9
• Posterior basal segment, S10

Segmental Arrangement

Lobe	Segment	Designation
Superior	Apical	S1
Superior	Posterior	S2
Superior	Anterior	S3
Middle	Lateral	S4
Middle	Medial	S5
Inferior	Superior	S6
Inferior	Medial basal	S7
Inferior	Anterior basal	S8
Inferior	Lateral basal	S9
Inferior	Posterior basal	S10

Segmental Bronchi

Each bronchopulmonary segment receives a segmental, or tertiary, bronchus.

The segmental bronchi arise through progressive branching of the lobar bronchi and conduct air toward increasingly smaller airways within their respective segments.

Pulmonary Arterial Supply

Branches of the pulmonary artery generally accompany the bronchial tree and supply the corresponding bronchopulmonary segments.

Segmental bronchi and pulmonary arterial branches therefore occupy relatively central, intrasegmental positions.

Pulmonary Venous Drainage

Pulmonary veins differ from bronchi and pulmonary arteries because their tributaries commonly travel within intersegmental planes.

These veins receive blood from adjacent segments before converging toward the superior and inferior pulmonary veins.

Visceral Pleura

The external surface of the right lung is covered by visceral pleura, except at the hilum where structures enter and leave.

Visceral pleura extends into both the horizontal and oblique fissures and covers the opposing surfaces of adjacent lobes.

Cardiac Impression

The mediastinal surface of the right lung bears a cardiac impression produced mainly by the right side of the heart and pericardium.

This impression is generally shallower than the corresponding cardiac impression on the left lung.

Superior Vena Cava Groove

The superior vena cava lies anterior and superior to the right lung root.

It can produce a vertical groove on the mediastinal surface of the right lung.

Azygos Vein Groove

The azygos vein arches over the superior aspect of the right lung root before entering the superior vena cava.

The arch may produce a curved groove above the hilum on the mediastinal surface.

Esophageal Impression

The esophagus lies posterior to the trachea and heart and is related to the posterior part of the mediastinal surface of the right lung.

This relationship may produce a shallow vertical groove posterior to the lung root.

Relationship to the Diaphragm

The base of the right lung rests upon the right dome of the diaphragm.

The liver lies immediately inferior to the diaphragm and elevates the right dome, contributing to the relatively short and broad shape of the right lung.

Relationship to the Liver

The liver does not directly contact the lung because the diaphragm and pleural structures intervene between them.

Nevertheless, the large right lobe of the liver strongly influences the position of the right hemidiaphragm and therefore the shape of the right lung base.

Relationship to the Thoracic Wall

The costal surface of the right lung conforms to the internal surfaces of the ribs and intercostal spaces.

Expansion of the thoracic cage during inspiration increases thoracic volume and permits expansion of the lung against the pleural surfaces.

Comparison with the Left Lung

Feature	Right Lung	Left Lung
Number of lobes	3	2
Oblique fissure	Present	Present
Horizontal fissure	Present	Absent
Middle lobe	Present	Absent
Lingula	Absent	Present
Cardiac notch	Absent	Present
Cardiac impression	Shallower	Deeper
Common segment count	10	Approximately 8 to 10

Middle Lobe and Lingula

The right middle lobe is often compared with the lingula of the left lung because both occupy relatively anterior regions and contain two commonly recognized bronchopulmonary segments.

However, the right middle lobe is a true separate lobe bounded by fissures, whereas the lingula is part of the left superior lobe.

Right Lung During Respiration

During inspiration, contraction of the diaphragm and movements of the thoracic wall increase the dimensions of the thoracic cavity.

The right lung expands, its inferior border descends, and its lobes move relative to one another along the pleura-lined fissures. During expiration, elastic recoil reduces lung volume.

Right Lung on Imaging

Chest radiography and computed tomography demonstrate the lobar and fissural organization of the right lung.

Computed tomography is particularly useful for identifying the horizontal and oblique fissures, lobar bronchi, pulmonary vessels, bronchopulmonary segments, and relationships of pulmonary lesions to individual lobes.

