(Radiographics. 2002;22:S103-S116.)
© RSNA, 2002
MEDIASTINUM, CHEST WALL, AND DIAPHRAGM |
Imaging of Diaphragmatic Injury: A Diagnostic Challenge?1
Sandrine Iochum, MD,
Thomas Ludig, MD,
Frédéric Walter, MD,
Hugues Sebbag, MD,
Gilles Grosdidier, MD and
Alain G. Blum, MD
1 From the Department of Radiology "Imagerie Guilloz" (S.I., T.L., F.W., A.G.B.) and Department of Surgery (H.S., G.G.), Hôpital Central, 29 Avenue de Lattre de Tassigny, 54035 Nancy, France. Presented as an education exhibit at the 2001 RSNA scientific assembly. Received February 27, 2002; revision requested April 1; final revision received June 14; accepted June 19. Address correspondence to S.I. (e-mail: s.iochum@chu-nancy.fr).
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Abstract
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Diaphragmatic injuries occur in 0.8%–8% of patients after blunt trauma. Although the diagnosis may be obvious at standard chest radiography or computed tomography (CT) in most situations, some more subtle signs require careful analysis of CT images and examination with magnetic resonance (MR) imaging in some specific situations. Each method of imaging evaluation has advantages and pitfalls according to the type of diaphragmatic rupture. MR imaging with breath-hold acquisition permits good visualization of diaphragmatic abnormalities, but this technique cannot be performed in emergency situations. Because of a dramatic reduction in motion and beam-hardening artifacts and significant improvement of spatial resolution, especially along the z axis, helical CT and multisection CT allow better demonstration 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 tools in the evaluation of patients with multiple traumatic injuries.
© RSNA, 2002
Index Terms: Diaphragm, injuries, 66.4124, 795.411 • Diaphragm, rupture, 66.4124, 795.411 • Trauma, 66.4124, 795.411
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LEARNING OBJECTIVES FOR TEST 5
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After reading this article and taking the test, the reader will be able to:
- Recognize the various signs of diaphragmatic rupture at chest radiography, CT, and MR imaging.
- List the most specific signs of right and left diaphragmatic ruptures.
- Discuss the advantages and pitfalls of CT, especially multisection CT.
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Introduction
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Diaphragmatic injuries remain a diagnostic challenge for both radiologists and surgeons. In most cases, the diagnosis may be obvious at chest radiography and computed tomography (CT); however, some specific signs require careful analysis with CT and magnetic resonance (MR) imaging. Furthermore, the high frequency of associated injuries (52%–100%) such as pelvic fractures, thoracic aortic injuries, central nervous system lesions, and splenic and hepatic injuries may distract from the diaphragmatic injury (1,2).
Early diagnosis and repair of diaphragmatic tears is desirable. Indeed, a decrease in the amount of fibrosis and avoidance of future visceral compromise due to the thoracic herniation are indications for early repair.
In addition, numerous patients with liver and splenic injuries are being treated conservatively without immediate surgery. Thus, the ability to detect diaphragmatic injuries with noninvasive techniques is increasingly important.
In this article, the anatomy of the diaphragm, the mechanisms of diaphragmatic injuries, and associated injuries are briefly described. The various signs of diaphragmatic rupture at chest radiography, CT, and MR imaging are illustrated. The advantages and pitfalls of multisection CT are highlighted. Imaging strategies are also discussed.
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Anatomy
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The diaphragm is a dome-shaped, musculotendinous structure located at the bottom of the pleural cavity and at the top of the abdominal cavity. It consists of a central tendon, with right and left leaflets composed of striated muscles (Fig 1). Three large openings disrupt the continuity of the diaphragm: the aortic, esophageal, and inferior vena caval apertures. The diaphragm is covered by parietal pleura and peritoneum except for the bare area of the liver. Anatomically, the diaphragm is composed of two parts: the lumbar diaphragm and costal diaphragm (3).
CT allows an accurate depiction of the two crura, parts of the lumbar area that arise from the anterolateral surface of the first three right lumbar vertebrae and the first two left lumbar vertebrae (Fig 2). CT provides a precise image of the median and lateral arcuate ligaments, which are part of the lumbar section (Fig 3). The arcuate ligaments, which are sometimes nodular, represent thickening of the thoracolumbar fascia overlying the anterior surface of the psoas and quadratus lumborum muscles.
