Lung Fissures: Variation, Age Influence, and Clinical Insights

Lung fissures are anatomical separations that divide the lobes of the lungs, playing a crucial role in respiratory function and medical assessments. Their structure varies between individuals, influencing both normal lung physiology and disease presentation. Understanding these differences is essential for accurate imaging interpretation and surgical planning.

Research indicates that age and developmental factors affect the appearance and integrity of lung fissures. These considerations are particularly relevant in diagnosing conditions like pleural effusions or segmental lung diseases.

Major Fissures in Each Lung

The human lungs are divided into lobes by deep invaginations of visceral pleura, which facilitate independent movement and function. These fissures allow for differential expansion and contraction, optimizing ventilation efficiency. The right lung, larger due to the heart’s position, contains two major fissures: the oblique and horizontal fissures. The left lung, being smaller, has only one, the oblique fissure.

The oblique fissure is present in both lungs, extending from the posterior surface near the T3 vertebra and terminating near the costochondral junction of the sixth rib. It separates the superior and inferior lobes in the left lung, while in the right lung, it divides the superior and middle lobes from the inferior lobe. Its orientation plays a role in segmental lung movement, particularly during forced respiration.

The right lung’s horizontal fissure runs transversely from the oblique fissure at the level of the fourth rib to the anterior lung border. It creates a distinct middle lobe, absent in the left lung. This extra lobe allows for a more compartmentalized distribution of airflow and can influence the localization of pulmonary pathologies such as pneumonia or atelectasis. The horizontal fissure’s position varies slightly among individuals, and its visibility on imaging depends on lung inflation and patient positioning.

Anatomical Variations and Accessory Fissures

Lung fissures exhibit considerable variability, with structural deviations influencing both physiological function and diagnostic imaging. While the oblique and horizontal fissures serve as primary boundaries, some individuals have additional separations known as accessory fissures. These are often remnants of embryological development and can complicate radiological interpretation by mimicking conditions such as atelectasis, pleural effusion, or lobar consolidation.

A common accessory fissure is the azygos fissure, found in the right lung due to an anomalous course of the azygos vein. Instead of following its usual path along the mediastinum, the vein invaginates into the lung parenchyma, forming a distinct fissure that encloses a small, separate azygos lobe. While this lobe does not function independently, its appearance on imaging can be misinterpreted as a pathological lesion. Similarly, the inferior accessory fissure, which separates a portion of the lower lobe, can be mistaken for an interlobar pleural effusion when fluid accumulates along its plane.

Less common variations, such as the superior accessory fissure, divide the superior segment of the lower lobe, creating an additional compartment that can affect airflow and disease spread. The prevalence of accessory fissures varies across populations. Studies indicate that the azygos fissure appears in about 1% of individuals, while the inferior accessory fissure is observed in 5-10% of cases. Awareness of these anomalies is crucial for accurate diagnosis and treatment planning.

Advanced Imaging for Structural Assessment

Detailed visualization of lung fissures is essential for assessing anatomical variations, diagnosing pulmonary conditions, and guiding surgical interventions. Conventional chest radiographs provide a basic outline of major fissures, but their sensitivity is limited by patient positioning and superimposed structures. High-resolution computed tomography (HRCT) offers precise delineation of fissures and their variations, allowing clinicians to evaluate fissure completeness, detect accessory fissures, and differentiate normal anatomy from pathology. This is particularly useful in planning procedures such as lobectomies, where incomplete fissures can increase the risk of postoperative complications like prolonged air leaks.

Advanced imaging techniques, including dual-energy CT (DECT) and magnetic resonance imaging (MRI), further refine fissure assessment. DECT enhances tissue contrast by differentiating structures based on atomic composition, improving the detection of incomplete fissures. A study in Radiology demonstrated that DECT highlights variations in pleural integrity that might be overlooked with conventional CT. While MRI is less commonly used for pulmonary imaging due to lower spatial resolution, ultrashort echo time (UTE) sequences have made it increasingly viable for lung morphology assessment without radiation exposure.

Functional imaging modalities such as four-dimensional (4D) CT and hyperpolarized gas MRI provide insights into dynamic lung mechanics. 4D CT captures real-time respiratory motion, helping assess fissure movement during breathing cycles. This is particularly valuable for evaluating ventilation heterogeneity, as incomplete fissures can alter airflow distribution. Hyperpolarized gas MRI maps ventilation patterns with exceptional sensitivity, correlating fissural integrity with regional lung function. These advancements are reshaping the approach to diagnosing and managing conditions influenced by fissure morphology, such as chronic obstructive pulmonary disease (COPD) and interstitial lung disease.

Age-Related Changes in Fissure Shape

Lung fissures undergo subtle alterations with age due to progressive remodeling of lung parenchyma, shifts in thoracic compliance, and cumulative environmental exposure. Over time, lung tissue elasticity diminishes, leading to increased stiffness in the interlobar pleura. This can make fissures less distinct on imaging, particularly in elderly individuals, where incomplete or irregular fissures are more common.

Age-related lung volume redistribution also influences fissure morphology. As alveolar walls thin and airspaces enlarge, fissures may appear more flattened or displaced. This effect is particularly noticeable in the oblique fissure, where reduced diaphragmatic excursion alters its positioning. HRCT studies show that older adults often exhibit a more posterior orientation of the oblique fissure, correlating with decreased pulmonary elastic recoil. These positional shifts may subtly impact ventilation efficiency by altering lobar expansion mechanics.

Significance in Clinical Evaluations

Lung fissures serve as important landmarks in medical imaging and surgical procedures, influencing the interpretation of pathological findings and intervention planning. Their completeness and orientation affect the spread of infections, tumor localization, and the effectiveness of procedures such as segmentectomy or lobectomy. In clinical settings, fissural anatomy is particularly relevant in diagnosing pleural effusions, as fluid accumulation along these planes creates distinct radiographic signs. Incomplete fissures, where pleural layers fail to fully separate lobes, may lead to atypical fluid distribution, complicating differentiation between effusion and parenchymal disease.

Fissure integrity is also critical in pulmonary disease management, particularly in conditions like COPD and interstitial lung disease. For example, fissure completeness influences the effectiveness of bronchoscopic lung volume reduction (BLVR) therapy, a minimally invasive treatment for severe emphysema. Patients with intact fissures tend to experience better outcomes, as the procedure relies on isolating diseased lobes and redirecting airflow to healthier regions. Similarly, in lung cancer staging, fissural involvement can alter tumor classification and surgical approach, affecting prognosis and treatment decisions. A study in The Annals of Thoracic Surgery highlighted that tumor extension through a fissure is associated with increased lymphatic spread, underscoring the need for precise preoperative imaging.