Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

CHEST RADIOLOGY
Year
: 2015  |  Volume : 25  |  Issue : 3  |  Page : 226--232

Blunt traumatic diaphragmatic hernia: Pictorial review of CT signs


Ravinder Kaur1, Anuj Prabhakar2, Suman Kochhar2, Usha Dalal3,  
1 Department of Radiodiagnosis, GMCH, Chandigarh, India
2 Department of Radiodiagnosis, PGIMER, Chandigarh, India
3 Department of General Surgery, GMCH, Chandigarh, India

Correspondence Address:
Dr. Ravinder Kaur
Associate Professor, Department of Radiodiagnosis, GMCH, Chandigarh 160030
India

Abstract

Blunt diaphragmatic rupture rarely accounts for immediate mortality and may go clinically silent until complications occur which can be life threatening. Although many imaging techniques have proven useful for the diagnosis of blunt diaphragmatic rupture, multidetector CT (MDCT) is considered to be the reference standard for the diagnosis of diaphragmatic injury. Numerous CT signs indicating blunt diaphragmatic rupture have been described in literature with variable significance. Accurate diagnosis depends upon the analysis of all the signs rather than a single sign; however, the presence of blunt diaphragmatic rupture should be considered in the presence of any of the described signs. We present a pictorial review of various CT signs used to diagnose blunt diaphragmatic injury. Multiplanar reconstruction is very useful; however, predominantly axial sections have been described in this pictorial review as the images shown are from dual-slice CT.



How to cite this article:
Kaur R, Prabhakar A, Kochhar S, Dalal U. Blunt traumatic diaphragmatic hernia: Pictorial review of CT signs.Indian J Radiol Imaging 2015;25:226-232


How to cite this URL:
Kaur R, Prabhakar A, Kochhar S, Dalal U. Blunt traumatic diaphragmatic hernia: Pictorial review of CT signs. Indian J Radiol Imaging [serial online] 2015 [cited 2019 Nov 22 ];25:226-232
Available from: http://www.ijri.org/text.asp?2015/25/3/226/161433


Full Text

 Introduction



The incidence of blunt traumatic diaphragm hernia in patients undergoing surgical exploration ranges between 3 and 8%. [1] The diagnosis is usually missed initially because of concurrent severe abdominal and thoracic visceral injuries and lack of awareness of various signs of diaphragmatic injury on imaging. Blunt diaphragmatic injuries usually present late with intrathoracic herniation of abdominal viscera and carry a mortality rate of 30-60%. [2],[3] Rapid and accurate diagnosis is essential as progressive herniation of visceral organs into the thoracic cavity can result in significant morbidity and mortality. In addition, preoperative identification allows for diaphragmatic repair during the initial exploratory laparotomy. Currently, multidetector CT (MDCT) is the modality of choice for detection of diaphragmatic injury with a sensitivity and specificity of 61-87% and 72-100%, respectively. [2],[4],[5],[6] On MDCT, various signs indicating diaphragmatic hernia have been described. These should be meticulously looked for in patients undergoing imaging for blunt trauma.

 Embryology and Anatomy



The diaphragm is a dome-shaped muscular structure which serves as a boundary between the thorax and the abdomen. Embryologically, it is formed by four major structures:

Septum transversumPleuroperitoneal membraneDorsal mesentery of the esophagusBody wall.

The diaphragm has a central tendon and a peripheral muscular component. The central tendon arises from the septum transversum, while the muscular component arises from the pleuroperitoneal membrane. Anteriorly, the diaphragm attaches to the posterior margins of the lower sternum and xiphoid process. The lateral or costal parts attach to the inner margins of the 6 th through 12 th ribs. Posteriorly, the lumbar part attaches to the medial and lateral arcuate ligaments. The right crus is attached to the first, second, and third lumbar vertebrae, while the left crus is attached to the first and second lumbar vertebrae [Figure 1]A and B. The fibrous margin of the right and left crura forms the median arcuate ligament. [7]{Figure 1}

The main function of the diaphragm is to act as a muscle of respiration. It acts along with the other accessory muscles of respiration including the sternocleidomastoid, scalene, and intercostal muscles to decrease the intrathoracic pressure during respiration. The diaphragm also aids in emesis, urination, and prevention of gastroesophageal reflux.