The anterior or costal part of the diaphragm is usually more difficult to identify than the lumbar part on transverse images (Fig 4). As described by Gale (4), the diaphragm characteristically assumes one of three appearances anteriorly, depending on the cephalocaudal relationship between the xiphoid and the middle leaflets of the central diaphragmatic tendon.
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Figure 4. CT scan (direct axial section) of the anterior diaphragm shows incomplete visibility of the diaphragm where it abuts structures of similar attenuation, such as the liver (bottom arrow). The hemidiaphragms are well demonstrated when they are marginated by peritoneal, retroperitoneal, or extraperitoneal fat (top arrow).
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In the type 1 configuration (48% of cases in the study by Gale [4]), the anterior diaphragm is concave posteriorly and smoothly continuous with the anterolateral diaphragmatic fibers, and then a line is formed as all fibers move downward and outward across the scanning plane from the middle and lateral leaflets of the central tendon (Fig 5a).
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Figure 5a. Configurations of the anterior diaphragm as described by Gale (4). (a) CT scan shows the type 1 configuration. The anterior component is concave posteriorly and continuous with the anterolateral diaphragmatic fibers (arrowheads). (b) CT scan shows the type 2 configuration. The anterior muscle fibers appear to be oriented at an angle in relation to the lateral fibers with midline discontinuity (arrowhead). (c) CT scan shows the type 3 configuration. The anterior muscle fibers lie anteriorly within a single plane.
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Figure 5b. Configurations of the anterior diaphragm as described by Gale (4). (a) CT scan shows the type 1 configuration. The anterior component is concave posteriorly and continuous with the anterolateral diaphragmatic fibers (arrowheads). (b) CT scan shows the type 2 configuration. The anterior muscle fibers appear to be oriented at an angle in relation to the lateral fibers with midline discontinuity (arrowhead). (c) CT scan shows the type 3 configuration. The anterior muscle fibers lie anteriorly within a single plane.
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Figure 5c. Configurations of the anterior diaphragm as described by Gale (4). (a) CT scan shows the type 1 configuration. The anterior component is concave posteriorly and continuous with the anterolateral diaphragmatic fibers (arrowheads). (b) CT scan shows the type 2 configuration. The anterior muscle fibers appear to be oriented at an angle in relation to the lateral fibers with midline discontinuity (arrowhead). (c) CT scan shows the type 3 configuration. The anterior muscle fibers lie anteriorly within a single plane.
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In the type 2 configuration (28% of cases in the study by Gale [4]), axial CT shows anterior divergence and apparent discontinuity of muscle fibers as they insert on costal cartilage. The right and left leaflets approximate each other on each successive cephalic level; they create an arch with its apex at the level of the xiphoid (Fig 5b).
The type 3 configuration (11% of cases in the study by Gale [4]) shows a middle leaflet inferior to the xiphoid. It is usually seen in patients with cardiomegaly, hepatomegaly, or emphysema (Fig 5c).
Only the portions of the hemidiaphragms centrally outlined by fat will be well depicted on axial sections. Indeed, when the diaphragm abuts structures of similar attenuation, such as the liver or spleen, the outline of the diaphragm is not visible (Fig 6) (3).
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Figure 6. CT scan shows that the diaphragm is not well demonstrated due to the proximity of the liver, which has the same attenuation. Note the diaphragmatic slips that attach to the ribs (arrowheads).
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These facts explain some of the limitations in the diagnosis of diaphragmatic tears at axial imaging. Indeed, the axial plane is tangential to the dome of the diaphragm. Therefore, the coronal and sagittal planes are better suited to analysis of the diaphragm.
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Mechanisms of Injuries
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Traumatic diaphragmatic injuries occur in 0.8%–8% of patients who sustain blunt trauma. Up to 90% of diaphragmatic ruptures from blunt trauma occur in young men after motor vehicle accidents (5,6).
Injuries to the left hemidiaphragm occur three times more frequently than injuries to the right side following blunt trauma, possibly due to a buffering effect of the liver on the right hemidiaphragm (7). However, the relative paucity of right-sided injuries may also have been associated with underdiagnosis (8).
