Imaging in Blunt Trauma Abdomen - I

Dr. D. Sunil Kumar

Mechanisms of Injury

• The most common causes of blunt abdominal trauma are motor vehicle collisions, falls from height, assaults, and sports accidents

• Three basic mechanisms explain the damage to the abdominal organs: – Deceleration– external compression– crushing injuries

• In approximate order of frequency, the most commonly injured abdominal organs are the spleen(25%), liver, kidneys, small bowel and/or mesentery, bladder, colon and/or rectum, diaphragm, pancreas, and major vessels

• Multiple organs are often affected simultaneously.

Multidetector CT Technique• IV contrast with portal phase imaging maximize

detection of parenchymal injuries.• Oral contrast material is no longer advised. • Rectal contrast is occasionally used to detect

colorectal injuries in patients with perineal lacerations and/or penetrating flank injuries.

• Delayed imaging of kidneys during urographic phase is used to detect collecting system and bladder injuries.

• Delayed imaging is also useful in specific situations for differentiating between active contrast extravasation from vascular injuries

• Recently, there is growing evidence that supports the addition of an arterial phase series (25–30 seconds after injection) of the abdomen and/or pelvis in selected trauma patients: – Severe mechanisms of injury– who have a displaced fracture of the pelvic ring

• Arterial phase images facilitate – detection of trauma to the major vessels – vascular injuries of the solid organs that are not

apparent on portal venous or delayed phase images.

Hemoperitoneum and Free Peritoneal Fluid• Injuries to solid and hollow viscera commonly have

associated hemoperitoneum.• Nonclotted blood (typical attenuation of 30–45 HU)

tends to flow freely between contiguous peritoneal recesses and may eventually fill the cavity completely.

• Blood located adjacent to the source of the hemorrhage is typically partially clotted and tends to be higher in attenuation (45–70 HU); this finding is termed the sentinel clot sign.

• The detection of a high-attenuation clot may be facilitated by using narrow window settings.

Sentinel clot sign. (a) Contrast-enhanced CT image shows a sentinel clot secondary to laceration along the fissure for the ligamentum teres (arrow), in the perihepatic space and lesser sac. (b) Contrast-enhanced CT image obtained in a patient who was undergoing anticoagulation therapy for a protein C deficiency shows a sentinel clot(arrow) surrounding the spleen.

• Occasionally, the attenuation values of hemoperitoneum may be less than 20 HU, for example, in patients with a – decreased serum hematocrit level,a preexistenting

anemia– hemorrhage that is more than 48 hours old.

• The finding of free intraperitoneal fluid in the absence of direct signs of solid or hollow visceral injury poses particular challenges, particularly in male patients.

• A thorough search for additional direct signs of organ injury is critical in these cases.

Splenic Injuries

• The spleen is the most commonly injured organ in blunt trauma.

• The traditional CT-based splenic injury scale system was developed by the American Association for the Surgery of Trauma (AAST) and accounts for the size and location of splenic lacerations and hematomas

• On CT images, – splenic lacerations - linear defects – Hematomas - relatively hypoattenuating geographic areas

in the parenchyma

Splenic laceration seen on contrastenhanced computed tomography scanas linear irregular hypodense area (arrow).

Parenchymal haematoma (arrow)seen on contrast-enhancedcomputed tomography scan asfocal hypodense area within theenhanced splenic parenchyma withan intact capsule

• Subcapsular haematomas appear as an elliptic collection of low-attenuation blood between the spleen capsules and enhanced splenic parenchyma that causes the indentation or flattening of the underlying spleen margin.

• Free intraperitoneal blood in the perisplenic space does not cause this effect on the underlying spleen parenchyma.

AAST Splenic Injury Scale (1994 Revision)

• However, this CT-based splenic injury grading system has been found to be a relatively poor predictor of patient outcome and, specifically, has been shown to be a poor predictor of the eventual success of nonsurgical management.

• In an effort to improve the ability of CT to help predict successful nonsurgical management in splenic trauma, several additional CT features of splenic trauma are important considerations.

• The presence of active hemorrhage and/or contained vascular injuries (pseudoaneurysms and arteriovenous fistulae) increases the risk of failed nonsurgical management.

Contrast Blush

• A contrast blush is defined as an area of high density with density measurements (Houndsfield Units) similar to the nearby vessel (or aorta).

