Musculoskeletal Imaging

Which Initial Imaging Is Best for Nonballistic Torso Trauma with an Unknown Trajectory?

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Which Initial Imaging Is Best for Nonballistic Torso Trauma with an Unknown Trajectory?

It’s 2 AM in the emergency department, and a patient arrives by ambulance following a reported stabbing during an altercation. The entry wound is on the left flank, but the depth and direction of the penetrating object are unknown. The patient is awake, alert, and hemodynamically stable with a normal blood pressure. You need to rapidly assess for potential injuries to the chest, abdomen, and pelvis, but the unclear trajectory means multiple body cavities are at risk. This article details the ACR-guided imaging workflow for this specific scenario: a normotensive adult with nonballistic penetrating torso trauma and an unknown trajectory. For this presentation, the American College of Radiology (ACR) rates a Radiography trauma series as Usually Appropriate as an initial step.

Who Fits This Clinical Scenario for Penetrating Torso Trauma?

This guidance applies to a specific subset of trauma patients. Correctly identifying if your patient fits this profile is crucial for applying the right imaging strategy and avoiding unnecessary radiation or delays in care.

Inclusion criteria for this workflow:

  • Patient: Adult
  • Mechanism: Nonballistic penetrating trauma (e.g., stab wound, impalement from a sharp object).
  • Hemodynamics: Normotensive and otherwise hemodynamically stable.
  • Trajectory: The path of the injury is unknown, cannot be reliably determined by physical exam, or is suspected to cross anatomic compartments (e.g., a thoracoabdominal wound).

Exclusion criteria (patients who require a different workflow):

  • Hypotensive Patients: A patient with penetrating trauma and hypotension is in a different, more urgent category. These patients often require immediate surgical consultation and may bypass initial imaging for the operating room or proceed directly to a comprehensive Computed Tomography (CT) scan. This is covered in the ACR variant for penetrating torso trauma in a hypotensive adult.
  • Ballistic Trauma: Gunshot wounds involve significantly different energy transfer and patterns of injury compared to stab wounds. They follow a separate imaging pathway detailed in the ACR variant for ballistic penetrating torso trauma.
  • Clearly Localized Trauma: If the physical exam confidently localizes the injury to a single compartment (e.g., a superficial wound clearly confined to the anterior abdominal wall with no peritoneal violation), a more focused imaging approach may be warranted.

What Diagnoses Are You Working Up with an Unknown Trajectory?

When the path of a penetrating object is unclear, the differential diagnosis must be broad, spanning multiple organ systems across the chest, abdomen, and retroperitoneum. The goal of initial imaging is to rapidly screen for life-threatening injuries that require immediate intervention.

Diaphragmatic Injury: This is a primary concern in any thoracoabdominal penetrating injury. A tear in the diaphragm can lead to the herniation of abdominal contents into the chest, which can be an occult injury that presents with complications years later if missed. The uncertainty of the trajectory makes this a high-priority diagnosis to exclude.

Hollow Viscus Injury: Perforation of the stomach, small bowel, or colon is a critical diagnosis. A missed bowel injury can lead to spillage of enteric contents, causing peritonitis and sepsis. The primary imaging finding is often extraluminal (free) air, which can be detected on initial radiographs.

Solid Organ Injury: Lacerations to the liver, spleen, or kidneys are common. While the patient is currently normotensive, these injuries can harbor contained hematomas or pseudoaneurysms that may rupture and cause delayed hemorrhage. Imaging helps identify the presence and extent of these injuries to guide management, which may range from observation to interventional radiology embolization or surgery.

Pneumothorax or Hemothorax: If the trajectory violates the pleural space, air or blood can accumulate, leading to lung collapse and respiratory compromise. A simple chest radiograph is highly effective at identifying a clinically significant pneumothorax or hemothorax, which may require chest tube placement.

Why Is a Radiography Trauma Series a Recommended First Step?

For a stable patient with an unknown injury trajectory, the ACR identifies multiple imaging pathways as Usually Appropriate, including both a radiography trauma series and a comprehensive CT scan. The choice often depends on institutional resources, workflow, and clinical judgment. However, starting with radiography offers distinct advantages as an initial screening tool.

A trauma series typically includes an upright chest radiograph, an abdominal radiograph, and a pelvic radiograph. This combination serves as a rapid, low-dose survey to answer several critical questions at the bedside without moving the patient. It is highly effective for detecting pneumothorax, significant hemothorax, free intraperitoneal air from a bowel perforation, and retained radiopaque foreign bodies (like a broken knife tip).

While CT chest abdomen pelvis with IV contrast is also rated Usually Appropriate and provides far more detail, the radiography series is often faster and can be performed portably in the trauma bay. This allows for the immediate identification of conditions requiring urgent intervention (e.g., chest tube for a large pneumothorax) while the trauma team continues its primary and secondary surveys. The radiation dose for a trauma series (☢☢☢ 1-10 mSv) is also considerably lower than that of a comprehensive CT (☢☢☢☢ 10-30 mSv) or CTA (☢☢☢☢☢ 30-100 mSv).