The normal openings in the diaphragm include the aortic hiatus at the thoraco-abdominal junction, the esophageal hiatus at the 10 th thoracic vertebral level, and the hiatus for the inferior vena cava at the 8 th thoracic vertebral level. [8]

 Epidemiology



Diaphragmatic injury may occur due to both penetrating and blunt traumas. The frequency with which either of these mechanisms leads to diaphragmatic injury varies according to the geographic location. [9] The incidence of post-traumatic blunt diaphragmatic injury varies from 0.16 to 5%. [10] However, in patients undergoing surgery, the incidence of diaphragmatic injury increases to 3-8%. [1],[11] Diaphragmatic tears are uncommon in children, with a reported prevalence of 0.07-6%. [12],[13] The most common cause of blunt diaphragmatic rupture is road traffic accidents. [10] Other rare causes are fall from height or a crushing blow. The mortality rate following acute diaphragm injury varies from 5.5 to 51%. [10],[14] Up to 70% of diaphragmatic tears are missed initially [15] and 7.2% of injuries that are missed in acute stage end up with complications. [16] Complications are mostly due to herniation of the viscera through the rent in the diaphragm and the resulting respiratory compromise. [16] Visceral incarceration may occur with or without strangulation or perforation. If strangulation occurs with herniation of viscera through the ruptured diaphragm, then the mortality rate varies from 30 to 80%. [9]

Many different modalities including conventional radiography, fluoroscopy, CT, and magnetic resonance imaging (MRI) have been used to evaluate the diaphragm; however, CT is the most commonly used modality.

 Location and Mechanism of Injury



The left hemidiaphragm is injured in 50-80% of blunt diaphragmatic rupture and the right hemidiaphragm in 12-40% of cases [Figure 2]. Injury to the left hemidiaphragm is more common due to an area of congenital weakness in its posterolateral aspect. Also, the liver plays a protective role in the right diaphragm injuries by preventing herniation of the abdominal viscera. [16] Anteroposterior elongation and shearing of diaphragm in lateral thoracoabdominal impact and transmission of abdominal pressure to diaphragm in frontal impact are the possible mechanisms resulting in blunt traumatic diaphragmatic hernia. [17]{Figure 2}

 Presentation



Traumatic diaphragmatic hernias are classified into three types depending upon the time interval for diagnosis: [18]

Type 1 hernia - when the diagnosis is made immediately following traumaType 2 hernia - when the diagnosis is made within the recovery periodType 3 hernia - when the diagnosis is made when the patient presents with ischemia or perforation of herniated organs.

 Imaging Findings on CT



CT scan has been accepted as the modality of choice in adults as well as pediatric patients whenever there is clinical or radiological suspicion of diaphragmatic injury.

The various significant signs which have been described in literature for blunt diaphragmatic rupture are as follows:

Diaphragm discontinuitySegmental non-recognition of diaphragm"Dangling diaphragm" sign"Dependent viscera" signIntrathoracic herniation of abdominal contents"Collar sign"Elevated abdominal organsThickened diaphragmThoracic fluid abutting intra-abdominal visceraHypoattenuated hemidiaphragm and associated fractured ribs.