• The differential diagnosis is:– Active arterial extravasation– Posttraumatic pseudoaneurysm– Posttraumatic AV fistula

• Active Hemorrhage:– Persistant blush in delayed phase image– grows larger with time on a delayed phase study.– A contract blush that is beyond the borders of the

organ, must be extravasation.

• In a pseudoaneurysm or AV fistula the contrast will wash away with the bloodstream in delayed images.

Axial contrast-enhanced CT image ina 19-year-old man who was in a motor vehicle collision demonstrates large splenic lacerationwith active hemorrhage seen emanating from the splenic injury into the peritoneal cavity (arrows).Note large degree of hemoperitoneum related tothis grade V splenic injury. Patient underwent emergent splenectomy

beyond the borders of the organ

Contrast-enhanced axial CT scansin 34-year-old man involved in motorcycleaccident. Transverse images in, A, arterial, B,portal venous, and, C, delayed phases showhyperattenuating contrast material (arrow)that persists and progressively enlarges atsubsequent delayed imaging. Findings wereconsistent with active extravasation. Patientunderwent splenectomy.

persists and progressively enlarges

Contrast blush washed out in delayed Phase

• Recently, a multidetector CT–based scale system that includes contained vascular injuries and active bleeding as part of the grading criteria has been proposed to improve the accuracy of predicting the need for intervention, as compared with the traditional AAST scale.

In the new system, patients with grade 4 injuries are candidates for splenic arteriography or splenic surgery.

Hepatic Injuries

• Similar to the approach to splenic trauma imaging, the AAST liver injury scale is commonly applied when assessing the severity of the acute hepatic injury.

• The liver injury scale is based on the presence, location, and size of liver lacerations and hematomas, as well as the presence of more extensive tissue maceration or devascularization in higher-grade injuries.

• Lacerations are the most frequently identified injury pattern in liver trauma and are identified as predominately linear branching hypoattenuating areas.

• Lacerations that extend to the posterosuperior region of segment VII, the bare area of the liver, may be associated with retroperitoneal hematomas around the IVC and accompanied by adrenal hematoma.

• Lacerations that extend to the porta hepatis are commonly associated with bile duct injury and are thus likely to lead to the development of a biloma.

Subcapsular hematoma. Contrast-enhancedCT scan shows multiple subcapsular hematomasin the right and left hepatic lobes (arrows). Multifocalintraparenchymal hematomas are also seen (arrowheads).

Intraparenchymal hematoma. ContrastenhancedCT scan shows a 5-cm intraparenchymalhematoma in the medial segment of the left hepaticlobe (arrow). Arrowheads indicate associated hemoperitoneumin the right subphrenic space

Contrast-enhancedCT scan shows active arterial bleeding (arrows).

• Additional imaging findings that have been found to be useful in guiding clinical management decisions include – (a) extension of the injury to involve the major

hepatic veins, which usually requires surgery to control ongoing hemorrhage

– (b) the presence of active bleeding into the peritoneal cavity

– (c) the presence of a large hemoperitoneum

Major Hepatic Venous Injury

• Major hepatic venous injuries are suspected if lacerations or hematomas extend into one or more major hepatic veins or the IVC.

• Such lesions can be life threatening and are an indication for surgical treatment.

Contrast-enhanced CT scan shows a laceration that extends into the IVC and cutoff of right hepatic venous drainage (arrow). Hemorrhagic fluid is seen around the IVC.Surgery revealed a laceration of the right hepatic vein.

Grade V hepatic injury. (20) Contrast-enhanced CT scan shows a large intraparenchymal hematomaand lacerations that involve the entire right hepatic lobe and the medial segment of the left hepatic lobe.(21) Contrast-enhanced CT scan shows a deep hepatic laceration that extends into the major hepatic veins. Note thediscontinuity of the left hepatic vein (arrowhead), a finding that indicates laceration. This finding was confirmed atsurgery.

Delayed Complications

• The growing trend toward nonsurgical management of hepatic injuries has increased the relevance and frequency of delayed complications.

• These posttraumatic complications include delayed hemorrhage, abscess, posttraumatic pseudoaneurysm and hemobilia, and biliary complications such as biloma and bile peritonitis and are more common in patient with severe, complex liver injuries

Bowel and Mesenteric Injuries

• Are rare, occurring in approximately 5% of patients with severe blunt abdominal trauma.

• Delays in diagnosis as short as 8–12 hours increase the morbidity and mortality from peritonitis and sepsis.

• Hence, one of the most essential tasks for the emergency radiologist is to recognize the often subtle CT signs of bowel trauma.

