Thoracentesis

Safety criteria and imaging control

The success and safety of thoracentesis directly depend on the choice of access site. The main conditions for the procedure are a fluid depth of at least 10 mm, the absence of lung tissue along the needle trajectory during deep inspiration, and a minimal risk of injuring adjacent organs (heart, liver, spleen).

The optimal approach is to perform the intervention under ultrasound guidance. This method is accessible, radiation-free, and allows for real-time identification of the largest pocket, which is especially important in multiloculated effusions. CT guidance is used less frequently: it is indicated for draining small pneumothoraces in patients with underlying pulmonary pathology (cystic fibrosis, interstitial lung diseases) or for accessing hard-to-reach areas, such as behind the ribs or in the paravertebral spaces.

Pleural cavity drainage

If there is an excessive amount of fluid, it is infected, or the patient develops a symptomatic pneumothorax, pleural drainage is indicated.

• Pneumothorax: Drained in the "safe triangle" (bounded by the lateral borders of the pectoralis major and latissimus dorsi muscles, and inferiorly by the nipple line). Most often performed on an emergency basis.
• Infected effusion: Drainage is established when pus, turbid fluid, or Gram-positive bacteria are detected. The most critical independent predictor for drainage is fluid pH < 7.2 (a catheter is placed even if cultures are negative). Since 40% of standard cultures show no growth, it is recommended to inoculate the fluid into blood culture bottles.
• Malignant effusion: Drainage is only one of the approaches alongside thoracoscopy, therapeutic punctures, or indwelling catheter placement. The choice depends on the patient's general condition and the degree of lung expansion.

For uncomplicated pneumothorax and free-flowing effusion, small-bore catheters (12–14 Fr) are sufficient. They are comparable in efficacy to large-bore tubes, but are much better tolerated by patients and require fewer analgesics. If the effusion is septated, a single drain is insufficient — administration of fibrinolytic agents is required.

Pleural biopsy

If imaging methods and clinical presentation do not allow to determine the cause of the effusion or pleural thickening, histological verification is required.

• Medical thoracoscopy: The method of choice when a malignant process is suspected. It allows for inspection of the cavity, targeted biopsy, and drain placement in a single procedure.
• Percutaneous core-needle biopsy: Performed under ultrasound or CT guidance. Its sensitivity for detecting adenocarcinoma and mesothelioma reaches 90%.
• Blind needle biopsy (Abrams needle) is obsolete and is only used in regions endemic for tuberculosis.

If the initial biopsy is inconclusive, PET-CT with 18F-FDG is used to identify the most metabolically active areas of pleural thickening. When mesothelioma is suspected, the number of interventions is minimized: the tumor tends to metastasize directly along the puncture or drainage tract.

Anatomical pitfalls and complications

The incidence of iatrogenic complications during punctures remains low. The main risks include bleeding, infection, pain, inadvertent puncture of parenchymal organs, and pneumothorax. Key causes of errors include lack of experience, poor visualization, and excessive dilation.

Intercostal artery injury It is a misconception that the artery is always hidden within the costal groove (sulcus costae). Originating from the aorta, it courses obliquely upward and laterally, settling into the groove only at the angle of the rib (angulus costae). Until that point on the posterior chest wall, the artery is unprotected. In elderly patients, it is additionally tortuous. The golden rule of safety: the needle must be advanced strictly along the cranial border of the underlying rib and lateral to its angle.

Iatrogenic pneumothorax Occurs in approximately 5% of thoracentesis cases (the risk increases in COPD and greater depth of the lesion). The vast majority of such pneumothoraces resolve on their own. Chest tube insertion is required in only ~2% of cases (with a large volume of air or pronounced symptoms).

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Management specifics of loculated effusions and the use of fibrinolytics.
• Topographic anatomy and sites of diaphragmatic attachment.
• Alternative management methods for malignant effusions (pleurodesis, thoracoscopy).
• Risk factors for iatrogenic pneumothorax during lung biopsy.

Other topics in the «Chest Radiology» section

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