Imaging in Diaphragm Injury and Paresis 

Diaphragm injuries can be caused by penetrating and blunt thoracoabdominal trauma (see the images below). Diaphragmatic injury is thought to result from an abrupt increase in intra-abdominal pressure during blunt trauma. This leads to a clinically significant increase in the pressure gradient between the pleural and peritoneal cavities.^{[1, 2, 3, 4, 5, 6]}

Approximately 80-90% of diaphragm injuries are related to automobile accidents; falls or crush injuries to the diaphragm are rarer causes. Indeed, a lateral-impact automobile accident is 3 times more likely than any other impact to result in diaphragmatic rupture. The mechanism of injury is thought to involve distortion of the thoracic wall and ipsilateral diaphragmatic shearing.^{[7, 8, 9]}

Tears of the diaphragm typically originate at the musculotendinous junction, mostly in the posterolateral aspect of the hemidiaphragms. Some 64-87% of these tears are on the left side. This finding is thought to represent either relative weakness of the left hemidiaphragm compared with the right hemidiaphragm or the protective effect of the liver on the right side. Irrespective of the cause, right-sided rupture is associated with increased severity of injury and, therefore, increased mortality and morbidity rates.^[10]

Patients with large diaphragmatic defects have critical problems shortly after trauma as a result of disturbed cardiorespiratory function associated with large herniation of abdominal contents into the pleural space. Other patients may be asymptomatic or have vague symptoms, which may cause the diagnosis to be delayed. Negative intrathoracic pressure during respiration presumably causes gradual herniation of the abdominal organs into the thorax and enlargement of the defect. The patient is at risk of strangulation, obstruction, and other life-threatening disorders if the diaphragmatic injury is not repaired. Penetrating injuries can produce small lacerations in the diaphragm. Organ herniation is uncommon, although not as uncommon as first thought.^{[11, 12, 13, 14]}

The most frequent cause of paralysis of the diaphragm is birth trauma or a postoperative complication as a result of cardiovascular surgery. Infections and tumors are less common causes of diaphragmatic paralysis. The consequence of diaphragmatic paralysis may be respiratory insufficiency. Diaphragmatic eventration, on the contrary, involves weakness or complete disappearance of the muscle fibers of the diaphragm. Eventration may be acquired with involvement of the phrenic nerve. It may also be associated with malformations; in this event, the prognosis is more guarded than it would be otherwise.^{[15, 16, 17, 18]}

The causes of unilateral diaphragmatic paralysis are many. The most common cause in adults is tumoral involvement of the phrenic nerve. In children, birth trauma and cardiorespiratory surgery are the most common causes. Diaphragmatic paralysis occasionally occurs as a complication of neurologic disease. Injury to the phrenic nerve from trauma to the thorax or cervical spine and pressure on the phrenic nerve from a substernal thyroid or aortic aneurysm can also cause diaphragmatic paralysis. Infectious disease involving the lungs, pleura, and/or mediastinum may result in temporary or permanent diaphragmatic paralysis. Finally, diaphragmatic paralysis may be idiopathic.^{[10, 19, 20, 21]}

Blunt or penetrating trauma to the abdomen can cause diaphragmatic rupture. Direct laceration may result from a penetrating object or from a fragment of a fractured rib. Diaphragmatic rupture is not a common finding in blunt abdominal trauma, and it may be overlooked because the dominant clinical symptoms may be related to other associated injuries.^{[3, 22, 23, 24]}

Asymmetry of a hemidiaphragm or changing diaphragmatic level is often the first clue of diaphragmatic injury on plain chest radiographs. The appearance of abdominal viscera (particularly hollow, gas-filled organs in the thorax) or the placement of a nasogastric (NG) tube in a herniated stomach allows for an accurate diagnosis. Intrathoracic herniation of abdominal solid organs (eg, the liver, spleen, kidneys, and omentum) appears as mushroom-shaped, homogeneous opacities in the thorax. The fluoroscopic demonstration of absent or decreased diaphragmatic motion is suggestive of diaphragmatic injury. Barium studies confirm the diagnosis by showing herniated viscera above the diaphragm and constriction through the diaphragmatic tear.^[6] Chest radiographs of diaphragm injuries are depicted in the images below.

