What are the causes of right diaphragmatic eventration?

Causes of Right Diaphragmatic Eventration

Right diaphragmatic eventration results from either congenital absence of muscle fibers in the diaphragm or acquired phrenic nerve injury, with the right side being less commonly affected (15%) compared to the left (85%). 1, 2

Congenital Causes

Primary Developmental Defects

• Incomplete diaphragmatic muscle development during the eighth week of gestation leads to congenital eventration, representing a failure of mesenchymal development in the posterolateral region 3, 1
• Congenital eventration involves absence or severe thinning of muscle fibers while maintaining all anatomical attachments of the diaphragm 4
• Right-sided congenital diaphragmatic defects occur in approximately 15% of cases, with left-sided predominance (85%) being the norm 1

Genetic Factors

• Alterations in FOG2, GATA4, or COUP-TFII genes interrupt molecular pathways critical for mesenchymal development in the posterolateral diaphragm 1
• No single genetic cause accounts for more than 1-2% of congenital diaphragmatic hernia cases, demonstrating significant genetic heterogeneity 1
• Genetic testing can identify a causative mutation in up to 30% of patients with non-isolated congenital diaphragmatic hernia 1

Acquired Causes

Phrenic Nerve Injury

• Phrenic nerve injury is the primary acquired cause of diaphragmatic paralysis-eventration, as the diaphragm is supplied exclusively by the phrenic nerves 2
• Surgical trauma during cardiothoracic, cervical, or mediastinal procedures can damage the phrenic nerve 2
• Traumatic injury from blunt or penetrating chest trauma may result in phrenic nerve dysfunction 2

Iatrogenic Causes

• Surgical procedures involving the chest, neck, or mediastinum carry risk of inadvertent phrenic nerve injury 2
• Post-surgical complications represent a significant proportion of acquired diaphragmatic dysfunction 5

Other Acquired Etiologies

• Tumor invasion or compression of the phrenic nerve from adjacent malignancies 2
• Infectious processes affecting the phrenic nerve or diaphragm muscle 2
• Neurological disorders affecting phrenic nerve function 5

Clinical Distinction: Eventration vs. Paralysis

Functional Differentiation

• Eventration demonstrates focal weakness with reduced or delayed orthograde excursion on deep breathing, but typically lacks paradoxical motion on sniffing 5
• Diaphragmatic paralysis shows absence of orthograde excursion with paradoxical motion on sniffing maneuvers 5
• Fluoroscopic imaging effectively differentiates eventration (no paradoxic motion) from paralysis (paradoxic motion) 6

Epidemiological Patterns

Side Predilection

• Right diaphragmatic eventration occurs in approximately 15-19% of cases 1, 4
• Left-sided involvement predominates in 81.5-85% of patients 1, 4
• Male patients are more frequently affected (76% male vs. 24% female) 4

Age Distribution

• Adult presentation of congenital eventration occurs at mean age of 40-44 years 3, 4
• Many congenital cases remain asymptomatic until adulthood when discovered incidentally 6

Important Clinical Pitfalls

• Diaphragmatic eventration is frequently asymptomatic and discovered incidentally on chest imaging, making it essential to distinguish from acute diaphragmatic pathology 6
• The condition can be easily missed in acute settings due to its rarity and nonspecific radiographic findings 3
• Right-sided eventration may be confused with hepatomegaly or subphrenic pathology on initial imaging 2
• Gradual diaphragmatic rise or relapse of symptoms can occur even after surgical plication, with 5 of 7 patients in one series experiencing recurrent elevation or symptoms 7