Both bilateral tears and extension of tears into the central tendon are uncommon. They are reported in 2%–6% of patients with diaphragmatic injury (2).
Mechanisms of injuries include a lateral impact, which distorts the chest wall and shears the diaphragm, and a direct frontal impact, which leads to increased intraabdominal pressure (2).
Most ruptures are longer than 10 cm and occur at the posterolateral aspect of the hemidiaphragm between the lumbar and intercostal attachments and spread in a radial direction (Fig 7). Indeed, this is the weakest point of the diaphragm, where the pleuroperitoneal membrane finally closes at embryogenesis (9). Further ruptures of the diaphragm can occur in its central portion and at the costal attachment spreading in a transverse direction. Peripheral detachment is the least frequent type of rupture observed at surgery (10).
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Figure 7. Sites of injuries. Drawing shows radial (A), transverse (B), and central (C) ruptures and a peripheral detachment (D). Radial tears appear to be the most frequently found injury at surgery, whereas peripheral detachments are the least frequent.
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Penetrating injuries such as gunshot wounds or stab injuries are more random (2:1 ratio of penetrating vs blunt trauma) and produce small diaphragmatic holes (usually <1 cm in diameter), which are often overlooked (11).
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Associated Injuries
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The anatomic location, its close relationship to adjacent intrathoracic and intraabdominal organs, and the severity of the trauma account for associated injuries in 52%–100% of patients with diaphragmatic tears (2). Common associated injuries include pelvic fractures (40%–55%), splenic injuries (60%), and renal injuries (2).
There is also a high frequency of liver injuries, which are more frequently associated with right than with left diaphragmatic tears. Indeed, liver injuries are seen in 93% of patients with right diaphragmatic injuries and 24% of patients with left-sided lesions (2).
Thoracic injuries such as pneumohemothoraces and rib fractures are seen in 90% of patients (2). Aortic thoracic injuries are reported in 5% of patients (12).
Therefore, there is a high frequency of associated life-threatening injuries following blunt trauma with ensuing morbidity and mortality. However, the occurrence of associated injuries in patients with penetrating trauma is variable and is largely dependent on the nature, velocity, and path of the weapon or projectile (13).
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Various Signs of Diaphragmatic Rupture
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Chest Radiography
Despite the technical limitations of chest radiography, which include supine positioning, use of portable radiography, and limited patient cooperation, chest radiography remains valuable in the acute phase for the detection of diaphragmatic rupture.
According to the literature, initial radiographs allow diagnosis of 27%–60% of left-sided injuries but only 17% of right-sided injuries (14). In fact, right diaphragmatic injuries are more difficult to detect on radiographs. Indeed, the liver serves to block herniation of abdominal contents into the lower right side of the chest. Moreover, herniation of the liver is often overlooked: Differentiation of a herniated liver through a diaphragmatic tear from other causes of elevated diaphragm such as atelectasis, pleural effusion, or pulmonary contusion or laceration remains difficult (2,11).
Specific diagnostic findings of diaphragmatic tears on chest radiographs include the following: (a) intrathoracic herniation of a hollow viscus (stomach, colon, small bowel) with or without focal constriction of the viscus at the site of the tear (collar sign) (Figs 8, 9) and (b) visualization of a nasogastric tube above the hemidiaphragm on the left side (Fig 9).
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Figure 8. Left diaphragmatic tear in a 24-year-old woman who was injured in a motor vehicle accident. Initial chest radiograph shows intrathoracic herniation of the stomach (S), a pleural effusion, a pulmonary contusion, and contralateral mediastinal shift.
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Figure 9. Left diaphragmatic tear in a 48-year-old man after a motor vehicle accident. Initial chest radiograph shows a gas-filled viscus above the left hemidiaphragm that corresponds to the colon (C). A nasogastric tube is clearly seen in the thoracic cavity (arrow).
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Findings suggestive of hemidiaphragmatic rupture include elevation of the hemidiaphragm, distortion or obliteration of the outline of the hemidiaphragm, and contralateral shift of the mediastinum (15).
However, concurrent pulmonary abnormalities related to the trauma such as pleural effusion, pulmonary contusion or laceration, atelectasis, and phrenic nerve palsy can mimic or mask diaphragmatic injury on chest radiographs. In addition, the positive pressure of ventilatory support may delay herniation of abdominal contents through a torn diaphragm (8). The rate of missed diaphragmatic rupture on chest radiographs ranges from 12% to 66% with the potential risk of a late visceral herniation through the diaphragmatic defect (16).