Diaphragmatic paralysis

Unilateral diaphragmatic paralysis and/or eventration is often discovered incidentally on chest radiographs. The diagnosis is made on the basis of an elevation of the diaphragm above the normal range; diminished, absent, or paradoxical movement on inspiration; mediastinal shift on inspiration; and paradoxical movement during sniffing. These signs need not be simultaneously present, but paradoxical movement during sniffing is generally considered to be definitive for the diagnosis of diaphragmatic paralysis. This sign, however, is not specific. The radiologic diagnosis of bilateral diaphragmatic paralysis can be difficult to establish. Fluoroscopic study of bilateral diaphragmatic paralysis requires simultaneous evaluation of diaphragmatic and chest-wall movement.^{[6, 25, 26]}

The right hemidiaphragm is normally slightly higher than the left. A common cause of alteration of this relationship is after lung surgery, when decreased volume in one hemithorax pulls the diaphragm upward. If the phrenic nerve is still intact, however, paradoxical motion should be absent on sniff testing.^[27]

The weak, or paretic, diaphragm may behave normally or paradoxically, depending on the degree of weakness.

When no movement is seen with various maneuvers, fixation of the diaphragm is seen in association with adjacent inflammation (such as pneumonia or subphrenic abscess). In the newborn with diaphragmatic paralysis, the chest radiograph demonstrates reduced lung volumes with unilateral or bilateral elevation of the hemidiaphragms and, possibly, atelectasis. The elevated hemidiaphragm is not prominent in radiographs early in the course of the disease.

Diaphragmatic rupture

The plain radiographic finding of a diaphragmatic rupture depends on the demonstration of abdominal contents in the thoracic cavity. In many cases, left-sided diaphragmatic rupture is diagnosed because of the intrathoracic presence of abdominal viscera, most frequently the large bowel. In blunt left diaphragmatic injury, chest radiographs often show an abnormal or wide mediastinum, even when the aorta is normal. The mediastinum should be investigated because of the association with aortic injury. In rare cases, a rupture on the right side can be diagnosed.^{[10, 28, 29, 30]}

Chest radiographs are the most important diagnostic images, and they may show elevation of the hemidiaphragm, a bowel pattern in the chest, or an NG tube passing into the abdomen and then curling up into the chest. The liver often protects a right-sided rupture from visceral herniation; therefore, these ruptures may appear only as an elevated hemidiaphragm from a partially herniated liver. Intrathoracic herniation of abdominal solid organs, such as the liver, spleen, kidneys, and omentum, appear as mushroom-shaped homogeneous opacities in the thorax. The fluoroscopic demonstration of absent or decreased diaphragmatic motion is suggestive of diaphragmatic injury. Barium studies confirm the diagnosis by showing herniated viscera above the diaphragm and constriction where they pass through the diaphragmatic tear.^{[31, 32, 33]}

Degree of confidence

Standard chest radiography is the primary screening method for detecting diaphragmatic rupture in patients with thoracoabdominal trauma; however, the diagnostic quality of bedside chest radiographs is often suboptimal because of the patient's supine position and inability to cooperate. Previous reports have suggested that a preoperative diagnosis is established on the basis of chest radiographs in only one third of patients.

False positives/negatives

Diaphragmatic rupture may be overlooked in the setting of blunt chest and/or abdominal trauma, as the diagnosis of diaphragmatic rupture is often difficult because of serious concurrent injuries, lack of specific clinical signs, and simultaneous lung disease that may radiologically mask or mimic the diagnosis.^[29]

On CT scans, herniation of an organ or omental fat may be visible through an abrupt discontinuity in the diaphragm. A waistlike constriction (collar sign) produced by diaphragmatic compression of herniated organs may be seen. Sagittal, coronal, and 3-dimensional reformation of CT scans may improve sensitivity.^{[34, 35, 29, 36, 37]}

The CT scan features of diaphragmatic rupture are diaphragmatic discontinuity, thickening of the diaphragm, intrathoracic herniation of abdominal organs and structures, and the collar sign, which is focal constriction of abdominal viscera (mostly bowel or stomach) at the site of the herniation. On axial images, it is difficult to differentiate abdominal organs displaced cephalad beneath an elevated hemidiaphragm from visceral or omental herniation through a defect in the diaphragm.^{[33, 38, 39]} The images below are scans of the same patient with a diaphragm injury.