• At least one-half of injuries to hollow viscera involve the small bowel(most commonly are the proximal jejunum and the distal ileum), followed in frequency by the colon and stomach.

• Patients with a Chancetype vertebral fracture and large abdominal wall hematoma have a higher risk of injury to the bowel or mesentery.

CT Findings• Specific signs of Bowel Injury– bowel wall discontinuity– extraluminal contrast material– Free intraperitoneal or retroperitoneal air

• The less specific (but more sensitive) CT signs of bowel trauma include– unequivocal focal wall thickening– abnormal bowel wall enhancement – Mesenteric foci of fluid, air, or fat stranding may be secondary to

bowel injury alone.– free intraperitoneal fluid

• Unfortunately, the more specific signs are not highly sensitive, and the more sensitive signs are not highly specific.

• However, the presence of a combination of these findings increases the likelihood of a clinically important injury

Axial CT images show a defect in the proximal jejunum (arrow in a) and a mesenteric hematoma in the left upper quadrant (arrow in b). Although no free air was seen on CT images, a blowout perforation in the antimesenteric aspect of the proximal jejunum was found at surgery. No mesenteric injury was described in the surgical report.

bowel wall discontinuity

• Extraluminal gas is a highly suggestive, but not pathognomonic, sign of bowel perforation. The amount of free gas varies widely.

• CT images should routinely be reviewed with lung or bone window settings, in addition to the routine soft-tissue settings for detection of small gas collections.

• All phases should be reviewed because, on occasion, pneumoperitoneum may appear only on delayed images.

• Retroperitoneal air is seen with duodenal injury or injury to the retroperitoneal aspect of the ascending or descending colon

• Causes of pneumoperitoneum without bowel trauma include – intraperitoneal rupture of the urinary bladder with an indwelling

Foley catheter– massive pneumothorax– barotrauma – benign pneumoperitoneum (eg, as observed in some patients with

systemic sclerosis)– occasional diagnostic peritoneal lavage.

• “Pseudopneumoperitoneum,” air confined between the abdominal wall and the parietal peritoneum, is another potential cause of a false-positive diagnosis of bowel rupture. This finding may be seen with extraperitoneal rectal injuries, rib fractures, pneumothorax or pneumomediastinum.

Bowel Wall Thickening• Isolated, localized, unequivocal bowel wall thickening may be

indicative of nonsignificant bowel injury like contusion or highly suggestive of a surgically important injury, such as – Hematoma– ischemia secondary to mesenteric vascular trauma– Perforation

• The likelihood of a focal bowel abnormality representing an injury that requires surgical intervention increases when found in association with – pockets of fluid in the adjacent mesentery – free fluid in the peritoneal cavity.

• Diffuse bowel wall thickening is usually not a result of direct trauma but more likely related to the hypoperfusion complex (“shock bowel”)

Abnormal Bowel Wall Enhancement

• Increased bowel wall enhancement may represent bowel injury with vascular involvement or may be part of the hypoperfusion complex.

• This is due to increased permeability due to hypoperfusion, which may result in interstitial leakage of contrast material.

• Areas of decreased or absent contrast enhancement are indicative of ischemic bowel

Bowel and mesenteric injuries in a 32-year-old woman after a motor vehicle accident. Axial (a) and coronal (b) CT images show abnormal hyperenhancing thickened jejunal loops (arrows in b) and high-attenuation foci of intraperitoneal fluid (arrowheads in a) consistent with blood. No free or focal air was visible on CT images. At surgery, mesenteric tears in a middle segment of the jejunum and a distal segment of the ileum were found, with bleeding mesenteric vessels and multiple areas of perforation in the middle segment of the jejunum and the proximal and middle segments of the ileum.

Axial source images also show a tear in the abdominal wall on the right side (arrow in a) and mesenteric fat stranding (arrow in b). Oblique coronal image also shows unenhanced small-bowel loops in the lower abdomen (arrow in c). At surgery, shearing injury to the small-bowel mesentery was found, with active bleeding and with complete devascularization and necrosis of a 90-inch (229-cm) segment of the distal jejunum and ileum and a perforation of the middle jejunum.

• Intraperitoneal and Retroperitoneal Fluid.• Without visible solid organ injury, the

presence of a moderate or large amount of free fluid is a useful sign of bowel and/or mesenteric injury and is a strong indicator for exploratory laparotomy

• The location of the fluid may indicate the location of injury.