Computed Tomography
The introduction of helical CT and new array detector technology in the 1990s has improved the accuracy of CT in the diagnosis of injuries in polytraumatized patients (17).
Indeed, previous reports suggest that conventional CT has a variable sensitivity of 14%–61% and specificity of 76%–99% in the diagnosis of diaphragmatic rupture (15,18,19). Helical CT has proved to be more valuable in the detection of diaphragmatic injuries with a sensitivity of 71% (78% for left-sided injuries and 50% for right-sided injuries), a specificity of 100%, and an accuracy of 88% for left-sided injuries and 70% for right-sided injuries (2,8).
Moreover, because of the high frequency of associated injuries with blunt diaphragmatic tears, most hemodynamically stable patients with suspected diaphragmatic injuries require an admission CT examination to evaluate the extent and anatomic sites of coexisting thoracoabdominal injuries to guide clinical management.
Findings suggestive of hemidiaphragmatic tears include the following:
- Direct discontinuity of the hemidiaphragm was seen in 71%–73% of cases in previous studies (Fig 10) (18,19). A diaphragmatic defect appears to be the most sensitive sign of rupture seen at conventional CT with a sensitivity of 73% and a specificity of 90% (18). However, the diagnosis of diaphragmatic rupture should not be exclusively based on this CT finding (see the section entitled "Pitfalls of CT").
- Intrathoracic herniation of abdominal contents has a sensitivity of 55% and a specificity of 100% (18). The stomach and colon are the most common viscera to herniate on the left side (Fig 10), and the liver is the most common viscus to herniate on the right side (Figs 11, 12).
- The collar sign, a waistlike constriction of the herniating hollow viscus at the site of the diaphragmatic tear, has a sensitivity of 36% with conventional CT (18) and 63% with helical CT (8) and is most frequently diagnosed. On the right side, the collar sign can appear as a focal indentation of the liver, a subtle sign easily overlooked on axial images (Figs 11, 12). This sign requires careful analysis of axial images and sagittal and coronal multiplanar reformatted images.
- The dependent viscera sign is an additional sign that was observed in 90% of cases in the study reported by Bergin et al (5). When a patient with a ruptured diaphragm lies supine at CT examination, the herniated viscera (bowel or solid organs) are no longer supported posteriorly by the injured diaphragm and fall to a dependent position against the posterior ribs (Fig 13). Consequently, the dependent viscera sign is present if the upper one-third of the liver abuts the posterior ribs on the right side or if the stomach, spleen, or bowel abuts the posterior ribs on the left side. However, this sign is rarely isolated but represents an early indication of diaphragmatic tear on axial images before visceral herniation can be confidently diagnosed by using sagittal and coronal multiplanar reformation.
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Figure 10a. Left diaphragmatic tear in a 65-year-old patient after blunt trauma. S = stomach. (a) CT scan obtained at the level of the hepatic hilum shows a defect in the continuity of the anterolateral left hemidiaphragm (arrows). C = colon. (b) CT scan of the midthoracic region shows intrathoracic herniation of the stomach. (c, d) Sagittal (c) and coronal (d) reformatted images show the intrathoracic herniation of the stomach more clearly. (e) Image from laparoscopy shows the intrathoracic herniation of the stomach and the diaphragmatic tear.
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Figure 10b. Left diaphragmatic tear in a 65-year-old patient after blunt trauma. S = stomach. (a) CT scan obtained at the level of the hepatic hilum shows a defect in the continuity of the anterolateral left hemidiaphragm (arrows). C = colon. (b) CT scan of the midthoracic region shows intrathoracic herniation of the stomach. (c, d) Sagittal (c) and coronal (d) reformatted images show the intrathoracic herniation of the stomach more clearly. (e) Image from laparoscopy shows the intrathoracic herniation of the stomach and the diaphragmatic tear.