These signs have been divided into direct and indirect signs and signs of uncertain or controversial origin [Table 1] according to Desir and Ghaye. [17]{Table 1}

Diaphragmatic discontinuity: This is the most frequent sign observed in blunt traumatic diaphragmatic hernia (95.7%). [1] The sensitivity and specificity of a directly visualized diaphragmatic tear are 36-82.7% and 88-95%, respectively. [16] This sign represents direct visualization of the injury and the free edge of the disrupted diaphragm is noted demarcating the defect [Figure 3]. The defect may be central or peripheral in location. Free edge may be thickened due to hemorrhage or muscle retraction{Figure 3}Segmental non-visualization of diaphragm: Segmental non-visualization of diaphragm is distinct from diaphragmatic discontinuity. This manifests as an isolated absence of a section of the injured diaphragm [Figure 4]. Sensitivity and specificity of this finding are 85.9% and 67.7%, respectively [16] for blunt diaphragmatic rupture. This sign may be falsely positive in elderly patients in whom segmental non-visualization of diaphragm may be a normal variant and in patients with basal atelectasis and hemothorax in whom the diaphragmatic margins may be blurred [2],[16]{Figure 4}Dangling diaphragm sign: The "dangling diaphragm" is a conspicuous sign of diaphragmatic injury. Free edge of the torn diaphragm is visible as it curls inward toward the center of the abdomen away from the chest wall at near right angle [Figure 3]. The sign differs from diaphragmatic discontinuity in that it results in comma-shaped fragment of the diaphragm, whether or not a gap in the diaphragm is appreciated. The dangling diaphragm sign has a sensitivity of 54% and a specificity of 98%. [18],[19] This sign is linked to the segmental diaphragmatic defectDependent viscera sign: Normally, the diaphragm prevents the upper abdominal viscera from coming in contact with the posterior chest wall in the supine position. When the diaphragmatic integrity is lost, the viscera herniate and shift posteriorly to lie in a "dependent" position against the chest wall [Figure 5]. On the left, the stomach or bowel either abuts the posterior ribs or is situated posterior to the spleen and on the right, the upper-third of the liver contacts the posterior chest wall. Some authors have emphasized that this sign has low sensitivity for the detection of small diaphragmatic ruptures, ruptures in an atypical location (e.g., an anterior location), and ruptures associated with a large pleural effusion [20]{Figure 5}Intrathoracic herniation of abdominal contents: When the diaphragm ruptures, the negative intrathoracic pressure may lead to herniation of abdominal viscera into the thoracic cavity. The specificity of this sign has been reported to be 94.1-100%, while its sensitivity is only 8-81%. [16] If only left-sided injury is taken into account, the sensitivity improves to 90.9%. [16] On the left, the stomach and the colon are most likely to herniate into the thorax [Figure 6], while on the right it is the liver that shows intrathoracic herniation [Figure 2]. Other intra-abdominal contents, including small bowel, omentum, and spleen, may also herniate [Figure 7]. This sign may be absent if the intrathoracic pressure is increased due to any reason (e.g., hemothorax or positive pressure ventilation){Figure 6}{Figure 7}Collar sign: When the abdominal contents herniate into the diaphragm, luminal narrowing is noted at the site of the diaphragm rent. This appearance is known as the "collar sign" on imaging [4] [Figure 8]. Multiple organs may combine to manifest this sign. This sign has a sensitivity of 25-85% and a specificity of 80-100%. The collar sign is less valuable for right-sided injuries{Figure 8}Elevated abdominal organs: When the left-sided abdominal organs are visible 4 cm or more above the dome of the right hemidiaphragm or the right-sided abdominal organs are visible 5 cm or more above the dome of the left hemidiaphragm, they are considered to be abnormally elevated [Figure 9]. The sensitivity and specificity for this sign are 78.1% and 92.8%, respectively [3]{Figure 9}Thickened diaphragm: Post-traumatic thickening occurs secondary to edema and haemorrhage within the substance of the diaphragm. The sensitivity and specificity of thickened hemidiaphragm are 36-60% and 58.4-77%, respectively. [16] The traumatized hemidiaphragm is compared with the opposite side to confirm the presence or absence of thickening. The measurement is taken 10 mm from the midline on both sides [2],[16]Thoracic fluid abutting abdominal viscera: Post-traumatic diaphragmatic rupture may be associated with pleural effusion. The herniating viscera may come in contact with this fluid [Figure 10]. The sensitivity of this sign is 44.4%, while its specificity is 68.5% [3]{Figure 10}Hypoattenuated hemidiaphragm and associated rib fractures: A hypoattenuated hemidiaphragm found in association with other features of blunt diaphragmatic rupture like segmental non-recognition and thickening of the diaphragm may indicate devascularization of the diaphragmatic muscle [Figure 11]. [2] Rib fractures are also an indicator of diaphragmatic rupture, as a fractured rib may lead to diaphragmatic laceration; however, this sign has poor sensitivity.{Figure 11}

