Eventration of the Diaphragm

Fig. 47.1

Chest X-ray showing eventration of left (a) and right (b) hemidiaphragm (arrows)

It is postulated that they occur embryologically because of abnormal migration of myoblasts from the upper cervical somites into two of the four embryological structures that contribute to diaphragm development: the septum transversum (beginning at 4 weeks of gestation) and the pleuroperitoneal membrane (at 8–12 weeks of gestation).

The loss of contractility leads to muscle atrophy with elevation of the hemidiaphragm.

It is usually congenital but may be acquired.

Complete eventration almost invariably occurs on the left side and is rare on the right.

It is more common in males than in females.

Congenital eventration of the diaphragm is commonly an isolated condition.

Sometimes it is associated with other developmental defects such as:

Cleft palate
Congenital heart disease
Situs inversus
Undescended testicle

Classification

Eventration of the diaphragm is divided into two types:
- Congenital
- Acquired
Congenital eventration results from:
- Inadequate development of the muscle of diaphragm
- Absence of the phrenic nerves
The most common cause of acquired eventration is injury to the phrenic nerve, resulting from:
- Traumatic birth leading to injury of phrenic nerve
- Thoracic surgery for congenital heart disease
- Rarely, tumors of the chest
- Obstetric injury may be combined with lesion of brachial plexus leading to a paralysis of the Erb–Duchenne type.
In the acquired form, the central tendon of diaphragm is normal and the diaphragm consists of normally developed muscle that is atrophic. Both sides of diaphragm are affected equally.
The defect in congenital eventration can be:
- Partial
- Diffuse
In the partial type, the defect is localized.
In the diffuse type, the diaphragm consists of a thin membrane that is attached peripherally to normal muscles.
Partial defects mostly affect the right hemidiaphragm (65 %) of children.
Diffuse eventration is more frequent on the left side.