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Figure 10c. Left diaphragmatic tear in a 65-year-old patient after blunt trauma. S = stomach. (a) CT scan obtained at the level of the hepatic hilum shows a defect in the continuity of the anterolateral left hemidiaphragm (arrows). C = colon. (b) CT scan of the midthoracic region shows intrathoracic herniation of the stomach. (c, d) Sagittal (c) and coronal (d) reformatted images show the intrathoracic herniation of the stomach more clearly. (e) Image from laparoscopy shows the intrathoracic herniation of the stomach and the diaphragmatic tear.
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Figure 10d. Left diaphragmatic tear in a 65-year-old patient after blunt trauma. S = stomach. (a) CT scan obtained at the level of the hepatic hilum shows a defect in the continuity of the anterolateral left hemidiaphragm (arrows). C = colon. (b) CT scan of the midthoracic region shows intrathoracic herniation of the stomach. (c, d) Sagittal (c) and coronal (d) reformatted images show the intrathoracic herniation of the stomach more clearly. (e) Image from laparoscopy shows the intrathoracic herniation of the stomach and the diaphragmatic tear.
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Figure 10e. Left diaphragmatic tear in a 65-year-old patient after blunt trauma. S = stomach. (a) CT scan obtained at the level of the hepatic hilum shows a defect in the continuity of the anterolateral left hemidiaphragm (arrows). C = colon. (b) CT scan of the midthoracic region shows intrathoracic herniation of the stomach. (c, d) Sagittal (c) and coronal (d) reformatted images show the intrathoracic herniation of the stomach more clearly. (e) Image from laparoscopy shows the intrathoracic herniation of the stomach and the diaphragmatic tear.
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Figure 11a. Right diaphragmatic tear in a 46-year-old man who experienced multiple injuries in a motor vehicle accident. (a) CT scan shows a subtle sign of a right diaphragmatic tear: a focal indentation in the posterolateral aspect of the liver with a contusion (arrow). (b) Coronal reformatted image clearly shows a waistlike constriction of the liver (arrowheads). (c) Coronal contrast material-enhanced fat-suppressed fast gradient-echo MR image shows a high position of the liver in the thoracic cavity. The constricting rim of the diaphragm is seen as a low-signal-intensity structure around the herniated liver (arrowheads).
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Figure 11b. Right diaphragmatic tear in a 46-year-old man who experienced multiple injuries in a motor vehicle accident. (a) CT scan shows a subtle sign of a right diaphragmatic tear: a focal indentation in the posterolateral aspect of the liver with a contusion (arrow). (b) Coronal reformatted image clearly shows a waistlike constriction of the liver (arrowheads). (c) Coronal contrast material-enhanced fat-suppressed fast gradient-echo MR image shows a high position of the liver in the thoracic cavity. The constricting rim of the diaphragm is seen as a low-signal-intensity structure around the herniated liver (arrowheads).
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Figure 11c. Right diaphragmatic tear in a 46-year-old man who experienced multiple injuries in a motor vehicle accident. (a) CT scan shows a subtle sign of a right diaphragmatic tear: a focal indentation in the posterolateral aspect of the liver with a contusion (arrow). (b) Coronal reformatted image clearly shows a waistlike constriction of the liver (arrowheads). (c) Coronal contrast material-enhanced fat-suppressed fast gradient-echo MR image shows a high position of the liver in the thoracic cavity. The constricting rim of the diaphragm is seen as a low-signal-intensity structure around the herniated liver (arrowheads).
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Figure 12a. Right diaphragmatic tear in a 35-year-old man after a motor vehicle accident. (a) Helical CT scan (direct axial section) shows a focal indentation at the posterolateral aspect of the liver (arrow), a finding suggestive of a right diaphragmatic tear. (b) Coronal reformatted image shows elevation and focal constriction of the liver. (c) Sagittal single-shot fast spin-echo MR image clearly shows the posterior diaphragm (arrow), which is outlined by hemoperitoneum and pleural effusion. (d) Coronal contrast-enhanced fast gradient-echo MR image clearly shows waistlike constriction of the liver at the level of the diaphragmatic tear.
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Figure 12b. Right diaphragmatic tear in a 35-year-old man after a motor vehicle accident. (a) Helical CT scan (direct axial section) shows a focal indentation at the posterolateral aspect of the liver (arrow), a finding suggestive of a right diaphragmatic tear. (b) Coronal reformatted image shows elevation and focal constriction of the liver. (c) Sagittal single-shot fast spin-echo MR image clearly shows the posterior diaphragm (arrow), which is outlined by hemoperitoneum and pleural effusion. (d) Coronal contrast-enhanced fast gradient-echo MR image clearly shows waistlike constriction of the liver at the level of the diaphragmatic tear.