• Retroperitoneal fluid may indicate injury of a retroperitoneal segment of bowel.

Injury to the descending colon was suspected in view of fluid collection at the left retroperitoneum (short arrow) and a thickened colonic wall (long arrow). Compare to the normal fat density surrounding the right ascending colon (open arrow). Serosal tear of the descending colon was proven at surgery.

• Specific signs of Mesenteric injury – extravasation of intravenous contrast material– abrupt termination and beading of vesselsLess specific findings include:

Mesentric hematomaMesenteric InfiltrationBowel features

– Mesentric injuries may be associated bowel ischaemia or infarction due to disruption of blood flow.

• Mesenteric Extravasation:

(a) Coronal CT image showsan unenhanced segment of small bowel, a feature consistent with a bowel infarct (arrow). (b, c) Axial images show mesenteric extravasation (arrow in b), mesenteric hematoma (arrow in c), and thickening and hypervascularity of the proximal jejunum (*). At surgery, an extensive small-bowel mesenteric tear was found, with active bleeding from a jejunal branch of the superior mesenteric artery

• Mesenteric Vascular Beading and abrupt termination:– Appears as an irregularity in mesenteric vessels.– indicative of vascular injury.

Axial CT image shows a change in caliber,or beading, of some mesenteric vessels in the area of injury (arrows). At surgery, a tear was found in the ileocecalmesentery that warranted resection of the terminal ileum, cecum, and ascending colon.

Sagittal reformattedimage from abdominal CT showslesser sac stranding (arrow) and abrupt terminationof the left gastric artery (arrowhead) at thelevel of stranding.

• Mesenteric Hematoma• Well-defined mesenteric hematoma indicative

of laceration of a mesenteric vessel.• Although specific to mesenteric injury,

mesenteric hematoma does not always indicate a need for surgery.

• Larger hematomas carry the risk of subsequent bowel ischemia and usually require surgical repair

Axial CT image shows a hematomasurrounded by fat stranding (arrow) in thesplenic flexure mesocolon, with no evidence of activebleeding. At surgery, a nonexpanding mesenteric hematomawas found that did not require repair

Axial CT image shows a sigmoid mesenteric hematoma (arrow) and a normal appearance of the sigmoid colon (arrowhead). A complete tear of the abdominal wall (*) is visible in the right lower quadrant. Avulsion of the sigmoid colon mesentery associated with an ischemic sigmoid colon segment (subsequently resected) was found at surgery.

• Bowel Injury• bowel wall discontinuity• extraluminal contrast material• Free intraperitoneal or retroperitoneal air

• Mesentric Injury:• extravasation of intravenous contrast material• abrupt termination and beading of vessels• Mesentric hematoma

• Common Findings:• Free Fluid• Mesentric fluid, fat stranding, haziness• Focal abnormal bowel thickening/enhancement

• If there is no other explanation for intraperitoneal fluid, bowel or mesenteric injury should be considered.

• Vast majority of bowel injuries have associated abnormalities in the mesentery

• But Mesenteric injuries can be an isolated finding on CT images.

• When nonspecific features of significant bowel or mesenteric injury are the only CT findings, the need for surgical intervention is highly dependent on clinical judgment.

• Reevaluation with CT within 6–8 hours after the initial evaluation may help to elucidate the significance of such findings.

Pancreatic and Duodenal Injuries

• Severe anteroposterior compression trauma against the spinal column from blows to the mid–upper abdomen with a steering wheel or bicycle handlebars are the typical mechanisms that injure the pancreas and/or the duodenum, often involving the left hepatic lobe and spleen as well.

• The duodenum and pancreas are injured simultaneously; isolated injuries are rare (<30%).

• The morbidity and mortality associated with a trauma to the duodenum and pancreas are remarkably high.

• The probability of complications after duodenal or pancreatic trauma ranges between 30% and 60% and in many cases is the result of missed findings or diagnostic delays or both.

• CT diagnosis of pancreatic injuries shows variable sensitivity and specificity because many findings are subtle, absent, or at times slow to develop.

• The neck and body of the gland are the most common sites of injury

• The injured pancreas may appear normal on CT images, particularly in the first 12 hours after a trauma injury.

