Costomediastinal Recess

The costomediastinal recess is a potential space within the pleural cavity formed where the costal pleura reflects onto the mediastinal pleura near the anterior aspect of the thorax. It provides space into which the anterior border of the lung can expand during inspiration.

Costomediastinal recesses are present on both sides of the thorax, but the left costomediastinal recess is larger and more clinically prominent. This asymmetry results primarily from the cardiac notch of the left lung and the corresponding displacement of the left anterior pleural and pulmonary boundaries by the heart.

Formation

The costomediastinal recess forms where the parietal pleura changes direction from the internal surface of the anterior thoracic wall onto the lateral surface of the mediastinum.

At this reflection, the costal and mediastinal layers of parietal pleura become closely apposed when the adjacent lung does not completely occupy the pleural cavity.

Location

The recess lies anteriorly near the sternum and the anterior mediastinum.

It is situated between the costal pleura lining the anterior thoracic wall and the mediastinal pleura covering the lateral surface of mediastinal structures.

Costal Pleura

The costal pleura lines the internal surfaces of the ribs, costal cartilages, sternum, and intercostal spaces.

Anteriorly, it reflects posteriorly onto the mediastinum and becomes continuous with the mediastinal pleura.

Mediastinal Pleura

The mediastinal pleura forms the lateral pleural covering of the mediastinum.

Anteriorly, it meets the costal pleura at the pleural reflection that creates the costomediastinal recess.

Potential Space

Like other pleural recesses, the costomediastinal recess is a potential space.

Its opposing parietal pleural surfaces normally lie close together, separated by the thin film of serous fluid within the pleural cavity. During lung expansion, the anterior lung margin can enter the recess and separate these surfaces.

Relationship to the Lung

The anterior border of the lung approaches the anterior pleural reflection but does not occupy the entire extent of the pleural cavity throughout the respiratory cycle.

The resulting potential space between the anterior lung margin and pleural reflection forms the functional recess.

Anterior Border of the Lung

The anterior border separates the costal and mediastinal surfaces of the lung.

Its course differs between the right and left lungs, particularly in the lower anterior thorax because of the cardiac notch of the left lung.

Right Costomediastinal Recess

The right costomediastinal recess is relatively narrow because the anterior border of the right lung closely follows the anterior pleural reflection through much of its course.

The right lung lacks the prominent cardiac notch found on the left side.

Left Costomediastinal Recess

The left costomediastinal recess is generally larger than the right.

It is particularly prominent near the region where the anterior border of the left lung deviates laterally to form the cardiac notch.

Cardiac Notch

The cardiac notch is an indentation along the anterior border of the left lung produced by the position of the heart.

Because the left lung margin deviates laterally around the heart, a larger region of the anterior pleural cavity is not occupied by lung tissue.

Relationship to the Heart

The heart projects predominantly toward the left side of the thorax and influences the contour of the left lung and pleural reflections.

This relationship contributes directly to the greater size of the left costomediastinal recess.

Cardiac Area

In the region of the cardiac notch, the anterior margin of the left lung does not completely cover the underlying pericardial region.

This creates an area where the heart and pericardium are relatively less covered by lung compared with neighboring regions.

Lingula

The lingula is a tongue-shaped projection of the superior lobe of the left lung located inferior to the cardiac notch.

During inspiration, the lingula and neighboring anterior lung tissue can move toward the left costomediastinal recess as the lung expands.

Pleural Reflections

The anterior pleural reflections mark the transition between costal and mediastinal pleura.

The right and left reflections approach one another behind the sternum in the superior and middle portions of the anterior thorax but diverge inferiorly, particularly on the left.

Right Anterior Pleural Reflection

The right pleural reflection descends near the midline behind the sternum before turning laterally toward the inferior pleural boundary.

The anterior border of the right lung follows this reflection relatively closely during much of its course.

Left Anterior Pleural Reflection

The left pleural reflection also approaches the midline superiorly.

Inferiorly, it deviates laterally because of the position of the heart, contributing to the larger left costomediastinal recess.

Retrosternal Relationship

The anterior pleural sacs approach one another behind the sternum.

This close relationship is important when considering access to mediastinal structures and the possibility of entering a pleural cavity during anterior thoracic procedures.

Changes During Inspiration

During inspiration, expansion of the lungs causes their anterior borders to move farther into the costomediastinal recesses.