Helical CT is the preferred method of examination because of its volumetric data acquisition during a single breath hold, which allows high-quality sagittal and coronal reformations. Narrow collimation is important, and coverage of 8-10 cm is sufficient to visualize the diaphragm in most cases. The intravenous administration of contrast medium is useful to improve identification of the various organs involved.^[40]

In certain patients, CT scanning may be indicated to assess potential causes of diaphragmatic paralysis caused by mediastinal pathology. Owing to its marked reduction in motion and beam-hardening artifacts and its improved spatial resolution (especially along the Z axis), helical and multisection CT improves delineation of the most subtle signs, such as a focal indentation of the liver or a right-sided collar sign. In addition, helical CT and multisection CT are useful for evaluating patients with multiple traumatic injuries.^[35]

False positives/negatives

False-positive and false-negative findings may occur. Diaphragmatic eventration may mimic diaphragmatic paralysis, and diaphragmatic hernias may mimic diaphragmatic rupture (and vice versa). The exact incidence of false-positive and false-negative findings with CT is unknown, though one would expect that the incidence with spiral and multisection CT is lower than that with conventional CT.

Direct sagittal and coronal MRI scanning provides a definitive diagnosis of left and right diaphragmatic rupture, and it can noninvasively show intrathoracic herniation of the abdominal viscera. Magnetic resonance imaging (MRI) with breath-hold acquisition permits good visualization of diaphragmatic abnormalities, but this technique is difficult to perform in an emergency setting.^{[20, 41]}

MRI enables easy recognition of the diaphragm and visceral herniation because it has the advantage of multiplanar imaging. MRI may be used in stable patients with an equivocal diagnosis based on other imaging results, in patients for whom laparotomy is not planned, and in some patients with penetrating injuries or late-appearing diaphragmatic ruptures.

Thoracoscopy has been used to improve visualization of the diaphragm when the diagnosis is unconfirmed and when laparotomy is not planned. With a delayed diagnosis of diaphragmatic rupture, standard chest radiography and studies performed with water-soluble or barium contrast material administered by means of an NG tube or enema may be used. In this instance, MRI is an ideal diagnostic modality.^[14]

Shanmuganathan et al concluded that MRI can be reliably used to diagnose or exclude diaphragmatic injury in patients with blunt trauma. In a retrospective evaluation, the authors reviewed 16 patients in whom chest radiographs were suggestive, but not diagnostic, of diaphragmatic injury. T1-weighted MRI scans were obtained in all patients, and fast gradient-echo MRIs were obtained in 11. All images acquired before MRI scanning and during follow-up, including chest radiographs and thoracoabdominal CT scans, were reviewed for evidence of diaphragmatic injury. MRI confirmed diaphragmatic injury in 7 patients (44%) and revealed an intact diaphragm in 9 (56%). In those 7 patients, MRIs correctly revealed the site of the diaphragmatic tear and the herniated abdominal viscera in the thoracic cavity. None of the 9 patients with intact diaphragms had a delayed presentation of a diaphragmatic rupture on follow-up.^[42]

Diaphragmatic eventration is a rare congenital abnormality that has features indistinguishable from those of congenital diaphragmatic hernia on prenatal sonography. Tsukahara et al described a 26-year-old pregnant woman (gravida 0, para 0, week 35) who was admitted with an ultrasonographic abnormality of the fetal thorax. The patient's MRI scans and sonograms showed features that strongly suggested congenital diaphragmatic eventration. These findings helped in differentiating this condition from congenital diaphragmatic hernia.^[43]

Taylor et al described the use of real-time magnetic resonance navigator-echo (NE) monitoring of the diaphragm. With this technique, temporal changes in the position of the diaphragm can be analyzed noninvasively.^[44]

Degree of confidence

The diagnosis of traumatic rupture of the diaphragm may be difficult to make despite the use of a variety of imaging options. In most cases, the diagnosis of a diaphragmatic rupture may be obvious during standard chest radiography or CT scanning, but more subtle signs require investigation with CT or MRI.

Each imaging evaluation has advantages and pitfalls according to the type of diaphragmatic rupture. MRI scanning of the neck is useful in investigating the cervical cord and brachial plexus in diaphragmatic paralysis. MRI also offers the advantage of multiplanar imaging. This modality, however, is difficult to perform when life-support devices are frequently needed.^{[36, 41]}

False positives/negatives

False-positive and false-negative findings may occur with MRI. Diaphragmatic eventration may mimic diaphragmatic paralysis, and diaphragmatic hernias may mimic a diaphragmatic rupture (and vice versa). The exact incidence of false-positive and false-negative findings with MRI has not been established.