Pancreatic Injuries

• Direct findings:– Laceration (linear region of nonenhancement)– Diffuse or focal pancreatic enlargement– Heterogenous enhancement– Active hemorrhage from the pancreas

• Indirect findings:– Peripancreatic fat stranding, fluid, hemorrhage– Fluid between the splenic vein and the pancreas– Injuries to adjacent organs or vessels– Trajectory of penetrating injury through the region of the

pancreas

Imaging findings in pancreatic injuries

Pancreatic fractures or lacerations can be missed on the initial CT images. Multiplanar reformation, thinslice axial image reconstruction, or pancreatic parenchymal phase CT can be beneficial to the quality of diagnosis

There is a linear focal area of non-enhancement in the body of the pancreas s/o laceration

(a) Axial contrast enhanced image and (b) coronal reformation show pancreatic contusion (arrow, a) as evidenced by afocal region of hypoattenuation.There is also mild peripancreatic hemorrhage (arrow, b).

Axial CECT image shows an extensive fracture of the pancreatic neck with a large intrapancreatic hematoma with active extravasation (arrow).

Grading Pancreatic Injury

The integrity of the pancreatic duct is the most important factor in the decision whether or not to operate.

Grade I pancreatic injury in a patient who experienced blunt abdominal trauma. Axial CT image shows a minor contusion of the pancreatic body (black arrow). There is no pancreatic duct injury and no active bleeding.

Grade III pancreatic injury. (a) Axial CT image shows diffuse edema of the pancreatic parenchyma with some defined areas of contusion (black arrow). There is a transection across the pancreatic body (white arrow).

Grade IV pancreatic injury. Axial CT images show a laceration of the pancreatic neck (arrow) with a pancreatic duct injury

Grade V injury. Axial CT image (A) shows massive disruption (arrowheads) of the pancreatic head.

• MRCP, in addition to showing the course of the pancreatic duct from the head to the tail, has the added advantage compared with ERCP in detecting pancreatic parenchymal abnormalities and associated adjacent abnormalities, such as concomitant biliary injuries, that may also go undetected on initial trauma CT.

• The role of ERCP may be confirmatory in indeterminate cases before definitive surgical intervention or may play a therapeutic role when stenting of the pancreatic duct is a feasible option

MRCP and ERCP

Pitfalls of Pancreatic Injury

• The most important pitfall is that CT findings of pancreatic injury may be either absent or subtle early after injury.

• Another pitfall in diagnosis of pancreatic injury is the presence of peripancreatic fluid, which may be related to either – aggressive resuscitation efforts– hemoperitoneum related to injuries of adjacent

organs.

• Isolated duodenal injuries are uncommon.• CT findings are similar to those for injuries involving

other segments of the gastrointestinal tract and include focal wall discontinuity, wall thickening, periduodenal fluid, and extraluminal gas in the retroperitoneum .

• Duodenal hematomas typically occur in younger patients: Blood accumulates in the submucosal or subserosal layer of the otherwise intact duodenal wall.

• Gastric outlet obstruction is a common complication of duodenal hematomas, particularly in the early stages after the injury.

• The management of isolated duodenal hematomas is conservative

Duodenal Injury

Renal Injuries

• Approximately 10% of all significant blunt abdominal traumatic injuries manifest with renal injury, although it is usually minor.

• The presence of hematuria (gross or icroscopic) after abdominal trauma is a good predictor of the presence of a urinary tract injury

Imaging Protocol

• Nonenhanced scan - helpful in detecting intraparenchymal hematoma that may become isoattenuating relative to the normal renal parenchyma at postcontrast CT

• late cortical or early nephrographic phase - allows identification of parenchymal injuries

• Delayed phase – collecting system injuries

• An AAST grading system is applied to classify the severity of renal trauma based on the size and location of renal lacerations and hematomas.

• The majority of traumatic renal injuries are treated conservatively with observation alone.

• Therapeutic interventions are reserved for disruptions of the collecting system and for vascular injuries.

• Grade 4 injuries: • Lacerations involving the collecting system are

characterized by the extravasation of opacified urine into the perirenal space.

• In all cases whenever significant perinephric fluid is seen around the renal hilum on nephrographic phase images, delayed excretory phase images must also be evaluated for urinary extravasation.

Right renal laceration extending into the collecting system (grade IV injury) in a 34-year-old man who was involved in a motor vehicle accident. (a) Corticomedullary phase CT scan shows a small amount of fluid along the posterior surface of the right kidney (arrow), a finding that was the only clue to the presence of a laceration. (b) Delayed excretory phase CT scan shows a subtle area of urinary extravasation (arrow).

• Segmental infarctions are caused by thrombosis, dissection, or laceration of an accessory-capsular artery or intrarenal segmental branch.

