Eventration of the diaphragm in adults

INTRODUCTION — The diaphragm is the most important inspiratory muscle of the body and also serves as a mechanical barrier between the abdominal and thoracic cavities. Diaphragmatic eventration is a thinning of a portion or all of the diaphragm where muscle has been replaced by fibroelastic tissue. It is prudent that the clinician recognizes this condition so that appropriate evaluation and treatment can be instituted.

The causes, diagnostic evaluation, and treatment of diaphragm eventration in adults will be reviewed here. The clinical evaluation and management of unilateral and bilateral diaphragmatic paralysis and evaluation of eventration in children are reviewed separately.

●(See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults".)

●(See "Diagnostic evaluation of adults with bilateral diaphragm paralysis".)

●(See "Treatment of bilateral diaphragmatic paralysis in adults".)

●(See "Eventration of the diaphragm in infants".)

●(See "Diaphragmatic paralysis in the newborn".)

NORMAL DIAPHRAGM ANATOMY AND FUNCTION

Anatomy — The diaphragm is a dome-shaped muscle that has two components:

●Central tendon – The noncontractile central tendon runs anteroposteriorly, separating the right and left sides and extends to the dome of each hemidiaphragm and the contracting muscle fibers [1-3].

●Muscle fibers – The diaphragmatic muscle fibers radiate centrifugally from the central tendon and insert peripherally onto the inner surface of the lower six ribs laterally, the costal cartilages and sternum anteriorly, and the arcuate ligaments that extend from the upper lumbar vertebrae to the 12^th ribs posteriorly [4]. The crura are posterior muscle bundles that run from the medial central tendon to the upper lumbar vertebral bodies posteriorly (L1 to L3 on the right, and L1 to L2 on the left).

The left and right sides of diaphragm are innervated by the ipsilateral phrenic nerves, which derive from cervical nerve roots three, four, and five [4]. Each nerve divides into four trunks that innervate the anterolateral, posterolateral, sternal, and crural portions of the diaphragm on the ipsilateral side.

Function — Contraction of the diaphragm with caudal (ie, downward) movement into the abdominal cavity during inspiration has the following effects that promote air movement into the lungs [1,3]:

●Decrease in intrapleural pressure

●Elevation of the rib cage, using the abdomen as a fulcrum

●Expansion of the rib cage by generating positive intra-abdominal pressure

Although the diaphragm performs most of the work of breathing, normal ventilation also requires the simultaneous contraction of some of the accessory muscles of respiration (eg, scalene and the parasternal portions of the internal and external intercostal muscles). These muscles elevate and expand the upper ribcage during inspiration and pull the ribcage down and in during expiration.

DEFINITION, ETIOLOGY, AND PATHOPHYSIOLOGY — Eventration is a condition, where all or a portion of the diaphragm muscle is replaced by a thin fibroelastic sheath from processes that either impair myofibroblast migration to the diaphragm (eg, congenital failure of diaphragmatic muscularization) or from muscle atrophy (eg, due longstanding irreversible phrenic nerve injury) [4,5].

Etiology — Eventration of the diaphragm can be congenital or acquired.

While some cases are due to congenital birth defects, eventration can also be associated with other congenital disorders (eg, spondylocostal dysostosis, Kabuki syndrome, Beckwith-Wiedemann syndrome, Poland syndrome, chromosomal defects, pulmonary hypoplasia, spinal muscular atrophy, malrotation, and congenital heart disease). These conditions are more commonly encountered in newborns and children. (See "Eventration of the diaphragm in infants".)

Acquired cases are more common in adults and are mostly due to etiologies associated with phrenic nerve injury and, consequently, muscle atrophy. However, the reason for an old phrenic nerve injury may not be apparent or may be remote. These etiologies are listed in the table (table 1) and are discussed separately. (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Etiology' and "Diagnostic evaluation of adults with bilateral diaphragm paralysis", section on 'Etiology'.)

Pathophysiology — The affected part of the diaphragm is replaced by fibroelastic tissue and becomes pliable, resulting in reduced function. The continuity of the diaphragm and normal attachments to the costal margin are maintained (ie, there is no herniation of abdominal contents).

Subclassifications — Both congenital and acquired eventration can be subclassified as the following:

●Partial (involving part of the hemidiaphragm)

OR

●Complete (involving the whole hemidiaphragm)

●Unilateral (involving one hemidiaphragm)

OR

●Bilateral (involving both hemidiaphragms)

In adults, partial unilateral eventration is the most commonly encountered subclass, explaining why most patients have no symptoms and present incidentally. Complete unilateral and bilateral eventrations are rare. (See 'Clinical manifestations' below.)

