What causes a hematoma?

Hematoma Causes

Hematomas result from blood vessel injury with subsequent extravasation of blood into surrounding tissues, most commonly caused by trauma (blunt or penetrating), vascular abnormalities, anticoagulation therapy, or surgical/procedural complications. 1

Primary Mechanisms of Hematoma Formation

Traumatic Causes

• Blunt trauma causes vessel disruption through shearing forces, sudden rotation, violent flexion/extension, or deceleration injuries, leading to blood accumulation in tissue spaces 2
• Penetrating injuries from stab wounds, gunshot wounds, or explosive fragments directly lacerate blood vessels 1
• Fractures can injure adjacent vessels—pelvic fractures commonly cause retroperitoneal hematomas, while rib fractures may injure intercostal arteries causing chest wall hematomas 1, 3
• High-energy mechanisms (motor vehicle crashes, falls from height) produce greater vascular damage and larger hematomas compared to low-energy trauma 1

Vascular Pathology

• Ruptured aneurysms (particularly aortic) cause massive retroperitoneal or intra-abdominal hematomas 1
• Arteriovenous malformations (AVMs) can spontaneously bleed or rupture 1
• Pseudoaneurysms secondary to inflammation (pancreatitis, duodenal ulcers) or infection may rupture into retroperitoneal space 1
• Intramural hemorrhage from ruptured vasa vasorum in diseased vessel walls, particularly in cystic medial degeneration 1

Iatrogenic Causes

• Surgical complications including vessel injury during procedures, particularly cesarean section (bladder flap, subfascial, perivaginal hematomas) 1
• Transfemoral catheterization causing retroperitoneal bleeding 1
• Spinal/epidural anesthesia represents the tenth most common cause of spinal hematomas 4
• Obstetric trauma from lacerations, uterine rupture, or incision extensions during delivery 1

Coagulopathy-Related

• Anticoagulant therapy is the second most common identifiable cause of spinal hematomas (after idiopathic), though it likely requires an additional predisposing factor ("locus minoris resistentiae") to trigger bleeding 4
• Acute coagulopathy from amniotic fluid embolism, placental abruption, HELLP syndrome, or severe pre-eclampsia 1
• Dilutional coagulopathy from massive fluid resuscitation depletes clotting factors and platelets 1, 2
• Hypothermia impairs platelet and coagulation enzyme function 1

Spontaneous/Idiopathic

• No identifiable cause accounts for approximately 30% of spinal hematomas 4
• Increased pressure in vertebral venous plexus combined with vessel wall weakness may cause spontaneous spinal hemorrhage 4
• Systemic connective tissue degeneration (as seen in patients with aortic aneurysms or dissection history) increases risk of unexpected large hematomas even from minor trauma 3

Location-Specific Etiologies

Postpartum Hematomas

• Uterine atony (>75% of cases) causes blood accumulation in uterine cavity 1, 5
• Retained products of conception (RPOC) in 1% of third-trimester deliveries 1
• Vascular complications including uterine artery pseudoaneurysms or failure of placental bed vessel obliteration 1

Retroperitoneal Hematomas

• Pelvic fractures with injury to pelvic vessels 1
• Spine fractures with associated vessel injury 1
• Visceral vessel rupture from pancreatic or duodenal pathology 1

Infantile Hemangiomas

• Ulceration (5-21% incidence) is the most common complication leading to bleeding, particularly in segmental lesions and specific anatomic locations (head, neck, perioral, perineal/perianal regions) 1
• Surface trauma from friction or minor injury causes hemorrhagic crusting 1

Critical Risk Factors

• Age extremes: Most spinal hematomas occur in patients 55-70 years old; infantile hemangiomas ulcerate more frequently in infants <4 months 1, 4
• Male sex: 63.9% of spinal hematoma patients are men 4
• Systemic vascular disease: Patients with aortic aneurysms or dissection history have progressive connective tissue degeneration increasing hematoma risk 3
• Combination therapy: Spinal/epidural procedures plus anticoagulation represent the fifth most common cause of spinal hematomas 4