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Figure 12c. Right diaphragmatic tear in a 35-year-old man after a motor vehicle accident. (a) Helical CT scan (direct axial section) shows a focal indentation at the posterolateral aspect of the liver (arrow), a finding suggestive of a right diaphragmatic tear. (b) Coronal reformatted image shows elevation and focal constriction of the liver. (c) Sagittal single-shot fast spin-echo MR image clearly shows the posterior diaphragm (arrow), which is outlined by hemoperitoneum and pleural effusion. (d) Coronal contrast-enhanced fast gradient-echo MR image clearly shows waistlike constriction of the liver at the level of the diaphragmatic tear.
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Figure 12d. Right diaphragmatic tear in a 35-year-old man after a motor vehicle accident. (a) Helical CT scan (direct axial section) shows a focal indentation at the posterolateral aspect of the liver (arrow), a finding suggestive of a right diaphragmatic tear. (b) Coronal reformatted image shows elevation and focal constriction of the liver. (c) Sagittal single-shot fast spin-echo MR image clearly shows the posterior diaphragm (arrow), which is outlined by hemoperitoneum and pleural effusion. (d) Coronal contrast-enhanced fast gradient-echo MR image clearly shows waistlike constriction of the liver at the level of the diaphragmatic tear.
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Figure 13a. Dependent viscera sign in a 28-year-old pregnant woman after a motor vehicle accident. (a) CT scan (direct axial section) shows intrathoracic herniation of the stomach and colon owing to left diaphragmatic rupture, a hepatic hematoma, and a pleural effusion. Note the dependent viscera sign. (b) Sagittal reformatted image shows a deformity of the aortic contour and an isthmic intimal flap, which indicate an aortic injury.
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Figure 13b. Dependent viscera sign in a 28-year-old pregnant woman after a motor vehicle accident. (a) CT scan (direct axial section) shows intrathoracic herniation of the stomach and colon owing to left diaphragmatic rupture, a hepatic hematoma, and a pleural effusion. Note the dependent viscera sign. (b) Sagittal reformatted image shows a deformity of the aortic contour and an isthmic intimal flap, which indicate an aortic injury.
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Advantages of CT
Previous studies suggested that conventional CT offered limited accuracy in revealing diaphragmatic injury. This limitation was, in part, related to the axial orientation of images paralleling the outline of the diaphragm, to volume averaging, to respiratory motion around the diaphragm, and to the generally poor quality of coronal and sagittal reformation images (18,19).
Presently, helical CT enables acquisition of volumetric data, eliminating respiratory motion while providing good-quality sagittal and coronal reformation images. Consequently, it is well suited to evaluation of the diaphragm and improves the accuracy of CT in diagnosis of diaphragmatic injuries (20,21).
Multisection CT with increased acquisition speed and higher in-plane and longitudinal spatial resolution may further improve the detection of diaphragmatic tears. The increased acquisition speed with multisection CT is due to higher pitch values and gantry rotation speeds. Higher longitudinal spatial resolution is the result of thinner collimation with a satisfactory section profile even when the covered area is long (17).
Thus, reformation images are of better quality and can be helpful in detecting subtle visceral herniations, especially in patients with right-sided injuries. The study of Killeen et al (8) showed that although sensitivity for left-sided injuries did not increase with the addition of reformation images, sensitivity increased from 16.7% to 50% in cases of right-sided rupture with the additional use of reformation images.
Furthermore, diaphragmatic injuries are rarely isolated; the speed and quality of helical acquisition are undeniable advantages of multi–detector row scanners in the management of less stable patients.
Pitfalls of CT
False-Positive Findings.—
A diaphragmatic defect is not specific for a rupture. Posterolateral defects, which are detected at CT in approximately 6% of asymptomatic adults, may mimic diaphragmatic tears (Fig 14) (22). These defects occur more commonly on the left side and are thought to represent congenital asymptomatic Bochdalek hernias. Acquired diaphragmatic defects are seen more commonly in women, in patients with emphysema, and with increasing age.