• At CT, they manifest as well-demarcated, linear or wedge-shaped nonenhancing areas extending through the renal parenchyma, with the base oriented toward the renal capsule and the apex pointing toward the hilum

• Contusions - blurred margins and enhance less than the normal adjacent parenchyma.

• Segmental infarctions - better-delineated margins and lack enhancement

Segmental infarction without associatedlaceration (grade IV injury)

• Grade V injuries represent the most severe type of renal trauma and include – shattered kidney– partial tears or complete laceration (avulsion) of

the ureteropelvic junction– thrombosis of the main renal artery or vein with

devascularization of the kidney

• The differentiation of ureteropelvic junction avulsion from incomplete tear is crucial, since the former usually requires surgical repair, whereas the latter may be treated conservatively or with stent placement.

• Partial tears - presence of contrast opacification in the ipsilateral ureter distal to the point of injury

• Avulsion - absence of contrast opacification in the ipsilateral ureter distal to the point of injury

Portal venous phase CT scan shows right hydronephrosis (*) and a smallamount of perinephric fluid near the renal hilum (arrow). (b) Delayed excretory phase CT scan helps confirm the presence of posteromedial urinary extravasation (arrows). The ureter distal to the point of injury was seen to beunenhanced.

a) Portal venous phase CT scan shows left hydronephrosis (*) and a smallamount of perinephric fluid (arrow). (b, c) Delayed excretory phase CT scans show medial perinephric urinary extravasation(arrow in b) and opacification of the distal ureter (arrowhead in c).

• The most common form of vascular pedicle injury is renal artery occlusion

• CT findings include a welldefined subtotal or global absence of parenchymal enhancement with no distortion of the renal contour.

• The abrupt termination of the renal artery at the point of occlusion can be confirmed with angiography but is sometimes seen on MPR and maximum-intensity-projection images

a) Portal venous phase CT scan reveals a geographic pattern of nephrographicabsence in the left kidney. The kidney shows only small areas of faint enhancement in the lower pole (arrows) and isclearly hypoattenuating relative to the normal right renal parenchyma. (b) Coronal maximum-intensity-projectionimage depicts the blind ending of the left main renal artery (arrow).

• Isolated renal vein injuries are the most uncommon type of vascular pedicle injury.

• Renal vein thrombosis virtually always occurs in combination with arterial or parenchymal injury.

• Contrast-enhanced CT reveals an enlarged renal vein containing a filling defect (thrombus) and renal changes secondary to acute venous hypertension including – nephromegaly – diminished nephrogram with delayed nephrographic

progression– decreased excretion of contrast material into the

collecting system

Adrenal glands

• The adrenal glands are injured in approximately 2% of patients who undergo blunt abdominal trauma.

• Right adrenal is involved in 75% of cases, the left adrenal in 15% and both adrenals in 10%.

• Unilateral adrenal hematomas usually resolve spontaneously, without any sequelae.

• Bilateral hemorrhage rarely manifests as life threatening adrenal insufficiency.

• On CT images, adrenal injuries typically manifest as – focal hyperattenuating hematomas – glandular enlargement with ill-defined

haemorrhage confined to or extending outside of the gland into the periadrenal or retroperitoneal fat.

AbdominalCT scan obtained with intravenous contrast materialshows a right adrenal hemorrhage (arrowheads) withperiadrenal hemorrhage (arrow).

Diaphragmatic Injuries• Diaphragmatic injuries are caused by a sudden increase in

intra abdominal pressure.• The rate of initially missed diagnoses on computed

tomography (CT) ranges from 12% to 63% and in most such cases, the right hemidiaphragm is affected.

• Unfortunately, diaphragmatic rupture does not resolve spontaneously, and the resultant complications may be disastrous.

• A missed diagnosis can later present as intrathoracic visceral herniation and strangulation with a mortality rate of 30%–60%

Mechanism of Injury

• Blunt diaphragmatic injuries result from considerable force and most often occur in vehicular impact (90% of cases), a fall from a height, or a crushing blow

• A lateral thoracoabdominal impact results in distortion and anteroposterior elongation of the chest wall, which may cause shearing of the diaphragm or avulsion of its attachments.

• In a frontal impact (eg, against the steering wheel of a car), an abrupt rise in intraabdominal pressure is transmitted to the diaphragm by the abdominal viscera

CT Signs

• These imaging findings include – direct visualization of diaphragmatic discontinuity– herniation of abdominal viscera into the thorax – collar sign, a waist like constriction of herniated

abdominal contents through a diaphragmatic rent

The axial helical CT scan shows thickening and focal discontinuity of the left hemidiaphragm on the anterior aspect (arrow).