EPIDEMIOLOGY — The incidence of complete diaphragmatic eventration is unknown. Our experience and case series suggest that it is rare, with an estimated incidence of 0.05 percent [6-8].

However, it is likely that complete diaphragmatic eventration is underdiagnosed, since most patients are asymptomatic and only come to the attention of a clinician when an elevated hemidiaphragm is found incidentally on chest imaging. Data suggesting a sex predominance are weak.

A large study in Japan demonstrated that the incidence of partial eventration of the right hemidiaphragm increases with age, particularly in women, being seen in more than 1 percent of the women above age 60 [6].

CLINICAL MANIFESTATIONS — Most adults with diaphragmatic eventration are asymptomatic, but depending upon the degree of involvement and associated comorbidities, symptoms may range from mild dyspnea to respiratory failure.

There are no laboratory findings specific for this condition.

Asymptomatic — In adults, diaphragmatic eventration is rarely symptomatic, likely because most cases are due to partial eventration of one hemidiaphragm rather than complete or bilateral disease. The diagnosis is generally suspected in patients who present incidentally with partial elevation in one hemidiaphragm on chest imaging (image 1). (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Incidental finding on chest radiography (ie, asymptomatic)'.)

Symptoms — Symptoms are more likely when patients have complete or bilateral eventration (which is uncommon) or have underlying comorbidities or lung disease.

Symptoms associated with complete unilateral diaphragmatic eventration are similar to those in patients with unilateral diaphragmatic paralysis, and symptoms of bilateral eventration are similar to those with bilateral paralysis. (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Less common presentations' and "Diagnostic evaluation of adults with bilateral diaphragm paralysis", section on 'Clinical manifestations'.)

Additional symptoms that have been described in patients with diaphragmatic eventration include tachypnea, palpitations, chest pain, chronic cough, and recurrent pneumonia [9]. Ventilatory failure is rare.

Gastrointestinal symptoms in the adult population may worsen with increased intra-abdominal pressure (eg, exercise, pregnancy, ascites, infection, fluid sequestration) and result in dyspepsia, dysphagia, gastroesophageal reflux, and/or epigastric pain.

Symptoms of severe congenital diaphragmatic eventration seen in newborns are discussed separately. (See "Eventration of the diaphragm in infants".)

Physical examination — In the majority of patients, the physical examination is unrevealing. However, severe eventration may be associated with decreased air entry and dullness to percussion on the affected side, epigastric tenderness, and bowel sounds in the thoracic cavity.

EVALUATION AND DIAGNOSIS

Chest radiography — For patients suspected as having diaphragmatic eventration, we perform an upright, inspiratory, posterior-anterior and lateral chest radiograph, if not already performed.

The diagnosis of partial diaphragmatic eventration (which is the most common subclass) is usually made by the demonstration on upright posteroanterior and lateral chest radiography of a localized region of one hemidiaphragm that is elevated (ie partial hemidiaphragmatic elevation (image 1)). It most commonly involves the anteromedial portion of the right hemidiaphragm [10]. The eventration usually has a smooth, sharply defined, thin edge that corresponds to the weakened or fibroelastic area of the hemidiaphragm, which is displaced upward into the hemithorax.

When the eventration is complete, however, the radiographic appearance is similar to and may be indistinguishable from that of unilateral diaphragmatic paralysis (image 2). For unclear reasons, the left hemidiaphragm is more commonly affected than the right hemidiaphragm. (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Imaging'.)

Bilateral involvement is rare in adults and is similar to that seen in patients with bilateral paralysis. (See "Diagnostic evaluation of adults with bilateral diaphragm paralysis", section on 'Imaging studies'.)

Differential diagnosis — The differential diagnosis of diaphragmatic eventration with partial or complete unilateral involvement, which are the most common subclasses, includes conditions that can cause an elevated hemidiaphragm (eg, unilateral diaphragmatic paralysis, subdiaphragmatic or diaphragmatic masses, diaphragmatic hernia, and subpulmonic pleural fluid). This differential is discussed in detail separately. (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Unilateral elevation of the hemidiaphragm'.)

Bilateral involvement is extremely rare in adults, but the differential in such cases is similar to that of bilateral diaphragmatic paralysis. (See "Diagnostic evaluation of adults with bilateral diaphragm paralysis", section on 'Differential diagnosis'.)