It is critical to understand why certain other studies are rated lower for this initial assessment:

  • CT chest abdomen pelvis without IV contrast is rated Usually not appropriate. Omitting intravenous contrast makes it impossible to adequately evaluate for solid organ injury, active bleeding (extravasation), or vascular damage. This study provides minimal benefit over a non-contrast radiograph while delivering a significant radiation dose.
  • MRI is also rated Usually not appropriate in the acute trauma setting. It is too time-consuming, has limited availability in most emergency departments, and poses a safety risk if an unsuspected metallic foreign body is present.

What’s Next After the Initial Radiographs? Downstream Workflow

The results of the initial trauma series will dictate the next steps in the patient’s workup. The workflow is a decision tree based on these initial findings.

  • If the radiographs are clearly positive: A finding like a large pneumothorax, significant hemothorax, or free air under the diaphragm requires immediate action. For a pneumothorax, this means chest tube placement. For free air, this necessitates an urgent surgical consultation for exploratory laparotomy. The patient may still require a CT scan for further characterization, but the life-threatening finding is addressed first.
  • If the radiographs are negative or equivocal: A normal trauma series does not rule out significant injury. Occult injuries to the diaphragm, solid organs (liver, spleen, kidneys), bowel, or major blood vessels are not reliably detected on plain radiographs. In a stable patient with a negative initial radiographic series but a high-risk mechanism (i.e., any penetrating torso wound with an unknown trajectory), the next step is nearly always a CT of the chest, abdomen, and pelvis with intravenous contrast. This provides the detailed anatomical information needed to definitively exclude these more subtle but potentially lethal injuries.
  • If the patient’s clinical status changes: If at any point the patient becomes hemodynamically unstable (e.g., develops hypotension or tachycardia), the algorithm changes. The focus shifts to rapid resuscitation and immediate surgical consultation. The patient may be taken directly to the operating room, bypassing further imaging.

Pitfalls to Avoid (and When to Get Help)

Navigating this scenario requires vigilance to avoid common diagnostic traps.

  • Over-relying on a negative radiograph: Do not be falsely reassured by a normal trauma series. It is a screening tool, not a definitive study. Maintain a high index of suspicion for occult injury and have a low threshold to proceed to CT.
  • Forgetting the diaphragm: In any injury near the thoracoabdominal junction, diaphragmatic rupture must be actively considered and ruled out, as it is notoriously difficult to diagnose. CT with multiplanar reconstructions is essential.
  • Ignoring the entry wound location: While the trajectory is “unknown,” the location of the wound can still guide your search. A flank wound, for example, places the retroperitoneal structures (kidneys, ureters, pancreas, major vessels) at high risk.
  • Ordering CT without contrast: As noted, a non-contrast CT in this setting is a low-yield study that fails to assess for the most critical injuries. Always specify IV contrast unless a strong contraindication exists.

If the CT scan reveals complex vascular injuries, active arterial extravasation, or injuries to organs like the pancreas or ureters, escalate immediately by consulting the appropriate surgical subspecialty (e.g., trauma surgery, vascular surgery) and interventional radiology.

Related ACR Topics and Tools

For a comprehensive overview of all clinical variants and imaging modalities in this domain, please consult our parent topic hub article. For tools to assist in ordering and interpreting these studies, see the resources below.

Frequently Asked Questions

If both radiography and CT are ‘Usually Appropriate’, how do I choose between them?

The choice depends on your clinical suspicion and institutional workflow. If the patient is stable and you need a rapid screen for major issues like pneumothorax or free air while other resuscitation efforts are underway, a portable trauma series is an excellent start. If your suspicion for internal organ injury is very high from the outset and the patient can be moved to the scanner quickly, proceeding directly to a CT with IV contrast is also a valid and often more efficient pathway.

What if the patient has a contrast allergy or renal insufficiency?

This complicates the workup. If a patient has a severe contrast allergy or significant renal failure, a CT without IV contrast is still rated ‘Usually not appropriate’ because of its low diagnostic yield for the key injuries. The decision requires a risk-benefit discussion with the radiology and trauma surgery teams. Options might include a non-contrast CT to look for hemorrhage or free air, followed by other modalities or diagnostic peritoneal lavage/laparoscopy, depending on the clinical scenario.

Does a ‘triple-rule-out’ CTA have a role here?

A ‘triple-rule-out’ CTA is a specific protocol designed to evaluate for pulmonary embolism, aortic dissection, and coronary artery disease, and is not the appropriate study for trauma. For penetrating trauma, a standard trauma protocol CT Angiography (CTA) of the chest, abdomen, and pelvis is used. This involves specific contrast timing to optimize visualization of solid organs and detect active vascular bleeding (extravasation).

What is the role of Focused Assessment with Sonography for Trauma (FAST) exam in this scenario?

The FAST exam is a critical tool in the initial assessment of trauma patients, especially those who are unstable. In a normotensive patient, it can be used to detect pericardial effusion or free fluid in the abdomen (hemoperitoneum). However, it has significant limitations: it is poor at detecting bowel injury, retroperitoneal hemorrhage, and diaphragmatic tears. A negative FAST exam in a stable patient with penetrating torso trauma does not rule out significant injury, and further imaging with CT is typically required.

Should I mark the entry and exit wounds with radiopaque markers before imaging?

Yes, absolutely. Placing radiopaque markers (like a paperclip taped to the skin) over all entry and potential exit wounds before sending the patient for radiography or CT is a crucial step. This helps the radiologist correlate the surface wounds with the internal trajectory and potential organ damage, significantly improving diagnostic accuracy.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 30, 2026