Horizontal Fissure on Imaging

The horizontal fissure can sometimes be identified on frontal or lateral chest radiographs and is more clearly demonstrated on cross-sectional imaging.

Its position provides an important landmark for distinguishing superior-lobe disease from middle-lobe disease.

Oblique Fissure on Imaging

The oblique fissure separates the inferior lobe from the superior and middle lobes and is particularly useful for localizing abnormalities on lateral radiographs and computed tomography.

Its exact position varies with respiration and individual anatomy.

Lobar Localization of Disease

Pneumonia, atelectasis, tumors, pulmonary edema, and other abnormalities may preferentially involve individual lobes or bronchopulmonary segments.

Knowledge of the fissures and lobar boundaries allows these abnormalities to be localized accurately.

Right Middle Lobe Atelectasis

The middle lobe has a relatively narrow bronchial pathway and may undergo partial or complete collapse in association with bronchial obstruction or surrounding disease.

Because the medial segment lies adjacent to the right heart border, middle-lobe disease may alter the normal appearance of that border on frontal chest radiographs.

Aspiration

The right main bronchus is generally wider, shorter, and more vertical than the left main bronchus.

As a result, aspirated material entering the tracheobronchial tree may preferentially pass toward the right lung, although its eventual distribution depends on body position and segmental bronchial anatomy.

Bronchoscopy

During bronchoscopy, the right main bronchus can be followed into the superior lobar bronchus and bronchus intermedius.

The bronchus intermedius then provides access to the middle and inferior lobar bronchi, which divide further into segmental bronchi.

Lobectomy

A lobectomy involves surgical removal of an entire pulmonary lobe.

On the right side, the superior, middle, or inferior lobe can be removed while preserving the remaining lobes when anatomical and clinical circumstances permit.

Bilobectomy

Because the right lung contains three lobes, certain disease patterns may require removal of two adjacent lobes, a procedure known as bilobectomy.

Examples include removal of the superior and middle lobes or the middle and inferior lobes, depending on the location and extent of disease.

Segmentectomy

A segmentectomy removes one or more bronchopulmonary segments while preserving neighboring pulmonary tissue.

This is anatomically possible because each segment has a relatively independent segmental bronchus and pulmonary arterial supply.

Pneumonectomy

A right pneumonectomy involves removal of the entire right lung.

The procedure requires division and secure management of the major bronchial and vascular structures forming the right lung root.

Key Anatomical Relationships

• The right lung contains three lobes.
• The lobes are superior, middle, and inferior.
• The horizontal fissure separates the superior and middle lobes.
• The oblique fissure separates the inferior lobe from the superior and middle lobes.
• The right lung is generally larger than the left lung.
• The right lung is relatively shorter and broader because of the elevated right hemidiaphragm.
• The mediastinal surface contains the pulmonary hilum.
• The superior lobar bronchus is eparterial.
• The bronchus intermedius supplies the middle and inferior lobes through their lobar bronchi.
• The right lung conventionally contains 10 bronchopulmonary segments.
• The superior lobe contains S1 to S3.
• The middle lobe contains S4 and S5.
• The inferior lobe contains S6 to S10.
• The azygos vein arches over the right lung root.
• The superior vena cava lies anterior and superior to the root.
• Visceral pleura covers the lung and extends into both major fissures.

Clinical Importance

The three-lobed organization of the right lung provides the structural framework for understanding its bronchial branching, vascular supply, radiological appearance, and surgical anatomy. The horizontal and oblique fissures separate the lung into superior, middle, and inferior lobes while permitting relative movement between adjacent lobes during respiration.

The right lung also has distinctive bronchovascular relationships. The superior lobar bronchus lies above the pulmonary artery, while the bronchus intermedius continues toward the middle and inferior lobes. Within the lobes, ten bronchopulmonary segments provide more precise anatomical subdivisions.

Understanding the right lung provides the anatomical foundation for studying pulmonary lobes, horizontal and oblique fissures, bronchopulmonary segments, pulmonary hilum, lung root, bronchus intermedius, pleural relationships, thoracic imaging, bronchoscopy, aspiration patterns, and pulmonary surgery.