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Figure 14a. Diaphragmatic defects in a 68-year-old patient. CT scans (direct axial sections) show diaphragmatic defects (arrow) of the right (a) and left (b) posterolateral hemidiaphragms.
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Figure 14b. Diaphragmatic defects in a 68-year-old patient. CT scans (direct axial sections) show diaphragmatic defects (arrow) of the right (a) and left (b) posterolateral hemidiaphragms.
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In addition, a diaphragmatic eventration can mimic a rupture. Coronal and sagittal reformation images are helpful to avoid false-positive diagnosis of diaphragmatic injury and to identify the site of injury (Fig 15).
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Figure 15a. Isolated elevation of the diaphragm in a 59-year-old man after blunt trauma. (a, b) CT scan (a) and sagittal reformatted image (b) show an isolated elevation of the diaphragm (arrow) without discontinuity. Note the right-sided rib fracture on the scan (a). (c, d) Sagittal single-shot fast spin-echo (c) and contrast-enhanced fat-suppressed fast gradient-echo (d) MR images show the diaphragm (arrow) as a thin hypointense band. Fat suppression and contrast enhancement (d) are used for better demonstration of the diaphragm and for differentiation between a pleural effusion and a pulmonary contusion or atelectasis (arrowhead).
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Figure 15b. Isolated elevation of the diaphragm in a 59-year-old man after blunt trauma. (a, b) CT scan (a) and sagittal reformatted image (b) show an isolated elevation of the diaphragm (arrow) without discontinuity. Note the right-sided rib fracture on the scan (a). (c, d) Sagittal single-shot fast spin-echo (c) and contrast-enhanced fat-suppressed fast gradient-echo (d) MR images show the diaphragm (arrow) as a thin hypointense band. Fat suppression and contrast enhancement (d) are used for better demonstration of the diaphragm and for differentiation between a pleural effusion and a pulmonary contusion or atelectasis (arrowhead).
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Figure 15c. Isolated elevation of the diaphragm in a 59-year-old man after blunt trauma. (a, b) CT scan (a) and sagittal reformatted image (b) show an isolated elevation of the diaphragm (arrow) without discontinuity. Note the right-sided rib fracture on the scan (a). (c, d) Sagittal single-shot fast spin-echo (c) and contrast-enhanced fat-suppressed fast gradient-echo (d) MR images show the diaphragm (arrow) as a thin hypointense band. Fat suppression and contrast enhancement (d) are used for better demonstration of the diaphragm and for differentiation between a pleural effusion and a pulmonary contusion or atelectasis (arrowhead).
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Figure 15d. Isolated elevation of the diaphragm in a 59-year-old man after blunt trauma. (a, b) CT scan (a) and sagittal reformatted image (b) show an isolated elevation of the diaphragm (arrow) without discontinuity. Note the right-sided rib fracture on the scan (a). (c, d) Sagittal single-shot fast spin-echo (c) and contrast-enhanced fat-suppressed fast gradient-echo (d) MR images show the diaphragm (arrow) as a thin hypointense band. Fat suppression and contrast enhancement (d) are used for better demonstration of the diaphragm and for differentiation between a pleural effusion and a pulmonary contusion or atelectasis (arrowhead).
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Motion artifacts due to respiratory movement decrease the quality of multiplanar reformation images and can mimic a diaphragmatic rupture, especially on the right side with pseudoherniation of the liver (Fig 16). When in doubt, a faster acquisition should be performed (Fig 17).
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Figure 16a. Motion artifact in a 28-year-old woman who was involved in a motor vehicle accident. Coronal (a) and sagittal (b) CT reformatted images show an apparent isolated liver herniation due to motion artifact, which could mimic a diaphragmatic tear.
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Figure 16b. Motion artifact in a 28-year-old woman who was involved in a motor vehicle accident. Coronal (a) and sagittal (b) CT reformatted images show an apparent isolated liver herniation due to motion artifact, which could mimic a diaphragmatic tear.
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Figure 17a. Motion artifacts in a 55-year-old woman who was involved in a motor vehicle accident. (a) Coronal CT reformatted image shows motion artifacts. (b) Coronal reformatted image from a shorter CT acquisition with thicker collimation and adequate breath holding shows an intact right hemidiaphragm.