Further evaluation

Patient selection — In asymptomatic patients in whom the diagnosis is clear on chest radiography, further evaluation is not typically necessary.

However, select patients require additional testing. This includes patients in whom the diagnosis is unclear on chest radiography, patients with symptoms, and/or patients who require differentiation of eventration from other conditions associated with diaphragm elevation.

Further testing involves obtaining chest computed tomography (CT) pulmonary function tests (PFTs) with respiratory muscle strength testing, and sniff testing.

Chest computed tomography — In patients with diaphragmatic eventration, chest CT better defines the smooth-contoured anatomy of the affected portion of the diaphragm as well as the anatomic extent of the eventration, when compared with chest radiography. Chest CT is also useful for ruling out subpulmonic, diaphragmatic, pleural, and subdiaphragmatic conditions associated with the appearance of an elevated hemidiaphragm. (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Unilateral elevation of the hemidiaphragm'.)

Pulmonary function tests, respiratory muscle strength testing — PFTs may be normal or show a slight restrictive pattern (eg, mild partial eventration) or more moderate restriction (eg, complete unilateral eventration). Similarly, depending on the degree of eventration, respiratory muscle strength testing may show reduced inspiratory muscle strength as evidenced by a reduced maximal inspiratory pressure (also known as PImax). (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Pulmonary function testing'.)

Sniff testing — When the eventration is unilateral and partial, fluoroscopic or ultrasonographic sniff testing may show near-normal or slightly reduced diaphragmatic motion or abnormal movement in only the affected portion of the diaphragm on the affected side.

When the eventration is unilateral and complete, the hemidiaphragm may appear immobile on sniff testing similar to that in patients with unilateral diaphragmatic paralysis, but paradoxical (ie upward) movement of the affected hemidiaphragm is typically absent. However, the absence of paradoxical motion is not specific for eventration, since it can be seen in the late phases of phrenic nerve injury-related unilateral paralysis (eg, by one year). (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Sniff test' and "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Pathophysiology'.)

Specific diaphragm or phrenic nerve testing — In rare cases, it may be difficult to distinguish long-standing unilateral diaphragm paralysis due to an old phrenic nerve injury from unilateral diaphragm eventration that is extensive.

While specific tests including diaphragmatic electromyography (EMG), measurement of transdiaphragmatic pressures (Pdi), or phrenic nerve conduction studies (PNCS) may facilitate this distinction, they are rarely performed since treatment of both unilateral diaphragmatic paralysis or eventration is similar, expertise in testing is required, and availability of testing is limited. For example, PNCS may be preserved in eventration but abnormal in unilateral diaphragm paralysis due to an old phrenic nerve injury.

Indications for their performance are similar to those in patients with suspected diaphragm paralysis (eg, preoperative testing for surgical plication), which is discussed separately. (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Patients with equivocal findings' and "Diagnostic evaluation of adults with bilateral diaphragm paralysis", section on 'Diagnostic evaluation in spontaneously breathing patients'.)

Diagnosis — In an asymptomatic patient, the diagnosis of partial unilateral diaphragm eventration is usually made by the demonstration on upright, inspiratory, posterior-anterior, and lateral chest radiography of a localized area of elevation in a region of the hemidiaphragm that has a smooth contour. (See 'Chest radiography' above.)

In patients with symptoms, patients in whom chest radiography is unclear, and/or patients who require differentiation of eventration from other conditions associated with diaphragm elevation, chest CT demonstrating the same smooth-contoured area can be diagnostic. (See 'Chest computed tomography' above.)

PFTs, respiratory muscle strength testing, and sniff testing provide supportive evidence for associated muscle weakness, depending on the degree of involvement. (See 'Pulmonary function tests, respiratory muscle strength testing' above and 'Sniff testing' above.)

More invasive tests of diaphragmatic or phrenic nerve function are rarely needed, unless surgery is planned. (See 'Further evaluation' above.)

TREATMENT AND PROGNOSIS

Asymptomatic or mild symptoms — In most cases, diaphragmatic eventration is unilateral with partial involvement, and patients have no or few symptoms. In such cases, we observe patients clinically and provide supportive care similar to that described for patients with unilateral diaphragmatic paralysis. (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'General therapies and rehabilitation' and "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Asymptomatic or mild symptoms'.)