There are various other signs described in literature like "hump and band sign" seen in right diaphragmatic hernia. Hump is due to herniation of liver and band sign is due to a linear area of hypoattenuation that transects the herniated liver between the torn edges of the diaphragm."Sinus cut-off sign" occurs in the presence of blunt diaphragmatic hernia with pleural effusion and is a variant of dependent viscera sign. Dependent abdominal contents like small bowel, spleen etc., which are peripheral to the diaphragm due to herniation, prevent the normal layering of pleural fluid. As a result, the posterior costophrenic angle or sulcus appears cut off abruptly. [17]

 Role of MRI



MR imaging may be used in more stable patients or where the CT examinations are equivocal. All the CT signs of diaphragmatic injury apply to MR also. MR imaging additionally provides excellent soft-tissue resolution and demonstrates the diaphragm as a thin sheet of muscle separating the thoracic and abdominal cavities. It has low signal intensity relative to that of other skeletal muscles with all MR imaging sequences. [21]

 Role of Ultrasonography



USG is a good modality to assess the diaphragm function, especially in critically ill patients, and has replaced fluoroscopy in many institutions because of portability, lack of ionizing radiation, visualization of structures above and below the diaphragm, and ability to quantify diaphragmatic motion. [22]

 Complications of Blunt Diaphragmatic Rupture



Intrathoracic herniation of abdominal viscera through a ruptured diaphragm may lead to various complications as follows:

Compression of the viscera at the site of herniationAbnormal location of the viscera relative to the mesentery, leading to abnormal rotation.

The various complications observed in our patients were: gastric outlet obstruction, large bowel obstruction, small bowel obstruction, volvulus, and tension gastrothorax.

Gastric outlet large and small bowel obstruction occurs in patients in whom diaphragmatic injury has been missed in the acute stage. On CT, gastric outlet obstruction is seen as a dilated stomach with no distal passage of oral contrast. Obstruction of large and small bowel loops leads to dilatation of the proximal bowel loops with multiple air fluid levels. CT topogram and plain radiograph of abdomen demonstrates these findings [Figure 12]. The axial sections also show multiple dilated bowel loops with luminal narrowing at the site of herniation.{Figure 12}

Gastric volvulus occurs in diaphragmatic rupture as the gastro-oesphageal junction remains at its normal location in the abdomen while the rest of the stomach rotates up through the defect into the thoracic cavity.

Tension gastrothorax is another complication of gastric herniation following diaphragmatic rupture. The obstructed stomach continues to dilate due to air entry leading to collapse of the ipsilateral lung and mediastinal shift to the opposite side. The clinical picture and imaging appearance are similar to tension pneumothorax [Figure 13].{Figure 13}

 Diagnostic Pitfalls



The potential diagnostic pitfalls are numerous and include anatomic variants, congenital and acquired abnormalities. There are a few confounding factors that may prevent normal visualization of the diaphragm:

Portions of the diaphragm may abut structures of similar attenuation like liver and spleen normallyFew segments of the diaphragm may be parallel to the normal axial planes that are used in CTNormal variants like diaphragmatic humps and areas of apparent discontinuity where the diaphragm inserts on the costal marginsLocalized thinning (eventration) with maintenance of diaphragmatic continuity.

 Conclusion



In conclusion, familiarity with all CT signs of diaphragmatic injury is required in establishing the diagnosis of diaphragmatic rupture and identifying its complications so that the patient can be adequately managed. Presence of a single sign should alert the radiologist to examine the diaphragm more closely and presence of two or more signs increases the probability of traumatic diaphragmatic hernia.

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