The potential space therefore becomes smaller as lung tissue occupies more of the available pleural cavity.

Deep Inspiration

During deep inspiration, greater expansion of the lungs allows the anterior margins to extend farther toward the anterior pleural reflections.

This movement is particularly relevant to the left lung near the cardiac notch and lingula.

Changes During Expiration

During expiration, elastic recoil reduces lung volume and the anterior borders withdraw from the pleural reflections.

The costal and mediastinal pleural surfaces consequently become apposed over a larger area, increasing the functional extent of the recess.

Respiratory Function

The costomediastinal recess provides reserve space for changes in the anterior dimensions of the lungs.

It allows lung expansion to occur smoothly as thoracic volume increases during inspiration.

Pleural Fluid

A thin film of serous fluid normally occupies the pleural cavity and lubricates the opposing pleural surfaces.

This allows the pleural layers to slide relative to one another as the lungs move into and out of the recess during breathing.

Relationship to the Costodiaphragmatic Recess

The costomediastinal recess and costodiaphragmatic recess are both potential spaces formed by reflections of the parietal pleura.

They differ primarily in their location and the pleural surfaces involved.

Comparison of Pleural Recesses

Feature	Costomediastinal Recess	Costodiaphragmatic Recess
Pleural surfaces	Costal and mediastinal pleura	Costal and diaphragmatic pleura
Location	Anterior pleural cavity	Inferior pleural cavity
Lung margin entering recess	Anterior border	Inferior border
Side difference	More prominent on left	Present extensively on both sides
Major anatomical association	Cardiac notch	Diaphragm and inferior lung border

Why the Left Recess Is Larger

The larger size of the left recess is primarily related to the position of the heart.

The cardiac impression and cardiac notch displace the anterior margin of the left lung laterally, leaving a larger potential pleural space anteriorly.

Surface Anatomy

The costomediastinal recess projects onto the anterior thoracic wall near the parasternal region.

Its exact extent varies with respiratory phase because the anterior border of the lung changes position during inspiration and expiration.

Relationship to the Sternum

The recess lies deep to the anterior thoracic wall and is closely related to the sternum and adjacent costal cartilages.

The pleural reflections on the two sides approach each other closely behind portions of the sternum.

Relationship to Costal Cartilages

The anterior pleural reflections lie deep to the costal cartilages as they descend along the anterior thoracic wall.

These relationships help define the surface projection of the anterior pleural boundaries.

Anterior Mediastinum

The costomediastinal recess lies adjacent to structures of the mediastinum.

Its presence must be considered when approaching mediastinal structures from the anterior thoracic wall because pleural reflections may extend close to the midline.

Relationship to the Pericardium

The mediastinal pleura is closely related to the fibrous pericardium.

On the left, the cardiac notch and larger costomediastinal recess contribute to an anterior region where the pericardium is less extensively overlapped by lung.

Pericardial Access

Knowledge of anterior pleural and pulmonary boundaries is important when planning access to the pericardial region.

Anatomical variation and respiratory movement must be considered because the pleural sacs can lie close to potential procedural pathways.

Clinical Imaging

The costomediastinal recess is less conspicuous on routine chest radiographs than the costodiaphragmatic recess.

Its anatomy is nevertheless important when interpreting anterior pleural boundaries and cross-sectional imaging of the thorax.

Computed Tomography

Computed tomography can demonstrate the relationship between the anterior lung margins, pleural cavities, mediastinum, and pericardium.

It is particularly useful for visualizing abnormalities involving the anterior pleural space or mediastinum.

Pleural Effusion

Free pleural fluid tends to accumulate primarily in dependent portions of the pleural cavity rather than preferentially within the costomediastinal recess in an upright individual.

However, larger effusions or loculated collections can extend into anterior pleural spaces.

Loculated Pleural Fluid

Pleural inflammation can produce adhesions that compartmentalize the pleural cavity.

When fluid becomes loculated, it may collect in unusual locations, including anterior pleural regions associated with the costomediastinal recess.

Pneumothorax

Air within the pleural cavity can occupy nondependent regions of the pleural space.

Depending on body position, pleural air may extend anteriorly and alter the normal relationship between the lung and the anterior pleural cavity.

Pleural Adhesions

Inflammation of the pleura can result in adhesions between normally mobile pleural surfaces.

Adhesions involving the costomediastinal recess may restrict movement of the anterior lung border during respiration.

