Rib Fracture Imaging and Diagnosis

The most common radiographic presentation of rib fractures is that of a minimally displaced, irregular lucent line across the cortex of the involved rib. Secondary findings of rib fractures include a localized extrapleural hematoma, which is seen as a focal pleural opacity. Most rib fractures are better seen on a tangent. The formal rib radiographic series that includes posterior and anterior oblique projections using bone exposure and bone filter represents the most sensitive radiographic test. The sensitivity of an ordinary portable chest radiograph for the detection of a nondisplaced rib fracture may result in a missed diagnosis (see the images below). ^[30]

A small focal pneumothorax or the presence of subcutaneous air (see the first 2 images below) may be the only initial radiographic sign of a rib fracture. A large pneumothorax may result in the shift of the trachea or other mediastinal structures away from the injury (see the third image below).

A fracture of the manubrium may be accompanied by presternal hematoma. Injury to the sternum is best evaluated with lateral and oblique views that are centered on the sternum.

After calcification, fractures of the costal cartilages may be detected by radiographs obtained in an anterior oblique projection.

Widening of the mediastinum suggests the possibility of both an aortic injury and associated rib or sternal fractures. In cases of suspected mediastinal bleeding, a lateral radiograph of the sternum can help to confirm a serious chest injury.

Blunt trauma to the chest may result in incomplete or nondisplaced rib fractures. Such injuries may not be visible on the initial chest radiographs. AP supine chest radiographs often fail to demonstrate rib detail. Approximately 10-15% of rib fractures are not visible on the standard chest image.

AP supine chest radiographs often fail to demonstrate rib detail. False-positive readings for rib fractures are associated with superimposed bowel gas over the lower ribs, resulting in the appearance of a lucent line that is not the result of a rib fracture. The costal-cartilage junction is often misinterpreted as a fracture. Artifacts due to clothing, skin folds, and intravenous (IV) lines can also lead to false suggestions of rib fractures.

Sano studied 217 rib fractures in 75 patients who underwent both chest CT and rib radiography. Rib radiography missed 43 fractures in 24 patients, with causes being overlap with organs in 15 cases, trivial fractures in 21 cases, and injury outside the imaging range in 7 cases. CT missed 21 rib fractures in 17 patients, with causes being horizontal fractures in 10 cases, trivial fractures in 9 cases, and insufficient breath holding in 1 case. ^[38]

Each thoracic CT examination that is performed for the evaluation of trauma offers an opportunity to diagnose rib fractures (see the images below). A direct sign of a rib fracture on an axial CT scan of the chest is the separation of 2 rib fragments with the associated sharp edges. The secondary findings related to rib fractures include a hemothorax, pneumothorax, and lung contusion. These findings are more easily seen on chest CT scans than on chest radiographs. ^{[33, 34, 35]}

(See the images below.)

All chest CT scans should be reviewed with a bone window setting, one that emphasizes the internal lung detail. The application of a bone CT scan algorithm increases the likelihood of finding fractures. Every effort should be made to decrease patient movement and breathing-related artifacts. The areas contiguous with pulmonary contusions and localized bleeding should be carefully examined for rib fractures as well.

With improvements in the resolution of CT scanners, the thoracic spine can be examined for fractures by using chest CT images (see the images below). Gas in the epidural space can arise via a thoracic spinal fracture that is associated with a pneumothorax. Associated injuries to the internal organs of the upper abdomen should be considered in all cases of lower rib fractures; posterior lower rib fractures are often complicated by splenic injury. Fractures of the posterior upper thorax may be complicated by associated scapular fractures.

(See the images below.)

In severe motor vehicle accidents, both anterior and posterior rib fractures may be seen in the same patient (see the images below). Multiple systemic trauma may lead to prolonged hypotension or hypoxia. Multiple cerebral infarcts may result from cerebral hypoxia or as a complication of direct cranial trauma (see the second image below).

Sternal fractures require special care. A clinically important fracture of the sternum may be seen on just a single axial CT image of the chest (see the first image below). Secondary findings of bleeding in the anterior mediastinum and possible aortic injury are important related patterns (see the second image below).

