Costodiaphragmatic Recess

recessus costodiaphragmaticus

The costodiaphragmatic recess is the most inferior and largest pleural recess, formed where the costal and diaphragmatic pleural reflections meet. It can accommodate approximately 200-300 mL of fluid before fluid becomes visible on upright chest X-ray. It extends from approximately the 8th rib anteriorly to the 12th rib posteriorly.

Anatomical Data

Boundaries & Contents

Location	Lowest part of each pleural cavity, around the lower edge of the lung, reaching about rib 8 in the midclavicular line, rib 10 in the midaxillary line and rib 12 near the spine
Boundaries	Costal pleura (outer) Diaphragmatic pleura (inner) Lower border of the lung (above, in quiet breathing)
Contents	Small amount of pleural fluid

Biomechanics

Function & Actions

Spare room that the lung fills in deep breaths. Being the lowest point when upright, it is where pleural fluid first collects (blunting of the angle on X-ray) and where a pleural tap is aimed.

Clinical Relevance

Clinical Notes

The costodiaphragmatic recess is the first location for pleural effusion accumulation, visible as blunting of the costophrenic angle on upright chest X-ray when 200-300 mL is present. Thoracentesis targets the recess at the 9th intercostal space in the midscapular line. Ultrasound-guided thoracentesis aims for the deepest point of the recess to avoid the diaphragm.

Pathology

Common Injuries & Conditions

Pleural Effusion in Costodiaphragmatic Recess

Fluid accumulation in the costodiaphragmatic recess blunting the costophrenic angle on chest X-ray, the earliest radiographic sign of pleural effusion, requiring thoracentesis when symptomatic or diagnostically necessary.

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