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Figure 17b. Motion artifacts in a 55-year-old woman who was involved in a motor vehicle accident. (a) Coronal CT reformatted image shows motion artifacts. (b) Coronal reformatted image from a shorter CT acquisition with thicker collimation and adequate breath holding shows an intact right hemidiaphragm.
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False-Negative Findings.—
It is frequently difficult to identify the margins of the hemidiaphragm following thoracic trauma because of pleural effusion, particularly in small tears and in the absence of herniation of intraabdominal viscera.
In addition, the types of diaphragmatic tears due to blunt trauma are not correlated with the sensitivity of CT for detection of diaphragmatic rupture.
MR Imaging
MR imaging can provide direct coronal and sagittal images, which are well suited for optimal visualization of the entire hemidiaphragm when motion is limited by respiratory and cardiac gating. However, these techniques are not well adapted to polytraumatized patients.
Development of faster imaging sequences, improved MR imaging–compatible physiologic monitoring, and improved life-support equipment allow MR imaging of most hemodynamically stable trauma patients. Shanmuganathan et al (23) commonly perform sagittal and coronal spin-echo T1-weighted imaging. Gradient-echo sequences are faster; however, circumferential chemical shift artifact may prevent accurate evaluation by mimicking an intact diaphragm.
Two additional pulse sequences are particularly well suited for analysis of the diaphragm: (a) a single-shot fast spin-echo sequence with a short echo time and a half-Fourier acquisition method; and (b) a fast gradient-echo sequence (fast multiplanar spoiled gradient-echo imaging, echo time = 1.5 msec, repetition time = 100 msec, 
= 60°) with injection of gadolinium contrast material (Dotarem; gadoterate meglumine, Guerbet, Roissy, France) and fat suppression. These two sequences are rapidly performed and decrease respiratory and motion artifacts. Injection of gadolinium contrast material allows a good analysis of thoracic injuries (contusion, hemothorax, etc). Although the diaphragm is not enhanced, it is well delineated owing to enhancement of pulmonary contusions and atelectasis. Normal pulmonary parenchyma is not enhanced except for its vascular structures. Pleural effusion and hemoperitoneum are also not enhanced but contribute to delineation of the diaphragm on both T2-weighted and contrast-enhanced images.
The normal diaphragm appears as a continuous hypointense band with both sequences due to its muscular and fibrous nature (Fig 15) (23,24). MR imaging signs of diaphragmatic rupture include abrupt disruption of the contour of the diaphragm and intrathoracic herniation of abdominal fat or viscera (Figs 11, 12). However, MR imaging is less readily adapted to the acute trauma setting and should be reserved for patients with an uncertain CT diagnosis or delayed signs of diaphragmatic tear.
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Imaging Strategies
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Admission supine chest radiography remains the initial and most commonly performed imaging study for evaluation of the thorax after trauma.
In the acute setting, because CT is more readily available and because there is a high frequency of acute diaphragmatic rupture with concurrent life-threatening associated injuries, CT is the next imaging study performed to evaluate patients with chest radiographic findings suggestive of a diaphragmatic injury (2,11). CT studies consist of exploration of the thorax, abdomen, and pelvis before and after enhancement. Helical CT and now multisection CT have become the method of choice for imaging most polytraumatized patients to evaluate both thoracic and abdominal trauma.
For patients with an uncertain diagnosis after CT, MR imaging should be performed.
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Conclusions
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Over the past decade, conventional CT has benefited from two major advances: the introduction of helical CT in the early 1990s and the introduction of multi–detector row CT in 1998. Despite these advances, CT findings remain unchanged. Nevertheless, detection of diaphragmatic injuries has improved with helical CT and should further improve with multisection CT. Two major factors are mainly responsible for this improvement. Indeed, in-plane spatial resolution has increased for more precise visualization of subtle signs such as focal indentation of the liver on axial images, and a higher longitudinal spatial resolution has allowed more accurate analysis of the diaphragm. In addition, increased acquisition speed significantly improves the management of polytraumatized patients and allows detection of frequent additional injuries.
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Footnotes
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See the commentary by Ko and Primack
following this article.
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References
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Abstract
LEARNING OBJECTIVES FOR TEST...