The occurrence of multiple rib fractures may be associated with critical vascular injuries to the aorta and, less commonly, the heart. Aortic tears are most commonly seen in the region of the ductus arteriosus or near the root of the aorta. Cardiac rupture has been diagnosed postmortem most often associated with sternal fractures or multiple rib fractures. Rupture of the heart has been reported in living patients. ^[8]

Delayed complications of multiple contiguous rib fractures may include heniation of a portion of the lung throught the chest wall defect. CT scan shown below demonstrates such a pulmonary herniation, which occurred on a delayed basis. 

Degree of confidence

Rib fractures that are seen on standard radiographs obtained with a rib detail protocol are not always clearly demonstrated on CT images viewed with a soft tissue window. CT scans obtained for trauma evaluation should be viewed using a bone window. CT scans can be reformatted into 2-mm-thick scan sections with a bone technique, which will demonstrate nearly all rib fractures. CT examinations performed with a multiple detectors allow faster scans, thinner sections, and less severe motion artifacts. In selected cases, multiplanar reformatted (MPR) images may be helpful.

Because the ribs lie in the axial plane, axial CT scans may not depict fractures that are otherwise easily seen on conventional radiographs. If the axial CT sections are obtained with scan thicknesses greater than 4 mm, nondisplaced fractures can be missed due to partial volume averaging. On the other hand, partial volume averaging may occasionally cause a depiction that suggests a rib fracture that is not present.

Anomalies of the ribs that thin, twist, or otherwise distort the ribs further contribute to possible false-positive diagnoses of rib fractures.

Small, loculated areas of pneumothorax and hemothorax can occur in the absence of rib fractures.

Artifacts caused by electrocardiograph (ECG) leads, IV tubing, and other devices may result in false-negative CT angiography studies.

The failure to correctly time the IV contrast bolus may result in a low Hounsfield unit (HU) value within the aorta. Dense contrast within the superior vena cava may generate a streak artifact near the ascending aortic root, which may falsely suggest a rib fracture.

Although intravenous contrast is not necessary for the diagnosis rib fractures, contrast-enhanced CT of the chest is recommended in order improve the sensitivity for the diagnosis of associated vascular injuries. ^[8]

Chest CT is considered the gold standard of detecting rib fractures, but the fractures may not be clinically significant. Chest CT is more important in general assessment of trauma for other injuries. Whole-body CT has become standard practice in the management of severely injured trauma patients, but it is necessary to improve rib fracture diagnosis accuracy on CT. Significant progress has been made in clinical applications based on deep learning techniques for medical image interpretation, such as algorithms based on deep convolutional neural networks (DCCN) for CT. ^{[1, 15, 16, 17, 18, 19, 20]}

Sano studied 217 rib fractures in 75 patients who underwent both chest CT and rib radiography. Rib radiography missed 43 fractures in 24 patients, with causes being overlap with organs in 15 cases, trivial fractures in 21 cases, and injury outside the imaging range in 7 cases. CT missed 21 rib fractures in 17 patients, with causes being horizontal fractures in 10 cases, trivial fractures in 9 cases, and insufficient breath holding in 1 case. ^[38]

Although magnetic resonance imaging (MRI) is not used as a primary means of detecting rib fractures, displaced or angulated lateral rib fractures as well as posterior rib fractures can be detected by MRI. Anterior chest wall movement with breathing may limit the visualization of nondisplaced fractures. Gradient-echo MRI, T2 fast-spin echo (FSE), and T2 short tau inversion recovery (STIR) sequences demonstrate the edema that is related to rib fractures. Spinal fractures may be associated with secondary effects of posterior rib fractures such as hemorrhage and edema. Lower cervical spine injury may be associated with fractures of the first or second ribs.

Breathing motion can cause artifacts, resulting in nondiagnostic MRIs of anterior rib fractures. Partial-volume effects may result in a false suggestion of a nondisplaced rib fracture.

Direct visualization of rib fractures is generally not possible with ultrasonography. However, the presence of a hemothorax can be confirmed with ultrasonography of the pleural space, and edema in the chest-wall muscles may be seen as thickening of the pleural space, as well as the alteration of the echogenic pattern within the chest-wall muscles. ^{[39, 40, 41, 42, 43]}

Hemothorax cannot be consistently differentiated from a pleural effusion. The visualization of a splenic or hepatic hematoma may indirectly suggest a search for a rib fracture. Ultrasonography is not effective in the visualization of a pneumothorax, small pleural effusions, and nondisplaced rib fractures.

