What are the causes of a subdermal hematoma?

Causes of Subdermal Hematoma

Subdermal (subgaleal/subcutaneous) hematomas result from bleeding into tissue spaces beneath the skin, most commonly caused by trauma, anticoagulant therapy, vascular abnormalities, or spontaneous bleeding in patients with coagulopathy.

Traumatic Causes

• Direct trauma is the most common cause, including blunt force injury, surgical procedures, or even minor trauma such as hair pulling or combing in susceptible individuals 1, 2
• Iatrogenic injury from surgical procedures or invasive interventions can lead to hematoma formation, particularly in patients on anticoagulation 3
• Subgaleal hematomas specifically can occur from minimal trauma, with tearing of emissary veins in the loose areolar tissue beneath the galeal aponeurosis 2

Medication-Related Causes

• Anticoagulant therapy is a major risk factor, with warfarin causing hemorrhage in any tissue or organ as its most serious complication 4
• Antiplatelet agents contribute to hematoma formation, with 13 of 17 hospitalized patients in one series taking anticoagulants, antiplatelet drugs, or both 3
• Therapeutic overdosing of anticoagulants was documented in 5 of 9 patients on warfarin or low molecular weight heparin who developed hematomas 3
• The FDA warns that warfarin can cause necrosis and/or gangrene of skin and other tissues (occurring in <0.1% of cases), which appears within days of starting therapy and is associated with local thrombosis 4

Vascular and Hematologic Causes

• Bleeding disorders including coagulopathies predispose to spontaneous hematoma formation 5
• Vascular malformations can present with bleeding into tissues, though these are congenital lesions that may only become clinically apparent later in life 6
• Cholesterol microembolization from warfarin therapy can cause purple toes syndrome and tissue compromise, presenting 3-10 weeks after initiation of anticoagulation 4

Spontaneous/Idiopathic Causes

• Chronic expanding hematomas can develop without recent trauma or identifiable medical disorders, presenting as slowly growing masses that progressively increase over time 5
• Age-related factors play a role, with hematomas typically occurring in elderly patients (mean age 71 years in one series) even without documented coagulopathy 3
• Four patients in one study developed hematomas with normal coagulation studies and no anticoagulant therapy, though they were younger (mean age 55 years) 3

High-Risk Anatomic Locations

• Lower extremities are the most common site, with all 17 patients in one series developing leg hematomas 3
• Scalp/subgaleal space allows extensive blood accumulation due to the loose areolar tissue, potentially causing massive swelling, facial edema, and even airway compromise 1, 2
• Flank and extremity soft tissues can harbor chronic expanding hematomas that mimic soft-tissue neoplasms 5

Critical Complications Leading to Tissue Damage

• Increased tissue pressure from blood accumulation causes necrosis of overlying skin 7
• Cellular and biochemical changes result in tissue ischemia and necrosis even without elevated compartment pressure 7
• Hematomas can progress to ulceration (3 of 17 cases), infection (11 of 17 cases presenting as inflammatory or infected), or skin compromise requiring debridement 3, 1

Common Clinical Pitfalls

• Hematomas frequently masquerade as thrombophlebitis or abscesses, particularly when inflammatory or febrile (7 of 17 patients were febrile) 3
• The ratio of leg hematomas to erysipelas is approximately 1:8 in dermatology departments, making this a not-uncommon presentation that requires awareness 3
• Prompt recognition and operative evacuation should be performed to avoid significant complications from tissue necrosis, rather than assuming all hematomas will self-resolve 7