What could cause sudden bruising on the left flank to back?

Sudden Bruising on Left Flank to Back: Urgent Evaluation Required

Sudden bruising on the left flank extending to the back requires immediate assessment for retroperitoneal hemorrhage or intra-abdominal bleeding, which can be life-threatening and demands urgent imaging and hemodynamic monitoring. 1

Immediate Assessment and Stabilization

Check vital signs immediately to identify hemorrhagic shock, looking specifically for systolic BP <100 mmHg, tachycardia >100 bpm, altered mental status, and decreased urine output, as these indicate significant blood loss requiring urgent intervention. 2, 1

• Apply direct pressure to the visible bruising site while simultaneously assessing for hemodynamic instability, as this is the first-line intervention for all bleeding presentations. 3, 1
• Obtain large-bore IV access and initiate crystalloid resuscitation if the patient shows any signs of hemodynamic compromise, targeting systolic blood pressure of 80-100 mmHg until bleeding source is identified and controlled. 2, 1
• Actively warm the patient to prevent hypothermia, which worsens coagulopathy and bleeding outcomes. 1

Critical Differential Diagnosis

The location of bruising on the left flank extending to the back is highly concerning for several life-threatening conditions:

• Retroperitoneal hemorrhage presents with back/flank/hip pain, tachycardia, and hypotension, and can lead to femoral neuropathy, hypovolemic shock, and death if not rapidly identified. 2
• Intra-abdominal bleeding (non-gastrointestinal) manifests as abdominal pain, distension, hypotension, and tachycardia, requiring urgent surgical evaluation. 2
• Spontaneous bleeding from anticoagulation should be suspected immediately, as flank bruising can indicate major hemorrhage in patients on warfarin or direct oral anticoagulants. 2, 4

Mandatory Immediate Investigations

For hemodynamically unstable patients, perform focused abdominal sonography for trauma (FAST) immediately to detect free fluid in the abdomen, as patients with significant free intra-abdominal fluid and hemodynamic instability require urgent surgery. 2

For hemodynamically stable patients, obtain CT abdomen and pelvis with IV contrast urgently, as this is the gold standard for identifying retroperitoneal hemorrhage, active extravasation, and other sources of bleeding in stable patients. 2, 1

Essential Laboratory Testing

Obtain baseline labs immediately, including:

• Complete blood count to assess hemoglobin drop (≥2 g/dL indicates major bleeding associated with increased mortality). 2, 1
• PT/INR and aPTT to identify coagulopathy or anticoagulant effect. 2, 5, 6
• Serum lactate and base deficit to estimate and monitor the extent of bleeding and shock, as these are superior markers compared to single hematocrit measurements. 2, 1
• Fibrinogen level to detect consumptive coagulopathy. 1

Do not rely on single hematocrit measurements alone, as they can be misleadingly normal in acute hemorrhage due to hemoconcentration before resuscitation. 2, 1

Medication History: Critical Priority

Immediately check anticoagulation status, as flank bruising in patients on warfarin, direct oral anticoagulants, or antiplatelet agents indicates potentially life-threatening bleeding requiring reversal. 2, 1, 4, 5, 6

• Warfarin-associated bleeding with flank bruising requires immediate reversal with prothrombin complex concentrates rather than waiting for vitamin K to take effect. 2, 1
• For patients on DOACs with serious bleeding and levels >50 ng/mL, anticoagulant reversal should be strongly considered. 2

Urgent Surgical Consultation Criteria

Patients with hemorrhagic shock and identified bleeding source require immediate surgical bleeding control unless initial resuscitation measures are successful. 2

Specific indications for urgent surgical intervention include:

• Ongoing hemodynamic instability despite adequate resuscitation, which indicates active bleeding requiring surgical or angiographic control. 2, 1
• Significant free intra-abdominal fluid on FAST with hemodynamic instability, which mandates urgent laparotomy. 2
• Active arterial extravasation on CT, which may require angiographic embolization or surgical packing. 2, 1

Special Considerations and Pitfalls

Never assume benign "easy bruising" when bruising appears suddenly on the flank/back, as this location is anatomically consistent with retroperitoneal or intra-abdominal hemorrhage rather than superficial trauma. 2, 7

• Chronic expanding hematoma can present as slowly growing flank masses without recent trauma, mimicking soft-tissue neoplasms, and may require surgical excision for definitive diagnosis. 7
• Elderly patients or those with bleeding disorders (von Willebrand disease, Ehlers-Danlos syndrome) may present with more severe bleeding from minor trauma. 2, 5, 6, 8
• Avoid excessive fluid resuscitation while bleeding is uncontrolled, as this worsens coagulopathy and dilutes clotting factors. 3

Disposition

Admit to ICU for close monitoring any patient with hemodynamic instability, ongoing bleeding, evidence of retroperitoneal hemorrhage, or significant hemoglobin drop. 1

For stable patients with confirmed superficial hematoma, arrange follow-up within 48-72 hours to reassess for expansion, compartment syndrome development, or delayed complications. 1