In a study by Celik et al comparing the diagnostic accuracy of US with that of CT for detecting rib fractures in 145 patients who presented to the ED with blunt chest trauma, diagnostic accuracy of US was 80%, with a sensitivity of 91.2% and a specificity of 72.7%. However, a positive US performed poorly in determining the exact location and number of the fractured ribs. ^[40]

In a study by Hwang and Lee of 201 patients with blunt chest trauma who underwent radiographic and US examinations, of the 132 patients who showed no rib fractures on radiography, 92 showed fractures on US. In addition, of the 69 patients with rib fractures detected on radiography, 33 had additional rib fractures detected on US. ^[42]

Nuclear medicine techniques are useful in the detection of subacute rib fractures, as well as costochondral separations. The bone-seeking ^99mTc-labeled phosphonates are selectively distributed into the areas that surround healing rib fractures. The dose of ^99mTc-medronate is usually 800 megabecquerels (MBq). Imaging is generally performed after a 4-5 hour delay to allow the clearing of the diagnostic agent from the blood pool.

If a localized lesion is under investigation, regional blood flow can be evaluated with a 3-phase study in which a flow phase, a blood-pool image, and delayed static images are obtained. The flow phase is obtained immediately. The static images are generally obtained 4 hours after the administration of the diagnostic agent.

Increased regional nuclear activity within a chest-wall contusion may be detected on immediate imaging. A positive result for a rib fracture is represented by a focal area of increased nuclear activity. In the case of a linear fracture, the increased activity is localized to the site of the injury. If a large area of the chest wall is injured, several ribs in multiple locations may demonstrate an increased uptake of the radionuclide. ^[44]

Degree of confidence

Increased radionuclide uptake in the area of chest-wall trauma indicates a rib fracture in most cases. The application of lateral, oblique, and single-photon emission computed tomography (SPECT) imaging techniques improve diagnostic accuracy. Standard radiographs and the results of CT scans of the chest should be compared with bone scans whenever possible.

Positive results with radionuclide imaging require a moderate degree of cooperation from the injured patient. Movement, including rapid breathing, results in poor image quality and decreased sensitivity. A rib fracture is generally seen as a site of increased nuclear activity after a short (12- to 24-hr) delay in a young patient. In older patients and in patients with metabolic bone disease, fractures may not be visible until 72 hours after an injury. Except for pathologic fractures, a bone scan that is directed toward the detection of rib fractures should be delayed 48-72 hours after the traumatic event.

Normal costochondral uptake in a child may be intense enough to suggest rib stippling when viewed from a posterior projection. Any disease or lesion of a rib that results in increased bone turnover may result in positive findings in the ribs. False-negative results may occur in patients who have received iron dextran injections. High levels of iron in the bone marrow interfere with the normal uptake of bone. Fractures or other lesions of the ribs may not be detected until the iron storages return to normal.

Selective angiography has a limited role in the evaluation of rib fractures. Thoracic angiograms may show a traumatic pseudoaneurysm or the extravasation of contrast material into the pleural space. Complications in cases of multiple trauma may include central vascular injury (aortic tear) and laceration of the subcostal artery. Direct visualization of active hemorrhage that is associated with a rib fracture is useful in the direction of surgical or angiographic intervention. Diagnostic angiography may be helpful in demonstrating a remote vascular injury and the delayed development of a pseudoaneurysm or arteriovenous fistula (AVF).

Degree of confidence

Thoracic angiography is both sensitive and specific for traumatic aortic injury. Injury to the subclavian artery may require selective injection of a contrast agent into the proximal subclavian artery to make the diagnosis of a traumatic pseudoaneurysm. The use of digital subtraction angiography (DSA) permits full evaluation of the injured artery without the artifacts that are caused by any superimposed bone.

The failure to identify an arterial laceration or pseudoaneurysm is most commonly associated with motion artifacts, rotation, or poor angiographic technique. Ulcerated plaques within the aortic arch of older patients have been mistaken for aortic trauma. The origin of branch vessels that is otherwise poorly filled has been mistaken for small aneurysms.