Unlike patients with unilateral paralysis, many of whom may improve over time (eg, patients with phrenic nerve injury due to cardiac surgery), patients with diaphragmatic eventration do not improve (or progress) over time.

Severe symptoms — In severe cases (eg, severe dyspnea, chronic respiratory failure, inability to wean from mechanical ventilation) and/or when patients fail to respond to medical management, surgical plication may be indicated. Limited data suggest that outcomes are similar to those in patients with unilateral diaphragmatic paralysis [11,12]. (See "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Surgical plication'.)

SUMMARY AND RECOMMENDATIONS

●Normal function – The diaphragm is a dome-shaped muscle that plays an important role in inspiration and also serves as a mechanical barrier between thoracic and abdominal compartments. It is innervated by the phrenic nerve. (See 'Normal diaphragm anatomy and function' above.)

●Definition and etiology – Eventration is a rare condition, where all or a portion of the diaphragm muscle is replaced by a thin fibroelastic sheath from processes that either impair myofibroblast migration to the diaphragm (eg, congenital conditions associated with failure of diaphragmatic muscularization) or induce muscle atrophy (eg, due phrenic nerve injury (table 1)). Eventration can be subclassified as partial or complete and unilateral or bilateral. Acquired cases of partial unilateral hemidiaphragmatic eventration are the most common forms seen in adults. (See 'Epidemiology' above and 'Definition, etiology, and pathophysiology' above.)

●Clinical presentation, diagnostic evaluation, and treatment – Most adults with diaphragmatic eventration are asymptomatic, presenting with an elevated hemidiaphragm found incidentally on chest radiography. (See 'Asymptomatic' above.)

Symptoms are more likely when patients have severe eventration (which is uncommon) or underlying comorbidities or lung disease. Symptoms include dyspnea, palpitations, chest pain, orthopnea, tachypnea, chronic cough, recurrent pneumonia, and gastrointestinal symptoms. Ventilatory failure is rare. (See 'Symptoms' above.)

●Evaluation – Our suggested approach is as follows (see 'Evaluation and diagnosis' above):

•Asymptomatic patients – In this population, the diagnosis of eventration is usually made by the demonstration on upright chest radiography of a localized area of elevation in the affected hemidiaphragm that has a smooth, sharply defined, thin edge which is displaced upward and contrasts with the unaffected portion of the diaphragm. These patients do not require additional testing. (See 'Evaluation and diagnosis' above and 'Chest radiography' above.)

•Symptomatic patients or unclear diagnosis – For patients with symptoms, patients in whom the diagnosis is unclear on chest radiography, and/or patients who require differentiation of eventration from other conditions associated with diaphragm elevation (eg, unilateral diaphragmatic paralysis, subdiaphragmatic or diaphragmatic masses, and subpulmonic pleural fluid), we perform additional testing, which may include:

-Chest computed tomography (CT) – Chest CT demonstrating a smooth and sharp-contoured region of the diaphragm can be diagnostic. (See 'Chest computed tomography' above.)

-Pulmonary function tests (PFTs) with respiratory muscle strength testing, and sniff testing – Depending on the degree of involvement, PFTs, respiratory muscle strength testing, and sniff testing provide supportive evidence of associated inspiratory muscle weakness. (See 'Pulmonary function tests, respiratory muscle strength testing' above.)

-Invasive testing such as diaphragmatic electromyography, measurement of transdiaphragmatic pressures, or phrenic nerve conduction studies is rarely needed, unless surgery is planned. (See 'Specific diaphragm or phrenic nerve testing' above.)

●Treatment – The following is a reasonable approach (see 'Clinical manifestations' above and 'Evaluation and diagnosis' above):

•Asymptomatic patients with classic-appearing chest radiography – For these patients, we suggest clinical observation and supportive care rather than surgical intervention (Grade 2C). The approach is generally similar to that described for patients with unilateral diaphragmatic paralysis with the exception that patients with diaphragm eventration do not improve or progress over time. (See 'Asymptomatic or mild symptoms' above and "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'General therapies and rehabilitation' and "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Asymptomatic or mild symptoms'.)

•Symptomatic patients – For patients with severe symptoms who fail to respond to supportive care, we suggest surgical plication of the affected diaphragm (Grade 2C). Observational data suggest that surgical outcomes in this population are similar to those in patients with unilateral diaphragm paralysis who undergo plication. (See 'Severe symptoms' above and "Diagnosis and management of nontraumatic unilateral diaphragmatic paralysis (complete or partial) in adults", section on 'Surgical plication'.)