CT image shows herniation of the liver (L) into the thorax through a diaphragmatic defect (arrows). The diaphragmatic segments that remain in place are thickened (arrowheads) (thickening of the diaphragm sign).

Sagittal contrast-enhanced reformatted CT image shows left-sided BDR, depicted as a 3-cm-long segmental diaphragmatic defect (arrowheads) through which a bowel loop (B) bulges into the thorax. The hernia is evident from the waistlike constriction of the bowel at the level of the diaphragm (collar sign). (b) The collar at the base of the herniated bowel (arrowheads) is more difficult to detect on the axial CT image than on reformatted images in other planes.

• The use of coronal and sagittal reformations led to the description of two additional variants of the collar sign: – the hump sign, in which a rounded portion of the

superior liver herniates through the diaphragmatic rent

– band sign, in which the torn free edge of the diaphragm causes a linear indentation in the herniated liver edge

Right-sided BDR in a 35-year-old man after a motor vehicle accident. (a) Coronal maximum intensity projection image from contrast-enhanced CT shows herniation of the liver dome through a diaphragmatic rupture (hump sign), with a smooth collar sign (arrows) and a linear area of subtle hypoattenuation (band sign) (arrowhead) extending across the base of the defect. (b) Axial contrast-enhanced CT image shows an area of hypoattenuation (arrowheads) in the dome of the liver, a finding that might correspond to the band visible in a.

• A high apex of the right hemidiaphragm could easily be mistaken for a hump sign. To avoid this error, an attentive search should be made for an associated collar sign.

• In addition, the contours of the liver should be carefully examined; they are not smoothly rounded in the presence of BDR as they are in the presence of an intact diaphragm

• Recently, the dangling diaphragm sign was described, a conspicuous sign in which the free edge of the injured diaphragm is seen to curl inwards and away from the chest wall

Major Vascular Injuries

• Injuries to the aorta and other major abdominal and pelvic vessels are uncommon but highly lethal, owing to the rapid rate of blood loss into the peritoneal cavity or retroperitoneal spaces.

• Diagnosis of aortic transection on CT images is obvious when accompanied by a large hematoma or active extravasation of contrast-enhanced blood.

• More subtle injuries, such as small pseudoaneurysms, intimal flaps, or even thrombosis may be very difficult to detect and require a proper CT technique (often with a CT angiographic phase) and a systematic review of the images by the radiologist

• Blunt injuries to the IVC are very rare, with only a few published reports in the literature

Aortic dissection in a 45-year-old man after a motor vehicle collision. Contrast-enhanced CT image shows rapid deceleration injury leading to a focal dissection in the abdominal aorta (arrow) with periaortic hemorrhage (arrowhead).

(a) Axial contrastenhanced CT image shows a filling defect (arrow) in the celiac artery,consistent with an intimal injury. (b) Sagittal oblique CT angiogram shows a curvilinear filling defect (arrow) sugg of intimal tear causing partial occlusion of the celiac artery. There was no evidence of end-organ ischemia. Conservative management was chosen, and repeat CT 2 days later showed resolution of the finding.

Retroperitoneal Hemorrhage• The retroperitoneum can be the source of considerable

blood loss that can remain occult to clinical examination and evaluation with FAST (focused assessment with sonography for trauma)

• They may occur secondary to injuries to major vessels, solid organs, hollow viscera, and/or the skeleton.

• The goals of imaging are to identify the retroperitoneal hemorrhage, its – Location– possible source – assess its relative stability on the basis of the size and presence (or

absence) of active extravasation of intravascular contrast material

• From a surgical standpoint, the retroperitoneum can be divided into zones because hematoma location has therapeutic implications.

• Zone I is the central midline retroperitoneum and contains the abdominal aorta, the IVC, the root of the mesentery, and portions of the pancreas and duodenum.

• Zone II is the lateral retroperitoneum and contains the kidneys, adrenal glands, renal vasculature, and ascending and descending colon.

• Zone III is the pelvic retroperitoneum

• Zone I retroperitoneal hemorrhage carries the highest risk of vascular injury because the major abdominal vessels lie in this zone

Abdominal CT scan obtained with intravenous contrast material shows a large, central midline retroperitoneal hematoma (arrowheads) with a large focus of active extravasation (arrow) displacing the duodenum and pancreas anteriorly. (b) Coronal reformattedCT image shows active extravasation of intravascular contrast material adjacent to the central superior mesenteric vein (arrow), which proved to be lacerated and was repaired at surgery.