On ultrasonograms, the diaphragm is seen as a curved echogenic sheet at its interfaces with the liver and spleen. The diaphragmatic crura may be seen as slightly sonolucent curvilinear structures anterior to and on either side of the abdominal aorta. Diaphragmatic slips representing normal, prominent muscular insertions may also be seen. No particular patient preparation is required for scanning. A 3.5-MHz or 5-MHz sector probe is routinely used, and the patient is scanned in the supine or erect position during quiet respiration. Lateral decubitus scanning may help in determining the presence of loculations within fluid collections.^[45]

Diaphragmatic hernia

Herniation through the diaphragm may be congenital or acquired. Ultrasonography may reveal herniation of the abdominal viscera into the thorax through a diaphragmatic defect. Depending on the type and site of the defect, herniated organs may include the liver, kidneys, omentum, or bowel. All of these structures may be recognizable on sonography. Hiatus hernias may be difficult to see unless they are outlined by fluid. In equivocal cases, examining the abdomen while the patient is drinking may demonstrate the anatomy of the distal esophagus.^[46]

Diaphragmatic rupture

Diaphragmatic rupture usually occurs as a result of blunt or penetrating injury; however, in rare cases it may be caused by the contiguous spread of hepatic abscesses (eg, those caused by amebiasis). The left side is more commonly affected than the right after blunt trauma. Diaphragmatic rupture is difficult to diagnose on imaging and may be overlooked in a patient with multiple trauma. Ultrasonography makes a limited contribution, but ultrasonograms may depict large defects with herniation of intra-abdominal viscera. Peristaltic bowel loops may be identified as passing upward into the thorax, although intraluminal bowel gas may obscure the diaphragm.^[46]

Abnormalities of diaphragmatic movement

Fluoroscopy has been the traditional imaging modality for the assessment of diaphragmatic motion. However, ultrasonography may be helpful for evaluating suspected abnormal diaphragmatic movement. Patients are scanned in the supine position. Symmetrical, fixed intercostal positions are chosen in the midaxillary line to achieve a satisfactory view of the diaphragm in full expiration and inspiration. This scanning position should include the maximal renal length. The part of the diaphragm adjacent to the midpoint of the upper kidney is marked in expiration and inspiration. The excursion of the diaphragmatic movement is measured between these points and expressed in centimeters. An average of 3 movements in quiet respiration and maximal excursion should be assessed.^[20]

The right-to-left ratio of maximum excursion is noted and compared with the normal range of 0.5-1.6 cm. Measurements outside this range are regarded as abnormal. Unilateral paralysis is reflected as absent or paradoxical motion on the affected side, with normal or exaggerated motion on the contralateral side. Paradoxical movement caused by diaphragmatic paralysis is readily identified on ultrasonography, and it may be elicited by performing the coughing and sniffing tests. Impaired diaphragmatic movement is a finding seen in a variety of conditions.^{[47, 48, 49]}

Juxtadiaphragmatic masses

The differential diagnosis of juxtadiaphragmatic masses includes the following:

• Pleuropericardial cysts
• Pericardial fat pads
• Foregut duplications
• Aortic aneurysms
• Hiatus hernias
• Pulmonary cysts, fluid-filled bullae, abscesses, hydatid cysts, and sequestration
• Subphrenic abscesses
• Hepatic abscesses, neoplasms, cysts, and hydatid cysts
• Fluid collections, loculated ascites
• Hydronephrosis
• Herniated kidney or liver

Disruption of diaphragmatic echoes

The differential diagnosis of the disruption of diaphragmatic echoes includes the following:

• Invading bronchial neoplasms
• Fibrosarcomas
• Metastases to the diaphragm (eg, ovarian malignancy)
• Aspiration of amebic debris via thoracentesis
• Diaphragmatic lacerations
• Diaphragmatic ruptures
• Rupture of the liver or a splenic abscess through the diaphragm
• Invasion or organization by adjacent abscesses or empyemas

Impaired diaphragmatic movement

Causes of impaired diaphragmatic movement include the following:

• Paralysis
• Pulmonary overinflation
• Pleural effusion
• Empyema
• Pulmonary inflammation (embolus or infection)
• Diaphragmatic hernia or eventration
• Subphrenic abscess
• Abdominal pain or peritonism
• Hepatosplenomegaly
• Ascites

Degree of confidence

Ultrasonography is a useful adjunct to chest radiography, providing an accurate assessment of anatomy and morphology of diaphragmatic humps, herniations, juxtadiaphragmatic masses, and diaphragmatic movement and function.^{[50, 51]}

In patients with trauma, ultrasonography is more commonly used to visualize large disruptions or herniation than for other indications. Ultrasonograms may miss small tears from penetrating injuries.

Ultrasonography may show herniation of the solid abdominal contents, such as the liver, omentum, and a bowel segment with peristaltic activity.