Innervation of the Costal Pleura

The costal pleura receives somatic sensory innervation from the intercostal nerves.

Irritation can therefore produce relatively localized pain corresponding to the involved thoracic wall region.

Innervation of the Mediastinal Pleura

The mediastinal pleura receives somatic sensory innervation primarily from the phrenic nerve.

This differs from the adjacent costal pleura, which is supplied by intercostal nerves.

Sensory Boundary

The costomediastinal recess is formed by two regions of parietal pleura with different principal somatic sensory supplies.

The costal component is associated with intercostal nerves, while the mediastinal component is associated primarily with the phrenic nerve.

Pleural Pain

Parietal pleura is sensitive to painful stimuli.

The perceived location of pain depends partly on whether irritation involves the costal or mediastinal component of the pleura.

Phrenic Referred Pain

Irritation involving mediastinal pleura can transmit sensory information through the phrenic nerve to cervical spinal cord levels C3-C5.

This can contribute to referred pain in the shoulder region.

Intercostal Pain

Irritation of the costal pleura transmits somatic sensory signals through intercostal nerves.

Pain is therefore generally perceived more locally in the corresponding thoracic wall distribution.

Relationship to Cardiac Examination

The cardiac notch of the left lung leaves part of the anterior cardiac region less covered by lung.

This relationship contributes to the anatomical basis for differences in percussion and auscultatory relationships over the anterior left thorax.

Anterior Lung Expansion

During inspiration, the anterior borders of the lungs move toward the anterior pleural reflections.

This expansion is accommodated by the costomediastinal recesses without requiring substantial movement of the pleural reflections themselves.

Anterior Lung Retraction

During expiration, lung recoil causes the anterior margins to withdraw from the recesses.

The pleural surfaces then return to closer apposition in regions no longer occupied by lung tissue.

Relationship to Thoracic Procedures

The variable position of the anterior lung margins and pleural reflections is important during procedures involving the sternum, anterior mediastinum, pericardium, and parasternal thoracic wall.

Knowledge of these relationships helps reduce unintended entry into the pleural cavity.

Anatomical Variation

The exact position of the anterior lung margins and pleural reflections varies among individuals.

Respiratory phase, body habitus, thoracic shape, and underlying pathology can further alter their relationships.

Right and Left Recess Comparison

Feature	Right Side	Left Side
Relative size	Generally smaller	Generally larger
Cardiac notch	Absent	Present
Anterior lung border	More closely follows pleural reflection	Deviates laterally near cardiac notch
Major neighboring influence	Right mediastinal structures	Heart and pericardium

Anatomical Boundaries

• Anterior and lateral component: costal pleura lining the internal thoracic wall
• Medial component: mediastinal pleura covering the mediastinum
• Adjacent pulmonary structure: anterior border of the lung
• Most prominent region: left anterior pleural cavity near the cardiac notch

Key Anatomical Relationships

• The costomediastinal recess is formed where costal pleura reflects onto mediastinal pleura.
• It is located in the anterior part of the pleural cavity.
• It is a potential rather than a normally open empty space.
• The anterior lung border moves into the recess during inspiration.
• The lung withdraws from the recess during expiration.
• The recess exists on both sides of the thorax.
• The left costomediastinal recess is generally larger than the right.
• The larger left recess is related to the cardiac notch of the left lung.
• The lingula lies inferior to the cardiac notch.
• The heart and pericardium influence the contour of the left recess.
• The costal pleura is supplied by intercostal nerves.
• The mediastinal pleura is supplied primarily by the phrenic nerve.
• The recess provides reserve space for anterior lung expansion.
• Its anatomy is important during anterior thoracic and mediastinal procedures.
• It differs from the costodiaphragmatic recess, which lies inferiorly between costal and diaphragmatic pleura.

Clinical Importance

The costomediastinal recess is important because it provides reserve space for movement of the anterior borders of the lungs during respiration. During inspiration, lung tissue expands farther into the recess, while expiration allows the anterior lung margins to withdraw.

The recess is particularly prominent on the left because the heart produces the cardiac notch in the anterior border of the left lung. This creates a larger region where costal and mediastinal pleura can approach one another without intervening lung tissue.

Understanding the costomediastinal recess provides the anatomical foundation for studying pleural reflections, anterior lung borders, the cardiac notch, lingula, respiratory lung movement, mediastinal anatomy, pleural innervation, pericardial relationships, and anterior thoracic procedures.