Small zone I (central) retroperitoneal hematoma in a 41-year-old man who was involved in a motor vehicle collision. Abdominal CT scan obtained with intravenous contrast material shows a small amount of intermediate-attenuation fluid (arrowheads) between the aorta and IVC, a finding that presumably represents venous hemorrhage.The patient was observed clinically and remained hemodynamically stable.

• Renal injuries account for the majority of Zone II hemorrhages.

• Many perirenal and pericolonic hematomas are self limiting, and patients can be treated with observation alone if they remain hemodynamically stable and no signs of active bleeding is seen.

Large zone II (lateral) retroperitoneal hematoma in a 17-year-old boy who was involved in a highspeed motor vehicle collision. Contrast-enhanced CT scan shows right-sided perirenal and posterior pararenal retroperitoneal hematoma (white arrowheads) from a right renal laceration, with active extravasation of intravascular contrast material (black arrow) from a renal parenchymal injury.

• Zone III encompasses the pelvic retroperitoneum and is the most common location of retroperitoneal hemorrhage, frequently in association with pelvic fractures.

Hypoperfusion Complex

• CT hypotension complex refers to the predominant abdominal imaging features that occur in the context of profound hypotension.

• Early recognition is valuable before an irreversible state of shock occurs in blunt abdominal trauma.

Visceral findings• Shock bowel• Abnormally enhancing small bowel loops with increased bowel wall

thickness more than 10 mm is seen in hypoperfusion complex– on non-contrasted images, hyperdense walls compared to the psoas

muscle– wall thickening is due to submucosal oedema– hyperenhancing mucosa

• colon is less involved than small bowel because of the less oxygen demand

• Diffuse dilation of fluid-filled bowel loops (>2.5 cm) is less frequent.• Reversible.

Shock bowel. CT scan showing intense mucosal wall enhancement of small bowel (small arrow). Also seen is dense renal parenchymal enhancement

• Abnormal adrenal enhancement• Intense and persistent enhancement of

adrenal gland is an important finding in hypoperfusion complex

• Due to sympathetic overactivity in hypovolemia, there is increased preferential blood flow to adrenal gland as a compensatory mechanism for hypovolemia causing enhancement more than that of adjacent IVC

• always bilateral

• Abnormal splenic enhancement:• Spleen normally enhances more than liver. • Splenic parenchymal enhancement less than

30 HU compared to liver in children and 20 HU in adults should raise suspicion of hypovolemia

• Splenic vascular pedicle injury may also show splenic nonenhancement, however, it is associated with additional findings like perisplenic or intraparenchymal hematoma

contrast-enhanced abdominal CT scan demonstrates increased adrenalgland enhancement (arrow head) and splenic hypoperfusion (thickarrow).

• Abnormal pancreatic enhancement• pancreas shows increased enhancement >20 HU than

liver.• Peripancreatic fluid in absence of pancreatitis or

pancreatic injury is highly suggestive of hypovolemic shock

• “White or black” kidney• Intense and prolonged

enhancement of kidneys (whitekidneys) is commonly observed due to increased glomerular efferent arteriolar vasoconstriction secondary to sympathetic activity that results in contrast stasis.

• In later stages, kidneys may show complete nonenhancement, described as “Black Kidney” by Catalano et al. and it is an ominous prognostic indicator suggestive of serious patient condition

Vascular manifestations

• IVC-flattening• Flattening of IVC or slit

sign is one of the earliest and consistent finding

• Slit-like IVC measuring – AP diameter <9 mm in

three consecutive segments; i.e. 20 mm both above and below the renal veins and the perihepatic portion

• “Halo sign”• Accumulation of extracellular fluid around a

collapsed intrahepatic IVC that results in a circumferential zone of hypoattenuation (<20 Hounsfield Units [HU]) is termed the halo sign

• Small aorta• A diameter of <13

mm at 2 cm above, at, and 2 cm below the origin of the renal artery is suggested to represent an abnormal finding

• Abnormal enhancement of mesenteric vessels

• Narrowing of superior mesenteric artery and vein with intense enhancement similar to aorta and IVC is also observed in hypovolemia.

• Generally, the presence of 2 or more vascular or visceral signs is required to establish the presence of HSC.